Autonomous sedimentation type bottom sediment purification device and measuring instrument for evaluating bottom sediment interface

Abstract

The bottoms of rivers, lakes, reservoirs, wetlands, and sewage treatment tanks are composed of non-Newtonian muddy sediment, where a soft surface layer and a firmer depth layer are superimposed. This presents a challenge in that simply lowering heavy equipment can cause it to sink too far or stop midway, making it difficult to autonomously and stably install it at the desired depth. [Solution] The ground pressure is set by a combination of the effective contact projection area with respect to the bottom sediment and the apparent load underwater. The device is configured to remain stationary or sink in stages according to the relationship between the ground pressure and the effective yield stress of the bottom sediment, and the sinking is controlled by trigger means such as fluid distribution supply or vibration application as needed.

Description

Technical Field

[0001] The present invention relates to the management and purification of non-Newtonian bottom sediments composed of organic sludge, silt-clay mixtures, biofilms, etc. deposited on the bottom of water areas such as lakes, ponds, reservoirs, rivers, waterways, and inner waters of harbors. More specifically, it relates to a self-settling type device that autonomously settles and stops near the interface between the bottom sediment and water or at a desired depth in the bottom sediment by utilizing the threshold relationship between the ground pressure p on the bottom sediment and the effective (apparent) yield stress τ*_y of the bottom sediment, and a measuring tool and a measuring kit for evaluating the bottom sediment interface to assist in its design and evaluation.

Background Art

[0002] Conventionally, aeration devices, microbial carrier blocks, purification mats, etc. have been proposed for bottom sediments such as organic sludge and silt-clay mixtures deposited on the bottom of water areas. However, many of these regard the bottom sediment as a rigid or uniform ground and simply install them thereon or sink them as a heavy object. Technologies for controlling the installation depth considering the non-Newtonian nature of the bottom sediment and the yield stress distribution in the depth direction have not been sufficiently developed.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Conventionally, aeration devices, microbial carrier blocks, purification mats, etc. have been proposed for bottom sediments such as organic sludge and silt-clay mixtures deposited on the bottom of water areas. However, many of these regarded the bottom sediment as a rigid or uniform ground and simply installed them thereon or sank them as a heavy object. However, organic sludge that actually accumulates in lakes, ponds, agricultural reservoirs, and river stagnant areas exhibits the properties of a non-Newtonian fluid, a mixture of silt, clay, organic matter, and biofilm, and its yield stress in a static state changes significantly with respect to the depth z. In such bottom sediments, it is difficult to design and control the penetration depth after installation based solely on the apparent underwater load and shape of the device, leading to problems such as the following. 1. Part or all of the device sinks excessively into the sediment, • The functional parts of the device (aeration holes, microbial carrier surface, flow path, etc.) become buried in the sludge. • It causes significant disturbance to the sediment, releasing malodorous components such as hydrogen sulfide. 2. Conversely, if the sediment is locally firm, • It stops at a higher position than expected, and is unable to adequately act on the anaerobic layer near the bottom of the water. 3. Furthermore, even within the same body of water, the thickness and characteristics of the sediment deposits differ from place to place, • When multiple devices with the same specifications are installed, the installation depth will vary, resulting in unstable purification effects. On the other hand, accurately identifying the yield stress profile of the sediment and the reference interface z_ref between the water body W and the non-Newtonian sediment S generally requires expensive and large-scale measuring equipment such as cone penetration testers and large shear testers. It has not been easy to simply measure these conditions in small lakes, agricultural reservoirs, or urban waterways and feed the results back into the design process. the result, (i) There is a lack of a device configuration that autonomously controls the installation depth by focusing on the non-Newtonian properties and yield stress of the bottom sediment. (ii) No simple, field-use measuring tools or kits were available for designing and evaluating such devices. This invention has been made in view of the problems of the prior art, 1. To provide an autonomous sedimentation device that autonomously soft-landes near the interface between the sediment and water, and exhibits a stepwise sedimentation behavior, based on the threshold relationship between the contact pressure p on the sediment and the effective (apparent) yield stress τ*_y of the sediment. 2. To provide a measuring tool / kit that can easily and reproducibly measure the reference interface z_ref between the water body W and the non-Newtonian sediment S, and the penetration depth s based on this reference, in order to contribute to the design and evaluation of the above-mentioned device. This is the purpose. [Means for solving the problem]

[0004] An autonomous sedimentation device according to one aspect of the present invention is an autonomous sedimentation device that targets bottom sediment or deposits (hereinafter referred to as "bottom sediment, etc.") deposited at the bottom of a body of water, The device comprises a support section that defines the effective contact projection area Aeff(s) with respect to the bottom sediment, and a ground pressure setting mechanism that sets a predetermined ground pressure p based on the apparent underwater load W′ of the device and the Aeff(s). Here, the ground pressure p is p(s) = W′ / Aeff(s) Defined as such, Aeff(s) is the effective area that includes the load-bearing contribution of the sides projected onto the bottom projection. Typical examples of target sediments include soft sedimentary layers containing clay and organic matter, such as sediments exhibiting non-Newtonian behavior, but the present invention is not limited to these. According to the present invention, by using the relationship between the effective (apparent) yield stress τ*_y(s) distributed in the depth direction of the sediment and the ground pressure p(s) of the device as a design index, At least in the desired penetration depth s_set p(s_set) < τ*_y(s_set) The apparent load W′ in water and the effective contact projection area Aeff(s) can be set such that the device is introduced into the water and the relationship between p(s) and τ*_y(s) is p(s)≧ τ*_y(s) In the depth range where this condition is met, the sinking continues due to its own weight, and when it reaches a depth where p(s) < τ*_y(s), the sinking stops and it becomes stationary. In this way, it is possible to autonomously install the device in the target depth range solely by sinking due to its own weight, without driving any external mechanical lifting means. In a preferred embodiment of the present invention, various triggering means may be further provided to locally change at least one or both of the ground pressure p(s) or the effective (apparent) yield stress τ*_y(s) of the sediment. For example, at least one or both of p(s) and τ*_y(s) can be controlled by distributing fluid to the sediment, applying mechanical vibration to the device or the surrounding sediment, locally adjusting temperature, chemical, or biological conditions, or adjusting the mass, buoyancy, or footprint (effective contact projection area) of the device. In this embodiment, the device may remain stationary in a predetermined layer of sediment, etc., as long as p(s) < τ*_y(s) holds, and a sedimentation event may occur only when τ*_y(s) locally decreases or p(s) increases due to the activation of the trigger means, natural changes in the state of sediment, etc., or a combination thereof, and p(s) ≥ τ*_y(s). In this case, a stepwise sedimentation behavior is realized in which the stationary phase and the sedimentation event switch autonomously according to the threshold condition. [Effects of the Invention]

[0005] According to the present invention, by using the relationship between the ground pressure p(s), defined based on the apparent underwater load W′ of the device and the effective contact projection area Aeff(s), and the effective (apparent) yield stress τ*_y(s) of the bottom sediment, etc., as a design indicator, the device can be autonomously installed to a desired penetration depth by gravity alone, without necessarily relying on external mechanical lifting means. As a result, the structure can be simplified compared to conventional devices that require a dedicated lifting mechanism, reducing the scale of the equipment and construction costs, while making it easy to arrange a large number of devices over a wide area of ​​water. Furthermore, according to a preferred embodiment of the present invention, by utilizing the threshold relationship between the ground pressure p(s) and the effective (apparent) yield stress τ*_y(s) of the sediment, a stably realized stepwise sedimentation behavior in which the stationary phase and discrete sedimentation events autonomously switch can be achieved. As a result, the device sinks to deeper depths in stages in response to changes in the state of the sediment and the progress of purification, enabling long-term purification and improvement of the sediment, and also making it possible to design and adjust the sedimentation timing and amount to some extent by controlling the trigger means. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1A is a half-sectional perspective view showing the configuration of the support section 5 and the microbial carrier block 6 of an autonomous sedimentation device 1 according to one embodiment of the present invention. Figure 1B is a plan view (bottom view) of the support section 5 shown in Figure 1A, viewed from the bottom side, and shows an example of the contour and opening arrangement of the support section 5. [Figure 2] Figure 2A is a half-section perspective view showing another configuration example of the autonomous sedimentation device 1 according to one embodiment of the present invention, illustrating a configuration in which the microbial carrier block 6 is installed inside the support portion 5. Figure 2B is a plan view (bottom view) of the support portion 5 and microbial carrier block 6 shown in Figure 2A, viewed from the bottom, schematically illustrating the definitions of the effective contact projection area Aeff(s) and the representative support projection diameter Dsupp. [Figure 3] Figure 3 is a schematic diagram showing that, when a reference interface z_ref is defined at the interface between the water and the sediment S within the water body W, and the depth from the water surface to z_ref is h_ref, and the vertical distance from the lower surface of the support part of the device 1 to z_ref is the penetration depth s, the installation depth and position of the device 1 in the sediment S can be uniquely determined based on h_ref and s without using the absolute position of the bottom surface. [Figure 4] Figure 4 is a schematic diagram showing an example of a small-scale vane test for determining the reference interface z_ref in the sediment S. [Figure 5] Figure 5 is a schematic graph showing the relationship between torque T and depth z obtained from the small vane test shown in Figure 4, and is a diagram illustrating the method for determining the reference interface z_ref. [Figure 6] FIG. 6 is a schematic view showing an example of the self-settling module 1 that settles stepwise relative to the fixed column 20. [Figure 7] FIG. 7A is a side view of a measuring tool 70 showing the relationship between the depth h_ref from the water surface W to the reference interface z_ref with the bottom sediment S and the penetration depth s from the reference interface z_ref to the stationary position of the interface follower 7b. FIG. 7B is a perspective view of the measuring tool 70 shown in FIG. 7A. [Figure 8] FIG. 8A is a side view showing an example of the connection part between the support member 7a and the interface follower 7b and the flexible element 7c and the latch mechanism 7d in the measuring tool 70 shown in FIG. 7A. FIG. 8B is a perspective view of the measuring tool 70 showing the arrangement of the flexible element 7c and the latch mechanism 7d shown in FIG. 8A. [Figure 9] FIG. 9A is a side view showing an example of a measurement kit 80 for measuring the penetration depth s from the reference interface z_ref to the stationary position of the measurement body 8b in a water area W where the reference interface z_ref is known. FIG. 9B is a perspective view of the measurement kit 80 shown in FIG. 9A, which is a diagram showing the configuration. [[ID=​​​​​​​​​​​​​​​​​​ In this specification, the yield stress τ_y(z,t) of the sediment S as a material is an idealized quantity representing the local shear resistance within the sample, caused by interparticle cohesive forces, consolidation due to self-weight, and pore water pressure. However, in actual bodies of water, in addition to the above, lateral adhesion and friction between the support and the bottom sediment S, suction (negative pressure) and undrained negative pressure in the bottom sediment S, and thixotropy and other structural viscosity and hysteresis effects are superimposed and appear as effective resistance directly beneath the support. Strictly separating these individual contributions is not the objective of this invention; in terms of device design, it is sufficient to be able to determine whether or not the bottom sediment S directly beneath the support "yields" to a given ground pressure p. Therefore, in this application, we define the effective yield stress τ*_y(z,t) as an apparent yield stress that collectively represents these effects. That is, τ*_y(z,t) is an effective indicator for determining whether the bottom sediment S directly beneath the support yields to an external force, including lateral adhesion and friction, suction and undrained negative pressure, structural viscosity and hysteresis effects, etc. In the following explanation, we assume quasi-static design conditions where time dependence is not an issue, and τ*_y(z,t) will be simply abbreviated as τ*_y(z). Furthermore, unless otherwise specified, "yield stress" in this specification refers to this effective yield stress τ*_y(z). In this specification, the effective yield stress at the position corresponding to the penetration depth s from the reference interface z_ref may be abbreviated as τ*_y(s) for convenience. In this case, τ*_y(s) is interpreted as being equivalent to τ*_y(z) at z = z_ref+s.

[0009] [Definition of Effective Contact Projection Area (Aeff(s)] In this application, the effective contact projection area Aeff(s) of the support portion refers to the equivalent area obtained by adding the projection area of ​​the bottom surface of the support portion to the contribution of side walls, etc., that penetrate into the substrate S, if such contribution is made to load support, by converting it to a bottom surface projection. In other words, Aeff(s) is the effective area for evaluating the apparent underwater load W' supported by the bottom sediment S at the penetration depth s in the form of average ground pressure p = W' / Aeff(s). The specific method for calculating Aeff(s) can be appropriately selected depending on the shape of the support and the treatment of lateral friction, and this application is not limited to a specific calculation formula.

[0010] [Non-restrictive supplement regarding theoretical formulas] This application is not bound by any specific constitutive law or theoretical model. The above interpretation of τ*_y(z) and Aeff(s) is a practical form for expressing the relationship between the ground pressure p=W′ / Aeff(s) and the effective yield stress τ*_y(z) as a design index. In other words, even when factors such as lateral adhesion, suction, structural viscosity, and other factors are present, by incorporating their effects into τ*_y(z) and Aeff(s), the design and evaluation of stepwise sedimentation behavior based on the relative magnitudes of equation p=W′ / Aeff(s) and τ*_y(z) can be made equivalent. Therefore, the mathematical formulas described in this application are non-limiting model formulas for explaining the technical concept of the present invention, and those skilled in the art can implement the present invention using other equivalent physical quantities or indicators based on a similar technical concept.

[0011] (1) Overall structure An autonomous sedimentation device 1 according to one embodiment of the present invention will be described with reference to Figures 1A and 1B, 2A and 2B, and 3. Device 1 is an autonomous sedimentation device that is installed on non-Newtonian sediment S deposited at the bottom of a body of water W, and autonomously settles and settles according to the relationship between the ground pressure p and the effective (apparent) yield stress τ*_y of the sediment S. In particular, the device 1 of this embodiment autonomously switches between a stationary state and a discrete sedimentation event based on the threshold relationship between the ground pressure p and the effective yield stress τ*_y. This is an example configuration that demonstrates stepwise sedimentation behavior and can be operated without relying on external mechanical lifting and lowering means.

[0012] (2) Support portion and effective contact projected area Aeff(s) Figures 1A and 1B, and 2A and 2B show examples of support parts in the autonomous sedimentation device of the present invention. Below, an annular (frame-shaped) support part 5 will be described as a representative example, but the present invention is not limited thereto. As shown in Figure 1A, the support portion 5 consists of a closed curved frame (annular / frame-shaped member), and a buoyancy chamber 5u and a flow channel portion 5a may be formed inside it in a preferred configuration. The buoyancy chamber 5u is an example of a buoyancy adjustment mechanism; a separate floating body may be attached instead, or the buoyancy adjustment mechanism may be omitted altogether. The flow channel section 5a is one form of a hollow section for circulating a medium, As shown in Figures 1A and 2A, the medium supply port 5b may be configured to communicate with a plurality of openings 5c. However, the present invention does not require the support portion 5 to always be hollow, and the flow path portion 5a may be omitted, and the support portion 5 may be configured as a substantially solid body or a sealed hollow body. In this case as well, the support portion 5 functions as a substantial load-bearing surface with respect to the substrate S. It is involved in the application of ground pressure p via the effective contact projection area Aeff(s). In the examples shown in Figures 1A and 1B, a number of openings, known as holes 5c, are formed on the lower surface of the support portion 5, forming a dispersed supply portion that can discharge fluids or gases dispersedly as needed. In another example shown in Figure 2A, the opening 5c ​​is provided on the upper side of the support portion 5. The system is configured to disperse and discharge water containing dissolved oxygen, fine bubbles, drug solutions, microbial suspensions, etc., into the upper water area W. The discharge direction from the opening 5c ​​may be downward, sideways, upward, or any other direction. The appropriate selection is made depending on the type of media and the condition of the substrate S. In either case, hole 5c is an example of an opening for dispersing and supplying the medium. The orientation, position, number, and type of medium supplied to the holes are as follows: The effective (apparent) yield stress τ*_y of the sediment S can be reduced, the ground pressure p can be adjusted, or a combination of both can be used to appropriately change the pressure within the range that triggers the threshold p>=τ*_y to be met. In the present invention, the trigger means that gives stepwise sedimentation behavior is Not limited to fluid supply through hole 5c, Mechanical vibration, localized temperature control, adjustment of chemical or photochemical conditions, Adjustment of biological or biochemical conditions, increase of p by ballast injection, etc. The various means listed in the claims, or their functional equivalents, can be used individually or in combination. On the outer periphery of the support part 5, there is a media supply port 5b, Ports 5d for introducing or removing ballast or fluid may be provided spaced apart in the vertical direction. The media supply port 5b communicates with the flow path section 5a and the opening 5c, It is used to introduce a medium such as air, oxygenated water, drug solution, or microbial suspension into the support section 5. Meanwhile, port 5d allows water, gas, or solid ballast to be added to or removed from the support section 5 or the buoyancy chamber 5u. It can be used as a site for adjusting the effective density. Note that the configuration for ballast adjustment is not limited to port 5d. Other parts of the support section 5, a separate ballast tank, an external weight, etc., may also be used. In the example shown in Figure 2A, the microbial carrier block 6 is mounted inside the support section 5 by the carrier support arm 6a. The microbial carrier block 6 is a carrier made of porous material, fibrous material, etc. Over time after installation, it functions as a substrate for the attachment and proliferation of various microorganisms in the surrounding water body W and bottom sediment S. It can retain organic matter, suspended particles, sludge flocs, biofilms, and moisture on its surface and inside. The placement of the microbial carrier block 6 is not limited to the inside of the support part 5, but may also be placed outside or around it. The structure can be modified as appropriate, as long as it does not impair its function of capturing and retaining sediment and microorganisms. Furthermore, if necessary, high-density materials such as gravel, mineral particles, and metal fragments may be filled into block 6 before installation. Block 6 itself can also function as part of the mass adjustment unit (ballast). Figure 2B is a view of the support section 5 and the microbial carrier block 6 from below. In the figure, the area indicated by the shaded lines represents the effective contact projection area Aeff(s) in the present invention. Aeff(s) includes the projected area of ​​the region where the bottom surface of the support part 5 contacts the substrate S, The contribution of the lateral portion that transmits the load to the bottom sediment S according to the penetration depth s is It is defined as the effective support surface included when projected in the direction of the base. The lateral contributions include the effects of shear stress transmission, suction, and undrained negative pressure in the sediment S. It is not treated as the pure geometric lateral surface area itself, but rather as an equivalent area for design purposes. Let Dsupp be the representative diameter of the support projection, where Dsupp is the diameter of the largest circumscribed circle for the convex hull of the horizontal projection contour of the support portion 5. This is used to calculate the geometric guideline s / Dsupp, which will be described later. In this example, a ring-shaped support is shown, The shape of the device may be circular, rectangular, polygonal, a footprint plate, skirt-shaped, etc. Aeff(s) and Dsupp can be defined as design metrics that do not depend on the shape of the support portion 5.

[0013] (3) Operation definition of the sediment S and reference interface z_ref The sediment S targeted by this invention is a non-Newtonian medium that exhibits an apparent (effective) yield stress in a static state. The sediment S may be a mixed system containing silt, clay, organic sludge, and biofilm, and has an effective (apparent) yield stress τ*_y(z) that includes the effects of lateral friction, suction, undrained negative pressure, thixotropy, etc. The reference interface z_ref is defined as the shallowest depth at which a significant increase in shear resistance occurs compared to measurements in the supernatant water. In other words, when a shear test is performed in the depth direction, the first depth at which the torque or resistance force clearly increases compared to the noise level of the measurement system can be considered the reference interface z_ref at which the bottom sediment S begins to support the load as a substantially continuous body. The reference interface z_ref is determined, for example, by the following method. (a) Small vane process Refer to Figures 4 and 5. As shown in Figure 4, small vanes 10A and 10B are attached to the tip of shaft 11 and rotated at different depths z in the water body W and bottom sediment S. The maximum torque T(z) for each depth is determined from the torque-rotation angle curve when the vanes are rotated at a predetermined low speed. The noise level of the measurement system is obtained by performing a supernatant water or empty test, and the range of variation above and below this noise level is defined as the noise band. When the maximum torque T(z) is measured while varying the depth z, the first depth at which T(z) clearly exceeds the noise band can be considered the reference interface z_ref. Figure 5 is a graph illustrating this schematic relationship, showing how T(z) remains near the noise level as the depth z increases, and then clearly rises near z_ref. Here, the specific width of the noise band and the criteria for determining "significantly exceeding" are set appropriately according to the measurement system and the type of sediment S, and the present invention is not limited to specific statistical quantities or numerical conditions. (b) Flat plate indenter method A small flat plate indenter is pressed into the surface of the bottom sediment S, and the change in sedimentation velocity in response to the load is measured. In the same measurement system, the shallowest depth at which the sedimentation velocity begins to continuously decrease in response to the increase in load, compared with the sedimentation behavior obtained in the supernatant water, may be defined as the reference interface z_ref. (c) Optical method (equivalent means) The side surface of the bottom sediment S is photographed using a transparent container or similar, and the brightness profile in the depth direction is determined. The position where the gradient of the brightness profile is maximum, or the position observed as the boundary between the water body and the bottom sediment, may be defined as the reference interface z_ref. The z_ref determined by these procedures is an operational interface based on relative determination that does not require absolute value calibration, and is reproducible by a third party using the same procedure. The penetration depth s is the vertical distance from the reference interface z_ref to the lowest contact point of the load support of the support part 5. Furthermore, in one embodiment, The reference interface z_ref may also be determined using the measuring tool 70 shown in Figures 7A, 7B, 8A, and 8B. That is, the measuring tool 70, which is equipped with a vertically extending support member (guide pipe) 7a and an interface follower 7b attached to its lower end, is inserted from the water surface W. The interface follower 7b moves with almost no resistance in the supernatant water, and the depth at which a clear rise in resistance is observed when it comes into contact with the bottom sediment S can be operationally defined as the position of the reference interface z_ref. In this specification, "water surface W" refers to a position that represents the free water surface (still water surface) in the water body W at the time of measurement. In this specification, the vertical distance from the water surface W to the reference interface z_ref may be described as h_ref, and this h_ref is used as a manipulated variable that represents the depth of the reference interface z_ref with respect to the water surface W. Unless otherwise specified in this specification, the subsoil S and the z_ref and penetration depth s related to the subsoil shall all be based on the operational definitions described in this section.

[0014] (4) Definition of ground pressure p and effective contact projection area Aeff(s) The autonomous sedimentation device 1 of the present invention applies a ground pressure p based on the underwater apparent load W′ and the effective contact projection area Aeff(s) to the bottom sediment S, thereby achieving autonomous sedimentation cessation at least a desired penetration depth. In a more preferred embodiment, it can generate a stepped sedimentation behavior in which a stationary phase and a sedimentation event alternate depending on a threshold condition. The apparent underwater load W′ of device 1 is defined as the resultant force obtained by subtracting the buoyancy component from the gravity of the entire device (for example, it can be expressed as W′ = W - ρ_w g V, but is not limited to this relationship). Here, W is the weight of the device, ρ_w is the density of water, g is the acceleration due to gravity, and V is the volume of the device removed underwater. In embodiments using the buoyancy adjustment unit 5u or the mass adjustment unit, W′ becomes a design parameter that can be changed according to the operating conditions. The effective contact projection area Aeff(s) is the area equivalently represented as a projection onto the horizontal plane of the portion that contributes to load support between the device 1 and the bottom material S when the device 1 penetrates to the bottom material S side by a penetration depth s from the reference interface z_ref. Aeff(s) includes the bottom projection of the support portion 5, as well as the portion where the side surface contributes to load support depending on the penetration depth s. For example, as shown in Figures 1A, 1B, 2A, and 2B, when the support portion 5 is ring-shaped, Aeff(s) can be defined as the equivalent area of ​​the bottom surface projection portion, which consists of the contact width and circumferential length of the ring's lower surface, plus the contribution of the ring's side surface according to the penetration depth s. The contribution of the side surface includes effects such as shear stress transmission and attraction of the bottom surface S, and is therefore treated as an equivalent area for design purposes, rather than the purely geometric side surface area itself. The ground pressure p is defined as the value obtained by dividing the apparent load W' in water by the effective contact projection area Aeff(s). p = W′ / Aeff(s) This ground pressure p is an index compared to the effective yield stress τ*_y(z) distributed in the depth direction in the bottom sediment S. Generally, it can be interpreted that when p is smaller than τ*_y(z) at the given depth, no plastic flow occurs and the device 1 remains stationary, and when p reaches or exceeds τ*_y(z), sedimentation proceeds. In embodiments with a triggering means, at least one or both of p and τ*_y(z) change over time, and the holding of this threshold condition p>=τ*_y(z) occurs discretely, resulting in a stepwise sedimentation behavior in which a stationary phase and discrete sedimentation events alternate. The representative dimension Dsupp of the support portion 5 is defined as the diameter of the largest circumscribed circle for the convex hull of the horizontal projection contour of the support portion 5 when viewed from below. Dsupp can be uniquely defined regardless of the shape of the device, such as circular, rectangular, ring-shaped, or skirt-shaped, and is used as a geometric index for the penetration ratio s / Dsupp, which will be described later. In this specification, the effective yield stress at the position corresponding to the penetration depth s from the reference interface z_ref may be abbreviated as τ*_y(s) for convenience, in which case τ*_y(s) is interpreted as corresponding to τ*_y(z) at z=z_ref+s. Here, the effective yield stress τ*_y(z) and effective contact projection area Aeff(s) as used herein are apparent quantities that include lateral friction, suction, undrained negative pressure, thixotropy, and other factors, and are not bound by any specific constitutive law or theoretical model. Equation p=W′ / Aeff(s) is a practical expression that gives a design index after incorporating these factors into τ*_y(z) and Aeff(s), and it is assumed that even if other factors exist, they can be treated as equivalent by absorbing them into τ*_y(z) and Aeff(s).

[0015] (5) Behavior of autonomous sedimentation and autonomous step sedimentation The autonomous sedimentation device 1 of the present invention achieves autonomous sedimentation cessation at least a desired penetration depth based on the threshold relationship between the ground pressure p and the effective yield stress τ*_y(z) of the sediment S. Furthermore, in a preferred embodiment comprising the configuration described in claim 14, autonomous stepwise sedimentation behavior is observed in which a stationary phase and a sedimentation event alternate. First, in the initial state when device 1 is placed in the water body W and quietly set on the reference interface z_ref, the ground pressure p, based on the apparent load W′ of device 1 in water and the effective contact projection area Aeff(s) corresponding to the penetration depth s, is set to be smaller than the effective yield stress τ*_y(z) of the bottom sediment S at the same depth (p<τ*_y(z)). In this case, the bottom sediment S does not undergo plastic flow, and device 1 remains stationary autonomously without the use of external mechanical lifting means (stationary phase). Subsequently, changes in the sediment S over time (changes in water content, growth or decomposition of biofilms, generation and dissipation of gases, redeposition, etc.) and changes in the state of the apparatus 1 (increase in W′ due to capture of sediments and biofilms, increase or decrease in W′ due to changes in the state of the buoyancy adjustment section 5u, deformation and expansion of components involved in A_eff(s), etc.) cause a local decrease in τ*_y(z), an increase in ground pressure p, or both, resulting in a change in the relationship between p and τ*_y(z) over time. Furthermore, in embodiments comprising trigger means corresponding to claims 3 and 4, the local τ*_y(z) of the sediment S can be reduced or the ground pressure p of the device 1 can be increased by means of dispersed fluid supply, mechanical vibration, local temperature adjustment, adjustment of chemical or photochemical conditions, adjustment of biological or biochemical conditions, ballast pouring or discharging, or other means. As a result of these actions, while p>=τ*_y(z) holds in the operating region directly below or near the support 5, plastic flow occurs in that region, and the device 1 sinks downward (settling event). During a sedimentation event, the penetration depth s changes as the position of device 1 changes, and accordingly, the effective contact projection area Aeff(s) and the depth corresponding to the effective yield stress τ*_y(z_ref+s) for comparison also change. When device 1 stops at the new depth, p < τ*_y(z) at that depth again, the flow of the sediment S stops, and the state returns to the stationary phase. In this way, the stationary phase and the sedimentation event switch autonomously depending on whether the threshold conditions p < τ*_y(z) and p >= τ*_y(z) between the ground pressure p and the effective yield stress τ*_y(z) are met or not. In this specification, "stepped sedimentation" refers to the behavior in which the apparatus 1 repeatedly alternates between a state in which it is stationary in the sediment S (stationary phase) and a state accompanied by discrete sedimentation (settling event) in response to changes in the threshold condition, as described above. In other words, unlike continuous self-weight sedimentation, sedimentation proceeds only when p>=τ*_y(z) is satisfied, and stops autonomously when p<τ*_y(z) returns. Even in an embodiment without a triggering mechanism, stepwise sedimentation may occur as W′ increases due to changes in the physical properties of the bottom sediment S after the installation of the device 1, or as sediment is captured by the device 1, causing a natural change in the relationship between p and τ*_y(z). In this case as well, the switching between the stationary phase and the sedimentation event is performed autonomously based on the threshold relationship between the ground pressure p and the effective yield stress τ*_y(z), and is understood as one embodiment of the autonomous stepwise sedimentation device described in claim 14.

[0016] (6) An example of a triggering mechanism (e.g., a microbubble ring) As shown in Figures 1A, 1B, 2A, and 2B, an annular flow channel 5a is formed inside the support section 5, and a medium can be supplied in a dispersed manner from a number of openings 5c provided on its lower or upper surface. A medium supply port 5b and a port 5d for introducing or removing ballast or fluid are provided on the outer peripheral side of the support section 5, spaced apart in the vertical direction. When a medium such as air, oxygenated water, drug solution, or microbial suspension is supplied from the medium supply port 5b, the medium is discharged in a dispersed manner from the openings 5c through the flow channel 5a. The orientation (bottom or top), arrangement, number, and diameter of the openings 5c, as well as the type of medium supplied, can be appropriately changed within the range that they function as triggers to reduce the effective (apparent) yield stress τ*_y of the sediment S, adjust the ground pressure p, or a combination of both. For example, this can involve supplying microbubbles directly below the sediment S to break down the floc structure and provide a local shear field and gas-liquid mixing, or dispersing and supplying oxygenated water, a drug solution, or a microbial suspension to the upper water body W to change the dissolved oxygen concentration and chemical / biological conditions of the water body W. For example, in one embodiment, the effective density within the buoyancy chamber 5u or support section 5 can be adjusted by introducing solid particles, sediment, water, or gas through the ballast port 5d, thereby increasing or decreasing the apparent load W' in the water. Note that the ballast is not limited to the inside of the support section 5 or buoyancy chamber 5u; weights attached to the outer circumference of the support section, an external ballast tank, or a separate floating body / weight member may also be used. Furthermore, the wall thickness, material density, or cross-sectional dimensions of the support section 5 and the flow path section 5a themselves can be appropriately selected to function as ballast. The specific arrangement and connection structure are arbitrary, and the present invention is not limited to a particular structure. As shown in Figures 1A and 1B, in the configuration in which the opening 5c ​​is provided on the lower side, supplying fine bubbles or an oxygenation medium from the opening 5c ​​provides local shear and gas-liquid mixing to the sediment S located directly below or near the support 5, thereby reducing the apparent yield stress τ*_y in that region. The degree of this reduction, its duration, and recovery behavior depend on the triggering means used and the composition, water content, sedimentation state, and other physical properties of the sediment S, and the present invention does not limit these to specific values ​​or time scales. Furthermore, this type of "triggering means acting from the lower side directly below the sediment S" is not limited to fluid supply from the opening 5c, but also includes means of changing the structure and thixotropy of the sediment S by mechanical vibration using a vibrator provided on the lower surface of the support 5, local heating using a heating element, light irradiation of the photocatalytic layer, etc. On the other hand, as shown in Figures 2A and 2B, in the configuration where the opening 5c ​​is located on the upper side, oxygenated water, drug solution, or microbial suspension can be dispersed and supplied from the opening 5c ​​to the water body W, thereby indirectly changing the τ*_y distribution and biological activity in the sediment S by adjusting the dissolved oxygen concentration, chemical conditions, or biological conditions of the water body W. This type of "indirect triggering means via the water body W" is not limited to upward fluid ejection; means of changing the temperature, pH, oxidation-reduction potential, or light environment of the water body W can also be used. The device 1 can be configured to trigger a limited settling event and come to rest again at a new equilibrium position when the ground pressure p=W' / Aeff(s) reaches or exceeds the apparent yield stress τ*_y of the bottom sediment S due to changes in τ*_y of the bottom sediment S caused by these direct or indirect triggers, as well as changes in the apparent underwater load W' due to ballast adjustment, etc. Thus, an autonomous stepwise sedimentation device (Claim 14) exhibiting "stepwise sedimentation behavior" is configured such that the stationary phase and the sedimentation event appear alternately in response to changes in external or internal conditions. Furthermore, the triggering means of the present invention is not limited to the fluid dispersion supply and ballast adjustment described above, but can also be used individually or in combination with mechanical vibration, local temperature adjustment, chemical or photochemical adjustment, biological or biochemical adjustment, or other means. These are intended to control the establishment of the threshold p>=τ*_y by reducing the effective (apparent) yield stress τ*_y of the sediment S or increasing the ground pressure p (at least one of the above), and the specific configuration and operating conditions can be appropriately designed and modified by those skilled in the art according to the sediment conditions.

[0017] (7) Ground pressure setting mechanism (mass, buoyancy, self-loading) The ground pressure p is determined by the apparent load in water W' and the effective contact projected area Aeff(s), as defined by p = W' / Aeff(s). Therefore, by making at least one of these adjustable, flexibility in the design and operation of the device 1 can be ensured. The ground pressure setting mechanism of the present invention is configured to adjust the mass distribution, buoyancy distribution, and Aeff(s) individually or in combination to obtain a desired p. In this embodiment, the support section 5 has a buoyancy chamber 5u formed inside it, into which air or a lightweight fluid is sealed and can be added or removed as needed to adjust the buoyancy. The buoyancy chamber 5u may be configured as a variable air chamber, a simple sealed space, a configuration that houses a separate buoyancy material such as foam, or a configuration in which a separate buoyancy body is attached to the outer circumference of the support section 5. This makes it possible to continuously or stepwise adjust the apparent underwater load W′ of the entire device 1 over a wide range. Furthermore, the microbial carrier block 6 is composed of porous material, fibrous material, etc., and over time after installation, it functions as a substrate for the attachment and proliferation of various microorganisms in the surrounding water body W and sediment S (a carrier for microbial colonies), and can retain organic matter, suspended particles, sludge flocs, biofilms, and moisture on its surface and inside. As a result, the total mass of the device 1 and the apparent load in water W'(t) change over time, and it can function as a self-loading module in which p(t)=W'(t) / Aeff(s) changes autonomously. Initially, buoyancy prevails, keeping the device near the surface with relatively low ground pressure. Subsequently, as sediment and biofilm accumulate, the device gradually becomes heavier, resulting in a stepped sedimentation behavior in which a stationary phase and a sedimentation event alternate, depending on the presence or absence of a trigger mechanism or its operation status. This allows for the realization of an operating mode as an autonomous stepped sedimentation device as described in claim 14. Furthermore, by filling the inside or surrounding area of ​​the microbial carrier block 6 with high-density materials such as gravel, mineral particles, or metal fragments before installation, the block 6 itself can also function as a mass adjustment section (ballast). The mass adjustment section is not limited to the block 6, but may be configured as detachable weights, ballast water chambers, or external ballast tanks placed inside or outside the support section 5. The specific arrangement and connection structure are arbitrary, and the mass distribution and center of gravity of the device 1 should be adjusted to set W' within the desired range, and the ground pressure p should be kept within the desired range by p = W' / Aeff(s). To adjust the effective contact projection area Aeff(s), a ring member, skirt-like member, footprint plate, variable rigidity mesh, etc., which can be expanded or contracted are provided on the outer circumference of the support part 5, and the Aeff(s) itself can be increased or decreased by deploying or retracting them after penetration. For example, in the initial stages of installation, a relatively small footprint can be used to allow the structure to sink to a certain depth, and then, once a predetermined penetration depth s is reached, the skirt-like member can be deployed to increase Aeff(s), reduce the ground pressure p, and stabilize the stationary phase. The support portion 5 may be configured as a hollow body with a flow channel portion 5a and an opening 5c, or as a substantially solid body or a sealed hollow body with the flow channel portion 5a omitted. In either embodiment, the horizontal projection surface on which the support portion 5 provides load support to the bottom sediment S constitutes a part of the effective contact projection area Aeff(s), and the ground pressure p can be set within the design range by combining it with the mass adjustment portion, buoyancy adjustment portion and self-loading module. These mass adjustment units, buoyancy adjustment units, Aeff(s) variable members, and self-loading modules constitute specific examples of the ground pressure setting mechanism according to claims 6 and 7, and may be used individually or in combination with other components. The specific shapes, materials, arrangement, and control methods of the components can be appropriately designed by those skilled in the art according to the target sediment conditions and desired step-level settling characteristics.

[0018] (8) Geometric pointer s / Dsupp As described above, Dsupp is defined as the maximum circumscribed circle diameter for the convex hull of the horizontal projection contour of the support portion 5, and the geometric guideline s / Dsupp is evaluated in combination with the penetration depth s. As shown in Figures 3 and 2B, when the device 1 is installed in a non-Newtonian sediment S, the penetration depth s is defined as the distance from the reference interface z_ref to the load-bearing surface of the support part 5. In the present invention, in a particularly preferred embodiment, the expected penetration depth s after the installation of the device 1 is set to a range of 0.05 to 0.40 times Dsupp. In extremely shallow installations where s / Dsupp is less than 0.05, contact stability with the bottom sediment S is insufficient, and horizontal drift due to water flow etc. tends to increase. In addition, the load support contribution of the support side surface does not rise sufficiently, and the reproducibility of stepwise settlement events tends to decrease. On the other hand, in deep installations where s / Dsupp exceeds 0.40, discrete settlement events tend to transition to continuous settlement due to reaching high-strength layers or the occurrence of non-localized creep, and the separation between the stationary phase and settlement events may become unclear. Therefore, by setting s / Dsupp within the above range, it is easier to obtain a stepwise sedimentation behavior in which the stationary phase and the sedimentation event are clearly separated, and the operational stability of the apparatus 1 is improved. Furthermore, this s / Dsupp range is a representative guideline for easily achieving the stepwise settlement behavior described in claim 14 in terms of design, based on the yield stress distribution of the sediment S and the device shape ratio. Depending on on-site conditions such as the composition and compaction of the sediment S, the stepwise settlement behavior described in claim 14 may be obtained even with an s / Dsupp outside this range. The technical scope of the device according to the present invention is not limited to the above numerical range, nor does it exclude installation outside this range.

[0019] (9) Relative settlement module (settlement along the column) Figure 6 shows an example of a modular configuration that settles in stages relative to the fixed column 20. The fixed column 20 is a supporting column erected in a non-Newtonian sediment S, and may be installed as an integral part of or separately from existing structures such as embankments, revetment structures, bridge piers, piers, pile foundations, etc. The autonomous sedimentation device 1 (relative sedimentation module configuration shown in Figure 6) is a unit that includes at least a support section 5 and optionally a microbial carrier block 6 or other functional members, and has a guide section that is slidable relative to the fixed column 20 in the vertical direction. The guide section may be a sleeve structure that penetrates the fixed column 20, or a clamp or slider structure that holds the outside or inside of the column 20, and its specific arrangement (whether the column is inside or outside) is arbitrary. The guide section allows module 1 to slide vertically along column 20, and it sinks relative to column 20 in accordance with each event of stepwise settlement. In this configuration as well, the support section 5 of module 1 defines an effective contact projection area Aeff(s) with respect to the bottom sediment S, and the ground pressure p=W' / Aeff(s) based on the underwater apparent load W' of module 1 and Aeff(s) is compared with the effective yield stress τ*_y(z) of the bottom sediment S, as in the above embodiments. In other words, while p < τ*_y(z), module 1 remains stationary at a predetermined penetration depth s, and a sedimentation event occurs only when p >= τ*_y(z) is satisfied due to the activation of the triggering means or a change in W′(t)·Aeff(s(t)), exhibiting a stepwise sedimentation behavior in which it becomes stationary again at a new depth. By using such a relative settlement module, even if the column 20 is fixed to a revetment structure or pier, for example, the module 1 can autonomously settle along the column 20, allowing for stepwise processing of the bottom sediment S in a desired depth range. Furthermore, since the relative position along the column 20 can be easily measured by independent sensors or scales, there is an advantage in the embodiment exhibiting stepwise settlement behavior, as described in claim 14, in particular, that the progress of the settlement process can be easily monitored. Furthermore, the fixed column 20 is not limited to one; a configuration using multiple guide columns is also possible, and the column 20 itself may also serve as part of a structure such as a quay, pile, or caisson. The specific structure of the guide section (sleeve, roller guide, slide rail, etc.) and the fixing method are arbitrary, and as long as module 1 can slide relative to column 20 in the vertical direction, any such configuration is included within the technical scope of the relative settlement module of the present invention.

[0020] (10) Measuring instrument for measuring the reference interface z_ref and penetration depth s Figure 7A is a side view showing the schematic configuration of a measuring instrument for measuring the reference interface z_ref and penetration depth s in a water body W, and Figure 7B is a perspective view of the same measuring instrument. Figures 8A and 8B show modified examples with a one-way locking mechanism. Conventionally, in non-Newtonian sediments S with yield stress, such as sludge, peat, and various types of sludge, there has been a lack of simple measurement methods that can reliably obtain the interface position and penetration depth based on the depth from the water surface W. To solve this problem, the measuring tool 70 of this embodiment provides a configuration that allows the reference interface z_ref and penetration depth s to be operationally defined by the relative distance from the water surface W. (10-1) Composition As shown in Figure 7A, the measuring instrument 70 comprises a slender guide pipe 7a extending vertically and a disc-shaped interface follower 7b attached to its lower end. The guide pipe 7a is, for example, a hollow rod-shaped body, and may have markings on its outer surface along its entire length, or it may be used in combination with an external scale. The guide pipe 7a is not limited to being positioned across the water surface W during use; it may protrude above the water surface W, or its length may be approximately to the water surface W, as long as it has a length that allows the vertical distance between the water surface W and the interface follower 7b to be read. The interface follower 7b is a substantially disc-shaped member attached to the lower end of the guide pipe 7a, and its outer shape is not limited to a circle, but may be polygonal, elliptical, ring-shaped, etc. The lower surface of the interface follower 7b is placed near the reference interface z_ref located at the boundary between the water body W and the bottom sediment S when in use, and has an area and shape such that when the interface follower 7b is moved horizontally above the bottom sediment S it slides substantially along the height of z_ref, and its weight and dimensions are designed so that it does not penetrate excessively deep into the bottom sediment S. In the embodiments shown in Figures 7A and 7B, a flexible element 7c made of a flexible tensile element (string, wire, tape, etc.) may be attached to the guide pipe 7a either inside or along its outer circumference. One end of the flexible element 7c is connected to the vicinity of the lower end of the interface follower 7b or the guide pipe 7a, and the other end is led out above the water surface W. The flexible element 7c is positioned such that when the guide pipe 7a is pushed further downward while the interface follower 7b is stationary and supported by the bottom sediment S near the reference interface z_ref, the flexible element 7c substantially extends or extends together with the interface follower 7b, and its length change corresponds to the penetration behavior of the interface follower 7b. A one-way locking mechanism 7d may be provided in the middle of the flexible element 7c or on the guide pipe 7a side. The one-way locking mechanism 7d allows relative movement of the flexible element 7c in the direction that pulls it out toward the water surface W, and locks relative movement in the opposite direction, i.e., toward the bottom sediment S. For example, a structure can be used in which a locking claw provided in a cylindrical housing, like a cable tie, slides the flexible element 7c when it moves in a predetermined direction, and engages with teeth to prevent it from returning in the opposite direction. With such a one-way locking mechanism 7d, when the interface follower 7b sinks slightly from near the reference interface z_ref, the flexible element 7c is extended by a length approximately corresponding to the amount of sinking, and this extended amount is maintained when the entire measuring tool 70 is subsequently pulled up toward the water surface W. The one-way locking mechanism 7d may also be provided directly between the guide pipe 7a and the interface follower 7b without the use of the flexible element 7c. In the embodiments shown in Figures 8A and 8B, the one-way locking mechanism 7d is configured by providing a sawtooth-shaped rack section or multiple locking grooves along the outer circumference of the guide pipe 7a, and providing locking claws on the interface follower 7b side that engage with these. In this case, the one-way locking mechanism 7d allows relative movement of the interface follower 7b toward the water surface W side with respect to the guide pipe 7a when the guide pipe 7a is further pushed while the interface follower 7b is in contact with the bottom sediment S, and locks relative movement of the interface follower 7b toward the bottom sediment S side that occurs in the opposite direction, i.e., when the measuring tool 70 is pulled up toward the water surface W side. As a result, the relative position between the guide pipe 7a and the interface follower 7b at the end of the measurement is maintained by the unidirectional locking mechanism 7d, and even after the device is raised above the water surface W, the relative distance can be directly measured to geometrically calculate the depth h_ref from the water surface W to the reference interface z_ref, and the penetration depth of the interface follower 7b. In addition to the guide pipe 7a, interface follower 7b, flexible element 7c, and unidirectional locking mechanism 7d, the measuring instrument 70 may further include a handle, a float, a guide member for stabilizing posture, etc. These additional components are optional elements to facilitate the measurement operation, and the basic functions of the measuring instrument 70, namely the identification of the reference interface z_ref and the measurement of the penetration depth s, are achieved by these components. (10-2) Measurement of reference interface z_ref and h_ref Next, the procedure for measuring the reference interface z_ref and the depth h_ref from the water surface W to the reference interface z_ref in the water body W using the measuring instrument 70 will be described. First, as shown in Figure 7A, the interface follower 7b is gently inserted into the water body W from the water surface W while the guide pipe 7a is held approximately vertically. While the interface follower 7b descends in the supernatant water, it moves smoothly with almost no resistance, but when it reaches the vicinity of the boundary with the bottom sediment S, its lower surface comes into contact with the bottom sediment S, and clear resistance appears to further sinking. The position of the interface follower 7b at this time corresponds to the reference interface z_ref described in [(3) Definition of operation of bottom sediment S and reference interface z_ref] above. Specifically, let h be the vertical distance between the water surface W at the time of measurement and a reference position set on the guide pipe 7a (for example, the top of the pipe, or an arbitrary reference mark). The depth h_ref from the water surface W to the reference interface z_ref can be determined as the difference between h and the vertical distance from the same reference position to the bottom surface of the interface follower 7b. If the thickness of the interface follower 7b cannot be ignored, this thickness may be corrected. Here, h_ref is a manipulated variable that represents the "depth from the water surface W to the reference interface z_ref," and uniquely defines the position of z_ref in the water body W without knowing the absolute elevation of the bottom surface. As shown in the embodiments of Figures 7A and 7B, when the measuring tool 70 is equipped with a flexible element 7c, the protruding length of the flexible element 7c when the interface follower 7b reaches z_ref can be measured, and the change in length when the guide pipe 7a is further pushed in can also be read, which can then be used to estimate the penetration depth s described later. On the other hand, in the modified examples shown in Figures 8A and 8B, the flexible element 7c is not used, and a one-way locking mechanism 7d is provided between the guide pipe 7a and the interface follower 7b. In this case, the one-way locking mechanism 7d allows the interface follower 7b to move relatively toward the water surface W while the guide pipe 7a is further pushed in with the interface follower 7b in contact with the bottom sediment S, and locks the relative movement of the interface follower 7b that would cause it to return to its original position when the entire measuring tool 70 is pulled up toward the water surface W. Therefore, if the distance between the guide pipe 7a and the interface follower 7b is measured directly after the measurement is completed, h_ref can be calculated in the same way as described above. (10-3) Definition of penetration depth s In this specification, "penetration depth s" is defined as the vertical distance from the reference interface z_ref to the load-bearing surface of any measuring object or device. That is, when h is the depth from the water surface W to the load-bearing surface at the time of measurement, and h_ref is the depth of the reference interface at the same time, the penetration depth s is expressed by the following equation. s = h -h_ref For example, if the total length of the flexible element 7c is 30 cm, and the depth from the water surface W when the interface follower 7b reaches the reference interface z_ref is h=27 cm, and then it sinks another 1 cm to s=1 cm, then h_ref becomes 26 cm. In this way, by using the penetration depth s, which is defined as the difference between h and h_ref, the relative amount of sinking from the reference interface z_ref can be uniquely evaluated without knowing the absolute bottom position of the sediment S. (10-4) General-purpose and monitoring applications Furthermore, the measuring instrument 70 is not limited to use in combination with the autonomous sedimentation device 1, but is also useful as a standalone measuring device for measuring the reference interface z_ref and the penetration depth s from the interface of **non-Newtonian sediment S (e.g., yield stress medium such as sludge, peat, etc.)** in any body of water W. In other words, the measuring instrument 70 itself provides a general-purpose measurement technique for determining z_ref operationally without directly identifying the bottom surface position and obtaining depth information based on z_ref. Furthermore, by repeatedly performing measurements using this measuring instrument 70 over time for the same water body W, it is possible to track the position of the reference interface z_ref and the change in resistance at a predetermined penetration depth s. This makes it possible to use it as a monitoring tool to understand changes in the layer structure due to the decomposition, consolidation, and redeposition of non-Newtonian sediment S, as well as changes in sediment properties over time caused by the operation of purification equipment (for example, whether z_ref is gradually decreasing). Thus, the measuring instrument 70 is useful not only for examining the design, installation, and operating conditions of the autonomous sedimentation device 1, but also as an independent measurement technique that contributes to diagnosing the condition of the sediment S and evaluating and managing the purification process. (10-5) Simple configuration and low cost Traditionally, determining the interface location and mechanical properties of non-Newtonian sediments (S) often required specialized equipment equipped with electrical exploration devices, pressure sensor probes, or expensive measuring instruments. However, these complex and costly systems were not always suitable for routine monitoring by general field workers. In contrast, the measuring tool 70 of this embodiment has a basic configuration consisting of an elongated guide pipe 7a and an interface follower 7b, and only requires the addition of a simple length measuring mechanism consisting of a flexible element 7c and a unidirectional locking mechanism 7d as needed. Therefore, its structure is extremely simple, and it can be manufactured lightly and inexpensively. In the simplest embodiment, the position of the reference interface z_ref can be determined using only the guide pipe 7a and the interface follower 7b, and if it is desired to quantitatively record the penetration depth s and its change over time, it is sufficient to add the length measuring mechanism equipped with the flexible element 7c and the unidirectional locking mechanism 7d. As a result, even small businesses and local government officials who do not have specialized measuring equipment readily available can easily measure and remeasure z_ref and penetration depth s on-site, and easily grasp the progress of decomposition, consolidation, and redeposition of the bottom sediment S.

[0021] (11) Measuring device (cube measuring tool) for evaluating penetration depth s Figure 9A is a side view showing the use of a measuring body for evaluating the penetration depth s from a reference interface z_ref, and Figure 9B is a perspective view thereof. Figures 10A and 10B show modified examples with the addition of a flexible element 8c and a unidirectional locking mechanism 8d. In this specification, h_ref is a manipulated variable representing the "depth from the water surface W to the reference interface z_ref" obtained using the measuring instrument 70 shown in Figures 7A and 7B, and Figures 8A and 8B. The measuring body 80 shown in Figure 9A is intended to easily evaluate the penetration depth s from the reference interface z_ref using this known h_ref, and aims to provide a test specimen* that allows for easy understanding of the relationship between p=W′ / Aeff(s) and the effective yield stress τ_y(z) of the non-Newtonian sediment S under field conditions. (11-1) Composition In the basic configuration shown in Figures 9A and 9B, the measuring body 80 comprises a vertically extending, elongated support member 8a, a measuring body block 8b attached to its lower end, and a flexible element 8c connected thereto. The support member 8a is a rigid member in the shape of a rod or pipe, and its length is appropriately selected according to the assumed water depth in the water body W and the depth of z_ref. The outer circumference of the support member 8a may be provided with scales or reference marks, and a guide portion may be provided to guide the flexible element 8c and the one-way locking mechanism 8d, which will be described later. The measuring block 8b is constructed as a rectangular parallelepiped (a so-called cube) of approximately 4 cm × 4 cm × 10 cm, with its downward-facing surface functioning as a load-bearing surface for the bottom sediment S. The planar shape and dimensions of block 8b can be appropriately changed according to the properties of the target bottom sediment S and the expected range of ground pressure, and are not necessarily limited to a square shape. The density and volume of block 8b are selected so that it has a net settling force in water, and when allowed to settle naturally in the bottom sediment S, it is configured to come to rest at a predetermined depth according to the balance between the effective yield stress τ*_y of the bottom sediment S and the ground pressure. The flexible element 8c is a flexible tensile element made of string, wire, tape, etc., with one end connected to the vicinity of the lower end of the measuring body block 8b or support member 8a, and the other end led out above the water surface W along the support member 8a. In the basic configuration shown in Figures 9A and 9B, the flexible element 8c is used simply as an auxiliary element for reading the change in length, and the penetration depth s can be estimated by measuring the difference in overhang length between the initial state and the state after sinking. In the modified examples shown in Figures 10A and 10B, a one-way locking mechanism 8d is provided in addition to the basic configuration. The one-way locking mechanism 8d is a mechanism that allows only relative movement of the flexible element 8c toward the bottom sediment S side, and locks relative movement in the opposite direction, i.e., movement that attempts to send the flexible element 8c back toward the water surface W side. For example, a locking claw can be integrally formed on the upper part of the support member 8a, and a ratchet mechanism can be used in which a jagged rack portion or knot portion is provided on a part of the flexible element 8c, and the rack portion and the locking claw engage. In this configuration, as the measuring body block 8b sinks toward the bottom sediment S, the flexible element 8c is gradually pulled out toward the bottom sediment S from the one-way locking mechanism 8d, and the overhang length of the flexible element 8c increases accordingly. Once pulled out, the one-way locking mechanism 8d prevents it from returning to the water surface W, so even if the support member 8a is pulled up above the water surface after the measurement is complete, the overhang length of the flexible element 8c retains the value it had at the end of sinking. Here, "effective length of flexible element 8c" refers to the length of the flexible element 8c that substantially extends from the reference position on the water surface W (e.g., the position of the one-way locking mechanism 8d) to the measurement block 8b. Its change ΔL can be used as an indicator of the change in the penetration depth s from the reference interface z_ref of the measurement block 8b. (11-2) Setting the reference position (s=0) Next, we will describe a method for evaluating the penetration depth s using the measuring body 80. First, the depth h_ref from the water surface W to the reference interface z_ref in the target water area W is obtained in advance using the measuring instrument 70 shown in Figures 7A and 7B, and Figures 8A and 8B. Next, as shown in Figure 9A, the measuring body block 8b is gently inserted into the water while holding the support member 8a vertically, and the support member 8a is pushed down until its lower surface reaches the vicinity of the reference interface z_ref. At this time, the position where the downward surface of the measuring body block 8b comes into contact with the bottom sediment S and clear resistance to further sinking appears, or the position estimated from the correspondence between the scale provided on the support member 8a and h_ref, can be considered as the reference position corresponding to s=0. In a configuration with a flexible element 8c, the effective length L0 of the flexible element 8c in the state s=0 is read as the length from the reference position on the water surface W to the connection position of the measuring body block 8b. In a simple configuration like those shown in Figures 9A and 9B, it is sufficient to record L1 once it has been read, and any means such as visual reading, marking with a marker, or taking a photograph can be used. (11-3) Reading of free settlement and penetration depth s As described above, after the reference position at s=0 is set, the measurement block 8b is allowed to freely settle in the sediment S. Specifically, the operator releases the support force of their hand that was resting on the support member 8a, and the measurement block 8b settles into the sediment S by its own weight. During settling, due to the relationship between the ground pressure p acting on the measurement block 8b and the effective yield stress τ*_y(z) of the sediment S distributed in the depth direction, when p < τ*_y(z) at a certain depth, no further plastic flow occurs, and the block 8b comes to rest at a new equilibrium position. In the simple configuration shown in Figures 9A and 9B, the effective length L1 of the flexible element 8c can be read again after the settlement is complete, and the difference ΔL = L1 - L0 can be used as an estimate of the penetration depth s of the measurement block 8b. If the flexible element 8c is guided almost linearly along the support member 8a and configured so that entanglement and slack do not occur, ΔL will be a value close to the actual penetration depth s. In the configuration with the unidirectional locking mechanism 8d shown in Figures 10A and 10B, after setting the effective length L0 of the flexible element 8c in the state where s=0, the unidirectional locking mechanism 8d is activated and the measuring body block 8b is allowed to sink freely. While the block 8b sinks into the bottom sediment S, the flexible element 8c is pulled out from the unidirectional locking mechanism 8d toward the bottom sediment S, and its effective length increases by that amount. Since the unidirectional locking mechanism 8d locks the flexible element 8c from returning toward the water surface W, even if the entire support member 8a is pulled up above the water surface after sinking, the effective length L1 of the flexible element 8c is maintained at the value at the end of sinking. Therefore, even in this configuration, the penetration depth s of the measurement block 8b can be easily evaluated by measuring ΔL=L1-L0. By using the one-way locking mechanism 8d, the reading operation on the water surface W can be performed slowly after sinking, making it easier to ensure measurement accuracy even in field environments with poor flow and visibility. The flexible element 8c and the unidirectional locking mechanism 8d are merely examples for reading the relative displacement corresponding to the penetration depth s. Any configuration that can measure the positional difference before and after penetration with a predetermined accuracy is included in the measuring body 80 of the present invention, such as a configuration combining a slide rod and a scale, or a configuration incorporating an optical or magnetic displacement sensor into the support member 8a. (11-4) Positioning and versatility of the measuring body 80 As described above, the measuring body 80 is used to evaluate the penetration depth s as an additional amount of sedimentation relative to h_ref (= depth from the water surface W to the reference interface z_ref), which has been previously obtained by the measuring instrument 70, etc. Once h_ref and s are obtained, the depth of the stationary position of the measuring body block 8b (for example, the depth from the water surface W to the bottom surface of block 8b) can be uniquely determined, and this can be used to design and evaluate the depth range that the support part 5 of the actual autonomous sedimentation device 1 can reach. The measuring body 80 exhibits the same behavior as the autonomous sedimentation device 1 of the present invention, remaining stationary and sinking on a non-Newtonian sediment S. However, because of its simple structure and ease of handling, it is useful as a test specimen for pre-confirming the effective yield stress distribution and penetration behavior of the sediment S, from laboratory scale to field scale. Furthermore, it can be used as a general-purpose tool to investigate the relationship between p=W′ / Aeff(s) and τ*_y(z) using cubes of different dimensions and masses for yield stress media such as sludge, peat, and various slurries, and to grasp the progress of consolidation and decomposition of the sediment S through time-series measurements. Furthermore, the measuring instrument 70 and the measuring body 80 are not limited to being used in combination with the autonomous sedimentation device 1, but are measuring devices or measuring kits that can constitute an independent inventive concept on their own. [Examples]

[0022] [Supplementary information regarding depth display] In this example, since the position of the bottom surface in the experimental tank is known, the position in the depth direction is conveniently described as "distance from the bottom surface." On the other hand, in an actual body of water W, it is not always easy to directly determine the position of the bottom surface. Therefore, in accordance with the "Operational Definition of Substrate S and Reference Interface z_ref" and the "Measuring Tool for Measuring Reference Interface z_ref and Penetration Depth s," the reference interface z_ref is first measured as the interface position between the water body W and the substrate S. Then, depth information such as the stopping position and vane strength profile can be converted to the "Penetration Depth s from z_ref" and used. In on-site design, even without knowing the absolute position of the base, it is sufficient to evaluate the relationship between the effective yield stress τ*_y(z_ref+s), which is reinterpreted as z = z_ref+s, and the ground pressure p=W′ / Aeff(s).

[0023] Comparative Example 1: Sedimentation behavior in a Newtonian fluid To confirm that the stepwise sedimentation behavior characteristic of the present invention does not occur in typical Newtonian fluids, the following comparative tests were conducted. (1) Test conditions A transparent water tank with internal dimensions of approximately 40 cm x 55 cm x 30 cm was used, and each tank was filled with saline solutions of different densities (approximately 1.00, 1.10, and 1.20 g / mL). An acrylic block (4 cm × 4 cm × 10 cm, mass approximately 180 g) was used as the test specimen. Under all conditions, it was gently lowered from the water surface, and its sinking behavior was observed. We conducted at least three tests (three trials) for each density condition to confirm the reproducibility of the behavior. (2) Observation results In the case of saline solution with a density of approximately 1.00 g / mL The acrylic block sank continuously to the bottom of the tank, sinking completely without pausing along the way. No clear pauses or step-like movements were observed during the sinking process. In the case of saline solution with a density of approximately 1.10 g / mL Although the sinking rate of the acrylic block is small, it continues to sink over time. It reached the bottom of the tank without stopping along the way. In this case as well, no discrete sedimentation events were observed, such as stopping midway and then re-sinking. In the case of saline solution with a density of approximately 1.20 g / mL After the acrylic block slightly immersed in the water, it floated due to the difference in density and came to rest at a certain point in the liquid. Even after coming to rest, no significant changes in sinking or rising were observed during the observation period. Furthermore, under conditions of 1.20 g / mL, the top of the water tank was manually shaken from side to side, applying surface waves with an amplitude of approximately 5 mm to 10 mm to the free surface for about 1 minute. When the position of the acrylic block was measured before and after applying this wide-area oscillation load, the amount of sedimentation was 0 mm within the measurement error, and no re-settling from the stationary position was observed. Similar comparative tests were repeated at least three times (three trials) over multiple days, and in each case, the same behavior as described above was obtained. (3) Summary Therefore, in a typical Newtonian fluid, It stopped briefly along the way. Such that discrete sedimentation steps occur in response to external stimuli. It was confirmed that the stepwise sedimentation behavior characteristic of the present invention does not occur.

[0024] Example 1: Creation of bentonite sediment and layer structure In this embodiment, a simulated sediment consisting of a bentonite dispersion system was prepared, and its layer structure and interface with the water body W (reference interface z_ref) were confirmed as an example of a non-Newtonian sediment S to which the present invention can be applied. (1) Test conditions and preparation method A transparent tank with internal dimensions of approximately 40 cm x 55 cm x 30 cm was placed horizontally, and 7 L (by volume) of commercially available powdered bentonite and 32 L of tap water were added to prepare a dispersion of approximately 39 L in total. The entire tank was thoroughly stirred using a stirring rod to ensure uniform dispersion of the bentonite. After that, the tank was left to stand at room temperature (approximately 20°C to 25°C) without any further mechanical stirring or vibration. (2) Observation of the layered structure Approximately 14 hours after the start of standing, a visual inspection of the tank cross-section revealed the formation of a clear layered structure as shown below. Top layer: Clear to nearly clear water layer (supernatant layer) Intermediate: A translucent to opaque suspension layer with relatively high fluidity (intermediate slurry layer). Bottom layer: A highly concentrated layer (high-concentration sediment layer) that appears gel-like to paste-like and is self-supporting. Even with further extensions of the standing time (e.g., more than 24 hours), this layered structure was maintained unless the entire dispersion was re-agitated, confirming that the supernatant water layer and the high-concentration sediment layer could coexist stably. When a similar bentonite dispersion system was prepared at least three times (three trials) under the conditions of this embodiment, a similar three-layer structure was reproducibly obtained in each case. (3) Summary From the above, it was confirmed that under the conditions of this embodiment, the bentonite dispersion system forms a high-concentration layer with a stable density-concentration gradient upon standing, and that this can be considered as an example of a non-Newtonian sediment S to which the present invention can be applied, and that its interface band corresponds to the reference interface z_ref.

[0025] Example 2: Measurement of the density (specific gravity) of the bentonite layer In this example, the density (specific gravity) gradient in the depth direction was quantitatively confirmed for the bentonite sediment S prepared in Example 1. (1) Test conditions and water sampling method The same tank used in Example 1 was employed, and measurements were taken after 14 hours of standing time. Representative samples for each depth were prepared using the following procedure. 1. Divide the planar position viewed from the top of the aquarium into 6 points (A, B, C, D, E, F). 2. Adjust the tip of the sampling hose so that it is positioned at the desired depth z, and collect approximately 25 mL of sample from each position A through F (totaling approximately 150 mL). 3. Mix the samples from A through F in a single beaker to obtain the "position-averaged" mixed sample at depth z. 4. Take 100 mL of the mixed sample into a 100 mL cylinder, measure its mass using an electronic balance, and calculate its specific gravity (g / mL). The following precautions were taken when collecting water samples. To ensure the straightness of the water sampling hose, a bamboo skewer was inserted into the hose to ensure that the tip was stably positioned at a predetermined depth. The first few milliliters immediately after the start of aspiration were considered to be residual water in the hose and were discarded, while the liquid that flowed out afterward was used as the sample. The sampling location was set 2 to 3 cm away from the bottom and side walls of the tank to avoid the effects of bottom and wall surfaces. We took care to prevent disturbances from shallow water sampling from affecting the deeper areas by first collecting water from the deeper areas and then collecting water from the shallow areas. Measurements were taken at least three times (three trials) for each depth, and the median value was used as the representative value. (2) Measurement results The median values ​​of typical specific gravities were obtained by organizing them by distance from the base, as follows: Depth approximately 25 mm (area relatively close to the bottom): Median specific gravity ≈ 1.23 g / mL Depth approximately 45 mm: Median specific gravity ≈ 1.14 g / mL Depth approximately 65 mm: Median specific gravity ≈ 1.05 g / mL In multiple measurements conducted on different days, the median values ​​for each depth generally fell within a range of approximately ±0.01 g / mL of the above values. Deep layer > Middle layer > Upper layer This hierarchy of weighting was consistently maintained. (3) Summary From the above, it was confirmed that in the bentonite sediment S, a clear density gradient is formed, with the specific gravity being higher towards the bottom and decreasing towards the top. Furthermore, the stepwise sedimentation behavior described later cannot be explained solely by static buoyancy equilibrium based on the "difference between sample density and fluid density," and it was suggested that it needs to be explained by the threshold relationship between the ground pressure p and the effective yield stress τ*_y(z).

[0026] Example 3: Depth-specific relative strength profiles obtained by vane shear testing of bentonite sediment. In this example, the yield stress distribution in the depth direction was determined as a relative index for the bentonite sediment S of Example 1 using a shear test with a small vane. (1) Test apparatus and method Shaft diameter: 4 mm round bar Vane section: A plastic plate approximately 0.5 mm thick was used, and four 10 mm x 5 mm vanes were attached in a cross shape. Torque measurement: A winding cylinder with a radius of approximately 8 mm was attached to the tip of the shaft, a thread was wound around it, and a 1 N spring scale was connected to the other end of the thread to measure the tensile force. Depth adjustment: Height adjustment blocks (approximately 19.2 mm pitch) were used to control the vertical position from the edge of the tank so that the vane center reached the desired depth. The test procedure was as follows: 1. Gently insert the vane to the desired depth z and leave it undisturbed for a few seconds to avoid disturbing the substrate too much. 2. Pull the string to maintain a constant, slow angular velocity and record the maximum reading F_max on the spring balance. 3. Repeat the operation at least three times (3 trials) for each depth, and use the median of F_max as the representative value for that depth. 4. The measurement order was as follows: near the bottom → middle layer → upper layer (near the interface), taking care not to disturb the lower layer during the upper layer test. Under identical adjustment conditions, multiple sets of this test were conducted on different days to confirm that the hierarchy of intensity with depth was reproducible. (2) Results (relative indicators) Based on the obtained maximum torque, a relative strength index r(z) was calculated for each distance from the bottom surface, and the median value was used as the representative value. A representative example is shown below. 70mm to 80mm (near the mud-water interface): Median of relative intensity index ≈ 7 50mm to 60mm: Median of relative intensity index ≈ 24 30mm to 40mm (area relatively close to the base): Median of relative intensity index ≈ 36 In all measurements, Bottom surface (30mm to 40mm) > Middle layer (50mm to 60mm) > Near the interface (70mm to 80mm) This hierarchy was consistently reproduced. The relative strength index used here is an arbitrary unit that depends on the vane shape and winding radius, and does not provide shear strength as an absolute value. However, it is a sufficient index for comparing different depths within the same system. (3) Summary Based on the above, it was confirmed that in bentonite sediment S, the effective yield stress τ*_y(z) increases with increasing depth, which is typical behavior for a non-Newtonian sediment. This depth-dependent relative intensity profile was shown to be consistent with the physical model of the present invention, which states that "settling stops in the layer where τ*_y(z) is greater than or equal to the ground pressure p," as demonstrated in the step-by-step sedimentation experiment described later.

[0027] Example 4 Stepwise sedimentation behavior in bentonite non-Newtonian sediments In this example, using the bentonite sediment S prepared and evaluated in Examples 1 to 3, it was confirmed that the settling behavior of the acrylic block exhibited a stepwise settling behavior consisting of alternating appearances of a "static phase" and "discrete settling events." (1) Test methods and definitions The same acrylic block (4 cm × 4 cm × 10 cm) used in Example 2 for determining specific gravity was used as the test specimen. The block was placed with one end face downwards and gently lowered into the water from above the water surface. The position where the sinking stopped was then read from outside the tank using a scale. The sedimentation behavior was evaluated by repeatedly performing the following steps: "leaving the sample undisturbed for a certain period of time → applying localized shear stimulation from an external source (light tapping of the block support) → measuring the sedimentation depth." In this specification, "discrete sedimentation event" refers to the following behavior: Measurements are taken at regular time intervals (in this embodiment, measurements are taken after 5 minutes of standing and approximately 1 to 2 minutes of stimulation). The difference between measurements taken immediately before and after a certain event appears as a step of several millimeters to tens of millimeters. During the subsequent period of standing, virtually no monotonous creep settlement exceeding the measurement error was observed. We conducted tests at least three times (three trials) for each condition to confirm the reproducibility of the behavior. (2) Experiment A: When the base is 4 × 4 cm An acrylic block was placed in the substrate with its 4x4 cm surface facing downwards and left to settle naturally. The initial resting position was measured at approximately 63 mm from the bottom. The following steps were then repeated. After standing for 5 minutes, there was no significant change in the sedimentation depth, and it remained constant within a measurement resolution of 1 mm. Lightly tap the block support at a constant rhythm (approximately 180 beats / minute) for about 1 to 2 minutes: The measurement immediately following was approximately 51 mm, indicating a settling step of about 12 mm from the previous measurement of 63 mm. After letting it stand for another 5 minutes, no significant change in sedimentation depth was observed. Perform the same light tapping motion again: The depth was approximately 42 mm, representing a subsidence step of about 9 mm from the previous depth of 51 mm. Allowed to stand for another 5 minutes: No significant changes. Furthermore, perform the same light tapping operation: The depth was approximately 37 mm, representing a subsidence step of about 5 mm from the previous depth of 42 mm. Even after standing for another 5 minutes, the depth remained almost constant at around 37 mm, and no further sedimentation was observed. In separate test sets, although there was some variation of a few millimeters in the size of the settling steps and the final stopping position, the gradual pattern of "stillness → step settling immediately after light impact → re-stillness" was consistently observed. (3) Experiment B: Base surface 4 × 10 cm (increase in effective contact area) Next, the same test was conducted using the 10 cm long side of the acrylic block as the bottom surface, with a 4 × 10 cm surface in contact with the substrate S. The purpose of this was to change the contact area, thereby altering the ground pressure p = W' / Aeff and verifying the difference in stopping depth. When the 4 × 10 cm surface was placed face down, the initial resting position was approximately 76 mm from the bottom. Subsequently, similar to Experiment A, 5 minutes of rest → light tapping (approximately 1 to 2 minutes) → 5 minutes of rest → light tapping… As a result of repeating the procedure, the following typical progression was obtained. Initial rest: 76 mm After 5 minutes of standing: No change. After light impact: 68 mm (8 mm sinking step) After 5 minutes of standing: No change. After another light tap: 60 mm (an additional 8 mm sinking step) Thus, even when the bottom area is large (Aeff is large), a stepwise sedimentation behavior in which the stationary phase and discrete sedimentation events alternate was observed. In addition, the stopping position was generally shallower compared to the 4×4 cm surface, and a tendency was observed that stopping was more likely in shallower layers as the ground pressure p decreased. (4) Summary Based on the above, in bentonite non-Newtonian sediment S, acrylic blocks During periods of standing, it hardly settles and remains stationary. Localized shear stimulation causes step sedimentation of several millimeters to more than ten millimeters. After that, it repeats the behavior of coming to a complete stop again. It was confirmed that the system exhibited a stepwise sedimentation behavior in which a stationary phase and discrete sedimentation events alternated. Furthermore, it was shown that reducing the ground pressure p tends to result in a shallower stopping position, which is consistent with the model of the present invention in which the stopping depth is determined by the threshold relationship between p and τ*_y(z).

[0028] Comparative Example 2: Behavior during widespread oscillation in non-Newtonian sediments To confirm that the stepwise sedimentation behavior characteristic of the present invention does not occur with broad, weak oscillating of the entire sediment, but is triggered by localized shear action directly beneath the support structure, the following comparative tests were conducted. (1) Test conditions Using the bentonite substrate S from Example 1, an acrylic block was submerged in the substrate and, after reaching a predetermined resting position, a wide-area oscillation was applied to the entire tank. Specifically, the top of the tank was manually shaken from side to side, applying surface waves with an amplitude of approximately 5 mm to 10 mm to the free surface for about 1 minute. The depth of the block was measured at least three times (three trials) before and after the oscillation to evaluate the amount of sedimentation. (2) Results and Summary In all trials, the amount of sedimentation before and after oscillation was 0 mm within the measurement error, and the discrete sedimentation steps observed in Example 4 did not occur. From the above, it was confirmed that the stepwise settling behavior characteristic of the present invention does not occur with weak disturbances such as widespread oscillation of the entire tank, but only when the effective yield stress τ*_y(z) directly below the support is temporarily reduced due to local shear action on the bottom sediment S directly below the support.

[0029] Example 5: Pre-design example of installation depth using a ring-shaped support (bentonite) In this example, the effective contact projection area Aeff(s) and ground pressure p were set by attaching the ring-shaped support to an acrylic block, and the stopping depth was pre-designed by comparing it with the relative profile of τ*_y(z) obtained in Example 3, and its validity was verified. (1) Test conditions Treatment site: A tank with bentonite bottom sediment S formed, as in Examples 1 to 4. Device body: Acrylic block (4 cm x 4 cm x 10 cm) Ring-shaped support part: Inner diameter ID = 60 mm (6.0 cm) Outer diameter OD = 79 mm (7.9 cm) Plate thickness t = 2.0 mm (0.20 cm) The ring was fixed around the bottom surface of the acrylic block, and configured so that the bottom surface of the ring was positioned below the bottom surface of the block. As a result, only the ring portion was in direct contact with the substrate S, while the central 40 mm x 40 mm portion remained in contact with the substrate S. (2) Calculation of the effective contact projection area Aeff The effective contact projected area Aeff of the ring is expressed by the following formula as the projected area of ​​the annular portion based on the difference between the inner and outer diameters. A_ring = (π / 4) × (OD^2 - ID^2) Substituting OD=7.9 cm and ID=6.0 cm, A_ring = (π / 4) × (7.9^2 - 6.0^2) ≈ 20.77 cm² In this embodiment, only the ring portion is considered to be involved in load support. Aeff ≒ A_ring ≒ 20.77 cm^2 ≈ 0.002077 m^2 That's what I decided. (3) Calculation of apparent load and ground pressure p in water The volume V of the ring is V = A_ring × t ≈ 20.77 cm² × 0.20 cm ≈ 4.15 cm³ Assuming a density difference Δρ between the acrylic material and water of approximately 0.18 g / cm³, the additional apparent load ΔW′ in the water due to the ring can be estimated as follows: ΔW′ ≈ Δρ × V × g ≒ 0.18 g / cm^3 × 4.15 cm^3 × 9.81 m / s^2 ≈ 0.007 N If the apparent underwater load W′0 of the acrylic block body is approximately 0.282 N, then the total apparent underwater load W′ including the ring is: W′ ≈ W′0 + ΔW′ ≈ 0.282 N + 0.007 N ≈ 0.289 N Therefore, the ground pressure p when the ring is supported is, p = W′ / Aeff ≈ 0.289 N / 0.002077 m^2 ≈ 1.39 × 10^2 Pa This is the result. (4) Prediction of stopping depth by comparison with vane profile When the depth-dependent vane relative index r(z) obtained in Example 3 is plotted against the height z from the bottom, a nearly linear profile is obtained in which r(z) increases monotonically as the depth approaches the bottom. In this specification, r(z) is considered a relative index representing the depth-direction profile of the effective yield stress τ*_y(z), and the stopping depth z* is evaluated from the relative magnitudes of the ground pressure p and τ*_y(z). In other words, In layers where τ*_y(z) < p (layers with small r(z)), the bottom sediment S directly beneath the support yields, and the device continues to sink. In layers where τ*_y(z) >= p (layers with sufficiently large r(z)), the bottom sediment S supports the device and sinking stops. In this sense, the stopping depth z* can be conceptually expressed as "the depth at which τ*_y(z*) ≈ p". When the measured values ​​of r(z) obtained in Example 3 are plotted against z, and the level corresponding to the ground pressure p calculated in this example is superimposed on the figure, it can be seen that the upper end of the region where r(z) begins to exceed that level is located approximately 73 mm to 75 mm from the bottom surface. Therefore, under the conditions of this embodiment, it is predicted that the device will stop near the interface zone approximately 73 mm to 75 mm from the bottom of the water. (5) Measurement results and summary An acrylic block with a ring attached was gently lowered into bentonite substrate S, and left to settle until it stopped. This test was conducted at least three times (three trials). As a result, in all trials, it was confirmed that the block stopped stably at a depth of approximately 73 mm to 75 mm from the bottom, with a median stopping depth of approximately 74 mm. Based on the above, the relative profile of τ*_y(z) obtained in Example 3 and the stop depth prediction based on the design using the ground pressure p in this example agree well, and the premise of the present invention The stopping depth can be designed using the threshold relationship between p = W' / Aeff(s) and τ*_y(z). The validity of this technological concept was confirmed.

[0030] Example 6: Creation and observation of the condition of sludge bottom sediment in a real-world reservoir. In this embodiment, bottom sediment deposited in an actual reservoir was used to confirm its state and layer structure as an example of a real-world bottom sediment S to which the present invention can be suitably applied. (1) Sample collection and tank preparation Approximately 40 liters of water containing sediment was collected from the bottom of a reservoir on private property and gently transferred to a transparent tank with internal dimensions similar to those of Example 1. A strong foul odor was emitted from the sediment during collection and when the sediment layer was stirred in the tank, confirming that it was typical organic sludge containing sulfides and other substances thought to be the result of anaerobic decomposition. (2) Observation results and summary When the tank was left undisturbed, a relatively clear water layer formed at the top, and below it, a dark brown to dark-colored, highly concentrated sludge layer formed. This sludge layer is an example of a real-world bottom sediment S to which the present invention can be suitably applied, and corresponds to organic sludge exhibiting non-Newtonian behavior. From the above, it was confirmed that even in the sludge of a reservoir in a real environment, a structure is formed in which the supernatant water and the high-concentration sludge layer are clearly separated and coexist, and a specific example of bottom sediment S to which the present invention can be applied was obtained.

[0031] Example 7: Measurement of the density (specific gravity) of layers in pond sludge. In this example, to confirm the density gradient in the depth direction of the pond sludge bottom sediment S prepared in Example 6, specific gravity measurements were performed by sampling 100 mL of water. (1) Test method After allowing the transparent water tank to settle, approximately 100 mL of sample was collected at multiple depths, starting from near the bottom and moving upwards, using a syringe or hose. The mass was measured using an electronic balance, and the specific gravity (g / mL) was calculated. Measurements were performed at least three times (three trials) under the same conditions at each depth, and the median value was used as the representative value. (2) Measurement results The typical median values ​​were as follows: Near the bottom: Approximately 104 g / 100 mL (median specific gravity ≈ 1.04 g / mL) Approximately 2 cm from the bottom: Approximately 104 g / 100 mL (median specific gravity ≈ 1.04 g / mL) Approximately 4 cm from the bottom: Approximately 103 g / 100 mL (median specific gravity ≈ 1.03 g / mL) Approximately 6 cm from the bottom: Approximately 101 g / 100 mL (median specific gravity ≈ 1.01 g / mL) (3) Summary From the above, it was confirmed that, similar to the bentonite dispersion system, a clear density gradient is formed in the sludge of reservoirs in real environments, with the specific gravity being higher towards the bottom and decreasing towards the top. This indicates that even in real-world sediment S, a stable density profile is formed due to gravity sedimentation, and that conditions exist under which the autonomous sedimentation device of the present invention can be applied.

[0032] Example 8: Relative strength profiles by depth obtained from vane shear tests in reservoir sludge. In this example, a shear test using a small vane was performed on the same reservoir sludge bottom sediment S as in Example 6, and the relative profile of the effective yield stress τ*_y(z) in the depth direction was determined. (1) Test method The vane shape and measurement procedure were the same as in Example 3 for the bentonite substrate. The vane center was adjusted so that it was near the bottom surface and at approximately +2 cm, +4 cm, and +6 cm from the bottom surface. Measurements were taken at least three times (three trials) for each position, and the median of the maximum torques was used as the representative value of the relative strength index. (2) Results and Summary Typical medians are as follows (in arbitrary units): Near the bottom: Median of the relative strength index ≈ 98 (almost impossible to rotate with a traction force of about 0.1 N) Approximately +2 cm from the base: Median of the relative intensity index ≈ 68 Approximately +4 cm from the base: Median of the relative intensity index ≈ 20 Approximately +6 cm from the base: Median of the relative intensity index ≈ 6.5 In any measurement, Near the base ≫ Base +2 cm > Base +4 cm > Base +6 cm This hierarchy was consistently reproduced, confirming that the typical behavior of non-Newtonian sediments—that "the deeper the sediment, the harder it is to rotate (τ*_y(z) is large)"—is clearly evident even in real-world reservoir sludge. From the above, it has been shown that, even in reservoir sludge, not only a density gradient but also a yield stress profile is formed in the depth direction, and that the stepwise sedimentation model based on p=W′ / Aeff(s) and τ*_y(z) of the present invention can be applied.

[0033] Example 9 Stepwise sedimentation behavior in reservoir sludge In this example, the stepwise settling behavior of the pond sediment S evaluated in Examples 6 to 8 was observed using acrylic blocks and ring-shaped support parts. (1) Test conditions As a test specimen, an acrylic block measuring 4 cm × 4 cm × 10 cm (density approximately 1.18 g / mL) was used, and the sedimentation stopping position was measured under the following three conditions. Condition A: When the 4 x 4 cm surface is facing downwards. Condition B: When the 4 x 10 cm surface is facing downwards. Condition C: When a ring-shaped support is attached to the lower perimeter of a 4×4 cm surface. In all cases, the samples were lowered gently, and the distance from the bottom was measured when the sinking naturally stopped. Each condition was tested at least three times (three trials), and the median value was used as the representative value. (2) Stop position when stationary Typical median values ​​are as follows: Condition A (4x4): Median stopping position from the base ≈ 6.1 cm Condition B (4 × 10): Median stopping position from the base ≈ 7.7 cm Condition C (4x4 + ring-shaped support): Median of the stopping position from the bottom surface ≈ 6.7 cm The amount of sedimentation during standing for several minutes (e.g., 5 minutes) was less than 1 mm, and all conditions were considered "static." (3) Stepwise sedimentation triggered by a trigger stimulus Subsequently, a "tapping experiment" was conducted at least three times (three trials) for each condition, in which the block support was lightly struck at a constant rhythm for approximately 1 to 2 minutes. As a result, in all conditions, a discrete settling step of several millimeters to 1 cm occurred immediately after striking, and then the behavior of coming to rest again was repeatedly observed. When similar tapping operations were continued, a similar degree of sedimentation steps appeared with each event, and the stepwise sedimentation behavior, in which a stationary phase and a sedimentation event alternated depending on the presence or absence of a trigger stimulus, was reproduced even in real-world sludge. Furthermore, when the effective contact projection area Aeff is large, such as in the 4 × 10 cm surface (Condition B), the contact pressure p becomes relatively smaller, and a tendency for the stopping position to be shallower overall was observed. Similar to the bentonite experiment, the behavior that "the smaller p, the shallower the layer at which it stops" was confirmed. (4) Summary Based on the above, in the actual environment of pond sludge bottom sediment S, similar to bentonite bottom sediment, During periods of standing still, there is a stationary phase in which there is almost no settling, Discrete sedimentation events triggered by localized shear stimuli A stepwise sedimentation behavior was observed, in which these two states alternate. Furthermore, since the stopping depth changes depending on the difference in ground pressure p, it was shown that the stepwise sedimentation model of the present invention can be applied to sludge in real environments.

[0034] Example 10: Preparation of kaolin sediment and layer structure In this example, a non-Newtonian sediment S was prepared using kaolin, a clay mineral, and its layered structure and interface z_ref were confirmed. (1)Adjustment method Approximately 30 L of tap water was placed in a transparent water tank with internal dimensions similar to those of Example 1, and 10 kg of commercially available kaolin powder was added. The entire mixture was thoroughly stirred with a stirring rod to form a uniform slurry, and then left to stand without further stirring or vibration. (2) Observation results and summary After standing, observation of the tank cross-section revealed that a very high-concentration, highly viscous kaolin layer had formed near the bottom, with a highly turbid suspension layer followed sequentially by a supernatant layer above it. Approximately 8.3 cm from the bottom, a band considered to be the boundary between water and kaolin sediment S was observed. Since the resistance of the small vanes rose significantly from the noise level in this area, it was determined that the reference interface z_ref is located near this band. From the above, it was confirmed that even in kaolin-based non-Newtonian sediments S, the supernatant water layer and the high-concentration sediment S are clearly separated, and the interface zone between them can be defined as the reference interface z_ref.

[0035] Example 11: Measurement of the density (specific gravity) of layers in kaolin sediment In this example, to confirm the density gradient in the depth direction of the kaolin sediment S prepared in Example 10, the specific gravity was measured by taking a 100 mL sample. (1) Test method The hose tip or syringe tip was adjusted to the desired depth by varying the distance from the bottom surface, and a 100 mL sample was collected, its mass measured, and its specific gravity (g / mL) calculated. At least three measurements (three trials) were performed for each depth, and the median value was used as the representative value. (2) Measurement results Typical median values ​​are as follows: The substance was so viscous and concentrated that it could not be aspirated using a syringe with a diameter of approximately 6 mm and a depth of approximately 2.8 cm from the bottom, making quantitative sampling difficult. Approximately 4.3 cm from the base: Median mass ≈ 144 g / 100 mL (Median specific gravity ≈ 1.44 g / mL) Approximately 6.3 cm from the base: Median mass ≈ 118 g / 100 mL (Median specific gravity ≈ 1.18 g / mL) Approximately 7.3 cm from the base: Median mass ≈ 113 g / 100 mL (Median specific gravity ≈ 1.13 g / mL) Approximately 8.3 cm from the base: Median mass ≈ 102 g / 100 mL (Median specific gravity ≈ 1.02 g / mL) (3) Summary From the above, it was confirmed that even in kaolin sediment S, a clear density gradient is formed where the specific gravity is higher towards the bottom and decreases towards the top. Also, it was revealed that in the vicinity of the bottom surface (about 2.8 cm), the viscosity is extremely high, and it shows different properties from bentonite sediment in that it is so highly concentrated that it is difficult to collect water even with a small-diameter syringe.

[0036] Example 12 Depth-wise relative strength profile by vane shear test in kaolin sediment In this example, for the kaolin sediment S of Example 10, a depth-wise relative strength profile was measured using the same small vane as in Example 3. (1) Test method Measurements were taken at positions approximately 2.3 cm, 4.3 cm, 6.3 cm, and approximately 8.3 cm (near z_ref) from the bottom surface. For each depth, at least 3 tests (3 trials) were conducted under the same conditions, and the median value of the maximum torque was used as the representative value of the relative strength index. (2) Results and summary The typical median values are as follows. Approximately 8.3 cm from the bottom surface (near the interface between mud and water: near z_ref) Median value of relative strength index: from 0 to about 1 (almost water-like behavior) Approximately 6.3 cm from the bottom surface Median value of relative strength index: about 5 Approximately 4.3 cm from the bottom surface Median value of relative strength index: about 13 Approximately 2.3 cm from the bottom surface Median value of relative strength index: about 26 In any of the measurement sets, Bottom vicinity (2.3 cm) > middle layer (4.3 cm) > upper layer (6.3 cm) ≫ interface vicinity (8.3 cm) The sequence of "the deeper, the more difficult to rotate (the larger τ*_y(z))" was maintained, and it was confirmed that the typical non-Newtonian sediment behavior was reproduced in the kaolin sediment S. From the above, it was shown that a yield stress profile consistent with the density gradient is formed for the kaolin sediment S, and that the stepwise sedimentation model of the present invention can be applied.

[0037] Example 13: Stepwise sedimentation behavior in kaolin sediment In this example, the stepwise sedimentation behavior of the kaolin sediment S evaluated in Examples 10 to 12 was observed using acrylic blocks and ring-shaped support structures. (1) Test conditions The test specimen was a 4 cm × 4 cm × 10 cm acrylic block, similar to those used in Examples 4 and 9, and the sedimentation stopping depth was measured under the following three conditions. Condition A: When the 4 x 4 cm surface is facing downwards. Condition B: When the 4 x 10 cm surface is facing downwards. Condition C: When a ring-shaped support is attached to the underside of a 4×4 cm surface. For each condition, a sedimentation test was conducted at least three times (three trials) under the same conditions, and the median value of the stopping depth from the bottom was used as the representative value. (2) Stopping depth when stationary Typical median values ​​are as follows: Condition A (4x4): Median stopping position ≈ 9.2 cm Condition B (4 × 10): Median stopping position ≈ 11.3 cm Condition C (4×4 + ring-shaped support): Median of stopping position ≈ 10.3 cm The amount of sedimentation during standing (several minutes) was less than 1 mm, and creep settlement was within the range of measurement error. (3) Triggered sedimentation and summary Subsequently, similar to the case of pond sludge, a trigger operation (tapping experiment) was performed at least three times (three trials) for each condition, in which the block support was lightly tapped at a constant rhythm for approximately 1 to 2 minutes. As a result, in all conditions, a settling step of several mm occurred immediately after tapping, and then the behavior of coming to a standstill again was observed. When similar tapping for approximately 1 to 2 minutes was repeated, discrete sedimentation of the same order occurred with each event, and the stepwise sedimentation behavior in which the stationary phase and sedimentation events alternated was reproduced in the kaolin sediment as well. However, the magnitude of the amount of settlement (settlement rate) for the same trigger conditions tended to be slightly smaller compared to the case of bentonite sediment and pond sludge, suggesting that the fluidity and structural relaxation after yielding differ in the kaolin sediment. From the above, it was confirmed that the stepwise settling behavior characteristic of the present invention was also observed in kaolin sediment S, and that the differences in flow characteristics of each material are reflected in the amount of settling steps.

[0038] Comparative Example 3: Turbidity and sludge stirring test when the reference interface is set up. To verify whether turbidity in the surrounding water and the stirring up of sediment are suppressed when the autonomous sedimentation device of the present invention is installed at the interface (z_ref) of a non-Newtonian sediment, the following comparative experiments were conducted on three types of sediment: bentonite sediment, kaolin sediment, and reservoir sludge sediment. (1) Test conditions For each type of substrate, the substrate and supernatant water were placed in a transparent tank with internal dimensions of approximately 40 cm x 55 cm x 30 cm, and a visual marker was placed in the center of the tank. In this state, the following three conditions were set. Condition A (criteria): Without installing any equipment or stirring sources, the tank was left undisturbed for 30 minutes, and the external appearance of the tank (how the labels appeared) was photographed during this time, recording a time-lapse video. Condition B (with unit): The device of the present invention was gently installed on the reference interface z_ref, and while supplying and draining DO water by a pump inside the device, it was observed for 30 minutes. During this period, the appearance of the markings was also photographed and recorded. Condition C (without unit, deep stirring): The device was not used, and a heavy air stone was placed at a position deeper than the reference interface to send air in and reproduce the condition of strongly stirring the bottom sediment S. The appearance of the markings and the turbidity in the water tank were recorded immediately after the placement. For each bottom sediment, the comparative test of the above three conditions was repeated at least three times (three trials). (2) Results and summary No clear difference was observed in the appearance between Condition A and Condition B, and the markings were visible throughout the 30-minute observation. On the other hand, in Condition C, the markings disappeared from sight within 10 seconds after the air stone was placed, and thereafter, the bottom sediment S was violently stirred up and the turbidity persisted. From the above, when the device of the present invention is installed on the reference interface z_ref and configured to circulate DO water inside the device, it can be operated without generating turbidity in the supernatant water or stirring up the bottom sediment S. In contrast, when strong stirring such as direct aeration is performed at the same position, it was confirmed that significant turbidity and stirring up of the bottom sediment occurred. This shows that the device of the present invention has the feature of "being able to supply oxygen to the vicinity of the bottom sediment while suppressing interface disturbance".

Industrial applicability

[0039] The self-settling type bottom sediment purification device 1 of the present invention can be suitably used for the management and purification of non-Newtonian bottom sediment S including organic sludge, silt-clay mixture, biofilm, etc. deposited at the bottom in water areas W such as lakes, ponds, reservoirs, agricultural ponds, regulating ponds, swimming pools, tidal flats, inner bays, waters in harbors, canals, waterways, etc. Furthermore, it can be applied to various treatment facilities where slurry-like or gel-like sediments form at the bottom, such as sedimentation tanks, adjustment tanks, anaerobic and aerobic tanks in sewage treatment plants and wastewater treatment facilities, and storage tanks for factory and livestock wastewater. It can be used as a long-term management method for sediment layers that have an effective (apparent) yield stress τ*_y, similar to the bottom sediment S. The autonomous sedimentation-type sediment purification device 1 according to the present invention does not have an external mechanical lifting mechanism as an essential component, and exhibits a stepwise sedimentation behavior that autonomously repeats a stationary phase and discrete sedimentation events based on a threshold relationship between the ground pressure p and the effective yield stress τ*_y of the sediment S. For this reason, it is suitable for applications that aim to improve sediment quality over the long term and gradually, while reducing energy consumption, construction costs, and environmental burden during construction, compared to conventional large-scale civil engineering works such as dredging and excavation. In particular, it is useful in water bodies where it is desirable to promote the decomposition of organic matter and changes in sediment structure while suppressing the resuspension of sediment and the generation of turbid water. Device 1 consists of a support section 5, a buoyancy adjustment section, a mass adjustment section (ballast body), a microbial carrier block 6, etc., and its main components can be formed from general-purpose materials such as resin, metal, concrete, porous material, and fiber mat, making modularization and mass production easy. It can also be retrofitted to existing revetment structures, pile foundations, piers, embankments, etc., by installing fixed columns 20 and then relatively lowering the autonomous sinking module in stages relative to them, making it easy to apply to both new construction and renovation projects. Furthermore, the apparatus 1 of the present invention has a relatively simple structure and can exhibit the desired gradual sedimentation behavior and bottom sediment improvement effect even from a single unit. Moreover, by arranging multiple units in a surface area, it can be gradually expanded as a bottom sediment management and purification system for a wide range of water bodies. For this reason, it has industrial utility value that can be flexibly adapted from small-scale trial introductions to large-scale deployments in public infrastructure, agricultural water, industrial water, recreational waters, etc. Furthermore, the measuring tool 70 for measuring the reference interface z_ref and the measuring kit 80 for measuring the penetration depth s according to the present invention can be used to easily evaluate the interface position and effective yield stress profile of non-Newtonian sediment S in the various water bodies W and treatment facilities mentioned above, and can be used to examine the design and installation conditions of the autonomous sedimentation type sediment purification device 1 and to evaluate its behavior after installation. Therefore, the present invention is extremely useful industrially because it can provide a sediment purification device and its design and evaluation means as an integrated technical package. [Explanation of Symbols]

[0040] 1. Autonomous sedimentation device (including the entire autonomous sedimentation module) 5. Support section (ring / frame / footprint section) 5a Flow channel section (annular flow channel, etc.) 5b Media supply port 5c opening (distributed supply hole) 5d Ballast port (ballast / fluid inlet / outlet) 5u buoyancy chamber (buoyancy adjustment section) 6. Microbial carrier block (carrier block) 6a Carrier support arm 10A, 10B Small vanes 11 shafts 20 Fixed posts (support posts, guide posts) 70 Measuring Tools 7a Guide pipe (support member) 7b Interface follower 7c Flexible elements (strings, wires, etc.) 7d One-way locking mechanism 80 Measurement Kit 8a Support member 8b Measured object (cube) 8c flexible element 8d One-way locking mechanism W Water area Water surface W, free water surface (still water surface) of water body W. S Bottom sediment (sediments, non-Newtonian sediments, etc.) z_ref Reference interface (Interface location between water body W and sediment S) h_ref Depth from water surface W to reference interface z_ref s Penetration depth Aeff(s) Effective contact projected area Dsupp support projection representative diameter W' Apparent load underwater p Ground pressure τ*_y(z) Effective (apparent) yield stress at depth z τ*_y(s) Effective (apparent) yield stress at penetration depth s(z=z_ref+s)

Claims

1. An autonomous sedimentation device for bottom sediment or deposits (hereinafter referred to as "bottom sediment, etc.") deposited at the bottom of a body of water, (a) A trigger means that performs an operation to locally act on the area of ​​action directly below the device to reduce the effective yield stress τ*_y of the sediment, (b) A support portion that defines the effective contact projection area Aeff(s) with respect to the sediment, etc., corresponding to the penetration depth s from the reference interface z_ref, (c) A ground pressure setting mechanism that sets a predetermined ground pressure p based on the apparent load W′ of the device underwater and the Aeff(s), Equipped with, The trigger means causes discrete sedimentation events to occur. The ground pressure p is defined as p = W' / Aeff(s), where Aeff(s) is the effective contact projection area, which includes the bottom projection of the support portion plus the load support contribution of the side surface corresponding to the penetration depth s, projected in the direction of the bottom surface. The ground pressure p is greater than or equal to the effective yield stress τ*_y(s) of the sediment at the position corresponding to the penetration depth s, and the sediment autonomously settles within this range, satisfying the condition p>=τ*_y(s). The device is configured to come to rest when it reaches a desired penetration depth s that satisfies the condition p < τ*_y(s), where the ground pressure p is less than τ*_y(s). An autonomous sedimentation device characterized by the following features.

2. In the autonomous sedimentation device described in claim 1, The aforementioned device is an autonomous sedimentation type device characterized by not being equipped with a mechanical lifting means that can apply an upward support force to the device from the outside.

3. In the autonomous sedimentation device described in claim 1, An autonomous sedimentation device characterized in that, in a fluid without a yield stress τ*_y (Newtonian fluid), the stepwise sedimentation behavior based on the threshold relationship between the ground pressure p and τ*_y is substantially absent.

4. In the autonomous sedimentation device described in claim 1, The trigger means, i. Dispersive supply of fluid (including an oxygenation medium, and at least one of a multi-pore, microporous diffusion material, fine bubbles, or tangential discharge), ii. Mechanical vibration or mechanical shock (including oscillation), iii. Local adjustment of temperature conditions, iv. Local adjustment of chemical or photochemical conditions, v. Local adjustment of biological or biochemical conditions, vi. Means for reducing the effective yield stress τ*_y of the sediment, An autonomous sedimentation device characterized by including at least one of the following.

5. An autonomous sedimentation device according to claim 4, characterized in that, when the maximum circumscribed diameter of the horizontal projection contour of the member that actually contacts the bottom sediment as a load support in the installed state is defined as the support projection representative diameter Dsupp, the center of the operating area of ​​the trigger means is located within a range of 3.0 × Dsupp or less with respect to the support projection representative diameter Dsupp, or is set in a region that is fluidly connected directly below the support part.

6. An autonomous sedimentation device according to claim 1, wherein the ground pressure setting mechanism is capable of setting the ground pressure p to a predetermined range by adjusting W' and / or adjusting Aeff(s).

7. An autonomous sedimentation device according to claim 6, wherein the ground pressure setting mechanism includes at least one of: (a) a mass adjustment section consisting of a detachable weight or a ballast water chamber; (b) a buoyancy adjustment section consisting of a variable float or an air chamber; (c) a deployable member consisting of a ring, a skirt or a variable footprint plate that can expand or contract the effective contact projection area Aeff(s); and (d) a passive module (self-load adjustment module) that changes (increases or decreases) the apparent load W′(t) in water over time due to the capture or release of sediment or biofilm after installation, increase or decrease in water content, infiltration or dewatering, or precipitation or dissolution.

8. In the autonomous sedimentation device according to claim 7, The representative diameter of the support projection Dsupp is defined as the maximum circumscribed circle diameter of the horizontal projection contour of the member that actually contacts the substrate or other materials as a load support in the installed state. When the penetration depth s is defined as the vertical distance from the reference interface z_ref, which is the interface between the water body W and the bottom sediment, to the lowest contact point of the load support, An autonomous sedimentation device configured so that s / Dsupp is between 0.05 and 0.

40.

9. An autonomous sedimentation device according to claim 1, wherein the device is configured to autonomously come to rest at a position where the effective yield stress τ*_y(s) of the sediment, etc., at a position corresponding to the penetration depth s from the reference interface z_ref substantially reaches the ground pressure p = W' / Aeff(s).

10. In the autonomous sedimentation device according to claim 9, When the diameter of the maximum circumscribed circle of the horizontal projection contour of a member that actually contacts the substrate or other material as a load support in the installed state is defined as the representative diameter of the support projection Dsupp, At a position where the ratio s / Dsupp of the penetration depth s from the reference interface z_ref to the representative diameter Dsupp of the support projection is between 0.05 and 0.40, An autonomous sedimentation device is set up so that the ground pressure p(s) = W' / Aeff(s) and the effective yield stress τ*_y(s) of the sediment are substantially equal (p(s) ≈ τ*_y(s)).

11. An autonomous sedimentation device according to claim 1, comprising: a fixed support column or support column; and an autonomous sedimentation module that is slidable along the column and includes at least a portion of a trigger means that acts locally on the support portion and the area of ​​action directly below the device to reduce the effective yield stress τ*_y of the sediment, wherein the autonomous sedimentation module sinks relative to the column.

12. An autonomous sedimentation device according to claim 1, wherein, as time elapses after the device is installed on the bottom sediment, the apparent load W′(t) in water changes (increases or decreases) due to the capture or release of suspended matter, settled particles or biofilms, increase or decrease in water content, infiltration or dewatering, precipitation or dissolution, and discrete sedimentation events occur when the ground pressure p(t) = W′(t) / Aeff(s(t)) substantially reaches or exceeds the effective yield stress τ*_y(s(t)) of the bottom sediment at a position corresponding to the penetration depth s(t) from the reference interface z_ref, either by the change in W′(t) alone or in combination with the change in the effective contact projection area Aeff(s(t)).

13. An autonomous step-settlement type device according to claim 1, characterized in that, based on a threshold relationship between the ground pressure p(s) = W' / Aeff(s) and the effective yield stress τ*_y(s) of the sediment at a position corresponding to the penetration depth s from the reference interface z_ref, the device maintains a stationary phase while p < τ*_y(s) holds, and generates discrete settlement events in which the support portion penetrates downward only when p >= τ*_y(s) holds, and autonomously repeats a step-settlement behavior in which the stationary phase and the discrete settlement events alternate.

14. A sediment treatment method using an autonomous sedimentation device according to any one of claims 1 to 13, comprising: (1) setting the device on sediment without using external mechanical lifting means; (2) keeping the device stationary while the ground pressure p(s) = W' / Aeff(s) is less than the effective yield stress τ*_y(s) of the sediment at a position corresponding to the penetration depth s from a reference interface z_ref; (3) sinking the device only when the ground pressure p(s) = W' / Aeff(s) becomes equal to or greater than the effective yield stress τ*_y(s) by an operation that locally reduces the effective yield stress τ*_y(s) of the sediment; and (4) treating the sediment in the stationary state in step (2), or treating the sediment while gradually sinking the device by repeatedly performing discrete events between the stationary state and the sedimentation state.

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