Model pile manufacturing, testing and monitoring method for seismic liquefaction model test

Abstract

The invention discloses a method for manufacturing, testing and monitoring a model pile for an earthquake liquefaction model test. The method comprises the steps of material selection and matching of simulated concrete, material selection and matching of simulated steel and mold design. The method is characterized in that cement soil is selected as the material of the simulated concrete, nylon wires are selected as the material of the simulated steel, and a viscous binder is adopted for bonding between the nylon wires and the cement soil. The invention completely provides a whole set of scheme of the model pile for the earthquake liquefaction model test, and according to the device and the method provided by the invention, the technical requirement is low; the obtained model pile can be used for the anti-liquefaction earthquake vibration table test of the model pile, and basically meets the requirements of a reduced scale model on the concrete strength, the elastic modulus and the bending strength of the model pile.

Description

Technical Field

[0001] The invention relates to the technical field of earthquake liquefaction model test, and in particular to a method for making, testing and monitoring a pile model used in an earthquake liquefaction model test. Background Art

[0002] Liquefaction of sandy soil is one of the most common earthquake disasters. During an earthquake, due to the dynamic effect of seismic waves, the saturated sandy soil and silt buried deep below the groundwater level tend to become dense due to mutual shearing, and the pore water cannot be discharged in time, resulting in excess pore water pressure, which reduces the effective stress of the soil particles and eventually puts them in a suspended state, presenting a liquid state (liquefaction of sandy soil). At this time, the soil completely loses its shear strength.

[0003] Pile foundation is one of the most commonly used foundation structures in my country's foundation engineering. It is widely used to reinforce soft sites to support superstructures including high-rise buildings, urban viaducts, and offshore platforms. Therefore, it is necessary to study the anti-liquefaction effect of pile foundations and test the deformation and damage of pile foundations under sand liquefaction conditions. Simulated earthquake shaking table tests can be used to study the anti-liquefaction effect of pile foundations.

[0004] The basic principle of the simulated earthquake shaking table test is to apply vibration to the scaled model according to the Bukingham-π theorem, and to evaluate the seismic performance of the model and prototype by measuring the response caused by the vibration. The reinforced concrete pile foundation model commonly used in the experiment is made of plexiglass, PVC, metal or steel wire (micro) concrete. With such a simulation method, it is difficult for the model size, elastic modulus, bending moment, etc. to simultaneously meet the Bukingham-π theorem; for example, even if the deformation meets the requirements, the damage of the pile foundation will not be observed during the test, so the damage of the superstructure after the pile foundation is damaged cannot be observed. In the previous research of this team, gypsum was used as a bonding material to make a pile foundation model for model testing under dry conditions. However, gypsum has the phenomenon of dissolving in water, which makes its mechanical properties unstable under saturated conditions, so it is not suitable for shaking table tests to study the liquefaction of sand layers. Summary of the invention

[0005] The purpose of the present invention is to meet the requirements of earthquake liquefaction model test on the mechanical properties of pile models, to manufacture model piles with target bending strength using cement soil + nylon wire as basic materials, and to refine and analyze the mechanical properties of the model piles through bending strength measurement and monitoring means.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a method for making a model pile for an earthquake liquefaction model test, which includes material selection for simulating concrete, material selection for simulating steel and mold design; the characteristic is that the material selection for simulating concrete is cement soil, the strength of which is estimated according to an empirical formula and is made to meet the requirements of the earthquake liquefaction model test; the material selection for simulating steel is nylon wire, the diameter of the nylon wire is determined according to the bending calculation and bending test results, and is made to meet the requirements of the earthquake liquefaction model test; a viscous adhesive is used to bond the nylon wire and the cement soil; the model pile is made by using a split mold and pre-applying tensile stress to the nylon wire.

[0007] The strength of the cement soil is estimated according to an empirical formula and is made to meet the requirements of the earthquake liquefaction model test. The curing time and water-cement ratio of the simulated material of the concrete are determined according to the similarity ratio required by the earthquake liquefaction model test using formulas (1)-(4): The concrete strength similarity ratio corresponding to the present invention can reach the order of 1 / 100. The empirical formulas for the strength of cement soil at different ages are as follows:

[0008] q u28 =(1.59~2.13)q u7 (1)

[0009] q u90 =(1.43~1.8)q u28 (2)

[0010] Where: q u Represents the unconfined compressive strength of cement soil, and the subscript number represents the age of the cement soil specimen. Using 42.5 grade ordinary Portland cement, under the conditions of cement paste water-cement ratio of 0.5, clay water content of 40%, and 7 days of curing, the empirical formula for cement soil strength corresponding to different cement addition amounts C (%) is as follows:

[0011] q u =75+20×C+0.3×C 2 (3)

[0012] Where: q u Unit: kPa. The empirical formula for cement soil strength corresponding to different water-cement ratios is as follows:

[0013]

[0014] Where: q u Unit is kPa; A and B are constants, which need to be determined based on the specific experimental soil; w is the water content of cement soil; C is the amount of cement added. Figure 4 Data, under the condition of 7-day maintenance, A=1627; B=1.28;

[0015] The present invention also provides a method for manufacturing a model pile for an earthquake liquefaction model test, characterized in that the model pile adopts a split mold and tensile stress is pre-applied to the nylon line.

[0016] The present invention also provides a method for testing the bending performance of a model pile used in an earthquake liquefaction model test, which is characterized by comprising the manufacture and use of bending test equipment, and the bending strength of the model pile is estimated by the bending test.

[0017] The bending test estimation adopts formula (6):

[0018]

[0019] Where: M cr is the bending moment when the model pile reaches the failure state; E is the elastic modulus of cement soil; α E is the ratio of the elastic modulus of nylon to the elastic modulus of cement soil; ε cr is the strain value of cement soil reaching the crushing state, and it is recommended to take 0.015; D is the diameter of the model pile; d is the diameter of the nylon wire; k M is a correction factor used to correct the change in bending strength caused by the neutral axis deviating from the geometric center of the cross section during failure. It is recommended to take 2.0. The elastic modulus E of the cement soil can be estimated using formula (5):

[0020] E=K·q u (5)

[0021] Where: K is a constant, and it is recommended to be 150; since the K of the prototype concrete is usually 500-1000, under the condition of satisfying the strength similarity ratio, the simulated concrete of the present invention can only approximately satisfy the elastic modulus similarity ratio in terms of magnitude. The simulated material of the concrete can have an elastic modulus similarity ratio of 1 / 100.

[0022] The present invention also provides a monitoring method for a model pile test process used in an earthquake liquefaction model test, which is characterized in that the actual deformation of the model pile is monitored in real time by means of a strain gauge, the strain gauge is a waterproof strain gauge, and the strain gauge is directly pasted on the surface of the model pile.

[0023] The nylon wire and the cement soil are bonded with a viscous adhesive, which may be HY-T160 transparent soft PE adhesive.

[0024] The strain gauge is a waterproof strain gauge, and can adopt a waterproof foil strain gauge of the Japanese Kyowa KFW series. The strain gauge can be directly pasted on the surface of the model pile.

[0025] The present invention provides a method for making, testing and monitoring model piles for earthquake liquefaction model tests, and completely proposes a complete set of solutions for model piles for earthquake liquefaction model tests. According to the device and method provided by the present invention, the technical requirements are low; the obtained model piles can be used for earthquake shaking table tests on the anti-liquefaction of model piles, and basically meet the requirements of the scaled model on three aspects: concrete strength, elastic modulus, and bending strength of the model piles.

[0026] The present improved method of the present invention is mainly embodied in:

[0027] 1) Cement soil can better simulate the properties of concrete in terms of strength and deformation in earthquake liquefaction shaking table tests. When cement soil is used to simulate concrete materials, the mechanical properties of cement soil will not change under saturated conditions. At the same time, by adjusting the water-cement ratio of cement soil and controlling the curing time, the strength of cement soil can be reduced to 1 / 100 of the strength of concrete. And the corresponding elastic modulus of cement soil can basically meet the requirements of similarity ratio.

[0028] 2) Nylon thread can be bonded to cement soil through a viscous agent, thereby forming a synchronous deformation of the nylon thread and cement soil.

[0029] 3) The model pile is made by using a mold, and the tensile material is arranged at the center of the cross section of the model pile, which has high production efficiency.

[0030] 4) Use bending test to control the manufacturing quality of model piles. In order to verify that the model piles have reached the expected quality, it is necessary to measure the bending strength. For this purpose, a bending test equipment with a total load of less than 5N and a corresponding loading method are designed.

[0031] 5) Waterproof strain gauges are used to monitor the deformation of model piles in earthquake liquefaction shaking table tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic diagram of a mold for making a model pile in Example 1;

[0033] Figure 2 Schematic diagram of a bending strength test device for a model pile according to an embodiment of the present invention;

[0034] Figure 3 It is a comparison chart of cement soil strength corresponding to different cement addition amounts;

[0035] Figure 4 It is a comparison chart of cement soil strength corresponding to different water-cement ratios.

[0036] Among them: pipe body 1, pipe segment 2, tape 3, hollow bolt 4, strong A-shaped clamp 5, nylon line 6, base 7, supporting round rod 8, positioning clamp 9, model pile 10, square hole 11, flexible rope 12, weight 13. DETAILED DESCRIPTION

[0037] The present invention will be further described below by way of examples and in conjunction with the accompanying drawings, with specific implementation details to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be implemented without one or more of these details. In other examples, some technical features known in the art are not described in order to avoid confusion with the present invention.

[0038] In order to fully understand the present invention, detailed steps and detailed structures will be proposed in the following description to illustrate the technical solution of the present invention. The preferred embodiments of the present invention are described in detail below, but in addition to these detailed descriptions, the present invention may also have other implementations.

[0039] Embodiment 1:

[0040] A method for making a model pile for an earthquake liquefaction model test, comprising material selection for simulating concrete, material selection for simulating steel and mold design; the characteristic is that the material selection for simulating concrete is cement soil, the strength of which is estimated according to an empirical formula and is made to meet the requirements of the earthquake liquefaction model test; the material selection for simulating steel is nylon wire, the diameter of which is determined according to bending calculation and bending test results and is made to meet the requirements of the earthquake liquefaction model test; a viscous adhesive is used to bond the nylon wire and the cement soil; the model pile is made by using a split mold and pre-applying tensile stress to the nylon wire.

[0041] The present invention also provides a method for testing the bending performance of a model pile for an earthquake liquefaction model test according to claim 1, comprising the manufacture and use of bending test equipment, wherein the bending strength of the model pile is estimated by a bending test.

[0042] The present invention also provides a monitoring method during a model pile test for an earthquake liquefaction model test according to claim 1, characterized in that the actual deformation of the model pile is monitored in real time by means of a strain gauge, the strain gauge is a waterproof strain gauge, and the strain gauge is directly pasted on the surface of the model pile.

[0043] The curing time and water-cement ratio of the concrete simulation material can be determined according to the similarity ratio required by the earthquake liquefaction model test using formulas (1)-(4). The concrete strength similarity ratio corresponding to the present invention can reach the order of 1 / 100.

[0044] The empirical formula for the strength of cement soil at different ages is as follows:

[0045] q u28 =(1.59~2.13)q u7 (1)

[0046] qu90 =(1.43~1.8)q u28 (2)

[0047] Where: q u represents the unconfined compressive strength of cement soil, and the subscript number represents the age of the cement soil specimen.

[0048] Under the condition of 7 days of curing, the empirical formula of cement soil strength corresponding to different cement addition amounts C (%) is as follows:

[0049] q u =75+20×C+0.3×C 2 (3)

[0050] Where: q u The unit is kPa. Formula (3) is based on Figure 3 of experimental data.

[0051] The empirical formula for cement soil strength corresponding to different water-cement ratios is as follows:

[0052]

[0053] Where: q u Unit is kPa; A and B are constants, which need to be determined based on the specific experimental soil; w is the water content of cement soil; C is the amount of cement added. Figure 4 Data, under the condition of 7-day maintenance, A=1627; B=1.28

[0054] This embodiment also provides a method for testing the bending performance of a model pile used in an earthquake liquefaction model test, which includes the manufacture and use of bending test equipment. The bending strength of the model pile is estimated by using the bending test.

[0055] The bending test estimation adopts formula (6):

[0056]

[0057] Where: M cr is the bending moment when the model pile reaches the failure state; E is the elastic modulus of cement soil; α E is the ratio of the elastic modulus of nylon to the elastic modulus of cement soil; ε cr is the strain of cement soil reaching the crushing state, and it is recommended to be 0.015; D is the diameter of the model pile; d is the diameter of the nylon wire; k M is a correction factor used to correct the change in bending strength caused by the neutral axis deviating from the geometric center of the cross section during failure. It is recommended to take 2.0. Due to differences in parameters such as clay material, water content, and cement soil density, E and ε cr , k MThere may be a large difference between the estimated value and the actual value of parameters such as , so it is necessary to conduct a bending test. It is recommended to adopt the three-point bending solution proposed in the present invention. In addition, formula (6) is the M proposed in the present invention cr Calculation method. The right side of formula (6), divided by k M The rest of the equations are derived from mechanical theory. M The value of 2 is based on the three-point bending test results of the model pile. In this test, the model pile parameters are: D = 1 cm, d = 1 mm, α E =40, E = 70 MPa, ε cr =0.015. The corresponding M cr is 0.2N·m. By reverse calculation, we can get k M Approximately equal to 2.

[0058] The elastic modulus similarity ratio of the concrete simulation material can reach the order of 1 / 100. The elastic modulus E of the simulation material can be estimated using formula (5):

[0059] E=K·q u (5)

[0060] Wherein: E is the elastic modulus of the simulated material (cement soil); K is a constant, which is recommended to be 150. Since the K of the prototype concrete is usually 500-1000, under the condition of satisfying the strength similarity ratio, the simulated concrete of the present invention can only approximately satisfy the elastic modulus similarity ratio in terms of magnitude.

[0061] It is recommended that nylon wire be used as the simulation material for the steel bars. The diameter of the nylon wire can be determined based on the above-mentioned bending calculation and bending test results to meet the requirements of the earthquake liquefaction model test on bending strength.

[0062] The nylon wire and the cement soil are bonded with a viscous adhesive, and it is recommended to use the HY-T160 transparent soft PE adhesive.

[0063] The strain gauge is a waterproof strain gauge. It is recommended to use the Japanese Kyowa KFW series waterproof foil strain gauge. The strain gauge can be directly pasted on the surface of the model pile.

[0064] This embodiment provides a model pile mold, such as Figure 1 As shown, the mold includes a tube body 1, the recommended material is plexiglass, a tube segment 2, the recommended material is plexiglass, a tape 3, two hollow bolts 4, and two strong A-shaped clamps 5, wherein the tube body 1 and the hollow bolts 4 are connected by threads; the tube body 1 is an incomplete tube body, and the tube body 1 and the tube segment 2 together form a complete tube body; the length of the tube segment 2 should be greater than the length of the model pile (for example, 1.2 times the length of the model pile); the diameter of the hole of the hollow spiral should be greater than the diameter of the nylon line 6 (for example, 1.2 times the diameter of the nylon line 6).

[0065] The process of making model piles using molds is briefly described as follows:

[0066] 1) Refer to the "Concrete Structure Design Standard" (GB / T50010-2010) and other specifications to estimate the nylon wire diameter required for the model pile.

[0067] 2) Assemble the mold. Screw two hollow bolts 4 into the two ends of the pipe body 1; insert the nylon wire 6 into the two hollow bolts 4; clamp the nylon wire 6 with a strong A-shaped clamp 5 close to the hollow bolts 4; twist the hollow bolts 4 to a proper distance and tighten the nylon wire 6 appropriately. Apply a proper amount of tung oil on the inner side of the pipe body 1 and the pipe segment 2. Place the pipe body 1 horizontally.

[0068] 3) According to formulas 1) and 2), considering the requirements for the strength and elastic modulus of the model pile, select the appropriate water-cement ratio and curing time to prepare the cement soil slurry.

[0069] 4) Fill the cement soil slurry in 3) above evenly into the mold assembled in 2) above, filling it to about 50% of the volume of the tube.

[0070] 5) Apply the adhesive evenly on the nylon thread.

[0071] 6) Continue to evenly fill the cement soil slurry in 3) above into the mold assembled in 2) above. Appropriately trim the slurry so that after the pipe segment 2 is closed, the cement soil slurry fills the cavity formed by the pipe body 1 and the pipe segment 2.

[0072] 7) Use adhesive tape 3 to fix the pipe body 1 and the pipe segment 2. The pipe segment 2 can be removed after the cement soil slurry is solidified.

[0073] 8) Maintenance.

[0074] Embodiment 2:

[0075] This embodiment provides a bending resistance test device, such as Figure 2 As shown, this experiment is actually a special bending test that ignores the influence of shear force. The recommended experimental scheme is shown in the following specific implementation method:

[0076] The device comprises a base 7, which is preferably made of stainless steel, two supporting round rods 8, which are preferably made of stainless steel, four positioning clips 9, a flexible rope 12, which is preferably made of hemp, and two weights 13. The base 7 has a square hole 11; the round rod 8 is fixed on the base 7.

[0077] The experimental process using the bending test device is briefly described as follows:

[0078] 1) Use a marker pen to make three marks on the model pile 10, namely two support rod position marks and one flexible rope position mark.

[0079] 2) Tie the flexible rope 12 to the model pile 10 and adjust the position of the flexible rope 12 to the marked position.

[0080] 3) Place the base 7 horizontally.

[0081] 4) Place the model pile 10 on the two supporting round rods 8 and adjust the contact point position to the marked position.

[0082] 5) Hang the first weight on the flexible rope 12. Hang weight 13 on the previous weight in sequence. Suggestion: The mass of each small weight is 10g; if the number of small weights hung is more than 10, remove the small weight and replace it with a large weight of appropriate mass.

[0083] 6) Increase the total mass of the hanging weights until the model pile 10 is destroyed.

[0084] The above describes the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and the devices and structures that are not described in detail should be understood to be implemented in a common manner in the art; any technician familiar with the art can use the above-disclosed methods and technical contents to make many possible changes and modifications to the technical solutions of the present invention without departing from the scope of the technical solutions of the present invention, or modify them into equivalent embodiments of equivalent changes, which does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention are still within the scope of protection of the technical solutions of the present invention.

Claims

1. A method for making a model pile for earthquake liquefaction model test, comprising selecting materials for simulating concrete, selecting materials for simulating steel and designing a mold; characterized in that The material selection for the simulated concrete is cement soil, and the strength of the cement soil is estimated according to an empirical formula and is made to meet the requirements of the earthquake liquefaction model test; the material selection for the simulated steel is nylon wire, and the diameter of the nylon wire is determined according to the bending test calculation and bending test results to meet the requirements of the earthquake liquefaction model test; the bonding between the nylon wire and the cement soil adopts a viscous adhesive; the strength of the cement soil is estimated according to an empirical formula and is made to meet the requirements of the earthquake liquefaction model test. The curing time and water-cement ratio of the simulated material of the concrete are determined according to the similarity ratio required by the earthquake liquefaction model test using formulas (1)-(4): The empirical formulas for the strength of cement soil at different ages are as follows: q u28 =(1.59~2.13)q u7 (1) q u90 =(1.43~1.8)q u28 (2) Where: q u represents the unconfined compressive strength of cement soil, and the subscript number represents the age of the cement soil specimen. Under the condition of 7 days of curing, the empirical formula for the strength of cement soil corresponding to different cement addition amounts C (%) is as follows: u =75+20×C+0.3×C 2 (3) Where: q u Unit: kPa. The empirical formula for cement soil strength corresponding to different water-cement ratios is as follows: Where: q u The unit is kPa; A and B are constants, and their values ​​need to be obtained through experiments based on the specific experimental soil; w is the water content of cement soil; C is the amount of cement added.

2. A method for making a model pile for earthquake liquefaction model test according to claim 1, characterized in that: The model pile adopts a split mold and pre-applies tensile stress to the nylon line.

3. A method for testing the bending performance of a model pile for earthquake liquefaction model test according to claim 1, characterized in that Including the production and use of bending test equipment, the bending strength of the model pile is estimated by bending test; the bending test estimation adopts formula (6): Where: M cr is the bending moment when the model pile reaches the failure state; E is the elastic modulus of cement soil; α E is the ratio of the elastic modulus of nylon to the elastic modulus of cement soil; ε cr is the strain value of cement soil reaching the crushing state; D is the diameter of the model pile; d is the diameter of the nylon wire; k M is a correction factor used to correct the change in bending strength caused by the neutral axis deviating from the geometric center of the cross section during failure; the elastic modulus of cement soil E can be estimated using formula (5): E=K·q u (5) Where: K is a constant.

4. A monitoring method during a model pile test for an earthquake liquefaction model test according to claim 1, characterized in that The actual deformation of the model pile is monitored in real time by means of strain gauges. The strain gauges are waterproof strain gauges and are directly attached to the surface of the model pile.

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