Cement-soil pile integrity detection method based on high-density resistivity method

Abstract

The invention discloses a cement-soil pile integrity detection method based on a high-density resistivity method. The method comprises the following steps: recording a background value of a pre-detection depth before construction; drilling holes or arranging in-hole electrodes by using original holes; the resistivity of the pile body after construction is measured by adopting a high-density resistivity method, and impedance inversion is carried out by using inversion software, so that complete resistivity tomography near the pile body is obtained, and the radius of each depth of the pile body is deduced according to the measurement result. The method is advanced and scientific, is simple to implement, conforms to the emerging information technology, can effectively and quickly obtain the continuous and complete depth profile of the pile body including the equivalent pile and the depth, obviously accelerates the measurement speed, greatly reduces the economic cost, obviously improves the measurement precision, and is suitable for popularization and application. The method has high reference value and guiding significance for detecting the diameter of the jet grouting pile.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation detection in geotechnical engineering, and in particular to a cement soil pile integrity detection method based on a high-density resistivity method. Background Art

[0002] High-pressure jet grouting is currently a commonly used technology for foundation reinforcement. The effectiveness of foundation reinforcement is closely related to the integrity of the pile body (including pile diameter and continuity). Piles that fail to meet design requirements have common problems such as broken piles, insufficient pile diameter, insufficient length, and mud packaging. Therefore, pile integrity testing is necessary.

[0003] At present, common detection methods include direct excavation inspection method, core drilling method, CPT cone injection test approximation method, sound tube method and ultrasonic detection. The results obtained by these detection methods are often not representative of the whole due to the small sampling space, and are easily misjudged by local variation. A large number of detection methods have the disadvantages of being uneconomical, time-consuming and labor-intensive. The high-density resistivity method has the ability to detect or monitor the 2D or 3D resistivity spatial distribution of the formation. It has the advantages of non-destructiveness, high construction efficiency and large detection range, which can make up for the shortcomings of existing detection methods and conduct more effective evaluation and detection of the integrity of foundation reinforcement piles.

[0004] In view of this, it is very necessary to design a method that can use the single-hole high-density resistivity method to quickly detect each pile and obtain the overall cross-sectional shape of the pile (including the pile diameter and depth continuity), which will effectively save costs and improve the accuracy of detection. Summary of the invention

[0005] The present invention aims to overcome the deficiencies of the above-mentioned prior art and methods and proposes a cement soil pile integrity detection method based on high-density resistivity method.

[0006] The present invention adopts the following technical solution: a cement soil pile integrity detection method based on high-density resistivity method, comprising the following steps:

[0007] S1, record the background value of the pre-detection depth before pile construction;

[0008] S2, drilling holes outside the pile body or using the original holes of the pile body to arrange the electrodes in the holes;

[0009] S3. Conduct pile integrity measurement, use high-density resistivity method to measure the resistivity of the pile after construction, use inversion software to perform impedance inversion, and obtain a complete resistivity tomography image near the pile body;

[0010] S4. Infer the overall cross-sectional shape of the pile body based on the measurement results.

[0011] Preferably, in step S1, the background value should be collected before the construction starts, a stable resistivity value is determined as the background value, and the background value collection depth is determined according to the buried depth of the pile to be tested.

[0012] Preferably, in step S2, for cement-soil piles with a diameter less than 3 m, single-hole measurement is adopted, and a single grouting pipe, PVC pipe or other non-metallic pipes in the pile body can be used to arrange the measurement line; for large-diameter (diameter greater than or equal to 3 m) cement-soil piles or cement-soil rigid composite piles, multi-hole measurement is adopted, and 2 or more holes can be drilled on the outside of the pile for measurement line arrangement.

[0013] For single-hole measurement, the recommended electrode arrangement method for the survey line is the Wenner-Schlumber arrangement (the measuring electrode MN remains stationary, and the power supply electrode AB is measured step by step in different directions). The dipole-dipole arrangement (the measuring electrode MN and the power supply electrode AB are placed in pairs) can be used, or the arrangement method can be set by yourself. For multi-hole measurement, the cross-hole dipole arrangement should be used (the power supply electrode AB remains stationary, and the measuring electrode MN is measured step by step downward).

[0014] For single-hole measurement, after the jet grouting of the jet pile is completed, the resistivity of the pile body must be measured as soon as possible at one time. If it is impossible to complete the measurement in one go, it is necessary to wait until the column solidifies before drilling. For multi-hole measurement, drilling should be carried out after the column solidifies.

[0015] Preferably, in step S3, for single-hole measurement, commercial two-dimensional inversion software is used to invert the results. According to the two-dimensional space assumption of the two-dimensional georesistance semi-infinite domain, the resistivity tomography in the axisymmetric hole is equivalent to the two-dimensional semi-infinite domain, and the interface between the pile body and the soil body can be determined; for multi-hole measurement, two-dimensional inversion software is used to invert the results for two holes, and three-dimensional inversion software is used to invert the results for three holes or more.

[0016] The pile integrity measurement adopts the high-density resistivity method to measure the resistivity of the pile after grouting is completed, and the change of pile diameter at different depths is judged according to the change of resistivity with depth and pile side profile.

[0017] According to the inversion results, various geoelectric unit structures can be analyzed. According to the distribution of geoelectric unit structures, the elevation and radius of the pile section can be inferred. By referring to the background value determined before construction, the relatively low-resistance structure and the relatively high-resistance structure can be determined.

[0018] Generally speaking, if the resistivity of a relatively low-resistance structure is ≤0.6Ω·m, it can be inferred to be a pile; if the resistivity of a relatively high-resistance structure is >0.6Ω·m, it can be inferred to be a soil.

[0019] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0020] The method of the present invention is advanced and scientific, in line with emerging information technology, simple to implement, and can effectively and quickly obtain a complete depth profile of the pile body including equivalent piles and continuity in depth. The measurement speed is significantly accelerated, the economic cost is greatly reduced, and the measurement accuracy is significantly improved. It has high reference value and guiding significance for the detection of the diameter of the jet grouting pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the flow chart of the method for predicting the diameter of a jet grouting pile according to the present invention;

[0022] Figure 2 It is a schematic diagram of a pile diameter detection device for small-diameter cement soil piles according to the present invention;

[0023] Figure 3 It is a schematic diagram of the pile diameter detection device for large-diameter cement soil piles or rigid piles according to the present invention.

[0024] In the figure: 1- measuring line, 2- electrode, 3- engineering electrical measuring instrument, 4- construction profile shape of cement soil pile, 5- design profile shape of cement soil pile, 6- single hole in pile core, 7- mud surface, 8- multiple holes outside the pile. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the application is further elaborated in detail below in conjunction with the accompanying drawings. The described embodiments are only a part of the embodiments involved in the present invention. All non-innovative embodiments of other researchers in the field on this embodiment belong to the protection scope of the present invention. At the same time, for the step numbering in the embodiment of the present invention, it is only set for the convenience of explanation, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0026] The present invention focuses on the goal of "detecting the diameter of jet grouting piles" and adopts a high-density resistivity method. By studying the difference between cement hydration resistivity and surrounding soil resistivity, a jet grouting pile integrity detection theory and method based on the high-density resistivity method is established to achieve accurate evaluation of the diameter and continuity of the jet grouting piles.

[0027] Detection of pile integrity: The detection of cement soil pile integrity can be roughly divided into pile diameter and continuity. The high-density resistivity method has the advantages of non-destructiveness, high construction efficiency and large detection range. It can make up for the shortcomings of existing detection methods and conduct more effective evaluation and detection of the integrity of the jet grouting pile.

[0028] High-density resistivity method: High-density resistivity method is one of the traditional geophysical detection technologies and has been widely used in geological surveys, engineering monitoring and pollution control monitoring. High-density resistivity detection method uses four electrodes as a group for measurement, two of which inject direct current into the ground, and then measure the voltage difference between the other two electrodes. Through the inverse calculation technique, the 2D or 3D image profile of the resistance value depth can be obtained. Through this image comparison with the geometric distribution of the pile body, the complete and accurate geometric shape of the improved column can be obtained.

[0029] In one embodiment of the present invention, a cement soil pile integrity detection method based on high-density resistivity method is used for jet grouting pile diameter detection, such as Figure 1 As shown, including:

[0030] S1, record the background value of the pre-test depth before construction;

[0031] S2, drilling holes or using existing holes to arrange in-hole measuring line electrodes;

[0032] S3. Use high-density resistivity method to measure the resistivity of the pile after construction, and use inversion software to perform impedance inversion to obtain a complete resistivity tomography image near the pile body;

[0033] S4. Infer the overall cross-sectional shape of the pile body based on the measurement results.

[0034] During specific implementation, the background value collection should be completed before the construction begins, a stable resistivity value should be determined as the background value, and the background value collection depth should be determined according to the buried depth of the pile being tested.

[0035] For cement soil piles with a diameter less than 3m, Figure 2 As shown, a single grouting pipe, a PVC pipe or other non-metallic pipe in the pile body can be used as a pile core single hole (6) to arrange the survey line (1).

[0036] For large diameter cement soil piles or rigid composite piles, such as Figure 3 As shown, two or more holes can be drilled outside the pile as pile outer multi-holes (6) to arrange the survey line (1).

[0037] For single hole measurement ( Figure 2 ), the arrangement method of the measuring line electrode (2) is recommended to use the Wenner Schlumber arrangement (the measuring electrode MN remains stationary, and the power supply electrode AB gradually measures in different directions), and the dipole-dipole arrangement (the measuring electrode MN and the power supply electrode AB are placed in pairs) can be used, or the arrangement method can be set by yourself; for multi-hole measurement ( Figure 3 ), a cross-hole dipole arrangement should be used (the power supply electrode AB remains stationary and the measuring electrode MN measures step by step downward).

[0038] For single hole measurement ( Figure 2), after the jet grouting of the jet grouting pile is completed, the resistivity of the pile body needs to be measured as soon as possible at one time. If the conditions for one-time measurement cannot be met, it is necessary to wait until the column solidifies before drilling. Among them, the pile body in the pre-construction design drawing is shown as the design cross-sectional shape of the cement soil pile (5), the actual construction cross-sectional shape of the cement soil pile (4), the measuring hole (6) is located at the center of the pile body, the measuring line (1) is located inside the measuring hole (6), the electrodes (2) are arranged on the measuring line (1) in a certain arrangement, and the electrical measuring instrument (3) is set on the outside of the mud surface (7) at the top of the pile body.

[0039] For multi-hole measurements ( Figure 3 ), and drilling should be carried out after the column solidifies. In the pre-construction design drawing, the pile body is shown as the cement soil pile design cross-sectional shape (5), the actual cement soil pile construction cross-sectional shape (4), multiple measuring holes (6) are located outside the pile body, the measuring line (1) is located inside the measuring hole (6), the electrodes (2) are arranged on the measuring line (1) in a certain arrangement, and the engineering electrical measuring instrument (3) is set in the middle of the mud surface (7) at the top of the pile body.

[0040] For single hole measurement ( Figure 2 ), commercial two-dimensional inversion software was used to invert the results. According to the two-dimensional space assumption of the two-dimensional georesistance semi-infinite domain, the axisymmetric borehole resistivity tomography is equivalent to a two-dimensional semi-infinite domain, and the interface between the pile and the soil can be determined.

[0041] For multi-hole measurements ( Figure 3 ), two-dimensional inversion software is used for the inversion of results for two holes, and three-dimensional inversion software is used for the inversion of results for three holes or more.

[0042] The high-density resistivity method is used to measure the resistivity of the pile body after grouting is completed. The change in pile diameter at different depths is determined based on the change in resistivity with depth and pile side profile, and the actual construction profile shape of the cement soil pile after construction is obtained (4).

[0043] According to the inversion results, various geoelectric unit structures can be analyzed. Referring to the background value determined before construction, the elevation and radius of the pile section can be inferred according to the distribution of the geoelectric unit structure. If the resistivity of the relatively low-resistance structure is ≤0.6Ω·m, it can be inferred to be a pile; if the resistivity of the relatively high-resistance structure is >0.6Ω·m, it can be inferred to be a soil.

[0044] In summary, the cement soil pile integrity detection method based on the high-density resistivity method of the present invention can effectively and quickly obtain a complete depth profile of the pile body including equivalent piles and continuity in depth. The measurement speed is significantly accelerated and the measurement accuracy is significantly improved. It has a high reference value and guiding significance for the detection of the diameter of the jet grouting pile.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A cement soil pile integrity detection method based on high-density resistivity method, characterized in that: The following steps are involved: S1, record the background value of the pre-detection depth before pile construction; S2. Drill holes outside the pile body or use the original holes in the pile body to arrange the electrodes in the holes; S3. Measure the integrity of the pile body. Use the high-density resistivity method to measure the resistivity of the pile body after construction. Use inversion software to perform impedance inversion and obtain a complete resistivity tomography image near the pile body. S4. Infer the overall cross-sectional shape of the pile body based on the measurement results.

2. The cement soil pile integrity detection method based on high-density resistivity method according to claim 1, characterized in that: In step S1, background value collection is completed before construction begins. A stable resistivity value is determined as the background value based on the local rock and ore resistivity historical data, and the background value collection depth is determined based on the buried depth of the pile being tested.

3. The cement-soil pile integrity detection method based on high-density resistivity method according to claim 1, characterized in that: In step S2, for cement-soil piles with a diameter less than 3m, single-hole measurement is adopted, and the measurement line is arranged using non-metallic pipes inside the pile body; the non-metallic pipes include: single grouting pipes and PVC pipes; For cement-soil piles or cement-soil reinforced composite piles with a diameter greater than or equal to 3m, multi-hole measurement is adopted. At least two holes are drilled on the outside of the pile body, and the measurement line is arranged in each hole.

4. The cement soil pile integrity detection method based on high-density resistivity method according to claim 3, characterized in that: In step S2, the in-hole electrodes are arranged. For single-hole measurement, the measuring line electrodes use the Wenner-Schlumber arrangement method, the measuring electrode MN remains stationary, and the power supply electrode AB gradually measures in different directions; for multi-hole measurement, the measuring line electrodes use the cross-hole dipole arrangement method, the power supply electrode AB remains stationary, and the measuring electrode MN gradually measures downward.

5. The cement soil pile integrity detection method based on high-density resistivity method according to claim 4, characterized in that: In single-hole measurement, the measuring electrode MN and the power supply electrode AB are arranged in a dipole-dipole arrangement and placed in pairs.

6. The cement soil pile integrity detection method based on high-density resistivity method according to claim 4, characterized in that: For single-hole measurement, the pile resistivity is measured once after the jet grouting is completed. If the one-time measurement cannot be completed, the pile body is allowed to solidify before drilling again. For multi-hole measurement, drilling is carried out after the jet grouting is completed and the pile body is allowed to solidify.

7. The cement-soil pile integrity detection method based on high-density resistivity method according to claim 1, characterized in that: In step S3, the pile integrity is measured by using a high-density resistivity method to measure the resistivity of the pile after grouting is completed. The change in pile diameter at different depths is determined based on the change in resistivity with depth and pile side profile.

8. The cement soil pile integrity detection method based on high-density resistivity method according to claim 7, characterized in that: In step S3, when measuring a single hole, impedance inversion is performed using two-dimensional inversion software. Based on the assumption that the two-dimensional ground resistance is a semi-infinite domain, the axisymmetric in-hole resistivity tomography is equivalent to a two-dimensional semi-infinite domain, and the interface between the pile and the soil is determined. When measuring multiple wells, two-dimensional inversion software is used for impedance inversion of two wells, and three-dimensional inversion software is used for impedance inversion of three wells or more.

9. The cement soil pile integrity detection method based on high-density resistivity method according to claim 1, characterized in that: Based on the inversion results, various geoelectric unit structures are analyzed. The pile elevation and radius are inferred based on the distribution of the geoelectric unit structures. With reference to the background values ​​collected in step S1 before construction, relatively low-resistance structures and relatively high-resistance structures are determined, and the overall condition of the pile body is inferred.

10. The cement soil pile integrity detection method based on high-density resistivity method according to claim 9, characterized in that: The relatively low-resistance structure has a resistivity of ≤0.6Ω·m, which is inferred to be a pile; the relatively high-resistance structure has a resistivity of >0.6Ω·m, which is inferred to be a soil.

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