A method for simulating traffic load on the ground above a prefabricated box culvert

Abstract

The application discloses a kind of prefabricated box culvert upper ground traffic load simulation test methods, including, model box is placed in counterforce steel frame base;Add soil to model box to predetermined height;The telescopic amount of telescopic rod of deformable pressure-bearing device is calculated and adjusted;Vertical loading is carried out;Push model sleeve in model slide rail from the round hole on the front steel plate of model box into model box interior, the soil that gushes into tunnel interior is dug, and the steel plate on model box is tightly closed;Monitoring device is inserted into square tunnel model interior;Install horizontal jack to carry out axial loading;Water is injected into box through model box bottom water pipe to the amount of water required, continue to adjust the above each jack loading to the required level;Through preset sensor, corresponding data is collected, deformation, convergence deformation of square tunnel model under the action of random external load and the pressure of surrounding soil on square tunnel model are measured;The application solves the problem that existing test device and method cannot meet actual working condition requirements.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of subway engineering, and particularly relates to a method for simulating test of ground traffic load above prefabricated box culvert. BACKGROUND

[0002] In recent years, with the continuous improvement of underground traffic system in large and medium-sized cities and the increasing number of tunnels, the long-term stress and strain influence of tunnels in operation on ground subsidence, surrounding buildings and underground pipelines due to the effect of driving load cannot be ignored. In order to avoid the deformation and excessive stress of the tunnel below caused by long-term driving load on the ground, which endangers the safety of tunnel operation, the excavation of the upper crossing foundation is often carried out in a zoned and blocked manner, and is matched with soil piling or counterweight counterpressure. In order to simulate and analyze the influence of long-term driving load on the box culvert above on the existing tunnel in operation below, a plurality of model test devices are designed and developed to carry out model test analysis on this working condition, but for the case that long-term driving load leads to excessive deformation and stress of the tunnel below, and for the test direction of downward pressure load in different regions, the model test devices developed at present all have some defects such as being unable to load the rock-soil material in the device in a zoned manner and being unable to unload in stages. In addition, the devices must first place the tunnel and then apply the load to make the soil body consolidate, which is inconsistent with the actual construction sequence. The deformation and convergence monitoring of the square tunnel model is not perfect. SUMMARY

[0003] The present application aims at solving the problem that the existing test device and method cannot meet the actual working condition requirements, and proposes a method for simulating test of ground traffic load above prefabricated box culvert.

[0004] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0005] A method for simulating test of ground traffic load above prefabricated box culvert, comprising:

[0006] S1: placing the model box on the counterforce steel frame base, and then fixing the openable and closable steel plate on the front of the model box on the model box by bolts;

[0007] S2: placing the water injection pipe at the bottom of the model box, then laying the coarse sand to completely bury the water injection pipe, adding the water-permeable stone on the upper part of the coarse sand, adding the soil body to the predetermined height according to the test scheme of the model box, and then lowering the lifting device to the lowest position;

[0008] S3: calculating and adjusting the extension amount of the telescopic rod of the deformable pressure bearing device;

[0009] S4: vertical loading: accurately applying the pressure to the soil body in the model box by the counterforce frame, the cross-shaped slide rail, the small vertical jack and the deformable pressure bearing device, and reaching the expected level, and the soil body in the model box is compressed;

[0010] S5. Push the model sleeve into the model box from the round hole on the front steel plate of the model box, and manually remove the soil that flows into the tunnel interior, and close the steel plate on the model box after the square tunnel model is completely placed;

[0011] S6. Extend the monitoring device into the square tunnel model;

[0012] S7. Install the horizontal jack and perform axial loading through the horizontal jack;

[0013] S8. Inject water into the box through the water pipe at the bottom of the model box to the required water injection amount, and continue to adjust the loading of the above-mentioned jacks to the required level;

[0014] S9. After the model is subjected to pressure, internal forces and deformations are generated, and corresponding data are collected through the preset sensor, and the deformation, convergence deformation of the square tunnel model under the action of random external load, and the pressure of the surrounding soil on the square tunnel model are measured.

[0015] As a further description of the above technical solutions:

[0016] The method for calculating the extension amount of the telescopic rod of the deformable pressure-bearing device in S3 comprises:

[0017] s1: completely add the soil into the model box, and make it reach the predetermined compactness;

[0018] s2: measure the height H of the soil in the model box, the density p of the soil, the specific gravity d of the soil particles, the water content ω of the soil, and the relationship between the void ratio e and the vertical stress p of the soil under lateral confinement; s

[0019] s3: calculate the specific weight γ of each group of soil according to the formula γ = ρg, and draw the relationship curve between the void ratio e and the vertical stress p of each group of soil in the lateral compression test, and calculate the compression coefficient a of each group of soil according to the formula

[0020] s4: divide the soil at the horizontal plane where the axis of the square tunnel model is located into a grid, and pre-set the total stress σ j of the soil at each longitudinal and horizontal intersection, and the value of σ j is equal to that in the actual working condition;

[0021] s5: calculate the self-weight stress σ zj of the soil at the place, calculate the additional stress p j of the soil at the place, and finally calculate the settlement value s j of the soil at the place;

[0022] s6: based on the settlement value s j ​​The deformation value of the rotating steel plate above the soil; the pitch P of the telescopic rod around the deformable pressure bearing device is measured, and the number of rotations of the telescopic rod at the position is calculated according to the formula

[0023] s7: based on the number of rotations of each telescopic rod obtained in s6 Adjust all telescopic rods, and then test according to the test requirements.

[0024] As a further description of the above technical solution:

[0025] The model box is placed in the counterforce steel frame with the opening upward, the counterforce steel frame is composed of a base and frame rods fixed vertically at four corners of the base; the model box has a square tunnel model placed front to back, the square tunnel model is internally provided with a monitoring device; the bottom of the box body is provided with a water injection pipe; the front side of the box body is provided with a model slide rail, the model slide rail has a model sleeve in the front-to-back direction; the frame rod is provided with a lifting device that can move up and down, the lifting device is vertically provided with an integral loading device, a plurality of split loading devices are distributed in a rectangular array below the integral loading device, and the split loading devices are placed above the soil layer; the integral loading device is driven by the lifting device to move up and down to increase or decrease the load of the split loading devices, to simulate the partition loading and stage unloading of the soil layer, and the monitoring device monitors the pressure change of the square tunnel model in the soil layer.

[0026] As a further description of the above technical solution:

[0027] The front side of the model box is composed of organic glass plates on the left and right sides and a middle steel plate, the upper and lower ends of the middle steel plate are fixed on the model box, a circular hole is opened in the middle of the middle steel plate, and the square tunnel model is placed in the model box through the circular hole; the front side of the middle steel plate is hingedly connected with a door plate, and the four corners of the door plate are tightly attached to the model box by bolt fastening to close the circular hole.

[0028] As a further description of the above technical solution:

[0029] The square tunnel model is a cylinder composed of a plurality of arc-shaped tunnel segments, the upper and lower ends of the rear side of the box body are fixed with a horizontal steel plate, a vertical steel plate is fixed between the two horizontal steel plates, a horizontal jack 8 is fixed in the middle of the front side of the vertical steel plate, and the front end of the horizontal jack is fixed on the square tunnel model.

[0030] As a further description of the above technical solution:

[0031] The front side of the model box is provided with an L-shaped support, and a horizontal rod is arranged between the L-shaped support and the vertical steel plate, the horizontal rod is arranged in the square tunnel model and coaxial with the square tunnel model; a plurality of laser range finders are arranged on the horizontal rod and distributed in an array from front to back, and the L-shaped support, the horizontal rod and the laser range finders jointly form a monitoring device.

[0032] As a further description of the above technical solution:

[0033] The model sleeve is composed of a plurality of circumferentially distributed curved plates, adjacent curved plates are engaged through a rabbet joint, the length of the model sleeve is 1.1 times the length of the square tunnel model, and the internal diameter of the model sleeve is the same as the external diameter of the square tunnel model; the model slide rail is a steel frame shaped like an inverted fish vertebra, and the model sleeve is arranged in the model slide rail.

[0034] As a further description of the above technical solution:

[0035] The lifting device is composed of a hollow lifting sleeve sleeved on the frame rod and a horizontal beam slide rail connected with the hollow lifting sleeves; the position above the height of the model box on the frame rod is provided with a sawtooth, the upper end surface of each sawtooth is flush, and the lower end surface is an upwardly inclined inclined surface; a plurality of vertically equidistant bolt holes are formed in the frame rod with sawteeth; a rotating rod is hingedly connected to one side of the sawtooth inside the hollow lifting sleeve, a pressing rod is hingedly connected to the end of the rotating rod away from the sawtooth, the lower end of the pressing rod is arranged between the sawteeth, and a spring is connected between the upper end of the pressing rod and the rotating rod.

[0036] As a further description of the above technical solution:

[0037] The integral loading device comprises a cross-shaped slide rail, a large vertical jack and a loading plate; the cross-shaped slide rail is arranged on the lifting device, the cross-shaped slide rail is provided with a large vertical jack capable of moving forward, backward, left and right, and the large vertical jack is provided with a loading plate below; the loading plate is composed of two pad plates and a plurality of I-beams between the two pad plates; the cross-shaped slide rail is composed of a hollow circular table and two mutually perpendicular T-shaped rods inserted thereon, the two ends of the T-shaped rods are fixed with a C-shaped component, and the C-shaped component is fixed and connected on the corresponding side of the horizontal beam slide rail through bolts; the upper end of the large vertical jack is fixed below the hollow circular table.

[0038] As a further description of the above technical solution:

[0039] The split loading device comprises small vertical jacks, deformable pressure bearing devices and partition plates; a plurality of small vertical jacks are arranged in a rectangular array on the lower end surface of the loading plate, and each small vertical jack is provided below with a deformable pressure bearing device; each deformable pressure bearing device is provided with a square frame-shaped partition plate, the corresponding small vertical jack is wrapped in the square frame-shaped partition plate, and adjacent partition plates are connected through bolt fastening; the deformable pressure bearing device comprises an upper rectangular steel plate, a lower rectangular steel plate is arranged directly below the upper rectangular steel plate, in the vertical direction, the vertices of the lower rectangular steel plate are respectively arranged at the middle of the side length of the upper rectangular steel plate, and a triangular rotating steel plate is hinged to each of the four sides of the lower rectangular steel plate; when the rotating steel plate is rotated to a horizontal position, the lower rectangular steel plate and the four rotating steel plates together form a steel plate which is equal in size to the upper rectangular steel plate; a telescopic rod is connected to the upper end surface of each rotating steel plate through a ball hinge, the upper end of the telescopic rod is fixed to the upper rectangular steel plate, and the upper steel plate, the telescopic rod and the lower steel plate and the rotating steel plate together form the deformable pressure bearing device. The outer edge surface of the telescopic rod of the deformable pressure bearing device is in threaded cooperation with the inner edge surface of one end of the ball hinge.

[0040] In summary, due to the adoption of the above technical solutions, the present application has the following beneficial effects:

[0041] (1) The deformable pressure bearing device in the present application can be coupled with the upper jack to accurately exert a continuously changing pressure on the lower soil body, so that the continuous loading process of the lower soil body can be realized, and the stress state of the actual engineering site can be more truly reflected.

[0042] (2) The present application can express the stress constraint form which cannot be directly observed in the test process into the displacement constraint form which can be directly observed, so that the soil body in the model box can be more intuitively and conveniently constrained at the initial stage of load application.

[0043] (3) The deformable pressure bearing pad in the present application can be coupled with the upper small vertical jack to accurately exert a continuously changing pressure on the lower soil body, so that the continuous loading process of the lower soil body can be realized, and the stress state of the actual engineering site can be more truly reflected.

[0044] (4) The device of the present application not only can simulate the synchronous excavation or counter-pressure working condition of any region or multiple regions on the upper side of the square tunnel model, but also can adjust the loading and unloading of each region at will, and can first fill the soil in the box, then load and unload, and then horizontally push the square tunnel model into the soil, so that not only the initial stress field of the stratum can be accurately simulated, but also the confining pressure of the surrounding soil on the square tunnel model is closer to the actual situation. Compared with the prior art, the present application can more accurately simulate and analyze the influence of the additional action of the partitioned excavation or stacked counter-pressure of various forms of foundation pits on the upper side of the operating shield tunnel on the deformation and internal force of the existing operating tunnel, and has more functions. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 A schematic diagram of the three-dimensional structure of the present application;

[0046] Figure 2 A schematic diagram of the three-dimensional structure of the interior of the present application after removing the model box 3 and the partition plate 19;

[0047] Figure 3 A schematic diagram of the three-dimensional structure of the whole loading device and the split loading device;

[0048] Figure 4 A schematic diagram of the three-dimensional structure of the deformable pressure-bearing device 18;

[0049] Figure 5 A schematic diagram of the three-dimensional structure of the counterforce steel frame and the lifting device 11;

[0050] Figure 6 A schematic diagram of the internal section of the lifting device 11;

[0051] Figure 7 A schematic diagram of the three-dimensional structure of the model sliding rail 9. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0053] Please refer to Figures 1-7 The present application provides a method for simulating the traffic load on the ground above a prefabricated box culvert:

[0054] A method for simulating the traffic load on the ground above a prefabricated box culvert, comprising:

[0055] S1: Place the model box 3 on the counterforce steel frame base 1, then fix the openable and closable steel plate on the front of the model box 3 on the model box 3 through bolts;

[0056] S2: Place the water injection pipe 5 at the bottom of the model box 3, then lay the coarse sand to completely bury the water injection pipe 5, add the water-permeable stone on the upper part of the coarse sand, add the soil to the predetermined height according to the test scheme of the model box 3, and then lower the lifting device 11 to the lowest position;

[0057] S3: Calculate and adjust the extension amount of the telescopic rod 23 of the deformable pressure-bearing device 18;

[0058] S4: Vertical loading: Using the reaction frame, cross-shaped slide rail, small vertical jack 17, and deformable pressure bearing device 18, the soil inside the model box 3 is precisely pressured and reaches the expected level, and the soil inside the model box 3 is compressed.

[0059] S5. Push the model sleeve 10 on the model slide rail 9 and enter the model box 3 through the round hole in the front steel plate of the model box 3. Manually remove the soil that has flowed into the tunnel. After the square tunnel model 4 is completely placed in, close the steel plate on the model box 3 tightly.

[0060] S6. Insert the monitoring device into the square tunnel model 4;

[0061] S7. Install the horizontal jack 8 and apply axial load through the horizontal jack 8;

[0062] S8. Fill the model box with water through the water pipe at the bottom of the box to the required amount, and continue to adjust the jacks to the required level.

[0063] S9. After the model is compressed, internal forces and deformations are generated. The corresponding data are collected by preset sensors to measure the deformation, convergence deformation, and pressure of the surrounding soil on the square tunnel model 4 under random external loads.

[0064] The method for calculating the extension and retraction of the telescopic rod 23 of the deformable pressure-bearing device 18 in S3 includes:

[0065] s1: Completely add the soil into the model box 3 and compact it to the predetermined degree;

[0066] s2: Measure the soil height H, soil density ρ, and soil particle specific gravity d inside model box 3. s The relationship between soil water content ω, soil void ratio e and vertical compressive stress p under lateral confinement conditions;

[0067] s3: Calculate the unit weight γ of each soil group according to the formula γ=ρg, and plot the relationship curve between the void ratio e and the vertical compressive stress p of each soil group in the lateral confined compression test. The compressibility coefficient 'a' of each soil group was calculated.

[0068] s4: The soil on the horizontal plane where axis 4 of the square tunnel model is located during the experiment is divided into grids, and the total soil stress σ at each intersection of the longitudinal and transverse lines is calculated. j Pre-setting, σ j The value is equal to the value in actual working conditions;

[0069] S5 calculates the soil inside model box 3, specifically the self-weight stress σ of the soil at that location. zj Calculate the additional stress p of the soil at this location. j Finally, the soil settlement value s at that location was calculated.j ;

[0070] s6: each soil body settlement value s based on s5 j , the corresponding rotating steel plate 22 deformation value above the soil body; the pitch P of the telescopic rod 23 around the deformable bearing device 18 is measured, and the number of rotations of the telescopic rod 23 at the place is calculated according to the formula

[0071] s7: the number of rotations of each telescopic rod 23 based on s6 Adjust all telescopic rods 23, and then test according to the test requirements.

[0072] The model box 3 is placed in the counterforce steel frame with the opening upward, the counterforce steel frame is composed of the base 1 and the frame rods 2 vertically fixed at the four corners of the base 1 respectively; the model box 3 has a square tunnel model 4 placed front and back, the square tunnel model 4 is internally provided with a monitoring device; the bottom of the box body is provided with a water injection pipe 5; the front side of the box body is provided with a model slide rail 9, and the model slide rail 9 has a model sleeve 10 in the front and back direction; the frame rod 2 is provided with a lifting device 11 capable of moving up and down, and an integral loading device is vertically arranged on the lifting device 11, a plurality of split loading devices are arranged in a rectangular array below the integral loading device, and the split loading devices are arranged above the soil layer; the integral loading device is driven by the lifting device 11 to move up and down, the load of the split loading devices is increased or decreased, the soil layer is simulated to be loaded in sections and unloaded in stages, and the pressure change of the square tunnel model 4 in the soil layer is monitored by the monitoring device.

[0073] The front side of the model box 3 is composed of the organic glass plates 24 on the left and right sides and the middle steel plate 25, the upper and lower ends of the middle steel plate 25 are fixed on the model box 3, a round hole is formed in the middle of the middle steel plate 25, and the square tunnel model 4 is placed in the model box 3 through the round hole; a door plate 26 is hingedly connected to the front side of the middle steel plate 25, and the door plate 26 is tightly attached to the model box 3 through bolt fastening at the four corners of the door plate 26, so that the round hole is closed.

[0074] The square tunnel model 4 is a cylinder composed of a plurality of arc-shaped tunnel segments, the upper and lower ends of the rear side of the box body are fixed with a horizontal steel plate 6, a vertical steel plate 7 is fixed between the two horizontal steel plates 6, a horizontal jack 8 is fixed in the middle of the front side of the vertical steel plate 7, and the front end of the horizontal jack 8 is fixed on the square tunnel model 4.

[0075] The front side of the model box 3 is provided with an L-shaped bracket 27, there is a cross bar 28 between the L-shaped bracket 27 and the vertical steel plate 7, the cross bar 28 is coaxial with the square tunnel model 4 and is arranged in the square tunnel model 4, a plurality of laser range finders 29 are circumferentially and front and back arrayed on the cross bar 28, and the L-shaped bracket 27, the cross bar 28 and the laser range finders 29 jointly compose the monitoring device.

[0076] The model sleeve 10 is composed of a plurality of circumferentially distributed curved plates 30, which are engaged by rabbet joints between adjacent curved plates 30. The length of the model sleeve 10 is 1.1 times the length of the square tunnel model 4, and the internal diameter of the model sleeve 10 is the same as the external diameter of the square tunnel model 4. The model slide rail 9 is a steel frame shaped like an inverted fish vertebra. The model sleeve 10 is placed in the model slide rail 9.

[0077] The lifting device 11 is composed of hollow lifting sleeves 36 fitted on the frame rods 2 and horizontal cross beam slide rails 37 connecting the hollow lifting sleeves 36. The frame rods 2 are provided with sawteeth 38 above the height of the model boxes 3. The upper end faces of each sawtooth 38 are flush, and the lower end faces are upwardly inclined. The frame rods 2 with sawteeth 38 are provided with a plurality of vertically and equidistantly distributed bolt holes 39. A rotating rod 40 is hingedly connected to the inside of the hollow lifting sleeve 36 on the side of the sawteeth 38. A pressing rod 41 is hingedly connected to the end of the rotating rod 40 away from the sawteeth 38. The lower end of the pressing rod 41 is placed between the sawteeth 38, and the upper end of the pressing rod 41 is connected to the rotating rod 40 via a spring 42.

[0078] The overall loading device includes a cross-shaped slide rail, a large vertical jack 14, and a loading plate. The cross-shaped slide rail is provided on the lifting device 11. The cross-shaped slide rail is provided with a large vertical jack 14 that can move forward, backward, left, and right. The large vertical jack 14 is provided with a loading plate below. The loading plate is composed of two upper and lower pads 15 and a plurality of I-beams 16 between the two pads 15. The cross-shaped slide rail is composed of a hollow circular table 43 and two mutually perpendicular T-shaped rods 44 inserted into the hollow circular table 43. The two ends of the T-shaped rods 44 are fixed with a C-shaped member 45. The C-shaped member 45 is fixedly connected to the corresponding side of the horizontal cross beam slide rail 37 via a bolt. The upper end of the large vertical jack 14 is fixed below the hollow circular table 43.

[0079] The split loading device comprises small vertical jacks 17, deformable pressure bearing devices 18 and partition plates 19; a rectangular array of small vertical jacks 17 is arranged on the lower end face of the loading plate, and each small vertical jack 17 is below a deformable pressure bearing device 18; each deformable pressure bearing device 18 has a square box-shaped partition plate 19, which wraps the corresponding small vertical jack 17, and adjacent partition plates 19 are connected by bolt fastening; the deformable pressure bearing device 18 comprises an upper rectangular steel plate 20, and a lower rectangular steel plate 21 is arranged directly below the upper rectangular steel plate 20; in the vertical direction, the vertices of the lower rectangular steel plate 21 are respectively arranged at the middle of the side length of the upper rectangular steel plate 20, and a triangular rotating steel plate 22 is hinged on each of the four sides of the lower rectangular steel plate 21; when the rotating steel plate 22 is rotated to the horizontal position, the lower rectangular steel plate 21 and the four rotating steel plates 22 together form a steel plate equal in size to the upper rectangular steel plate 20; a telescopic rod 23 is connected to the upper end face of each rotating steel plate 22 through a ball hinge, and the upper end of the telescopic rod 23 is fixed to the upper rectangular steel plate 20; the upper steel plate, the telescopic rod 23 and the lower steel plate and the rotating steel plate 22 together form the deformable pressure bearing device 18. The outer edge surface of the telescopic rod 23 of the deformable pressure bearing device 18 is in threaded cooperation with the inner edge surface of one end of the ball hinge.

[0080] Working principle:

[0081] In the device, the lifting device 11 can freely ascend and descend along the sawtooth 38, thereby changing the height of the lifting device 11, and the bolt hole 39 can be used to fix the lifting device 11. The vertical partition plates 19 are arranged in a vertical and horizontal array and are connected by bolts, which are used to divide the soil in the box and can prevent the deformable pressure bearing device 18 from tilting. During the test, the monitoring device is inserted into the square tunnel model 4 to measure the compression and tensile deformation, i.e. the convergence deformation, of the square tunnel model 4. The miniature soil pressure sensor is installed at the bottom of the deformable pressure bearing device 18 to monitor the pressure on the deformable pressure bearing device 18.

[0082] The entire square tunnel model 4 is made of organic glass selected according to the similarity theory calculation and is spliced by custom-made pure aluminum welding wire bolts, which more accurately simulates the block splicing characteristics of the shield tunnel segment, thereby simulating the actual working condition to the greatest extent; during the test, the miniature soil pressure sensor is pasted on the outer arc surface of the square tunnel model 4 to measure the soil pressure acting on the square tunnel model 4. During the test, the strain gauge is pasted on the inner arc surface of the square tunnel model 4, which can monitor the deformation of the square tunnel model 4.

[0083] When the geotechnical material is added into the model box 3 and the load is applied, the model sleeve 10 can be inserted into the geotechnical body at the reserved circular hole position of the model box 3, and then the soil in the model sleeve 10 is removed and placed into the square tunnel model 4, and then the model sleeve 10 is taken out in pieces, which plays a role of assisting the square tunnel model 4 to be placed into the model box 3.

[0084] In use, first, the model box 3 is placed on the counterforce steel frame base 1, and then the openable and closable steel plate on the front of the model box 3 is fixed on the model box 3 by bolts.

[0085] The water injection pipe 5 is placed at the bottom of the model box 3, and then the coarse sand is laid flat to completely bury the water injection pipe 5, and the water-permeable stone is added on the upper part of the coarse sand, and the soil is added to the predetermined height according to the test scheme in the model box 3, and then the lifting device 11 is lowered to the lowest position.

[0086] The extension amount of the telescopic rod 23 of the deformable bearing device 18 is calculated and adjusted, including:

[0087] s1: the soil is completely added into the model box 3 and reaches the predetermined compaction degree;

[0088] s2: the height H of the soil in the model box 3 is measured, and for the vertically layered areas of the soil in the box, the height H of each layer of soil is measured i ; at this time, according to the type distribution of the soil in the model box 3, a plurality of groups of undisturbed soil in different areas are appropriately selected for soil density test, soil particle specific gravity test, soil moisture content test, and indoor side limit compression test; after the soil is taken, the same state soil is added to the original soil taking position; and the results of the soil tests in S1 are recorded: the soil density ρ, the soil particle specific gravity d s , the soil moisture content ω, and the relationship between the void ratio e and the vertical stress p of the soil under the side limit condition;

[0089] s3: the specific weight γ of each group of soil is calculated according to the formula γ = ρg, and the relationship curve between the void ratio e and the vertical stress p of each group of soil in the side limit compression test is drawn, and the compression coefficient a of each group of soil in S1 is calculated according to the formula ;

[0090] s4: the soil in the horizontal plane where the axis of the square tunnel model 4 is located is divided into a grid, and the total stress σ j of the soil at each longitudinal and horizontal line intersection is preset, and the value of σ j is equal to that in the actual working condition, and the specific values are as follows:

[0091] The automobile load is simplified as a static load by using the pseudo-static method: F = k1k2P0;

[0092] The dynamic stress of the subgrade surface

[0093] Calculation of the self-weight stress of soil in actual working conditions

[0094] Calculation of the total stress σ of soil j a +σ za ;

[0095] Wherein, k1 is the superposition coefficient, k2 is the dispersion coefficient, P0 is the static load of the wheel, A is the unit length area of the roadbed surface, γ a represents the specific weight of each layer of soil, H a represents the height of the soil corresponding thereto.

[0096] s5: calculation of the soil in the model box, calculation of the self-weight stress σ zj of the soil at this place, calculation of the additional stress p j of the soil at this place, and finally calculation of the soil settlement value s j at this place, which is as follows:

[0097] Self-weight stress σ of soil zj Calculation formula:

[0098] Additional stress p of soil j Calculation formula: p j = σ-σ z ;

[0099] Soil settlement value s j Calculation formula:

[0100] Wherein, γ i represents the specific weight of each layer of soil, H i represents the height of the soil corresponding thereto.

[0101] s6: based on the soil settlement value s j obtained by s5, the deformation value of the corresponding rotating steel plate 22 above the soil at this place is obtained; the pitch P of the telescopic rod 23 around the deformable pressure bearing device 18 is measured, and the number of rotations of the telescopic rod 23 at this place is calculated according to the formula

[0102] s7: based on the number of rotations of each telescopic rod 23 obtained in s6 Adjust all telescopic rods 23.

[0103] ​The vertical partition plate 19 is installed on the top of the soil in the model box 3, and the deformable pressure bearing device 18 is placed inside the vertical partition plate 19. The small vertical jack 17 is placed on the upper part of the deformable pressure bearing device 18, and then a pad 15 is placed above the jack. A plurality of I-beams 16 are placed on the pad 15, and then a pad 15 is placed above the I-beams 16 to form a loading plate. Then the hollow circular table 43 is assembled with the cross-shaped sliding rail, four specific buckles are buckled on the four sides of the lifting device 11, and the cross-shaped sliding rail is connected with the buckles through bolts at each end. The large vertical jack 14 is suspended below the hollow circular table 43, the height of the lifting device 11 is adjusted, the cross-shaped sliding rail is slid to adjust the large vertical jack 14 to the appropriate position, vertical loading is performed, then the deformation degree of the deformable pressure bearing device 18 is adjusted, and then the small vertical jack 17 is used for loading.

[0104] After the above steps are completed and the applied pressure reaches the expected level, the front bolts of the model box 3 are unscrewed to open the front window, and the circular steel plate outside the window is removed. The model sliding rail 9 is vertically placed on the front of the model box 3, and the center of the model sliding rail 9 is aligned with the center of the window of the model box 3. The outer surface of the model sleeve 10 is coated with activated carbon, and then the sleeve is completely wrapped with polyethylene film. Then the model sleeve 10 is divided into pieces and placed into the model sliding rail 9 from one end, and the model sleeve 10 is inserted into the soil until it abuts against the other side of the model box 3. The soil inside the model sleeve 10 is manually excavated, and then the assembled square tunnel model 4 is placed into the model sleeve 10. The model sleeve 10 is pulled out piece by piece, and then the front window of the model box 3 is tightly closed by bolts. The monitoring device is inserted through the small window obtained by removing the circular steel plate. The counterforce frame is connected with the back plate of the model box 3 through bolts on the back of the model box 3, the horizontal jack 8 is installed, and the horizontal jack 8 is used to load the axial force. Water is injected into the box through the water pipe at the bottom of the model box 3 to the required amount of water injection. Continue to adjust the loading of the above jacks to the required level.

[0105] In the present application, the expected stress constraint is converted into displacement constraint by calculating the extension and retraction amount of the telescopic rod 23 of the deformable pressure bearing device 18. With different displacement constraints applied by each deformable pressure bearing device 18 above the filled soil, the soil in the model box 3 is compressed, thereby generating pressure on the square tunnel model 4. After the model is pressed, internal forces and deformations are generated. By presetting the sensor to collect corresponding data, the deformation, convergence deformation, and pressure of the surrounding soil on the square tunnel model 4 under the action of random external load can be measured. The degree of deformation of the square tunnel model 4 is collected by the foil strain gauge attached to the inside of the square tunnel model 4 and the displacement sensor inserted into the inside of the square tunnel model 4.

[0106] The shield tunnel non-uniform force integrated loading model test device in the application can complete the following tests: under the action of the vertical jack loading, the square tunnel model 4 is subjected to three-dimensional loading pressure to generate deformation, and the deformation law of the tunnel under the action of the non-uniform load can be analyzed; the vertical jack is first loaded to the required level to make the tunnel have certain deformation, then the pressure of the jack is reduced to make the surrounding soil of the tunnel be unloaded, to simulate the foundation pit excavation in the actual engineering, and to study the stress and deformation influence of the foundation pit excavation on the underlying tunnel.

[0107] The above is only the preferred specific embodiment of the application, but the protection scope of the application is not limited to this. Those skilled in the art can make equivalent replacements or changes according to the technical solution and the inventive concept of the application within the technical range disclosed by the application, which should be covered in the protection scope of the application.

Claims

1. A method for simulating ground traffic loads above precast box culverts, characterized in that, S1: Place the model box (3) on the reaction steel frame base (1), and then fix the openable steel plate on the front of the model box (3) to the model box (3) with bolts; S2: Place the water injection pipe (5) at the bottom of the model box (3), then spread coarse sand to completely bury the water injection pipe (5), cover the coarse sand with permeable stones, add soil to the model box (3) to the predetermined height according to the test plan, and then lower the lifting device (11) to the lowest position. S3: Calculate and adjust the extension and retraction of the telescopic rod (23) of the deformable pressure-bearing device (18); S4: Vertical loading: Using the reaction frame, cross-shaped slide rail, small vertical jack (17), and deformable pressure bearing device (18), the soil in the model box (3) is precisely pressured and reaches the expected level, and the soil in the model box (3) is compressed. S5: Push the model sleeve (10) on the model slide rail (9) and enter the model box (3) through the round hole on the front steel plate of the model box (3). Manually remove the soil that has flowed into the tunnel. After the square tunnel model (4) is completely placed in, close the steel plate on the model box (3). S6: Insert the monitoring device into the square tunnel model (4); S7: Install the horizontal jack (8) and apply axial load through the horizontal jack (8); S8: Fill the tank with water through the water pipe at the bottom of the model box to the required amount, and continue to adjust the load of each jack to the required level; S9: After the model is compressed, internal forces and deformations are generated. The corresponding data are collected by preset sensors to measure the deformation, convergence deformation and pressure of the surrounding soil on the square tunnel model (4) under random external load.

2. The method for simulating ground traffic load above a precast box culvert according to claim 1, characterized in that, The calculation method for the extension and retraction of the telescopic rod (23) of the deformable pressure-bearing device (18) described in S3 includes: s1: Completely add the soil into the model box (3) and make it reach the predetermined compaction degree; s2: measure the relationship between the height H of the soil body, the density p of the soil, the specific gravity d of the soil particles, the water content ω of the soil, the void ratio e of the soil under lateral restraint, and the vertical compressive stress p in the model box (3) s ; s3: Calculate the unit weight γ of each soil group according to the formula γ=ρg, and plot the relationship curve between the void ratio e and the vertical compressive stress p of each soil group in the lateral confined compression test. The compressibility coefficient 'a' of each soil group was calculated. s4: the soil in the horizontal plane where the axis of the square tunnel model (4) is located is meshed, and the total stress σ j of the soil at each intersection of the longitudinal and lateral lines is calculated j The value is equal to the size in the actual working condition; s5: calculate the self-weight stress σ of the soil in the model box (3) zj , calculate the additional stress p of the soil j , and finally calculate the settlement value s of the soil j ; s6: Soil settlement value s at each location obtained based on s5 j That is, the deformation value of the rotating steel plate (22) corresponding to the soil above the location; measure the pitch P of the telescopic rods (23) around the deformable bearing device (18), and calculate the number of rotations of the telescopic rods (23) at that location according to the formula. s7: The number of rotations of each telescopic rod (23) obtained in s6 Adjust all telescopic rods (23) and then conduct the test according to the test requirements.

3. The method for simulating ground traffic load above a precast box culvert according to claim 1, characterized in that, The model box (3) is placed in the reaction steel frame with its opening facing upward. The reaction steel frame consists of a base (1) and support rods (2) that are vertically fixed at the four corners of the base (1). Inside the model box (3) is a square tunnel model (4) placed back to back. The square tunnel model (4) is equipped with a monitoring device. A water injection pipe (5) is provided at the bottom of the box. A model slide rail (9) is provided on the front side of the box. A model sleeve (10) along the front-back direction is provided on the model slide rail (9). A lifting device (11) that can move up and down is provided on the support rod (2). An overall loading device is vertically provided on the lifting device (11). Multiple split loading devices are distributed in a rectangular array below the overall loading device. The split loading devices are placed above the soil layer. The overall loading device is moved up and down by the lifting device (11) to increase or decrease the load on the multiple split loading devices, simulating the partitioned loading and phased unloading of the soil layer. The pressure change generated by the square tunnel model (4) in the soil layer is monitored by the monitoring device.

4. The method for simulating ground traffic load above a precast box culvert according to claim 3, characterized in that, The front side of the model box (3) consists of organic glass plates (24) on the left and right sides and a steel plate (25) in the middle. The upper and lower ends of the steel plate (25) are fixed to the model box (3). A round hole is opened in the middle of the steel plate (25), through which the square tunnel model (4) is placed inside the model box (3). A door panel (26) is hinged to the front side of the steel plate (25). The door panel (26) is fastened to the model box (3) by bolts at the four corners, thus closing the round hole.

5. The method for simulating ground traffic load above a precast box culvert according to claim 3, characterized in that, The square tunnel model (4) is a cylinder composed of multiple arc-shaped tunnel segments. A horizontal steel plate (6) is fixed at both the upper and lower ends of the rear side of the box. A vertical steel plate (7) is fixed between the two horizontal steel plates (6). A horizontal jack (8) is fixed in the middle of the front side of the vertical steel plate (7). The front end of the horizontal jack (8) is fixed on the square tunnel model (4).

6. The method for simulating ground traffic load above a precast box culvert according to claim 3, characterized in that, The model box (3) is provided with an L-shaped support (27) on the front side. There is a crossbar (28) between the L-shaped support (27) and the vertical steel plate (7). The crossbar (28) is placed inside the square tunnel model (4) and is coaxial with the square tunnel model (4). Multiple laser rangefinders (29) are evenly distributed around the crossbar (28) and arranged in a front and rear array. The L-shaped support (27), the crossbar (28), and the laser rangefinders (29) together form a monitoring device.

7. The method for simulating ground traffic load above a precast box culvert according to claim 3, characterized in that, The model sleeve (10) is composed of multiple circumferentially distributed curved plates (30), and adjacent curved plates (30) are interlocked by tongue and groove joints. The length of the model sleeve (10) is 1.1 times that of the square tunnel model (4), and the inner diameter of the model sleeve (10) is the same as the outer diameter of the square tunnel model (4). The model slide rail (9) is a steel frame shaped like an inverted fish belly bone, and the model sleeve (10) is placed inside the model slide rail (9).

8. The method for simulating ground traffic load above a precast box culvert according to claim 3, characterized in that, The lifting device (11) consists of a hollow lifting sleeve (36) mounted on the frame (2) and a horizontal beam slide rail (37) connecting each hollow lifting sleeve (36); the frame (2) is provided with serrations (38) above the height of the model box (3), the upper end face of each serration (38) is flush, and the lower end face is an upward inclined surface; the frame (2) with serrations (38) has multiple vertically equidistant bolt holes (39); inside the hollow lifting sleeve (36), a rotating rod (40) is hinged to one side of the serrations (38), and a pressure rod (41) is hinged to one end of the rotating rod (40) that is facing the serrations (38). The lower end of the pressure rod (41) is placed between the serrations (38), and a spring (42) is connected between the upper end of the pressure rod (41) and the rotating rod (40).

9. The method for simulating ground traffic load above a precast box culvert according to claim 3, characterized in that, The overall loading device includes a cross-shaped slide rail, a large vertical jack (14), and a loading plate. A cross-shaped slide rail is provided on the lifting device (11), and a large vertical jack (14) that can move forward, backward, left, and right is provided on the cross-shaped slide rail. There is a loading plate below the large vertical jack (14). The loading plate is composed of two upper and lower pads (15) and multiple I-beams (16) between the two pads (15). The cross-shaped slide rail is composed of a hollowed-out truncated cone (43) and two mutually perpendicular T-shaped rods (44) inserted on it. A C-shaped component (45) is fixed at both ends of the T-shaped rod (44). The C-shaped component (45) is bolted to the horizontal beam slide rail (37) on the corresponding side. The upper end of the large vertical jack (14) is fixed below the hollowed-out truncated cone (43).

10. A method for simulating ground traffic loads above a precast box culvert according to claim 9, characterized in that, The split loading device includes small vertical jacks (17), deformable pressure-bearing devices (18), and partition plates (19); multiple small vertical jacks (17) are arranged in a rectangular array on the lower end face of the loading plate, and each small vertical jack (17) has a deformable pressure-bearing device (18) below it; each deformable pressure-bearing device (18) has a square partition plate (19) on it, and the partition plate (19) encloses the corresponding small vertical jack (17), and adjacent partition plates (19) are fastened together by bolts; the deformable pressure-bearing device (18) includes an upper rectangular steel plate (20), and a lower rectangular steel plate (21) is located directly below the upper rectangular steel plate (20). In the vertical direction, the apex of the lower rectangular steel plate (21) is divided into The upper rectangular steel plate (20) is not placed in the middle of its side length. A triangular rotating steel plate (22) is hinged on each of the four sides of the lower rectangular steel plate (21). When the rotating steel plate (22) is rotated to the horizontal position, the lower rectangular steel plate (21) and the four rotating steel plates (22) together form a steel plate of the same size as the upper rectangular steel plate (20). A telescopic rod (23) is connected to the upper end of each rotating steel plate (22) through a ball hinge. The upper end of the telescopic rod (23) is fixed on the upper rectangular steel plate (20). The upper steel plate, the telescopic rod (23), the lower steel plate, and the rotating steel plate (22) together form a deformable pressure-bearing device (18). The outer edge of the telescopic rod (23) of the deformable pressure-bearing device (18) and the inner edge of one end of the ball hinge are threaded together.

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