A method for monitoring the integrity of a caisson wall based on an out-of-well near-wall hole and an in-well wall electrode

Abstract

The application discloses a kind of based on well outside near wall hole and well wall electrode's open caisson well wall integrity monitoring method, is set outside well outside near wall hole and is arranged in hole outside electrode column, is arranged in well inside well wall electrode column;For different target well wall, by being located in the vicinity of the two ends of target well wall and being respectively in the outside and inside of well wall adjacent electrode column forms single-face well wall penetration monitoring unit, the data of each monitoring unit is respectively collected, stored, imaged and evaluated.For rectangular open caisson, two outside electrode columns and two well wall electrode columns can be circumferentially arranged alternately and shared by adjacent monitoring units.The method is beneficial to form a main sensitive zone for the target well wall, reduce the influence of far-field soil electrical property changes, and achieve the dynamic monitoring of the well wall integrity of open caisson in the construction process.

Description

Technical Field

[0001] This invention relates to the fields of structural health monitoring of caisson engineering, geophysical electrical resistivity tomography, and nondestructive testing of underground engineering, specifically to a method for monitoring the integrity of the caisson wall based on electrodes near the outer wall and the inner wall of the caisson. Background Technology

[0002] Caissons are widely used foundation structures in the construction of bridge foundations, hydraulic engineering, municipal engineering, underground shafts, and large underground structures. They are typically constructed with reinforced concrete walls and are gradually lowered to the design elevation through processes such as soil removal and self-weight sinking. Caisson construction is a long process with complex stress conditions. During fabrication, extension, sinking, correction, and sealing, the caisson walls are susceptible to uneven earth pressure, groundwater effects, construction disturbances, and concrete quality defects, leading to structural defects such as cracks, voids, honeycombing, mud inclusions, leakage channels, and localized damage. These defects pose risks to construction safety and project quality. Therefore, timely and accurate monitoring of the caisson wall integrity is a crucial technical aspect for ensuring the safety of caisson construction and operation.

[0003] Electrical resistivity testing is a geophysical detection method that uses the difference in resistivity of underground media to identify structural anomalies. By applying a stable current to the target medium and measuring the potential difference or apparent resistivity change at different locations, it can identify cracks, cavities, leakage channels and other internal defects. It has the characteristics of being non-destructive, fast and suitable for large-scale structural monitoring, and has been widely used in geotechnical engineering, underground structure and concrete structure inspection.

[0004] Currently, electrical resistivity monitoring for the integrity of caisson walls typically employs a dual-hole cross-hole electrical resistivity method. This involves installing monitoring holes in the soil on both sides of the caisson, with electrodes installed in each hole. Power is supplied and measurements are taken between the two external monitoring holes, and the resistivity inversion results are used to analyze whether there are any anomalies in the caisson and surrounding medium. However, this technology has the following shortcomings in practical applications: First, the monitoring target is a large, overall area, making it impossible to distinguish individual well walls. This method is essentially a comprehensive cross-well monitoring system, where the current propagation path sequentially passes through the surrounding soil, one well wall, the well interior, the other well wall, and the surrounding soil on the other side, ultimately obtaining a comprehensive electrical response from the combined effects of multiple media. When a defect appears locally on one well wall, its abnormal response is easily superimposed on the responses of other well walls and the surrounding soil, reflecting only the overall anomaly and failing to accurately determine the well wall to which the anomaly belongs, making independent evaluation of different well walls difficult.

[0005] Secondly, the soil around the well causes significant interference, resulting in low accuracy in defect identification. The soil around the well is often saturated, has high water content, or is disturbed by mud, leading to large fluctuations in resistivity. Traditional cross-hole electrical resistivity methods require the current to pass through a long distance of soil around the well, and changes in the soil's electrical properties can easily interfere with the monitoring results. In conditions with abundant groundwater or a large amount of construction mud, it may even mask abnormal responses of the well wall itself.

[0006] Third, it cannot meet the needs of refined monitoring of rectangular caissons. Rectangular caissons typically consist of four walls, and the stress conditions, construction quality, and damage evolution processes of each wall differ. Traditional external double-hole cross-hole electrical resistivity tomography (EDT) methods cannot establish independent monitoring units for each wall; they can only obtain overall electrical change information and cannot evaluate the integrity status of each wall separately. This makes it difficult to meet the engineering requirements of refined monitoring, independent early warning, and targeted treatment throughout the entire construction process.

[0007] In summary, the core technical challenge of monitoring the integrity of caisson walls is not simply increasing the number of monitoring holes, but rather establishing a zoned, penetrating electrical resistivity tomography (EDT) method for monitoring single-sided target walls. This method allows each electrode assembly to correspond to one target wall, forming a highly sensitive primary sensing zone within the target wall and its adjacent area. This enables independent acquisition, imaging, and evaluation of each target wall, thereby improving the precision of monitoring and the ability to locate anomalies. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for monitoring the integrity of caisson walls based on electrodes near the outer wall and the inner wall. This method solves the problems of excessive monitoring coverage, inability to independently evaluate a single caisson wall, significant interference from the surrounding soil, and insufficient accuracy in locating defects in the caisson wall, which are present in traditional dual-hole cross-hole electrical resistivity tomography. This method enables zoned, refined, and dynamic monitoring of the caisson walls throughout the entire process.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a method for monitoring the integrity of a caisson wall based on electrodes near the well wall outside and inside the well wall, comprising the following steps: S1 Target Monitoring Area Division: Based on the caisson structure, the caisson wall is divided into at least two distinct target monitoring areas along the circumference of the caisson. Each target monitoring area corresponds to one target caisson wall or one caisson wall partition.

[0010] Specifically, for rectangular caissons, the four walls are designated as the first target caisson wall, the second target caisson wall, the third target caisson wall, and the fourth target caisson wall in sequence along the circumference, with each target caisson wall serving as an independent monitoring object; for circular or polygonal caissons, the caisson walls are divided into several target monitoring areas according to the circumference or structural partitions.

[0011] S2 monitoring electrode system layout: An external near-wall hole is set on the outside of each target monitoring area, and an external electrode array is arranged along the depth direction inside the external near-wall hole; an internal wall electrode array is arranged on the inside of each target monitoring area along the height direction of the well wall; for each target monitoring area, an external electrode array and an internal wall electrode array are respectively set near its two circumferential ends, and the external electrode array and the internal wall electrode array are located on the outside and inside of the target well wall, respectively; an adjacent external electrode array and an internal wall electrode array are combined to form a single-sided well wall penetration monitoring unit, and the monitoring units of adjacent target monitoring areas can share the external electrode array or the internal wall electrode array.

[0012] In a preferred embodiment, when the caisson is rectangular, two rows of external electrodes and two rows of internal electrodes are provided. The two rows of external electrodes are respectively arranged in the near-wall holes at two diagonal positions on the outside of the caisson, and the two rows of internal electrodes are respectively arranged at the other two diagonal positions on the inside of the caisson. The four rows of electrodes are arranged alternately along the circumference of the caisson in the order of internal electrode, external electrode, internal electrode, external electrode. Adjacent rows of electrodes are combined to form four single-sided wall penetration monitoring units corresponding to the four target walls. Each row of electrodes is shared by two adjacent monitoring units.

[0013] Furthermore, the near-wall hole outside the well is set along the height direction of the target well wall, and the hole depth covers the monitoring depth range of the target well wall; the distance between the near-wall hole outside the well and the outer surface of the target well wall satisfies the following: the main sensitive area formed by the electrode combination of the corresponding monitoring unit covers the monitoring range of the target well wall, and the interference of the far-field surrounding soil on the monitoring response is reduced; the near-wall hole outside the well can adopt hole-like structures such as boreholes, reserved holes, casing holes, and monitoring pipe holes, and its distance from the target well wall can be determined by electric field forward modeling, sensitivity distribution analysis, and field calibration test.

[0014] Furthermore, the external electrode array includes multiple external electrodes arranged along the depth of the hole, which can be arranged with equal or non-equal spacing, and the key monitoring areas can be locally densified; the external electrodes can be stainless steel electrodes, copper electrodes, graphite electrodes, conductive alloy electrodes, etc., and maintain stable electrical contact with the hole wall through conductive filling material or radial contact structure, and are connected to the electrical resistivity acquisition device through cables.

[0015] The inner wall electrode array of the well includes multiple internal electrodes arranged along the height of the well wall, and the vertical arrangement range matches the corresponding external electrode array. The internal electrodes can be installed by pre-embedded, embedded, attached, or anchored methods. New caissons can be pre-embedded during the construction or extension of the well wall, while existing caissons can be installed by surface fixing, shallow trench burial, or other post-installation methods. After the internal electrodes are installed, insulation, waterproofing, and cable protection measures are taken.

[0016] S3 zoned penetration electrical resistivity tomography (ERT) data acquisition: For each single-sided well wall penetration monitoring unit, power supply electrodes and measuring electrodes are selected between its external electrode array and the inner wall electrode array to combine power supply and potential measurement, and electrical response data of the corresponding target monitoring area are acquired; the electrical response data of each monitoring unit are numbered and stored separately, and when the current monitoring unit is acquiring data, the other electrodes that are not participating in the acquisition are in a disconnected or high-resistance isolation state.

[0017] Furthermore, each single-sided well wall penetration monitoring unit collects data in a preset sequence. When the current monitoring unit is collecting data, the other electrodes that are not participating in the data collection are disconnected or in a high-resistance isolation state to reduce electrical crosstalk. Each set of collected data is associated with and recorded with the corresponding target well wall number, monitoring unit number, electrode number and spatial coordinates, collection time and caisson sinking depth.

[0018] During data acquisition, power supply electrodes A and B and measurement electrodes M and N are selected from the two columns of electrodes in the monitoring unit. A combination of power supply electrode A and measurement electrode M selected from the same column and power supply electrode B and measurement electrode N selected from another column can be used. The electrodes are switched step by step according to a preset interval and scanning sequence. Electrical response parameters such as power supply current, potential difference, resistance, and apparent resistivity are collected and recorded.

[0019] The penetration acquisition refers to the placement of the external electrode array and the inner wall electrode array on the inner and outer sides of the target well wall, close to both ends. The electrode combination forms an observation area that extends obliquely from the outer side of the well wall to the inner side, passing through the target well wall and along the length and height of the well wall. A main sensitive area with higher relative sensitivity to non-target well walls and far-field soil is formed in the target well wall and its adjacent area.

[0020] S4 Zone Integrity Evaluation: When the well wall is in a known intact or relatively stable state, benchmark electrical data and zone benchmark electrical models are acquired or established for each target monitoring area. The electrical response data currently collected by each monitoring unit is preprocessed and electrical imaging is performed. The current electrical response data or imaging results are compared with the benchmark data, benchmark model or results of the previous monitoring time at the same data level of the corresponding target monitoring area to identify electrical anomaly areas. The integrity of the well wall in each target monitoring area is evaluated independently.

[0021] Furthermore, during electrical imaging, a forward model and an inversion model are established for each single-sided well wall penetration monitoring unit. The model incorporates the target well wall, adjacent well walls, near-wall soil, well space, well wall reinforcement, near-wall holes outside the well, and electrode contact conditions. Inversion constraints are set for the main sensitive area corresponding to the target well wall based on the sensitivity distribution, so that the inversion imaging results specifically reflect the electrical changes in the target well wall area.

[0022] Furthermore, when the well wall is in a complete and stable state, initial electrical data are collected for each target monitoring area, and a partitioned initial electrical model is established for each target monitoring area as the benchmark electrical data for well wall integrity evaluation. The initial electrical model can take the form of initial resistance value, apparent resistivity dataset, resistivity distribution map, etc. Different target well walls are modeled separately to eliminate the background influence caused by differences in well wall thickness, reinforcement, and materials.

[0023] Furthermore, the current electrical imaging results are compared with the baseline electrical data of the corresponding target monitoring area or the monitoring data at the previous moment, or the current electrical imaging results are compared with the corresponding baseline imaging results or the imaging results at the previous monitoring moment to identify electrical anomaly areas that exceed the preset threshold. Combining the spatial location, shape, change trend and on-site working conditions of the anomaly areas, it is determined whether there are defects such as cracks, cavities, honeycombs, mud inclusions or leakage channels in the well wall, and the integrity of the well wall is divided into different levels according to the abnormal amplitude, range and development rate.

[0024] Furthermore, during the caisson sinking construction, the inner wall electrode array sinks synchronously with the caisson, while the outer electrode array in the near wall hole outside the caisson remains fixed relative to the strata. Before each acquisition, the relative elevation relationship between the inner and outer electrodes is updated according to the current sinking depth of the caisson, an electrode combination with matching elevation is selected, and the updated electrode coordinates are used to establish a forward and inverse model for electrical imaging. Acquisition is repeated according to preset time intervals, preset sinking amounts, preset construction nodes, or preset risk conditions to eliminate false anomalies caused by changes in electrode position.

[0025] S5 Whole Well Results Fusion: The integrity evaluation results of each target monitoring area are spliced ​​and merged according to their actual spatial location on the caisson to generate an overall well wall integrity zoning evaluation map and comprehensive early warning information. The output includes comprehensive monitoring results containing abnormal location, depth, amplitude, change trend, integrity level and treatment suggestions.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1) Achieve independent monitoring of well wall zones, and clearly identify the source of anomalies; This invention establishes a single-sided well wall penetration monitoring unit for different well walls of the caisson, making each well wall an independent monitoring object, which solves the technical problem of mixed responses of different well walls and difficulty in distinguishing the source of anomalies in the traditional external double-hole cross-hole electrical resistivity method. 2) Forming a primary sensitive zone on the target well wall to improve defect response sensitivity; Through cross-column combination observation of external electrodes near the well wall and internal wall electrodes, a primary sensitive zone with high relative sensitivity relative to non-target well walls and far-field soil is formed on the target well wall and its adjacent area, significantly improving the response capability to changes in the integrity of a single well wall. 3) Shorten the soil coupling path and reduce the impact of environmental interference; the external near-wall borehole is set close to the target well wall, which shortens the soil propagation distance between the external electrode and the target well wall, reduces the contribution of the far-field well perimeter soil to the monitoring response, and helps to reduce the interference of high water content soil, groundwater and construction mud changes on the monitoring results. 4) Supports zonal imaging and whole-well fusion, balancing precision and integrity; it can collect, image and evaluate multiple zones of the four walls of a rectangular caisson or other shaped caissons separately, and can also spatially fuse the results of each zone to form a zonal evaluation result of the integrity of the entire caisson wall, meeting the monitoring needs of different levels. 5) Adapt to dynamic monitoring throughout the entire construction process and track the evolution of defects; it can repeatedly collect data throughout the entire cycle of caisson fabrication, heightening, sinking, correction, sealing and operation. Through the independent initial electrical model and time-series monitoring data of each caisson wall, it can identify the generation, expansion, migration and development trend of caisson wall anomalies and realize dynamic early warning. 6) Flexible deployment and strong engineering adaptability; the internal electrodes support multiple installation methods such as pre-embedding, embedding, attaching, and post-installation; the near-wall holes and external electrode arrays can be flexibly adjusted according to the caisson structure and construction conditions, making it suitable for both new and existing caissons and adaptable to various engineering scenarios. 7) Shared electrode arrangement scheme to reduce implementation costs; In the preferred scheme for rectangular caissons, two rows of external electrodes and two rows of inner wall electrodes are arranged alternately around the circumference. Adjacent monitoring units share the same electrode rows. While forming four zone monitoring units, the number of external boreholes, electrodes, cables and acquisition channels is reduced, thereby reducing system deployment costs and construction interference. 8) Main sensitive area constraint inversion improves the interpretability of results: By incorporating the main sensitive area constraint of the target well wall into the inversion modeling, the imaging results are more focused on the target well wall area, improving the relevance and engineering interpretation capability of the monitoring data and reducing interference and misjudgment in non-target areas. Attached Figure Description

[0027] The accompanying drawings, as part of this invention, are provided to further illustrate the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation thereof. Clearly, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0028] Figure 1 A top-view schematic diagram of the overall layout for zoned monitoring of the four sides of the caisson; Figure 2 A top view of a rectangular caisson with four rows of electrodes arranged in a circumferentially alternating and shared zoned penetration monitoring configuration; Figure 3 A schematic diagram of the elevation layout of the near-wall boreholes outside the well and the electrode array inside the well; Figure 4 Flowchart for dynamic monitoring of the integrity of the caisson wall; Explanation of reference numerals in the attached figures: 1. First well inner wall electrode array; 2. First well outer wall near-wall hole; 3. Second well inner wall electrode array; 4. Second well outer wall near-wall hole. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention. It should be understood that the various steps described in the method embodiments of the present invention can be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of the present invention is not limited in this respect.

[0030] The term "comprising" and its variations as used herein are open-ended inclusions, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". Definitions of other terms will be given in the description below.

[0031] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, any variations of the terms "comprising" and "having," etc., are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0032] It should be noted that the terms "a" and "a plurality of" used in this invention are illustrative rather than restrictive. Those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0033] A method for monitoring the integrity of a caisson wall based on external near-wall holes and internal wall electrodes is disclosed. According to the spatial distribution of the caisson wall, different caisson walls or caisson wall zones are identified as corresponding target monitoring areas, and a single-sided wall penetration monitoring unit is established for each target monitoring area. Each single-sided wall penetration monitoring unit includes at least one column of external electrodes located on the outside of the target caisson wall and one column of internal wall electrodes located on the inside of the target caisson wall. The external electrode column is deployed within the external near-wall holes, and the external and internal electrode columns are located near the two ends of the target caisson wall, respectively, on the outside and inside sides. By selecting power supply electrodes and measuring electrodes from adjacent columns of electrodes to combine power supply and potential measurement, the corresponding target caisson wall and its adjacent area form a main sensitive area, thereby obtaining the electrical response of each target caisson wall. Monitoring units of adjacent target caisson walls can share either the external electrode column or the internal wall electrode column, but the data from different monitoring units are numbered, stored, processed, and evaluated separately.

[0034] In a preferred embodiment of a rectangular caisson, two sets of external near-wall holes are respectively located at two opposite corners on the outer side of the caisson, and two sets of internal wall electrode arrays are respectively located at two other opposite corners on the inner side of the caisson, so that the two sets of external electrode arrays and the two sets of internal wall electrode arrays are alternately arranged along the circumference of the caisson; two adjacent electrode arrays are combined to form a monitoring unit, and each electrode array is shared by two adjacent monitoring units, thereby using four electrode arrays to form four monitoring units corresponding to the four target caisson walls respectively; for caissons with larger size, irregular shape, or requiring improved spatial resolution, independent external near-wall holes and internal wall electrode arrays can also be set for each target caisson wall. Example

[0035] A method for monitoring the integrity of a caisson wall based on electrodes near the well wall and inside the well, such as... Figure 4 As shown, the specific implementation steps are as follows: (1) Determination of caisson wall zoning and target monitoring area The area of ​​the well wall to be monitored is determined based on the structure of the caisson; such as... Figure 1 As shown, for a rectangular caisson, the four walls are identified as the first target caisson wall, the second target caisson wall, the third target caisson wall, and the fourth target caisson wall in sequence along the circumference of the caisson. The first target caisson wall is located on the upper side of the diagram, the second target caisson wall is located on the right side of the diagram, the third target caisson wall is located on the lower side of the diagram, and the fourth target caisson wall is located on the left side of the diagram. Each target caisson wall is considered as an independent or relatively independent monitoring object.

[0036] For circular or polygonal caissons, the caisson wall can be divided into several target monitoring areas according to the circumference or structural partitions, and corresponding penetration monitoring units can be established by external electrode arrays located near both ends of the corresponding target monitoring area and internal wall electrode arrays.

[0037] (2) Establish a single-sided wellbore penetration monitoring unit For each target monitoring area, a corresponding single-sided wellbore penetration monitoring unit should be established; such as Figure 2 As shown, each monitoring unit includes an external electrode array set in the near-wall hole outside the target well wall, an internal wall electrode array set in the inner side of the target well wall, an electrical resistivity acquisition device connected to the electrode array, and a data processing module for data processing, anomaly identification, and integrity evaluation. In the preferred embodiment of the rectangular caisson shown in the figure, a total of four rows of electrodes are provided, namely, a first inner wall electrode row 1, a first outer electrode row disposed in a first outer near-wall hole 2, a second inner wall electrode row 3, and a second outer electrode row disposed in a second outer near-wall hole 4; the first inner wall electrode row 1 is disposed on the inner side of the well at the intersection of the first target well wall and the fourth target well wall; the first outer near-wall hole 2 is disposed on the outer side of the well at the intersection of the first target well wall and the second target well wall; the second inner wall electrode row 3 is disposed on the inner side of the well at the intersection of the second target well wall and the third target well wall; and the second outer near-wall hole 4 is disposed on the outer side of the well at the intersection of the third target well wall and the fourth target well wall.

[0038] The first inner wall electrode array 1 and the first outer electrode array in the first near-wall hole 2 of the well combine to form the first monitoring unit, corresponding to the first target well wall main sensitive area (first main sensitive area); the first outer electrode array in the first near-wall hole 2 of the well combine to form the second inner wall electrode array 3 of the well combine to form the second monitoring unit, corresponding to the second target well wall main sensitive area (second main sensitive area); the second inner wall electrode array 3 of the well combine to form the third monitoring unit, corresponding to the third target well wall main sensitive area (third main sensitive area); the second outer electrode array in the second near-wall hole 4 of the well combine to form the fourth monitoring unit, corresponding to the fourth target well wall main sensitive area (fourth main sensitive area); thus, the four electrode arrays are arranged alternately along the circumference of the well in the order of inner wall electrode array, outer electrode array, inner wall electrode array, and outer electrode array, with each electrode array shared by two adjacent monitoring units.

[0039] (3) Setting of near-wall boreholes outside the well An external wellbore near the outer surface of the target wellbore is constructed; for example... Figure 2As shown, for the rectangular caisson illustrated, the first near-wall hole 2 and the second near-wall hole 4 are respectively located at two diagonal positions on the outer side of the caisson, maintaining a distance from the outer surface of the caisson wall that meets the requirements for construction safety, caisson sinking, and monitoring sensitivity. Each near-wall hole contains a row of external electrodes, and the rows of external electrodes in the two near-wall holes are shared by the monitoring units of the adjacent target caisson walls. The near-wall holes can be drilled holes, reserved holes, casing holes, monitoring pipe holes, or other hole-like structures capable of accommodating rows of external electrodes. Preferably, the near-wall holes are located along the height direction of the target caisson wall, and their depth is determined based on the target caisson wall height and sinking depth. The well sinking depth and actual monitoring range are determined; the distance between the near-wall hole outside the well and the target well wall is determined based on the well wall thickness, the electrical properties of the surrounding soil, the construction space, and the monitoring accuracy requirements. The distance should ensure that the main sensitive area of ​​the corresponding electrode combination covers the monitoring range of the target well wall, while minimizing the contribution of the surrounding soil far from the target well wall to the monitoring response. A reasonable distance can be determined through electric field forward modeling, sensitivity distribution analysis, field calibration tests, or test section testing. In some embodiments, the distance between the near-wall hole outside the well and the outer surface of the target well wall is less than or close to the target well wall thickness, but this distance does not constitute a limitation on the scope of protection of this invention.

[0040] (4) Layout of external electrode array like Figure 2-3 As shown, multiple external electrodes are respectively installed along the depth direction in the first and second near-wall boreholes 2 and 4 of the well, forming a first external electrode column and a second external electrode column. Each column of external electrodes can be accessed by the monitoring units corresponding to the target well walls on its two adjacent sides. The external electrodes can be stainless steel electrodes, copper electrodes, graphite electrodes, conductive alloy electrodes, conductive rubber electrodes, or other electrodes that meet the requirements of underground electrical resistivity tomography (EDT) monitoring; the external electrodes can be arranged at equal intervals, or non-equal intervals or locally denser arrangements can be made according to the key monitoring areas of the target well wall.

[0041] The external electrode can be fixed to an electrode cable, insulating bracket, borehole sleeve, or electrode mounting rod, and connected to the electrical resistivity acquisition device via a connecting cable. To ensure stable electrical contact between the external electrode and the surrounding medium near the borehole wall, conductive slurry, conductive mortar, conductive bentonite, or other conductive filling materials can be filled into the borehole wall. Alternatively, an elastic support structure, electrode ring, conductive brush, or radial telescopic structure can be used to maintain stable contact between the external electrode and the borehole wall.

[0042] (5) Layout of electrode array on the inner wall of the well like Figure 2-3As shown, a first inner wall electrode array 1 and a second inner wall electrode array 3 are respectively set at two other diagonal positions on the inner side of the caisson along the height direction of the caisson wall. The first inner wall electrode array 1 is shared by the first monitoring unit and the fourth monitoring unit, and the second inner wall electrode array 3 is shared by the second monitoring unit and the third monitoring unit. Each inner wall electrode array includes multiple internal electrodes arranged along the height direction of the caisson wall. The internal electrodes can be arranged in a pre-embedded, embedded, attached, anchored, channel-mounted, conductive adhesive-fixed, or detachable manner. For newly built caissons, the internal electrodes can be pre-embedded or embedded in the inner side of the caisson wall during the caisson wall construction or segmented heightening process. For existing caissons, the internal electrodes can be installed on the inner side of the caisson wall through surface fixing, shallow trenching, mechanical anchoring, or other post-installation methods.

[0043] The position and vertical layout of the electrode array inside the well should be adapted to the layout of the external electrode array inside and outside the near-wall borehole to ensure continuous monitoring coverage of the corresponding target well wall in the vertical direction. After installation, the internal electrodes should be kept in a stable position and insulated, waterproofed, protected by cables, and numbered and labeled.

[0044] (6) Penetration-type electrical resistivity tomography data acquisition The electrical data acquisition device performs combined power supply and potential measurement between the external electrode array and the inner wall electrode array of the corresponding monitoring unit. Each acquisition selects power supply electrodes A and B and measurement electrodes M and N from the two electrode arrays of the current monitoring unit. In one embodiment, power supply electrode A and measurement electrode M are selected from one electrode array, and power supply electrode B and measurement electrode N are selected from another electrode array, and are switched step by step according to a preset interval and scanning sequence. Other cross-array four-electrode combinations suitable for imaging the target well wall can also be used. Electrical response parameters such as power supply current, potential difference, resistance, transmission resistance, apparent resistivity or normalized potential are acquired and recorded.

[0045] The aforementioned penetrating monitoring refers to the external electrode array and the inner wall electrode array being located on the outer and inner sides of the target well wall, respectively, close to both ends of the target well wall, so that the corresponding electrode combination forms an observation area that obliquely penetrates the target well wall area from the outer side to the inner side, and extends along the length and height directions of the target well wall; the external electrode array and the inner wall electrode array do not need to be directly opposite each other in the direction of well wall thickness, nor are they limited to all current propagating only inside the well wall concrete.

[0046] The target well wall main sensitive area refers to the area where the target well wall and its adjacent area have higher relative sensitivity compared to the non-target well wall and far-field soil, under the electrode arrangement and observation combination of the corresponding monitoring unit; the boundary of the main sensitive area in the attached figure is only used to indicate its spatial location and extension direction, and does not indicate the absolute boundary of current propagation or sensitivity distribution; the actual main sensitive area should be determined by forward modeling, sensitivity calculation or field calibration based on the electrode position, well wall geometry, reinforcement, well medium and surrounding soil electrical conditions.

[0047] (7) Electrical monitoring of each wellbore zone The monitoring units are rotated and collected in the order of the first monitoring unit, the second monitoring unit, the third monitoring unit, and the fourth monitoring unit. When collecting data on the first target well wall, the first inner wall electrode array 1 and the first outer electrode array in the first near-wall hole 2 are activated. When collecting data on the second target well wall, the first outer electrode array in the first near-wall hole 2 and the second inner wall electrode array 3 are activated. When collecting data on the third target well wall, the second inner wall electrode array 3 and the second outer electrode array in the second near-wall hole 4 are activated. When collecting data on the fourth target well wall, the second outer electrode array in the second near-wall hole 4 and the first inner wall electrode array 1 are activated.

[0048] The two columns of electrodes corresponding to the current monitoring unit are connected to the electrical data acquisition device by an electrode switching device or a multiplexing module, and the other electrodes not participating in the current acquisition are in a disconnected, high-impedance isolated or preset protection state to reduce electrical crosstalk between different monitoring units. For shared electrode columns, after scanning one target well wall, the connection relationship is switched according to the electrode combination corresponding to the next target well wall.

[0049] Each set of observation data should be associated with at least the target wellbore number, monitoring unit number, external near-wall borehole number, internal wall electrode array number, power supply electrode and measuring electrode number, actual spatial coordinates of the electrodes, acquisition time, and caisson sinking depth. The data from the four monitoring units should be stored, processed, inverted, and evaluated separately to avoid directly mixing the electrical responses of the four wellbores into the same overall response.

[0050] (8) Establish the initial wellbore electrical model for each zone. When the well wall is in a known intact or relatively stable state, initial data are collected for each of the four monitoring units, and initial electrical models are established for the first, second, third, and fourth target well walls, respectively. The initial electrical models can utilize initial resistance values, apparent resistivity datasets, resistivity distribution maps, potential response data, normalized electrical parameters, or other data formats capable of characterizing the initial state of the target well wall. Different initial electrical models are established for each target well wall to reduce the impact of background electrical differences caused by variations in well wall thickness, reinforcement, water content, construction batches, or concrete materials on the evaluation results. When it is difficult to obtain initial data in an absolutely defect-free state, a reference electrical model can be established using design models, numerical forward modeling results, data from similar intact areas, or data from multiple stable monitoring times.

[0051] (9) Dynamic monitoring of the entire construction process During the construction of the caisson, data is repeatedly collected from four monitoring units according to preset time intervals, preset sinking amounts, preset construction nodes, or preset risk triggering conditions. Monitoring can be carried out after the caisson is segmented and heightened, before and after sinking, before and after correction, before and after well wall repair or water-stopping treatment, before and after bottom sealing construction, and after abnormal water inrush, sudden sinking, tilting, or local damage occurs. It can also be automatically triggered when the tilt angle, settlement, water level, soil pressure, or other construction monitoring parameters are abnormal.

[0052] Since the inner wall electrode array 1 and the inner wall electrode array 3 of the first and second wells sink together with the caisson, while the external electrode arrays in the near-wall holes 2 and 4 of the first and second wells remain fixed or substantially fixed relative to the formation, the relative elevation relationship between the inner and outer electrodes is updated before each data acquisition based on the caisson sinking depth, the initial coordinates of the inner and outer electrodes, and the current coordinates. Electrode combinations with corresponding height ranges or satisfying preset misalignment ranges are selected. During data processing, the updated actual electrode coordinates are used to establish forward and inverse models to reduce false anomalies caused by changes in electrode position. By continuously recording electrical resistivity data of the same target well wall at different construction times, independent time-series monitoring data of the four target well walls are formed.

[0053] (10) Data processing and electrical imaging Data collected from four single-sided wellbore penetration monitoring units underwent preprocessing, including contact resistance checking, outlier removal, repeatability testing, reciprocity error testing, noise filtering, power frequency interference suppression, temperature effect correction, current normalization, and data consistency correction at different monitoring times. Based on the power supply current, potential difference, electrode number, actual electrode location, and device geometry, measured resistance, transmission resistance, apparent resistivity, normalized potential, or other electrical parameters were calculated. Corresponding forward and inverse models were established for each monitoring unit based on its actual electrode arrangement, enabling resistivity inversion or electrical parameter imaging of the target wellbore area.

[0054] The forward and inverse models can incorporate the target wellbore, adjacent wellbore, near-wall soil, well space, wellbore reinforcement, near-wall holes, and electrode contact conditions into the calculations. Inversion constraints are set for the main sensitive area of ​​the target wellbore based on the sensitivity distribution. For the four-column electrode arrangement shown in the figure, models corresponding to four electrode combinations (1-2, 2-3, 3-4, and 4-1) are established respectively, so that the four sets of results reflect the electrical changes of the first to fourth target wellbore.

[0055] (11) Wellbore anomaly identification The current monitoring results are compared with the initial electrical model of the corresponding target wellbore, data from the previous monitoring time, or data from adjacent intact areas to obtain the absolute electrical distribution or temporal difference distribution of the main sensitive area of ​​the corresponding target wellbore. When a local area of ​​the target wellbore shows an increase, decrease, or continuous change in resistivity exceeding a preset threshold, the area is identified as an electrical anomaly area. Based on the electrical characteristics, spatial location, morphology, continuity, and trend of the anomaly area, the possibility of cracks, cavities, honeycombing, mud inclusions, segregation, leakage channels, local damage, or other integrity defects in the target wellbore is analyzed. Since the electrical performance of different defects may be affected by the water content of cracks, filling medium, concrete materials, steel reinforcement distribution, and environmental conditions, this invention does not directly determine the defect type based on a single high or low resistivity characteristic, but rather makes a comprehensive judgment based on the initial electrical model, temporal changes, anomaly morphology, and on-site conditions. If necessary, core drilling, ultrasonic testing, radar testing, visual inspection, or leakage inspection can be used to verify the anomaly area.

[0056] (12) Evaluation of zoning integrity Based on the amplitude, area, location, continuity, development rate, and duration of electrical anomalies in each target wellbore, an integrity evaluation is conducted for each target wellbore. Wellbore integrity can be classified into levels such as normal, minor anomaly, significant anomaly, and severe anomaly. Normal indicates that the electrical response of the target wellbore is stable, and no continuous anomalies exceeding the threshold are found. Minor anomalies indicate that there are small-scale or weak electrical changes in a local area, requiring continued observation. Significant anomalies indicate that the amplitude, area, or continuity of the anomaly reaches the preset conditions, and there may be structural defects, requiring on-site verification. Severe anomalies indicate that the anomaly range is large, the continuity is strong, the development rate is fast, or there is a tendency for it to penetrate, requiring timely repair, reinforcement, grouting, or water-stopping measures. The evaluation threshold can be determined based on the caisson structural parameters, initial electrical model, test calibration results, historical monitoring data, and engineering safety requirements.

[0057] (13) Integration and output of whole well monitoring results The monitoring and evaluation results of the first to fourth monitoring units are spliced ​​or merged according to their actual spatial location in the caisson to form an overall caisson wall integrity zoning evaluation map. The monitoring results include the target caisson wall where the anomaly is located and the corresponding main sensitive area, the plane location and depth range of the anomaly, the amplitude and impact range of the anomaly, the trend of the anomaly over time, the integrity level of each caisson wall, and the corresponding early warning information and handling suggestions.

[0058] Using the above method, four monitoring units can be formed by four rows of circumferentially alternating electrodes, each corresponding to one of the four target well walls. This allows for separate data collection, imaging, and evaluation of different well walls, and on this basis, a comprehensive integrity evaluation result for the entire caisson can be generated.

[0059] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for monitoring the integrity of a caisson wall based on electrodes near the well wall and inside the well wall, characterized in that, Includes the following steps: S1 Target Monitoring Area Division: Based on the caisson structure, the caisson wall is divided into at least two distinct target monitoring areas along the circumference of the caisson. Each target monitoring area corresponds to one target caisson wall or one caisson wall partition. S2 monitoring electrode system layout: An external near-wall hole is set on the outside of the caisson, and an external electrode array is arranged along the depth direction inside the external near-wall hole; an internal wall electrode array is arranged along the height direction of the caisson wall on the inside side; for each target monitoring area, an external electrode array and an internal wall electrode array are respectively set near its two circumferential ends, and the external electrode array and the internal wall electrode array are located on the outside and inside sides of the target caisson wall, respectively; an adjacent external electrode array and an internal wall electrode array are combined to form a single-sided caisson wall penetration monitoring unit, and monitoring units of adjacent target monitoring areas can share an external electrode array or an internal wall electrode array; S3 zoned penetration electrical resistivity tomography (ERT) data acquisition: For each single-sided well wall penetration monitoring unit, power supply electrodes and measuring electrodes are selected between its external electrode array and the inner wall electrode array to combine power supply and potential measurement, and electrical response data of the corresponding target monitoring area are collected; the data of each monitoring unit are numbered and stored separately, and when the current monitoring unit is collecting data, the other electrodes not participating in the collection are in a disconnected or high-resistance isolation state; S4 Zone Integrity Evaluation: When the well wall is in a known intact or relatively stable state, benchmark electrical data are collected for each target monitoring area and a zone benchmark electrical model is established. The electrical response data collected by each monitoring unit is preprocessed and electrical imaging is performed. The current electrical response data or imaging results are compared with the benchmark data, benchmark model or results of the previous monitoring time at the same data level of the corresponding target monitoring area to identify electrical anomaly areas. The integrity of the well wall in each target monitoring area is evaluated independently.

2. The method for monitoring the integrity of a caisson wall based on near-wall holes on the outside and electrodes on the inside of the well, as described in claim 1, is characterized in that... When the caisson is rectangular, two rows of external electrodes and two rows of internal electrodes are set up. The two rows of external electrodes are respectively arranged in the near-wall holes at two diagonal positions on the outside of the caisson, and the two rows of internal electrodes are respectively arranged at the other two diagonal positions on the inside of the caisson. The four rows of electrodes are arranged alternately along the circumference of the caisson in the order of internal electrode, external electrode, internal electrode, external electrode. The combination of two adjacent rows of electrodes forms four single-sided well wall penetration monitoring units corresponding to the four target well walls. Each row of electrodes is shared by two adjacent monitoring units.

3. A method for monitoring the integrity of a caisson wall based on electrodes near the well wall outside and inside the well wall, as described in claim 1 or 2, characterized in that... The near-wall holes outside the well are set along the height direction of the target well wall, and the depth of the holes covers the monitoring depth range of the target well wall. The distance between the near-wall holes outside the well and the outer surface of the target well wall satisfies the following: the main sensitive area formed by the electrode combination of the corresponding monitoring unit covers the monitoring range of the target well wall, and the interference of the far-field surrounding soil on the monitoring response is reduced.

4. The method for monitoring the integrity of a caisson wall based on near-wall holes on the outside and electrodes on the inside of the well, as described in claim 1, is characterized in that... The external electrode array consists of multiple external electrodes arranged at equal or non-equal intervals along the hole depth. The external electrodes maintain stable electrical contact with the hole wall near the well wall through conductive filling material or radial contact structure. The internal electrode array consists of multiple internal electrodes arranged along the height direction of the well wall. The internal electrodes are installed on the inner side of the well wall in a pre-embedded, embedded, attached, or anchored manner, and the vertical arrangement range matches the arrangement range of the corresponding external electrode array.

5. The wellbore integrity monitoring method based on near-wall holes outside the well and electrodes inside the well as described in claim 1, characterized in that, In step S3, each single-sided well wall penetration monitoring unit collects data in a preset order; when the current monitoring unit is collecting data, the other electrodes that are not participating in the collection are in a disconnected or high-resistance isolation state; each set of collected data is associated with the corresponding target well wall number, monitoring unit number, electrode number and spatial coordinates, collection time and caisson sinking depth.

6. The method for monitoring the integrity of a caisson wall based on near-wall holes on the outside and electrodes on the inside of the well, as described in claim 1, is characterized in that... During the caisson sinking construction, the inner wall electrode array sinks synchronously with the caisson, while the outer electrode array in the near wall hole outside the caisson remains fixed relative to the strata. Before each data acquisition, the relative elevation relationship between the inner and outer electrodes is updated according to the current sinking depth of the caisson. An electrode combination with matching elevation is selected, and the updated electrode coordinates are used to establish a forward and inverse model for electrical imaging. Data acquisition is repeated according to preset time intervals, preset sinking amounts, preset construction nodes, or preset risk conditions.

7. The wellbore integrity monitoring method based on near-wall holes on the outside of the well and electrodes on the inside of the well, as described in claim 1, is characterized in that... When the well wall is in a complete and stable state, initial electrical data are collected for each target monitoring area, and a partitioned initial electrical model is established for each target monitoring area as the benchmark electrical data for well wall integrity evaluation.

8. The method for monitoring the integrity of a caisson wall based on near-wall holes on the outside of the well and electrodes on the inside of the well, as described in claim 1, is characterized in that... In step S4, the current electrical imaging result is compared with the baseline electrical data of the corresponding target monitoring area or the monitoring data at the previous moment, or the current electrical imaging result is compared with the corresponding baseline imaging result or the imaging result at the previous monitoring moment to identify electrical abnormal areas that exceed the preset threshold. Based on the spatial location, shape, trend of change, and on-site conditions of the abnormal area, determine whether there are defects such as cracks, cavities, honeycombs, mud inclusions, or leakage channels in the well wall, and classify the integrity of the well wall into different levels according to the abnormal amplitude, range, and development rate.

9. A method for monitoring the integrity of a caisson wall based on electrodes near the well wall and inside the well wall, as described in claim 1, is characterized in that... Step S4 is followed by a well result fusion step: the integrity evaluation results of each target monitoring area are spliced ​​and fused according to their actual spatial location on the caisson to generate an overall well wall integrity zoning evaluation map and comprehensive early warning information.

10. A method for monitoring the integrity of a caisson wall based on near-wall holes on the outside of the well and electrodes on the inside of the well, as described in claim 1, is characterized in that... In step S4, when performing electrical imaging, a forward model and an inversion model are established for each single-sided well wall penetration monitoring unit. The model incorporates the target well wall, adjacent well walls, near-wall soil, well space, well wall reinforcement, near-wall holes outside the well, and electrode contact conditions. Inversion constraints are set for the main sensitive area corresponding to the target well wall according to the sensitivity distribution, so that the inversion imaging results specifically reflect the electrical changes in the target well wall area.

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