Inter-pipe freezing frontal surface position detection method based on circumferential focusing theory

Abstract

The invention discloses an inter-pipe freezing frontal surface position detection method based on an annular focusing theory, and belongs to the technical field of frozen soil curtain form detection of freezing engineering. Firstly, the depth of a detection stratum is determined, then a freezing pipe is selected, seven working electrodes are arranged in the 180-degree range in the circumferential direction of the freezing pipe according to the 30-degree interval, circumferential 360-degree loop electrodes are arranged at the positions, with the same depth, of the freezing pipe on the right opposite side, the second electrode, the third electrode, the fourth electrode, the fifth electrode and the sixth electrode in the seven working electrodes serve as emission electrodes, and the third electrode and the fourth electrode serve as emission electrodes. Electrodes on the two sides of the emission electrode automatically serve as shielding electrodes, and focusing is achieved by setting the equipotential condition of the shielding electrodes and the emission electrode, so that four arc-shaped current beams and one horizontal current beam are formed between the two freezing pipes; and establishing a function relationship between the non-dimensionalized freezing frontal surface position and the non-dimensionalized inter-tube resistance, and performing inversion to obtain the freezing frontal surface position in the range of the first and fifth inter-tube current beam paths by combining the on-site actual measurement non-dimensionalized resistance based on a focused direct current resistivity system.

Description

Technical Field

[0001] The invention relates to a method for detecting the position of a freezing front between pipes based on a toroidal focusing theory, and belongs to the technical field of frozen soil curtain morphology detection in freezing engineering. Background Art

[0002] The freezing project is a concealed project. The formation quality and final form of the frozen soil curtain determine the mechanical properties of the frozen soil curtain during the excavation period. The freezing front is the boundary of the frozen soil curtain and the basis for outlining the shape of the frozen soil curtain. The existing freezing front detection methods mainly include direct method (temperature measurement) and indirect method (geological radar, ultrasound, resistivity, etc.). These detection methods are based on either engineering scale or inter-tube stratum scale, and most of the information obtained is discrete point information, and the spatial form of the frozen soil curtain cannot be obtained. In the early stage, the research team introduced the current focusing method to theoretically overcome the interference of the lateral strata, and at the same time focused the detection range between two freezing pipes, greatly improving the interpretation accuracy of the detection results. This technology has been authorized by invention patent (a method for detecting the thickness of frozen soil curtains in large-scale urban underground freezing projects, ZL202110088361.6). However, it was found in the actual detection process that this technology can only obtain the freezing front position of a point on the horizontal path. It is not applicable to the freezing front of irregular shapes, especially the situation where the freezing fronts on the left and right sides have different advancing speeds, and further research and solution are urgently needed. Summary of the invention

[0003] In view of the shortcomings of the existing technology, a method for detecting the position of the freezing front between tubes based on the annular focusing theory is proposed. The method can effectively detect the irregular shaped freezing front that appears during the freezing process of heterogeneous strata, especially when the advancing speeds of the freezing fronts on the left and right sides are different, and the distance information of different positions of the freezing front is obtained. The method is simple and effective.

[0004] Technical content: To achieve the above technical objectives, the present invention discloses a method for detecting the position of the freezing front between pipes based on the annular focusing theory, which is characterized by comprising the following steps:

[0005] a. Select a freezing pipe section of the same horizontal height from two adjacent parallel freezing pipes as the detection pipe section, and set an insulating coating on the outer side of the two freezing pipe sections;

[0006] b. Arrange seven working electrodes on one of the freezing pipe sections, and arrange the seven working electrodes at intervals of 30° along the circumferential range of 180° along the semicircular arc surface facing another freezing pipe, and set a loop electrode around the freezing pipe on the other adjacent freezing pipe on the opposite side; the height of the cross section where the longitudinal center of the transmitting electrode is located is the same as the height of the cross section where the longitudinal center of the loop electrode is located, and the transmitting electrode and the loop electrode must be set before the freezing begins;

[0007] c. Connect the working electrode and the loop electrode to the ground detection host through wires, and number the working electrodes in sequence;

[0008] d. When the freezing front position needs to be detected during the freezing process, the first and seventh working electrodes only serve as focusing electrodes, and the ground detection host controls the second to sixth working electrodes to sequentially serve as transmitting electrodes to transmit current to the loop electrode. When any working electrode from the second to sixth working electrodes serves as a transmitting electrode, the two working electrodes adjacent to the working electrode simultaneously serve as shielding electrodes to cooperate with the transmitting electrode in emitting the same polarity current, and focusing is achieved according to the equipotential conditions of the shielding electrode and the transmitting electrode. At this time, the lateral diffusion range of the emission current is compressed by the focusing effect, and at the same time, due to the horizontal traction effect of the loop electrode, four arc current beam paths and one horizontal current beam path are formed between the two freezing pipe sections;

[0009] Each current beam path passes through frozen soil, unfrozen soil and frozen soil in turn. The functional relationship between the dimensionless total resistance R of frozen soil and unfrozen soil at different freezing times and the dimensionless freezing front position s at this time is used: s / L=k﹒R / R0. The freezing front positions within the range of the five current beam paths are obtained in real time, where k is a constant, L is the freezing pipe spacing, and R0 is the initial resistance of the stratum between the two freezing pipes before freezing.

[0010] Furthermore, the total resistance R of the unfrozen soil and the frozen soil is calculated using the formula R=U / I, where: U is the voltage of the transmitting electrode in the focused detection mode, and I is the current of the transmitting electrode in the focused detection mode.

[0011] Furthermore, the circumferential length and longitudinal height of the working electrode are both 1 / 10 of the circumference of the freezing tube, and the height of the loop electrode is 1 / 5 of the circumference of the freezing tube.

[0012] Furthermore, model tests were carried out based on actual freezing projects to obtain the inter-tube resistance R0 before freezing, the resistance R corresponding to the five current beam paths during the freezing process, and the freezing front position s based on temperature measurement, where s is the distance from the outer wall of the freezing pipe to the freezing point line in the formation. A relationship curve between the dimensionless freezing front position s / L and the dimensionless resistance R / R0 was established, the slope of the fitted relationship curve was the constant k, and the relationship function between k and freezing time was obtained.

[0013] Furthermore, when the freezing front advancing speeds on the opposite surfaces between the two freezing pipes are different, the dimensionless freezing front positions on the left and right sides and the dimensionless resistance between the pipes conform to the same functional relationship, but the constant k is different and is taken according to the model test results.

[0014] Beneficial effects: The present invention enriches the directional focusing method, takes into account the plum blossom alternating arrangement scheme of freezing pipes, and the situations where there are multiple rows of freezing pipes and two rows of freezing pipes are arranged alternately. The present invention can obtain the real-time contour morphology of the freezing front around the freezing pipes, overcomes the limitations of the existing focusing detection methods, and expands the freezing front position that can only detect a point on the horizontal path between two freezing pipes in the prior art to freezing plane information. For irregular-shaped freezing fronts, especially when the freezing fronts on the left and right sides have different advancing speeds, the spatiotemporal advancement information of the freezing front can also be obtained. The present invention is of great significance for obtaining the actual frozen soil curtain morphology, guiding excavation, and optimizing theoretical design. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a working schematic diagram of the method for detecting the position of the freezing front between tubes based on the annular focusing theory of the present invention. DETAILED DESCRIPTION

[0016] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0017] The present invention discloses a method for detecting the position of freezing fronts between pipes based on the circumferential focusing theory. The method comprises the following steps: firstly determining the depth of the detection stratum, then selecting a freezing pipe, arranging seven working electrodes at intervals of 30° along a 180° circumferential range of the freezing pipe, and setting a circumferential 360° loop electrode at the same depth position on the freezing pipe directly opposite to the freezing pipe. The second electrode to the sixth electrode of the seven working electrodes are used as transmitting electrodes, and the electrodes on both sides of the transmitting electrode are automatically used as shielding electrodes. Focusing is achieved by setting equal potential conditions of the shielding electrode and the transmitting electrode, such as Figure 1 As shown, four arcs and one horizontal current beam are formed between the two freezing tubes; a functional relationship between the dimensionless freezing front position and the dimensionless inter-tube resistance is established, and combined with the field measured dimensionless resistance based on the focused DC resistivity system, the freezing front position within the first and fifth current beam paths between the tubes is obtained by inversion.

[0018] Specifically:

[0019] a. First, select a freezing pipe (fixed depth) and an adjacent freezing pipe, and set an insulating coating on the outside of the freezing pipe and the adjacent freezing pipe;

[0020] b. Then, seven working electrodes are arranged at 30° intervals along a 180° circumferential range on a freezing tube (the circumferential length and longitudinal height of the transmitting electrode are both 1 / 10 of the circumference of the freezing tube), and a 360° circumferential loop electrode is set on the adjacent freezing tube on the opposite side (the height of the loop electrode is 1 / 5 of the circumference of the freezing tube). The cross-sectional height of the longitudinal center of the working electrode is the same as the cross-sectional height of the longitudinal center of the loop electrode. The working electrode and the loop electrode must be set before the freezing begins;

[0021] c. Connect the working electrode, focusing electrode and loop electrode to the ground detection host through wires;

[0022] d. During the freezing process, starting from the second electrode to the sixth electrode, the second working electrode to the sixth working electrode are used as the transmitting electrodes to sequentially transmit current, and the shielding electrode and the transmitting electrode transmit current of the same polarity; when any working electrode transmits current, the two working electrodes adjacent to the working electrode work together as shielding electrodes, and focus is achieved according to the equipotential conditions of the shielding electrode and the working electrode. At this time, the lateral diffusion range of the transmitting current is compressed by the focusing effect, and at the same time, due to the horizontal traction of the loop electrode, four arc current beam paths and one horizontal current beam path are formed. Each current beam path passes through the frozen soil, unfrozen soil and frozen soil in turn. The functional relationship between the dimensionless total resistance R of the frozen soil and unfrozen soil at different freezing times and the dimensionless freezing front position s at this time is used: s / L=k﹒R / R0, where k is a constant, L is the freezing pipe spacing, and R0 is the initial resistance of the two freezing pipe formations before freezing, and the freezing front position within the range of the first and fifth current beam paths is obtained in real time.

[0023] The total resistance R of the unfrozen soil and the frozen soil is calculated using the formula R=U / I, where: U is the voltage of the transmitting electrode in the focused detection mode, and I is the current of the transmitting electrode in the focused detection mode.

[0024] According to the actual freezing project, the model test was carried out at a geometric scale of 1:10, and the test data was verified to obtain the inter-tube resistance R0 before freezing and the resistance R corresponding to the five current beam paths during the freezing process, as well as the freezing front position s based on temperature measurement. The relationship curve between the dimensionless freezing front position s / L and the dimensionless resistance R / R0 was established, and the slope of the fitting relationship curve was the constant k, and the relationship function between k and freezing time was obtained. When the freezing front advancing speeds on both sides are different, the dimensionless freezing front positions on the left and right sides and the dimensionless resistance between the tubes conform to the same functional relationship, but the constant k is different, and the values ​​are taken according to the model test results.

[0025] There are many specific implementation ways of the present invention. The above is only the preferred implementation mode of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A method for detecting the position of the freezing front between pipes based on the annular focusing theory, characterized in that The steps include: a. Select a freezing pipe section of the same horizontal height from two adjacent parallel freezing pipes as the detection pipe section, and set an insulating coating on the outer side of the two freezing pipe sections; b. Arrange seven working electrodes on one of the freezing pipe sections, and arrange the seven working electrodes at intervals of 30° along the circumferential range of 180° along the semicircular arc surface facing another freezing pipe, and set a loop electrode around the freezing pipe on the other adjacent freezing pipe on the opposite side; the height of the cross section where the longitudinal center of the transmitting electrode is located is the same as the height of the cross section where the longitudinal center of the loop electrode is located, and the transmitting electrode and the loop electrode must be set before the freezing begins; c. Connect the working electrode and the loop electrode to the ground detection host through wires, and number the working electrodes in sequence; d. When the freezing front position needs to be detected during the freezing process, the first and seventh working electrodes only serve as focusing electrodes, and the ground detection host controls the second to sixth working electrodes to sequentially serve as transmitting electrodes to transmit current to the loop electrode. When any working electrode from the second to sixth working electrodes serves as a transmitting electrode, the two working electrodes adjacent to the working electrode simultaneously serve as shielding electrodes to cooperate with the transmitting electrode in emitting the same polarity current, and focusing is achieved according to the equipotential conditions of the shielding electrode and the transmitting electrode. At this time, the lateral diffusion range of the emission current is compressed by the focusing effect, and at the same time, due to the horizontal traction effect of the loop electrode, four arc current beam paths and one horizontal current beam path are formed between the two freezing pipe sections; Each current beam path passes through frozen soil, unfrozen soil and frozen soil in turn. The functional relationship between the dimensionless total resistance R of frozen soil and unfrozen soil at different freezing times and the dimensionless freezing front position s at this time is used: s / L=k﹒R / R0. The freezing front positions within the range of the five current beam paths are obtained in real time, where k is a constant, L is the freezing pipe spacing, and R0 is the initial resistance of the stratum between the two freezing pipes before freezing.

2. The method for detecting the position of the inter-tube freezing front based on the annular focusing theory according to claim 1, characterized in that: The total resistance R of unfrozen soil and frozen soil is calculated using the formula R = U / I, where: U is the voltage of the transmitting electrode in the focused detection mode, and I is the current of the transmitting electrode in the focused detection mode.

3. The method for detecting the position of the inter-tube freezing front based on the annular focusing theory according to claim 1, characterized in that: The circumferential length and longitudinal height of the working electrode are both 1 / 10 of the circumference of the freezing tube, and the height of the loop electrode is 1 / 5 of the circumference of the freezing tube.

4. The method for detecting the position of the inter-tube freezing front based on the annular focusing theory according to claim 1, characterized in that: A similar model test was carried out based on the actual freezing project to obtain the inter-tube resistance R0 before freezing, the resistance R corresponding to the five current beam paths during the freezing process, and the freezing front position s based on temperature measurement. s is the distance from the outer wall of the freezing pipe to the freezing point line in the formation. A relationship curve between the dimensionless freezing front position s / L and the dimensionless resistance R / R0 was established, the slope of the fitting relationship curve is the constant k, and the relationship function between k and freezing time is obtained.

5. The method for detecting the position of the freezing front between pipes based on the annular focusing theory according to claim 2, characterized in that: When the freezing front advancing speeds on the opposite surfaces between the two freezing pipes are different, the dimensionless freezing front positions on the left and right sides and the dimensionless resistance between the pipes conform to the same functional relationship, but the constant k is different and is taken according to the model test results.

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