Method for determining horizontal ultimate bearing capacity of distributed post-grouting pile foundation

Abstract

The invention is suitable for the technical field of pile foundation bearing capacity prediction, and relates to a distributed post-grouting pile foundation horizontal ultimate bearing capacity determination method, which comprises the following steps: obtaining the structure size and material parameters of a pile foundation, the physical and mechanical parameters of a soil body, the grouting amount and the grouting material parameters; establishing a pile-soil three-dimensional finite element model; selecting a soil constitutive model, and inputting the parameters into the soil constitutive model; pile-soil contact interface parameters, pile end ultimate bearing capacity standard values and pile end spring stiffness are determined; grid division is conducted on the pile-soil three-dimensional finite element model; a gravity load is applied to the pile-soil three-dimensional finite element model, and a horizontal load is applied to the pile top; boundary conditions are applied to the pile-soil three-dimensional finite element model; calculating and analyzing the pile-soil three-dimensional finite element model to obtain a P-Y curve of pile top horizontal displacement and load, a pile body stress distribution curve and a pile body internal force distribution curve; and determining the horizontal ultimate bearing capacity of the pile foundation. According to the method, the accuracy of the determined horizontal ultimate bearing capacity of the pile foundation is effectively guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of pile foundation bearing capacity prediction, and in particular relates to a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation. Background Art

[0002] Piles are the most common foundation form used in buildings at present. They have many advantages such as high bearing capacity, strong adaptability, and simple construction. Therefore, they are widely used in urban high-rise buildings, transmission lines, transmission towers and other tall buildings, port and terminal projects, bridge projects, landslide anti-slide pile projects, earthquake-resistant projects and other projects. In order to improve the bearing capacity of pile foundations, pile foundation post-grouting technology came into being. The stress and deformation characteristics of post-grouting pile foundations under horizontal loads are issues that must be paid attention to in the design process. At present, the engineering practice of distributed post-grouting is ahead of theoretical research. There is still a lack of systematic research on the reinforcement mechanism of distributed post-grouting technology, the bearing mechanism of distributed post-grouting pile foundations, and the load transfer law. Therefore, the horizontal ultimate bearing capacity of distributed post-grouting pile foundations is mainly determined by field measurement methods, but the field measurement method has the disadvantages of low efficiency and accuracy, long cycle, large material consumption, and poor regularity.

[0003] The patent with announcement number CN113821863B provides a method for predicting the vertical ultimate bearing capacity of pile foundation, including step S1, establishing an initial population; step S2, using the fitness function of the improved radial movement algorithm to calculate the fitness value of each individual in the initial population, and determining the optimal position of the contemporary by comparing the fitness values ​​of the individuals one by one, and defining it as the initial center position; step S3, using the update condition to generate a new pre-position point within the range of ±0.5(xjmax-xjmin)wk of the kth generation center position, and calculating the fitness value, and updating the position information; step S4, determining the global optimal position, and calculating the fitness value of the global optimal position; step S5, assigning the weight and threshold of the global optimal position to the BP neural network model, training and simulating the BP neural network model to obtain the optimal prediction value of the vertical ultimate bearing capacity of the pile foundation. The method disclosed in this patent is relatively one-sided for the calculation of pile foundation, with fewer parameters, the established data model is not accurate enough, and the efficiency and accuracy of horizontal ultimate bearing capacity prediction are low.

[0004] Therefore, how to accurately and efficiently predict and determine the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation is an urgent problem to be solved by personnel in this technical field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation, so as to solve the problem that the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation in the prior art is mainly determined by on-site measurement method, resulting in low prediction efficiency and accuracy.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation, comprising the following steps:

[0008] S10, obtaining the structural dimensions and material parameters of the pile foundation, the physical and mechanical parameters of the soil, the grouting amount and the grouting material parameters according to the on-site construction data;

[0009] S20, establishing a pile-soil three-dimensional finite element model according to the structural dimensions of the pile foundation;

[0010] S30, selecting a soil constitutive model, and inputting the soil physical and mechanical parameters into the soil constitutive model;

[0011] S40, determining pile-soil contact interface parameters, standard value of ultimate bearing capacity of pile end and spring stiffness of pile end according to structural dimensions and material parameters of the pile foundation and physical and mechanical parameters of the soil;

[0012] S50, meshing the pile-soil three-dimensional finite element model and assigning material properties;

[0013] S60, applying a gravity load to the pile-soil three-dimensional finite element model, and applying a horizontal load to the pile top;

[0014] S70, applying boundary conditions to the pile-soil three-dimensional finite element model;

[0015] S80, setting a pile foundation horizontal loading finite element model calculation step, performing calculation and analysis on the pile-soil three-dimensional finite element model, and obtaining a PY curve of pile top horizontal displacement and load, a pile body stress distribution curve, and a pile body internal force distribution curve;

[0016] S90, determining the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation according to the PY curve of the pile top horizontal displacement and load and the pile body stress distribution curve, and in combination with the horizontal ultimate bearing capacity determination conditions of the pile foundation.

[0017] Furthermore, the pile-soil three-dimensional finite element model in step S20 includes a soil model, a post-grouting pile foundation model, a pile-soil contact model and a grouting body model; the soil model is simulated using a hardened soil constitutive model, the normal directions around the soil model are constrained, the X, Y, and Z directions at the bottom of the soil model are constrained, and the top is a free surface; the post-grouting pile foundation model is simulated using a beam unit, and the beam unit constrains the Z-direction rotation; the pile-soil contact model is simulated using an interface unit, the grouting body is simplified to a grouting sphere, and a solid unit is used. The grouting sphere radius calculation formula is as follows:

[0018]

[0019] Where, T is the grouting volume; N is the number of grouting balls; r is the radius of the grouting balls; ρ is the grouting density.

[0020] Furthermore, in step S30, the soil constitutive model is a hardened soil constitutive model, and the mechanical parameters of the hardened soil constitutive model include soil strength parameters, deformation parameters and small strain parameters.

[0021] Furthermore, the soil strength parameters include effective cohesion c, effective internal friction angle φ, shear dilation angle ψ and failure ratio R f , the calculation formula of the dilatancy angle ψ is as follows:

[0022]

[0023] The destruction ratio R f It is related to the soil porosity ratio e. The relationship between the damage ratio and the porosity ratio is:

[0024]

[0025] Furthermore, the deformation parameters include the reference stress p ref , Tangent compression modulus corresponding to reference stress Secant modulus corresponding to 0.5 times the deviatoric stress under reference stress Unloading and reloading modulus at reference stress Normal consolidation static lateral pressure coefficient and the power exponent m related to the stiffness stress level;

[0026] The normal consolidation static lateral pressure coefficient The calculation formula is:

[0027]

[0028] in, is the normal consolidation static lateral pressure coefficient, is the effective internal friction angle;

[0029] The value of the stiffness stress level related power exponent m is related to the soil properties. For sandy soil, the stiffness stress level related power exponent m is 0.7, and for clay soil, the stiffness stress level related power exponent m is 0.65.

[0030] Furthermore, the small strain parameter includes a small strain reference initial shear modulus The shear strain γ corresponding to the decay of the secant shear modulus to 0.7 times the initial shear modulus 0.7 ; The small strain refers to the initial shear modulus Determined by the following empirical formula:

[0031]

[0032] Among them, e is the soil void ratio, OCR is the overconsolidation ratio;

[0033] The shear strain γ corresponding to the decay of the secant shear modulus to 0.7 times the initial shear modulus 0.7 In clay soil, the range is (2.4~4.2)×10 -4 , with an average value of 3.2×10 -4 , in sandy soil, the range is (2.9~5.2)×10 -4 , with an average value of 3.9×10 -4 .

[0034] Furthermore, the pile-soil contact interface parameters in step S40 include the standard value of the ultimate lateral friction resistance of the pile body, the shear stiffness modulus k t , normal stiffness modulus k n The standard value of the ultimate lateral friction resistance of the pile body is determined according to the type of soil, and the shear stiffness modulus k t Take 10 times the elastic modulus of the soil, the normal stiffness modulus k n The elastic modulus of the soil is 100 times, the standard value of the ultimate bearing capacity of the pile end is determined according to the type of the soil, and the spring stiffness of the pile end is the elastic resistance coefficient of the soil.

[0035] Furthermore, the calculation steps of the pile foundation horizontal loading finite element model in step S80 are as follows:

[0036] S801, activate the soil, apply gravity and soil constraints, and then clear the displacement;

[0037] S802, activating the pile foundation, interface unit, pile end unit, and grouting ball, and applying rotation constraint to the pile foundation in the Z direction;

[0038] S803, perform the displacement clearing operation again;

[0039] S804. Divide the horizontal load on the pile top into n incremental steps for step-by-step loading, and then submit for calculation and analysis.

[0040] Furthermore, the conditions for determining the horizontal ultimate bearing capacity of the pile foundation in step S90 are as follows:

[0041] According to the characteristic curve of the change of pile top horizontal displacement with load, that is, the PY curve characteristic, for pile foundations with a pile body reinforcement ratio of not less than 0.65%, 75% of the load corresponding to a horizontal displacement of 10mm at the ground is taken as the horizontal ultimate bearing capacity of the pile foundation;

[0042] For pile foundations with a pile reinforcement ratio of less than 0.65%, when the maximum principal stress of the pile foundation reaches the material yield strength under horizontal load conditions, 75% of the horizontal load is taken as the horizontal ultimate bearing capacity of the pile foundation.

[0043] Furthermore, the minimum principal stress of the pile foundation under the determination conditions satisfies the compressive strength of the pile foundation itself.

[0044] Compared with the prior art, the method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided by the present invention has at least the following beneficial effects:

[0045] In the prior art, the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation is mainly determined by the field measurement method, but the field measurement method has the disadvantages of low efficiency and accuracy, long cycle, large material consumption, poor regularity, etc. The present invention has a simple process and convenient operation, and establishes a distributed post-grouting pile foundation horizontal loading calculation model, which can not only simulate the horizontal loading process of the pile foundation and the interaction between the pile foundation-grouting body-soil, but also calculate the PY curve and the stress and internal force distribution of the pile body, providing data support for the optimization design of the pile foundation reinforcement; the present invention has the advantages of adjustable calculation accuracy, fast calculation convergence speed, high calculation efficiency, simple PY curve acquisition process, accurate calculation results, etc., and can also comprehensively and accurately reflect the mechanical response of the distributed post-grouting pile foundation, and has a certain guiding role in the optimization of the distributed post-grouting scheme and the economic rationality design of the pile foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the scheme of the present invention, a brief introduction is given below to the figures required for use in the description of the embodiments. Obviously, the figures described below are some embodiments of the present invention. For ordinary technicians in this field, other figures can be obtained based on these figures without paying any creative work.

[0047] Figure 1 A flow chart of a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided by an embodiment of the present invention;

[0048] Figure 2 A schematic diagram of a pile-soil three-dimensional finite element model in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided in an embodiment of the present invention;

[0049] Figure 3 A schematic diagram of a post-grouting pile foundation model in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided in an embodiment of the present invention;

[0050] Figure 4 A comparison diagram of the calculation results and test results of the pile foundation PY curve in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided in an embodiment of the present invention;

[0051] Figure 5 A calculation curve diagram of the maximum principal stress of a pile body in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided by an embodiment of the present invention;

[0052] Figure 6 A calculation curve diagram of the minimum principal stress of a pile body in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided by an embodiment of the present invention;

[0053] Figure 7 A calculation curve diagram of the pile body axial force in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided in an embodiment of the present invention;

[0054] Figure 8 A curve diagram for calculating the bending moment of a pile body in a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0057] The present invention provides a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation, which is applied to the prediction process of the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation. The method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation comprises the following steps:

[0058] S10, obtaining the structural dimensions and material parameters of the pile foundation, the physical and mechanical parameters of the soil, the grouting amount and the grouting material parameters according to the on-site construction data;

[0059] S20, establishing a pile-soil three-dimensional finite element model according to the structural dimensions of the pile foundation;

[0060] S30, selecting a soil constitutive model, and inputting soil physical and mechanical parameters into the soil constitutive model;

[0061] S40, determining pile-soil contact interface parameters, standard value of ultimate bearing capacity of pile end and spring stiffness of pile end according to structural dimensions and material parameters of pile foundation and physical and mechanical parameters of soil;

[0062] S50, meshing the pile-soil three-dimensional finite element model and assigning material properties;

[0063] S60, applying a gravity load to the pile-soil three-dimensional finite element model, and applying a horizontal load to the pile top;

[0064] S70, applying boundary conditions to the pile-soil three-dimensional finite element model;

[0065] S80, setting a calculation step of a pile foundation horizontal loading finite element model, performing calculation and analysis on a pile-soil three-dimensional finite element model, and obtaining a PY curve of pile top horizontal displacement and load, a pile body stress distribution curve, and a pile body internal force distribution curve;

[0066] S90. According to the PY curve of pile top horizontal displacement and load and the pile body stress distribution curve, combined with the horizontal ultimate bearing capacity determination conditions of the pile foundation, the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation is determined.

[0067] The invention has a simple process and is easy to operate, and effectively ensures the accuracy of the determined horizontal ultimate bearing capacity of the pile foundation.

[0068] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings.

[0069] Embodiment 1

[0070] Taking the horizontal loading model test of distributed post-grouting pile foundation as an example, the location of post-grouting of pile foundation is as follows: Figure 3 As shown, the grouting positions are 0.1m, 0.5m, 0.9m, and 1.3m of the pile foundation, the grouting amount is 8kg, the material is C30 concrete, the diameter of the test pile foundation is 0.05m, the length is 1.6m, the material is C35 concrete, the reinforcement ratio is 0.8%, and the model test soil is fine sand. The physical parameters of fine sand are shown in Table 1:

[0071] Table 1

[0072]

[0073] The present invention provides a method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation, which is applied to the prediction process of the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation. Figures 1 to 8 In this embodiment, the method for determining the horizontal ultimate bearing capacity of the distributed rear pile foundation includes the following steps:

[0074] S10, obtaining the structural dimensions and material parameters of the pile foundation, the physical and mechanical parameters of the soil, the grouting amount and the grouting material parameters according to the on-site construction data;

[0075] S20. According to the structural dimensions of the pile foundation, a pile-soil three-dimensional finite element model is established. The pile-soil three-dimensional finite element model is as follows: Figure 2 As shown;

[0076] Specifically, in this embodiment, the pile-soil three-dimensional finite element model in step S20 includes a soil model, a post-grouting pile foundation model, a pile-soil contact model and a grouting body model; the soil model is simulated using a hardened soil constitutive model, the normal directions around the soil model are constrained, the X, Y, and Z directions of the bottom of the soil model are constrained, and the top is a free surface with a size of 3.6m×3.6m×3.4m (X×Y×Z); the post-grouting pile foundation model is simulated using beam units, and the beam units constrain the Z-direction rotation; the pile-soil contact model is simulated using interface units, the grouting body is simplified to a grouting sphere, and a solid unit is used. The grouting ball radius calculation formula is as follows:

[0077]

[0078] Among them, the grouting volume T is 8 kg; the number of grouting balls N is 4; the radius of the grouting ball r is 0.058 m; the grouting density ρ is 2.5×10 3 kg / m 3 . .

[0079] S30, selecting a soil constitutive model, and inputting soil physical and mechanical parameters into the soil constitutive model;

[0080] Specifically, in this embodiment, in step S30, the soil constitutive model is a hardened soil (small strain stiffness) constitutive model, and the mechanical parameters of the hardened soil (small strain stiffness) constitutive model include soil strength parameters, deformation parameters and small strain parameters.

[0081] Furthermore, soil strength parameters include effective cohesion c, effective internal friction angle φ, shear dilatancy angle ψ and failure ratio R f , the calculation formula of shear dilatancy angle ψ is as follows:

[0082]

[0083] Among them, the shear dilatation angle ψ of fine sand is 1.5°; the internal friction angle of fine sand is It is 31.5°.

[0084] Destruction ratio R f It is related to the soil porosity ratio e. The relationship between the destruction ratio and the porosity ratio is:

[0085]

[0086] Among them, the porosity ratio e of fine sand is 0.75, and the damage ratio R of fine sand is f is 0.95.

[0087] Deformation parameters include reference stress p ref , Tangent compression modulus corresponding to reference stress Secant modulus corresponding to 0.5 times the deviatoric stress under reference stress Unloading and reloading modulus at reference stress Normal consolidation static lateral pressure coefficient and the power exponent m related to the stiffness stress level;

[0088] Conventional geotechnical engineering investigation reports usually only provide the compression modulus E corresponding to the consolidation test of 100-200 kPa. s1-2 , With E s1-2 The relationship is shown in Table 2:

[0089] Table 2

[0090]

[0091] Normal consolidation static lateral pressure coefficient The calculation formula is:

[0092]

[0093] The effective internal friction angle of fine sand is is 31.5°, normal consolidation static lateral pressure coefficient It is 0.48.

[0094] The value of the power exponent m related to the stiffness stress level is related to the properties of the soil. For sandy soil (including sandy silt), the power exponent m related to the stiffness stress level is 0.7, and for clay soil (including clay silt), the power exponent m related to the stiffness stress level is 0.65. Therefore, the power exponent m related to the stiffness stress level of the fine sand described in this embodiment is 0.7.

[0095] Small strain parameters include small strain reference initial shear modulus The shear strain γ corresponding to the decay of the secant shear modulus to 0.7 times the initial shear modulus 0.7 ; Small strain reference initial shear modulus Determined by the following empirical formula:

[0096]

[0097] Among them, the small strain refers to the initial shear modulus is 93.2MPa, the soil porosity ratio e is 0.75, and the overconsolidation ratio OCR is 1.0;

[0098] The shear strain γ corresponding to the decay of the secant shear modulus to 0.7 times the initial shear modulus 0.7 In clay soil (including clayey silt), the range is (2.4~4.2)×10 -4 , with an average value of 3.2×10 -4 , in sandy soil (including sandy silt) the range is (2.9~5.2)×10 -4 , with an average value of 3.9×10 -4 , so the shear strain γ of the fine sand in this embodiment is 0.7 Take 3.9×10 -4 MPa.

[0099] Input the constitutive model parameters of hardened soil (small strain stiffness) obtained by converting the physical and mechanical parameters of the test soil in step S10 into the soil constitutive model;

[0100] S40, determining pile-soil contact interface parameters, standard value of ultimate bearing capacity of pile end and spring stiffness of pile end according to structural dimensions and material parameters of pile foundation and physical and mechanical parameters of soil;

[0101] Specifically, in this embodiment, the pile-soil contact interface parameters in step S40 include the standard value of the pile body ultimate lateral friction resistance, the shear stiffness modulus k t , normal stiffness modulus k n The standard value of the ultimate lateral friction resistance of the pile body is 55 kPa according to the Appendix 5.3.5-1 of the Technical Specifications for Building Pile Foundations (JGJ94-2008). The shear stiffness modulus k t Take 720MPa, normal stiffness modulus k n Take 7200MPa, the standard value of the ultimate bearing capacity of the pile end is 1800kPa according to Appendix 5.3.5-2 in the "Technical Specifications for Building Pile Foundations" (JGJ94-2008), and the spring stiffness of the pile end is the elastic resistance coefficient of the soil, which is 10MPa / m.

[0102] S50, meshing the pile-soil three-dimensional finite element model and assigning material properties;

[0103] Specifically, in this embodiment, the material types include C30 concrete and C35 concrete. The parameters of C30 concrete and C35 concrete are shown in Table 3:

[0104] Table 3

[0105] Material Elastic modulus / (GPa) <![CDATA[Density / (kg / m 3 )]]> Poisson's ratio C30 Concrete 3.0 2500 0.25 C35 Concrete 3.15 2500 0.25

[0106] S60, applying a gravity load to the pile-soil three-dimensional finite element model, and applying a horizontal load to the pile top;

[0107] Specifically, in this embodiment, the horizontal load value is the horizontal displacement load, and the applied horizontal displacement load is 15 mm.

[0108] S70, applying boundary conditions to the pile-soil three-dimensional finite element model;

[0109] Specifically, in this embodiment, the soil in the pile-soil model is subject to normal constraints on all sides, the bottom is subject to X, Y, and Z constraints, and the top is a free surface; the pile structure in the pile-soil model is subject to Z-axis rotation constraints.

[0110] S80, setting a calculation step of a pile foundation horizontal loading finite element model, performing calculation and analysis on a pile-soil three-dimensional finite element model, and obtaining a PY curve of pile top horizontal displacement and load, a pile body stress distribution curve, and a pile body internal force distribution curve;

[0111] Specifically, the calculation steps of the pile foundation horizontal loading finite element model in step S80 are as follows:

[0112] S801, activate the soil model, gravity load and land constraint, calculate the initial ground stress, and then reset the displacement to make the ground stress in a balanced state;

[0113] S802, activating the pile foundation, interface unit, pile end unit, and grouting ball model, and activating the rotation constraint of the pile foundation in the Z direction;

[0114] S803, performing a displacement clearing operation again to prevent the displacement calculated in step 2 from affecting subsequent displacement calculation results;

[0115] S804. Activate the pile top horizontal displacement load, divide the horizontal loading into 15 increments, and set the output of the calculation results of each increment, and then submit them for calculation analysis.

[0116] The more incremental steps there are, the higher the calculation accuracy will be. The corresponding incremental steps can be set according to the requirements of calculation accuracy.

[0117] S90. According to the PY curve of pile top horizontal displacement and load and the pile body stress distribution curve, combined with the horizontal ultimate bearing capacity determination conditions of the pile foundation, the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation is determined. Figure 4 The py curve comparison diagram of the calculation results and the test results of this embodiment shows that the change trends of the calculation results and the test results curves are basically consistent, and the degree of agreement between the two is high, which verifies the accuracy and reliability of the calculation method provided by the present invention.

[0118] Furthermore, through the embodiment of the present invention, the maximum principal stress distribution curve, the minimum principal stress distribution curve, the axial force distribution curve and the bending moment distribution curve of the pile body can also be obtained, as shown in FIG. Figures 5 to 8As shown in the figure, the bearing mechanism of distributed post-grouting pile foundation can be clarified and the load transfer law can be revealed through the variation curves of pile axial force and bending moment, so as to promote the theoretical research on the bearing capacity of distributed post-grouting pile foundation.

[0119] Specifically, the conditions for determining the horizontal ultimate bearing capacity of the pile foundation in step S90 are as follows:

[0120] According to the characteristic curve of the pile top horizontal displacement changing with load, namely the PY curve characteristic, for pile foundations with a pile body reinforcement ratio of not less than 0.65%, 75% of the load corresponding to a horizontal displacement of 10 mm at the ground (for buildings sensitive to horizontal displacement, a horizontal displacement of 6 mm) is taken as the horizontal ultimate bearing capacity of the pile foundation;

[0121] For pile foundations with a pile body reinforcement ratio of less than 0.65%, when the maximum principal stress of the pile foundation reaches the material yield strength under horizontal load conditions, 75% of the horizontal load is taken as the horizontal ultimate bearing capacity of the pile foundation. The minimum principal stress of the pile foundation under the above conditions must meet the compressive strength of the pile foundation itself.

[0122] Since the reinforcement ratio of the pile foundation in Example 1 is 0.8%, the horizontal ultimate bearing capacity of the pile foundation in Example 1 is determined by the former condition of the judgment condition. There is no sensitive building in Example 1. Figure 4 In the calculation, when the horizontal displacement of the pile foundation is 10mm, the corresponding horizontal load is 5.32kN. Figure 6 When the horizontal displacement of the middle pile foundation is 10mm, the minimum principal stress is -21300kPa, which meets the compressive strength of C35 concrete material (-23400kPa), and the calculated value of the horizontal ultimate bearing capacity of the pile foundation is 3.99kN.

[0123] Compared with the prior art, the method for determining the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation described in the above embodiment mainly relies on the field measurement method to determine the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation in the prior art. However, the field measurement method has the disadvantages of low efficiency and accuracy, long cycle, large material consumption, poor regularity, etc. The present invention has a simple process and convenient operation. It establishes a distributed post-grouting pile foundation horizontal loading calculation model, which can not only simulate the pile foundation horizontal loading process and the interaction between the pile foundation-grouting body-soil, but also calculate the PY curve and the pile body stress and internal force distribution, providing data support for the optimization design of pile foundation reinforcement;

[0124] The present invention has the advantages of adjustable calculation accuracy, fast calculation convergence speed, high calculation efficiency, simple PY curve acquisition process, accurate calculation results, etc. It can also comprehensively and accurately reflect the mechanical response of distributed post-grouting pile foundations, and has a certain guiding role in the optimization of distributed post-grouting schemes and the economic rationality design of pile foundations.

[0125] Obviously, the embodiments described above are only preferred embodiments of the present invention, rather than all embodiments. The preferred embodiments of the present invention are shown in the accompanying drawings, but they do not limit the patent scope of the present invention. The present invention can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Although the present invention has been described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions recorded in the aforementioned specific embodiments, or to perform equivalent replacements for some of the technical features therein. Any equivalent structure made using the contents of the specification and drawings of the present invention, directly or indirectly used in other related technical fields, is also within the scope of patent protection of the present invention.

Claims

1. A method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation, characterized in that: The following steps are involved: S10, obtaining the structural dimensions and material parameters of the pile foundation, the physical and mechanical parameters of the soil, the grouting amount and the grouting material parameters according to the on-site construction data; S20, establishing a pile-soil three-dimensional finite element model according to the structural dimensions of the pile foundation; S30, selecting a soil constitutive model, and inputting the soil physical and mechanical parameters into the soil constitutive model; S40, determining pile-soil contact interface parameters, standard value of ultimate bearing capacity of pile end and spring stiffness of pile end according to structural dimensions and material parameters of the pile foundation and physical and mechanical parameters of the soil; S50, meshing the pile-soil three-dimensional finite element model and assigning material properties; S60, applying a gravity load to the pile-soil three-dimensional finite element model, and applying a horizontal load to the pile top; S70, applying boundary conditions to the pile-soil three-dimensional finite element model; S80, setting a pile foundation horizontal loading finite element model calculation step, performing calculation and analysis on the pile-soil three-dimensional finite element model, and obtaining a PY curve of pile top horizontal displacement and load, a pile body stress distribution curve, and a pile body internal force distribution curve; S90, determining the horizontal ultimate bearing capacity of the distributed post-grouting pile foundation according to the PY curve of the pile top horizontal displacement and load and the pile body stress distribution curve, and in combination with the horizontal ultimate bearing capacity determination conditions of the pile foundation.

2. A method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 1, characterized in that: The pile-soil three-dimensional finite element model in step S20 includes a soil model, a post-grouting pile foundation model, a pile-soil contact model and a grouting body model; the soil model is simulated using a hardened soil constitutive model, the normal directions around the soil model are constrained, the X, Y and Z directions of the bottom of the soil model are constrained, and the top is a free surface; the post-grouting pile foundation model is simulated using a beam unit, and the beam unit constrains the Z-direction rotation; the pile-soil contact model is simulated using an interface unit, the grouting body is simplified to a grouting sphere, and a solid unit is used. The grouting sphere radius calculation formula is as follows: Where, T is the grouting volume; N is the number of grouting balls; r is the radius of the grouting balls; ρ is the grouting density.

3. The method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 1, characterized in that: In the step S30, the soil constitutive model is a hardened soil constitutive model, and the mechanical parameters of the hardened soil constitutive model include soil strength parameters, deformation parameters and small strain parameters.

4. A method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 3, characterized in that: The soil strength parameters include effective cohesion c, effective internal friction angle Shear dilatancy angle ψ and failure ratio R f , the calculation formula of the dilatancy angle ψ is as follows: The destruction ratio R f It is related to the soil porosity ratio e. The relationship between the damage ratio and the porosity ratio is:

5. A method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 4, characterized in that: The deformation parameters include the reference stress p ref , Tangent compression modulus corresponding to reference stress Secant modulus corresponding to 0.5 times the deviatoric stress under reference stress Unloading and reloading modulus at reference stress Normal consolidation static lateral pressure coefficient and the power exponent m related to the stiffness stress level; The normal consolidation static lateral pressure coefficient The calculation formula is: in, is the normal consolidation static lateral pressure coefficient, is the effective internal friction angle; The value of the stiffness stress level related power exponent m is related to the soil properties. For sandy soil, the stiffness stress level related power exponent m is 0.7, and for clay soil, the stiffness stress level related power exponent m is 0.

65.

6. A method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 5, characterized in that: The small strain parameters include the small strain reference initial shear modulus The shear strain γ corresponding to the decay of the secant shear modulus to 0.7 times the initial shear modulus 0.7 ; The small strain refers to the initial shear modulus Determined by the following empirical formula: Among them, e is the soil void ratio, OCR is the overconsolidation ratio; The shear strain γ corresponding to the decay of the secant shear modulus to 0.7 times the initial shear modulus 0.7 In clay soil, the range is (2.4~4.2)×10 -4 , with an average value of 3.2×10 -4 , in sandy soil, the range is (2.9~5.2)×10 -4 , with an average value of 3.9×10 -4 .

7. The method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 1, characterized in that: The pile-soil contact interface parameters in step S40 include the standard value of the ultimate lateral friction resistance of the pile body, the shear stiffness modulus k t , normal stiffness modulus k n The standard value of the ultimate lateral friction resistance of the pile body is determined according to the type of soil, and the shear stiffness modulus k t Take 10 times the elastic modulus of the soil, the normal stiffness modulus k n The elastic modulus of the soil is 100 times, the standard value of the ultimate bearing capacity of the pile end is determined according to the type of the soil, and the spring stiffness of the pile end is the elastic resistance coefficient of the soil.

8. The method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 1, characterized in that: The calculation steps of the pile foundation horizontal loading finite element model in step S80 are as follows: S801, activate the soil, apply gravity and soil constraints, and then clear the displacement; S802, activating the pile foundation, interface unit, pile end unit, and grouting ball, and applying rotation constraint to the pile foundation in the Z direction; S803, perform the displacement clearing operation again; S804. Divide the horizontal load on the pile top into n incremental steps for step-by-step loading, and then submit for calculation and analysis.

9. The method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 1, characterized in that: The conditions for determining the horizontal ultimate bearing capacity of the pile foundation in step S90 are as follows: According to the characteristic curve of the change of pile top horizontal displacement with load, that is, the PY curve characteristic, for pile foundations with a pile body reinforcement ratio of not less than 0.65%, 75% of the load corresponding to a horizontal displacement of 10mm at the ground is taken as the horizontal ultimate bearing capacity of the pile foundation; For pile foundations with a pile reinforcement ratio of less than 0.65%, when the maximum principal stress of the pile foundation reaches the material yield strength under horizontal load conditions, 75% of the horizontal load is taken as the horizontal ultimate bearing capacity of the pile foundation.

10. A method for determining the horizontal ultimate bearing capacity of a distributed post-grouting pile foundation according to claim 9, characterized in that: The minimum principal stress of the pile foundation under the above-mentioned judgment conditions all meets the compressive strength of the pile foundation itself.

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