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CN-122019931-A - Calculation method for axial limit pulling resistance and pulling resistance torque of positive spiral pile foundation

CN122019931ACN 122019931 ACN122019931 ACN 122019931ACN-122019931-A

Abstract

The invention discloses a calculation method of axial limit pulling resistance and pulling resistance torque of a positive screw pile foundation, which comprises the steps of constructing a corresponding control equation and boundary conditions to solve and obtain stress components of a plastic region, obtaining the association relation between the outer radius of the plastic region and the current small hole radius and small hole pressure based on the boundary conditions according to radial stress and integral constant, and considering the vertical and horizontal soil squeezing effects as the expansion process of spherical holes and cylindrical holes respectively by the action of axial pulling load and the equivalent of the behavior of the soil body around the positive screw pile pulling face to be circular hole expansion, and simultaneously determining reaming pressure based on a cylindrical hole expansion model with a non-zero initial radius based on a rock-soil medium small hole expansion theory so as to correct a classical cylindrical shearing model, thereby considering the radial stress effect generated on a cylindrical shearing breaking face due to the soil squeezing effect of the pulling face, so that the self-strengthening function of the positive screw pile is theoretically explained while accurately calculating the pulling resistance bearing capacity of the positive screw pile.

Inventors

  • WANG KUNPENG
  • ZHANG RUNDAN

Assignees

  • 大连海事大学

Dates

Publication Date
20260512
Application Date
20260109

Claims (7)

  1. 1. A calculation method of axial limit pulling resistance and pulling resistance torque of a positive spiral pile foundation is characterized by comprising the following steps: S1, taking a drawing surface of a positive spiral pile as an elastic area, taking a soil body around the pile as a plastic area, and based on a small hole expansion theory, equivalently treating the behavior of extruding the soil body around the pile by the drawing surface of the positive spiral pile under the action of axial drawing load as a circular hole expansion problem, and combining The strength yield criterion builds a corresponding control equation and boundary conditions; S2, solving and obtaining a stress component of the plastic region according to a control equation and a boundary condition, wherein the stress component of the plastic region comprises radial stress and tangential stress; utilizing the continuity of elastic-plastic interface stress components to obtain an integral constant according to the radial stress and tangential stress; S3, based on boundary conditions, according to radial stress and integral constant, obtaining the association relation between the outer radius of the plastic region and the current aperture radius and aperture pressure; S4, decomposing the extrusion action of the positive spiral pile drawing surface on the soil body around the pile into a vertical component and a horizontal component, adopting a spherical hole expansion model and a cylindrical hole expansion model to perform equivalent characterization to obtain a vertical spherical hole and a horizontal cylindrical hole, and simultaneously setting the synchronous expansion of the vertical spherical hole and the horizontal cylindrical hole in the axial drawing loading process; Taking the corresponding small hole inner pressure in the expansion final state as the radial stress acted on the cylindrical shearing damage surface when the positive spiral pile reaches the bearing capacity limit state under the axial drawing load action; S5, based on a cylindrical shear model, obtaining soil shear strength according to the radial stress obtained in the S4, and obtaining shear resistance on a cylindrical shear failure surface according to the soil shear strength; and S6, acquiring an included angle between the acting force direction corresponding to the shearing resistance and the pile axis of the positive spiral pile, decomposing the shearing resistance into a vertical component and a horizontal component according to the included angle, and respectively calculating and acquiring the ultimate pulling resistance and ultimate torque of the positive spiral pile according to the vertical component and the horizontal component.
  2. 2. The method for calculating the axial limit pulling resistance and the pulling resistance torque of the foundation of the positive screw pile according to claim 1, wherein the control equation in S1 is constructed by the following formula: wherein: Representing design parameters; Representing tangential stress in the stress component of the plastic region; representing radial stress in the stress component of the plastic region; Represents the hole radius of the expansion of the round hole; the boundary conditions are expressed as follows: wherein: The method is characterized in that the radius of the hole is continuously increased from an initial value a 0 to a pressure value corresponding to a current value a; p represents the current pore pressure; Representing the number of intermediate parameters; Representing the internal friction angle of the soil body; representing the cohesive force of soil; indicating that the conditions are satisfied during the orifice expanding process Threshold of the strength yield criterion.
  3. 3. The method for calculating the axial limit pulling resistance and the pulling resistance torque of the foundation of the positive screw pile according to claim 2, wherein the step S2 specifically comprises the steps of: S21, solving and obtaining stress components of the plastic region according to a control equation and boundary conditions, wherein the stress components of the plastic region comprise radial stress And tangential stress The expression is: s22, obtaining an integral constant according to radial stress and tangential stress by utilizing the continuity of elastic-plastic interface stress components The expression is: 。
  4. 4. The method for calculating the axial limit pulling resistance and the pulling resistance torque of the foundation of the positive screw pile according to claim 3, wherein the correlation between the outer radius c of the plastic region and the current small hole radius a and the small hole pressure p is obtained in the step S3, and the expression is as follows; 。
  5. 5. the method for calculating the axial limit pulling resistance and the pulling resistance torque of the foundation of the positive screw pile according to claim 4, wherein the step S4 specifically comprises the steps of: S41, decomposing the extrusion action of a positive spiral pile drawing surface on a pile periphery soil body into a vertical component and a horizontal component, and adopting a spherical hole expansion model and a cylindrical hole expansion model to perform equivalent characterization to obtain a vertical spherical hole and a horizontal cylindrical hole, and simultaneously setting that the vertical spherical hole and the horizontal cylindrical hole are synchronously expanded in the axial drawing and loading process; s42, confirming that when the radius of the vertical spherical hole expands to a plastic region to meet a set condition based on a small hole expansion theory, the positive screw pile reaches an axial drawing bearing capacity limit state; And the expression of the setting condition is: wherein: representing a scaling factor; Representing the outer boundary dimension of the vertical spherical hole expansion model; s43, according to the plastic region radius meeting the set condition Taking half of the diameter of the positive spiral pile as the value of the current small hole radius a, substituting the value of the current small hole radius a into the association relation obtained in the step S3 to obtain the corresponding small hole pressure in the expansion final state ; S44, taking the corresponding small hole inner pressure in the expansion final state as the radial stress acted on the cylindrical shearing breaking surface when the positive spiral pile reaches the bearing capacity limit state under the axial drawing load The method comprises the following steps: 。
  6. 6. The method for calculating the axial limit pulling resistance and the pulling resistance torque of the foundation of the positive screw pile according to claim 5, wherein the step S5 specifically comprises the steps of: s51, based on a cylindrical shear model, obtaining the soil shear strength according to the radial stress obtained in the S4, wherein the soil shear strength is as follows: wherein: representing the shear strength of soil; S52, acquiring the shearing resistance on the cylindrical shearing damage surface according to the shearing strength of the soil body, wherein the shearing resistance is as follows: wherein: represents shear resistance; respectively representing the burial depths of the bottommost and topmost spiral structures, and z represents the depth of the foundation soil body.
  7. 7. The method for calculating the axial limit pulling resistance and the pulling resistance torque of the foundation of the positive screw pile according to claim 6, wherein the step S6 specifically comprises the steps of: s61, obtaining the included angle between the acting force direction corresponding to the shearing resistance and the pile axis of the positive spiral pile The expression is: wherein, theta represents the torsion angle of the pile body, delta represents the friction angle of the pile-soil interface; s62, decomposing the shearing resistance into a vertical component and a horizontal component according to the included angle, and respectively calculating and obtaining the ultimate pulling resistance and ultimate torque of the positive screw pile according to the vertical component and the horizontal component; The obtaining formula of the ultimate pulling resistance and ultimate torque of the positive spiral pile is as follows: wherein: Representing the ultimate pullout resistance of the positive screw pile; Representing the limit torque of the positive screw pile.

Description

Calculation method for axial limit pulling resistance and pulling resistance torque of positive spiral pile foundation Technical Field The invention relates to the technical field of pile foundation anti-pulling bearing capacity calculation in geotechnical engineering, in particular to a calculation method of axial limit anti-pulling force and anti-pulling torque of a positive spiral pile foundation. Background In the rock-soil and foundation engineering, the evaluation of pile foundation bearing capacity is a key technical problem in foundation design and construction, and the result directly influences the stress performance and long-term stability of the structure. The rationality of the bearing capacity assessment is not only related to pile selection, structural parameter determination and construction process formulation, but also plays an important role in preventing excessive deformation or structural instability caused by improper bearing capacity estimation. By developing scientific bearing capacity analysis, the design scheme can be optimized on the premise of meeting the safety requirement, and potential safety hazards or engineering cost increase caused by design deviation are avoided. In the engineering sites with complex geological conditions, accurate bearing capacity evaluation is particularly important for improving the reliability and applicability of basic engineering, and is also an important guarantee that engineering design and construction meet the requirements of relevant specifications. In the prior art, researches on the positive screw pile are focused on a model test [3, 4] (such as considering the influence of a mounting method, a pile body structure and soil conditions on mounting resistance and axial bearing capacity [5-12]), an in-situ test [13] or a finite element simulation [14-16], and few researches relate to horizontal bearing capacity analysis [3, 4], but no method capable of accurately calculating the axial limit pull-out bearing capacity of the positive screw pile is formed. Engineering practice shows that the ultimate anti-pulling bearing capacity of the positive spiral pile is far higher than the theoretical calculation value based on a classical cylindrical shear model, and the phenomenon is called a self-strengthening function [2, 17], and a method capable of reasonably and accurately calculating the anti-pulling bearing capacity of the positive spiral pile is not developed at present because of the existence of the phenomenon. In the engineering, the pulling-resistant bearing capacity of the positive spiral pile is measured through an in-situ load test, so that a large amount of resources are consumed, and the popularization and the application of the positive spiral pile in the global scope are severely restricted. The classical cylindrical shearing model only produces shearing action [1, 10] on soil body when the pile body is drawn, ignores additional radial stress produced by extruding soil body around the pile on the drawing surface of the positive spiral pile, only calculates the shearing strength of the cylindrical shearing damage surface by using initial horizontal ground stress, and causes the calculated value to be far lower than the measured value [2, 10, 11], and cannot reflect the self-strengthening function. In addition, the existing rock-soil medium small hole expansion theory is applied to bearing capacity calculation of structures such as plate anchors, helical blade piles and the like, but a mathematical physical model is not established according to a pile-soil action mechanism of the positive helical pile so as to form a systematic anti-pulling bearing capacity calculation scheme, so that the technical problem of accurate calculation of the anti-pulling bearing capacity of the positive helical pile still cannot be solved. Disclosure of Invention The invention provides a calculation method of axial limit pulling resistance and pulling resistance torque of a positive spiral pile foundation, which aims to overcome the technical problems. In order to achieve the above object, the technical scheme of the present invention is as follows: a calculation method of axial limit pulling resistance and pulling resistance torque of a positive spiral pile foundation comprises the following steps: S1, taking a drawing surface of a positive spiral pile as an elastic area, taking a soil body around the pile as a plastic area, and based on a small hole expansion theory, equivalently treating the behavior of extruding the soil body around the pile by the drawing surface of the positive spiral pile under the action of axial drawing load as a circular hole expansion problem, and combining The strength yield criterion builds a corresponding control equation and boundary conditions; S2, solving and obtaining a stress component of the plastic region according to a control equation and a boundary condition, wherein the stress component of the plastic region comprises ra