Method for detecting thickness of frozen soil curtain based on current focusing principle under seepage condition

Abstract

The invention discloses a frozen soil curtain thickness detection method based on a current focusing principle under a seepage condition, and relates to the technical field of frozen soil curtain detection. The method comprises the following steps: establishing a correlation function between the focusing resistivity and the frozen soil curtain thickness by combining an indoor test with a numerical simulation method before freezing circle crossing, after freezing circle crossing and in an excavation process, wherein the correlation function considers the influence of four factors including underground water flow velocity, flow direction, freezing temperature, freezing pipe spacing and the like; the freezing pipes are coated with insulating coatings in sequence, two sets of orthogonal focusing electrode systems are arranged on the insulating coatings, and on the basis of the three sets of correlation functions, the thickness information of the frozen soil curtain between the pipes is obtained in real time according to the actual measured specific numerical values of the four factors before freezing and the focusing resistivity in the freezing process.

Description

Technical Field

[0001] This application relates to the technical field of frozen soil curtain detection, and particularly to a method for detecting the thickness of a frozen soil curtain based on the principle of current focusing under seepage conditions. Background Art

[0002] The thickness of the frozen soil curtain is the key to controlling the mechanical stability of the frozen soil curtain. However, affected by the abnormal change of the local hydrogeological conditions of the freezing site and the insufficient fineness of the initial engineering survey, the development quality of the frozen soil curtain often shows anomalies, resulting in the deviation of the frozen soil curtain thickness from the design value and presenting an irregular development trend. If such abnormal development of the frozen soil curtain thickness cannot be captured in time during the freezing process, it will pose a safety hazard for subsequent excavation.

[0003] In the prior art, based on the focusing electrode system parameters corresponding to the optimal focusing effect, a correlation function between the position of the freezing front and the focusing resistivity between freezing pipes was established, and it was verified based on typical freezing projects, forming "a method for detecting the thickness of a frozen soil curtain in a large urban underground freezing project". However, the correlation function established in this technology cannot capture the abnormal changes of the frozen soil curtain during the freezing process, resulting in deviations in the detection of the frozen soil curtain thickness and affecting the decision-making of frozen soil construction. Summary of the Invention

[0004] Based on this, it is necessary to provide a method for detecting the thickness of a frozen soil curtain based on the principle of current focusing under seepage conditions to solve the problem that the abnormal changes of the frozen soil curtain during the freezing process cannot be captured, resulting in deviations in the detection of the frozen soil curtain thickness.

[0005] This specification adopts the following technical solutions: This specification provides a method for detecting the thickness of a frozen soil curtain based on the principle of current focusing under seepage conditions, including: Considering four factors including the spacing between freezing pipes, the formation freezing temperature, the underground water flow velocity, and the underground water flow direction, an orthogonal test table is established, and through the orthogonal test table, typical soil types are selected to conduct indoor tests and numerical simulation tests in sequence, and the focusing resistivity at three stages before the freezing circles meet, after the freezing circles meet, and during the excavation process of the freezing pipes is obtained; Based on the focusing resistivity at the above three stages, a first correlation function between the normalized focusing resistivity before the freezing circles meet and the normalized frozen soil curtain thickness, a second correlation function between the normalized focusing resistivity after the freezing circles meet and the normalized frozen soil curtain thickness, and a third correlation function between the normalized focusing resistivity during the excavation process and the normalized frozen soil curtain thickness are constructed; the correlation equations between the coefficients of the first correlation function, the coefficients of the second correlation function, the coefficients of the third correlation function and the four factors are established by using the multiple nonlinear regression method; In the actual detection process, before freezing construction, the surfaces of two adjacent freezing pipes are coated with insulation to form a thermally conductive insulating coating, and the membrane-type transmitting electrode and the membrane-type loop electrode are arranged on the thermally conductive insulating coating on the surface of the same freezing pipe, and two groups of orthogonal focusing electrode systems are arranged in parallel with the direction of the connection between the two freezing pipes and perpendicular to the direction of the connection between the two freezing pipes; Through the focusing electrode system, the focusing resistivity around the frozen pipe is obtained in real time in three stages, including before the freezing circle, after the freezing circle and during the excavation process. Through the first correlation function parallel to the direction of the connection between the two frozen pipes and the second and third correlation functions perpendicular to the direction of the connection between the two frozen pipes, combined with the four measured factors, the coefficients of the first correlation function, the coefficients of the second correlation function and the coefficients of the third correlation function and the correlation equations between the four factors are jointly established with the first correlation function, the second correlation function and the third correlation function to determine the thickness information of the frozen soil curtain.

[0006] Preferably, the focusing resistivity of the frozen pipe at three stages before freezing, after freezing and during excavation is obtained, specifically including: According to the four factors, and considering multiple values for each factor, an orthogonal test table is established; According to the orthogonal test table, typical soils were selected to carry out indoor tests to obtain the freezing point and temperature-resistivity relationship function; and according to the freezing temperature of the stratum, the freezing temperature field was obtained through numerical simulation experiments; Obtain the resistivity field according to the temperature-resistivity relationship function and the freezing temperature field; According to the resistivity field, the focused resistivity of the frozen pipe in three stages: before freezing, after freezing and during excavation was obtained.

[0007] Preferably, the first correlation function is established based on the detection results of the focusing electrode system parallel to the direction of the line connecting the two freezing tubes.

[0008] Preferably, the second correlation function and the third correlation function are established by detecting results of a focusing electrode system perpendicular to the direction of the line connecting the two freezing tubes.

[0009] Preferably, the freezing circle closing time is the time when the sum of the thicknesses of the left and right parts of the frozen soil curtain between the freezing pipes is equal to the spacing between the freezing pipes.

[0010] Preferably, The first correlation function is ; The second correlation function is ; The third correlation function is ; In the formula, is the initial resistivity of the formation, is the freezing pipe spacing, , and are the thicknesses of the frozen soil curtain before, after and during the excavation of the intersection circle respectively, , and are the focused resistivity before, after and during the excavation of the intersection circle respectively; The normalized focused resistivity is the ratio between the focused resistivity obtained by real-time detection and the initial resistivity of the formation; The normalized frozen soil curtain thickness is the ratio between the frozen soil curtain thickness and the spacing of the freezing pipes.

[0011] Preferably, the correlation equations between the coefficients of the first correlation function, the second correlation function and the third correlation function and the 4 factors are: ; ; ; wherein, , and are the coefficients of the first correlation function, the second correlation function and the third correlation function respectively, , , , , , , and are all non-linear regression coefficients, obtained by fitting numerical simulation data through MATLAB software, , , , are the measured spacing of the freezing pipes, the formation freezing temperature, the groundwater flow velocity and the groundwater flow direction before freezing.

[0012] The above at least one technical solution adopted in this specification can achieve the following beneficial effects: Compared with the existing inventions, this specification can not only realize the detection before the intersection of freezing, but also realize the detection of the thickness of the frozen soil curtain after the intersection of freezing and during the excavation; during the detection process, compared with the existing inventions, this specification realizes the detection of the thickness of the frozen soil curtain in the direction of the connection line of parallel freezing pipes (before the intersection of freezing) and in the direction perpendicular to the connection line of freezing pipes (after the intersection of freezing and during the excavation) by preparing two sets of orthogonal focused electrode arrays on the surface of the freezing pipes and based on the strategy of arranging the transmitting electrode and the loop electrode in the same pipe.

[0013] This specification takes into account the seepage effect, establishes the correlation functions before the freezing circle is formed, after the freezing circle is formed, and during the excavation process by focusing on the resistivity between the pipes, so as to detect the thickness of the frozen soil curtain in the directions parallel and perpendicular to the connection line of the freezing pipes, and realizes the detection of the process from the formation of the freezing front circle to the stabilization of the frozen soil curtain thickness, and the degradation or even "window opening" of the frozen soil curtain affected by the internal temperature rise and external seepage erosion. Brief Description of the Drawings

[0014] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings: Figure 1 It is a schematic flow chart of the method for detecting the thickness of the frozen soil curtain based on the current focusing principle under seepage conditions provided in this embodiment. Detailed Description of the Embodiments

[0015] To make the purpose, technical solutions and advantages of this specification clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the specific embodiments of this specification and the corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0016] The technical solutions provided in each embodiment of the present application will be described in detail below in conjunction with the drawings.

[0017] Figure 1 It is a method flow chart of the method for detecting the thickness of the frozen soil curtain based on the current focusing principle under seepage conditions in this embodiment, which specifically includes the following steps: S101: Consider four factors including the freezing pipe spacing, formation freezing temperature, groundwater flow velocity, and groundwater flow direction, establish an orthogonal test table, and through the orthogonal test table, select typical soil types to conduct indoor tests and numerical simulation tests in turn, and obtain the focused resistivity of the freezing pipes at three stages: before the freezing circle is formed, after the freezing circle is formed, and during the excavation process.

[0018] Optionally, obtaining the focused resistivity of the freezing pipes at three stages: before the freezing circle is formed, after the freezing circle is formed, and during the excavation process, includes: An orthogonal test table is established based on 4 factors, with each factor considering 5 levels. According to the orthogonal test table, typical soil types are selected to conduct laboratory tests to obtain the freezing point and the temperature-resistivity relationship function. Based on the formation freezing temperature, a freezing temperature field is obtained through numerical simulation experiments. According to the temperature-resistivity relationship function and the freezing temperature field, a resistivity field is obtained. According to the resistivity field, the focused resistivity of the freezing pipes at three stages, namely before the freezing circle connection, after the freezing circle connection, and during the excavation process, is obtained.

[0019] Specifically, the freezing pipe spacing can be selected at 5 levels such as 0.6m, 0.8m, 1.0m, 1.2m, and 1.4m. The formation freezing temperature can be selected at 5 levels such as -5°C, -10°C, -15°C, -20°C, and -25°C. The groundwater flow velocity can be selected at 5 levels such as 0m / d, 2m / d, 4m / d, 8m / d, and 16m / d. The groundwater flow direction is selected at 5 levels such as 0°, 15°, 30°, 60°, and 90° according to the angle between it and the normal direction of the excavation surface. Measured data of common water-rich sand layers in the city or the published results in the published paper "Freezing Front Location Method Based on Focused DC Resistivity" are selected, and then a numerical simulation orthogonal test table is established according to the above 4 factors and 5 levels. Through numerical simulation experiments, the temperature field, resistivity field, and the focused resistivity around a single pipe between two pipes are obtained in sequence.

[0020] S102: Construct a first correlation function between the normalized focused resistivity before the freezing circle connection and the normalized frozen soil curtain thickness, a second correlation function between the normalized focused resistivity after the freezing circle connection and the normalized frozen soil curtain thickness, and a third correlation function between the normalized focused resistivity during the excavation process and the normalized frozen soil curtain thickness through the focused resistivity at the three stages; establish a correlation equation between the coefficients of the first correlation function, the coefficients of the second correlation function, the coefficients of the third correlation function, and the 4 factors by using the multiple nonlinear regression method.

[0021] Optionally, the first correlation function is established based on the detection results of the focused electrode array in the direction of the connection line of two parallel freezing pipes; the second correlation function and the third correlation function are established through the detection results of the focused electrode array in the direction perpendicular to the connection line of two freezing pipes.

[0022] Optionally, the freezing circle connection moment is the moment when the sum of the frozen soil curtain thicknesses on the left and right sides between the freezing pipes is equal to the freezing pipe spacing.

[0023] Optionally, the first correlation function is ; the second correlation function is ; the third correlation function is ; where is the initial resistivity of the formation, is the freezing pipe spacing, , and are the thicknesses of the frozen soil curtain before the intersection, after the intersection, and during the excavation process, respectively , and are the focused resistivities before the intersection, after the intersection, and during the excavation process, respectively

[0024] Optionally, by adopting the multiple nonlinear regression method, an association equation is established between the coefficients of the first association function, the coefficients of the second association function, the coefficients of the third association function, and the four factors. The formula is as follows: ; ; ; In the formula, , and are the coefficients of the first association function, the second association function, and the third association function, respectively , , , , , , and are all nonlinear regression coefficients , , , are the measured spacing between freezing pipes, formation freezing temperature, groundwater flow velocity, and groundwater flow direction before freezing

[0025] S103: During the actual detection process, before the freezing construction, the surfaces of adjacent two freezing pipes are coated with insulation to form a thermal insulation coating, and the membrane type emitting electrode and the membrane type loop electrode are arranged on the thermal insulation coating on the surface of the same freezing pipe. Two groups of orthogonal focused electrode arrays are arranged in the direction parallel to the connection line of the two freezing pipes and the direction perpendicular to the connection line of the two freezing pipes

[0026] Specifically, the main material of the insulation coating is an alumina particle-based polymer material with thermal insulation function. The on-site coating thickness is 100 - 200 μm. The surface of the freezing pipe needs to be derusted before coating. The coating height range of the freezing pipe at a certain test depth layer is 3 m, that is, 1.5 m above and below the detection depth. The focused electrode array is a conductive thin film with a thickness not exceeding 100 μm, which is composed of an emitting electrode, two pairs of symmetrically arranged shielding electrodes, two pairs of monitoring electrodes for potential monitoring, and a loop electrode arranged in the same pipe. The focused electrode array is connected to the external focused electrical logging equipment through wires; the circumferential angle of the focused electrode is 60°, and the height and spacing are selected based on the published results in the published paper "Freezing Front Location Method Based on Focused DC Resistivity". One group is parallel to the connection line between the pipes, and one group is perpendicular to the connection line between the pipes

[0027] S104: Through the focusing electrode system, the focusing resistivity around the frozen pipe is obtained in real time in three stages, including before the freezing circle, after the freezing circle and during the excavation process. Through the first correlation function parallel to the direction of the connection between the two frozen pipes and the second and third correlation functions perpendicular to the direction of the connection between the two frozen pipes, combined with the four measured factors, the coefficients of the first correlation function, the coefficients of the second correlation function and the coefficients of the third correlation function and the correlation equations between the four factors are jointly established with the first correlation function, the second correlation function and the third correlation function to determine the thickness information of the frozen soil curtain.

[0028] Specifically, the freezing pipe spacing and freezing temperature are freezing design parameters, which are directly obtained according to the freezing design plan. The groundwater flow rate and flow direction are directly obtained according to the geological survey report. The three correlation functions are obtained according to step S102.

[0029] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for detecting the thickness of frozen soil curtain based on the principle of current focusing under seepage conditions, characterized in that, include: Considering four factors including freezing pipe spacing, ground freezing temperature, groundwater velocity and groundwater flow direction, an orthogonal test table was established. Through the orthogonal test table, typical soils were selected to carry out indoor tests and numerical simulation tests in turn, and the focusing resistivity of the freezing pipes in three stages: before freezing, after freezing and during excavation was obtained. Through the focus resistivity of the three stages, the first correlation function, the second correlation function and the third correlation function of the normalized focus resistivity of the three stages and the normalized frozen soil curtain thickness are constructed; the correlation equations between the coefficients of the first correlation function, the coefficients of the second correlation function and the coefficients of the third correlation function and the four factors are established by adopting the multivariate nonlinear regression method; Through the first correlation function parallel to the direction of the connection between the two freezing pipes and the second and third correlation functions perpendicular to the direction of the connection between the two freezing pipes, combined with the four measured factors, the coefficients of the first correlation function, the coefficients of the second correlation function and the coefficients of the third correlation function and the correlation equations between the four factors are jointly established with the first correlation function, the second correlation function and the third correlation function to determine the thickness information of the frozen soil curtain.

2. The method for detecting the thickness of frozen soil curtain based on the principle of current focusing under seepage conditions according to claim 1, characterized in that, Before determining the thickness information of the frozen soil curtain, the method further includes: During the actual detection process, before the freezing construction, the surfaces of the two adjacent frozen pipes are coated with insulation to form a thermally conductive insulating coating, and the membrane transmitting electrode and the membrane loop electrode are arranged on the thermally conductive insulating coating on the surface of the same frozen pipe. Two groups of orthogonal focusing electrode systems are arranged in a direction parallel to and perpendicular to the direction connecting the two frozen pipes. Through the focusing electrode system, the focusing resistivity around the frozen pipe is obtained in real time in three stages, including before the freezing circle, after the freezing circle, and during the excavation process.

3. The method for detecting the thickness of frozen soil curtain based on the principle of current focusing under seepage conditions according to claim 1, characterized in that The first correlation function is established based on the detection results of the focusing electrode system parallel to the direction of the connection line of the two freezing tubes.

4. The method for detecting the thickness of frozen soil curtain based on the principle of current focusing under seepage conditions according to claim 1, characterized in that The second correlation function and the third correlation function are established by detecting the results of a focusing electrode system perpendicular to the direction of the line connecting the two freezing tubes.

5. The method for detecting the thickness of frozen soil curtain based on the principle of current focusing under seepage conditions according to claim 1, characterized in that, The freezing circle closing moment is the moment when the sum of the thicknesses of the left and right parts of the frozen soil curtain between the freezing pipes is equal to the spacing between the freezing pipes.

6. The method for detecting the thickness of frozen soil curtain based on the current focusing principle under seepage conditions according to claim 1, characterized in that: The first correlation function is ; The second correlation function is ; The third correlation function is ; In the formula, is the initial formation resistivity, is the spacing of freezing pipes, , and are the thicknesses of the frozen soil curtain before, after and during the excavation respectively, , and are the focused resistivities before, after and during the excavation respectively; The normalized focused resistivity is the ratio between the focused resistivity obtained by real-time detection and the initial resistivity of the formation; The normalized frozen soil curtain thickness is the ratio of the frozen soil curtain thickness to the freezing pipe spacing.

7. The method for detecting the thickness of a frozen soil curtain based on the principle of current focusing under seepage conditions as described in claim 1, wherein, The correlation equations between the coefficients of the first correlation function, the coefficients of the second correlation function, and the coefficients of the third correlation function and the four factors are: ； ； ； Wherein, , and are the coefficients of the first correlation function, the second correlation function and the third correlation function respectively, , , , , , , and are all non-linear regression coefficients, obtained by fitting numerical simulation data, , , , are the measured freezing pipe spacing, formation freezing temperature, groundwater flow velocity and groundwater flow direction before freezing.

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