A method for evaluating the stability of a cast-in-place bored pile hole wall

Abstract

The present application relates to the technical field of data processing, and more particularly to a method for evaluating the stability of the hole wall of a cast-in-place pile, comprising: obtaining the design parameters, geological parameters and construction parameters of the cast-in-place pile; selecting a plurality of measuring points along the depth direction of the pile body, calculating the hole wall safety factor for each measuring point; establishing an evaluation index system and extracting the actual values of the evaluation indexes corresponding to each measuring point; establishing a critical stability reference sequence as the reference value of the evaluation indexes, using a variable weight grey correlation analysis method to obtain the comprehensive correlation degree of each measuring point; calculating the safety margin index and the state correlation degree index to combine and construct the comprehensive stability evaluation index; and performing double-index joint determination according to the minimum comprehensive stability evaluation index and the minimum hole wall safety factor to perform hierarchical evaluation of the stability of the hole wall of the cast-in-place pile. The technical scheme of the present application realizes more accurate and comprehensive evaluation of the stability of the hole wall of the cast-in-place pile.

Description

Technical Field

[0001] This invention relates to the field of data processing technology, and in particular to a method for evaluating the stability of the borehole wall of a bored pile. Background Technology

[0002] Drilled piles, as an important form of deep foundation, are widely used in high-rise buildings, bridges, and docks. The construction process involves drilling into the ground to form a pile hole, followed by pouring concrete to form the pile. Since the pile hole is in a free-floating state before pile formation, either unsupported or only supported by mud slurry, the stability of the hole wall directly affects construction safety and pile quality. Hole wall instability can lead to serious accidents such as hole collapse, diameter reduction, and stuck drill bits, causing delays and economic losses. Therefore, scientifically evaluating the stability of drilled pile hole walls has significant engineering practical importance.

[0003] The factors influencing borehole wall stability are complex and diverse, primarily including soil strength parameters, groundwater conditions, drilling mud properties, borehole geometry, and construction techniques. These factors interact and influence each other, making borehole wall stability evaluation a typical multi-factor coupled problem. Currently, the evaluation methods for borehole wall stability in engineering practice mainly include methods based on a single safety factor, methods based on multi-index comprehensive evaluation, and methods based on numerical simulation. While the single safety factor method is clear in principle and simple to calculate, it only considers mechanical equilibrium conditions and fails to comprehensively reflect the influence of non-strength factors such as drilling mud properties and construction techniques. Multi-index evaluation methods can consider the combined effects of multiple factors, but the index weights usually use fixed constant weights, failing to reflect the dynamic changes in the importance of each factor under different working conditions, and the evaluation results lack a direct connection with the safety factor indicators of concern in engineering practice. Numerical simulation methods are theoretically rigorous, but their high computational cost and difficulty in obtaining parameters make them unsuitable for rapid on-site evaluation and real-time decision-making during construction.

[0004] Chinese patent CN201610020594.1 discloses an evaluation method for the collapse risk of bored pile foundations. This method, based on the fundamental principles of fuzzy mathematics, analyzes and evaluates the stability of the bored pile borehole wall and the collapse risk through multi-factor analysis. The method selects ten evaluation indicators to construct an evaluation system, including sand layer thickness, sand layer proportion, average SPK of the sand layer, relative density of the sand, average particle size of the sand, sand uniformity coefficient, borehole soil structure, borehole design depth, groundwater level fluctuation, and groundwater level depth. The method uses an over-standard multiple weighting method to determine the weight of each evaluation indicator, and employs a parabolic membership function to calculate the membership degree values ​​corresponding to different collapse risk levels for each evaluation indicator. Based on the principle of maximum membership, the collapse risk level of the evaluation unit is determined, classifying the borehole wall stability of bored piles into three levels: low risk, medium risk, and high risk. Although the patented method considers multiple influencing factors, it still suffers from problems such as fixed evaluation index weights, failure to reflect the coupling effect between indicators, and lack of direct correlation between evaluation results and mechanical safety factor. These issues result in insufficient accuracy and weak comprehensiveness in the evaluation of hole wall stability. Summary of the Invention

[0005] In view of this, the present invention proposes a method for evaluating the stability of the borehole wall of bored piles, in order to solve the problems of insufficient accuracy and weak comprehensiveness in the existing technology for evaluating borehole wall stability.

[0006] The technical solution of this invention is implemented as follows: This invention provides a method for evaluating the stability of the borehole wall of a bored pile, comprising the following steps:

[0007] S1. Obtain the design parameters, geological parameters, and construction parameters for the bored pile;

[0008] S2. Select several measurement points along the depth direction of the pile body. Based on the design parameters, geological parameters and construction parameters, calculate the stress state of the borehole wall for each measurement point based on the theory of elasticity. Establish a calculation model for the borehole wall safety factor using the failure criterion to obtain the borehole wall safety factor for each measurement point.

[0009] S3. Establish an evaluation index system that includes soil strength characteristics, mud wall performance and geometric conditions, and extract the actual values ​​of the evaluation indexes corresponding to each measurement point based on geological parameters and construction parameters.

[0010] S4. Establish a critical stable reference sequence as the reference value of the evaluation index, and use the variable weight grey relational analysis method to analyze the correlation between the actual value and the reference value of the evaluation index of each measurement point. In the process of correlation calculation, state sensitivity mechanism, variable weight mechanism and coupling correction mechanism are introduced for correction to obtain the comprehensive correlation of each measurement point.

[0011] S5. Based on the hole wall safety factor of each measurement point, the safety margin index is obtained; based on the comprehensive correlation of each measurement point, the state correlation index is obtained; and the safety margin index and the state correlation index are combined to obtain the comprehensive stability evaluation index of each measurement point.

[0012] S6. The borehole wall stability of bored piles is assessed by a dual-index joint determination based on the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor.

[0013] Based on the above technical solutions, preferably, in step S1, the design parameters include pile diameter, pile length, casing depth and mud level elevation; the geological parameters include stratum distribution, physical and mechanical parameters of each soil layer and groundwater level; the physical and mechanical parameters include soil layer thickness, unit weight, cohesion, internal friction angle, void ratio and permeability coefficient; and the construction parameters include mud unit weight, mud viscosity, sand content and mud level elevation.

[0014] Based on the above technical solutions, preferably, step S2 specifically includes:

[0015] S21. Set up several measurement points along the depth of the pile body. The measurement points are located at the stratigraphic interface, the location of the weak interlayer, and the groundwater level.

[0016] S22. Calculate the mud pressure at each measuring point according to the hydrostatic pressure principle, calculate the vertical earth pressure and horizontal earth pressure according to the soil layer self-weight stress theory and the static earth pressure coefficient method, calculate the pore water pressure according to the hydrostatic pressure method, and obtain the effective horizontal earth pressure based on the difference between the horizontal earth pressure and the pore water pressure.

[0017] S23. Based on the elasticity theory, the effective horizontal earth pressure is used as the far-field stress and the mud pressure is used as the internal pressure to calculate the tangential stress of the borehole wall at each measurement point.

[0018] S24. Based on the failure criterion, establish a borehole wall safety factor calculation model with cohesion and internal friction angle as strength parameters and borehole wall tangential stress and effective horizontal earth pressure as stress parameters. Use the strength reduction method to solve for the borehole wall safety factor at each measurement point.

[0019] Based on the above technical solutions, preferably, in step S24, the formula for calculating the hole wall safety factor is as follows:

[0020] in, For depth The cohesion of the soil layer For depth The internal friction angle of the soil layer in which it is located. For depth The mud pressure at the location, For depth Effective horizontal earth pressure at the location.

[0021] Based on the above technical solutions, preferably, in step S3, the evaluation index system includes cohesion and internal friction angle characterizing soil strength characteristics, mud unit weight characterizing mud wall performance, borehole radius and calculation depth characterizing geometric conditions, extracting the actual values ​​of the evaluation indexes corresponding to each measurement point, and normalizing the actual values ​​of the evaluation indexes to obtain a normalized index vector.

[0022] Based on the above technical solutions, preferably, step S4 specifically includes:

[0023] S41. Set a baseline safety factor, calculate the critical values ​​of each evaluation index under critical stability state based on the construction parameters and soil strength parameters of each measurement point, and normalize the critical values ​​to obtain the critical stability reference sequence.

[0024] S42. Calculate the difference sequence between the normalized index vector of each measurement point and the critical stable reference sequence, and determine the minimum and maximum differences based on the difference sequence;

[0025] S43. Calculate the state deviation of each index at each measurement point based on the difference sequence. Obtain the state sensitivity resolution coefficient through the state sensitivity mechanism based on the state deviation and the soil layer sensitivity coefficient. Calculate the initial grey relational coefficient of each index at each measurement point using the state sensitivity resolution coefficient and the difference sequence.

[0026] S44. Calculate the state coefficient of each indicator at each measurement point, and dynamically adjust the constant weight of each indicator through a variable weighting mechanism based on the state coefficient to obtain the variable weighting vector.

[0027] S45. The initial grey relational coefficients are corrected by strength coupling correction mechanism for cohesion and internal friction angle, and by stress coupling correction mechanism for mud density, to obtain the corrected grey relational coefficients.

[0028] S46. Calculate the comprehensive correlation degree of each measurement point based on the variable weight vector and the corrected grey relational coefficient.

[0029] Based on the above technical solutions, preferably, in step S44, the weighting mechanism is to calculate the state coefficient of the actual value and reference value of each indicator at each measurement point, and to use an exponential weighting function to increase the weight of indicators with a state coefficient less than 1; to maintain the constant weight for indicators with a state coefficient greater than or equal to 1; and to calculate the weighting based on the state weighting vector and the constant weight.

[0030] Based on the above technical solutions, preferably, in step S45, the coupling correction mechanism includes strength index coupling correction and stress index coupling correction. The strength index coupling correction targets cohesion and internal friction angle, and calculates the strength coupling coefficient based on their complementary relationship in soil strength, thereby correcting the grey relational coefficients of cohesion and internal friction angle. The stress index coupling correction targets mud unit weight index, and calculates the stress balance coefficient based on the stress balance relationship between mud pressure and effective horizontal earth pressure, thereby correcting the grey relational coefficient of mud unit weight.

[0031] Based on the above technical solutions, preferably, the formula for calculating the comprehensive stability evaluation index is as follows:

[0032]

[0033]

[0034] in, Let be the safety margin index for the j-th measurement point. Let the safety factor of the borehole wall be the value at the j-th measurement point. As a baseline safety factor, Let the comprehensive correlation of the j-th measurement point be denoted as . For the combined weighting coefficients, This represents the safety margin weight in the geometric mean.

[0035] Based on the above technical solutions, preferably, in step S6, the graded evaluation adopts a dual-index joint judgment rule to divide the borehole wall stability of the bored pile into four levels: Level I Excellent, Level II Good, Level III Average and Level IV Poor. The minimum comprehensive stability evaluation index and the minimum borehole wall safety factor among all measurement points are found, and the corresponding stability level is determined according to the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor.

[0036] The criteria for determining a Class I "excellent" level are: minimum comprehensive stability evaluation index ≥ 1.30 and minimum borehole wall safety factor ≥ 1.50; for a Class II "good" level, the criteria are: minimum comprehensive stability evaluation index 1.05~1.3 and minimum borehole wall safety factor 1.3~1.5; for a Class III "average" level, the criteria are: minimum comprehensive stability evaluation index 0.85~1.05 or minimum borehole wall safety factor 1.15~1.30; and for a Class IV "poor" level, the criteria are: minimum comprehensive stability evaluation index < 0.85 or minimum borehole wall safety factor < 1.15.

[0037] The method for evaluating the stability of the borehole wall of cast-in-place piles of the present invention has the following advantages over the prior art:

[0038] (1) By combining the calculation of the borehole wall safety factor with the variable weight grey relational analysis method, a comprehensive evaluation system integrating mechanical evaluation and multi-factor evaluation was established. A comprehensive stability evaluation index considering soil strength characteristics, mud wall performance and geometric conditions was constructed. The stability of the borehole wall was graded and evaluated by the dual-index joint judgment rule, which realized a more accurate and comprehensive evaluation of the borehole wall stability of the bored pile, and provided an effective technical means for decision-making and quality control in the construction process.

[0039] (2) Based on the mechanical equilibrium condition of the hole wall, the present invention calculates the critical index value corresponding to the benchmark safety factor. The reference sequence changes with depth and is related to the stress state. It characterizes the threshold level of each index when the hole wall reaches the critical stable state, so that the multi-factor evaluation results are directly linked to the mechanical safety factor, and the mechanical rationality of the evaluation is improved.

[0040] (3) The state-sensitive mechanism and variable weight mechanism introduced in this invention enable the index weight to be dynamically adjusted according to the working conditions. When the state of a certain index is worse than the critical stability requirement, the weight of the index is automatically increased, which effectively reflects the constraint effect of the weak link on the stability of the hole wall. At the same time, the synergistic effect and complementary relationship between the strength index and the stress index are considered through the coupling correction mechanism. Compared with the traditional fixed weight method, the evaluation improves the ability and accuracy of identifying unfavorable working conditions.

[0041] (4) The comprehensive stability evaluation index constructed in this invention adopts a weighted geometric-arithmetic average combination form, which reflects the evaluation concept of safety factor as the main factor and multi-factor comprehensive balance. The established dual-index joint judgment rule comprehensively considers the minimum comprehensive stability evaluation index and the minimum hole wall safety factor for graded evaluation, avoiding the possible deviation of single index judgment. Differentiated construction control measures are formulated for different stability levels, realizing the direct connection between evaluation results and construction decisions, and enhancing the engineering practicality of the method. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a flowchart of the borehole wall stability evaluation method of the present invention;

[0044] Figure 2 This is a flowchart of the dual-indicator joint evaluation process of the present invention. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] like Figure 1 As shown, the present invention provides a method for evaluating the stability of the borehole wall of a bored pile, comprising the following steps:

[0047] S1. Obtain the design parameters, geological parameters, and construction parameters for the bored pile;

[0048] S2. Select several measurement points along the depth direction of the pile body. Based on the design parameters, geological parameters and construction parameters, calculate the stress state of the borehole wall for each measurement point based on the theory of elasticity. Establish a calculation model for the borehole wall safety factor using the failure criterion to obtain the borehole wall safety factor for each measurement point.

[0049] S3. Establish an evaluation index system that includes soil strength characteristics, mud wall performance and geometric conditions, and extract the actual values ​​of the evaluation indexes corresponding to each measurement point based on geological parameters and construction parameters.

[0050] S4. Establish a critical stable reference sequence as the reference value of the evaluation index, and use the variable weight grey relational analysis method to analyze the correlation between the actual value and the reference value of the evaluation index of each measurement point. In the process of correlation calculation, state sensitivity mechanism, variable weight mechanism and coupling correction mechanism are introduced for correction to obtain the comprehensive correlation of each measurement point.

[0051] S5. Based on the hole wall safety factor of each measurement point, the safety margin index is obtained; based on the comprehensive correlation of each measurement point, the state correlation index is obtained; and the safety margin index and the state correlation index are combined to obtain the comprehensive stability evaluation index of each measurement point.

[0052] S6. The borehole wall stability of bored piles is assessed by a dual-index joint determination based on the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor.

[0053] In one embodiment of the present invention, step S1 includes: obtaining basic data of the bored pile based on the geotechnical engineering investigation report and design documents. Design parameters include pile diameter, pile length, casing depth, and mud level. Geological parameters include stratum distribution, physical and mechanical parameters of each soil layer, and groundwater level. The physical and mechanical parameters specifically include soil layer thickness, unit weight, cohesion, internal friction angle, void ratio, and permeability coefficient. For soil layers below the groundwater level, it is necessary to distinguish between natural unit weight and buoyant unit weight; buoyant unit weight is calculated by subtracting the unit weight of water from the saturated unit weight. For layered soils, the starting and ending depths and corresponding parameters of each soil layer should be recorded layer by layer. For strata with weak interlayers or special soil properties, their location and properties need to be specifically marked. Construction parameters include mud unit weight, mud viscosity, sand content, and mud level. Mud unit weight is a key parameter affecting borehole stability and is generally measured using a hydrometer or densitometer, with units of kilonewtons per cubic meter. The mud level needs to be accurately measured. It should generally be 1.5 to 2.0 meters above the groundwater level or 0.5 to 1.0 meters above the ground surface.

[0054] In one embodiment of the present invention, step S2 includes the following sub-steps:

[0055] S21. Set up several measuring points along the depth of the pile, placing them at stratigraphic interfaces, weak interlayers, and groundwater levels. Set measuring points every 3-5 meters at conventional depths to ensure the stability of unfavorable strata and critical depths can be captured. Number the measuring points downwards from the ground surface. The depth of each measurement point is denoted as The value is positive when counting downwards from the ground.

[0056] S22. Calculate the mud pressure at each measuring point based on the hydrostatic pressure principle, calculate the vertical earth pressure and horizontal earth pressure based on the soil layer self-weight stress theory and the static earth pressure coefficient method, calculate the pore water pressure based on the hydrostatic pressure method, and obtain the effective horizontal earth pressure based on the difference between the horizontal earth pressure and the pore water pressure.

[0057] Specifically, the mud pressure at each measuring point is calculated based on the principle of hydrostatic pressure. The formula for calculating mud pressure is:

[0058]

[0059] in For depth The mud pressure at the location, The mud is of high density. This represents the height of the mud slurry above the ground; when the mud slurry level is below the ground, a negative value is used.

[0060] Vertical earth pressure is calculated based on the soil self-weight stress theory, for depth... If the point is located at the th In the soil layer, the vertical earth pressure is:

[0061]

[0062] in For depth Vertical earth pressure at the location, For the first The unit weight of the soil layer is used; below the groundwater level, the buoyant unit weight is used. For the first Thickness of soil layer , For the first The depth of the top surface of the soil layer.

[0063] The formula for calculating horizontal earth pressure using the at-rest earth pressure coefficient method is as follows:

[0064]

[0065] in For depth Horizontal earth pressure at the location, For depth The coefficient of earth pressure at rest at a given location is given by the Jaky empirical formula for normally consolidated soil. calculate, This is the internal friction angle of the soil layer at that depth.

[0066] Pore ​​water pressure is calculated using the hydrostatic pressure method when the depth is... The pore water pressure when the groundwater level is below is:

[0067]

[0068] in For depth Pore ​​water pressure at the location, The specific weight of water is taken as 10 kN / m 3 , This refers to the depth of the groundwater level.

[0069] The effective horizontal earth pressure is obtained by subtracting the pore water pressure from the horizontal earth pressure. The calculation formula is as follows:

[0070]

[0071] in For depth Effective horizontal earth pressure at the location.

[0072] S23. Based on elasticity theory, the effective horizontal earth pressure is used as the far-field stress and the mud pressure is used as the internal pressure to calculate the tangential stress of the borehole wall at each measurement point.

[0073] Specifically, under isotropic compressive stress in the far field, the tangential stress at the hole wall of the circular hole is twice the far field stress minus the internal pressure, and the calculation formula is as follows:

[0074]

[0075] in For depth The tangential stress at the hole wall. This simplification assumption reduces the actual non-uniform stress state to an isocompressive state, which introduces a certain error. The simplification overestimates the tangential stress by about 30% to 50%, and is a conservative assumption.

[0076] S24. Based on the failure criterion, establish a borehole wall safety factor calculation model with cohesion and internal friction angle as strength parameters and borehole wall tangential stress and effective horizontal earth pressure as stress parameters. Use the strength reduction method to solve for the borehole wall safety factor at each measurement point.

[0077] Specifically, a calculation model for the hole wall safety factor is established based on the Mohr-Coulomb failure criterion. The cohesion and internal friction angle are simultaneously divided by the safety factor using the strength reduction method. Based on the balance relationship between tangential and radial stresses at the borehole wall, the simplified formula for calculating the borehole wall safety factor is derived as follows:

[0078]

[0079] in, For depth Safety factor of the borehole wall at the location, For depth The cohesion of the soil layer in which it is located For depth The internal friction angle of the soil layer in which it is located. For depth The mud pressure at the location, For depth The effective horizontal earth pressure at that point. The numerator of this formula is the resistance term, which includes the contribution of cohesion. and frictional contribution The denominator is the driving force term, i.e., the effective circumferential tensile stress. For all measurement points along the depth direction, the safety factor is calculated point-by-point. Find the minimum value and denote it as The depth corresponding to this minimum safety factor is the most unfavorable position of the borehole wall.

[0080] In one embodiment of the present invention, step S3 includes: establishing a comprehensive evaluation index system that includes soil strength characteristics, mud wall performance, and geometric conditions. The evaluation index system selects five key indicators, namely, cohesion characterizing soil strength characteristics. and internal friction angle Mud density, which characterizes the wall-supporting performance of mud. Drilling radius characterizing geometric conditions and computational depth This constitutes the evaluation index set. For the first [item] along the depth direction There are 1 measurement point with a depth of 1. The soil parameters corresponding to this depth constitute the evaluation index vector. ,in The cohesion of the soil layer at that depth, The internal friction angle of the soil layer at that depth. For mud density, For the drilling radius, This represents the depth of the measurement point. To eliminate the influence of dimensions and unify the direction of the indicators, the original indicators are normalized. For positive indicators, this includes... , , Using the normalization formula ,in For the first The measurement point is the first The normalized value of each indicator. For contrarian indicators, including... , Using the normalization formula .in and The first The maximum and minimum values ​​of each indicator across all depth points or within a reasonable engineering range. Normalized indicator values. A larger value indicates a better state for that indicator. The Analytic Hierarchy Process (AHP) is used to determine the constant weights of each indicator. A judgment matrix is ​​constructed for pairwise comparisons, and the constant weight vector is obtained after consistency testing. The recommended weight is set to 1. .

[0081] In one embodiment of the present invention, step S4 includes the following sub-steps:

[0082] S41. Set a baseline safety factor, calculate the critical values ​​of each evaluation index under critical stability state based on the construction parameters and soil strength parameters of each measurement point, and normalize the critical values ​​to obtain the critical stability reference sequence.

[0083] Specifically, in this embodiment of the invention, a baseline safety factor is taken. For a given depth point The actual construction parameters, i.e., the actual mud density, are used. and mud level Calculate the mud pressure at this depth. and effective horizontal earth pressure According to the safety factor formula, when At this point, the combined relationship between cohesion and internal friction angle under critical conditions can be obtained:

[0084]

[0085] Define soil type coefficient Characterizing the contribution of cohesion to total strength, based on the actual cohesion of the soil layer. and internal friction angle Value, combined with the actual stress state and Calculate the contribution ratio of cohesion:

[0086]

[0087] Based on this ratio, the reference values ​​for cohesion and internal friction angle under critical conditions are as follows:

[0088]

[0089]

[0090] For mud density, the support pressure coefficient is defined. ,when Recommended support pressure coefficient The critical mud specific weight is For geometric parameters, the critical value of the borehole radius. Take the design aperture as the critical value for calculating the depth. The value is taken as 50% of the design pile length. The above critical value is then normalized to obtain the normalized vector of the critical stability reference sequence. ,in , For the first The measurement point is the first The critical reference normalized value of each indicator. This reference sequence varies with depth and is related to the mechanical state, representing the threshold level of each indicator when the depth point reaches a critical steady state.

[0091] S42. Calculate the difference sequence between the normalized index vector of each measurement point and the critical stable reference sequence, and determine the minimum and maximum difference based on the difference sequence.

[0092] No. The first indicator in the The absolute difference of the measurement points is ,in For the first The measurement point is the first The difference between each indicator. Then calculate the minimum difference between all indicators at all measurement points. and maximum difference .

[0093] S43. Calculate the state deviation of each index at each measurement point based on the difference sequence. Obtain the state sensitivity resolution coefficient through the state sensitivity mechanism based on the state deviation and the soil layer sensitivity coefficient. Calculate the initial grey relational coefficient of each index at each measurement point using the state sensitivity resolution coefficient and the difference sequence.

[0094] No. The first indicator in the The state deviation of each measurement point is:

[0095]

[0096] in For the first The measurement point is the first The degree of deviation of each indicator's status. To avoid small quantities with a denominator of zero.

[0097] The deviation from the critical value reflects the degree of deviation between the actual value and the critical value. Further considering the influence of soil properties, a soil sensitivity coefficient is defined. For sandy and silty soil layers with very low cohesion, i.e. ,Pick For silty clay layers with moderate cohesion, i.e. ,Pick For clay layers with high cohesion, i.e. ,Pick Taking into account both the deviation from the state and the soil layer sensitivity, the first... The first indicator in the The state sensitivity resolution coefficient of each measurement point is: ,in For the first The measurement point is the first The state sensitivity resolution coefficient of each indicator As the reference resolution coefficient, This is the sensitivity adjustment parameter. The formula reflects that as the state deviation increases, the resolution coefficient decreases exponentially, and the system's sensitivity to this indicator increases. The initial grey relational coefficients for each indicator at each measurement point are calculated using the state sensitivity resolution coefficient and the difference sequence:

[0098]

[0099] in For the first The measurement point is the first The initial grey relational coefficient of each indicator. This relational coefficient... The larger the value, the closer the actual state of the indicator is to the critical stable state or the better it is to the critical state.

[0100] S44. Calculate the state coefficients of each indicator at each measurement point. Based on the state coefficients, dynamically adjust the constant weights of each indicator through a variable weighting mechanism to obtain the variable weight vector.

[0101] Calculate the state coefficients of each index at each measurement point, and use them as the ratio of the actual normalized value to the reference normalized value. ,in For the first The measurement point is the first The state coefficient of each indicator. When This indicates that the index is below the critical stability requirement, and the condition is poor; when This indicates that the index meets or exceeds the critical stability requirement, and the state is relatively good. An exponential state-weighted vector is constructed. ,in For the first The measurement point is the first The state-variance coefficients of each indicator, when When using an exponential weighting function Increase the weight when Maintaining permanent power Among them, the variable weight intensity coefficient The value is set to 1.0, which is larger than the 0.5 used in conventional variable weight theory, reflecting the high sensitivity of orifice wall stability evaluation to weak points. Variable weights are calculated based on the state-variable weight vector and constant weights. ,in For the first The measurement point is the first The variable weights of each indicator. These variable weights satisfy the normalization condition. .

[0102] S45. The initial grey relational coefficients are corrected by strength coupling correction mechanism for cohesion and internal friction angle, and by stress coupling correction mechanism for mud density, to obtain the corrected grey relational coefficients.

[0103] The coupling correction mechanism includes strength index coupling correction and stress index coupling correction. The strength index coupling correction targets cohesion and internal friction angle, and calculates the strength coupling coefficient based on the complementary relationship between the two in soil strength, thereby correcting the grey relational coefficients of cohesion and internal friction angle. The stress index coupling correction targets mud unit weight index, and calculates the stress balance coefficient based on the stress balance relationship between mud pressure and effective horizontal earth pressure, thereby correcting the grey relational coefficient of mud unit weight.

[0104] Specifically, for the indices of cohesion and internal friction angle, the strength coupling coefficient is calculated based on their complementary relationship in soil strength:

[0105]

[0106] in For the first The strength coupling coefficient of each measurement point This is a sign function. When both cohesion and the angle of internal friction deviate from their critical values ​​and their directions are consistent... The coupling is enhanced; when the two deviate in opposite directions, There is compensation. The initial grey relational coefficients for cohesion and internal friction angle are corrected to obtain:

[0107]

[0108]

[0109] in and The first Corrected grey relational coefficients of cohesion and internal friction angle at each measurement point.

[0110] For the mud density index, the stress ratio index is defined. ,in For the first The stress ratio at each measurement point is used to calculate the stress balance coefficient based on the stress balance relationship between mud pressure and effective horizontal earth pressure.

[0111]

[0112] in For the first Stress balance coefficient at each measurement point The optimal stress ratio is determined by correcting the initial grey relational coefficient of the mud unit weight, resulting in:

[0113]

[0114] in For the first The corrected grey relational coefficient for mud unit weight at each measurement point. For geometric parameters, namely borehole radius and calculated depth, their effects are relatively independent and no coupled correction is performed. , ,in and The first Corrected grey relational coefficients for borehole radius and calculated depth at each measurement point.

[0115] S46. Calculate the comprehensive correlation degree of each measurement point based on the variable weight vector and the corrected grey relational coefficient.

[0116] The comprehensive correlation degree of each measurement point is calculated based on the variable weight vector and the corrected grey relational coefficient. ,in For the first The overall correlation of the measurement points. This overall correlation. The larger the value, the closer the comprehensive state of the multi-index at the measurement point is to or better than the critical stable state, and the better the stability of the hole wall.

[0117] In the aforementioned variable-weight grey relational analysis method, this invention establishes a critical stability reference sequence, transforming the evaluation benchmark from an ideal state to a critical stable state, thus establishing a direct link between the evaluation results and the mechanical safety factor. By introducing a state-sensitive mechanism and a variable-weight mechanism, the index weights are dynamically adjusted according to the state, effectively highlighting the constraining effect of weak links on the stability of the borehole wall. Furthermore, by introducing a coupling correction mechanism, the synergistic effect between strength and stress indices is considered, improving the accuracy of the evaluation. Compared to conventional fixed-weight multi-index evaluation methods, this method improves the ability to identify unfavorable working conditions, providing a more reliable basis for construction decisions.

[0118] In one embodiment of the present invention, step S5 includes: obtaining a safety margin index based on the hole wall safety factor at each measurement point. The safety margin index reflects the degree of margin of the safety factor at that depth point relative to the benchmark safety factor, and is calculated as follows: ,in For the first Safety margin index for each measurement point For the first The safety factor of the borehole wall at each measuring point The baseline safety factor is 1.3. A safety margin index ≥ 1.0 indicates that the basic safety requirements are met; the higher the value, the higher the safety margin.

[0119] The state correlation index is obtained based on the comprehensive correlation of each measurement point. The state correlation index is the comprehensive grey correlation calculated in step S4. ,in For the first The comprehensive correlation degree of each measurement point characterizes the overall state level of multiple factors. The comprehensive stability evaluation index for each measurement point is obtained by combining the safety margin index and the state correlation index, and the calculation formula is as follows:

[0120]

[0121] in, For the first The comprehensive stability evaluation index of each measurement point For the first Safety margin index for each measurement point For the first The safety factor of the borehole wall at each measuring point As a baseline safety factor, For the first The overall correlation of the measurement points For the combined weighting coefficients, The safety margin weight in the geometric mean is used. In the above stability evaluation index formula, the geometric mean term uses an exponential form to reflect the weakest link effect, meaning that if any dimension is too low, the evaluation result will be significantly reduced. The safety margin has a greater weight than the state correlation degree, highlighting the dominant role of the safety factor. The arithmetic mean term directly reflects the safety margin as the basic term for stability evaluation, ensuring that even if the state correlation degree is low, a reasonable evaluation can still be obtained as long as the safety factor is high enough. In the combined form, the geometric term reflects the coupling effect of multiple factors and the requirement for balance, while the safety margin term ensures the decisive role of the safety factor. The two terms work together to achieve the evaluation concept of safety factor as the dominant factor and comprehensive balance of multiple factors. For all measurement points along the depth direction, the comprehensive stability evaluation index is calculated point by point. Find the minimum value and denote it as ,in It is the minimum comprehensive stability evaluation index among all measurement points.

[0122] In one embodiment of the present invention, such as Figure 2 As shown, step S6 includes: classifying the borehole wall stability of the bored pile based on a dual-index joint judgment using the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor. The borehole wall stability is divided into four levels: Level I (Excellent), Level II (Good), Level III (Average), and Level IV (Poor). The minimum comprehensive stability evaluation index E is then determined from all measurement points. min and minimum hole wall safety factor F s，min The corresponding stability level is determined based on the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor, and the lower of the two levels is taken as the final stability level of the borehole wall of the bored pile.

[0123] Among them, the criteria for judging Class I as excellent are a minimum comprehensive stability evaluation index ≥1.30 and a minimum borehole wall safety factor ≥1.50. At this time, the borehole wall stability is sufficient, the condition of each influencing factor is excellent, and conventional construction can be carried out without special measures. In terms of construction, conventional or slightly faster drilling speeds are adopted, and mud management can be maintained according to existing parameters. The monitoring frequency is conventional monitoring, measuring mud performance once every 2 hours, and the borehole time can be appropriately extended.

[0124] The criteria for a good Class II borehole condition are a minimum comprehensive stability evaluation index ≥1.05 and <1.30, and a minimum borehole wall safety factor ≥1.30 and <1.50. At this point, the borehole wall is basically stable and the safety reserve meets the requirements, but the trend of change needs to be monitored. In terms of construction, conventional drilling speed is adopted, and mud management needs to maintain a specific gravity of 1.15~1.25 and a viscosity of 20~25s. The monitoring frequency is to strengthen the monitoring and measure the mud performance once every 1 hour. The borehole time should be appropriately controlled to not exceed 18 hours in cohesive soil.

[0125] The general criteria for determining Level III are a minimum comprehensive stability evaluation index between 0.85 and 1.05 or a minimum borehole wall safety factor between 1.15 and 1.30. At this point, the borehole wall safety reserve is insufficient and there is a risk of local instability, requiring improvement measures. In terms of construction, the drilling speed needs to be reduced, and mud management is a key measure. The mud specific gravity needs to be increased to 1.20-1.30, the viscosity increased to 25-30s, the sand content strictly controlled, and mud stabilizers added. The monitoring frequency is intensive monitoring, with mud performance measured once every 30 minutes. The borehole time needs to be strictly controlled to no more than 12 hours in cohesive soil and no more than 8 hours in sandy or silty soil.

[0126] The criteria for determining a Class IV defect are a minimum comprehensive stability evaluation index < 0.85 or a minimum borehole wall safety factor < 1.15. In this case, there is a significant risk of borehole wall instability, and reinforcement measures or adjustments to the construction plan must be taken. Emergency measures include immediately stopping drilling and analyzing the cause. Adjustments to the plan may involve significantly improving the mud performance, such as increasing the mud specific gravity to 1.25~1.35, increasing the viscosity to 30~40s, replacing all mud with fresh, high-quality mud, and adding a high-efficiency stabilizer. After settling, a reassessment should be conducted. If the defect is still Class IV, wall reinforcement measures such as steel casing or full casing construction should be adopted, or an assessment should be made as to whether the pile type or pile location can be changed.

[0127] A dynamic evaluation and adjustment mechanism should be established during construction. Parameters should be re-collected and evaluated every 3-5 meters of drilling or when encountering changes in strata to promptly grasp the trend of borehole wall stability changes. When the evaluation level drops from high to low, the cause should be analyzed immediately and corresponding improvement measures should be taken. When three consecutive measurement points are all at level I or II, the construction progress can be appropriately accelerated. When level III or IV is reached, the construction recommendations for that level must be strictly followed, and the progress should not be blindly accelerated. For projects with complex geological conditions, it is recommended to conduct evaluations at the drilling stage, in the middle critical strata, and near the bottom of the borehole to ensure that the borehole wall stability is controllable throughout the entire process. Evaluation results should be recorded promptly and compiled into a construction log to provide a reference for similar projects.

[0128] The proposed method for evaluating the stability of bored pile borehole walls combines the calculation of borehole wall safety factors based on elasticity theory with variable-weight grey relational analysis to establish a comprehensive evaluation system that considers soil strength characteristics, mud wall performance, and geometric conditions. It introduces state-sensitive mechanisms, variable-weight mechanisms, and coupling correction mechanisms to modify the correlation degree, constructs a comprehensive stability evaluation index, and employs a dual-index joint judgment rule for graded evaluation. This method achieves a more accurate, comprehensive, and scientific evaluation of bored pile borehole wall stability, providing an effective technical means for decision-making and quality control during construction.

[0129] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the stability of the borehole wall of a bored pile, characterized in that: Includes the following steps: S1. Obtain the design parameters, geological parameters, and construction parameters for the bored pile; S2. Select several measurement points along the depth direction of the pile body. Based on the design parameters, geological parameters and construction parameters, calculate the stress state of the borehole wall for each measurement point based on the theory of elasticity. Establish a calculation model for the borehole wall safety factor using the failure criterion to obtain the borehole wall safety factor for each measurement point. S3. Establish an evaluation index system that includes soil strength characteristics, mud wall performance and geometric conditions, and extract the actual values ​​of the evaluation indexes corresponding to each measurement point based on geological parameters and construction parameters. S4. Establish a critical stable reference sequence as the reference value of the evaluation index, and use the variable weight grey relational analysis method to analyze the correlation between the actual value and the reference value of the evaluation index of each measurement point. In the process of correlation calculation, state sensitivity mechanism, variable weight mechanism and coupling correction mechanism are introduced for correction to obtain the comprehensive correlation of each measurement point. S5. Based on the hole wall safety factor of each measurement point, the safety margin index is obtained; based on the comprehensive correlation of each measurement point, the state correlation index is obtained; and the safety margin index and the state correlation index are combined to obtain the comprehensive stability evaluation index of each measurement point. S6. The borehole wall stability of bored piles is assessed by a dual-index joint determination based on the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor. Step S2 specifically includes: S21. Set up several measurement points along the depth of the pile body. The measurement points are located at the stratigraphic interface, the location of the weak interlayer, and the groundwater level. S22. Calculate the mud pressure at each measuring point according to the hydrostatic pressure principle, calculate the vertical earth pressure and horizontal earth pressure according to the soil layer self-weight stress theory and the static earth pressure coefficient method, calculate the pore water pressure according to the hydrostatic pressure method, and obtain the effective horizontal earth pressure based on the difference between the horizontal earth pressure and the pore water pressure. S23. Based on the elasticity theory, the effective horizontal earth pressure is used as the far-field stress and the mud pressure is used as the internal pressure to calculate the tangential stress of the borehole wall at each measurement point. S24. Based on the failure criterion, establish a hole wall safety factor calculation model with cohesion and internal friction angle as strength parameters and hole wall tangential stress and effective horizontal earth pressure as stress parameters, and use the strength reduction method to solve the hole wall safety factor at each measurement point. Step S4 specifically includes: S41. Set a baseline safety factor, calculate the critical values ​​of each evaluation index under critical stability state based on the construction parameters and soil strength parameters of each measurement point, and normalize the critical values ​​to obtain the critical stability reference sequence. S42. Calculate the difference sequence between the normalized index vector of each measurement point and the critical stable reference sequence, and determine the minimum and maximum differences based on the difference sequence; S43. Calculate the state deviation of each index at each measurement point based on the difference sequence. Obtain the state sensitivity resolution coefficient through the state sensitivity mechanism based on the state deviation and the soil layer sensitivity coefficient. Calculate the initial grey relational coefficient of each index at each measurement point using the state sensitivity resolution coefficient and the difference sequence. S44. Calculate the state coefficient of each indicator at each measurement point, and dynamically adjust the constant weight of each indicator through a variable weighting mechanism based on the state coefficient to obtain the variable weighting vector. S45. The initial grey relational coefficients are corrected by strength coupling correction mechanism for cohesion and internal friction angle, and by stress coupling correction mechanism for mud density, to obtain the corrected grey relational coefficients. S46. Calculate the comprehensive correlation degree of each measurement point based on the variable weight vector and the corrected grey relational coefficient.

2. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: In step S1, the design parameters include pile diameter, pile length, casing depth and mud level elevation; the geological parameters include stratum distribution, physical and mechanical parameters of each soil layer and groundwater level; the physical and mechanical parameters include soil layer thickness, unit weight, cohesion, internal friction angle, void ratio and permeability coefficient; and the construction parameters include mud unit weight, mud viscosity, sand content and mud level elevation.

3. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: In step S24, the formula for calculating the hole wall safety factor is: ； in, For depth The cohesion of the soil layer For depth The internal friction angle of the soil layer in which it is located. For depth The mud pressure at the location, For depth Effective horizontal earth pressure at the location.

4. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: In step S3, the evaluation index system includes cohesion and internal friction angle, which characterize the strength characteristics of the soil; unit weight of mud, which characterizes the mud wall performance; and borehole radius and calculated depth, which characterize the geometric conditions. The actual values ​​of the evaluation indexes corresponding to each measurement point are extracted, and the actual values ​​of the evaluation indexes are normalized to obtain a normalized index vector.

5. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: In step S44, the weighting mechanism is to calculate the state coefficient of the actual value and the reference value of each indicator at each measurement point, and to use an exponential weighting function to increase the weight of indicators with a state coefficient less than 1. For indicators with a state coefficient greater than or equal to 1, the constant weight remains unchanged; The variable weights are calculated based on the state variable weight vector and the constant weights.

6. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: In step S45, the coupling correction mechanism includes strength index coupling correction and stress index coupling correction. The strength index coupling correction targets cohesion and internal friction angle, calculates the strength coupling coefficient based on their complementary relationship in soil strength, and corrects the grey relational coefficients of cohesion and internal friction angle. The stress index coupling correction targets mud unit weight index, calculates the stress balance coefficient based on the stress balance relationship between mud pressure and effective horizontal earth pressure, and corrects the grey relational coefficient of mud unit weight.

7. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: The formula for calculating the comprehensive stability evaluation index is as follows: in, Let be the safety margin index for the j-th measurement point. Let the safety factor of the borehole wall be the value at the j-th measurement point. As a baseline safety factor, Let the comprehensive correlation of the j-th measurement point be denoted as . For the combined weighting coefficients, This represents the safety margin weight in the geometric mean.

8. The method for evaluating the stability of the borehole wall of a bored pile as described in claim 1, characterized in that: In step S6, the graded evaluation adopts a dual-index joint judgment rule to divide the borehole wall stability of the bored pile into four levels: Level I Excellent, Level II Good, Level III Average, and Level IV Poor. The minimum comprehensive stability evaluation index and the minimum borehole wall safety factor among all measurement points are found, and the corresponding stability level is determined according to the minimum comprehensive stability evaluation index and the minimum borehole wall safety factor. The criteria for determining a Class I "excellent" level are: minimum comprehensive stability evaluation index ≥ 1.30 and minimum borehole wall safety factor ≥ 1.50; for a Class II "good" level, the criteria are: minimum comprehensive stability evaluation index 1.05~1.3 and minimum borehole wall safety factor 1.3~1.5; for a Class III "average" level, the criteria are: minimum comprehensive stability evaluation index 0.85~1.05 or minimum borehole wall safety factor 1.15~1.30; and for a Class IV "poor" level, the criteria are: minimum comprehensive stability evaluation index < 0.85 or minimum borehole wall safety factor < 1.15.

Images