A test device and a test method for simulating differential settlement

Abstract

The application discloses a test device and a test method for simulating differential settlement, which comprises a mounting frame, a soil body filling chamber, a pre-settlement control assembly, a weighing sensor and a vertical load applying assembly; the soil body filling chamber comprises a soil body rigid support assembly and two side plates; the soil body rigid support assembly comprises long rigid blocks and short rigid blocks staggered along the length direction of the base; each pre-settlement control assembly comprises a needle cylinder, a piston, a piston rod and a piston drive assembly; the piston drive assembly can drive the piston to ascend and descend and control the ascending and descending speed of the piston; the vertical load applying assembly can apply a vertical load to the soil body to be settled in the soil body filling chamber. The application can not only control the ascending and descending displacement to be suitable for studying the mechanical and deformation properties of roadbeds and garbage landfills and other projects in the filling process, but also simulate the influence of stress and deformation on the inside of the roadbeds and garbage landfills under the action of cyclic dynamic load such as traffic vibration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical test, in particular to a test device and test method for simulating differential settlement. BACKGROUND

[0002] With the rapid development of economy and urbanization in China, the demand for transportation resources is increasing, and the production of municipal solid waste is increasing rapidly. Infrastructure needs to be built under complex conditions, such as pile-supported embankment. The modulus of pile is much larger than that of soil between piles, so the settlement of pile is much smaller than that of soil between piles. Stress redistribution and uneven settlement occur in the embankment.

[0003] 1. In order to meet the increasing demand for landfill of municipal solid waste, the construction scale and expansion project of landfill are increasing. During the construction process, the landfill has complex composition, high compressibility, uneven spatial distribution, and local corrosion of solid waste. The underlying soil of the landfill liner system is prone to local uneven settlement or local subsidence.

[0004] 2. In order to meet the increasing demand for highway transportation, highway reconstruction and expansion projects are gradually increasing. The deformation of the combination parts such as new and old roadbed and bridge transition section is not coordinated, which leads to uneven settlement, misplacement and large-scale sliding of the retaining wall of the roadbed.

[0005] In these projects, not only the self-weight or filling load needs to be considered, but also the effect of complex load, such as the long-term traffic dynamic load of heavy trucks and other vehicles on the internal structure of the structure cannot be ignored.

[0006] The above-mentioned pile-supported embankment, landfill liner system, new and old roadbed splicing and bridge transition section and other projects all have the problem of uneven stress and deformation. In addition, it is necessary to consider the effect of complex load on the surface after the construction filling process and after the construction is completed. Therefore, it is necessary to study the stress and deformation mechanism of such problems. SUMMARY

[0007] The technical problem to be solved by the present application is to solve the above-mentioned problems of the prior art. The test device and test method for simulating differential settlement can not only control the lifting displacement to study the mechanical and deformation properties of roadbed and landfill engineering during the filling process, but also simulate the effect of traffic vibration and other cyclic dynamic load on the internal stress and deformation of the roadbed and landfill.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is:

[0009] A test device for simulating differential settlement, comprising a mounting frame, a soil filling chamber, a pre-settlement control assembly, a weighing sensor and a vertical load applying assembly.

[0010] The mounting frame comprises a base, a crossbeam and two side columns; the crossbeam is located directly above the base, and the two side columns are used to connect the base and the crossbeam.

[0011] The soil filling chamber is arranged in the middle of the two side columns and comprises a soil rigid support assembly and two side plates.

[0012] The soil rigid support assembly comprises m long rigid blocks and n short rigid blocks staggered along the length direction of the base.

[0013] The cross section of each long rigid block and each short rigid block is rectangular, and all the side walls are smooth walls; the height of the long rigid block is greater than that of the short rigid block, and the width of the long rigid block is equal to that of the short rigid block.

[0014] The two side plates are sealingly attached to the two sides of the soil rigid support assembly and connected to the two side columns.

[0015] The soil to be settled is filled between the two side plates directly above the soil rigid support assembly.

[0016] The number of the pre-settlement control assembly is m+n, and it is located directly below the m long rigid blocks and the n short rigid blocks.

[0017] Each pre-settlement control assembly comprises a syringe, a piston, a piston rod and a piston driving assembly.

[0018] The syringe is vertically arranged on the base, and the piston can slide up and down in the syringe; the bottom end of the piston rod is connected to the piston, and the top end of the piston rod is detachably connected to the bottom end of the long rigid block or the short rigid block directly above through one of the weighing sensors.

[0019] The piston driving assembly can drive the piston to rise and fall and control the rising and falling speed of the piston.

[0020] The vertical load applying assembly can apply a vertical load to the soil to be settled in the soil filling chamber.

[0021] A scale is arranged on the syringe in the height direction, and the scale accuracy can reach 0.01 mm; by observing the scale value when the piston stops in the syringe, the settlement value of the soil directly above the piston can be directly obtained.

[0022] It further comprises a settlement observation camera, at least one side plate of the soil filling chamber is a transparent plate, and the settlement observation camera is arranged outside the transparent plate.

[0023] The data acquisition instrument is connected with the weighing sensor, and the computer is connected with the data acquisition instrument, the pre-settling control assembly and the vertical load applying assembly.

[0024] Each piston driving assembly comprises an air pipe, an external air source, an on-off valve and a flow regulating valve; the air pipe is arranged at the bottom of the needle cylinder, and the tail end is connected with the external air source; the on-off valve and the flow regulating valve are arranged on the air pipe from top to bottom.

[0025] Each piston bottom is provided with a rubber pad.

[0026] A test method for simulating differential settlement, comprising the following steps.

[0027] Step 1, selecting a settlement similar soil: selecting an aluminum rod to simulate real soil particles, mixing aluminum rods of different sizes according to a set ratio to form a settlement similar soil with an average particle size of ; wherein the average particle size is determined according to the internal friction angle of the real soil body.

[0028] Step 2, pile arrangement: according to the real pile spacing in the settlement condition to be simulated, the number m of long rigid blocks, the number n of short rigid blocks and the arrangement position are determined, the spacing between two adjacent long rigid blocks is equal to the real pile spacing; the height difference between the long rigid block and the short rigid block needs to be greater than the settlement value of the real soil body to be simulated, but less than the filling height H of the settlement similar soil.

[0029] Step 3, pile driving: inflating the bottom of each long rigid block and each short rigid block to make them rise to a set height and stop inflating; at this time, the bottoms of all long rigid blocks and all short rigid blocks are at the same height.

[0030] Step 4, filling the settlement similar soil: filling the settlement similar soil selected in step 1 on the top of all long rigid blocks and all short rigid blocks completed in step 3 until the set filling height H is reached; at this time, the initial weights of the settlement similar soil on the top of the m long rigid blocks and the initial weights of the settlement similar soil on the top of the n short rigid blocks are recorded; wherein the initial weights of the settlement similar soil on the top of the m long rigid blocks are respectively recorded as: W 11 , W 12 , W 13 , …, W 1i , …, W 1m ; the initial weights of the settlement similar soil on the top of the n short rigid blocks are respectively recorded as: W 21 , W 22 , W 23 , …, W 2j , …, W 2n ; 1≤i≤m, 1≤j≤n.

[0031] Step 5, pre-settlement: uniformly release air at the bottom of each long rigid block and each short rigid block, and stop releasing air after the pre-settlement to a set height; the pre-settlement is used to simulate the settlement of the real soil under the action of gravity;

[0032] Step 6, settlement: apply a vertical load on the top of the settlement similar soil, and the settlement similar soil is settled.

[0033] Step 7, settlement observation: during the pre-settlement of step 5 and the settlement of step 6, the settlement amount is observed in real time; when the settlement similar soil settles by a set value a, the real-time weight of the m long rigid blocks on the top of the settlement similar soil and the real-time weight of the n short rigid blocks on the top of the settlement similar soil are recorded once; wherein the real-time weight of the m long rigid blocks on the top of the settlement similar soil is recorded as: W 11 ′, W 12 ′, W 13 ′, …, W 1i ′, …, W 1m ′; the initial weight of the n short rigid blocks on the top of the settlement similar soil is recorded as: W 21 ′, W 22 ′, W 23 ′, …, W 2j ′, …, W 2n ′.

[0034] Step 8, calculate load transfer efficiency: in step 7, when the settlement similar soil settles by a set value a, the load transfer efficiency E of each long rigid block is calculated once; wherein the calculation formula of the load transfer efficiency E corresponding to the i-th long rigid block is:

[0035]

[0036] Wherein:

[0037] F 1i = W 1i ′- W 1i

[0038]

[0039] F 2j = W 2j ′- W 2j

[0040] In the formula, F 1i is the pile top load borne by the i-th long rigid block; F 2j is the inter-pile load borne by the j-th short rigid block; F 总 is the total load of the real soil in the simulated settlement working condition.

[0041] In step 1, the average particle size The relationship between the real soil internal friction angle is:

[0042]

[0043] In the formula, A, B and C are fitting coefficients, which are obtained by fitting the direct shear test data.

[0044] In step 5, by controlling the air release rate and air release amount at the bottom of each short rigid block, the settlement at different positions in the real settlement working condition can be simulated, and differential settlement can be realized. The real settlement working condition includes the settlement working condition of a waste landfill site, the settlement working condition of a new and old roadbed joint part and the settlement working condition of a pile-supported embankment.

[0045] In step 7, the observation mode of the settlement amount includes scale observation and image observation. The scale observation can directly read out the settlement displacement of the settlement similar soil at the current time. The image observation indirectly observes the settlement distribution of the settlement similar soil by real-time shooting of the settlement image of the settlement similar soil.

[0046] The present application has the following beneficial effects:

[0047] 1. The pre-settlement control assembly of the present application adopts a needle tube type design, which can adjust different initial positions to produce differential pre-settlement at different settlement rates.

[0048] 2. In the present application, long rigid blocks are used to simulate pile bodies, and by changing the positions of the long and short rigid blocks, the simulation of the soil body to be settled at different pile spacings can be realized. The present application can conduct test research on pile-supported embankments by replacing the long and short alternating rigid blocks. When the same size rigid blocks are uniformly replaced, the test research on uneven settlement problems such as the transition section of the waste landfill site liner system and the new and old roadbed can be conducted.

[0049] 3. The present application uses aluminum rods to simulate real soil, which has the characteristics of controllable test and no compression deformation. Geotechnical engineering is a kind of granular material, and the interaction between particles determines the mechanical properties. The settlement similar soil formed by the aluminum rods simulates the contact characteristics between real soil particles, has the characteristics of strong operability, convenient displacement field monitoring and low cost. In addition, the average particle size of the settlement similar soil is determined according to the real soil internal friction angle, so it has high similarity with the real soil.

[0050] 4. The setting of the transparent plate and the settlement observation camera in the soil filling chamber can indirectly observe the settlement distribution of the settlement similar soil.

[0051] 5. The present application can quantitatively calculate the load transfer efficiency, so that the internal stress transfer of the filler can be clearly obtained.

[0052] 6. The rigid block is evenly smeared with vaseline on both sides, which can reduce the friction of the contact part of the rigid block and improve the measurement accuracy of the test results.

[0053] 7. The vertical load applying assembly can realize monotonic loading, step loading, loading and unloading, cyclic loading and other functions, thereby meeting the needs of different working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 The structure schematic diagram of the test device for simulating differential settlement is shown.

[0055] Figure 2 The structure schematic diagram of the mounting frame in the application is shown.

[0056] Figure 3 The enlarged structure diagram of the pre-settlement control assembly in the application is shown.

[0057] Figure 4 The enlarged diagram of the mounting structure of the load cell in the application is shown.

[0058] Figure 5 The settlement image schematic diagram of the similar soil in the application is shown.

[0059] Figure 6 The relationship curve diagram of the pile top load and the inter-pile load and the relative displacement in the application is shown.

[0060] Figure 7 The relationship curve of the external air source pressure and the force in the application is shown.

[0061] Among them:

[0062] 10, mounting frame; 11, cross beam; 12, stand; 13, base;

[0063] 21, transparent plate;

[0064] 30, soil body rigid support assembly; 31, long rigid block; 32, short rigid block;

[0065] 40, pre-settlement control assembly;

[0066] 41, syringe; 411, scale; 412, tripod;

[0067] 42, piston; 421, slide rail; 422, rubber pad;

[0068] 43, piston rod; 431, funnel-shaped connecting seat; 432, piston connecting nut;

[0069] 44, piston driving assembly; 441, air pipe; 442, on-off valve; 443, flow regulating valve;

[0070] 45, fixed angle iron;

[0071] 50, weighing sensor;

[0072] 60, vertical load applying assembly; 61, loading plate; 62, loading electric cylinder; 63, rigid connecting seat;

[0073] 70, settlement observation camera;

[0074] 80, data acquisition instrument;

[0075] 90, computer. DETAILED DESCRIPTION

[0076] The application will be described in further detail below in conjunction with the accompanying drawings and specific preferred embodiments.

[0077] In the description of the application, it should be understood that the terms "left side", "right side", "upper part", "lower part" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and "first", "second" and the like do not represent the importance of the parts, and therefore cannot be understood as a limitation on the application. The specific dimensions used in the embodiments are only for the purpose of illustrating the technical solutions and do not limit the protection scope of the application.

[0078] As shown in Figure 1 , a test device for simulating differential settlement, comprising a mounting frame 10, a soil filling chamber, a pre-settlement control assembly 40, a weighing sensor 50, a vertical load applying assembly 60, a settlement observation camera 70, a data acquisition instrument 80 and a computer 90.

[0079] As shown in Figure 2 , the mounting frame comprises a crossbeam 11, two side columns 12 and a base 13.

[0080] The crossbeam is located directly above the base, and the two side columns are used to connect the base and the crossbeam.

[0081] The soil filling chamber is arranged in the middle of the two side columns and comprises a soil rigid support assembly 30 and two side plates. At least one of the side plates is a transparent plate 21, and in the present application, both side plates are preferably organic glass plates, and a settlement observation camera is arranged outside one of the organic glass plates.

[0082] The soil rigid support assembly comprises m long rigid blocks 31 and n short rigid blocks 32 arranged alternately along the length direction of the base.

[0083] The cross section of each long rigid block and each short rigid block is rectangular, and all the side walls are smooth walls; the height of the long rigid block is greater than the height of the short rigid block, and the width of the long rigid block is equal to the width of the short rigid block.

[0084] In this embodiment, the height of the long rigid block is preferably 10 cm, and the height of the short rigid block is preferably 5 cm; the cross section of each long rigid block and each short rigid block is preferably a square with a side length of 5 cm.

[0085] The two side plates are sealingly attached on both sides of the soil rigid support assembly and are connected with the two side columns.

[0086] The soil to be settled is filled between the two side plates directly above the soil rigid support assembly.

[0087] The number of pre-settlement control assemblies is m+n, which are located directly below the m long rigid blocks and n short rigid blocks, and correspond to the m long rigid blocks and n short rigid blocks one by one.

[0088] As shown in Figure 3 each pre-settlement control assembly includes a syringe 41, a piston 42, a piston rod 43, a piston drive assembly 44 and a fixed angle iron 45.

[0089] The syringe is vertically arranged, and the bottom end is preferably placed on the base through a tripod 412, and the top end is preferably on the fixed angle iron 45; the fixed angle iron 45 is preferably horizontally arranged, and the two ends are respectively connected with the two side columns, and the height position is fixed, and a through hole is arranged in the center of the fixed angle iron.

[0090] The syringe is provided with a scale 411 in the height direction, and the scale accuracy can reach 0.01 mm; by observing the scale value when the piston stops on the syringe, the settlement value of the soil directly above the piston can be obtained.

[0091] A vertical slide rail 421 is preferably arranged in the syringe.

[0092] The piston can vertically slide up and down along the slide rail in the syringe, and a rubber pad 422 is preferably arranged at the bottom of the piston to prevent the piston from sliding too fast.

[0093] The bottom end of the piston rod is preferably detachably connected with the piston through a funnel-shaped connecting seat 431 and a piston connecting nut 432, and the top end of the piston rod penetrates the through hole in the fixed angle iron and is detachably connected with the bottom end of the long rigid block or the short rigid block.

[0094] A weighing sensor 50 is installed on each piston rod above the fixed angle iron, as shown in Figure 4As shown, the weighing sensor is preferably a S-shaped tension and pressure sensor made of alloy steel, with a range of 0-20kg and a sensitivity of 2.0mV / V, and the tension and pressure borne by the upper and lower screw holes are measured.

[0095] The piston driving assembly can drive the piston to ascend and descend and control the ascending and descending speed of the piston.

[0096] Each piston driving assembly comprises an air pipe 441, an external air source, an on-off valve 442 and a flow regulating valve 443; the top end of the air pipe is arranged at the bottom of the needle cylinder, and the tail end is connected with the external air source; the on-off valve and the flow regulating valve are arranged on the air pipe from top to bottom.

[0097] The on-off valve is preferably a one-word valve, which is opened when the one word of the on-off valve is parallel to the air pipe, and is closed when the one word of the on-off valve is perpendicular to the air pipe.

[0098] The flow regulating valve is a valve capable of regulating the air inflow and outflow and speed, thereby regulating the descending speed of the piston and realizing differential settlement at different positions.

[0099] The vertical load applying assembly can apply a vertical load to the soil to be settled in the soil filling chamber. The vertical load applying assembly preferably comprises a loading plate 61, a loading electric cylinder 62 and a rigid connecting seat 63.

[0100] The loading plate 61 is located directly above the soil rigid support assembly, and the top is connected with the loading electric cylinder 62, and the top of the loading electric cylinder 62 is connected with the cross beam through the rigid connecting seat 63.

[0101] The stroke of the loading electric cylinder is preferably 50cm, the loading load is 100kg, and the loading frequency is 0-10Hz, which can realize loading modes such as monotonic loading, cyclic loading and unloading, constant frequency cyclic loading and variable frequency cyclic loading; the loading electric cylinder is provided with a built-in pressure sensor, and the range is 0-100kg.

[0102] The data acquisition instrument is connected with the weighing sensor, and the computer is connected with the data acquisition instrument, the pre-settlement control assembly and the vertical load applying assembly respectively.

[0103] A test method for simulating differential settlement, comprising the following steps.

[0104] Step 1, selecting a settlement similar soil, preferably comprising the following steps.

[0105] Step 1-1, real soil sampling

[0106] The real settlement working condition in the application preferably includes a landfill settlement working condition, a new and old roadbed joint part settlement working condition and a pile-supported embankment settlement working condition.

[0107] The invention needs to obtain real soil samples according to different settlement conditions.

[0108] A, landfill settlement conditions

[0109] The soil sample is obtained by drilling into the soil layer by a drilling machine, and generally one undisturbed soil sample is taken every 0.5-1 m. When sampling, attention should be paid to: for small area and flat terrain landfill sites, adopt quincunx point method for sampling, 5-10 points per block; for medium-sized landfill sites but uneven soil samples, adopt chessboard point method for sampling, 10-15 points per block; for large-scale landfill sites, adopt snake point method, 15-20 points per block.

[0110] B, subgrade

[0111] The settlement conditions of the new and old subgrade joint part and the pile-supported embankment settlement condition all belong to the subgrade category, and the deep soil sample is obtained by drilling into the soil layer by drilling every 50-100 m 2 There should be a test point. The ring cutter method is used to measure the surface soil parameters. When sampling, the surface soil is removed at the sampling site, and when a certain depth is reached, the ring cutter edge is placed vertically on the soil sample, the ring cutter handle is covered on the ring cutter back; hammer the ring cutter handle to make the ring cutter cut into the soil sample vertically and uniformly, stop hammering when the soil sample rises out of the ring cutter; use an iron shovel to shovel into the side of the ring cutter and take out the ring cutter.

[0112] Step 1-2, test the internal friction angle of real soil The real soil sampled in step 1-1 is subjected to indoor direct shear test and triaxial test to obtain the internal friction angle of the real soil

[0113] Step 1-3, determine the settlement similar soil type

[0114] When selecting the soil of the actual project, if the filler is used as the actual soil sample, the compaction degree of the actual soil is difficult to control and deformation is easy to occur, and the test result is difficult to believe; in order to overcome the problems in the test, the aluminum rod is used to simulate the real soil, which has the characteristics of controllable test and no compression deformation. Rock and soil is a kind of granular material, the interaction between particles determines the mechanical properties, the aluminum rod similar soil simulates the contact characteristics between real soil particles, has the characteristics of strong operability, convenient displacement field monitoring and low cost.

[0115] The aluminum rod settlement similar soil assembly is composed of aluminum rods and intermediate gaps, and the force is transmitted through the contact points between the aluminum rods one by one. The aluminum rod is a rigid material, and its own deformation is not considered, so the deformation of the aluminum rod similar soil is only caused by the displacement deformation of the aluminum rod, and the internal deformation is also caused by the displacement.

[0116] The present application selects aluminum rods to simulate real soil particles, and the use of aluminum rods to simulate similar soil can further convert the test into a two-dimensional condition, eliminate the friction force of the front and back side plates, and greatly improve the accuracy and repeatability of the test. In addition, the similarity difference between the model test and the prototype test is reduced in the 1g test with self-loading.

[0117] Step 1-4, determine the average particle size of the settlement similar soil

[0118] In order to reflect the aluminum rod specifications and the ratio according to the actual soil strength parameters, it is necessary to study the relationship between the average coordination number of the aluminum rod and the total contact number in the system.

[0119]

[0120] Where Z is the average coordination number; N c The total number of particle contacts is N, and the total number of particles is N. It can be seen that the smaller the coordination number, the fewer the contacts between the particles, and the more loose the structure, which is more prone to deformation and even instability. The larger the coordination number, the more the contacts between the particles, and the more compact the structure, which is more stable and less prone to deformation. The direct shear test is used to test aluminum rods of different specifications and weight ratios, and the average particle size and the relationship between the internal friction angle of the real soil body is:

[0121]

[0122] In the formula, A, B and C are fitting coefficients, which are obtained by fitting the direct shear test data.

[0123] Step 1-5, determine the specifications and ratio of the aluminum rods

[0124] According to the average particle size determined in step 1-4 determine the ratio of aluminum rods of different sizes.

[0125] In this embodiment, three different diameter aluminum rods are used, which are 1.6mm, 2mm and 3mm, to improve the average contact coefficient, and the weight ratio is 3:3:2, which are uniformly mixed.

[0126] Step 2, pile arrangement: according to the real pile spacing in the simulated settlement working condition, determine the number m of long rigid blocks, the number n of short rigid blocks and the arrangement position, the spacing between two adjacent long rigid blocks is equal to the real pile spacing; the height difference between the long rigid block and the short rigid block needs to be greater than the settlement value of the real soil body to be simulated, but less than the filling height H of the settlement similar soil.

[0127] According to the determined pile spacing of the indoor test, the number of long rigid blocks and short rigid blocks is adjusted, and the filling height of the upper aluminum bar similar soil is adjusted. The height difference between the long and short rigid blocks is greater than the settlement value to be adjusted, so as to meet the test requirements. The following table is the test scheme table.

[0128] Test No. Long rigid block Short rigid block Pile spacing L Fill height H 1 2 2 10 cm 5 cm / 10 cm / 20 cm 2 2 3 15 cm 7.5 cm / 15 cm / 30 cm 3 2 4 20 cm 10 cm / 20 cm / 40 cm

[0129] The two sides of each rigid block are evenly smeared with a layer of vaseline. The vaseline is smeared to reduce the friction on the two sides of the rigid block to ensure that the rigid block can slide without friction.

[0130] Step 3, pile

[0131] Open the on-off valve and the flow regulating valve, inflate the bottom of each long rigid block and each short rigid block, and make them all rise to the set height, then close the on-off valve to stop inflation. At this time, the bottoms of all long rigid blocks and all short rigid blocks are at the same height.

[0132] In this embodiment, the relationship between the external air source pressure and the force (supporting force) is as shown in Figure 7

[0133] Step 4, filling of settlement similar soil

[0134] The settlement similar soil selected in step 1 is preferably filled in layers on the top of all long rigid blocks and all short rigid blocks completed in step 3 until the set filling height H is reached.

[0135] During the filling process, in order to facilitate the observation of the displacement of the filling material during the test, a layer of gypsum powder is evenly scattered between each layer. When each layer is laid to the predetermined layer height, the filling material is leveled and repeatedly compacted. The above process is repeated until the predetermined filling height is reached.

[0136] After filling is completed, the initial weights of the settlement similar soil on the top of the m long rigid blocks and the initial weights of the settlement similar soil on the top of the n short rigid blocks are recorded. The initial weights of the settlement similar soil on the top of the m long rigid blocks are respectively recorded as:

[0137] W 11 i 12 i 13 i 1i i 1m ; the initial weights of the settlement similar soil on the top of the n short rigid blocks are respectively recorded as: W 21 j 22 j 23 j 2j j 2n ; 1≤i≤m, 1≤j≤n.

[0138] ​Step 5, pre-settlement: uniformly release air at the bottom of each long rigid block and each short rigid block, and stop releasing air after the pre-settlement to a set height; the pre-settlement is used to simulate the settlement of the real soil under the action of gravity.

[0139] The present application can simulate the settlement at different positions in the real settlement working condition by controlling the air release rate and air release amount at the bottom of each short rigid block, and can realize differential settlement.

[0140] In actual engineering, the compression deformation curve of the soil is close to linear, and then slowly tends to be stable, and the settlement rate is uniform, so the pre-settlement in the model test is carried out at a constant rate, which can simulate the settlement of the soil in the landfill, the joint part of the new and old roadbed, and the pile-supported embankment under the action of gravity. The air inlet amount and rate of the different short rigid blocks through the flow regulating valve are used to simulate the settlement at different positions in the real engineering, so as to realize differential settlement.

[0141] In actual engineering, the deformation of the soil under the action of gravity is generally not more than 30 cm, and taking the model similarity ratio of 1:10 as an example, 3 cm is selected as the test stop mark in the test. When the settlement value is reached, the flow regulating valve and the on-off valve are closed, and the long rigid block and the short rigid block are fixed at this time.

[0142] Step 6, settlement: a vertical load is applied at the top of the settlement similar soil, and the settlement similar soil is settled.

[0143] The applied vertical load can be divided into several working conditions: ① constant static load: simulating the filling grade of the actual engineering; ② equal frequency vibration load: simulating the vibration of the road roller in the actual engineering; ③ variable frequency vibration load: simulating different vehicle loads in the actual engineering. At this time, valve A and valve B are both in the closed state. At this time, the weighing sensor reading does not need to be recorded.

[0144] In this embodiment, after the predetermined downward movement amount is reached, the loading system is started, the electric cylinder is extended, the loading plate just contacts the surface of the test filling, and the vertical pressure is cleared. Start loading, apply a load of 6kPa to the surface of the filling through the loading plate, keep for 1min to ensure that the load and deformation are stable, and then unload. After unloading, still need to wait for 1min to ensure stability, and then apply loads of 8kPa and 10kPa according to the same steps.

[0145] Step 7, settlement observation: during the pre-settlement of step 5 and the settlement of step 6, the settlement amount is observed in real time; when the settlement similar soil settles by a set value a (preferably 0.2mm), the real-time weight of the m long rigid block top settlement similar soil and the real-time weight of the n short rigid block top settlement similar soil are recorded once; wherein the real-time weight of the m long rigid block top settlement similar soil is recorded as: W 11 ′, W 12 ′, W13 ', …, W 1i ', …, W 1m '; the initial weights of the n short rigid blocks are respectively recorded as: W 21 ', W 22 ', W 23 ', …, W 2j ', …, W 2n '.

[0146] The observation mode of the settlement amount includes scale observation and image observation; the scale observation can directly read the settlement displacement of the settlement similar soil at the current time; the image observation can obtain the color scale of different settlement ranges by real-time shooting the settlement image of the settlement similar soil through the settlement observation camera, and the color of different colors represents different settlement values, so that the settlement distribution of the aluminum rod similar soil can be indirectly observed, and then the displacement deformation distribution of the soil sample can be collected, so that the mechanical behavior of the accumulation body can be quantitatively analyzed. Figure 5

[0147] In the application, the relationship curve between the collected relative displacement (i.e. settlement amount) and the pile top load and the inter-pile load is as shown in Figure 6 .

[0148] Through Figure 5 and Figure 6 , it can be seen that the test method can more accurately simulate the load transfer and deformation process of the pile-supported embankment, with the increase of the relative displacement, the soil load between the piles is gradually transferred to the top of the pile, and the local displacement field is monitored, it can be seen that the top of the pile and the soil between the piles form an "arch effect", with the gradual increase of the relative displacement, the internal deformation of the embankment gradually tends to be stable, and finally a stable "arch" structure is formed.

[0149] Step 8, calculating the load transfer efficiency: in step 7, the load transfer efficiency E of each long rigid block is calculated once when the settlement similar soil is settled by a set value a; wherein the calculation formula of the load transfer efficiency E corresponding to the i-th long rigid block is:

[0150]

[0151] Wherein:

[0152] F 1i =W 1i '-W 1i

[0153]

[0154] F 2j =W 2j '-W 2j ​

[0155] F = Fp+ Fi+ Fj 1i Fp= pile top load of the i th long rigid block; F 2j Fj= inter-pile load of the j th short rigid block; F 总 F = total load of the real soil in the settlement condition to be simulated.

[0156] The load transfer efficiency described above can represent the stress transfer in the filler. It can be seen that, as the differential settlement increases, the pile top load gradually increases, and the inter-pile load gradually decreases, indicating that the load transfer in the filler occurs.

[0157] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above-described embodiments. Within the technical concept of the present application, various equivalent transformations can be made to the technical solutions of the present application, and these equivalent transformations all belong to the protection scope of the present application.

Claims

1. A test apparatus for simulating differential settlement, characterised in that: The installation frame, the soil filling chamber, the pre-settlement control assembly, the weighing sensor and the vertical load applying assembly are included. The installation frame includes a base, a crossbeam and two side columns; the crossbeam is located directly above the base, and the two side columns are used to connect the base and the crossbeam; The soil filling chamber is arranged in the middle of the two side columns and includes a soil rigid support assembly and two side plates; The soil rigid support assembly includes m long rigid blocks and n short rigid blocks staggered along the length direction of the base; The cross section of each long rigid block and each short rigid block is rectangular, and all the side walls are smooth walls; the height of the long rigid block is greater than that of the short rigid block, and the width of the long rigid block is equal to that of the short rigid block; The two side plates are sealed and arranged on the two sides of the soil rigid support assembly and connected with the two side columns; The soil to be settled is filled between the two side plates directly above the soil rigid support assembly; The number of the pre-settlement control assembly is m+n, and it is located directly below the m long rigid blocks and the n short rigid blocks; Each pre-settlement control assembly includes a needle cylinder, a piston, a piston rod and a piston driving assembly; The needle cylinder is arranged vertically on the base, and the piston can slide up and down in the needle cylinder; the bottom end of the piston rod is connected with the piston, and the top end of the piston rod is detachably connected with the bottom end of the long rigid block or the short rigid block directly above through one of the weighing sensors; The piston driving assembly can drive the piston to rise and fall and control the rising and falling speed of the piston Each piston driving assembly includes an air pipe, an external air source, an on-off valve and a flow regulating valve; the top end of the air pipe is arranged at the bottom of the needle cylinder, and the tail end is connected with the external air source; the on-off valve and the flow regulating valve are arranged on the air pipe from top to bottom; The vertical load applying assembly can apply a vertical load to the soil to be settled in the soil filling chamber.

2. The test apparatus for simulating differential settlement according to claim 1, wherein: A scale is arranged on the needle cylinder in the height direction, and the scale accuracy can reach 0.01 mm; by observing the scale value when the piston stops in the needle cylinder, the settlement value of the soil directly above the piston can be directly obtained.

3. The test apparatus for simulating differential settlement of claim 1, wherein: A settlement observation camera is further included, at least one side plate of the soil filling chamber is a transparent plate, and the settlement observation camera is arranged outside the transparent plate.

4. The test apparatus for simulating differential settlement according to claim 3, wherein: A data acquisition instrument and a computer are further included; the data acquisition instrument is connected with the weighing sensor, and the computer is connected with the data acquisition instrument, the pre-settlement control assembly and the vertical load applying assembly.

5. The test device for simulating differential settlement of claim 1, wherein: A rubber pad is arranged at the bottom of each piston.

6. A test method for simulating differential settlement, based on the test apparatus for simulating differential settlement according to any one of claims 1 to 5, characterized in that: The method includes the following steps: Step 1, selecting a similar soil for sedimentation: an aluminum rod is selected to simulate real soil particles, and aluminum rods of different sizes are mixed according to the set ratio to form a similar soil for sedimentation with an average particle size of ; wherein the average particle size is determined according to the internal friction angle of the real soil ; Step 2, pile arrangement: according to the real pile spacing in the settlement condition to be simulated, the number m of long rigid blocks, the number n of short rigid blocks and the arrangement positions are determined; the spacing between two adjacent long rigid blocks is equal to the real pile spacing; the height difference between the long rigid block and the short rigid block needs to be greater than the settlement value of the real soil to be simulated, but less than the filling height H of the settlement similar soil; Step 3, pile lifting: the bottom of each long rigid block and each short rigid block is inflated, so that it rises to the set height and stops inflating; at this time, the bottom of all long rigid blocks and all short rigid blocks are located at the same height; Step 4, filling the settlement similar soil: fill the settlement similar soil selected in step 1 on the top of all long rigid blocks and all short rigid blocks completed in step 3 until reaching the set filling height H; at this time, record the initial weight of the m long rigid block top settlement similar soil and the initial weight of the n short rigid block top settlement similar soil; wherein the initial weight of the m long rigid block top settlement similar soil is respectively recorded as: ; the initial weight of the n short rigid block top settlement similar soil is respectively recorded as: ; 1≤i≤m, 1≤j≤n; Step 5, pre-settlement: the bottom of each long rigid block and each short rigid block is uniformly deflated, so that it pre-settles to the set height and stops deflating; the pre-settlement is used to simulate the settlement of the real soil under the action of gravity; Step 6, settlement: vertical load is applied on top of the settlement similar soil, and the settlement similar soil is settled; Step 7, settlement observation: during the pre-settlement of step 5 and the settlement process of step 6, the settlement amount is observed in real time; when the settlement of the similar soil is set value a each time, the real-time weight of the top of m long rigid blocks of the similar soil and the real-time weight of the top of n short rigid blocks of the similar soil are recorded once; wherein the real-time weight of the top of m long rigid blocks of the similar soil is respectively recorded as: ; the initial weight of the top of n short rigid blocks of the similar soil is respectively recorded as: ; Step 8, calculating load transfer efficiency: in step 7, the load transfer efficiency is calculated once for each long rigid block when the settlement of the similar soil reaches a set value a ; wherein the load transfer efficiency of the i-th long rigid block is calculated according to the following formula: ​ ； Wherein: ； ； ； wherein Ptop,i is the pile top load taken by the ith long rigid block; Pint,j is the inter-pile load taken by the jth short rigid block; Ptotal is the total load of the real soil in the settlement condition to be simulated.

7. The test method for simulating differential settlement of claim 6, wherein: In step 1, the average particle size The relationship between the real soil internal friction angle is: ； In the formula, A, B and C are fitting coefficients, which are obtained by fitting the direct shear test data.

8. The test method for simulating differential settlement of claim 6, wherein: In step 5, by controlling the air release rate and air release amount at the bottom of each short rigid block, the settlement at different positions in the actual settlement working condition can be simulated, and differential settlement can be realized. The actual settlement working condition includes the settlement working condition of the waste landfill site, the settlement working condition of the new and old roadbed joint part, and the settlement working condition of the pile-supported embankment.

9. The test method for simulating differential settlement of claim 6, wherein: In step 7, the observation method of the settlement amount includes scale observation and image observation; wherein, the scale observation can directly read out the settlement displacement of the settlement similar soil at the current time; the image observation indirectly observes the settlement distribution of the settlement similar soil by real-time shooting of the settlement image of the settlement similar soil.

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