Method and apparatus for measuring ground strength

Abstract

To provide a ground strength measuring method and a ground strength measuring machine for easily measuring the strength of the ground while suppressing an influence on a stress state of the ground.SOLUTION: A soil strength measuring method includes a step of inserting a cylindrical body provided at a tip of a rod into a borehole, rotating the rod around an axis, and measuring a frictional force between a hole wall of the borehole and the cylindrical body at a predetermined depth, and a step of deploying a blade outward from the cylindrical body, rotating the rod around the axis, and measuring a rotational resistance force at the predetermined depth.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a ground strength measurement method and a ground strength measurement device. [Background technology]

[0002] Patent Document 1 discloses a method for determining the shear strength of soil when a certain vertical load is applied to the shear surface by using a bladed cone attached to the tip of a rod, loading the rod in the direction of the rod and applying a vertical load to the shear surface to the soil around the cone while rotating the rod around its axis and measuring torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-227786 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the bladeless cone is removed from the tip of the rod, and the shear strength measuring device is replaced with a bladed cone and pushed in, so there is a risk that the blades will change the stress state in the ground before reaching the depth to be measured, which could affect the ground strength measurement. In addition, the need to replace the tip of the rod requires time for the measurement work.

[0005] The present disclosure provides a ground strength measurement method and a ground strength measurement device that can easily measure ground strength while minimizing the impact on the stress state of the ground compared to a configuration in which the tip of the rod is replaced. [Means for solving the problem]

[0006] The first embodiment of the ground strength measurement method comprises the steps of inserting a cylindrical body attached to the tip of a rod into a borehole, rotating the rod around its axis, and measuring the friction force between the borehole wall and the cylindrical body at a predetermined depth, and extending blades outward from the cylindrical body, rotating the rod around its axis, and measuring the rotational resistance force at the predetermined depth.

[0007] In this embodiment, a cylindrical body attached to the tip of the rod is inserted into a borehole, and blades are deployed outward from the cylindrical body at a predetermined depth.This makes it possible to easily measure ground strength while minimizing the impact on ground strength measurement compared to a configuration in which the tip of the rod is replaced.

[0008] A second embodiment of a ground strength measuring device comprises a rod having a cylindrical body at its tip that is inserted into a borehole, a rotational force transmission unit that is provided on the ground side of the rod and rotates the rod around its axis, a load cell that is provided between the cylindrical body and the rotational force transmission unit, a plurality of blades that are provided inside the cylindrical body and deploy outward from slits formed in the cylindrical body, and a blade deployment unit that is operated from the ground side of the rod and converts axial or axial movement into deployment force of the blades, and the load cell measures a first torque acting on the borehole wall and the outer surface of the cylindrical body when the rod is rotated around its axis, and also measures a second torque acting on the blades when the blades are deployed outward from the cylindrical body and the rod is rotated around its axis.

[0009] In this embodiment, the first torque and the second torque are measured by changing the deployment state of the blades at a predetermined depth underground, so that the ground strength can be measured without changing the state of stress in the ground.

[0010] The blade deployment portion of the ground strength measuring device of the third aspect maintains the blades in a state where they are deployed outward from the slits when operated to a predetermined position from the ground side of the rod.

[0011] In this embodiment, the blade deployment section maintains the blades deployed from the cylindrical body, so that the blades will not return to the inside of the cylindrical body even if they receive a reaction force from the ground during strength measurement.

[0012] The blades of the ground strength measuring device of the fourth aspect are provided with limiting portions formed at the ends thereof that limit the deployment force of the blades.

[0013] In this aspect, excessive deployment of the blades from the inside to the outside of the cylindrical body can be restricted. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a ground strength measurement method and a ground strength measuring device that can easily measure the strength of the ground while reducing the impact on the stress state of the ground compared to a configuration in which the tip of the rod is replaced. [Brief explanation of the drawings]

[0015] [Figure 1] 1A is a front view showing a state in which the blades are deployed outside the large diameter portion, and FIG. 1B is a front view showing a state in which the blades are housed inside the large diameter portion, in a ground strength measuring device according to an embodiment of the present disclosure. [Figure 2] (a) is a bottom view corresponding to FIG. 1(a), and (b) is a bottom view corresponding to FIG. 1(b). [Figure 3] In the large diameter part of the ground strength measuring device of this embodiment, (a) is a front cross-sectional view showing the state in which the blades are deployed outside the large diameter part, and (b) is a front cross-sectional view showing the state in which the blades are stored inside the large diameter part. [Figure 4] 3 is a conceptual diagram showing the relationship between the ground strength measuring device of the present embodiment and the groundwater level. FIG. [Figure 5] In the ground strength measurement method according to the embodiment of the present disclosure, (a) is a front view showing a state in which a ground strength measurement device is inserted into a borehole, (b) is a front view showing a state in which the ground strength measurement device with its blades housed inside the large diameter part is rotated around its axis, (c) is a front view showing a state in which the blades are extended from the ground strength measurement device to the outside of the large diameter part, and (d) is a front view showing a state in which the ground strength measurement device with its blades extended outside the large diameter part is rotated around its axis. [Figure 6] This is an example showing how to determine the failure line using the Mohr-Coulomb failure criterion. [Figure 7] Graph (a) shows an example of estimating adhesion when the ground being measured is clay, and graph (b) shows an example of estimating internal friction angle when the ground being measured is sand. [Figure 8] FIG. 2 is a front view showing a first modified example of the ground strength measuring device of the present embodiment. [Figure 9] FIG. 10 is a bottom cross-sectional view showing a second modified example of the ground strength measuring device of the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] An example of an embodiment of the technology of the present disclosure (the present embodiment) will be described below with reference to the drawings. The same reference numerals are used to designate the same components and parts in the drawings. The dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0017] In the figure, arrow D indicates the horizontal depth direction, and arrow W indicates the horizontal width direction. Arrow H indicates the vertical direction (up-down direction). The depth direction, width direction, and up-down direction are perpendicular to each other. In this specification, the above directions are used for explanation, but the position of the ground strength measuring device is not limited to these directions.

[0018] <Overall structure> The ground strength measuring device 10 of this embodiment is a measuring device that performs a strength test on the hole wall BW of a borehole BH in the ground G at a construction site and measures the adhesion force c and internal friction angle φ of the ground G. As shown in Figure 4, the ground strength measuring device 10 is an elongated measuring device that is inserted into the borehole BH with its longitudinal direction aligned in the up-down direction.

[0019] As shown in FIG. 1( a ), the ground strength measuring device 10 includes a rod 20 , a handle 30 , a load cell 40 , a blade member 50 , and a blade deployment portion 60 .

[0020] (rod) The rod 20 is a long tube that is inserted into the borehole BH with its longitudinal direction aligned in the vertical direction. Multiple rods 20 are connected in the vertical direction by joints (not shown), making the vertical length adjustable. Note that multiple rods 20 do not necessarily have to be connected. The rod 20 has a small diameter portion 22 and a large diameter portion 24.

[0021] The small diameter portion 22 forms the upper and lower upward side portion of the rod 20 .

[0022] The large diameter portion 24 is a bottomed cylinder having an outer diameter and an inner diameter larger than those of the small diameter portion 22, and is connected to the vertically lower side of the small diameter portion 22, forming the vertically lower portion of the rod 20. The large diameter portion 24 is an example of a cylindrical body provided at the tip of the rod 20. The large diameter portion 24 rotates as the small diameter portion 22 rotates around the axis of the rod 20. A slit 26 and a through hole 28 are formed in the large diameter portion 24.

[0023] The slits 26 are rectangular holes formed in the cylindrical surface 24A of the large diameter portion 24, and are elongated holes extending in the vertical direction. A plurality of slits 26 are formed in the cylindrical surface 24A, and in this embodiment, four slits 26 are formed at equal intervals on the cylindrical surface 24A.

[0024] 3(a) and 3(b), the through-hole 28 is a through-hole formed in the upper surface 24B of the large diameter portion 24. The through-hole 28 connects the space inside the small diameter portion 22 and the space inside the large diameter portion 24 along the axial center of the rod 20.

[0025] (handle) As shown in FIG. 1( a), the handle 30 is attached to the upper and lower ends of the small diameter portion 22 of the rod 20 and is a rod extending in the width direction. The handle 30 allows a measurer (not shown) on the ground to rotate the rod 20 about its axis. The handle 30 is an example of a rotational force transmission unit. In this embodiment, the handle 30 is configured to allow the measurer to rotate the rod 20, but this is not limiting. For example, a motor (not shown) may be used as the rotational force transmission unit instead of the handle 30. In this case, a motor shaft (not shown) is attached to the rod 20 so as to rotate the rod 20 about its axis.

[0026] (load cell) The load cell 40 is disposed between the large diameter portion 24 of the rod 20 and the handle 30 in the vertical direction, and is attached to the small diameter portion 22 of the rod 20 to measure the torque T relative to the rotation about the axis applied to the handle 30. The load cell 40 measures the torque T by, for example, outputting a voltage corresponding to the amount of strain of a plurality of strain gauges (not shown) that are configured in a bridge circuit. The torque T measured by the load cell 40 is acquired as data by a data logger 70 on the ground via a wire.

[0027] The torque T acquired as data may be transmitted to the data logger 70 wirelessly.

[0028] (Blade material) The blade member 50 is disposed at the tip of the rod 20 and is a blade-shaped member that applies shear force to the ground G. In this embodiment, the blade member 50 is disposed at the large diameter portion 24 of the rod 20.

[0029] 2(a), the blade members 50 are arranged along the radial direction of the large diameter portion 24, at equal intervals around the axis of the rod 20, with a portion of the blade members 50 extending in all four directions. In this embodiment, the blade members 50 extend at 90° intervals, and the distance between the blade centers of two blade members 50 that are 180° out of phase with each other is d.

[0030] As shown in FIG. 3( a ), the blade member 50 includes a blade 52 , an attachment portion 54 , a rotating portion 56 , and a limiting portion 58 .

[0031] The blades 52 are plates that extend in the vertical direction and protrude from the large diameter portion 24 in a direction perpendicular to the vertical direction. In this embodiment, the blades 52 are shaped like an isosceles triangle, with a portion of the blades 52 being disposed inside the large diameter portion 24 and the remainder of the blades 52 extending from the slits 26 to the outside of the large diameter portion 24.

[0032] The mounting portion 54 is a rectangular plate extending in the vertical direction, and the blades 52 are attached to the outer side in the plate thickness direction. The vertical length of the mounting portion 54 is equal to the vertical length of the blades 52. The mounting portion 54 is also disposed in the space inside the large diameter portion 24.

[0033] The rotating portions 56 are members configured so that one side can rotate relative to the other side around a direction perpendicular to the up-down direction. One side of the rotating portions 56 is attached to the lower end of the mounting portion 54 in the up-down direction, and the other side of the rotating portion 56 is attached to the inner circumferential surface of the large diameter portion 24. When one side of the rotating portions 56 rotates relative to the other side, the blades 52 move between the inside and outside of the large diameter portion 24. In other words, the rotating portions 56 can apply a deployment force to the blades 52 via the mounting portion 54.

[0034] The limiting portions 58 are plates that protrude upward from the upper and lower raised ends of the mounting portion 54. In other words, the limiting portions 58 are formed on the base end side, radially opposite to the tip end of the blade 52. The length of the limiting portions 58 in the vertical direction is set so as to cover the upper side of the slit 26. Together with the inner surface of the large diameter portion 24, the limiting portions 58 limit the deployment force applied to the blade 52 via the mounting portion 54 as one of the rotating portions 56 rotates relative to the other.

[0035] (Blade deployment section) The blade deployment portion 60 is a member that enables the blades 52 of the blade member 50 to move. As shown in Figures 1(b) and 2(b), the ground strength measuring device 10 is capable of storing the blade member 50 inside the large diameter portion 24 by the action of the blade deployment portion 60. The blade deployment portion 60 includes a cylindrical portion 62 and a wire 64.

[0036] 3(a), the cylindrical portion 62 is a cylinder that extends along the axial center of the rod 20, is disposed inside the large diameter portion 24, and is movable up and down within the space inside the large diameter portion 24. The outer diameter of the cylindrical portion 62 is larger than the diameter of the through-hole 28 and is set so that the blades 52 do not come into contact with the mounting portion 54 and the rotating portion 56 when deployed from the slits 26. The vertical length (height) of the cylindrical portion 62 is set shorter than the vertical length of the mounting portion 54.

[0037] The wire 64 is made of a bundle of multiple fiber steel materials and is arranged to pass through the inside of the rod 20 and the through-hole 28. One end of the wire 64 supports the upper surface of the cylindrical portion 62, and the other end is supported by a hoisting device (not shown) on the ground.

[0038] When the wire 64 is wound up by the winding device, the cylindrical portion 62 moves upward in the vertical direction, and when the wire 64 is let out by the winding device, the cylindrical portion 62 moves downward in the vertical direction.

[0039] In this embodiment, when the wire 64 is wound up to the first position by the winding device, the cylindrical portion 62 moves to the first position shown in FIG. 3(a). Winding up is an example of an operation. The first position is a position where the blades 52 remain deployed outward from the large diameter portion 24. In other words, the first position is an example of a predetermined position.

[0040] On the other hand, when the wire 64 is fed to the second position by the winding device, the cylindrical portion 62 moves to the second position shown in Fig. 3(b). The second position is a position where the blades 52 remain housed inside the large diameter portion 24. The blades 52 shown by the two-dot chain line in the figure represent the blades 52 shown in Fig. 3(a).

[0041] The ground strength measuring device 10 is configured as described above.

[0042] <Explanation of an example of what to measure> Next, an example of a measurement target will be described. The ground G shown in Figure 4 is assumed to be composed of a first layer S1 and a second layer S2, in that order from the layer closest to the ground surface (top to bottom). In the ground G, the groundwater level WL is assumed to exist at a distance L1 (m) from the ground surface. Furthermore, the center of the blade 52 of the ground strength measuring device 10 inserted into the borehole BH is assumed to be located at a position distance L2 (m) from the groundwater level WL. In other words, the center of the blade 52 is assumed to be located at a predetermined depth indicated by the sum of the distance L1 and the distance L2 from the ground surface.

[0043] (Estimation of overburden pressure) Next, a method for estimating the overburden pressure P acting on the shear surface of the blade 52 will be described. Note that the overburden pressure P is assumed to be the case when the groundwater level is WL at a given depth. Using the unit weight γ (kN / m^3) of the second layer S2 of the ground G at a given depth and the unit weight of water 9.8 (kN / m^3), the air weight of the ground G above the groundwater level WL, γ × L1 (kN / m^2), and the submerged weight of the ground G below the groundwater level WL, (γ - 9.8) × L2 (kN / m^2), are obtained. The sum of these values ​​is then estimated as the overburden pressure P (kN / m^2) at the given depth.

[0044] If it is necessary to obtain multiple values ​​of overburden pressure P, the following method can be used. For example, if the depth is changed within the same soil layer while maintaining the groundwater level WL, the overburden pressure P changes as only the distance L2 changes. As another example, if a pump (not shown) is used to pump water from the ground G to change the groundwater level WL without changing the depth, the overburden pressure P changes as the distances L1 and L2 change.

[0045] <Method for measuring ground strength> Next, the ground strength measurement method of this embodiment will be described using Figures 5(a) to 5(d). It is assumed that the borehole BH is drilled by a well-known method when carrying out the ground strength measurement method. The diameter of the borehole BH is the same as the diameter of the large diameter portion 24 of the rod 20 of the ground strength measurement device 10.

[0046] As shown in Figure 5(a), the large diameter portion 24 provided on the rod 20 of the ground strength measuring device 10 is inserted into the borehole BH from above to below. During the insertion, the blade member 50 and the blade deployment portion 60 of the large diameter portion 24 of the ground strength measuring device 10 are positioned in the second position (see Figure 3(b)).

[0047] As shown in Figure 5(b), the rod 20 inserted into the borehole BH is rotated around its axis, and the first torque T1 generated by friction between the borehole wall BW of the borehole BH and the large diameter portion 24 is measured at a predetermined depth, for example, about TP-5m. In this embodiment, the first torque T1 is measured at a predetermined depth in the second layer S2 of the ground G. The first torque T1 generated by friction is an example of a frictional force.

[0048] As shown in FIG. 5(c), while maintaining the predetermined depth, the wire 64 is wound up, causing the columnar portion 62 to move to the first position (see FIG. 3(a)).

[0049] When the cylindrical portion 62 moves from the second position (see FIG. 3(b)) to the first position, the cylindrical portion 62 pushes up the mounting portion 54 from below in the vertical direction. When the mounting portion 54 is pushed up, the blades 52 move from the inside to the outside of the large diameter portion 24 through the slits 26. When the restricting portions 58 come into contact with the inner surface of the large diameter portion 24, the blades 52 are deployed outward from the slits 26. The deployed blades 52 are inserted into the second layer S2 at the predetermined depth.

[0050] As shown in Figure 5(d), while the blade 52 remains inserted in the second layer S2, the rod 20 is rotated around its axis to measure the total torque (second torque) T2 generated by shear and friction between the second layer S2, the blade 52, and the large diameter portion 24 at the predetermined depth. The total torque T2 is an example of rotational resistance. From the measurement, the shear force SF in the second layer S2 is calculated based on the difference between the second torque T2 and the first torque T1.

[0051] The shear force SF is calculated by multiplying the difference between the second torque T2 and the first torque T1 by 2 and then dividing the result by the distance d between the centers of the blades 52. The shear stress τ, which will be described later, is calculated by dividing the shear force SF by the effective cross-sectional area A of the blades 52.

[0052] The ground strength measuring method of this embodiment is carried out as described above.

[0053] <Estimation of adhesion and internal friction angle> Next, we explain how to estimate the cohesion force c and the internal friction angle φ as strength constants of ground G. Figure 6 shows a graph with vertical stress σ on the horizontal axis and shear stress τ on the vertical axis. As mentioned above, the overburden pressure P when the groundwater level is WL at a given depth and the shear stress τ corresponding to that overburden pressure P correspond to a single point on the graph. Plotting the combination of overburden pressure P (P1, P2) and shear stress τ (τ1, τ2) as coordinates of two points (P1, τ1) and (P2, τ2) on the graph yields a linear function whose vertical intercept corresponds to the cohesion force c and whose slope corresponds to the internal friction angle φ. Note that plotting the coordinates of two points can be done using a method that requires multiple overburden pressure P values, as mentioned above.

[0054] As another example, if the ground G is clay or sand, the cohesion c or the internal friction angle φ may be obtained according to the Mohr-Coulomb failure criterion using the shear stress τ and the overburden pressure P (P1, P2). As an example, if the ground G is clay, the internal friction angle φ is set to zero and only the cohesion c is obtained simply, as shown in FIG. 7(a). As another example, if the ground G is sand, the cohesion c is set to zero and only the internal friction angle φ is obtained simply, as shown in FIG. 7(b).

[0055] <Action and effect> The ground strength measurement method of this embodiment includes the steps of inserting the large diameter portion 24 attached to the tip of the rod 20 of the ground strength measuring device 10 into the borehole BH, rotating the rod 20 around its axis, and measuring the first torque T1 generated by friction between the borehole wall BW of the borehole BH and the large diameter portion 24 at a predetermined depth, and deploying the blades 52 outward from the large diameter portion 24, rotating the rod 20 around its axis, and measuring the second torque T2 generated by shear and friction at the predetermined depth.

[0056] According to this method, the large diameter portion 24 at the tip of the rod 20 is inserted into the borehole BH, and the blades 52 are deployed outward from the large diameter portion 24 at a predetermined depth. Therefore, compared to a configuration in which the tip of the rod 20 is replaced, the strength of the ground G can be easily measured while minimizing the impact on the strength measurement of the ground G.

[0057] The ground strength measuring device 10 of this embodiment comprises a rod 20 having a large diameter portion 24 at its tip which is inserted into a borehole BH, a handle 30 which is provided on the ground side of the rod 20 and rotates the rod 20 around its axis, a load cell 40 which is provided between the large diameter portion 24 and the handle 30, a plurality of blades 52 which are provided inside the large diameter portion 24 and which deploy outward from slits 26 formed in the large diameter portion 24, and a blade deployment portion 60 which is operated from the ground side of the rod 20 and converts axial movement into a deployment force of the blades 52, and the load cell 40 measures a first torque acting on the hole wall BW of the borehole BH and the outer surface of the large diameter portion 24 when the rod 20 is rotated around its axis, and also measures a second torque acting on the blades 52 when the blades 52 are deployed outward from the large diameter portion 24 and the rod 20 is rotated around its axis.

[0058] According to this configuration, the first torque T1 and the second torque T2 are measured at a predetermined depth underground by changing the deployment state of the blades 52, so that the ground strength can be measured without changing the stress state of the ground G.

[0059] In addition, in the ground strength measuring device 10 of this embodiment, the blade deployment portion 60 maintains the blades 52 deployed outward from the slits 26 when the wire 64 is operated from the ground side of the rod 20 to the first position.

[0060] According to this configuration, the blade deployment section 60 maintains the blade 52 deployed from the large diameter section 24, so that even if the blade 52 receives a reaction force from the ground G during strength measurement, the blade 52 will not return to the inside of the large diameter section 24.

[0061] In the ground strength measuring device 10 of this embodiment, the blades 52 are provided with limiting portions 58 formed at the upper ends in the vertical direction, which limit the deployment force of the blades 52.

[0062] According to this configuration, excessive expansion of the blades 52 from the inside to the outside of the large diameter portion 24 can be restricted.

[0063] <Modification> In addition, the present disclosure can be configured by partially combining the configurations illustrated in the attached drawings. As described above, the present disclosure includes various embodiments not described above, and the technical scope of the present disclosure is defined only by the invention-specifying matters in the claims that are appropriate from the above description.

[0064] (First Modification) As shown in Figure 8, the ground strength measuring device 110 according to the first modified example differs from the ground strength measuring device 10 according to the above embodiment in that a conical portion 80 is attached to the bottom surface of the large diameter portion 24. The ground strength measuring device 110 has the same configuration as the ground strength measuring device 10 except for the attachment of the conical portion 80. The conical portion 80 is a cone with a diameter approximately the same as the outer diameter of the large diameter portion 24. This configuration makes it easier to insert the ground strength measuring device 110 into the borehole BH in the ground G.

[0065] (Second Modification) As shown in Figure 9, the ground strength measuring device 210 of the second modified example differs from the ground strength measuring device 10 of the above embodiment and the ground strength measuring device 110 of the first modified example in the shapes of the blade member 50 and the blade deployment portion 60.

[0066] Specifically, in the above embodiment, the wire 64 of the blade deployment section 60 is wound up or let out in the vertical direction, thereby moving the blades 52 of the blade member 50 in the radial direction of the large diameter section 24. In other words, in the above embodiment, the movement in the axial direction is converted into movement in a direction perpendicular to the axial direction.

[0067] On the other hand, in the second modified example, the wire 64 of the blade deployment portion 60 is replaced with a shaft 264 of the blade deployment portion 260, and the blades 252 of the blade member 250 are attached so as to be deployable outward from the slits 226 of the large diameter portion 224. Specifically, a rotating portion 256 extending along the vertical direction of the shaft 264 is attached to the outer circumferential surface of the shaft 264, and the blades 252 are attached so as to be rotatable relative to the rotating portion 256. As shown in FIG. 9(b), when inserting the ground strength measuring device 210 into the borehole BH, the blades 252 are inserted into the borehole BH with the blades 252 housed inside the large diameter portion 224. When measuring the second torque (see FIGS. 5(c) and 5(d)), the shaft 264 is rotated axially counterclockwise inside the rod (not shown in FIG. 9) as viewed from below, and the blades 252 are inserted into the ground G.

[0068] As described above, in the second modified example, it is possible to convert the rotational motion around the axis of the shaft 264 into linear motion in a direction perpendicular to the axial direction. In the second modified example, it is possible to make the internal space of the large diameter portion 24 more compact in the vertical direction than in the above embodiment.

[0069] (Other variations, etc.) In the ground strength measuring device 10 of the above embodiment, the blade deployment unit 60 maintains the blades 52 deployed outward from the slits 26 when the rod 20 is operated from the ground side of the rod 20 to the first position, but this is not limited to this. As long as the blades 52 are maintained in a state of being deployed outward from the slits 26, the blade deployment unit 60 does not have to be in a specific first position. Specifically, it is sufficient that the blade deployment unit 60 is operated into a predetermined area on the back side of the mounting unit 54.

[0070] In the ground strength measuring device 10 of the above embodiment, the blades 52 are provided with the limiting portions 58 formed at the upper end in the vertical direction and limiting the deployment force of the blades 52, but this is not limited to this. For example, the blades 52 may have the limiting portions 58 formed at the lower end in the vertical direction.

[0071] Although the number of blades 52 is four in the above embodiment, the present invention is not limited to this. For example, the number of blades 52 may be any number, particularly an even number. It is preferable to have a larger number of blades 52.

[0072] Although the shape of the blade 52 has been described as being triangular in the portion that unfolds outward from the slit 26, this is not limited to this. For example, the unfolded portion of the blade 52 may be semicircular or rectangular. In these cases, the edge of the unfolded portion of the blade 52 becomes the shear surface.

[0073] Although the slits 26 are in an open state, this is not limiting. For example, a brush (not shown) or a film (not shown) may be attached to cover the slits 26. In this case, it is possible to prevent the crushed ground G from entering the inside of the large diameter portion 24 from the outside of the large diameter portion 24 through the slits 26.

[0074] The torque T does not necessarily have to be acquired as data by the data logger 70. For example, the torque T may be acquired by directly reading the dial scale. In this case, the configuration of the ground strength measuring device 10 is simplified.

[0075] Although the ground strength measuring device 10 is inserted into the borehole after boring, this is not limited to this. For example, the ground strength measuring device 10 may be equipped with a boring sampler (not shown) attached to the tip of the rod 20, and measure the strength of the ground G while sampling it by boring. In this case, the strength of the ground G at any depth above the sampler can be measured.

[0076] The ground strength measuring device 10 is assumed to be a measuring device that measures the adhesion force c and internal friction angle φ of the ground G. In addition, the ground strength measuring device 10 can measure the residual strength of the ground G. For example, with the handle 30 of the ground strength measuring device 10 changed to a motor (not shown), the rod 20 is rotated repeatedly clockwise and counterclockwise to repeatedly load the ground G. By applying an infinite amount of shear displacement to the ground G, the residual strength of the ground G can be measured. Furthermore, by using the ground strength measuring device 10, nonlinearity information of the ground G can be obtained to predict seismic motion. [Explanation of symbols]

[0077] 10. Ground strength measuring device 20 rods 22 Small diameter section 24 Large diameter section 24A Cylindrical surface 24B Top surface 26 Slit 28 Through Hole 30 Handle 40 load cells 50 Blade member 52 Feather 54 Mounting part 56 Rotating part 58 Restrictions 60 Blade deployment section 62 Cylinder 64 wire 70 Data Logger 80 Cone section 110 Ground strength measuring device 210 Ground strength measuring device 224 Large diameter section 226 Slit 250 Blade member 252 Feather 256 Rotating part 260 Blade deployment section 264 Shaft BH borehole BW hole wall C Adhesion G Ground P overlay pressure T Torque

Claims

1. a step of inserting a cylindrical body attached to the tip of a rod into a borehole, rotating the rod around its axis, and measuring the friction force between the borehole wall and the cylindrical body at a predetermined depth; deploying blades outward from the cylindrical body and rotating the rod around its axis to measure the rotational resistance at the predetermined depth; A method for measuring ground strength.

2. a rod having a cylindrical body at its tip that is inserted into a borehole; a rotational force transmission unit provided on the ground side of the rod and configured to rotate the rod around its axis; a load cell provided between the cylindrical body and the rotational force transmission unit; a plurality of blades provided inside the cylindrical body and extending outward from slits formed in the cylindrical body; a blade deployment unit that is operated from the ground side of the rod and converts axial or circumferential movement of the rod into deployment force for the blade; Equipped with The load cell measures a first torque acting on the wall of the borehole and the outer surface of the cylindrical body when the rod is rotated around its axis, and also measures a second torque acting on the blade when the blade is deployed outward from the cylindrical body and the rod is rotated around its axis, in a ground strength measuring device.

3. the blade deployment portion maintains the blades in a state where they are deployed outward from the slits when operated to a predetermined position from the ground side of the rod. The ground strength measuring device according to claim 2.

4. The blade has a limiting portion formed at an end thereof to limit the deployment force of the blade. The ground strength measuring device according to claim 3.

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