A cushion layer for similarity test of CFG pile composite foundation and its assembly method

Abstract

A cushion layer and assembly method for similarity testing of CFG pile composite foundations, belonging to the technical field of similarity testing of civil engineering foundations, comprises an upper wooden board, an upper filler, a polystyrene foam board, a lower filler, and a lower wooden board. This cushion layer has the advantage of having physical and mechanical parameters similar to those in prototype tests. It is used to study the bearing mechanism and load transfer behavior of CFG pile composite foundations, achieving the coordinated operation of the "CFG pile-soil-cushion layer" system. When specifically applied to tests, the cushion layer more closely resembles the load transfer behavior of prototype tests of CFG pile composite foundations. Furthermore, the cushion layer can be prepared according to the dimensions required by the engineering design, resulting in a simple process, convenient preparation, and low testing costs.

Description

Technical Field

[0001] The invention belongs to the technical field of similarity tests for civil engineering foundations, and in particular relates to a cushion layer for similarity tests of CFG pile composite foundations and an assembling method thereof. Background Art

[0002] Soft soil foundations are widely distributed across my country's land and islands, from east to west and north to south. These soils vary in nature and moisture content, primarily consisting of sedimentary foundation materials such as river, lake, marine, and aeolian deposits. These foundations are characterized by low bearing capacity and large deformation, making them difficult to meet the needs of civil engineering construction. CFG pile composite foundations are a widely used composite foundation reinforcement technology. They generally utilize the coordinated effects of displacement, drainage, compaction, and a cushion layer to improve the bearing capacity of the reinforced regional foundation and the bearing capacity of deep, well-grounded foundations. CFG pile composite foundations have a short construction period, are easily controlled in terms of quality, are convenient for testing, and offer low project costs, making them widely used in civil engineering construction.

[0003] To ensure the safety of CFG pile composite foundations, their design primarily follows a technical approach that combines theoretical design with static load testing. In regions with limited construction experience, prototype static load testing is affected by factors such as test plan, pile load, and test duration. This can be expensive and time-consuming, increasing construction costs and negatively impacting the initial design and optimization of CFG pile composite foundations. Therefore, conducting similar tests on CFG pile composite foundations would help address this issue.

[0004] In similarity tests of CFG pile composite foundations, the cushion layer is the key component for achieving the coordinated operation of the three elements (CFG pile, soil, and cushion layer). It must meet the similarity test conditions for both geometric similarity and physical and mechanical parameter similarity. However, current similarity tests primarily use geometric similarity for the cushion layer, making it difficult to achieve similar physical and mechanical parameters in similarity tests of CFG pile composite foundations. Summary of the Invention

[0005] In order to solve the problem that the physical and mechanical parameters of the cushion layer in the existing CFG pile composite foundation similarity test are difficult to achieve similarity, this patent provides a cushion layer for the similarity test of CFG pile composite foundation. The advantage of this cushion layer is that the physical and mechanical parameters of the cushion layer are similar to those in the prototype test. It is used to study the bearing mechanism and load transfer law of the CFG pile composite foundation, and realize the coordinated work of "CFG pile-soil-cushion layer" to achieve the prototype test effect. The specific technical solution is as follows:

[0006] A mattress layer for a similar test of a CFG pile composite foundation comprises an upper wooden board 1, an upper filling body 2, a polystyrene foam board 3, a lower filling body 4, and a lower wooden board 5. The lower surface of the upper wooden board 1 is bonded to the upper surface of the upper filling body 2 by an adhesive, the lower surface of the upper filling body 2 is bonded to the upper surface of the polystyrene foam board 3 by an adhesive, the lower surface of the polystyrene foam board 3 is bonded to the upper surface of the lower filling body 4 by an adhesive, and the lower surface of the lower filling body 4 is bonded to the upper surface of the lower wooden board 5 by an adhesive. The structure is as follows: Figure 1-2 As shown;

[0007] The upper wooden board 1 and the lower wooden board 5 are poplar plywood with a thickness of 5 to 9 mm;

[0008] The density of the polystyrene foam board 3 is 18-20 kg / m 3 , thickness is 3 to 8 mm;

[0009] The thickness of the filling body is 1 to 5 mm;

[0010] The filling material is silt sand, and the maximum particle size of the silt sand is less than 1 / 4 of the maximum particle size of the prototype test cushion material;

[0011] The adhesive is a mixture of epoxy resin glue and curing agent, with a mass ratio of epoxy resin glue: curing agent = (1-3): (2-5);

[0012] The cushion layer assembly method of the CFG pile composite foundation similarity test of the present invention comprises the following steps:

[0013] Step 1: Cut the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 to a size with a side length of the pile spacing L + 6 times the pile diameter D, lightly polish the surfaces of the upper wooden board 1 and the lower wooden board 5 with fine sandpaper, and then wipe the surfaces of the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 with a dry cloth to remove impurities;

[0014] Step 2: Place the processed upper wooden board 1, lower wooden board 5 and polystyrene foam board 3 on a flat and clean ground;

[0015] Step 3, mixing the epoxy resin glue and the curing agent according to a mass ratio to prepare an adhesive;

[0016] Step 4: Evenly apply adhesive to the lower surface of the upper wooden board 1, the upper and lower surfaces of the polystyrene foam board 3, and the upper surface of the lower wooden board 5. Then, evenly spread the upper filler 2 on the lower surface of the upper wooden board 1, and evenly spread the lower filler 4 on the upper surface of the lower wooden board 5.

[0017] Step 5: Align and bond the surface of the upper wooden board 1 covered with the filler to the upper surface of the polystyrene foam board 3, with the installation error controlled within ±2mm;

[0018] Step 6: Align and bond the lower surface of the polystyrene foam board 3 with the surface of the lower wooden board 5 where the filler is spread, with the installation error controlled within ±2mm;

[0019] Step 7: Place a steel plate on the upper surface of the upper wooden board 1 and apply pressure. After the adhesive is cured, a cushion layer similar to the CFG pile composite foundation test is prepared.

[0020] Compared with the prior art, the cushion layer of the CFG pile composite foundation similarity test and the assembly method thereof of the present invention have the following beneficial effects:

[0021] 1. The mattress layer of the present invention is a mattress layer composed of multiple materials, wherein the upper wooden board serves to fix the upper filling body, the upper filling body, the polystyrene foam board, and the lower filling body serve to simulate the deformation of the mattress layer material, and the lower wooden board serves to fix the lower filling body. The multiple material combination is applied to similar tests, and its geometric similarity and physical and mechanical properties are highly similar to the mattress layer of graded sand and gravel in the prototype project, and the coordinated work of "CFG pile-soil-cushion layer" can be achieved in similar tests.

[0022] 2. The specific application of the cushion layer of the present invention in the test solves the problem that the cushion layer of the similarity test of CFG pile composite foundation only considers geometric similarity. The cushion layer of the present invention simultaneously meets the geometric similarity conditions and physical and mechanical parameter similarity conditions of the similarity test, making the similarity test of CFG pile composite foundation closer to the load transfer law of the prototype test of CFG pile composite foundation. The test data is significantly better than the test data of the cushion layer of the prior art.

[0023] 3. The mattress layer of the present invention can be prepared according to the size required by engineering design, with simple process, convenient preparation and low test cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Side view of the cushion layer assembly for a similar test of CFG pile composite foundation: 1-upper wooden board, 2-upper filling body, 3-polystyrene foam board, 4-lower filling body, 5-lower wooden board.

[0025] Figure 2 Top view of the mattress assembly for a similar test of a CFG pile composite foundation: 1-upper wooden board; DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to specific implementation cases, but the present invention is not limited to these embodiments.

[0027] Example 1

[0028] A mattress layer for a similarity test of a CFG pile composite foundation comprises an upper wooden board 1, an upper filling body 2, a polystyrene foam board 3, a lower filling body 4, and a lower wooden board 5. The lower surface of the upper wooden board 1 is bonded to the upper surface of the upper filling body 2 by an adhesive, the lower surface of the upper filling body 2 is bonded to the upper surface of the polystyrene foam board 3 by an adhesive, the lower surface of the polystyrene foam board 3 is bonded to the upper surface of the lower filling body 4 by an adhesive, and the lower surface of the lower filling body 4 is bonded to the upper surface of the lower wooden board 5 by an adhesive.

[0029] The upper wooden board 1 and the lower wooden board 5 are poplar plywood with a thickness of 5 mm;

[0030] The polystyrene foam board 3 has a density of 18 kg / m 3 , thickness is 4mm;

[0031] The thickness of the filling body is 3mm;

[0032] The filling material is silt sand, more than 50% of which has a particle size less than 0.0075 mm, and the maximum particle size of the silt sand is less than 10 mm;

[0033] The adhesive is a mixture of epoxy resin glue and curing agent, with a mass ratio of epoxy resin glue: curing agent = 1:4;

[0034] A method for assembling a cushion layer for a similarity test of a CFG pile composite foundation comprises the following steps:

[0035] Step 1: Cut the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 to a size of 360 mm in side length, lightly polish the surfaces of the upper wooden board 1 and the lower wooden board 5 with fine sandpaper, and then wipe the surfaces of the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 with a dry cloth to remove impurities;

[0036] Step 2: Place the processed upper wooden board 1, lower wooden board 5 and polystyrene foam board 3 on a flat and clean ground;

[0037] Step 3, mixing the epoxy resin glue and the curing agent according to a mass ratio to prepare an adhesive;

[0038] Step 4: Evenly apply adhesive to the lower surface of the upper wooden board 1, the upper and lower surfaces of the polystyrene foam board 3, and the upper surface of the lower wooden board 5. Then, evenly spread the upper filler 2 on the lower surface of the upper wooden board 1, and evenly spread the lower filler 4 on the upper surface of the lower wooden board 5. The thickness of the filler is 3 mm.

[0039] Step 5: Align and bond the surface of the upper wooden board 1 covered with the filler to the upper surface of the polystyrene foam board 3, with the installation error controlled within ±2mm;

[0040] Step 6: Align and bond the lower surface of the polystyrene foam board 3 with the surface of the lower wooden board 5 where the filler is spread, with the installation error controlled within ±2mm;

[0041] Step 7: Place a steel plate on the upper surface of the upper wooden board 1 and apply pressure. After the adhesive is cured, a cushion layer similar to the CFG pile composite foundation test is prepared.

[0042] The cushion layer of the prototype CFG pile composite foundation uses graded sand and gravel with a maximum particle size of no more than 25mm, a thickness of 300mm, a cohesion of 1kPa, an internal friction angle of 40°, and a weight of 20kN / m 3 ; Elastic modulus 80MPa, Poisson's ratio 0.3.

[0043] According to the geometric similarity ratio of 15:1 between the prototype and the model, the CFG pile composite foundation combined cushion layer of the present invention was made. After testing, the cohesion was 0.1kPa, the internal friction angle was 28°, and the weight was 19kN / m 3 ; Elastic modulus 8MPa, Poisson's ratio 0.2, the mattress filling material of the similarity test is highly similar to the mattress material of the prototype test, and the similarity condition value (1.053) is close to 1.0, which meets the test requirements.

[0044] The variable cross-section CFG pile has a pile length of 53cm, the inner and outer diameters of the upper expanded section are 40mm and 36mm respectively, and the pile spacing is 120mm. The foundation material is composed of an upper foundation, i.e., a clay layer, and a lower foundation, i.e., a sand layer. The lower foundation is made of a soil with a moisture content of 24.133% and a wet density of 19kN / m 3 The medium sand was compacted by layered vibration; the lower foundation consisted of prepared clay with a moisture content of 24.0%, an internal friction angle of 12.86°, and a cohesion of 7.581 kPa, respectively. The load-settlement test data for the CFG pile composite foundation are shown in Table 1. Before the 12th load level, the curve exhibited inverse curvature and discontinuity. This was due, on the one hand, to the disturbance and underconsolidation of the soft soil foundation, and, on the other hand, to the varying degrees of synergy between the pile-soil synergy, including the cushion layer, inter-pile soil, and reinforcement. After the 13th load level, the curve became relatively continuous, with a curvature approaching a constant slope, indicating that the standard pile section located in the sand exerted a greater load-bearing effect. The ultimate load in the model test was 13.569 kPa, corresponding to a load plate center displacement of 13.582 mm.

[0045] Table 1 Load-settlement test data

[0046]

[0047]

[0048] Example 2

[0049] A mattress layer for a similarity test of a CFG pile composite foundation comprises an upper wooden board 1, an upper filling body 2, a polystyrene foam board 3, a lower filling body 4, and a lower wooden board 5. The lower surface of the upper wooden board 1 is bonded to the upper surface of the upper filling body 2 by an adhesive, the lower surface of the upper filling body 2 is bonded to the upper surface of the polystyrene foam board 3 by an adhesive, the lower surface of the polystyrene foam board 3 is bonded to the upper surface of the lower filling body 4 by an adhesive, and the lower surface of the lower filling body 4 is bonded to the upper surface of the lower wooden board 5 by an adhesive.

[0050] The upper wooden board 1 and the lower wooden board 5 are poplar plywood with a thickness of 6 mm;

[0051] The polystyrene foam board 3 has a density of 18 kg / m 3 , thickness is 3mm;

[0052] The thickness of the filling body is 4mm;

[0053] The filling material is silt sand, more than 50% of which has a particle size less than 0.0075 mm and the maximum particle size of the silt sand is less than 15 mm;

[0054] The adhesive is a mixture of epoxy resin glue and curing agent, with a mass ratio of epoxy resin glue: curing agent = 2:5;

[0055] A method for assembling a cushion layer for a similarity test of a CFG pile composite foundation comprises the following steps:

[0056] Step 1: Cut the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 to a size of 360 mm in side length, lightly polish the surfaces of the upper wooden board 1 and the lower wooden board 5 with fine sandpaper, and then wipe the surfaces of the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 with a dry cloth to remove impurities;

[0057] Step 2: Place the processed upper wooden board 1, lower wooden board 5 and polystyrene foam board 3 on a flat and clean ground;

[0058] Step 3, mixing the epoxy resin glue and the curing agent according to a mass ratio to prepare an adhesive;

[0059] Step 4: Evenly apply adhesive to the lower surface of the upper wooden board 1, the upper and lower surfaces of the polystyrene foam board 3, and the upper surface of the lower wooden board 5. Then, evenly spread the upper filler 2 on the lower surface of the upper wooden board 1, and evenly spread the lower filler 4 on the upper surface of the lower wooden board 5. The thickness of the filler is 4 mm.

[0060] Step 5: Align and bond the surface of the upper wooden board 1 covered with the filler to the upper surface of the polystyrene foam board 3, with the installation error controlled within ±2mm;

[0061] Step 6: Align and bond the lower surface of the polystyrene foam board 3 with the surface of the lower wooden board 5 where the filler is spread, with the installation error controlled within ±2mm;

[0062] Step 7: Place a steel plate on the upper surface of the upper wooden board 1 and apply pressure. After the adhesive is cured, a cushion layer similar to the CFG pile composite foundation test is prepared.

[0063] The cushion layer of the prototype CFG pile composite foundation uses graded sand and gravel with a maximum particle size of no more than 25mm, a thickness of 300mm, a cohesion of 1kPa, an internal friction angle of 40°, and a weight of 20kN / m 3 ; Elastic modulus 80MPa, Poisson's ratio 0.3.

[0064] According to the geometric similarity ratio of 15:1 between the prototype and the model, the CFG pile composite foundation combined cushion layer of the present invention was made. After testing, the cohesion was 0.13kPa, the internal friction angle was 26°, and the weight was 21kN / m 3 ; Elastic modulus 8.6MPa, Poisson's ratio 0.2, the mattress filling material of the similar test is highly similar to the mattress material of the prototype test, and the similarity condition value (1.11) is close to 1.0, which meets the test requirements.

[0065] The variable cross-section CFG pile has a pile length of 53cm, the inner and outer diameters of the upper expanded section are 40mm and 36mm respectively, and the pile spacing is 120mm. The foundation material is composed of an upper foundation, i.e., a clay layer, and a lower foundation, i.e., a sand layer. The lower foundation is made of a soil with a moisture content of 24.133% and a wet density of 19kN / m 3 The medium sand was compacted by layered vibration; the lower foundation consisted of prepared clay with a moisture content of 24.0%, an internal friction angle of 12.86°, and a cohesion of 7.581 kPa, respectively. The load-settlement test data for the CFG pile composite foundation are shown in Table 2. The ultimate load in the model test was 10.745 kPa, corresponding to a load plate center displacement of 12.163 mm.

[0066] Table 2 Load-settlement test data

[0067]

[0068]

[0069] Example 3

[0070] A mattress layer for a similarity test of a CFG pile composite foundation comprises an upper wooden board 1, an upper filling body 2, a polystyrene foam board 3, a lower filling body 4, and a lower wooden board 5. The lower surface of the upper wooden board 1 is bonded to the upper surface of the upper filling body 2 by an adhesive, the lower surface of the upper filling body 2 is bonded to the upper surface of the polystyrene foam board 3 by an adhesive, the lower surface of the polystyrene foam board 3 is bonded to the upper surface of the lower filling body 4 by an adhesive, and the lower surface of the lower filling body 4 is bonded to the upper surface of the lower wooden board 5 by an adhesive.

[0071] The upper wooden board 1 and the lower wooden board 5 are poplar plywood with a thickness of 8 mm;

[0072] The polystyrene foam board 3 has a density of 21 kg / m 3 , thickness is 4mm;

[0073] The thickness of the filling body is 3mm;

[0074] The filling material is silt sand, more than 50% of which has a particle size less than 0.0075 mm and the maximum particle size of the silt sand is less than 15 mm;

[0075] The adhesive is a mixture of epoxy resin glue and curing agent, with a mass ratio of epoxy resin glue: curing agent = 3:5;

[0076] A method for assembling a cushion layer for a similarity test of a CFG pile composite foundation comprises the following steps:

[0077] Step 1: Cut the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 to a size of 360 mm in side length, lightly polish the surfaces of the upper wooden board 1 and the lower wooden board 5 with fine sandpaper, and then wipe the surfaces of the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 with a dry cloth to remove impurities;

[0078] Step 2: Place the processed upper wooden board 1, lower wooden board 5 and polystyrene foam board 3 on a flat and clean ground;

[0079] Step 3, mixing the epoxy resin glue and the curing agent according to a mass ratio to prepare an adhesive;

[0080] Step 4: Evenly apply adhesive to the lower surface of the upper wooden board 1, the upper and lower surfaces of the polystyrene foam board 3, and the upper surface of the lower wooden board 5. Then, evenly spread the upper filler 2 on the lower surface of the upper wooden board 1, and evenly spread the lower filler 4 on the upper surface of the lower wooden board 5. The thickness of the filler is 3 mm.

[0081] Step 5: Align and bond the surface of the upper wooden board 1 covered with the filler to the upper surface of the polystyrene foam board 3, with the installation error controlled within ±2mm;

[0082] Step 6: Align and bond the lower surface of the polystyrene foam board 3 with the surface of the lower wooden board 5 where the filler is spread, with the installation error controlled within ±2mm;

[0083] Step 7: Place a steel plate on the upper surface of the upper wooden board 1 and apply pressure. After the adhesive is cured, a cushion layer similar to the CFG pile composite foundation test is prepared.

[0084] The cushion layer of the prototype CFG pile composite foundation uses graded sand and gravel with a maximum particle size of no more than 25mm, a thickness of 300mm, a cohesion of 1kPa, an internal friction angle of 40°, and a weight of 20kN / m 3 ; Elastic modulus 80MPa, Poisson's ratio 0.3.

[0085] According to the geometric similarity ratio of 15:1 between the prototype and the model, the CFG pile composite foundation combined cushion layer of the present invention was made. After testing, the cohesion was 0.15kPa, the internal friction angle was 28°, and the weight was 21.5kN / m 3 ; Elastic modulus 8.7MPa, Poisson's ratio 0.2, the mattress filling material of the similarity test is highly similar to the mattress material of the prototype test, and the similarity condition value (1.15) is close to 1.0, which meets the test requirements.

[0086] The variable cross-section CFG pile has a pile length of 53cm, the inner and outer diameters of the upper expanded section are 40mm and 36mm respectively, and the pile spacing is 120mm. The foundation material is composed of an upper foundation, i.e., a clay layer, and a lower foundation, i.e., a sand layer. The lower foundation is made of a soil with a moisture content of 24.133% and a wet density of 19kN / m 3 The medium sand was compacted layer by layer using vibration; the lower foundation consisted of prepared clay with a moisture content of 24.0%, an internal friction angle of 12.86°, and a cohesion of 7.581 kPa, respectively. The load-settlement test data for the CFG pile composite foundation are shown in Table 3. The ultimate load in the model test was 9.596 kPa, corresponding to a load plate center displacement of 11.458 mm.

[0087] Table 3 Load-settlement test data

[0088]

[0089]

[0090] Example 4

[0091] A mattress layer for a similarity test of a CFG pile composite foundation comprises an upper wooden board 1, an upper filling body 2, a polystyrene foam board 3, a lower filling body 4, and a lower wooden board 5. The lower surface of the upper wooden board 1 is bonded to the upper surface of the upper filling body 2 by an adhesive, the lower surface of the upper filling body 2 is bonded to the upper surface of the polystyrene foam board 3 by an adhesive, the lower surface of the polystyrene foam board 3 is bonded to the upper surface of the lower filling body 4 by an adhesive, and the lower surface of the lower filling body 4 is bonded to the upper surface of the lower wooden board 5 by an adhesive.

[0092] The upper wooden board 1 and the lower wooden board 5 are poplar plywood with a thickness of 3 mm;

[0093] The polystyrene foam board 3 has a density of 20 kg / m 3 , thickness is 8mm;

[0094] The thickness of the filling body is 5mm;

[0095] The filling material is silt sand, more than 50% of which has a particle size less than 0.0075 mm and the maximum particle size of the silt sand is less than 15 mm;

[0096] The adhesive is a mixture of epoxy resin glue and curing agent, with a mass ratio of epoxy resin glue: curing agent = 1:2;

[0097] A method for assembling a cushion layer for a similarity test of a CFG pile composite foundation comprises the following steps:

[0098] Step 1: Cut the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 to a size of 360 mm in side length, lightly polish the surfaces of the upper wooden board 1 and the lower wooden board 5 with fine sandpaper, and then wipe the surfaces of the upper wooden board 1, the lower wooden board 5, and the polystyrene foam board 3 with a dry cloth to remove impurities;

[0099] Step 2: Place the processed upper wooden board 1, lower wooden board 5 and polystyrene foam board 3 on a flat and clean ground;

[0100] Step 3, mixing the epoxy resin glue and the curing agent according to a mass ratio to prepare an adhesive;

[0101] Step 4: Evenly apply adhesive to the lower surface of the upper wooden board 1, the upper and lower surfaces of the polystyrene foam board 3, and the upper surface of the lower wooden board 5. Then, evenly spread the upper filler 2 on the lower surface of the upper wooden board 1, and evenly spread the lower filler 4 on the upper surface of the lower wooden board 5. The thickness of the filler is 5 mm.

[0102] Step 5: Align and bond the surface of the upper wooden board 1 covered with the filler to the upper surface of the polystyrene foam board 3, with the installation error controlled within ±2mm;

[0103] Step 6: Align and bond the lower surface of the polystyrene foam board 3 with the surface of the lower wooden board 5 where the filler is spread, with the installation error controlled within ±2mm;

[0104] Step 7: Place a steel plate on the upper surface of the upper wooden board 1 and apply pressure. After the adhesive is cured, a cushion layer similar to the CFG pile composite foundation test is prepared.

[0105] The cushion layer of the prototype CFG pile composite foundation uses graded sand and gravel with a maximum particle size of no more than 25mm, a thickness of 300mm, a cohesion of 1kPa, an internal friction angle of 40°, and a weight of 20kN / m 3 ; Elastic modulus 80MPa, Poisson's ratio 0.3.

[0106] According to the geometric similarity ratio of 15:1 between the prototype and the model, the CFG pile composite foundation combined cushion layer of the present invention was made. After testing, the cohesion was 0.1kPa, the internal friction angle was 28°, and the weight was 21kN / m 3 ; Elastic modulus 7.5MPa, Poisson's ratio 0.2, the mattress filling material of the similarity test is highly similar to the mattress material of the prototype test, and the similarity condition value (1.035) is close to 1.0, which meets the test requirements.

[0107] The variable cross-section CFG pile has a pile length of 53cm, the inner and outer diameters of the upper expanded section are 40mm and 36mm respectively, and the pile spacing is 120mm. The foundation material is composed of an upper foundation, i.e., a clay layer, and a lower foundation, i.e., a sand layer. The lower foundation is made of a soil with a moisture content of 24.133% and a wet density of 19kN / m 3 The medium sand was compacted layer by layer using vibration; the lower foundation consisted of prepared clay with a moisture content of 24.0%, an internal friction angle of 12.86°, and a cohesion of 7.581 kPa, respectively. The load-settlement test data for the CFG pile composite foundation are shown in Table 4. The ultimate load in the model test was 9.749 kPa, corresponding to a load plate center displacement of 12.458 mm.

[0108] Table 4 Load-settlement test data

[0109]

Claims

1. A cushion layer for a similarity test of a CFG pile composite foundation, comprising an upper wooden board (1), an upper filling body (2), a polystyrene foam board (3), a lower filling body (4) and a lower wooden board (5), wherein the lower surface of the upper wooden board 1 is bonded to the upper surface of the upper filling body (2) by an adhesive, the lower surface of the upper filling body (2) is bonded to the upper surface of the polystyrene foam board (3) by an adhesive, the lower surface of the polystyrene foam board (3) is bonded to the upper surface of the lower filling body (4) by an adhesive, and the lower surface of the lower filling body (4) is bonded to the upper surface of the lower wooden board (5) by an adhesive; The filler is silt sand, and the maximum particle size of the silt sand is less than 1 / 4 of the maximum particle size of the prototype test mattress material; the thickness of the filler is 1-5 mm; the upper wooden board (1) and the lower wooden board (5) are poplar plywood, with a thickness of 5-9 mm; the density of the polystyrene foam board (3) is 18-20 kg / m 3 , with a thickness of 3 to 8 mm; the upper wooden board (1), the lower wooden board (5) and the polystyrene foam board (3) are cut to a size with a side length of the pile spacing L + 6 times the pile diameter D; the adhesive is a mixture of epoxy resin glue and curing agent, with a mass ratio of epoxy resin glue: curing agent = (1 to 3): (2 to 5); the mattress layer simultaneously meets the geometric similarity conditions and physical and mechanical parameter similarity conditions of the similarity test.

2. The method for assembling the cushion layer of the CFG pile composite foundation similarity test according to claim 1 is characterized in that: The steps include: Step 1: Cut the upper wooden board (1), the lower wooden board (5) and the polystyrene foam board (3) to a size with a side length of the pile spacing L + 6 times the pile diameter D, lightly polish the surfaces of the upper wooden board (1) and the lower wooden board (5) with fine sandpaper, and then wipe the surfaces of the upper wooden board (1), the lower wooden board (5) and the polystyrene foam board (3) with a dry cloth to remove impurities; Step 2: Place the processed upper wooden board (1), lower wooden board (5) and polystyrene foam board (3) on a flat and clean ground; Step 3, mixing the epoxy resin glue and the curing agent according to a mass ratio to prepare an adhesive; Step 4, evenly apply adhesive to the lower surface of the upper wooden board (1), the upper / lower surface of the polystyrene foam board (3), and the upper surface of the lower wooden board (5), and then evenly spread the upper filler (2) on the lower surface of the upper wooden board (1), and evenly spread the lower filler (4) on the upper surface of the lower wooden board (5); Step 5: Align and bond the surface of the upper wooden board (1) on which the filler is spread with the upper surface of the polystyrene foam board (3), with the installation error controlled within ±2 mm; Step 6: Align and bond the lower surface of the polystyrene foam board (3) with the surface of the lower wooden board (5) on which the filler is spread, with the installation error controlled within ±2 mm; Step 7: Place a steel plate on the upper surface of the upper wooden board (1), apply pressure, and after the adhesive is cured, form a cushion layer similar to the test of the CFG pile composite foundation.

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