A detection operation method suitable for detecting the length of an ultra-long pile foundation

Abstract

The application discloses a kind of detection operation methods suitable for detecting the length of super-long pile foundation.The conventional pile burying depth detection method has certain limitation.The application specifically includes S1: survey engineering analysis;S2: for the geological condition of detection operation, carry out simulation study to site model, summarize the characteristics of site pile foundation response;S3: carry out drilling on both sides of the pile foundation to be detected, respectively put a certain amount of electrode in two adjacent drill holes, carry out a series of cross-hole power supply, measurement, obtain data, and then obtain the resistivity distribution between well-well by inversion;S4: according to the resistivity size and the trend of contour line in the contour map inverted by actual measurement value, combined with the model research result, judge whether the pile foundation has defect, the length of pile foundation.The application detects the length of super-long pile, and identifies the defect position, which improves the level of pile foundation detection.

Description

Technical Field

[0001] This invention belongs to the field of engineering testing technology, specifically relating to a testing method suitable for detecting the length of ultra-long pile foundations. Background Technology

[0002] Currently, the most common substructure form in high-rise and super high-rise buildings is the pile foundation. Conventional methods for detecting pile depth include low-strain dynamics, high-strain dynamics, core drilling, and acoustic wave propagation, but each has certain limitations. The low-strain dynamics method is effective only when the pile length-to-diameter ratio is less than 30; for ultra-long piles, it often cannot detect the reflected signal at the pile bottom. The high-strain dynamics method requires a certain amount of operating space, and heavy hammering can easily damage or even destroy the pile. The acoustic wave propagation method requires the pre-embedded sonic logging tube, and the pile diameter must be no less than 600mm, which is inconvenient for construction and increases costs. Core drilling is relatively direct, but it can damage the integrity of the pile, and deviation during drilling can easily occur, leading to misjudgments. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a detection method suitable for detecting the length of ultra-long pile foundations, ensuring the safety, efficiency and accuracy of the detection operation, and providing technical support for the detection of ultra-long pile foundations.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A detection method suitable for detecting the length of ultra-long pile foundations, characterized by the following steps:

[0006] S1: Survey Engineering Analysis

[0007] S2: Based on the geological conditions of the testing operation, conduct a simulation study on the site model and summarize the characteristics of the site pile foundation response;

[0008] S3: Drill holes on both sides of the pile foundation being tested, and place a certain number of electrodes in two adjacent holes to perform a series of cross-hole power supply and measurement. After obtaining the data, the resistivity distribution map between the wells is obtained by inversion.

[0009] S4: Based on the resistivity and contour line trend in the contour map derived from the measured values, and combined with the model research results, determine whether the pile foundation has defects and the length of the pile foundation.

[0010] Furthermore, S1 specifically involves: analyzing the pile foundation testing environment, familiarizing oneself with the location of the testing work area, and, in conjunction with the engineering design, developing testing and geological interpretation technical solutions based on the requirements.

[0011] Furthermore, S2 specifically refers to:

[0012] S2.1: Establish site background resistivity models for various types of piles under different construction and pile-forming processes;

[0013] S2.2: Perform forward modeling on the site background resistivity model, and then perform inversion on the forward modeling data to obtain the model inversion map;

[0014] S2.3: Analyze the electrical response characteristics of different pile foundation types.

[0015] In S2.1, the site background resistivity model is established using the ultra-high density direct current method.

[0016] In S2.3, the electrical response characteristics include resistivity distribution and contour line trend.

[0017] In S2.2, the forward modeling is mainly based on the finite element method, as detailed below:

[0018] Suppose that in an infinite medium with resistivity ρ(x, y, z), at point C(x... C y C , z C There exists a current source at point () with current intensity I. For the steady-state current field potential function U, the differential equation it satisfies is:

[0019] V.(σVU)=-Iδ(rr c ), r, r∈Ω (1)

[0020] Where σ(S / m) represents conductivity (the reciprocal of resistivity), I(V / m) represents electric field strength, and r c This indicates the location of the current electrode.

[0021] Furthermore, solving the differential equation (1) involves three boundary conditions:

[0022] (1) First type of boundary conditions

[0023]

[0024] In the above equation, Γ represents the boundary of the study area. It is a known function defined on Γ;

[0025] (2) Second type of boundary condition (Neumann condition)

[0026]

[0027] In the formula, n is the outward normal of the study area;

[0028] (3) Third type of boundary conditions (mixed boundary conditions)

[0029]

[0030] In the above formula, A is a known positive number.

[0031] Furthermore, in step S2.2, the data obtained from the forward modeling is inverted, and the partial differential equation for the inversion is:

[0032]

[0033] In the formula:

[0034] Φ d (m)=||W d (d0-d(m))|| 2

[0035] Φ m (m)=||W m (m-m0)|| 2

[0036] m is the measured resistivity, λ is the Lagrange operator, d(m) is the electric field data generated by the forward iteration; d0 is the actual measured electric field data; m0 is the resistivity of the initial inversion model; W d and W m As a weighting factor, it controls the amount of correction to the model during the calculation process, and its value depends on the signal-to-noise ratio of the measured data.

[0037] Furthermore, in step S3, holes are drilled on both sides of the pile foundation being tested, and the hole depth must be greater than the pile bottom depth.

[0038] Furthermore, in step S3, a resistivity distribution map between wells is obtained.

[0039] The beneficial effects of this invention are:

[0040] 1) This invention addresses the problem of the difficulty in implementing traditional detection depths for high-rise and super high-rise pile foundations. For the first time, it proposes a working mode based on ultra-high density electrical resistivity tomography and establishes a technical method for detecting ultra-long pile foundations. This method can meet the technical requirements for detecting ultra-long pile foundations, provides technical support for detecting the length of ultra-long pile foundations, and improves the level of detection technology.

[0041] 2) The site background resistivity model of this invention is established by ultra-high density DC resistivity method, which improves the reliability of data and improves work efficiency. Through 2.5-dimensional inversion technology, the exploration accuracy is greatly improved.

[0042] 3) Based on the simulation research of geoelectric models of single piles, long and short piles and pile groups, this invention analyzes the response characteristics of single piles, long and short piles and pile groups; it can detect the length of ultra-long piles and identify defective parts, making up for the lack of detection capability of ultra-long pile foundations, providing technical support for the detection of ultra-long pile foundations of high-rise and super high-rise buildings, and improving the level of pile foundation detection. Attached Figure Description

[0043] Figure 1 A schematic diagram of the planar location of an ultra-high density resistivity borehole between wells;

[0044] Figure 2 Figure for simulation study of a single pile model;

[0045] Figure 3 Inversion diagram of measured inter-well resistivity. Detailed Implementation

[0046] The present invention will now be described in detail with reference to specific embodiments.

[0047] The present invention specifically includes the following steps:

[0048] S1: Exploration and engineering analysis, specifically: analyzing the pile foundation testing work environment, understanding the location of the testing work area, and developing testing and geological interpretation technical solutions based on the requirements and engineering design.

[0049] like Figure 1 As shown, the engineering analysis in step S1 mainly includes the following technical aspects: Based on the regional distribution of the testing work area, through the collection, analysis, and organization of basic data, the approximate depth of the pile foundations, the ground elevation of the pile tops, and the location of the pile tops in the area to be tested are determined. The approximate depth and ground location of the pile foundations are prerequisites for subsequent testing operations. According to the requirements of the testing work, the proposed pile foundation layout and pile-forming process are determined. A basic understanding of the geological structure, strata lithology, adverse geological conditions, and soil-rock structure of the survey area is obtained. Based on this understanding, a pile foundation testing plan is designed.

[0050] S2: Based on the geological conditions of the testing operation, a site model is simulated and studied to summarize the characteristics of the site pile foundation response, specifically:

[0051] S2.1: Based on the site's geological structure, stratigraphic lithology, adverse geological conditions, and soil and rock mass structure, establish site background resistivity models for various types of piles (single piles, long and short piles, and pile groups, etc.) under different construction and pile-forming processes; the site background resistivity models are established using the ultra-high density direct current resistivity method.

[0052] Ultra-high density direct current resistivity (UHDC) resistivity measurement operates on the principle of resistivity and employs an array-based exploration approach. In field measurements, all electrodes (dozens to hundreds) are placed at the measurement point, connected to the instrument via multi-core cables, and then rapidly and automatically acquired data using a programmable electrode selector switch and a microcomputer-controlled engineering electrical measuring instrument. UHDC acquisition encompasses all device types in a single process, providing multiple coverages of the observation point, thus improving data reliability and work efficiency. Furthermore, the use of 2.5D inversion technology significantly enhances exploration accuracy.

[0053] S2.2: Perform forward modeling on the site background resistivity model, and then perform inversion on the forward modeling data to obtain the model inversion map;

[0054] The working method of the inter-well ultra-high density resistivity imaging technology is to place a certain number of electrodes in two adjacent boreholes, perform a series of cross-hole power supply and measurement, and after measuring the dV / I data, invert the resistivity distribution map between the wells to analyze the correspondence between the rock and soil medium and resistivity, and interpret the geological information.

[0055] The process of finding the electric field distribution from the known spatial distribution of resistivity is called forward modeling or solving the forward problem; conversely, the process of finding the spatial distribution of resistivity from the known electric field distribution is called inversion.

[0056] When using the finite element method to solve for the potential field distribution of a steady current field, the first step is to apply a variational method to transform the boundary value problem into a corresponding variational problem, i.e., to find the extremum of the functional. Then, the continuous solution domain is discretized, and a set of high-order linear equations with the potential values ​​of each node as unknowns are derived. Finally, the equations are solved to obtain the potential values ​​of each node, and then an inverse Fourier transform is performed to obtain the potential field distribution of the steady current field in the spatial domain.

[0057] When performing data inversion, first set up a theoretical geoelectric model, use the theoretical geoelectric model to perform forward modeling to obtain the theoretical resistivity value; then calculate the fitting difference between the measured data and the theoretical data; then correct the theoretical resistivity to obtain a new theoretical resistivity distribution model; repeat the above steps and iterate continuously until the fitting difference is small enough, and take the theoretical resistivity model at this time as the final inversion result.

[0058] In S2.2, the forward modeling is mainly based on the finite element method, as detailed below:

[0059] Suppose that in an infinite medium with resistivity ρ(x, y, z), at point C(x... C y C , z C There exists a current source at point () with current intensity I. For the steady-state current field potential function U, the differential equation it satisfies is:

[0060] V.(σVU)=-Iδ(rr c ), r, r∈Ω (1)

[0061] Where σ(S / m) represents conductivity (the reciprocal of resistivity), I(V / m) represents electric field strength, and r c This indicates the location of the current electrode.

[0062] Solving differential equation (1) requires three boundary conditions:

[0063] (1) First type of boundary conditions

[0064]

[0065] In the above equation, Γ represents the boundary of the study area. It is a known function defined on Γ;

[0066] (2) Second type of boundary condition (Neumann condition)

[0067]

[0068] In the formula, n is the outward normal of the study area;

[0069] (4) Third type of boundary conditions (mixed boundary conditions)

[0070]

[0071] In the above formula, A is a known positive number.

[0072] In S2.2, the data obtained from the forward modeling is inverted, and the inverted partial differential equation is:

[0073]

[0074] In the formula:

[0075] Φ d (m)=||W d (d0-d(m))|| 2

[0076] Φ m (m)=||W m (m-m0)|| 2

[0077] m is the measured resistivity, λ is the Lagrange operator, d(m) is the electric field data generated by the forward iteration; d0 is the actual measured electric field data; m0 is the resistivity of the initial inversion model; W d and W m As a weighting factor, it controls the amount of correction to the model during the calculation process, and its value depends on the signal-to-noise ratio of the measured data.

[0078] S2.3: Analyze the electrical response characteristics of different pile foundation types. The electrical response characteristics include resistivity distribution and contour line trend.

[0079] S3: Drill holes on both sides of the pile foundation being tested, and place a certain number of electrodes in two adjacent holes to perform a series of cross-hole power supply and measurement. After obtaining the data, the resistivity distribution map between the wells is obtained by inversion.

[0080] like Figure 3 As shown, in step S3, according to the design work plan, on-site geological stratification, lithology and other parameters are recorded. Holes are drilled on both sides of the pile foundation to be tested. The hole depth should be greater than the pile bottom depth. A certain number of electrodes are placed in the two adjacent holes to carry out a series of cross-hole power supply and measurement. The resistivity between wells is measured at the pile foundation testing site. After obtaining the measured value, the data is inverted using 2.5D inversion software to obtain the resistivity inversion contour map.

[0081] S4: Based on the resistivity and contour line trend in the contour map derived from the measured values, and combined with the model research results, determine information such as whether the pile foundation has defects, the length of the pile foundation, the burial depth of the pile foundation, and the location of pile foundation defects.

[0082] The specific implementation method is as follows:

[0083] Located at a construction site in Jiangsu Province, a high-rise residential building is planned to be constructed. Due to a significant discrepancy between the actual concrete volume poured and the designed volume, the construction company has doubts about the quality of the pile foundation construction. Figure 1 As shown, the site uses a full-area concrete cast-in-place pile foundation with a designed depth of 60m (5m for the pile head), a pile diameter of 700mm, and a pile spacing of 2m.

[0084] Holes ZK1, ZK2, ZK3 and ZK4 were pre-drilled on site, each with a depth of 65m. The distance between holes ZK1 and ZK2 was 16.5m, and the distance between holes ZK3 and ZK4 was 15.5m.

[0085] Due to the large detection depth and limitations of the instrument itself (32 electrodes per cable), a cable with an electrode spacing of 1m was used for measurement to obtain higher resolution. Each set of inter-well ultra-high density resistivity measurements was divided into upper and lower parts. The ultra-high density resistivity measurements for each set of wells were also inverted according to the upper and lower parts, and then pieced together. The specific fieldwork method was as follows: For the ultra-high density resistivity of wells ZK1 to ZK2, the lowest electrode of the cable inside the ZK1 and ZK2 boreholes was first placed at -61m on the Y-axis, and the measurement was taken from -61 to -30mm in the Y direction. Then, the lowest electrode of the cable inside the ZK1 and ZK2 boreholes was placed at -31m in the Y direction, and the upper part was measured from -31 to 0mm. Similarly, for the ultra-high density resistivity of wells ZK3 to ZK4, the measurement was first taken from -62.5 to -31.5mm in the Y direction, and then from -31m to 0m.

[0086] The parameters for this operation were as follows: electrode spacing 1.0m, 32 electrodes per cable, power supply voltage 120V, and sampling time 2s.

[0087] like Figure 3 As shown, the X-axis represents distance and the Y-axis represents depth. The burial depth of the 8 piles between sections ZK1 and ZK2 was obtained and is summarized in the table below.

[0088] The pile foundation burial depth between boreholes ZK1 and ZK2

[0089] Numbering / from left to right 1 2 3 4 5 6 7 8 Inferred burial depth / m 52 55 57 58 59 60 59 57

[0090] like Figure 3 As shown, the X-axis represents distance and the Y-axis represents depth. In the figure, approximately 3m in the X-direction and -55m in the Y-direction show an anomaly in low resistivity, suggesting potential defects such as mud inclusion, necking, or broken piles. The burial depths of the eight piles between sections ZK3 and ZK4 are summarized in the table below.

[0091] The pile foundation burial depth between boreholes ZK3 and ZK4

[0092] Numbering / from left to right 1 2 3 4 5 6 7 8 Inferred burial depth / m 60 60 59 57 56.5 56 56 56

[0093] The burial depth of 16 piles was obtained in this study, of which 3 piles were qualified (burial depth greater than 60m), resulting in a pass rate of 18.75%. Based on the geophysical exploration results, the construction unit conducted a test pile on the first pile on the right side of borehole ZK1, and the bearing capacity did not meet the design requirements. Subsequently, after recalculation by the design unit, additional piles were added at certain locations on the site. A static load test of the foundation was then conducted, and the test was successful, demonstrating that the bearing capacity met the design requirements.

[0094] This technical solution addresses the challenge of achieving sufficient depth for traditional pile foundation testing in high-rise and super high-rise buildings. For the first time, it proposes a working mode based on ultra-high-density electrical resistivity tomography (EDT) and establishes a technical method for testing ultra-long pile foundations. This method meets the technical requirements for testing ultra-long pile foundations, provides technical support for pile length testing of ultra-long pile foundations, and improves the level of testing technology.

[0095] The content of this invention is not limited to the embodiments listed. Any equivalent modifications made by those skilled in the art to the technical solutions of this invention by reading this specification are covered by the claims of this invention.

Claims

1. A detection method suitable for detecting the length of ultra-long pile foundations, characterized in that: Specifically, the steps include the following: S1: Survey Engineering Analysis S2: Based on the geological conditions of the testing operation, conduct a simulation study on the site model and summarize the characteristics of the site pile foundation response; S3: Drill holes on both sides of the pile foundation being tested, and place a certain number of electrodes in two adjacent holes to perform a series of cross-hole power supply and measurement. After obtaining the data, the resistivity distribution map between the wells is obtained by inversion. S4: Based on the resistivity and the trend of the contour lines in the contour map derived from the measured values, and combined with the model research results, determine whether the pile foundation has defects and the length of the pile foundation; Specifically, S1 is: Analyze the working environment for pile foundation testing, familiarize yourself with the location of the testing work area, and, in conjunction with the engineering design, develop testing and geological interpretation technical solutions based on the requirements. Specifically, S2 is: S2.1: Establish site background resistivity models for various types of piles under different construction and pile-forming processes; S2.2: Perform forward modeling on the site background resistivity model, and then perform inversion on the forward modeling data to obtain the model inversion map; S2.3: Analyze the electrical response characteristics of different pile foundation types; In S2.1, the site background resistivity model is established using the ultra-high density direct current method; In S2.3, the electrical response characteristics include resistivity distribution and contour line trend. In step S2.2, the data obtained from the forward modeling is inverted, and the inverted partial differential equation is: In the formula: m is the measured resistivity. Let d(m) be the Lagrange operator, and d(m) be the electric field data generated by forward iteration. d0 represents the actual measured electric field data; m0 represents the resistivity of the initial inversion model; W d and W m As a weighting factor, it controls the amount of correction to the model during the calculation process, and its value depends on the signal-to-noise ratio of the measured data.

2. The detection method for detecting the length of ultra-long pile foundations according to claim 1, characterized in that: In S2.2, the forward modeling is mainly based on the finite element method, as detailed below: Assuming the resistivity is In an infinite medium, located at point There exists a point current source with current intensity I. For the steady current field potential function U, the differential equation it satisfies is: in Represents electrical conductivity. Represents electric field strength. This indicates the location of the current electrode.

3. The detection method for detecting the length of ultra-long pile foundations according to claim 1, characterized in that: In step S3, holes are drilled on both sides of the pile foundation being tested, and the hole depth must be greater than the pile bottom depth.

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