Molding bag grouting pile detection method based on resistivity method

Abstract

The invention relates to the technical field of pile foundation detection, and discloses a mold bag grouting pile detection method based on a resistivity method, comprising the following steps: S1, performing data collection, field investigation and equipment debugging before detection; s2, performing array arrangement on the electrodes; s3, applying low-frequency alternating current, synchronously recording M-N electrode counter potential data, and marking electrode coordinates and timestamps while storing original data; s4, preprocessing the data and establishing a three-layer medium model; and S5, feature recognition is conducted on the mold bags, and pile forming quality grading is conducted according to the damage degree. According to the invention, the problem that the traditional detection method needs to break the road or pre-embed the device, which makes it difficult to meet the requirement of detection while passing the vehicle is effectively avoided, the detection efficiency is improved, the detection precision is increased, and the practicability is strong.

Description

Technical Field

[0001] This invention relates to the field of pile foundation testing technology, and in particular to a method for testing geotextile grouting piles based on resistivity method. Background Technology

[0002] Grouting with geotextile bags is a foundation treatment or seepage prevention and plugging technique. It involves placing specially designed geotextile bags into ground pores, boreholes, or karst caves, and then injecting grout such as cement slurry. The geotextile bag's filtration effect achieves consolidation. After geotextile bag grouting is completed, the pile foundation needs to be tested, thus requiring specialized testing methods.

[0003] Currently, core drilling and sonic logging are commonly used in pile foundation testing. While these methods can detect ordinary pile foundations, they have significant limitations for grouting piles in geotextile bags. For example, core drilling is prone to borehole deviation due to pile shape interference, resulting in low testing efficiency; sonic logging cannot be pre-embedded with acoustic logging tubes, making it difficult to detect; high / low strain methods are affected by the working interface, making them difficult to detect; static load tests have long cycles and high costs, making them unsuitable for large-area testing. Furthermore, all of these methods require damaging the road surface or pre-embedding testing devices, failing to meet the "low-damage, rapid testing" requirements of existing roads. Therefore, we provide a testing method for grouting piles in geotextile bags based on resistivity. Summary of the Invention

[0004] To address the problem that traditional detection methods in the aforementioned background technology require road breaking or pre-embedded devices, making it difficult to meet the requirement of "detection while traffic is open", this invention provides a method for detecting geotextile grouting piles based on resistivity method.

[0005] This invention is achieved using the following technical solution: a method for detecting geotextile-filled grouting piles based on resistivity method, comprising the following steps: S1. Conduct thorough data collection, site surveys, and equipment debugging before testing; S2. Arrange the electrodes in an array; S3. Apply low-frequency alternating current and simultaneously record the potential data of the MN electrode pair. When storing the raw data, mark the electrode coordinates and timestamp. S4. Preprocess the data and establish a three-layer media model; S5. Perform feature identification on the formwork bags and classify the pile quality according to the degree of damage.

[0006] As a further improvement to the above scheme, the data collection includes obtaining the design drawings and construction records of the geotextile grouting piles, and clarifying the pile diameter and length.

[0007] As a further improvement to the above scheme, the on-site investigation includes detecting the road surface structure, the location of underground pipelines, and measuring the surface elevation. The on-site investigation uses ground-penetrating radar or pipeline positioning instruments for location.

[0008] As a further improvement to the above solution, the equipment debugging includes verifying the resistivity meter, electrodes, and multi-channel acquisition system.

[0009] As a further improvement to the above scheme, the specific process of arranging the electrodes in an array is as follows: Area detection: Detection is carried out using a Wenner device or a dipole device, with the horizontal / vertical spacing of the detection device Δx=Δy=0.5-2m, and the spacing of the power supply electrodes is 1.5-2 times the detection depth, covering 3-5 rows of piles; Single pile reinforcement: With the pile center as the origin, arrange 3-5 circles of electrodes within a radius of 1-3m, with an inner circle spacing of 0.5m and an outer circle spacing of 1-2m; Grounding optimization: Insert the electrode 20-30cm into the ground surface, fill the surrounding area with conductive paste or saturated salt water, and ensure that the grounding resistance is ≤100Ω and the distance between adjacent electrodes is ≥3 times the electrode length.

[0010] As a further improvement to the above scheme, the data preprocessing includes: Abnormal data with grounding resistance >100Ω were removed, and high-frequency noise was filtered out using wavelet transform; Terrain correction is performed based on surface elevation data to compensate for the influence of slope on resistivity distribution.

[0011] As a further improvement to the above scheme, the three-layer medium for establishing the three-layer medium model includes a mold bag, cement grout solidified body and surrounding soil. A three-dimensional resistivity distribution model is generated by using a regularized inversion algorithm to make the number of data iterations ≥200 times and the fitting error ≤5%.

[0012] As a further improvement to the above solution, the feature recognition of the molding bag includes: Normal pile body: The resistivity image shows that the central low-resistivity zone is surrounded by a continuous high-resistivity ring, and the boundary error with the design pile diameter is ≤5%; Damage assessment: The high-resistivity ring is interrupted, and the resistivity of the surrounding soil is ≤80Ω. The abnormally low resistance region of m.

[0013] As a further improvement to the above scheme, the pile quality grading includes: Grade I (Excellent): No leakage, high-resistance ring intact, low-resistance region uniform; Level II (Qualified): The area of ​​the escaping zone is less than 15% of the cross-sectional area of ​​the pile body, and no continuous channel is formed; Level III (Unqualified): Evaporation area ≥15% or passage length ≥50cm, additional stakes required.

[0014] As a further improvement to the above scheme, when storing the original data and marking the electrode coordinates and timestamps, it is necessary to use lock-in amplification technology to filter out 50Hz power frequency noise.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention eliminates the need for drilling or pre-burying acoustic tubes. Only an electrode array needs to be arranged before testing, which reduces preparation time by 60% and avoids the risk of failure of pre-buried devices.

[0016] 2. This invention utilizes a molding bag (1000-5000Ω) m) and cement grout (10-50Ω) The resistivity threshold difference of m) can locate grout leakage areas of more than 10cm², with a resolution of 5% of the pile diameter (e.g., identifying a 5cm defect in a 1m pile diameter), thereby improving detection accuracy.

[0017] 3. This invention provides objective data for project acceptance by classifying the area and shape of the escaping zone and combining it with construction parameters (such as grouting pressure), thereby avoiding errors caused by manual interpretation.

[0018] 4. The single-area electrode placement time of this invention is ≤30 minutes, and it supports vehicle-mounted dynamic acquisition. The detection efficiency is 300% higher than that of traditional methods, meeting the requirement of "detecting while the vehicle is in motion". Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the electrode arrangement of the present invention; Figure 2 This is a diagram of the resistivity model of the three-layer dielectric of the present invention; Figure 3 This is a schematic diagram showing the arrangement of the power supply electrodes and measuring electrodes of the present invention. Detailed Implementation

[0020] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0021] Example 1: Please combine Figure 1-3 This embodiment of a method for detecting geotextile-filled grouting piles based on resistivity method includes the following steps: S1. Conduct thorough data collection, site surveys, and equipment debugging before testing; S2. Arrange the electrodes in an array; S3. Apply low-frequency AC current (0.1-10Hz, 2-5Hz recommended), current magnitude 10-50mA (adjust according to soil resistivity, use smaller values ​​for clay and larger values ​​for sand), single acquisition time ≤2 minutes / pile location, and simultaneously record MN electrode potential data (accuracy ±0.1mV), while marking electrode coordinates and timestamps when storing raw data; S4. Preprocess the data and establish a three-layer media model; S5. Perform feature identification on the formwork bags and classify the pile quality according to the degree of damage.

[0022] Data collection includes obtaining design drawings of the geotextile bag grouting pile (including geotextile bag material and thickness), construction records (grouting pressure and cement ratio), and clarifying the pile diameter (0.5-1.5m) and length (5-20m).

[0023] On-site investigation includes detecting the road surface structure (thickness of asphalt / concrete layers), the location of underground pipelines, and measuring the surface elevation. Ground-penetrating radar or pipeline positioning instruments are used for on-site investigation, ensuring that the electrodes are positioned at least 1 meter away from the pipelines. The surface elevation is measured, and the original soil resistivity is recorded (obtained through in-situ testing or an investigation report; 50-200Ω for sandy soil). m, clay 20-100Ω m).

[0024] Equipment commissioning includes calibrating the resistivity meter (resolution ≤1Ω). m), electrodes (copper / stainless steel, power supply electrode diameter ≥10mm, length 0.8-1.2m, measuring electrode diameter 5-8mm, length 0.5-1m) and a multi-channel acquisition system.

[0025] The specific process of arranging the electrodes in an array is as follows: Area detection (grid array): Detection is carried out using Wenner devices or dipole devices, and the horizontal / vertical spacing of the detection devices is Δx=Δy=0.5-2m (take the smaller value when the pile diameter is ≤1m). The spacing of the power supply electrodes is 1.5-2 times the detection depth, covering 3-5 rows of piles. Single pile densification (ring array): With the pile center as the origin, 3-5 circles of electrodes are arranged within a radius of 1-3m, with an inner circle spacing of 0.5m (for fine detection of the mold bag boundary) and an outer circle spacing of 1-2m (for evaluating the pile-soil interface). Grounding optimization: Insert the electrode 20-30cm into the ground surface and fill the surrounding area with conductive paste (graphite powder: water = 1:3) or saturated salt water to ensure that the grounding resistance is ≤100Ω (real-time monitoring) and the distance between adjacent electrodes is ≥3 times the electrode length.

[0026] Asphalt pavement uses magnetic electrodes and conductive adhesive to enhance contact and avoid contact with high resistivity pavement (≥500Ω). m) affects the signal.

[0027] When near metal pipelines, interference can be reduced by using bandpass filtering (to filter out abnormal signals in the 0-10Hz range) or offset electrode arrays (≥2m from the pipeline).

[0028] Data preprocessing includes: Abnormal data with grounding resistance >100Ω were removed, and high-frequency noise was filtered out using wavelet transform; Terrain correction is performed based on surface elevation data to compensate for the influence of slope on resistivity distribution.

[0029] The three dielectric layers used to establish the three-layer dielectric model include a mold bag (resistivity 1000-5000Ω). m, thickness 2-5mm), cement grout solids (10-50Ω) The model uses a regularized inversion algorithm (such as least squares combined with genetic algorithm) to generate a three-dimensional resistivity distribution model, including the surrounding soil (according to the survey report) and a regularized inversion algorithm to iterate the data ≥200 times while keeping the fitting error ≤5%. Before testing, the material of the geotextile bag (polypropylene / polyester, etc.) and its resistivity (obtained through material testing) must be clearly defined to avoid misjudging the geotextile bag itself as a defect (e.g., mistakenly identifying a 1000Ω geotextile bag as defective). (The high-resistivity layer is considered as a void). During the iteration process, the fitting error is monitored, and the process is terminated when the error change is less than 1% for 10 consecutive iterations, ensuring that the resistivity image resolution is ≤20cm.

[0030] Feature recognition of molded bags includes: Normal pile body: Resistivity image shows a low-resistivity zone in the center (10-50Ω) m, corresponding to cement grout) is continuously subjected to a high-resistance ring (1500-3000Ω). m, the body of the molded bag) is wrapped, and the boundary error between the design pile diameter and the actual pile diameter is ≤5%; Damage assessment: The high-resistivity ring is interrupted, and the resistivity of the surrounding soil is ≤80Ω. The abnormally low resistivity region of m (connected to the central low resistivity region, with blurred boundaries).

[0031] The quality grading of pile foundation includes: Grade I (Excellent): No leakage, high-resistance ring intact, low-resistance region uniform; Level II (Qualified): The area of ​​the escaping zone is less than 15% of the cross-sectional area of ​​the pile body, and no continuous channel is formed; Level III (Unqualified): Evaporation area ≥15% or passage length ≥50cm, additional stakes required.

[0032] Example 2: The further improvement of this embodiment based on embodiment 1 is that when storing the original data and marking the electrode coordinates and timestamps, lock-in amplification technology is required to filter out 50Hz power frequency noise.

[0033] All components of this invention are general standard parts or parts known to those skilled in the art. Their structure and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods. It is obvious to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this invention is defined by the appended claims rather than the foregoing description, and therefore all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0034] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for detecting geotextile-filled grouting piles based on resistivity method, characterized in that, Includes the following steps: S1. Conduct thorough data collection, site surveys, and equipment debugging before testing; S2. Arrange the electrodes in an array; S3. Apply low-frequency alternating current and simultaneously record the potential data of the MN electrode pair. When storing the raw data, mark the electrode coordinates and timestamp. S4. Preprocess the data and establish a three-layer media model; S5. Perform feature identification on the formwork bags and classify the pile quality according to the degree of damage.

2. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 1, characterized in that, The data collection includes obtaining design drawings and construction records for geotextile grouting piles, and clarifying the pile diameter and length.

3. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 2, characterized in that, The on-site investigation includes detecting the road surface structure, the location of underground pipelines, and measuring the ground surface elevation. The on-site investigation uses ground-penetrating radar or pipeline positioning instruments for location.

4. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 3, characterized in that, The equipment debugging includes verifying the resistivity meter, electrodes, and multi-channel acquisition system.

5. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 4, characterized in that, The specific process of arranging the electrodes in an array is as follows: Area detection: Detection is carried out using a Wenner device or a dipole device, with the horizontal / vertical spacing of the detection device Δx=Δy=0.5-2m, and the spacing of the power supply electrodes is 1.5-2 times the detection depth, covering 3-5 rows of piles; Single pile reinforcement: With the pile center as the origin, arrange 3-5 circles of electrodes within a radius of 1-3m, with an inner circle spacing of 0.5m and an outer circle spacing of 1-2m; Grounding optimization: Insert the electrode 20-30cm into the ground surface, fill the surrounding area with conductive paste or saturated salt water, and ensure that the grounding resistance is ≤100Ω and the distance between adjacent electrodes is ≥3 times the electrode length.

6. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 5, characterized in that, The data preprocessing includes: Abnormal data with grounding resistance >100Ω were removed, and high-frequency noise was filtered out using wavelet transform; Terrain correction is performed based on surface elevation data to compensate for the influence of slope on resistivity distribution.

7. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 6, characterized in that, The three-layer medium model includes a geotextile bag, cement grout solidified material, and surrounding soil. A three-dimensional resistivity distribution model is generated by using a regularized inversion algorithm to ensure that the data iteration count is ≥200 times and the fitting error is ≤5%.

8. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 7, characterized in that, The feature recognition of the molded bag includes: Normal pile body: The resistivity image shows that the central low-resistivity zone is surrounded by a continuous high-resistivity ring, and the boundary error with the design pile diameter is ≤5%; Damage assessment: The high-resistivity ring is interrupted, and the resistivity of the surrounding soil is ≤80Ω. The abnormally low resistance region of m.

9. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 8, characterized in that, The pile quality grading includes: Grade I (Excellent): No leakage, high-resistance ring intact, low-resistance region uniform; Level II (Qualified): The area of ​​the escaping zone is less than 15% of the cross-sectional area of ​​the pile body, and no continuous channel is formed; Level III (Unqualified): Evaporation area ≥15% or passage length ≥50cm, additional stakes required.

10. The method for detecting geotextile-filled grouting piles based on resistivity method as described in claim 9, characterized in that, When storing raw data and annotating electrode coordinates and timestamps, lock-in amplification technology is required to filter out 50Hz power frequency noise.

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