A method for detecting the bearing capacity of a foundation pit supporting structure based on an NT-CEP pile

Abstract

The present application relates to the technical field of foundation pit support structure bearing detection, and relates to a foundation pit support structure bearing detection method based on NT-CEP piles.The present application carries out a heaped load test on the foundation pit support structure after construction according to a set gradient heaped load, and synchronously collects pile body monitoring data and wall surface monitoring data;analyzes the measured bending moment distribution and the principal stress trace distribution of each pile body;analyzes the bending moment absolute value borne by the bearing expansion disc of each pile body according to the measured bending moment distribution of each pile body, and calculates the bending moment contribution degree, and simultaneously analyzes the stress distribution area of the wall surface based on the principal stress trace distribution;analyzes the maximum bearing heaped load of the support structure according to the bending moment contribution degree of the bearing expansion disc and the stress distribution area of the wall surface under the current heaped load, and evaluates the bearing of the foundation pit support structure according to the maximum bearing heaped load of the support structure.The safety of the detection process and the reliability of the results are improved;major safety accidents such as foundation pit collapse and instability are effectively prevented.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation pit support structure bearing detection, and relates to a foundation pit support structure bearing detection method based on an NT-CEP pile. BACKGROUND

[0002] As a new type of combined support pile, the NT-CEP pile sets a bearing expansion disc in the key stress section of the pile body, uses the close contact between the expansion disc and the surrounding soil to significantly improve the vertical bearing capacity and anti-overturning performance of the pile body, and has been widely used in complex engineering scenes such as deep foundation pits and soft soil foundations. However, the setting of the bearing expansion disc changes the traditional stress mode of the pile body, making the stress distribution and bending moment transmission path of the foundation pit support structure more complex, and the traditional bearing detection method based on ordinary piles cannot accurately and comprehensively evaluate the real bearing limit of the support structure.

[0003] However, the prior art has the following problems: 1. The prior art only calculates the bending moment by the overall displacement or stress of the pile body, without separately quantifying the bending moment contribution of the bearing expansion disc, which has the problem of insufficient detection pertinence, resulting in inaccurate identification of the actual bearing effect of the bearing expansion disc, which may overestimate or underestimate the bearing capacity of the support structure, affecting the reliability of the detection result.

[0004] 2. The prior art only focuses on the stress value change of the support wall surface, without considering the stress trace distribution of the support wall surface, thereby ignoring the influence of the stress concentration area of the wall surface on the overall bearing capacity, resulting in the omission of local failure hidden dangers caused by stress concentration of the wall surface, and further causing instability of the overall support structure, threatening the safety of the project. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a foundation pit support structure bearing detection method based on an NT-CEP pile.

[0006] The technical solution adopted by the present application to solve its technical problems is: a foundation pit support structure bearing detection method based on an NT-CEP pile, comprising: performing a pile loading test on the foundation pit support structure according to a set pile loading, and synchronously collecting pile body monitoring data and wall surface monitoring data under the current pile loading.

[0007] Based on the internal and external strain values of each pile body at each monitoring height in the pile body monitoring data, the measured bending moment distribution of each pile body is analyzed, and based on the strain characteristics of each wall surface monitoring point in the wall surface monitoring data, the main stress trace distribution of the wall surface is analyzed.

[0008] According to the measured bending moment distribution of each pile body, the bending moment absolute value borne by the bearing expansion disc of each pile body is analyzed, the bending moment contribution of the bearing expansion disc is calculated, and the stress distribution area of the wall surface is analyzed based on the main stress trace distribution.

[0009] According to the bending moment contribution degree of the force expansion disc and the stress distribution area of the wall surface, it is judged in real time whether the current pile load reaches the maximum bearing pile load of the supporting structure, if the maximum bearing pile load of the supporting structure is not reached under the current pile load, the set pile load is gradient adjusted until the maximum bearing pile load is determined.

[0010] According to the maximum bearing pile load of the supporting structure, the bearing property of the foundation pit supporting structure is evaluated.

[0011] Compared with the prior art, the present application has the following beneficial effects: (1) The present application analyzes the measured bending moment distribution of each pile body by the inner and outer strain values of each monitoring height of each pile body, analyzes the bending moment absolute value borne by the force expansion disc of each pile body, calculates the bending moment contribution degree of the force expansion disc, thereby quantifying the force bearing effect of the force expansion disc, improving the detection pertinence of the bearing property of the foundation pit supporting structure, making the detection result match the structural characteristics of the NT-CEP pile, and improving the accuracy of the bearing property detection.

[0012] (2) The present application analyzes the principal stress trace distribution of the wall surface based on the strain characteristics of each wall surface monitoring point in the wall surface monitoring data, analyzes the stress distribution area of the wall surface based on the principal stress trace distribution, clearly determines the stress transmission law and local risk points of the supporting structure, effectively avoids the problem of local failure hidden danger of the wall surface, thereby improving the stability of the overall supporting structure and the safety of the foundation pit supporting structure.

[0013] (3) The present application judges in real time whether the current pile load reaches the maximum bearing pile load of the supporting structure according to the bending moment contribution degree of the force expansion disc and the stress distribution area of the wall surface, effectively balances the engineering safety and construction cost by determining the maximum bearing pile load of the supporting structure.

[0014] (4) The present application evaluates the bearing property of the foundation pit supporting structure according to the maximum bearing pile load of the supporting structure, realizes accurate evaluation of the bearing property of the supporting structure, provides a reliable basis for safety decision-making in the engineering construction and operation stage, and effectively prevents major safety accidents such as foundation pit collapse and instability. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0016] Figure 1 It is a method step flowchart of the present application.

[0017] Figure 2 It is a pile body cross section schematic diagram of the foundation pit supporting structure of the present application.

[0018] Figure 3 The method for obtaining the absolute value of the bending moment shared by the force bearing enlarged disc in the application is shown in the following steps.

[0019] Figure 4 The flow chart of the analysis method steps of the stress distribution area of the wall surface in the application is shown in the following steps.

[0020] The drawings show that: 1 represents the top height of the force bearing enlarged disc, 2 represents the disc core height of the force bearing enlarged disc, and 3 represents the bottom height of the force bearing enlarged disc. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. Note that the relative arrangement, numerical expressions, and numerical values of the components and steps set forth in these embodiments are not limiting to the scope of the present application unless otherwise specifically stated. Also, it should be understood that the dimensions of the various parts shown in the drawings are not drawn to scale for the sake of convenience of description.

[0022] The following description of at least one example embodiment is merely illustrative in nature and is in no way limiting to the scope of the application and its applications or uses. Techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but should be understood to be part of the specification, where appropriate.

[0023] In all examples shown and discussed herein, any specific values should be interpreted as merely illustrative and not as limiting. Thus, other examples of the example embodiments can have different values.

[0024] Referring to Figure 1 As shown, the application provides a detection method for the bearing capacity of a foundation pit support structure based on an NT-CEP pile, which comprises the following steps: S1, collecting monitoring data of the foundation pit support structure during a heaped load test.

[0025] S11, performing a heaped load test on the foundation pit support structure according to a set heaped load.

[0026] Specifically, in this embodiment, the preset maximum bearing heaped load corresponding to the support structure is first extracted from the foundation pit support structure detection background database. The heaped load is divided into gradient heaped load levels from small to large according to 50 equal divisions, and the heaped load of the heaped load test closest to the current time among the historical heaped loads is extracted from the foundation pit support structure detection background database. The heaped load corresponding to the next level is obtained as the current set heaped load in combination with the gradient heaped load levels.

[0027] S12, and simultaneously collect pile monitoring data and wall monitoring data under the current load. In a specific embodiment of the present invention, the method for acquiring the pile monitoring data includes: S121, determining the monitoring height set along the pile axis direction of each NT-CEP pile according to a preset vertical spacing, and determining the key height of each pile according to the bearing expansion plate of each pile.

[0028] S122. If the monitoring height set does not contain all critical heights, then the missing critical heights will be added to the monitoring height set.

[0029] like Figure 2 As shown, the key heights include the top height, bottom height, and center height of the load-bearing expansion plate. The top and bottom heights of the load-bearing expansion plate are located at the junction of the load-bearing expansion plate and the main body of the pile, while the center height is located at the outermost turning point of the load-bearing expansion plate. These are all special stress points and should not be overlooked when setting up monitoring points.

[0030] S123. Set internal strain monitoring points on the outer steel reinforcement section profile near the wall at each monitoring height, and set external strain monitoring points symmetrically on the outer steel reinforcement section profile and the internal strain monitoring points.

[0031] S124. Collect the strain values ​​of the internal strain monitoring points and external strain monitoring points at each monitoring height, and record them as internal strain value and external strain value respectively, and use them as pile body monitoring data.

[0032] In addition, the method for obtaining wall monitoring data includes: establishing a plane rectangular coordinate system with the midpoint of the bottom edge of the foundation pit wall as the origin, the bottom edge of the wall as the X-axis, the perpendicular to the wall as the Y-axis, and the vertical height as the Z-axis; dividing the wall into a grid at a set interval; and recording the intersection of each grid as a wall monitoring point. In this embodiment, the grid is divided at a set interval of 0.1m.

[0033] Strain sensors were deployed at each wall monitoring point to collect the transverse strain in the X-axis direction, the vertical strain in the Z-axis direction, and the strain in the 45° direction between X and Z. The shear strain of the wall was calculated based on the 45° direction strain, the transverse strain, and the vertical strain.

[0034] The formula for calculating shear strain is: .

[0035] in These represent shear strain, transverse strain, vertical strain, and strain in the 45° direction, respectively. The calculation formula for shear strain is existing technology and will not be described in detail in this invention.

[0036] The transverse strain, vertical strain, and shear strain at each wall monitoring point were collected as wall monitoring data.

[0037] S2, acquire the measured bending moment distribution of each pile body and the main stress trace distribution of the wall surface.

[0038] Considering that the force enlarging disc of the NT-CEP pile changes the traditional stress mode of the pile body, the bending moment sharing effect cannot be accurately captured by only monitoring the overall displacement or the average stress.

[0039] Meanwhile, considering that the stress distribution of the wall surface is complex, and the discrete point monitoring cannot reflect the main stress transmission path and the concentrated area, the stress distribution of the wall surface can be more specifically and objectively reflected by analyzing the main stress trace distribution.

[0040] Therefore, S21, based on the inner and outer strain values of each pile body at each monitoring height in the pile body monitoring data, the measured bending moment distribution of each pile body is analyzed.

[0041] In the specific embodiment of the present application, the measured bending moment distribution is acquired by comprehensively analyzing the difference between the outer strain value and the inner strain value at each monitoring height and the interval of the inner and outer strain monitoring points to obtain the measured bending moment value at each monitoring height, and constructing the measured bending moment distribution.

[0042] The calculation formula of the measured bending moment value is as follows: .

[0043] wherein, represents the measured bending moment value, represents the elastic modulus of the pile body material, which can be obtained from the foundation pit supporting structure detection background database, and in this embodiment, C30 concrete is used, and the value is 30 GPa, represents the cross-sectional moment of inertia of the pile body, which reflects the geometric measure of the cross-sectional resistance to bending deformation, and can be calculated by the formula , represents the difference between the outer strain value and the inner strain value, represents the interval of the inner and outer strain monitoring points. The calculation formula of the measured bending moment value and the calculation formula of the cross-sectional moment of inertia are both prior art, and will not be described in detail.

[0044] S22, based on the strain characteristics of each wall surface monitoring point in the wall surface monitoring data, the main stress trace distribution of the wall surface is analyzed.

[0045] The acquisition method of the main stress trace distribution of the wall surface is as follows: first, the strain characteristics of each wall surface monitoring point are extracted from the wall surface monitoring data, including the transverse strain, the vertical strain and the shear strain.

[0046] Secondly, the stress components of each wall surface monitoring point are calculated according to the transverse strain, the vertical strain and the shear strain, a continuous stress field covering the entire wall surface is generated by the interpolation method, the maximum principal stress and its direction angle of all points in the continuous stress field are calculated, and the maximum principal stress direction field is obtained.

[0047] Specifically, the method for obtaining the stress components of each wall monitoring point is to obtain the transverse stress of the X-axis, the vertical stress of the Z-axis, and the shear stress by substituting the transverse strain, the vertical strain, and the shear strain of each wall monitoring point into the relationship expression in the generalized Hook's law of the plane stress state.

[0048] The specific expression of the transverse stress is as follows: .

[0049] The specific expression of the vertical stress is as follows: .

[0050] The expression of the shear stress is as follows: .

[0051] The transverse stress, the vertical stress, and the shear stress are respectively represented by σx, σz, and τxy. The Poisson's ratio represents the ability of the material to be stretched in the transverse direction and to be shortened in the vertical direction during deformation, which is a material property of the wall concrete, and the value range is usually 0.15-0.25. The value can be extracted from the database of the foundation pit supporting structure detection background, and in the embodiment, the value is 0.2.

[0052] The steps of generating the continuous stress field covering the entire wall surface by the interpolation method are as follows: in the wall surface area, all target points are set according to the required resolution (such as 0.01 m x 0.01 m), all wall monitoring points in the circular range with the target point as the center and a set radius (such as 0.2 m) are obtained, the straight line distances from each target point to each wall monitoring point in the circular range are calculated, the stress components of each wall monitoring point in the circular range are obtained, the stress components of each target point are calculated by weighted average calculation through the inverse distance as the weight, and the continuous stress field covering the entire wall surface is obtained.

[0053] The maximum principal stress and the direction angle of the maximum principal stress are calculated by substituting the stress components of each point in the field, the transverse stress, the vertical stress, and the shear stress, into the maximum principal stress calculation formula and the maximum principal stress direction angle calculation formula of the two-dimensional stress state, so that the maximum principal stress direction field is obtained. The maximum principal stress calculation formula and the maximum principal stress direction angle calculation formula are both prior art, and will not be described in detail.

[0054] Then, a seed point is selected from all points in the continuous strain field, and the numerical integration is performed based on the maximum principal stress direction of each seed point to obtain the next integration point, and the maximum principal stress direction of the integration point is obtained by bringing the integration point into the maximum principal stress direction field.

[0055] Specifically, in the present embodiment, the cosine value of the seed point direction angle is multiplied by a set step size, and the sum of the result and the X-axis coordinate of the seed point is taken as the X-axis coordinate of the next integral point; similarly, the sine value of the seed point direction angle is multiplied by a set step size, and the sum of the result and the Z-axis coordinate of the seed point is taken as the Z-axis coordinate of the next integral point; the X and Z coordinate values of the next integral point are taken into the maximum principal stress direction field to obtain the maximum principal stress direction of the integral point, wherein the set step size can be 1 / 10 of the grid length, and the implementer can also set other specific numerical values.

[0056] Finally, continue to perform numerical integration based on the maximum principal stress direction of the integral point to obtain the next integral point, connect each integral point to form the principal stress trace corresponding to each seed point starting from the seed point, remove all seed points on the trace after obtaining the corresponding principal stress trace based on a seed point, and sequentially obtain the principal stress trace of the remaining seed points in the wall surface according to the above method, and so on until all seed points are in the trace, and the principal stress trace distribution is obtained by synthesizing all principal stress traces in the entire wall surface.

[0057] The present application analyzes the absolute value of the bending moment shared by the load bearing expansion disc of each pile body according to the measured bending moment distribution of each pile body, calculates the bending moment contribution degree of the load bearing expansion disc, and analyzes the stress distribution area of the wall surface based on the principal stress trace distribution, thereby quantifying the load bearing contribution and stress distribution of the load bearing expansion disc, avoiding the adaptability defects of the traditional method of using ordinary pile body analysis logic for new pile bodies, and improving the reliability and authority of the evaluation results.

[0058] S3, obtaining the bending moment contribution degree of the load bearing expansion disc and the stress distribution area of the wall surface.

[0059] Considering that the load bearing expansion disc plays an important load bearing role in the pile body, the advantage of the NT-CEP pile lies in the improvement of the bearing capacity of the load bearing expansion disc, which directly affects the stress distribution of the entire supporting structure as the main load bearing component of the pile body, and the sharing role of the load bearing expansion disc can be obtained by analyzing the bending moment distribution of each monitoring height above the expansion disc combined with the measured bending moment value of the expansion disc, thereby reflecting the load bearing change of the pile body; if the load bearing sharing role is ignored, the real load bearing change rule of the pile body cannot be accurately captured.

[0060] S31, analyzing the absolute value of the bending moment shared by the load bearing expansion disc of each pile body according to the measured bending moment distribution of each pile body.

[0061] As shown in Figure 3 In the preferred embodiment of the present application, the method for obtaining the absolute value of the bending moment shared by the load bearing expansion disc of each pile body comprises: S311, screening the measured bending moment values of each monitoring height higher than all key heights from the measured bending moment distribution, and fitting the bending moment curve without the influence of the disc body based on the measured bending moment values of each monitoring height.

[0062] Specifically, the steps for fitting the bending moment curve without the influence of the bearing plate are as follows: Based on the measured bending moment value of the pile section above the top of the bearing plate, a quadratic polynomial and exponential decay model is selected. Each monitoring height above the critical height is taken as the independent variable, and the corresponding measured bending moment value is taken as the dependent variable and substituted into the model. The model coefficients are solved by the least squares method. The final fitted model is obtained based on the model coefficients. For all independent variables, they are substituted into the fitted model to output the predicted bending moment value.

[0063] The average value of each monitoring height above the critical height, the measured bending moment value, and the predicted bending moment value of each model are substituted into the formula for calculating the coefficient of determination to obtain the coefficient of determination for each model. The fitted model with the highest coefficient of determination is selected, and the bending moment curve is plotted based on the fitted model.

[0064] S312. Record all monitoring heights within the height range consisting of the maximum and minimum heights of the critical height of the load-bearing expansion plate as the plate monitoring height.

[0065] S313. Substitute the monitoring height of each plate of the load-bearing expansion plate into the bending moment curve to obtain the corresponding bending moment value, which is recorded as the reference bending moment value.

[0066] S314. Perform difference analysis between the measured bending moment value at each monitoring height and the reference bending moment value at the corresponding monitoring height to obtain the absolute value of the bending moment at each monitoring height. Use the maximum value as the absolute value of the bending moment shared by the bearing expansion plate of each pile.

[0067] S32. Calculate the bending moment contribution of the load-bearing enlarged disk.

[0068] In a preferred embodiment of the present invention, the method for calculating the bending moment contribution of the bearing expansion plate includes: extracting the reference bending moment value of the plate center height from the reference bending moment value corresponding to the monitoring height of each plate of each pile.

[0069] The ratio of the absolute value of the bending moment borne by the bearing expansion plate of each pile to the reference bending moment value of the center height of the plate is recorded as the bending moment contribution of the bearing expansion plate of each pile.

[0070] S33. Simultaneously, analyze the stress distribution area of ​​the wall surface based on the principal stress trace distribution.

[0071] like Figure 4 As shown, the method for analyzing the stress distribution area of ​​a wall surface based on the principal stress trace distribution is as follows: S331, count the number of principal stress traces passing through each grid on the wall surface, and record the ratio of the number of traces to the grid area as the trace density.

[0072] S332. Calculate the average and standard deviation of the trace density of each grid, and set the high density range based on the average and standard deviation.

[0073] Specifically, in this embodiment, the sum of the average value and three times the standard deviation is taken as the minimum value of the high-density range, that is, the high-density range is set as... .

[0074] S333. Compare the trace density of each grid with the high density range, and record the grids that are in the high density range as high density grids.

[0075] S334. By clustering adjacent high-density grids, each stress concentration region is obtained, and the area of ​​each stress concentration region is used as the stress distribution area.

[0076] Specifically, in this embodiment, the eight nearest neighboring grids of each grid are designated as its neighboring grids. Taking a given high-density grid as the starting grid, a search is conducted to determine if any high-density grids exist among its neighboring grids. If so, this high-density grid is grouped into the same cluster as the starting grid. The process then iterates through the neighboring high-density grids of all other high-density grids within the cluster (excluding the starting grid), integrating them into the same cluster to obtain the cluster. The regions contained within each cluster are designated as stress concentration regions. The area of ​​each stress concentration region is obtained by combining the number of grids within the region with the grid area.

[0077] This invention determines in real time whether the current load has reached the maximum bearing capacity of the support structure based on the bending moment contribution of the load-bearing expansion plate and the stress distribution area of ​​the wall surface. This enables real-time and accurate determination of the maximum bearing capacity of the foundation pit support structure. It can not only determine the maximum bearing capacity, but also simultaneously locate potential weak points in the structure, thus improving the reliability of the results.

[0078] S4. Determine the maximum load-bearing capacity of the support structure based on the moment contribution of the bearing expansion plate and the stress distribution area of ​​the wall.

[0079] Considering that the moment contribution of the load-bearing expansion plate should increase continuously as the load increases, if the moment contribution of a certain load level begins to decrease, it is considered that the pile has reached the maximum load capacity.

[0080] It should be further explained that when the growth rate of the area or the growth rate of the peak principal stress exceeds the set growth threshold, it is considered that the area of ​​the principal stress concentration area or the peak principal stress has increased abnormally, indicating a stress mutation. The current load is determined to be the maximum load on the wall. By starting from the stress perspective, the critical value of the maximum load can be determined in advance.

[0081] Based on this S41, the current load is determined in real time based on the bending moment contribution of the load-bearing expansion plate and the stress distribution area of ​​the wall surface to determine whether the current load has reached the maximum load-bearing capacity of the support structure.

[0082] The specific method for determining whether the current load is the maximum load of the supporting structure under the current load includes: first extracting the bending moment contribution corresponding to the historical load closest to the current load from the background database of the foundation pit supporting structure detection, and recording it as the previous bending moment contribution.

[0083] If the bending moment contribution of the enlarged disc of a certain pile under the current load is less than the previous bending moment contribution, it is determined that the current load is the maximum load of the supporting structure.

[0084] Otherwise, the area growth rate and the peak principal stress growth rate of each stress concentration area are calculated based on the area of each stress concentration area.

[0085] In specific embodiments of the present application, the area of each stress concentration area under the current load is calculated by difference from the area of the stress concentration area of the previous level, and the ratio of the difference to the adjacent load level is recorded as the area growth rate of the stress concentration area. Similarly, the peak principal stress of each stress concentration area under the current load is calculated by difference from the peak principal stress of the stress concentration area of the previous level, and the ratio of the difference to the adjacent load level is recorded as the peak principal stress growth rate.

[0086] If the area growth rate of a certain stress concentration area under the current load is greater than the set area growth rate threshold, or the peak principal stress growth rate is greater than the set principal stress growth rate threshold, the current load is the maximum load of the supporting structure.

[0087] In addition, it needs to be further pointed out that the setting method of the area growth rate threshold and the principal stress growth rate threshold includes: according to the position of each stress concentration area, extracting the area of each stress concentration area under each level of historical load from the background database of the foundation pit supporting structure detection, and grouping them into the area sequence of each stress concentration area.

[0088] The area of each stress concentration area under the current load is calculated by difference from the area of the stress concentration area of the previous level, and the ratio of the difference to the adjacent load level is recorded as the area growth rate of the stress concentration area. Similarly, the peak principal stress of each stress concentration area under the current load is calculated by difference from the peak principal stress of the stress concentration area of the previous level, and the ratio of the difference to the adjacent load level is recorded as the peak principal stress growth rate.

[0089] The maximum value of the maximum principal stress of each point in each stress concentration area is obtained, which is recorded as the peak principal stress of each stress concentration area. The peak principal stress growth rate threshold is obtained based on the area growth rate threshold, and the specific steps are as follows: the adjacent peak principal stress of each region peak principal stress sequence is analyzed by difference, and the peak principal stress growth rate sequence of each stress concentration area is obtained. The average value and the standard deviation of the peak principal stress growth rate in each peak principal stress growth rate sequence are calculated, and the sum of the average value and three times the standard deviation is taken as the peak principal stress growth rate threshold.

[0090] S42, if the maximum bearing load of the supporting structure is not reached under the current load, then the gradient adjustment test is carried out on the set load until the maximum bearing load is determined.

[0091] According to the set load level, the set load of the next level under the current load is obtained, and the analysis whether it is the maximum bearing load of the supporting structure is continued according to the above steps until the test is stopped after the maximum bearing load is determined.

[0092] The present application can determine whether the current load reaches the maximum bearing load of the supporting structure according to the bending moment contribution of the bearing expansion disc under each level of load and the stress distribution area of the wall surface, realizes the real-time and accurate determination of the maximum bearing capacity of the foundation pit supporting structure, and improves the safety of the detection process and the reliability of the results.

[0093] S5, evaluating the bearing property of the foundation pit supporting structure according to the maximum bearing load of the supporting structure.

[0094] In the specific embodiments of the present application, the specific method for evaluating the bearing property of the foundation pit supporting structure according to the maximum bearing load of the supporting structure includes extracting the maximum load of each type of construction vehicle in the construction process from the foundation pit supporting structure detection background database, and extracting the maximum value as the maximum expected load of the supporting structure.

[0095] If the overall maximum load capacity of the foundation pit supporting structure is less than the maximum expected load, it is determined that the bearing property of the foundation pit supporting structure is unqualified.

[0096] Otherwise, it is determined that the bearing property of the foundation pit supporting structure is qualified.

[0097] The present application can evaluate the bearing property of the foundation pit supporting structure according to the maximum bearing load of the supporting structure, combine the wall and pile of the supporting structure, make the evaluation result more accurate, provide a reliable basis for safety decision-making in the engineering construction and operation stage through analyzing the overall maximum load capacity, and effectively prevent major safety accidents such as foundation pit collapse and instability.

[0098] The above embodiments can be realized in whole or in part by software, hardware, firmware or any combination thereof. When realized by software, the above embodiments can be realized in whole or in part in the form of a computer program product.

[0099] Those skilled in the art can realize that the modules and algorithm steps of the examples described in combination with the embodiments disclosed herein can be realized by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized by hardware or software depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0100] In addition, each function module in each embodiment of the present application can be integrated in one processing module, or each module can be physically present alone, or two or more modules can be integrated in one module.

[0101] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0102] Finally, the above is only a preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for testing the bearing capacity of foundation pit support structures based on NT-CEP piles, characterized in that, include: A load test was conducted on the foundation pit support structure according to the set load, and monitoring data of the pile body and wall surface under the current load were collected simultaneously. Based on the internal and external strain values ​​of each pile at each monitoring height in the pile monitoring data, the measured bending moment distribution of each pile is analyzed. At the same time, based on the strain characteristics of each wall monitoring point in the wall monitoring data, the principal stress trace distribution of the wall is analyzed. Based on the measured bending moment distribution of each pile, the absolute value of the bending moment shared by the bearing expansion plate of each pile is analyzed, the bending moment contribution of the bearing expansion plate is calculated, and the stress distribution area of ​​the wall surface is analyzed based on the principal stress trace distribution. Based on the moment contribution of the load-bearing expansion plate and the stress distribution area of ​​the wall, it is determined in real time whether the current load has reached the maximum load capacity of the support structure. If the current load has not reached the maximum load capacity of the support structure, a gradient adjustment test is performed on the set load until the maximum load capacity is determined. The load-bearing capacity of the foundation pit support structure is assessed based on the maximum load-bearing capacity of the support structure.

2. The method for testing the bearing capacity of foundation pit support structures based on NT-CEP piles according to claim 1, characterized in that, The method for acquiring pile monitoring data includes: Along the axis of each NT-CEP pile, the monitoring height set is determined according to the preset vertical spacing, and the critical height of each pile is determined according to the bearing expansion plate of each pile. If the monitoring height set does not contain all critical heights, then the missing critical heights will be added to the monitoring height set. Internal strain monitoring points are set on the outer steel bar section profile near the wall at each monitoring height, and external strain monitoring points are set symmetrically on the outer steel bar section profile and the internal strain monitoring points. The strain values ​​of the internal strain monitoring points and external strain monitoring points at each monitoring height are collected and recorded as internal strain value and external strain value, respectively, and used as pile body monitoring data.

3. The method for testing the bearing capacity of foundation pit support structures based on NT-CEP piles according to claim 2, characterized in that, The method for obtaining the measured bending moment distribution includes: The difference between the external strain value and the internal strain value at each monitoring height is combined with the spacing between the corresponding internal and external strain monitoring points for comprehensive analysis to obtain the measured bending moment value at each monitoring height and construct the measured bending moment distribution.

4. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 3, characterized in that, The method for obtaining the absolute value of the bending moment shared by the bearing expansion plate of each pile includes: Measured bending moment values ​​at each monitoring height that are higher than all critical heights are selected from the measured bending moment distribution. Based on the selected measured bending moment values ​​at each monitoring height, a bending moment curve without the influence of the disk is fitted. All monitoring heights within the height range formed by the maximum and minimum heights of the critical height of the load-bearing expansion plate are recorded as the plate monitoring heights. The corresponding bending moment value is obtained by substituting the monitoring height of each plate of the load-bearing expansion plate into the bending moment curve, and is recorded as the reference bending moment value. The measured bending moment value at each monitoring height of the pile body is compared with the reference bending moment value at the corresponding monitoring height to obtain the absolute value of the bending moment at each monitoring height. The maximum value of the bending moment is taken as the absolute value of the bending moment shared by the load-bearing expansion plate of each pile body.

5. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 1, characterized in that, The method for obtaining the principal stress trace distribution on the wall surface includes: Strain characteristics of each wall monitoring point are extracted from the wall monitoring data, including lateral strain, vertical strain, and shear strain. The stress components of each wall monitoring point are calculated based on the transverse strain, vertical strain and shear strain. A continuous stress field covering the entire wall is generated by interpolation. The maximum principal stress and its direction angle at all points in the continuous stress field are calculated to obtain the direction field of the maximum principal stress. Seed points are selected from all points in the continuous strain field. Numerical integration is performed based on the maximum principal stress direction of each seed point to obtain the next integration point. The seed point is then substituted into the maximum principal stress direction field to obtain the maximum principal stress direction of the integration point. Numerical integration is performed based on the direction of the maximum principal stress at the integration point to obtain the next integration point. Starting from the seed point, each integration point is connected to form the principal stress traces corresponding to various sub-points. All principal stress traces in the entire wall surface are synthesized to obtain the principal stress trace distribution.

6. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 4, characterized in that, The method for calculating the bending moment contribution of the load-bearing expanded disk includes: Extract the reference bending moment value of the center height from the reference bending moment value corresponding to the monitoring height of each disc of each pile; The ratio of the absolute value of the bending moment borne by the bearing expansion plate of each pile to the reference bending moment value of the center height of the plate is recorded as the bending moment contribution of the bearing expansion plate of each pile.

7. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 5, characterized in that, The method for analyzing the stress distribution area of ​​a wall surface based on the principal stress trace distribution includes: The number of principal stress traces passing through each grid on the wall surface is counted, and the ratio of this number to the grid area is recorded as the trace density. Calculate the average and standard deviation of the trace density for each grid, and set the high density range based on the average and standard deviation; Compare the trace density of each grid with the high density range, and record the grids that are in the high density range as high density grids; By clustering adjacent high-density grids, each stress concentration region is obtained, and the area of ​​each stress concentration region is used as the stress distribution area.

8. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 7, characterized in that, The specific methods for determining whether the current load is the maximum load-bearing capacity of the support structure include: Extract the bending moment contribution value corresponding to the historical load closest to the current load from the database of the foundation pit support structure detection background, and record it as the previous bending moment contribution value; If the moment contribution of the enlarged plate of a certain pile under the current load is less than the moment contribution of the previous load, then the current load is determined to be the maximum bearing load of the support structure. Conversely, the area growth rate and peak principal stress growth rate of each stress concentration region are calculated based on the region area of ​​each stress concentration region. If the area growth rate of a stress concentration region under the current load is greater than the set area growth rate threshold, or the peak principal stress growth rate is greater than the set principal stress growth rate threshold, then the current load is the maximum load-bearing load of the support structure.

9. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 7, characterized in that, The methods for setting the area growth rate threshold and the principal stress growth rate threshold include: Based on the location of each stress concentration area, extract the area of ​​each stress concentration area under historical loading levels from the foundation pit support structure detection database, and form a sequence of area of ​​each stress concentration area. The area difference analysis of adjacent load level areas in the area sequence of each stress concentration area is performed to obtain the area growth rate sequence of the area. The mean and standard deviation of the area growth rate sequence of each stress concentration area are calculated, and the area growth rate threshold is set according to the mean and standard deviation. The maximum value of the maximum principal stress at each point within each stress concentration region is obtained and recorded as the peak principal stress of each stress concentration region. The peak principal stress growth rate threshold is obtained based on the region area growth rate threshold method.

10. The method for testing the bearing capacity of a foundation pit support structure based on NT-CEP piles according to claim 1, characterized in that, The specific method for evaluating the bearing capacity of the foundation pit support structure based on the maximum load-bearing capacity of the support structure includes: Extract the maximum load of each type of construction vehicle during the construction process from the database of the foundation pit support structure detection backend, and extract the maximum value as the maximum expected load of the support structure. If the overall maximum load capacity of the foundation pit support structure is less than the maximum expected load, the bearing capacity of the foundation pit support structure is deemed unqualified. Conversely, if the bearing capacity of the foundation pit support structure is deemed qualified, then the foundation pit support structure is deemed qualified.

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