A method for manufacturing, testing and monitoring model piles for seismic liquefaction model tests

Abstract

The application discloses a model pile production, testing and monitoring method for a seismic liquefaction model test, which comprises material selection for simulating concrete, material selection for simulating steel and mold design; the material selection for simulating concrete is to select cement soil, the material selection for simulating steel is to select nylon wire, and the adhesion between the nylon wire and the cement soil adopts viscous adhesive. The application completely provides a complete scheme of the model pile for the seismic liquefaction model test; according to the device and the method, the technical requirement is low; the obtained model pile can be used for the seismic shaking table test of the model pile against liquefaction, and basically meets the requirements of the scale model on the concrete strength, the elastic modulus, the model pile bending strength and the like.

Description

Technical Field

[0001] This invention relates to the field of earthquake liquefaction model testing technology, and in particular to a method for fabricating, testing and monitoring a pile model used in earthquake liquefaction model testing. Background Technology

[0002] Liquefaction of sandy soil layers is one of the most common earthquake hazards. During an earthquake, due to the dynamic action of seismic waves, saturated sandy soil and silt buried below the groundwater level tend to become denser due to shearing between soil particles. Pore water cannot be discharged in time, resulting in excess pore water pressure. This reduces the effective stress of the soil particles, eventually causing them to be suspended and liquid (liquefaction of sandy soil layers). At this point, the soil completely loses its shear strength.

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

[0004] The basic principle of simulated earthquake shaking table tests is based on the Bukingham-π theorem. Vibration is applied to a scaled-down model, and the seismic performance of the model and prototype is evaluated by measuring the response to the vibration. Reinforced concrete pile foundation models commonly used in experiments are made of materials such as plexiglass, PVC, metal, or wire (micro)concrete. However, with this simulation method, it is difficult for the model dimensions, elastic modulus, and bending moment to simultaneously satisfy the Bukingham-π theorem. For example, even if the deformation meets the requirements, pile foundation failure will not be observed during the test, thus making it impossible to observe the damage to the superstructure after pile foundation failure. In our team's previous research, gypsum was used as a bonding material to fabricate pile foundation models for model tests under dry conditions. However, gypsum dissolves in water, leading to unstable mechanical properties under saturated conditions, making it unsuitable for shaking table tests studying sand liquefaction. Summary of the Invention

[0005] The purpose of this invention is to meet the requirements of earthquake liquefaction model tests on the mechanical properties of pile models. A model pile with target bending strength is made using cement-soil + nylon thread as the basic material, and the mechanical properties of the model pile are analyzed in detail through bending strength measurement and monitoring.

[0006] To achieve the above objectives, the present invention provides a method for fabricating a model pile for earthquake liquefaction model testing. This method includes material selection for simulated concrete, material selection for simulated steel, and mold design. The simulated concrete material selection uses cement-soil, the strength of which is estimated based on empirical formulas to meet the requirements of earthquake liquefaction model testing. The simulated steel material selection uses nylon thread, the diameter of which is determined based on bending calculations and bending test results to meet the requirements of earthquake liquefaction model testing. A viscous adhesive is used to bond the nylon thread to the cement-soil. The model pile is fabricated using a split mold and a method of pre-applying tensile stress to the nylon thread.

[0007] The strength of the cement-soil is estimated based on empirical formulas and made to meet the requirements of the earthquake liquefaction model test. The curing time and water-cement ratio of the simulated concrete are used. According to the similarity ratio required by the earthquake liquefaction model test, the similarity ratio of the concrete strength corresponding to this invention can reach the order of 1 / 100. The empirical formulas for the strength of cement-soil at different ages are as follows:

[0008] =(1.59~2.13) (1)

[0009] = (1.43~1.8) (2)

[0010] In the formula: The values ​​represent the unconfined compressive strength of cement-soil, with the subscripts indicating the age of the cement-soil specimen. Using 42.5 grade ordinary Portland cement, under conditions of a cement paste water-cement ratio of 0.5, clay moisture content of 40%, and 7 days of curing, the empirical formulas for cement-soil strength corresponding to different cement admixture amounts C (%) are as follows:

[0011] qu=75+20×C+0.3×C 2 (3)

[0012] In the formula: q u The unit is kPa. The empirical formulas for the strength of cement-soil corresponding to different water-cement ratios are as follows:

[0013] (4)

[0014] In the formula: q u The unit is kPa; A and B are constants, which need to be determined experimentally based on specific soil samples; w is the water content of the cement-soil mixture; C is the amount of cement added. According to... Figure 4 Based on the data, assuming a 7-day maintenance period, A = 1627; B = 1.28;

[0015] The present invention also provides a method for manufacturing model piles for earthquake liquefaction model tests, characterized in that the model piles are made using split molds and tensile stress is pre-applied to the nylon thread.

[0016] The present invention also provides a method for testing the bending performance of a model pile for earthquake liquefaction model tests, characterized by including the fabrication and use of bending test equipment, and the bending strength of the model pile being estimated by bending test.

[0017] The bending test estimation is performed using formula (6):

[0018] (6)

[0019] In the formula: Mcr is the bending moment at which the model pile reaches the failure state; E is the elastic modulus of the cement-soil mixture; α E ε is the ratio of the elastic modulus of nylon to the elastic modulus of cement-soil; cr The strain value for cement-soil reaching a crushed state is recommended to be 0.015; D is the diameter of the model pile; d is the diameter of the nylon thread; k M The correction factor is used to correct for the change in flexural strength caused by the neutral axis deviating from the geometric center of the section at 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] In the formula: K is a constant, and it is recommended to take it as 150; since K of the prototype concrete is usually 500 to 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 on the order of magnitude. The simulated concrete material has an elastic modulus similarity ratio on the order of 1 / 100.

[0022] The present invention also provides a monitoring method for model piles used in earthquake liquefaction model tests, 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 the strain gauges are directly pasted on the surface of the model pile.

[0023] The bonding between the nylon thread and the cement soil is achieved using a viscous adhesive, such as HY-T160 transparent soft PE adhesive.

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

[0025] This invention provides a method for fabricating, testing, and monitoring model piles for earthquake liquefaction model tests. It presents a complete solution for model piles used in earthquake liquefaction model tests. According to the device and method provided by this invention, the technical requirements are low. The obtained model piles can be used for earthquake shaking table tests on model piles to resist liquefaction, and basically meet the requirements of scaled-down models in terms of concrete strength, elastic modulus, and bending strength of model piles.

[0026] The main improvements of this invention are as follows:

[0027] 1) Cement-soil can effectively simulate the properties of concrete in terms of strength and deformation during earthquake liquefaction shaking table tests. Using cement-soil to simulate concrete, its mechanical properties remain unchanged under saturated conditions. Furthermore, by adjusting the water-cement ratio and controlling the curing time, the strength of cement-soil can be reduced to as low as 1 / 100th of that of concrete. The corresponding elastic modulus of cement-soil also largely meets the requirements for similarity ratios.

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

[0029] 3) The model pile is made using molds, and the tensile material is placed at the center of the cross-section of the model pile, which results in high production efficiency.

[0030] 4) Bending tests were used to control the fabrication quality of the model piles. To verify that the model piles met the expected quality, their bending strength needed to be measured. Therefore, bending test equipment and corresponding loading methods with a total load of less than 5N were designed.

[0031] 5) Waterproof strain gauges are used to monitor the deformation of model piles in earthquake liquefaction shaking table tests. Attached Figure Description

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

[0033] Figure 2 This is a schematic diagram of the bending strength test device for the model pile in an embodiment of the present invention;

[0034] Figure 3 This is a comparison chart of cement-soil strength corresponding to different cement admixture amounts;

[0035] Figure 4 This is a comparison chart of the strength of cement-soil with different water-cement ratios.

[0036] The components include: 1. Tube body; 2. Tube segment; 3. Adhesive tape; 4. Hollow bolt; 5. Strong A-clamp; 6. Nylon thread; 7. Base; 8. Supporting round rod; 9. Positioning clamp; 10. Model pile; 11. Square hole; 12. Flexible rope; 13. Weight. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments and accompanying drawings, providing a more thorough understanding of the invention through specific implementation details. However, it will be apparent to those skilled in the art that the present invention can be practiced without one or more of these details. In other examples, some technical features well-known in the art have not been described to avoid confusion with the present invention.

[0038] To fully understand this invention, detailed steps and structures will be presented in the following description to illustrate the technical solution of this invention. Preferred embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0039] Example 1:

[0040] A method for fabricating a model pile for earthquake liquefaction model testing includes material selection for simulated concrete, material selection for simulated steel, and mold design. The simulated concrete material selection uses cement-soil, the strength of which is estimated based on empirical formulas to meet the requirements of the earthquake liquefaction model test. The simulated steel material selection uses nylon thread, the diameter of which is determined based on bending calculations and bending test results to meet the requirements of the earthquake liquefaction model test. A viscous adhesive is used to bond the nylon thread to the cement-soil. The model pile is fabricated using a split mold and by pre-applying tensile stress to the nylon thread.

[0041] The present invention also provides a method for testing the bending performance of a model pile for earthquake liquefaction model tests, including the fabrication and use of bending test equipment, wherein the bending strength of the model pile is estimated by bending test.

[0042] The present invention also provides a monitoring method for model piles used in earthquake liquefaction model tests, 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 the strain gauges are directly pasted on the surface of the model pile.

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

[0044] The empirical formulas for the strength of cement-soil at different ages are as follows:

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

[0046] q u90=(1.43~1.8)q u28 (2)

[0047] In the formula: q u This represents the unconfined compressive strength of cement-soil, and the subscript number represents the age of the cement-soil test block.

[0048] Under 7-day curing conditions, the empirical formula for cement-soil strength corresponding to different cement admixture amounts C (%) is as follows:

[0049] q u =75 + 20 × C + 0.3 × C 2 (3)

[0050] In the formula: q u The unit is kPa. Equation (3) is based on... Figure 3 Experimental data.

[0051] The empirical formulas for the strength of cement-soil with different water-cement ratios are as follows:

[0052] (4)

[0053] In the formula: q u The unit is kPa; A and B are constants, which need to be determined experimentally based on specific soil samples; w is the water content of the cement-soil mixture; C is the amount of cement added. According to... Figure 4 Based on the data, under the recommended 7-day maintenance condition, A = 1627; B = 1.28.

[0054] This embodiment also provides a method for testing the bending performance of a model pile for earthquake liquefaction model tests. It includes the fabrication and use of bending test equipment, and the bending strength of the model pile is estimated by bending test.

[0055] The bending test estimation is performed using formula (6):

[0056] (6)

[0057] In the formula: Mcr is the bending moment at which the model pile reaches the failure state; E is the elastic modulus of the cement-soil mixture; α E ε is the ratio of the elastic modulus of nylon to the elastic modulus of cement-soil; cr The strain value for cement-soil reaching a crushed state is recommended to be 0.015; D is the diameter of the model pile; d is the diameter of the nylon thread; k M This is a correction factor used to correct for changes in flexural strength caused by the neutral axis deviating from the geometric center of the section at failure; a value of 2.0 is recommended. Due to differences in parameters such as clay material, water content, and cement-soil compaction, E and ε... cr k MThe estimated values ​​of parameters may differ significantly from the actual values, therefore a bending test is necessary. The three-point bending test scheme proposed in this invention is recommended. Furthermore, equation (6) represents the M proposed in this invention. cr Calculation method. The right-hand side of equation (6), divided by k... M The remaining parts are derived from mechanical theory. The suggested value of k... M The value of 2 is based on the results of a three-point bending test of the model pile. In this test, the model pile parameters were:

[0058] D = 1 cm, d = 1 mm, α E =40, E=70MPa, ε cr =0.015. The corresponding M cr It is 0.2 N·m. The k value is calculated by reverse calculation. M Approximately equal to 2.

[0059] The simulated concrete material has an elastic modulus similarity on the order of 1 / 100. The elastic modulus E of the simulated material can be estimated using formula (5):

[0060] E = K·q u (5)

[0061] In the formula: E is the elastic modulus of the simulated material (cement-soil); K is a constant, which is recommended to be 150. Since K of the prototype concrete is usually 500 to 1000, under the condition of satisfying the strength similarity ratio, the simulated concrete of this invention can only approximately satisfy the similarity ratio of the elastic modulus on the order of magnitude.

[0062] The recommended material for simulating the reinforcing bars is nylon wire. Based on the above bending calculations and bending test results, the diameter of the nylon wire can be determined to meet the bending strength requirements of the earthquake liquefaction model test.

[0063] The bonding between the nylon thread and the cementitious soil is achieved using a viscous adhesive. It is recommended to use HY-T160 transparent soft PE adhesive.

[0064] The strain gauges are waterproof. It is recommended to use the Japanese KFW series waterproof foil strain gauges. The strain gauges can be directly adhered to the surface of the model pile.

[0065] This embodiment provides a model pile mold, such as Figure 1As shown, the mold includes a tube body 1, which is recommended to be made of plexiglass; a tube segment 2, which is recommended to be made of plexiglass; tape 3; two hollow bolts 4; and two strong A-clamps 5. 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 are combined to 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 in the hollow spiral should be greater than the diameter of the nylon thread 6 (for example, 1.2 times the diameter of the nylon thread 6).

[0066] The process of making model piles using molds is briefly described below:

[0067] 1) Estimate the diameter of the nylon wire required for the model pile by referring to the "Standard for Design of Concrete Structures" (GB / T50010-2010) and other standards.

[0068] 2) Assemble the mold. Screw the two hollow bolts 4 into both ends of the tube body 1; thread the nylon thread 6 through the two hollow bolts 4; clamp the nylon thread 6 tightly against the hollow bolts 4 with a strong A-clamp 5; tighten the hollow bolts 4 to a suitable distance, and appropriately tighten the nylon thread 6. Apply an appropriate amount of tung oil to the inside of the tube body 1 and the tube segment 2. Place the tube body 1 horizontally.

[0069] 3) Based on equations 1) and 2), taking into account the requirements for the strength and elastic modulus of the model pile, select an appropriate water-cement ratio and curing time, and prepare cement-soil slurry.

[0070] 4) Fill the cement-soil slurry from 3) above evenly into the mold assembled in 2). Fill it to approximately 50% of the pipe's volume.

[0071] 5) Apply the adhesive evenly to the nylon thread.

[0072] 6) Continue to fill the cement-soil slurry from 3) into the mold assembled in 2). Adjust the slurry appropriately so that the cement-soil slurry fills the cavity formed by the pipe body 1 and the pipe segment 2 after the pipe segment 2 is closed.

[0073] 7) Secure the pipe body 1 and the pipe segment 2 with tape 3. The pipe segment 2 can be removed after the cement slurry has solidified.

[0074] 8) Maintenance.

[0075] Example 2:

[0076] This embodiment provides a bending resistance testing device, such as... Figure 2 As shown, this experiment is actually a special bending test that neglects the effect of shear force. The suggested experimental procedure is detailed in the following implementation method:

[0077] The device includes a base 7 (suggested material: stainless steel), two supporting round rods 8 (suggested material: stainless steel), four positioning clips 9, a flexible rope 12 (suggested material: hemp), and two weights 13. The base 7 has a square hole 11; the round rods 8 are fixed to the base 7.

[0078] The experimental procedure using the bending resistance testing apparatus is briefly described below:

[0079] 1) Make three marks on the model pile 10 with a marker: two marks for the position of the support rods and one mark for the position of the flexible rope.

[0080] 2) Tie the flexible rope 12 to the model pile 10 and adjust the position of the flexible rope 12 to the marked position.

[0081] 3) Place base 7 horizontally.

[0082] 4) Place the model pile 10 on the two supporting round rods 8 and adjust the contact point position to the marked position.

[0083] 5) Hang the first weight on the flexible rope 12. Then hang the weight 13 on top of the previous weight in sequence. Recommendation: Each small weight should weigh 10g; if more than 10 small weights are hung, remove them and replace them with a larger weight of appropriate weight.

[0084] 6) Increase the total mass of the hanging weights until the model pile 10 is destroyed.

[0085] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and the devices and structures not described in detail should be understood as being implemented in a conventional manner in the art. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. This 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 present invention's technical solutions still fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a model pile for a seismic liquefaction model test, comprising a material selection for simulating concrete, a material selection for simulating steel, and a mold design; characterized in that, The simulated concrete material selection is cement-soil, the strength of which is estimated according to empirical formulas and made to meet the requirements of the earthquake liquefaction model test; the simulated steel material selection is nylon wire, the diameter of which is determined according to bending calculation and bending test results and made to meet the requirements of the earthquake liquefaction model test; the bonding between the nylon wire and the cement-soil is made of viscous HY-T160 transparent soft PE adhesive; the model pile adopts a split mold and tensile stress is pre-applied to the nylon wire, the strength of which is estimated according to empirical formulas and made to meet the requirements of the earthquake liquefaction model test; the curing time and water-cement ratio of the simulated concrete material are determined according to the similarity ratio required by the earthquake liquefaction model test and are determined by 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) In the formula: q u The values ​​represent the unconfined compressive strength of cement-soil, and the subscripts indicate the age of the cement-soil specimen. Using 42.5 grade ordinary Portland cement, under conditions of a cement paste water-cement ratio of 0.5, clay moisture content of 40%, and 7-day curing, the empirical formulas for the cement-soil strength corresponding to different cement admixtures C (%) are as follows: q u =75+20×C+0.3×C 2 (3) In the formula: q u Units kPa; The empirical formulas for the strength of cement-soil with different water-cement ratios are as follows: (4) In the formula: qu is in kPa; A and B are constants, which need to be determined experimentally based on the specific soil; w is the water content of the cement-soil; C is the amount of cement added. The mold for this model pile includes a tube body, a tube segment, adhesive tape, two hollow bolts, and two strong A-clamps. The tube body is threadedly connected to the hollow bolts. The tube body is an incomplete tube body, which is combined with the tube segment to form a complete tube body. The length of the tube segment is greater than the length of the model pile. The diameter of the hole in the hollow spiral is greater than the diameter of the nylon thread. The process of making the model pile using this mold is as follows: 1) Estimate the diameter of the nylon thread required for the model pile; 2) Assemble the mold: Screw two hollow bolts into both ends of the tube; thread the nylon thread through the two hollow bolts; clamp the nylon thread tightly against the hollow bolts with a strong A-clamp; tighten the hollow bolts to tighten the nylon thread; apply tung oil to the inside of the tube and the tube segments, and place the tube horizontally. 3) Based on steps 1) and 2), and considering the requirements for the strength and elastic modulus of the model pile, select the water-cement ratio and curing time, and prepare the cement-soil slurry. 4) Fill the cement slurry from step 3) evenly into the mold assembled in step 2), filling it to 50% of the pipe's volume. 5) Apply the adhesive evenly to the nylon thread; 6) Continue to fill the cement-soil slurry from step 3) into the mold assembled in step 2), and trim the slurry so that the cement-soil slurry fills the cavity formed by the pipe body and the pipe segment after the pipe segment is closed. 7) Secure the pipe body and segments with tape, and remove the segments after the cement slurry has solidified. 8) Maintenance.

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