On-site test method and test device for soil shear characteristics of rectangular pipe jacking construction pipe in water-free sand layer

Abstract

The application discloses a field test method and a test device for soil shearing characteristics of a rectangular pipe in anhydrous sand layer construction pipe. The test method comprises the following steps: concrete block manufacturing; site leveling and pretreatment; preparation of drag-reducing mud; preparation and testing of mud-soil mixture; grouting condition simulation and test block placement; shearing test, interface shearing test is carried out, and the shearing characteristics under the conditions of no grouting and different grouting are simulated respectively; data arrangement and analysis, and analysis of the change law of the interface shearing characteristics with the mud-soil ratio, vertical pressure and standing time. The field test method and the test device for soil shearing characteristics of the rectangular pipe in the anhydrous sand layer construction pipe provided by the application carry out field large-size direct shear test, consider the influence of mud-soil mixing and construction pause interval, the test condition is closer to the engineering practice compared with the traditional indoor direct shear test, and the jacking force prediction result can well meet the engineering demand. The application is simple in operation, scientific and practical, cost-saving, and is worthy of being used as reference by relevant engineering.

Description

Technical Field

[0001] This invention relates to the field of civil engineering construction technology, and in particular to geotechnical testing. Specifically, it relates to a field test method and test apparatus for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers. Background Technology

[0002] my country has become a major country in the development of underground space, with urban underground space development and utilization showing a large-scale growth trend, and the requirements for urban underground space planning and construction are constantly increasing. Compared with the traditional "shallow burial method" and "direct burial method", pipe jacking construction technology is widely used due to its advantages such as small footprint, minimal ground disturbance, fast construction progress, and no road excavation or traffic closure. Among them, rectangular pipe jacking construction technology has broad application prospects due to its high space utilization rate and good adaptability to shallow overburden. To meet the needs of urban underground space development and utilization, my country's rectangular pipe jacking construction technology is developing towards larger cross-sectional dimensions and longer jacking distances, which in turn places increasingly higher demands on the jacking force. Excessive jacking force can cause problems such as pipe section rupture and back wall instability, while insufficient jacking force can prevent the pipe section from advancing normally, and in some cases, it is necessary to add intermediate stations to provide sufficient power. Therefore, accurate prediction of the jacking force is particularly important before rectangular pipe jacking construction.

[0003] The jacking force of pipe jacking mainly consists of two parts: the face support reaction force and the sidewall skin friction, with the sidewall skin friction being the primary component. Currently, mature theoretical methods have been developed for calculating the face support reaction force. However, due to the complexity of the pipe-soil contact state, significant disagreements remain regarding the calculation of the sidewall skin friction. Therefore, it is necessary to conduct more in-depth research on the pipe-soil shear characteristics under grouting conditions. To date, research on the pipe-soil contact characteristics of pipe jacking has primarily relied on indoor direct shear tests to obtain data on shear stress, shear displacement, and vertical displacement at the pipe-soil interface under different vertical loads. However, the sample size is generally small, exhibiting a significant size effect, and the direct shear box restricts the shear deformation of the soil sample, resulting in significant deviations between the soil sample boundary conditions and actual engineering conditions. Furthermore, for loosely structured and highly permeable strata such as sandy soil, the assumption of full-pipe-grout contact no longer holds. As the pipe section advances, the sand collapsing onto the pipe section mixes with the drag-reducing grout to form a grout-soil mixture. Under the action of grouting, three contact forms simultaneously exist on the pipe section: pipe-soil contact, pipe-grout contact, and pipe-grout-soil mixture contact. Moreover, due to the thixotropic nature of the drag-reducing grout, the shear characteristics exhibited by the same pipe-soil contact form differ under different construction pauses. Therefore, the calculated value of the sidewall friction resistance of the pipe jacking based on indoor direct shear tests deviates significantly from the actual engineering situation. The jacking force prediction based on this cannot well meet the engineering requirements. It is necessary to consider the influence of grout-soil mixing and construction pauses, and to conduct large-scale field direct shear tests to study the pipe-soil shear characteristics of rectangular pipe jacking construction in anhydrous sand layers. Summary of the Invention

[0004] The first technical problem to be solved by the present invention is to provide a simple, practical, scientific and cost-effective field test method for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers, so as to at least partially solve the problems existing in the prior art.

[0005] The second technical problem to be solved by the present invention is to provide an apparatus that can realize the field test method of the shear characteristics of the soil-tube.

[0006] To achieve the above objectives, the present invention is specifically implemented as follows:

[0007] This invention first provides a field test method for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers, comprising the following steps:

[0008] (1) Concrete block fabrication: Concrete blocks with a surface roughness similar to that of the actual pipe jacking section are fabricated.

[0009] (2) Site leveling and pretreatment: Select the waterless sand layer that can represent the strata through which the rectangular jacking pipe passes as the test site after the construction site is excavated and exposed, and pretreatment is carried out.

[0010] (3) Mud preparation, preparation of drag-reducing mud;

[0011] (4) Preparation and testing of slurry-soil mixture: Samples were taken from the waterless sand layer that represents the strata through which the rectangular jacking pipe passes, which was exposed during the excavation at the construction site. The drag-reducing mud and the soil sample were mixed according to different slurry-soil ratio coefficients η to prepare slurry-soil mixtures. The density, cohesion, internal friction angle and compressibility coefficient of the slurry-soil mixtures under different ratio coefficients were tested.

[0012] (5) Grouting condition simulation and test block placement: A test area is demarcated on the test site, and concrete blocks are placed within the test area to simulate the shear behavior of the pipe and soil under no grouting conditions and different grouting conditions.

[0013] (6) Shear test: Conduct an interface shear test. Apply different vertical loads at the center of the top surface of the concrete block and apply horizontal thrust at the center of the rear end face of the concrete block to make the concrete block undergo horizontal shear sliding under different vertical loads, and simulate the shear characteristics under no grouting conditions and different grouting conditions respectively.

[0014] (7) Data processing and analysis: The data of shear force, shear displacement and vertical displacement monitored by field shear test under different grouting conditions and different resting time are processed to obtain the shear stress-shear displacement, shear strength-normal stress, strength-residual ratio-normal stress, normal displacement-shear displacement and friction coefficient-normal stress curves under each test condition. The variation law of interface shear characteristics with grout-soil ratio, vertical pressure and resting time is analyzed.

[0015] In some embodiments, the front bottom edge of the concrete block is an arc surface, which is tangent to the adjacent surfaces on both sides, and the rear bottom edge of the concrete block overlaps with one side edge of the test range and is located in the middle of it.

[0016] In some embodiments, the pretreatment includes cutting, filling and leveling the test soil layer, with each leveling area being 2×2m as the test site. After the site is leveled, preloading is performed, and the magnitude of the preloading pressure is 1.2 times the magnitude of the overburden pressure at the centerline of the jacking pipe.

[0017] The definition of a test area is to draw a 1×1m area in the center of a 2×2m test site.

[0018] In some embodiments, the preparation of drag-reducing mud includes preparing mud using a drag-reducing mud formula suitable for rectangular pipe jacking construction in anhydrous sand layers, which has been optimized through indoor orthogonal experiments. The mass ratio of the mud is sodium bentonite: sodium hydroxymethyl cellulose (CMC): soda ash (Na2CO3): water = 100:2:5:893.

[0019] In some embodiments, after sampling, impurities in the soil sample are removed by sieving with a standard sieve with a aperture of 2 mm, and drag-reducing mud and the sieved soil sample are mixed according to the mud-soil ratio coefficient η of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.5, 2 and ∞ to prepare mud-soil mixture.

[0020] In some embodiments, when simulating no grouting conditions, the influence of construction interruptions is not considered. When simulating different grouting conditions, a grout-soil mixture with a certain thickness ξ and different grout-soil ratio coefficients η is first laid in the test site, and then concrete blocks are placed on the grout-soil mixture.

[0021] In some embodiments, when simulating no grouting conditions, a series of vertical loads of 0.06, 0.08, 0.1, 0.12, 0.14, and 0.16 MPa are applied to the center of the top surface of the concrete block. When simulating different grouting conditions, the concrete block is left to stand for 0, 2, 4, 6, 8, 10, 12, 24, and 48 hours after the series of vertical loads are applied to the top surface of the concrete block.

[0022] In some embodiments, during the data processing and analysis, the density, cohesion, internal friction angle, and compression coefficient of the slurry-soil mixture under different slurry-soil ratio coefficients η are first processed to obtain density-slurry-soil ratio, cohesion-slurry-soil ratio, internal friction angle-slurry-soil ratio, and compression coefficient-slurry-soil ratio curves, and the variation law of density, cohesion, internal friction angle, and compression coefficient of the slurry-soil mixture with the slurry-soil ratio is analyzed.

[0023] The present invention also provides a test apparatus for a field test method of shear characteristics of rectangular pipe jacking construction in the aforementioned anhydrous sand layer, comprising:

[0024] Concrete blocks were placed within the test area of ​​the test site;

[0025] The normal loading system includes a vertical loading frame and a vertically separate hydraulic jack. The vertical loading frame is fixed in the test site. The vertically separate hydraulic jack is installed on the vertical loading frame, facing the concrete block below. A ball bearing and a force transmission steel plate are placed sequentially between the loading end of the vertically separate hydraulic jack and the concrete block.

[0026] The horizontal shear loading system includes a horizontally separate hydraulic jack and a reaction support structure. The reaction support structure is anchored in the stratum within the test site. The horizontally separate hydraulic jack is located on the rear side of the concrete block, with one end facing the center of the rear side of the concrete block and the other end abutting against the reaction support structure.

[0027] The monitoring system includes a displacement gauge, a pressure gauge, and a multi-functional data acquisition device. The displacement gauge is installed on the front side of the concrete block and contacts the front surface of the concrete block. The pressure gauge is connected to a separate hydraulic jack. The displacement gauge and the pressure gauge are connected to the multi-functional data acquisition device.

[0028] In some embodiments, the vertical loading frame consists of a crossbeam, a loading beam, and an anchor rod. The anchor rod is vertically anchored in the strata within the test site. The crossbeam and the loading beam form an I-shaped frame structure and are fixed to the anchor rod. The vertically detachable hydraulic jack is installed below the loading beam via a bearing support.

[0029] In some embodiments, the reaction support structure consists of a reaction support steel plate and three triangular steel plates with trapezoidal flanges, the triangular steel plates being wedged into the strata within the test site.

[0030] The advantages of this invention compared to existing technologies are as follows: This invention provides a field test method and apparatus for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers. It conducts large-scale direct shear tests in the field, considering the effects of grout-soil mixing and construction pauses, to study the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers. The invention analyzes the variation of the density, cohesion, internal friction angle, and compressibility coefficient of the grout-soil mixture with the grout-soil ratio. It organizes the shear force, shear displacement, and vertical displacement data monitored in the field shear tests under different grouting conditions and different settling times, obtaining shear stress-shear displacement, shear strength-normal stress, strength-residual ratio-normal stress, normal displacement-shear displacement, and friction coefficient-normal stress curves under various test conditions. It analyzes the variation of interfacial shear characteristics with grout-soil ratio, vertical pressure, and settling time, and reveals its microscopic mechanism. Compared to traditional indoor direct shear tests, the test conditions are closer to actual engineering conditions, and the jacking force prediction based on the test results can well meet engineering requirements. The method is simple to operate, practical, scientifically applicable, and cost-effective, making it worthy of reference in related engineering projects. The field testing method, drag-reducing mud formulation, and testing apparatus of this invention are particularly aimed at studying the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers.

[0031] It should be understood that the implementation of any embodiment of the present invention does not mean that it will simultaneously possess or achieve multiple or all of the above-mentioned beneficial effects. Attached Figure Description

[0032] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0033] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0034] Figure 1 This is a side view of the field tube-soil shear characteristic testing device disclosed in the embodiments of this application;

[0035] Figure 2 This is a top view of the field tube-soil shear characteristic testing device disclosed in the embodiments of this application;

[0036] Figure 3 This is a top view of the concrete block disclosed in the embodiments of this application;

[0037] Figure 4 This is a side view of the concrete block disclosed in the embodiments of this application;

[0038] Figure 5 This is a diagram showing the internal reinforcement of the concrete block disclosed in the embodiments of this application;

[0039] Figure 6 This is a drawing of a concrete block manufacturing mold disclosed in an embodiment of this application;

[0040] Figure 7 This is a structural diagram of the split hydraulic jack disclosed in the embodiments of this application. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0042] In the description of this invention, the terms "comprising / including," "consisting of," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a product, apparatus, process, or method that comprises a list of elements includes not only those elements but may also include, where necessary, other elements not expressly listed, or elements inherent to such a product, apparatus, process, or method. Without further limitation, an element defined by the phrases "comprising / including," "consisting of," does not exclude the presence of additional identical elements in the product, apparatus, process, or method that includes said element.

[0043] It should be understood that, unless otherwise explicitly specified and limited, the terms "set up," "install," "connect," "link," and "fix" should be interpreted broadly. For example, they can refer to any suitable setting method; they can be a fixed connection, a detachable connection, or an integral part; they can be a mechanical connection or an electrical connection; they can be a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] It should also be understood that the terms “upper,” “lower,” “front,” “back,” “left,” “right,” “top,” “bottom,” “inner,” “outer,” and “center,” etc., which indicate orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device, component, or structure referred to must have a specific orientation, be constructed or operated in a specific orientation, and should not be construed as a limitation of the present invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0046] For rectangular pipe jacking construction in anhydrous sand layers, the calculation of sidewall friction is insufficient for practical engineering applications due to the complexity of the pipe-soil contact state. Conventional indoor direct shear test specimens are generally small, exhibiting significant size effects, and the boundary conditions of the soil samples deviate considerably from actual engineering conditions. For loosely structured and highly permeable strata such as sand, three contact forms—pipe-soil contact, pipe-grout contact, and pipe-grout-soil mixture contact—simultaneously exist on the pipe section under grouting. Moreover, due to the thixotropic nature of the drag-reducing grout, the shear characteristics exhibited by the same pipe-soil contact form differ under different construction pauses. The prediction of jacking force cannot adequately meet engineering requirements. Therefore, this invention considers the influence of grout-soil mixing and construction pauses, and conducts large-scale field direct shear tests to study the pipe-soil shear characteristics of rectangular pipe jacking construction in anhydrous sand layers.

[0047] The following describes each step of the analysis method in detail with reference to preferred implementation methods and specific illustrations.

[0048] This invention first provides a field test method for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers, mainly including the following steps: First step, concrete block fabrication; second step, site leveling and pretreatment; third step, mud preparation; fourth step, mud-soil mixture preparation and testing; fifth step, grouting condition simulation and test block placement; sixth step, shear test; seventh step, data processing and analysis.

[0049] The first step is to make concrete blocks, which have the same or similar surface roughness as the actual pipe jacking sections.

[0050] It is easy to understand that in actual production, it is difficult to make the surface roughness of the concrete block exactly the same as that of the actual pipe jacking section. It is sufficient to make it as similar as possible to the actual pipe jacking section and meet the test requirements.

[0051] like Figure 3 , Figure 4 The concrete block 10 is a single C50 concrete block, measuring 0.6 × 0.6 × 0.2 m. A 2 cm radius rounded corner 11 is made on one side of the bottom edge, tangent to the adjacent surfaces on both sides. By rounding the bottom corner of the concrete block 10 facing forward, soil scraping at the corner during shearing is prevented, which could affect the accuracy of the test results. For a 60 cm concrete block, the 2 cm radius represents a very small proportion of 60 cm; the bottom of the concrete block can be approximated as a flat plane, and the presence of the rounded corner has minimal impact on the test results.

[0052] like Figure 5 The concrete block 10 is internally reinforced with No. 8, No. 10 and No. 16 threaded steel bars, and the top surface is equipped with four U-shaped No. 16 round steel bar handles for lifting and transporting. The concrete block 10 is reinforced in three layers. At each of the four corners, a No. 16 threaded steel bar with a length of 0.15m is placed. The outer side is reinforced with three layers of 0.56×0.56m stirrups made of No. 8 threaded steel bars. Each layer of stirrups is lapped with three No. 10 threaded steel bars with a length of 0.56m horizontally and vertically. Finally, four U-shaped handles made of No. 16 round steel bars are placed. All steel bar joints are fixed with tie wire. A total of 4 No. 16 threaded steel bars, 3 No. 8 threaded stirrups and 18 No. 10 threaded steel bars are used.

[0053] like Figure 6 For C50 concrete block molds, first lay a 0.02m thick layer of concrete at the bottom of the mold, then place the tied steel mesh in the center and continue pouring. Use a thin stick to tamp down all the dead corners of the steel bars during pouring to prevent voids and air bubbles. Stop pouring when the concrete is level with the mold opening, smooth the concrete surface with a tool, and place it in a curing box for 28 days to complete the production of the concrete block.

[0054] It is easy to understand that concrete block 1 is designed with a surface roughness similar to that of the actual pipe section, and is used in the experiment to simulate the shearing effect of the pipe section on the soil layer.

[0055] The second step is to select an anhydrous sand layer that can represent the strata through which the rectangular jacking pipe passes as the test site, and to pre-treat it.

[0056] After selecting the test site, the soil was cut, filled and leveled. Each leveled area was 2×2m as the test site. After the site was leveled, steel plates and lead blocks were placed on top for preloading. The magnitude of the preloading pressure was 1.2 times the magnitude of the soil pressure at the center axis of the jacking pipe.

[0057] The third step is to prepare drag-reducing mud.

[0058] The drag-reducing mud mix ratio is sodium bentonite: sodium hydroxymethyl cellulose (CMC): soda ash (Na2CO3): water = 100:2:5:893. Weigh the ingredients according to the ratio, and add soda ash, sodium bentonite, and CMC to the water sequentially. Simultaneously stir with a mixer at a speed of 550–600 r / min. After all ingredients have been added and thoroughly mixed, cover with plastic wrap and continue stirring for 24 hours. The drag-reducing mud mix is ​​then ready. This ratio was optimized through indoor orthogonal experiments and is suitable for rectangular pipe jacking construction in anhydrous sand layers.

[0059] The fourth step is to take samples from the anhydrous sand layer that represents the strata through which the rectangular jacking pipe will pass, which is exposed during the excavation at the construction site. The sampling site can be the test site selected in the first step, or a different site, as long as the properties of the soil exposed during the excavation are similar to those of the soil through which the jacking pipe will pass.

[0060] After sampling, the prepared drag-reducing mud was mixed with the soil sample according to different mud-soil ratio coefficients η to prepare mud-soil mixtures, and the density, cohesion, internal friction angle and compressibility coefficient of the mud-soil mixtures under different ratio coefficients were tested.

[0061] Sampling was carried out in the anhydrous sand layer that could represent the strata through which the rectangular jacking pipe was pierced, and impurities in the soil sample were removed by sieving with a standard sieve with a 2mm aperture. The drag-reducing mud and the sieved soil sample were mixed with the mud-soil ratio coefficient η at mass ratios of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.5, 2 and ∞ to prepare mud-soil mixture.

[0062] The fifth step is to delineate a test area on the test site and place concrete blocks with a surface roughness similar to that of the actual pipe jacking sections within the test area to simulate the pipe-soil shear behavior under conditions without grouting and under different grouting conditions.

[0063] Remove the steel plates and lead blocks from the test site, and delineate a 1×1m test area in the center of the 2×2m test area to conduct the interface shear test.

[0064] The concrete block is preferably a C50 concrete block with a surface roughness of 0.6×0.6×0.2m, which is similar to that of the actual pipe section. The bottom rear edge of the concrete block overlaps with one side edge of the test range and is located in the middle of it, which facilitates the positioning of the concrete block relative to the device.

[0065] When simulating no grouting conditions, without considering the impact of construction interruptions, C50 concrete blocks with a surface roughness similar to that of actual pipe sections (0.6×0.6×0.2m) are placed directly within the test area, with the rear bottom edge of the concrete block overlapping one side edge of the test area and positioned in the middle. When simulating different grouting conditions, grout-soil mixtures with different grout-soil ratio coefficients η and a certain thickness ξ are first laid in the test site. Then, the concrete blocks are placed on the grout-soil mixtures. After applying different vertical loads to the top surface of the concrete blocks and allowing them to stand for a predetermined time, horizontal thrust is applied.

[0066] In this invention, the thickness ξ is calculated as shown in formula (1):

[0067]

[0068] Where: Δp—the difference between mud pressure and groundwater pressure; when there is no groundwater, the grouting pressure is used; d 10 —The effective particle size of the soil, that is, the mass of soil particles smaller than this size accounts for 10% of the total mass; τ s —Shear resistance of the mud, taken as the dynamic shear force value; n —Porosity of the soil; f —Parameter considering the size and curvature of the soil seepage path, generally taken as 0.3.

[0069] The sixth step is to conduct an interfacial shear test. Different vertical loads are applied to the center of the top surface of the concrete block, and a horizontal thrust is applied to the center of the rear end face of the concrete block, so that the concrete block undergoes horizontal shear sliding under different vertical loads, simulating the shear characteristics under no grouting conditions and under different grouting conditions.

[0070] Vertical loads of 0.06, 0.08, 0.1, 0.12, 0.14, and 0.16 MPa were applied to the center of the top surface of the concrete block, respectively. Under simulated conditions without grouting, and without considering the effects of construction interruptions, a horizontal thrust was applied to the center of the rear end face of the concrete block, causing horizontal shear sliding under different vertical loads. The maximum sliding distance was set at 10 cm. Shear force, shear displacement, and vertical displacement data were monitored and recorded for subsequent processing and analysis. The experiment could be repeated within the same test site. By simulating the shear characteristics under conditions without grouting, a control group for subsequent grouting conditions was established to analyze the effect of grouting during rectangular pipe jacking construction on the shear characteristics of the soil in anhydrous sand layers.

[0071] When simulating different grouting conditions, different vertical loads were applied to the top surface of the concrete block and then left to stand for 0, 2, 4, 6, 8, 10, 12, 24, and 48 hours before shear tests were conducted. The implementation of horizontal thrust and monitoring was the same as under no-grouting conditions. After each test, the test site area needed to be changed and the bottom surface of the concrete block needed to be cleaned and wiped.

[0072] The seventh step involves data processing and analysis. Shear force, shear displacement, and vertical displacement data from field shear tests under different grouting conditions and settling times are processed to obtain shear stress-shear displacement, shear strength-normal stress, strength-residual ratio-normal stress, normal displacement-shear displacement, and friction coefficient-normal stress curves for each test condition. The variation of interfacial shear characteristics with grout-to-soil ratio, vertical pressure, and settling time is analyzed. Analysis of the five sets of curves yields the shear characteristics of the pipe-soil mixture. These obtained shear characteristics can be used for predicting jacking force and soil deformation.

[0073] In this invention, data processing and analysis also include first processing the density, cohesion, internal friction angle, and compressibility coefficient of the slurry-soil mixture under different slurry-soil ratio coefficients η to obtain density-slurry-soil ratio, cohesion-slurry-soil ratio, internal friction angle-slurry-soil ratio, and compressibility coefficient-slurry-soil ratio curves, and analyzing the variation laws of the density, cohesion, internal friction angle, and compressibility coefficient of the slurry-soil mixture with the slurry-soil ratio. By first understanding the variation law of the physical and mechanical properties of the slurry-soil mixture with the slurry-soil ratio, the intrinsic mechanism of the variation of the shear characteristics of the pipe-soil mixture with the slurry-soil ratio is revealed.

[0074] To complete the field test method for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers, this invention provides a field test device for the shear characteristics of rectangular pipe jacking construction in anhydrous sand layers. The device mainly includes a concrete block 10, a normal loading system 20, a horizontal shear loading system 30, and a monitoring system 40. The following will describe the device in conjunction with... Figures 1 to 7 To elaborate in detail.

[0075] like Figure 1 , Figure 2 As shown, a 2×2m area was selected as the test site S1, and a 1×1m area was selected in the center of the test site S1 as the test range S2. The test range S2 was used to place concrete blocks 10.

[0076] See also Figure 1 , Figure 2 The normal loading system 20 includes a vertical loading frame and a vertically separate hydraulic jack 21. The vertical loading frame is fixed in the test site S1. The vertically separate hydraulic jack 21 is installed on the vertical loading frame, facing the concrete block 10 below. A ball bearing row 22 and a force transmission steel plate 23 are placed sequentially between the loading end of the vertically separate hydraulic jack 21 and the concrete block 10.

[0077] In this invention, the vertical loading frame consists of a horizontal beam 24, a loading beam 25, and an anchor rod 26. The anchor rod 26 is vertically anchored in the stratum within the test site S1. The horizontal beam 24 and the loading beam 25 form an I-shaped frame structure, which is installed and fixed on the anchor rod 26. A vertically detachable hydraulic jack 21 is installed below the loading beam 25 via a bearing support 27. The bearing support 27 is installed on the loading beam 25 using nuts and washers.

[0078] There are four anchor bolts (26), which are spiral-shovel anchors with a spiral shovel at the bottom. Each bolt provides 2.5t of anchoring force. There are two crossbeams (24), which can be made of I-beams, with an ultimate load of 5t. There is one loading beam (25), which can also be made of I-beams, with an ultimate load of 10t. There is one set of vertically detachable hydraulic jacks (21), with a cylinder bottom diameter of 190mm, a cylinder outer diameter of 120mm, a height of 320mm, and a load-bearing capacity of 10t.

[0079] The normal loading system is used to simulate the overburden pressure, specifically the overburden pressure experienced by the pipe jacking section.

[0080] See also Figure 1 , Figure 2 The horizontal shear loading system 30 includes a horizontally separate hydraulic jack 31 and a reaction support structure. The reaction support structure is anchored in the stratum within the test site S1. The horizontally separate hydraulic jack 31 is located on the rear side of the concrete block 10, with one end facing the center of the rear side of the concrete block 10 and the other end abutting against the reaction support structure.

[0081] In this invention, the reaction support structure consists of a reaction support steel plate 32 and three triangular steel plates 33 with trapezoidal flanges. The reaction support steel plate 32 is chiseled perpendicularly into the test area S2, parallel to the loading beam 25, with the central axis of that side as the central axis. The exposed portion of the steel plate is guaranteed to be 0.2m long. The three triangular steel plates 33 with trapezoidal flanges are then chiseled perpendicularly into the rear three sections of the steel plate, completing the installation of the reaction support structure. If necessary, wooden blocks 34 are laid to align the center of the jack plunger end with the center of the rear end face of the concrete block.

[0082] The horizontally split hydraulic jack 31 is used in one set, with a cylinder bottom diameter of 190mm, a cylinder outer diameter of 120mm, a height of 320mm, and a load-bearing capacity of 10t.

[0083] One reaction support steel plate 32, with dimensions of 1.0×0.5×0.02m and a short edge with a blade on one end; three triangular steel plates 33 with trapezoidal flanges, with dimensions of 0.5×0.5×0.01m.

[0084] The horizontal shear loading system is used to simulate the pushing effect of jacks on pipe sections during pipe jacking construction.

[0085] It should be understood that the present invention Figure 2 The left side is the front side and the right side is the rear side, but the so-called front side and rear side are relative directional indicators. The horizontal loading direction can be understood as the front side, and the opposite direction of the horizontal loading direction can be understood as the rear side, depending on the setting position of the loading device and the loading direction.

[0086] The monitoring system 40 includes a displacement gauge 41, a pressure gauge 42, and a multi-function data acquisition device (not shown in the figure). The displacement gauge 41 is installed on the front side of the concrete block 10 and contacts the front side of the concrete block 10. The pressure gauge 42 is connected to two separate hydraulic jacks. The displacement gauge and the pressure gauge are connected to the multi-function data acquisition device.

[0087] The displacement gauge 41 is installed on the front side of the concrete block 10 via the gauge support plate 43 and the magnetic gauge base 44. Specifically, two gauge support plates 43 are symmetrically inserted about the central axis of the concrete block at a position of 0.2m in front of the concrete block. A magnetic gauge base 44 is attached to each gauge support plate 43, and a displacement gauge 41 is installed on each magnetic gauge base 44, so that the probe of the displacement gauge 41 is in contact with the front end face of the concrete block 10.

[0088] The displacement gauge 41 is a resistance strain gauge sensor with a range of 0-100 mm and a resolution of 0.01 mm. The pressure gauge 42 is a resistance strain gauge sensor with a range of 0-100 MPa and a resolution of 0.01 MPa. One multi-functional data acquisition instrument is included, which can collect, store, analyze and process monitoring data from the displacement gauge and pressure gauge. It features strong anti-interference ability, high integration, high performance, low power consumption, and good sensitivity and stability.

[0089] During on-site implementation, the concrete block 10 was first made and cured using molds.

[0090] Reference Figure 1 , Figure 2 The crossbeam 24 and loading beam 25 are fixed with screws and nuts, perpendicular to each other in an "I" shape. The preloaded steel plate and lead block are removed. When placing the crossbeam 24 and loading beam 25, ensure that the bearing support 27 is located at the center of the test range S2 and that the loading beam 25 is parallel to one side of the test range S2. Mark the test site S1 positions corresponding to the pre-drilled holes at both ends of the crossbeam 24. Remove the crossbeam 24 and loading beam 25. Install anchor rods 26 with augers at the marked positions, ensuring that the exposed length of the anchor rods 26 is 0.6m. Then, install the crossbeam 24 and loading beam 25 as a whole on the four anchor rods 26 to complete the installation of the vertical loading frame.

[0091] At a distance of 0.3m from the edge of the test range S2 parallel to the loading beam 25, and with the center axis of that side as the center axis, use a sledgehammer to vertically chisel into the reaction support steel plate 32, ensuring that the steel plate protrudes for a length of 0.2m. At the three equal division positions on the back side of the steel plate, vertically chisel into three triangular steel plates 33 with trapezoidal flanges to complete the installation of the horizontal reaction support structure.

[0092] When simulating different grouting conditions, a grout mixture is laid within the test range S2, and a concrete block 10 is placed. After the concrete block 10 is aligned with the bearing support 27, a force transmission steel plate 23, a ball bearing assembly 22, and a vertically separate hydraulic jack 21 are placed on top of it in sequence. The plunger end of the jack is then installed into the bearing support 27. The height of the jack can be adjusted by inserting a pad at the bottom or by extending or retracting the plunger. When simulating no grouting conditions, the test is conducted directly without laying the grout mixture.

[0093] Two gauge support plates 43 are symmetrically inserted about the central axis of the concrete block 10 at a position 0.2m in front of the concrete block 10. A magnetic gauge base 44 is attached to each of the gauge support plates 43. A displacement meter 41 is installed on each of the magnetic gauge bases 44, so that the probe of the displacement meter 41 is in contact with the front end face of the concrete block 10.

[0094] Place a horizontally split hydraulic jack 31 on the central axis of the rear side of the concrete block 10, and lay wooden blocks 34 to align the center of the jack plunger end with the center of the rear end face of the concrete block 10.

[0095] Connect the displacement gauge 41 and the oil pressure gauge 42 to the multi-functional data acquisition instrument, such as Figure 7 As shown, the hydraulic pump rod of the reciprocating normal loading system applies vertical load to the target value. Then, the hydraulic pump rod of the reciprocating horizontal loading system applies horizontal load to conduct the test. Data is collected and recorded in real time during the test.

[0096] It will be readily understood by those skilled in the art that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the soil shear properties of a rectangular jacking pipe in an anhydrous sand layer, characterized in that, The method comprises the following steps: (1) concrete block making, making concrete blocks similar to the surface roughness of the actual pipe section; (2) site leveling and pretreatment, selecting the water-free sand layer exposed by excavation at the construction site as the test site, which can represent the stratum through which the rectangular pipe passes, and pretreating it; (3) mud preparation, preparing drag-reducing mud; (4) preparation and testing of slurry-soil mixture, sampling the water-free sand layer exposed by excavation at the construction site, which can represent the stratum through which the rectangular pipe passes, mixing and preparing the slurry-soil mixture according to different slurry-soil proportioning coefficients η, and testing the density, cohesive force, internal friction angle and compression coefficient of the slurry-soil mixture under different proportioning coefficients; (5) grouting condition simulation and test block placement, demarcating a test range on the test site and placing concrete blocks in the test range to simulate the pipe-soil shear behavior under no grouting condition and different grouting conditions; (6) shear test, interface shear test is conducted, different vertical loads are applied to the center of the top surface of the concrete block, and horizontal thrust is applied to the center of the end surface of the back side of the concrete block, so that the concrete block slides horizontally under the action of different vertical loads to simulate the shear characteristics under no grouting condition and different grouting conditions; when simulating no grouting condition, the influence of construction stoppage is not considered, the concrete block is directly placed in the test range, a series of vertical loads are applied to the top surface of the concrete block, and horizontal thrust is applied; when simulating different grouting conditions, a certain thickness ξ of the slurry-soil mixture with different slurry-soil proportioning coefficients η is laid on the test site, the concrete block is placed on the slurry-soil mixture, a series of vertical loads are applied to the top surface of the concrete block, and then the horizontal thrust is applied after the concrete block is left for a predetermined time; (7) data arrangement and analysis, the shear force, shear displacement and vertical displacement data monitored in the field shear test under different grouting conditions and different standing times are arranged to obtain the shear stress-shear displacement, shear strength-normal stress, strong residual ratio-normal stress, normal displacement-shear displacement, friction coefficient-normal stress curves under each test condition, and the variation law of the interface shear characteristics with the slurry-soil ratio, vertical pressure and standing time is analyzed.

2. The field test method for pipe-soil shear characteristics of rectangular pipe construction in water-free sand layer according to claim 1, characterized in that: the front side bottom edge of the concrete block is a circular arc surface, the circular arc surface is tangent to the two adjacent surfaces, and the back side bottom edge of the concrete block overlaps the middle of one side edge of the test range.

3. The field test method for pipe-soil shear characteristics of rectangular pipe construction in water-free sand layer according to claim 1, characterized in that: the pretreatment includes cutting and leveling the test soil layer, each leveling range is 2x2m as the test site, the site is leveled and then pre-pressed, and the pre-pressing pressure is 1.2 times the soil pressure at the position of the pipe center line; the demarcated test range is a 1x1m range in the center of the 2x2m test site.

4. The field test method for pipe-soil shear characteristics of rectangular pipe construction in water-free sand layer according to claim 1, characterized in that: The preparation of the drag reduction mud includes mud preparation by using the drag reduction mud formula suitable for rectangular pipe jacking construction in waterless sand layer selected by indoor orthogonal test, and the mass ratio of the formula is sodium bentonite: sodium carboxymethylcellulose (CMC): soda (Na2CO3): water = 100:2:5:

893.

5. The pipe-soil shear property field test method for rectangular pipe jacking construction in waterless sand layer according to claim 1, characterized in that: After sampling, impurities in the soil sample are removed by a standard sieve with a pore size of 2 mm, and the drag reduction mud is mixed with the sieved soil sample to prepare a soil-mud mixture according to a slurry-soil ratio coefficient η of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.5, 2 and ∞.

6. The pipe-soil shear property field test method for rectangular pipe jacking construction in waterless sand layer according to claim 1, characterized in that: When simulating the condition without grouting, a series of vertical loads of 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16 MPa are applied to the center of the top surface of the concrete block, and when simulating different grouting conditions, the series of vertical loads are applied to the center of the top surface of the concrete block and then left to stand for 0, 2, 4, 6, 8, 10, 12, 24 and 48 h.

7. The pipe-soil shear property field test method for rectangular pipe jacking construction in waterless sand layer according to claim 1, characterized in that: When the data is arranged and analyzed, first, the density, cohesion, internal friction angle and compression coefficient of the soil-mud mixture under different slurry-soil ratio coefficients η are arranged to obtain the density-slurry ratio, cohesion-slurry ratio, internal friction angle-slurry ratio and compression coefficient-slurry ratio curves, and the variation law of the density, cohesion, internal friction angle and compression coefficient of the soil-mud mixture with the slurry ratio is analyzed.

8. A test device for the field test method of the soil shear properties of the rectangular jacking pipe construction pipe in the waterless sand layer according to any one of claims 1 to 7, characterized in that, It comprises: a concrete block placed in the test range of the test site; a normal loading system comprising a vertical loading frame and a vertical split hydraulic jack, the vertical loading frame being fixed in the test site, the vertical split hydraulic jack being installed on the vertical loading frame, facing the concrete block below, and a ball row and a force transmission steel plate being sequentially placed between the loading end of the vertical split hydraulic jack and the concrete block; a horizontal shear loading system comprising a horizontal split hydraulic jack and a counterforce support structure, the counterforce support structure being anchored in the stratum of the test site, the horizontal split hydraulic jack being arranged at the back side of the concrete block, one end facing the center of the back side of the concrete block and the other end abutting against the counterforce support structure; a monitoring system comprising a displacement meter, a pressure gauge and a multifunctional acquisition instrument, the displacement meter being installed at the front side of the concrete block, in contact with the front side of the concrete block, the pressure gauge being connected with the split hydraulic jack, and the displacement meter and the pressure gauge being connected to the multifunctional acquisition instrument.

9. The test device according to claim 8, characterized in that: the vertical loading frame is composed of a cross beam, a loading beam and an anchor rod, the anchor rod being vertically anchored in the stratum of the test site, the cross beam and the loading beam forming a I-shaped frame structure and being fixedly installed on the anchor rod, and the vertical split hydraulic jack being installed below the loading beam through a bearing support.

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