A test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure

Abstract

The present invention provides a test method for simulating the influence of soft and hard interlayered bedrock on the deformation and damage of pile foundation. The method comprises: preparing a combination sample A simulating soft and hard interlayered bedrock and a comparative combination sample B simulating hard layered bedrock by a mold, and performing a loading test on the model piles in the combination sample A and the comparative combination sample B, wherein the loading method adopts graded loading; drawing the axial stress-axial displacement relationship curve of the model piles in the two combination samples according to the test results, and drawing the two groups of test curves in the same coordinate system to obtain a comparative curve diagram of the two groups of tests, and providing a theoretical basis for the optimization of pile length in soft and hard interlayered bedrock in the later stage by observing the relationship between the two groups of curves. The present invention utilizes an existing triaxial compression testing machine and adopts a combination sample to simulate the influence of soft and hard interlayered bedrock on pile foundation, and provides a reference basis for optimizing the length of pile foundation through the test comparison results.

Description

Technical Field

[0001] The present invention relates to the field of rock mechanics and engineering, and in particular to a test method for simulating the influence of soft and hard interbedded bedrock on pile foundation deformation and failure. Background Art

[0002] Bored piles are widely used as foundations in various construction projects due to their simple construction process and quick construction time. Interbedded soft and hard rock is a common type of rock mass encountered during underground construction projects such as tunnels and foundation pits. Specifically, this refers to a rock mass composed of two or more interbedded rock masses with significant strength differences. With the continuous development of underground engineering, pile foundation construction inevitably involves areas with interbedded soft and hard rock, such as red beds and metamorphic rocks.

[0003] During existing pile foundation construction, to ensure stability and holding power, the pile is typically embedded in the rock. Prior to construction, the rock formations in the construction area are surveyed, and the pile length and embedment depth are designed based on the survey report. Generally, the more intact the rock formation, the better the holding power, and the smaller the embedment depth, so the survey results directly influence the pile length design. Because existing survey and sampling techniques have a low sampling rate for soft rock, in interbedded rock masses, to ensure that pile foundation designs meet requirements, the strength of the interbedded layers is often assigned a lower value during geological stratification. This fails to fully consider the strength-enhancing effect of the deep rock mass's confining pressure, resulting in increased designed pile lengths and costs.

[0004] In the actual construction process, the pile body will be affected by the confining pressure. Therefore, in the process of pile foundation construction in the soft and hard interlayer, there is a large error in dividing the strength of the geological stratification into a lower value. However, there is currently no research on the influence of the soft and hard interlayer bedrock on the deformation and damage of the pile foundation, so it is impossible to provide a relevant theoretical basis for the optimization of the pile length in the soft and hard interlayer. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a test method for simulating the influence of soft and hard interlayered bedrock on the deformation and damage of pile foundations. The method designs a method using existing test instruments to study the influence of soft and hard interlayered bedrock on pile foundations, and by designing a comparative test of the influence of hard layer bedrock on pile foundations, the two test results are compared to provide a theoretical basis for optimizing pile length in soft and hard interlayered bedrock.

[0006] To solve the above technical problems, the present invention provides a test method for simulating the influence of soft and hard interbedded bedrock on pile foundation deformation and failure, which is characterized by the following specific steps:

[0007] (1) Prepare the sample mold: the mold is made of a transparent plate and a steel frame, a push block is provided at the bottom of the mold, a top cover is provided at the top, a push hole is provided on the bottom plate of the mold, and a construction hole is provided on the top cover, and the diameter of the construction hole matches the pile diameter of the model pile; after the mold is assembled, vaseline is coated on the inner wall of the transparent plate of the mold, and the horizontal compaction line of the soft and hard interlayer bedrock is drawn on the side of the transparent plate of the mold according to the thickness of each hard rock layer and soft rock layer, and then the horizontal compaction line of the soil layer is drawn according to the thickness of the soil layer, and finally, a horizontal excavation dotted line is drawn on the upper part of the transparent plate of the mold according to the length of the model pile, and the horizontal excavation dotted line is lower than the height of the horizontal compaction line of the soil layer;

[0008] (2) Prepare sample materials, including hard rock layer, soft rock layer and soil layer materials: the hard rock layer is cut from intact rock, and the intact rock is cut into rock plates for preparing combined sample A simulating soft and hard interbedded bedrock and rock blocks for preparing comparative combined sample B simulating hard layer bedrock; the thickness of the rock plates matches the height between the horizontal compaction lines of two adjacent soft and hard interbedded bedrocks, the thickness of the rock blocks is equal to the height of the horizontal compaction line of the uppermost soft and hard interbedded bedrock, and the cross-sectional sizes of the rock plates and rock blocks match the size of the loading test equipment; the soft rock layer materials and soil layer materials are both made of coarse sand, medium sand, bentonite, double fly ash and water, wherein the density of the soft rock layer is 2.0 to 2.2 g / cm 3 , soil density is 1.0~1.2g / cm 3 ;

[0009] (3) Prepare a composite sample A, using the sample mold in step (1) and the rock plate, soft rock layer and soil layer materials in step (2) to prepare the composite sample A, the specific process is as follows:

[0010] a. First, a rock plate is laid in the mold as a hard rock layer, the thickness of which is consistent with the horizontal compaction line of the first layer of soft and hard interbedded bedrock. Then, the soft rock layer material prepared in step (2) is laid and compacted to the horizontal compaction line of the second layer of hard interbedded bedrock as a soft rock layer. The soft and hard interbedded bedrock can be made by alternating the completion of the steps;

[0011] b. Continue to lay the soil material prepared in step (2) into the mold and compact it to the horizontal compaction line of the soil;

[0012] c. Then, cover the top cover with holes, drill holes from the construction holes of the top cover, place wire cages made of wire into the holes, and inject cement mortar to prepare model piles;

[0013] d. When the cement mortar solidifies to 50% of the design strength, remove the top cover, excavate the soil layer to the horizontal excavation imaginary line, and push the push block through the push hole on the mold bottom plate to push out the prepared composite specimen A in the mold for curing;

[0014] (4) Prepare a comparative composite sample B, using the sample mold in step (1) and the rock and soil materials in step (2) to prepare the composite sample B, the specific process is as follows:

[0015] a. First, place a rock block of appropriate size in the mold. The height of the rock block should be consistent with the horizontal compaction line of the uppermost soft and hard interbedded bedrock in the mold.

[0016] b. Then lay the soil material prepared in step (2) into the mold and compact it to the horizontal compaction line of the soil;

[0017] c. Then, cover the top cover with holes, drill holes from the construction holes of the top cover, place wire cages made of wire into the holes, and inject cement mortar to prepare model piles;

[0018] d. When the cement mortar solidifies to 50% of the design strength, remove the top cover, excavate the soil layer to the horizontal excavation dotted line, and push the push block through the push hole on the mold bottom plate to push out the comparison composite sample B prepared in the mold for curing;

[0019] (5) Loading tests are performed on the model piles in the combined sample A prepared in step (3) and the comparative combined sample B prepared in step (4), respectively, and the loading method adopts step-by-step loading; based on the obtained test data, the axial stress-axial displacement relationship curve of the model pile in the combined sample A simulating the soft and hard interbedded bedrock and the axial stress-axial displacement relationship curve of the model pile in the comparative combined sample B simulating the hard bedrock are respectively drawn, and the two groups of test curves are drawn in the same coordinate system to obtain a comparison curve diagram of the two groups of tests, and the comparison curve diagram is used as the theoretical basis for the optimization design of pile length in the soft and hard interbedded bedrock.

[0020] A further technical solution of the present invention is as follows: the composite sample A and the comparative composite sample B are respectively prepared in two groups; the first group of composite sample A and the comparative composite sample B are respectively placed in a triaxial test compressor and directly loaded to failure, and the peak stress σ of the composite sample A is obtained. c1 Compared with the peak stress σ of the combined sample B c2 Then, based on the first set of test data, the increment of each load level in the step-by-step loading test of the second set of combined specimens A and the comparison combined specimens B is determined to be 0.1σ respectively. c1 and 0.1σ c2 The pressure stabilization time for each level is 2h, and the loading rate is controlled by controlling the axial displacement at a rate of 0.12mm / min.

[0021] A better technical solution of the present invention: the mold in step (1) is a rectangular mold, which is made of four rectangular transparent acrylic plates, a square steel base plate and four angle steels, a push hole is provided in the middle of the square steel base plate of the mold, and the transparent acrylic plate is the side wall of the mold, which is fixed by the angle steel; the soft and hard interlayer bedrock horizontal compaction lines are provided with multiple solid lines, and the spacing between the multiple soft and hard interlayer bedrock horizontal compaction lines is equal, the uppermost soft and hard interlayer bedrock horizontal compaction line is located in the middle of the mold, and the height of the uppermost soft and hard interlayer bedrock horizontal compaction line matches the thickness of the simulated soft and hard interlayer bedrock.

[0022] The preferred technical solution of the present invention is as follows: in step (2), the rock with intact surface is subjected to ultrasonic inspection to ensure its integrity and homogeneity, and then cut into rock slabs and rock blocks of specific sizes for use in combined sample A and comparative combined sample B respectively.

[0023] A preferred technical solution of the present invention: the soft rock layer material in step (2) is prepared by using coarse sand, medium sand, bentonite, double fly ash and water in a mass ratio of 6:6:2:1:1.5; the soil layer is prepared by using coarse sand, medium sand, bentonite, double fly ash and water in a mass ratio of 20:5:3:2:3.

[0024] The preferred technical solution of the present invention is as follows: in the step (3), the mass of the material required for the soft rock layer is calculated based on the density of the prepared soft rock layer material and the volume between the horizontal compaction lines of the two adjacent soft and hard interlayer bedrocks, and the corresponding mass of the soft rock layer material is laid in the mold and compacted as the soft rock layer; the soil layer in the steps (3) and (4) is calculated based on the density of the soil layer and the volume between the horizontal compaction line of the uppermost soft and hard interlayer bedrock and the horizontal compaction line of the soil layer, and the corresponding mass of the soil layer material is compacted to the horizontal compaction line of the soil layer above the horizontal excavation dotted line.

[0025] A preferred technical solution of the present invention: in the step (5), the model pile of the combined sample is loaded using a triaxial compression testing machine, the combined sample A and the comparison combined sample B are of the same size, and the side dimensions of the two combined samples match the dimensions of the push plate provided with the triaxial compression testing machine, and the diameters of the model piles in the two combined samples match the diameters of the circular pad and the pressure head on the upper part of the triaxial compression testing machine.

[0026] A further technical solution of the present invention: the steps for installing the combined specimen in the loading test in step (5) are as follows: first, press the push plate release button and the lowering button to increase the internal spacing, then remove the upper pressure plate, and evenly apply vaseline on the surfaces of the four horizontal push plates of the triaxial compression testing machine; place the combined specimen on the chassis of the triaxial compression testing machine through the lower square pad, press the push plate tightening button to fix the specimen in the center of the chassis, and stop pushing when the pointers of the pressure gauges on the four horizontal push plates of the combined specimen all show a slight float; finally, place the upper circular pad on the upper part of the model pile of the combined specimen, install the pressure plate and press the lifting button to control the horizontal hydraulic device of the triaxial compression testing machine to rise synchronously with the chassis, and stop pressing the lifting button when the pointer of the pressure gauge on the pressure plate shows a slight float.

[0027] A preferred technical solution of the present invention is as follows: the axial stress of the model pile in the combined specimen is measured by the pressure head on the pressure plate of the triaxial compression testing machine and recorded in a computer; the axial displacement of the model pile in the combined specimen is the vertical distance that the horizontal hydraulic device and the chassis are synchronously lifted, and is recorded by a computer.

[0028] A further technical solution of the present invention is as follows: the direct loading test and the step-by-step loading test are both achieved by controlling the synchronous lifting rate of the horizontal hydraulic device and the base plate of the triaxial compression testing machine; during the direct loading and step-by-step loading tests, the push plate of the triaxial compression testing machine is used to limit the lateral deformation of the combined specimen and does not apply force; the step-by-step loading process is achieved by computer-controlled synchronous rising of the horizontal hydraulic device with the push plate and the chassis, thereby achieving stress control while limiting the lateral deformation of the combined specimen.

[0029] The triaxial compression testing machine in the present invention is a commonly used device in existing loading tests, and its loading process is also a conventional method.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention effectively simulates the influence of soft and hard interlayer bedrock on pile foundation deformation and damage and the influence of hard layer bedrock on pile foundation deformation and damage through two groups of combined specimens, and draws the axial stress-axial displacement relationship curves of the model pile respectively. By comparing the two groups of curves, the relationship between the soft and hard interlayer bedrock and the hard layer bedrock on the destructive strength of the pile foundation can be known, which provides a theoretical basis for the optimization of pile length in soft and hard interlayer bedrock in the later stage. The present invention is simple and easy to understand, low in cost, and can provide a new thinking direction for subsequent similar experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of the mold in the present invention;

[0033] Figure 2 It is a schematic structural diagram of the combined sample A of the present invention;

[0034] Figure 3 is a diagram of the preparation process of combined sample A;

[0035] Figure 4 is the state diagram of the combined specimen A in the mold;

[0036] Figure 5 Schematic diagram of the structure of comparative combination sample B in the present invention;

[0037] Figure 6 is a diagram of the preparation process of comparative composite sample B;

[0038] Figure 7 is a schematic diagram of the axial pressure applied to the model pile in the composite specimen;

[0039] Figure 8 This is a front view of the combined specimen loading test of the present invention;

[0040] Figure 9 It is a cross-sectional view of the combined test loading test of the present invention.

[0041] In the figure: 1-interlayered bedrock; 2-model pile; 3-soil layer; 4-rock block; 5-push hole; 6-mold; 600-horizontal compaction line of interlayered bedrock, 601-horizontal compaction line of soil layer, 602-horizontal excavation dotted line, 7-top cover; 700-construction hole, 8-wire cage; 9-push block; 10-pressure plate; 11-horizontal hydraulic device; 12-lifting chassis; 13-testing machine base; 14-upper circular pad; 15-push plate; 16-lower square pad; 17-vertical rod; 18-push plate tightening or loosening button; 19-lifting or lowering button; 20-computer. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings of the present invention. The technical solutions shown in the accompanying drawings are specific solutions of the embodiments of the present invention and are not intended to limit the scope of the invention claimed for protection. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] In the description of the present invention, it should be understood that the terms "upper", "lower", "inside", "outside", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product is conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. These are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0044] The combined sample A in the embodiment of the present invention and the comparative combined sample B are of the same size and are both prepared using a mold 6. The mold 6 used is as follows: Figure 1 As shown, the tool is a rectangular parallelepiped mold 6, which is made of four rectangular transparent acrylic plates, a square steel bottom plate and four angle steels. A push hole 5 is provided in the middle of the square steel bottom plate of the mold 6. The transparent acrylic plate is the side wall of the mold 6 and is fixed by the angle steel. A push block 9 is provided at the bottom of the mold 6 and a top cover 7 is provided on the top. A construction hole 700 is opened on the top cover 7. The aperture of the construction hole 700 matches the pile diameter of the model pile 2. After the mold 6 is assembled, vaseline is applied to the inner wall of the transparent plate of the mold 6, and the soft and hard interlayer bedrock level is drawn on the side of the transparent plate of the mold 6 according to the thickness of each hard rock layer and soft rock layer. Compaction line 600, then draw the soil layer horizontal compaction line 601 according to the thickness of the soil layer 3, and finally draw the horizontal excavation dotted line 602 on the upper part of the transparent plate of the mold 6 according to the length of the model pile 2, and the horizontal excavation dotted line 602 is lower than the height of the soil layer horizontal compaction line 601; the soft and hard interlayer bedrock horizontal compaction lines 600 are provided with multiple, all of which are solid lines, and the spacing between the multiple soft and hard interlayer bedrock horizontal compaction lines 600 is equal, the uppermost soft and hard interlayer bedrock horizontal compaction line 600 is located in the middle of the mold 6, and the height of the uppermost soft and hard interlayer bedrock horizontal compaction line 600 matches the thickness of the soft and hard interlayer bedrock 1.

[0045] In the embodiment of the present invention, a triaxial compression tester is used to load the model pile 2 in the composite sample. The side dimensions of the composite sample A and the comparative composite sample B match the dimensions of the push plate 15 provided with the triaxial compression tester. The diameters of the model piles 2 in the two composite samples match the diameters of the circular pad 14 and the indenter on the upper portion of the triaxial compression tester. Figure 8 and Figure 9 As shown, the steps for installing the combined specimen in the loading test are as follows: first, press the push plate release button 18 and the lowering button 19 to increase the internal spacing, then remove the upper pressure plate 10, and evenly apply vaseline on the surfaces of the four push plates 15 provided with the triaxial compression testing machine; place the combined specimen on the chassis 12 provided with the triaxial compression testing machine through the lower square pad 16, press the push plate tightening button 18 to fix the combined specimen in the center of the chassis 12, and stop pushing when the pressure gauge pointers on the four push plates 15 of the combined specimen all show a slight float; finally, place the upper circular pad 14 on the upper part of the model pile 2 of the combined specimen, install the pressure plate 10 and press the lifting button 19 to control the horizontal hydraulic device 11 of the triaxial compression testing machine to rise synchronously with the chassis 12, and stop pressing the lifting button 19 when the pressure gauge pointer on the pressure plate 10 shows a slight float.

[0046] The embodiment provides a test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and damage. The specific construction steps are as follows:

[0047] (1) Prepare the sample mold 6: The mold 6 is made of a transparent plate and a steel frame. A push block 9 is provided at the bottom of the mold 6 and a top cover 7 is provided at the top. A push hole is provided on the bottom plate of the mold 6 and a construction hole 700 is provided on the top cover. The diameter of the construction hole 700 matches the pile diameter of the model pile 2. After the mold 6 is assembled, vaseline is coated on the inner wall of the transparent plate of the mold 6. A horizontal compaction line 600 of the soft and hard interlayer bedrock is drawn on the side of the transparent plate of the mold 6 according to the thickness of each hard rock layer and soft rock layer. Then, a horizontal compaction line 601 of the soil layer is drawn according to the thickness of the soil layer 3. Finally, a horizontal excavation dotted line 602 is drawn on the upper part of the transparent plate of the mold 6 according to the length of the model pile 2. The horizontal excavation dotted line 602 is lower than the height of the horizontal compaction line 601 of the soil layer.

[0048] (2) Prepare sample materials, including hard rock layer, soft rock layer and soil layer materials: select intact rock as the preparation material of hard rock layer, conduct ultrasonic inspection on the rock material to ensure its integrity and homogeneity, and then cut it into rock plates and rock blocks 4 of specific sizes for preparing combined sample A simulating soft and hard interbedded bedrock 1 and comparative combined sample B simulating hard bedrock. The thickness of the rock plate matches the height between the horizontal compaction lines 600 of two adjacent soft and hard interbedded bedrocks, the thickness of the rock block 4 is equal to the height of the horizontal compaction line 600 of the uppermost soft and hard interbedded bedrock, and the cross-sectional size of the rock plate and rock block 4 matches the size of the loading test equipment; the soft rock layer material is made of coarse sand, medium sand, bentonite, double fly ash and water in a mass ratio of 6:6:2:1:1.5, and the density of the soft rock layer is 2.0-2.2 g / cm 3 The soil layer 3 is made of coarse sand, medium sand, bentonite, double fly ash and water in a mass ratio of 20:5:3:2:3, and the soil density is 1.0~1.2g / cm 3 .

[0049] (3) Prepare the combined sample A. Use the sample mold 6 in step (1) and the rock plate, soft rock layer and soil layer materials in step (2) to prepare the combined sample A. The specific process is as follows: Figure 3 As shown:

[0050] a. First, a rock slab is laid in the mold 6 as the hard rock layer. The thickness of the rock slab is consistent with the horizontal compaction line 600 of the first soft and hard interbedded bedrock layer. Then, the mass of the soft rock material required for this layer is calculated based on the density of the prepared soft rock material and the volume between the horizontal compaction line 600 of the second soft and hard interbedded bedrock layer and the horizontal compaction line 600 of the first soft and hard interbedded bedrock layer. The corresponding mass of soft rock material is laid in the mold 6 and compacted to form the soft rock layer. By completing these steps alternately, the soft and hard interbedded bedrock layer 1 can be produced.

[0051] b. Calculate the mass of the required soil material based on the density of the soil layer 3 and the volume between the uppermost soft and hard interbedrock horizontal compaction line 600 and the soil layer horizontal compaction line 601, and compact the corresponding mass of soil material to the soil layer horizontal compaction line 601 above the horizontal excavation dotted line 602 to prepare the soil layer 3;

[0052] c. After covering the top cover with holes 7, drilling operations are carried out from the construction hole 700 of the top cover 7. After the hole is formed, the wire cage 8 made of wire is placed into the hole and cement mortar is injected to prepare the model pile 2;

[0053] d. When the cement mortar solidifies to 50% of the design strength, remove the top cover 7, excavate the soil layer 3 to the horizontal excavation dotted line 602, push the push block 9 through the push hole on the bottom plate of the mold 6, and then push out the prepared composite sample A in the mold 6 for curing;

[0054] (4) Prepare a comparative composite sample B, using the sample mold 6 in step (1) and the rock block 4 and soil material in step (2) to prepare the composite sample B. The specific process is as follows: Figure 6 As shown:

[0055] a first laid in the mold 6 a piece of rock 4 of the corresponding size, the height of the rock 4 and the mold 6 uppermost soft and hard interbedrock horizontal compaction line 600 height consistent;

[0056] b. Then, the mass of the required soil material is calculated based on the density of the soil layer 3 and the volume between the uppermost soft and hard interbedrock horizontal compaction line 600 and the soil layer horizontal compaction line 601. The corresponding mass of soil material is compacted to a level above the horizontal excavation dotted line 602 to prepare the soil layer 3;

[0057] c. After covering the top cover with holes 7, drilling operations are carried out from the construction hole 700 of the top cover 7. After the hole is formed, the wire cage 8 made of wire is placed into the hole and cement mortar is injected to prepare the model pile 2;

[0058] d. When the cement mortar solidifies to 50% of the design strength, remove the top cover 7, excavate the soil layer 3 to the horizontal excavation dotted line 602, push the push block 9 through the push hole on the bottom plate of the mold 7, and then push out the comparison composite sample B prepared in the mold 6 for curing;

[0059] (5) Loading tests are performed on the model pile 2 inside the combined sample A prepared in step (3) and the comparative combined sample B prepared in step (4), respectively, and the loading method adopts step-by-step loading using a triaxial compression testing machine; based on the obtained test data, the axial stress-axial displacement relationship curve of the model pile 2 in the combined sample A simulating the soft and hard interlayer bedrock 1 and the axial stress-axial displacement relationship curve of the model pile 2 in the comparative combined sample B simulating the hard layer bedrock are respectively drawn, and the two groups of test curves are drawn in the same coordinate system to obtain a comparative curve diagram of the two groups of tests, and the relationship between the influence of the simulated soft and hard interlayer bedrock 1 on the model pile and the influence of the simulated hard layer bedrock on the model pile is observed as a theoretical basis for the optimal design of the pile length in the soft and hard interlayer bedrock 1. For the convenience of recording, the triaxial compression testing machine can be communicatively connected to the computer 20. The axial stress of the model pile 2 in the combined specimen is measured by the indenter on the pressure plate 10 of the triaxial compression testing machine and recorded in the computer 20. The axial displacement of the model pile 2 in the combined specimen is the vertical distance that the horizontal hydraulic device 11 and the chassis 12 are synchronously lifted, and is recorded by the computer 20.

[0060] The composite sample A and the comparative composite sample B described in the above embodiment were prepared in two groups respectively; the preparation method of the two groups of samples was the same. The first group of composite sample A and the comparative composite sample B were placed in a triaxial test compressor and loaded directly to failure, and the peak stress σ of composite sample A was obtained. c1 Compared with the peak stress σ of the combined sample B c2 Then, based on the first set of test data, the increment of each load level in the step-by-step loading test of the second set of combined specimens A and the comparison combined specimens B is determined to be 0.1σ respectively. c1 and 0.1σ c2 The pressure stabilization time for each level is 2 hours, and the loading rate is controlled by controlling the axial displacement at a rate of 0.12 mm / min. Both the direct loading test and the step-by-step loading test are performed by controlling the synchronous lifting rate of the horizontal hydraulic device 11 and the chassis 12 of the triaxial compression testing machine. During the direct loading and step-by-step loading tests, the push plate 15 of the triaxial compression testing machine is used to limit the lateral deformation of the composite specimen and does not apply any force. The step-by-step loading process is achieved by controlling the synchronous lifting of the horizontal hydraulic device 11 with the push plate 15 and the chassis 12 by a computer 20, achieving stress control while also limiting the lateral deformation of the composite specimen.

[0061] The above description illustrates the principles and advantages of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure, characterized in that The specific steps are as follows: (1) Prepare the sample mold: the mold is made of a transparent plate and a steel frame, with a push block at the bottom and a top cover at the top. The bottom plate of the mold is provided with a push hole, and the top cover is provided with a construction hole. The diameter of the construction hole matches the diameter of the model pile. After the mold is assembled, vaseline is coated on the inner wall of the transparent plate of the mold. The horizontal compaction line of the soft and hard interlayer bedrock is drawn on the side of the transparent plate of the mold according to the thickness of each hard rock layer and soft rock layer. The horizontal compaction line of the soil layer is then drawn according to the thickness of the soil layer. Finally, a horizontal excavation dotted line is drawn on the upper part of the transparent plate of the mold according to the length of the model pile, and the horizontal excavation dotted line is lower than the height of the horizontal compaction line of the soil layer. (2) Prepare sample materials, including hard rock layer, soft rock layer and soil layer materials: the hard rock layer is cut from intact rock, and the intact rock is cut into rock plates for preparing combined sample A for simulating soft and hard interbedded bedrock and rock blocks for preparing comparative combined sample B for simulating hard layer bedrock; the thickness of the rock plates matches the height between the horizontal compaction lines of two adjacent soft and hard interbedded bedrocks, the thickness of the rock blocks is equal to the height of the horizontal compaction line of the uppermost soft and hard interbedded bedrock, and the cross-sectional sizes of the rock plates and rock blocks match the size of the loading test equipment; the soft rock layer materials and soil layer materials are both prepared from coarse sand, medium sand, bentonite, double fly ash and water; wherein, the soft rock layer materials are prepared from coarse sand, medium sand, bentonite, double fly ash and water in a mass ratio of 6:6:2:1:1.5, and the density of the soft rock layer is 2.0~2.2g / cm 3 The soil layer is made of coarse sand, medium sand, bentonite, double fly ash and water in a mass ratio of 20:5:3:2:3, and the soil density is 1.0~1.2g / cm 3 ; (3) Prepare the composite sample A. Use the sample mold in step (1) and the rock plate, soft rock layer and soil layer materials in step (2) to prepare the composite sample A. The specific process is as follows: a. First, a rock plate is laid in the mold as the hard rock layer, and the thickness of the rock plate is consistent with the horizontal compaction line of the first layer of soft and hard interbedded bedrock. Then, the soft rock layer material prepared in step (2) is laid and compacted to the horizontal compaction line of the second layer of soft and hard interbedded bedrock as the soft rock layer. The soft and hard interbedded bedrock can be made by alternating the steps. b. Continue to lay the soil material prepared in step (2) into the mold and compact it to the horizontal compaction line of the soil layer; c. Then, cover the top cover with holes, drill holes from the construction holes of the top cover, place wire cages made of wire into the holes, and inject cement mortar to prepare model piles; d. When the cement mortar solidifies to 50% of the design strength, remove the top cover, excavate the soil layer to the horizontal excavation dotted line, push the push block through the push hole on the mold bottom plate, and then push out the prepared composite sample A in the mold for curing; (4) Prepare the comparative composite sample B. Use the sample mold in step (1) and the rock and soil materials in step (2) to prepare the composite sample B. The specific process is as follows: a. First, place a rock block of appropriate size in the mold. The height of the rock block should be consistent with the horizontal compaction line of the uppermost soft and hard interbedded bedrock in the mold. b. Then lay the soil material prepared in step (2) into the mold and compact it to the horizontal compaction line of the soil layer; c. Then, cover the top cover with holes, drill holes from the construction holes of the top cover, place wire cages made of wire into the holes, and inject cement mortar to prepare model piles; d. When the cement mortar solidifies to 50% of the design strength, remove the top cover, excavate the soil layer to the horizontal excavation dotted line, push the push block through the push hole on the mold bottom plate, and then push out the comparison composite sample B prepared in the mold for curing; (5) Loading tests are performed on the model piles in the combined sample A prepared in step (3) and the comparative combined sample B prepared in step (4), respectively, and the loading method is step-by-step loading; based on the obtained test data, the axial stress-axial displacement relationship curve of the model pile in the combined sample A simulating the soft and hard interbedded bedrock and the axial stress-axial displacement relationship curve of the model pile in the comparative combined sample B simulating the hard bedrock are respectively drawn, and the two groups of test curves are drawn in the same coordinate system to obtain a comparison curve diagram of the two groups of tests, and the comparison curve diagram is used as the theoretical basis for the optimization design of pile length in the soft and hard interbedded bedrock.

2. The test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 1, characterized in that: The composite sample A and the comparative composite sample B were prepared in two groups respectively; the first group of composite sample A and the comparative composite sample B were placed in a triaxial test compressor and loaded directly to failure, and the peak stress of composite sample A was obtained. Peak stress of comparison sample B Then, based on the first set of test data, the increments of each level of load in the step-by-step loading test of the second set of combined specimens A and the comparison combined specimens B are determined to be and The pressure stabilization time for each level is 2h, and the loading rate is controlled by controlling the axial displacement at a rate of 0.12mm / min.

3. A test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 1 or 2, characterized in that: The mold in step (1) is a rectangular mold, which is made of four rectangular transparent acrylic plates, a square steel base plate and four angle steels. A push hole is provided in the middle of the square steel base plate of the mold. The transparent acrylic plate is the side wall of the mold and is fixed by the angle steel. There are multiple horizontal compaction lines of the soft and hard interlayer bedrock, all of which are solid lines, and the spacing between the multiple horizontal compaction lines of the soft and hard interlayer bedrock is equal. The uppermost horizontal compaction line of the soft and hard interlayer bedrock is located in the middle of the mold, and the height of the uppermost horizontal compaction line of the soft and hard interlayer bedrock matches the thickness of the simulated soft and hard interlayer bedrock.

4. A test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 1 or 2, characterized in that: In step (2), the rock with intact surface is subjected to an acoustic inspection to ensure its integrity and homogeneity, and then cut into rock slabs and rock blocks of specific sizes for use in the combined sample A and the comparative combined sample B, respectively.

5. A test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 1 or 2, characterized in that: The laying of the soft rock layer in step (3) is based on the density of the prepared soft rock layer material and the volume between the horizontal compaction lines of the two adjacent soft and hard interlayer bedrocks to calculate the mass of the material required for the soft rock layer, and the corresponding mass of the soft rock layer material is laid in the mold and compacted as the soft rock layer; the soil layer in steps (3) and (4) is based on the density of the soil layer and the volume between the horizontal compaction line of the uppermost soft and hard interlayer bedrock and the horizontal compaction line of the soil layer to calculate the mass of the required soil layer material, and the corresponding mass of the soil layer material is compacted to the horizontal compaction line of the soil layer above the horizontal excavation dotted line.

6. The test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 2, wherein: In the step (5), the model piles of the combined specimens are loaded using a triaxial compression testing machine. The combined specimen A and the comparison combined specimen B are of the same size, and the side dimensions of the two combined specimens match the dimensions of the push plates provided with the triaxial compression testing machine. The diameters of the model piles in the two combined specimens match the diameters of the circular pads and the indenter on the upper portion of the triaxial compression testing machine.

7. The test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 6, characterized in that: The steps for installing the combined specimen in the loading test in step (5) are as follows: first, press the push plate release button and the lowering button to increase the internal spacing, then remove the upper pressure plate, and evenly apply vaseline on the surfaces of the four horizontal push plates of the triaxial compression testing machine; place the combined specimen on the chassis of the triaxial compression testing machine through the lower square pad, press the push plate tightening button to fix the specimen in the center of the chassis, and stop pushing when the pointers of the pressure gauges on the four horizontal push plates of the combined specimen all show a slight float; finally, place the upper circular pad on the upper part of the model pile of the combined specimen, install the pressure plate and press the lifting button to control the horizontal hydraulic device of the triaxial compression testing machine to rise synchronously with the chassis, and stop pressing the lifting button when the pointer of the pressure gauge on the pressure plate shows a slight float.

8. The test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 6, characterized in that: The axial stress of the model pile in the combined specimen is measured by the pressure head on the pressure plate of the triaxial compression testing machine and recorded in a computer; the axial displacement of the model pile in the combined specimen is the vertical distance that the horizontal hydraulic device and the chassis are lifted synchronously, and is recorded by a computer.

9. The test method for simulating the effect of soft and hard interbedded bedrock on pile foundation deformation and failure according to claim 6, characterized in that: Both the direct loading test and the step-by-step loading test are achieved by controlling the synchronous lifting rate of the horizontal hydraulic device and the base plate of the triaxial compression testing machine; during the direct loading and step-by-step loading tests, the push plate of the triaxial compression testing machine is used to limit the lateral deformation of the combined specimen and does not apply force; the step-by-step loading process is achieved by computer-controlled synchronous rising of the horizontal hydraulic device with the push plate and the base plate, thereby achieving stress control while limiting the lateral deformation of the combined specimen.

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