A multi-level pore water pressure observation device with the same hole and its installation method

Abstract

This application relates to a multi-level pore water pressure observation device in the same hole and its installation method. A multi-level pore water pressure observation device in the same hole includes: a plurality of digital piezometer probe assemblies arranged in a monitoring hole from bottom to top, a stage interval seepage cylinder assembly connected between two adjacent digital piezometer probe assemblies, and a watertight joint assembly for connecting adjacent digital piezometer probe assemblies and stage interval seepage cylinder assemblies; the digital piezometer probe assembly includes a hollow permeable cylinder, a pore water pressure gauge assembly arranged in the permeable cylinder, a highly permeable material filled between the inner wall of the permeable cylinder and the pore water pressure gauge assembly, and a water-permeable geotextile wrapping the highly permeable material; a multi-core cable is electrically connected between adjacent pore water pressure gauge assemblies. The multi-level pore water pressure observation device in the same hole and its installation method provided by this application have the characteristics of integrated design, prefabrication and installation of pore water pressure monitoring equipment and backfill materials, simplify the on-site installation process, and reduce the monitoring cost.

Description

Technical Field

[0001] This application belongs to the technical field of pore water pressure monitoring, and particularly relates to a multi-level pore water pressure observation device in the same hole and an installation method thereof. Background Technique

[0002] Pore water pressure is the pressure exerted by the water existing in soil, rock or other porous media. This pressure acts between particles or pores, and is divided into static pore water pressure and excess pore water pressure. Pore water pressure has an important impact on the mechanical properties and stability of rock and soil masses. Therefore, pore water pressure observation has become the main monitoring content in geotechnical engineering, and is widely used in slope engineering, dam engineering, foundation and subgrade engineering, foundation pit excavation, and soft foundation vacuum preloading, and is an important data support for the analysis of rock and soil deformation and stability.

[0003] At present, the special instrument for pore water pressure observation is a pore water pressure gauge, also known as a piezometer. When in use, it is necessary to drill a hole and install the piezometer buried in the hole. The burial quality of the piezometer directly affects the later observation effect, and the following key technical requirements need to be met: (1) accurately install the piezometer at the designed depth; (2) ensure smooth seepage around the piezometer; (3) ensure that the water pressure in the formation where the piezometer is located is isolated from the water pressures in other formations, and there is no vertical connection and mutual interference between the water pressures of each layer. To achieve the above technical requirements, people usually adopt a step-by-step and layer-by-layer burial method: (1) use auxiliary tools such as drill pipes and hanging rods to lower the piezometer to the specified depth; (2) put medium and coarse sand around the piezometer to form a sand pad filter layer; (3) put bentonite or highly disintegrating clay balls to form a hole-sealing layer.

[0004] In order to more accurately grasp the variation law of the pore water pressure inside the rock and soil mass with depth, many engineering projects need to bury multiple (i.e., multi-level) piezometers at different soil layer depths. Compared with the traditional single-hole and single-point layout scheme, adopting the multi-level layout scheme in the same hole (that is, densely installing multiple piezometers in a single drill hole) can not only effectively reduce the total number of drill holes and save project costs, but more importantly, all the observation data are derived from the same monitoring section, and the data between different observation points are more relevant and consistent.

[0005] When implementing the multi-level layout scheme in the same hole, it is first necessary to ensure the horizontal connection between the piezometers at each depth and the corresponding rock and soil layers, so that the pore water pressure in the same-layer rock and soil can be conducted to the piezometer with a pressure gradient loss. The current process is to fill sand around the piezometer, and the pore water pressure can be effectively transmitted through the contact between the sand grains and the rock and soil hole wall. Secondly, since the pore water pressures of the formations at different depths are different, it is also necessary to ensure the vertical isolation between the piezometers to prevent water leakage between the upper and lower piezometers. For this purpose, materials such as clay need to be filled between the upper and lower piezometers, and through the step-by-step burial and layer-by-layer isolation method, ensure that the piezometers at each depth work independently.

[0006] The traditional step-by-step and layer-by-layer embedding method is complex in technology, cumbersome in operation process, and time-consuming. Moreover, when encountering complex geological conditions such as deep-hole operations and soft soil layers, it becomes particularly difficult to control the precise placement of backfill materials. This directly leads to the difficulty in constructing an effective water seepage filter layer around the pore water pressure gauge probe, and there are problems such as difficulty in sealing or improper sealing between the upper and lower pore water pressure gauge probes, thus affecting the installation quality and unable to ensure the accuracy of measurement data. Therefore, there is an urgent need to innovate and design the multi-level pore water pressure observation device in the same hole, and reform and simplify the traditional embedding process flow to achieve the reliable embedding of the pore water pressure gauge and ensure the accuracy of the measured values. Summary of the Invention

[0007] In view of this, the present application provides a multi-level pore water pressure observation device in the same hole and its installation method, which is used to simplify the complex installation and embedding process of the multi-level pore water pressure gauge in the same hole, shorten the operation time, and at the same time solve the problem of limited measurement accuracy of pore water pressure data caused by the difficulty in placing backfill materials.

[0008] In the first aspect, the present application provides a multi-level pore water pressure observation device in the same hole, adopting the following technical solutions:

[0009] A multi-level pore water pressure observation device in the same hole includes: a plurality of digital piezometer probe assemblies arranged at intervals from bottom to top in a monitoring hole, a stage interval seepage cylinder assembly connected between two adjacent digital piezometer probe assemblies, and a watertight joint assembly used to connect the adjacent digital piezometer probe assemblies and the stage interval seepage cylinder assembly;

[0010] Each of the digital piezometer probe assemblies includes a long and hollow permeable cylinder, a pore water pressure gauge assembly arranged in the permeable cylinder, a highly permeable material filled in the gap between the inner wall of the permeable cylinder and the pore water pressure gauge assembly, and a water-permeable geotextile wrapping the highly permeable material;

[0011] A multi-core cable is electrically connected between adjacent pore water pressure gauge assemblies, and the multi-core cable passes through the stage interval seepage cylinder assembly between the adjacent pore water pressure gauge assemblies.

[0012] By adopting the above technical solution, the present application integrates the backfill material into the preparation process of the pore water pressure observation device: on the one hand, a coarse sand filter layer is directly prefabricated inside the digital piezometer probe assembly; on the other hand, the stage interval seepage cylinder assembly is integrally prepared in the factory and forms an efficient hole-sealing layer. This design concept changes the mutually separated mode of the factory preparation of the pore water pressure observation device and the on-site backfill of highly permeable materials in the traditional method, and realizes the integrated design, preparation and installation of the monitoring equipment and the backfill material. During on-site installation, no additional backfill steps are required, which greatly simplifies the installation process, shortens the operation time, and can significantly improve the standardization and normalization level of buried installation, ensuring the accuracy and reliability of pore water pressure monitoring.

[0013] The multi-level pore water pressure observation device provided by the present application can densely arrange multiple digital piezometer probe assemblies in a single borehole, such as arranging 1 digital piezometer probe assembly every 3 meters. This can not only effectively reduce the number of monitoring boreholes and save project costs, but also all the observed data are derived from the same monitoring profile, and the observed data at different observation points are more correlated and consistent.

[0014] Traditional pore water pressure gauges adopt a multi-wire system, and each probe requires an independent cable. When installing n probes, n cables are required, which is costly and cumbersome to install. Through the digital and bus design method of the digital piezometer probe assembly in the present application, all the probes in a single borehole share a multi-core cable (two cores for power supply and two cores for data transmission), which greatly reduces the observation cost and simplifies the installation process.

[0015] Optionally, the stage interval seepage cylinder assembly includes one seepage isolation cylinder or multiple seepage isolation cylinders connected in series;

[0016] Each of the seepage isolation cylinders includes a central tube and a grid cage that are concentrically arranged from the inside to the outside. An absorbent expansion material wrapped by a water-soluble film is filled between the central tube and the grid cage;

[0017] The multi-core cable extends out from both ends of the central tube and is respectively connected to two adjacent pore water pressure gauge assemblies.

[0018] By adopting the above technical solution, the combination of the grid cage and the water-soluble film is used to provide a support framework and an external wrapping for the absorbent expansion material, which is convenient for transportation and installation. The water-soluble film will dissolve when encountering the water in the hole, and is used to unblock the contact path between the water body and the absorbent expansion material. The powder-like absorbent expansion material will rapidly expand and solidify in the seepage isolation cylinder after absorbing water, and is used to replace the traditional bentonite or highly disintegrating clay balls to form an efficient hole-sealing layer, effectively isolating the upper and lower layer waters, and ensuring that the water pressure of the formation where the digital piezometer probe assembly is located is isolated from the water pressures of other formations.

[0019] Optionally, a plurality of water-permeable holes are provided on the side wall of the water-permeable cylinder. The upper and lower ends of the water-permeable cylinder are provided with cylinder covers, and joint pipes for connecting one end of the watertight joint assembly are provided on the cylinder covers.

[0020] The multi-core cable connected to the pore water pressure gauge assembly passes through the joint pipe and extends into the stage interval seepage cylinder assembly. Potting glue is provided on the inner wall of the joint pipe.

[0021] By adopting the above technical solution, the water-permeable holes can ensure smooth water seepage around the pore water pressure gauge assembly. The joint pipe is used to connect with the watertight joint assembly, and the potting glue is used to seal the stainless steel joint pipe to prevent leakage of highly permeable materials.

[0022] Optionally, the watertight joint assembly includes a threaded sleeve and a silicone gasket arranged with upper and lower openings.

[0023] A transverse plate that divides the threaded sleeve into upper and lower chambers is provided inside the threaded sleeve. A central hole is provided in the transverse plate for the multi-core cable to pass through.

[0024] The silicone gaskets are respectively laid on both sides of the transverse plate, and the chambers on both sides of the transverse plate are respectively used for threaded connection with the joint pipe and the stage interval seepage cylinder assembly.

[0025] By adopting the above technical solution, the silicone gasket serves as a separation layer to prevent the water-swellable material from invading the gap between the digital piezometric probe assembly and the hole wall during the water swelling process, affecting the smooth water seepage around the digital piezometric probe assembly.

[0026] Optionally, the pore water pressure gauge assembly includes a packaging shell, a small lock nut, a large lock nut, a collection circuit board, a pore water pressure sensor electrically connected to the collection circuit board and its signal wire, and a probe multi-core cable electrically connected to the collection circuit board.

[0027] Part of the probe multi-core cable, the signal wire and the collection circuit board are all located inside the packaging shell. The small lock nut is used to block the place where the signal wire extends out of the packaging shell, and the large lock nut is used to block the place where the probe multi-core cable extends out of the packaging shell.

[0028] By adopting the above technical solution, the packaging shell closely cooperates with the small lock nut and the large lock nut to form a sealed chamber for packaging part of the multi-core cable of the probe, the cable of the pore water pressure sensor, and the collection circuit board. It can provide waterproof protection for the electronic components and cable interfaces inside the collection circuit in a harsh environment, ensuring the safe operation of the collection circuit.

[0029] Optionally, the collection circuit board includes:

[0030] An MCU microcontroller integrated with a storage module;

[0031] An excitation sweep frequency module, a signal processing module, and a temperature acquisition module that are all electrically connected to the MCU microcontroller;

[0032] A bus communication module and a power supply module that are all electrically connected to the MCU microcontroller;

[0033] A pore water pressure sensor that is electrically connected to the excitation sweep frequency module, the signal processing module, and the temperature acquisition module.

[0034] By adopting the above technical solution, the MCU microcontroller is used to control the excitation sweep frequency module, the signal processing module, the temperature acquisition module, and the bus communication module, and independently complete the acquisition, storage, and upload of pore water pressure and ambient temperature, as well as the reception and response of host computer instructions. The excitation sweep frequency module is used for the excitation and sweep frequency of the pore water pressure sensor. The signal processing module is used for filtering, amplifying, and ADC conversion of the chord signal, and sending the digital vibration string frequency to the MCU microcontroller. The temperature acquisition module is used for collecting the ambient temperature signal of the vibrating wire type pore water pressure gauge, converting it into a digital quantity, and sending it to the MCU microcontroller. The bus communication module is connected to the data transmission bus in the multi-core cable and is used for data interaction between the MCU microcontroller and the ground acquisition station.

[0035] Optionally, the high-permeability material is medium-coarse sand, the water-absorbing expansion material is water-absorbing expansion resin, and the outside of the acquisition circuit board is hermetically coated with epoxy resin.

[0036] By adopting the above technical solution, medium-coarse sand is placed around the pore water pressure gauge assembly, and a coarse sand filter layer is prefabricated inside the digital piezometer probe assembly. The water-absorbing expansion resin material expands rapidly within a few hours after encountering water, and the maximum volume can increase to 700 times, tightly filling the entire borehole space to form a sealing layer, which can effectively isolate the up-and-down connection and mutual leakage between adjacent digital piezometer probes. Epoxy resin is used for the waterproof protection of the acquisition circuit board.

[0037] Optionally, the multiple digital piezometer probe assemblies, the seepage isolation cylinder, and the watertight joint assembly are all integrally prefabricated.

[0038] By adopting the above technical solution, the factory preparation of the multi-level pore water pressure observation device in the same hole is integrated with the on-site backfill of the backfill material, greatly simplifying the installation process and solving the problem that it is difficult to guarantee the backfill quality under complex geological conditions. In addition, the integrated preparation design also facilitates the flexible splicing, assembly, disassembly, and transportation of the digital piezometer probe assembly, ensuring that each level of probe can be accurately installed to the predetermined depth under the hole, improving the installation efficiency and monitoring accuracy.

[0039] Optionally, when the stage interval seepage isolation cylinder assembly includes multiple sections of seepage isolation cylinders connected in series, a watertight joint assembly is connected between each seepage isolation cylinder;

[0040] The watertight joint assembly further includes fastening screws, and threaded holes are provided in the threaded sleeve corresponding to the fastening screws.

[0041] By adopting the above technical solution, when the stage interval seepage cylinder assembly includes multiple series-connected seepage cylinders, the watertight joint assembly is also used to connect adjacent seepage cylinders, and the fastening screws tightly fix the threaded sleeve and the seepage cylinder.

[0042] In a second aspect, the present application provides an installation method for a multi-stage pore water pressure observation device in the same hole, adopting the following technical solution:

[0043] An installation method for a multi-stage pore water pressure observation device in the same hole, for the aforementioned multi-stage pore water pressure observation device in the same hole, includes the steps of:

[0044] According to the observation design requirements, a drilling rig is called to construct a borehole at the site to be measured, and the wellbore is protected by a drilling casing. The drilling depth reaches a position deeper than the design depth by the length of one seepage cylinder. The drill rod is pulled out, and a temporary working platform is built near the hole mouth to prepare the equipment and materials required for installing the multi-stage pore water pressure observation device in the same hole;

[0045] According to the monitoring design requirements, the corresponding number of each digital piezometer probe assembly, each seepage cylinder, and each watertight joint assembly are transported to the site;

[0046] Before embedding, all digital piezometer probe assemblies are soaked in clean water for more than 24 hours to discharge the air in the probes inside the digital piezometer probe assemblies;

[0047] Before embedding, each seepage cylinder in the interval seepage cylinder assembly is assembled on the ground. First, two adjacent seepage cylinders are connected by a watertight joint assembly;

[0048] Using auxiliary devices such as wellhead tools and ropes, in a step-by-step installation method, the first-stage stage interval seepage cylinder assembly is placed into the monitoring hole and the first-stage digital piezometer probe assembly is connected to the upper end through a watertight joint assembly; then the second-stage stage interval seepage cylinder assembly is placed into the monitoring hole and connected to the upper end of the first-stage digital piezometer probe assembly through a watertight joint assembly; in this order, until all digital piezometer probe assemblies, stage interval seepage cylinder assemblies, and watertight joint assemblies sink into the hole;

[0049] Install the ground acquisition station, debug and detect the working status of the probes of each stage digital piezometer probe assembly and the integrity of data transmission, ensure that the probes of each digital piezometer probe assembly work normally, and the data transmission and clock synchronization are accurate;

[0050] Pull out the casing from the hole and conduct full-hole water injection. Through the volume expansion of the water-absorbing and swelling material upon contact with water, a hole-sealing layer is formed between the digital piezometric probe assemblies at all levels, achieving mutual isolation of the formation water pressures at the locations of the digital piezometric probe assemblies at all levels, and preventing vertical communication and mutual leakage between the pore water pressure gauge assemblies at all levels.

[0051] In summary, the present application includes at least one of the following beneficial technical effects:

[0052] The present application includes at least one of the following beneficial technical effects: It avoids the segmentation problem in the traditional pore water pressure observation method, that is, regarding the preparation of the pore water pressure observation device and the application of the backfill material as two independent steps. At the same time, it avoids the problems of complex and lengthy installation processes and difficult-to-guarantee backfill quality in complex working environments caused by the traditional step-by-step and layer-by-layer embedding strategy.

[0053] The present application integrates the backfill material into the preparation process of the pore water pressure observation device, realizing the integrated design, preparation, and installation of the observation device and the backfill material. Specifically, a coarse sand cushion layer is directly prefabricated inside the permeable cylinder, and at the same time, a novel material combination of a water-absorbing and swelling material and a water-soluble film is introduced to form inside the impermeable cylinder cavity, replacing the traditional bentonite or highly disintegrating clay balls to form an efficient hole-sealing layer. This design concept changes the traditional construction mode, eliminating the need for additional backfill materials during on-site installation and greatly simplifying the installation process. More importantly, through the factory preparation mode, the standardization and normalization of the embedding and installation can be ensured, effectively guaranteeing the installation quality, making the pore water pressure monitoring data more accurate and reliable, and providing a solid technical support for engineering monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is an overall structural schematic diagram of a multi-level pore water pressure observation device in the same hole reflecting the present application;

[0055] Figure 2 is a structural schematic diagram of the digital piezometric probe assembly reflecting the present application;

[0056] Figure 3 is a cross-sectional view of the digital piezometric probe assembly reflecting the present application;

[0057] Figure 4 is a schematic diagram of the circuit module of the multi-level pore water pressure observation device in the same hole reflecting the present application;

[0058] Figure 5 is a structural schematic diagram of the inter-level impermeable cylinder assembly reflecting the present application;

[0059] Figure 6 is a cross-sectional view of the inter-level impermeable cylinder assembly reflecting the present application;

[0060] Figure 7It is an exploded structural schematic diagram of the watertight joint assembly embodying the present application;

[0061] Figure 8 It is a combined structural sectional view of the watertight joint assembly embodying the present application;

[0062] Figure 9 It is a schematic diagram of the initial installation state of the same-hole multi-level pore water pressure observation device embodying the present application;

[0063] Figure 10 It is a schematic diagram of the installation-in-progress state of the same-hole multi-level pore water pressure observation device embodying the present application;

[0064] Figure 11 It is a schematic diagram of the installation-completed state of the same-hole multi-level pore water pressure observation device embodying the present application.

[0065] Explanation of reference numerals:

[0066] 1. Monitoring hole;

[0067] 10. Digital piezometric probe assembly; 11. Permeable cylinder; 111. Permeable holes; 112. Cylinder cover; 113. Joint pipe; 12. Pore water pressure gauge assembly; 121. Encapsulation housing; 122. Small lock nut; 123. Large lock nut; 124. Acquisition circuit board; 125. Pore water pressure sensor; 126. Signal wire; 127. Probe multi-core cable;

[0068] 13. Highly permeable material; 14. Permeable geotextile;

[0069] 2. Stage interval seepage prevention cylinder assembly; 20. Seepage prevention cylinder; 21. Central pipe; 22. Grille cage; 23. Water-soluble film; 24. Water-absorbing and swelling material;

[0070] 30. Watertight joint assembly; 31. Threaded sleeve; 311. Horizontal plate; 32. Silicone rubber gasket; 33. Fastening screw;

[0071] 40. Multi-core cable;

[0072] 100. Ground acquisition station. Detailed implementation manners

[0073] The following further elaborates on the present application in conjunction with the attached Figures 1 - 11 for a more detailed description.

[0074] The embodiments of the present application disclose a same-hole multi-level pore water pressure observation device.

[0075] Please refer to Figure 1 、 Figure 2 and Figure 3, a monitoring hole 1 is drilled on the site to be measured. A multi-level pore water pressure observation device in the same hole includes: a plurality of digital piezometer assemblies 10 (one digital piezometer assembly 10 is schematically shown in the figure) arranged at intervals from the orifice to the bottom of the monitoring hole 1. The plurality of digital piezometer assemblies 10 together form a linearly distributed pore water pressure observation array to observe the variation law of pore water pressure at different depths on the same monitoring section in real time. Between the first-stage digital piezometer assembly 10 and the ground acquisition station 100, and between adjacent digital piezometer assemblies 10, they are electrically connected through a multi-core cable 40.

[0076] The distance between two adjacent digital piezometer assemblies 10 is not limited, and a stage interval permeable cylinder assembly 2 is connected between them. The adjacent digital piezometer assembly 10 and the stage interval permeable cylinder assembly 2 are connected through a watertight joint assembly 30 (see Figure 7 and Figure 8 ).

[0077] The digital piezometer assembly 10 includes a long tubular and hollow permeable cylinder 11, and the diameter of the permeable cylinder 11 is slightly smaller than the diameter of the monitoring hole 1. A pore water pressure gauge assembly 12 for monitoring pore water pressure is arranged in the permeable cylinder 11. A plurality of crescent-shaped water permeable holes 111 for water in the formation to enter the permeable cylinder 11 are uniformly arranged at intervals on the side wall of the permeable cylinder 11. A highly permeable material 13 is filled in the inner wall of the permeable cylinder 11 and the pores of the pore water pressure gauge assembly 12. The highly permeable material 13 is medium-coarse sand, and the highly permeable material 13 is wrapped with a water-permeable geotextile 14, and the water-permeable geotextile 14 is non-woven geotextile.

[0078] Figure 2 The figure schematically shows the situation where the water-permeable geotextile 14 directly wraps the highly permeable material 13, but it is not limited to this. Of course, the water-permeable geotextile 14 can also be wrapped outside the permeable cylinder 11, and then indirectly wrap the highly permeable material 13.

[0079] The upper and lower ends of the permeable cylinder 11 are provided with cylinder covers 112, and the cylinder covers 112 can be threadedly connected or welded to the permeable cylinder 11. A stainless steel joint pipe 113 for connecting one end of the watertight joint assembly 30 is welded on the cylinder cover 112. The multi-core cable 40 connected to the pore water pressure gauge assembly 12 passes through the cylinder cover 112 and the joint pipe 113 in sequence. Potting glue is arranged on the inner wall of the joint pipe 113 to block the stainless steel joint pipe 113 and prevent the leakage of the highly permeable material 13.

[0080] The pore water pressure gauge assembly 12 includes an encapsulation housing 121, a small locknut 122, a large locknut 123, a data acquisition circuit board 124, a pore water pressure sensor 125 electrically connected to the data acquisition circuit board 124 and its signal line 126, and a probe multi-core cable 127 electrically connected to the data acquisition circuit board 124. The probe multi-core cable 127 is connected to a multi-core cable 40 outside the encapsulation housing 121.

[0081] The probe multi-core cable 127, a part of the signal line 126, and the data acquisition circuit board 124 are all located inside the encapsulation housing 121. The small locknut 122 is used to block the interface where the signal line 126 extends out of the encapsulation housing 121, and the large locknut 123 is used to block the interface between the probe multi-core cable 127 and the encapsulation housing 121. The encapsulation housing 121, the small locknut 122, and the large locknut 123 form a sealed chamber to ensure the safety of the electronic components inside the data acquisition circuit board 124 and the cable interfaces in a harsh environment.

[0082] The pore water pressure sensor 125 selects a high-precision vibrating wire type pore water pressure gauge sold on the market. The multi-core cable 40 uses multi-core signal lines, and four of them are used. Among them, two cores are power supply cables for powering the pore water pressure sensor 125 and the data acquisition circuit board 124; two cores are data transmission buses for data transmission between the data acquisition circuit board 124 and the ground acquisition station 100.

[0083] Please refer to Figure 4 simultaneously. The data acquisition circuit board 124 includes an MCU microcontroller integrated with a storage module. The MCU microcontroller can calculate the received data, and the storage module is used for data storage; the MCU microcontroller is electrically connected to an excitation frequency sweep module, a signal processing module, a temperature acquisition module, a bus communication module, and a power supply module respectively. Among them, the MCU microcontroller and the storage module are composed of an STM32 single-chip microcomputer, a memory, and their peripheral circuits. By controlling the excitation frequency sweep module, the signal processing module, the temperature acquisition module, and the bus communication module, the acquisition, storage, and upload of pore water pressure and ambient temperature, as well as the reception and response of host computer instructions, can be completed independently. The excitation frequency sweep module is used for the excitation and frequency sweep of the vibrating wire type pore water pressure gauge. The signal processing module is used for the filtering, amplification, and ADC conversion of the chord signal, and sends the digital vibrating wire frequency to the MCU microcontroller. The temperature acquisition module is used for acquiring the ambient temperature signal of the vibrating wire type pore water pressure gauge, converting it into a digital quantity, and sending it to the MCU microcontroller. The bus communication module is connected to the data transmission bus in the multi-core cable 40 for data interaction between the MCU microcontroller and the ground acquisition station 100. The power supply module is connected to the power supply cable in the multi-core cable 40 to provide power for the MCU microcontroller.

[0084] The acquisition circuit board 124 is installed in a sealed chamber formed by the packaging shell 121, the small locknut 122, and the large locknut 123, and is respectively welded to the signal line 126 of the pore water pressure sensor 125 and the multi-core cable 40, and is sealed and waterproofed with epoxy resin. The small locknut 122 and the large locknut 123 respectively lock the signal line 126 of the pore water pressure sensor 125 and the probe multi-core cable 127 to ensure stable cable connection and excellent waterproof performance.

[0085] The combination of the permeable geotextile 14, the stainless steel permeable cylinder 11, and the highly permeable material 13 can ensure smooth seepage around the pore water pressure sensor 125.

[0086] Please refer to Figure 1 、 Figure 5 and Figure 6 and Figure 1 The cases where the stage interval seepage cylinder assembly 2 includes one seepage cylinder 20 or two series-connected seepage cylinders 20 are respectively shown in . The stage interval seepage cylinder assembly 2 located below the digital piezometric probe assembly 10 includes one seepage cylinder 20, and the stage interval seepage cylinder assembly 2 located above the digital piezometric probe assembly 10 includes two seepage cylinders 20. The length and quantity of the stage interval seepage cylinder assembly 2 are both prepared according to the monitoring design requirements. One customization example is as follows: The digital piezometric probe assembly 10 is 0.6 m long, the seepage cylinder 20 is 1.2 m long, and one digital piezometric probe assembly 10 is assembled every two seepage cylinders 20, forming a digital piezometric probe array layout with a 3-meter interval.

[0087] Each seepage cylinder 20 includes a central tube 21 and a grid cage 22 that are concentrically arranged from the inside to the outside. The multi-core cable 40 extends and is laid inside the central tube 21. The inner chamber of the central tube 21 is used for the multi-core cable 40 to route and is sealed with potting glue. The chamber between the central tube 21 and the grid cage 22 is the outer chamber, which is used to fill the water-absorbing and swelling material 24. The water-absorbing and swelling material 24 is in powder form and is wrapped by a water-soluble film 23 before encountering water. The two ends of the multi-core cable 40 in the central tube 21 of the adjacent digital piezometric probe assemblies 10 are connected with watertight male and female connectors, and the two ends of the multi-core cable 40 on the pore water pressure gauge assembly 12 are also connected with watertight male and female connectors.

[0088] The multi-core cable 40 in the adjacent digital piezometric probe assemblies 10 and the multi-core cable 40 in the central tube 21 of the seepage cylinder 20 are connected by plugging a watertight male head and a watertight female head. The multi-core cable 40 in the central tubes 21 of the two adjacent seepage cylinders 20 is also connected by plugging a watertight male head and a watertight female head.

[0089] The water-soluble film 23 is a film-like material that is easily degradable when exposed to water, such as a water-soluble film. Small holes are provided on the water-soluble film 23 to facilitate the infiltration of water inside the monitoring hole 1. When the dissolution rate of the water-soluble film 23 is slow, the infiltrating water can not only accelerate the water-swelling time of the water-swellable material 24, but also cause the water-swellable material 24 to burst the water-soluble film 23 during the swelling process, thereby further accelerating the process of seepage isolation in the borehole.

[0090] The outer diameter of the grille cage 22 of the seepage isolation cylinder 20 is the same as the outer diameter of the permeable cylinder 11, and the outer diameter of the central tube 21 is the same as the outer diameter of the stainless steel joint tube 113.

[0091] The water-swellable material 24 can be selected as a water-swellable resin. This material begins to swell after several hours of contact with water, and its maximum swelling volume reaches 700 times. It can extend out of the grille cage 22 to completely occupy the entire borehole space, forming a sealing layer to effectively prevent the upper and lower communication and mutual leakage between adjacent digital piezometric probe assemblies 10.

[0092] Please refer to Figure 7 and Figure 8 At both ends of the central tube 21, external threads are provided. The external threads are used to connect the watertight joint assembly 30. The watertight joint assembly 30 includes a threaded sleeve 31 with upper and lower openings and a silicone rubber gasket 32. A transverse plate 311 that divides it into upper and lower chambers is provided inside the threaded sleeve 31.

[0093] The central opening of the transverse plate 311 is for the multi-core cable 40 to pass through. Silicone rubber gaskets 32 are respectively laid on both sides of the transverse plate 311. The chambers on both sides of the transverse plate 311 are respectively used for threaded connection with the joint tube 113 and the central tube 21 of the stage interval seepage isolation cylinder assembly 2. Specifically, one chamber is used to insert and threadedly connect the central tube 21 of the digital piezometric probe assembly 10, and the other chamber is used to insert and threadedly connect the joint tube 113 on the lid 112 of the permeable cylinder 11. Threaded holes for inserting fastening screws 33 are provided at both the upper and lower parts of the threaded sleeve 31 to respectively tighten the outer walls of the joint tube 113 and the central tube 21.

[0094] The silicone rubber gasket 32 serves as a separation layer to prevent the water-swellable material 24 from invading the gap between the digital piezometric probe assembly 10 and the hole wall during the water-swelling process, which may affect the smooth seepage around the digital piezometric probe assembly 10.

[0095] When the stage interval seepage isolation cylinder assembly 2 includes multiple series-connected seepage isolation cylinders 20, the adjacent seepage isolation cylinders 20 are also connected using the watertight joint assembly 30 in the same manner as described above.

[0096] The multi-level pore water pressure observation device with the same hole adopts the factory integrated preparation method. The assembly of multiple digital piezometric probe assemblies 10, the welding and encapsulation of their internal circuits, the assembly of each unit of the impermeable cylinder 20 and the wiring encapsulation of its internal circuits, and the watertight joint assembly 30 are all completed in advance in the factory, simplifying the cumbersome on-site assembly process.

[0097] The whole multi-core cable 40 is segmented into the cable in the permeable cylinder 11 and the cable in the impermeable cylinder 20. Each segment is respectively routed and encapsulated in the permeable cylinder 11 and the inner cavity of the stage impermeable cylinder assembly 2, avoiding friction and damage of the cable caused by cable exposure during transportation and installation. The joints between each segment of the cable between the permeable cylinder 11 and the stage impermeable cylinder assembly 2 adopt the plugging method of the watertight male head and the watertight female head. The watertight joint assembly 30 is set at the joint between the impermeable cylinder 20 and the permeable cylinder 11 of each stage impermeable cylinder assembly 2, and is plugged and assembled during on-site installation, providing waterproof performance. In the unassembled state, the male and female ports of the watertight joint assembly 30 are protected by caps and plugs respectively.

[0098] The embodiment of the present application also discloses an installation method for the above-mentioned multi-level pore water pressure observation device with the same hole.

[0099] Please refer to Figure 9 、 Figure 10 and Figure 11 , an installation method for a multi-level pore water pressure observation device with the same hole, for the above-mentioned multi-level pore water pressure observation device with the same hole, including the following steps:

[0100] S1. According to the observation design requirements, a drilling rig is used to construct a borehole in the site to be measured, and the borehole wall is protected by a drilling casing to prevent borehole collapse. The borehole reaches a depth one section of the impermeable cylinder 20 longer than the designed depth, the drill rod is pulled out, and a temporary working platform is built near the hole mouth, and all the equipment and materials required for installation are prepared.

[0101] S2. Customize the multi-level pore water pressure observation device with the same hole and transport it to the site in a disassembled form. The number of digital piezometric probe assemblies 10, the length and number of the stage impermeable cylinder assemblies 2 between adjacent two-level digital piezometric probe assemblies 10 are all prepared according to the monitoring design requirements. One customization example is as follows: The overall length of the digital piezometric probe assembly 10 is 0.6m, the length of each section of the impermeable cylinder 20 is 1.2m, and one digital piezometric probe assembly 10 is assembled every two sections of the impermeable cylinder 20, forming a digital piezometric probe array layout method with a 3-meter interval.

[0102] S3. Before burial, all digital piezometric probe assemblies 10 are soaked in clean water on the ground for more than 24h to remove the air in the internal detection heads of the digital piezometric probe assemblies 10.

[0103] S4. Meanwhile, before burial, assemble each seepage isolation cylinder 20 in the multi-stage seepage isolation cylinder assembly 2 on the ground. First, butt the end heads of the connecting cylinders of two adjacent seepage isolation cylinders 20 with the watertight joint assembly 30, and then use the internal thread of the screw sleeve 31 to rotate and connect and the fastening screw 33 to tightly fix. The multi-core cables 40 in the central pipes 21 of two adjacent seepage isolation cylinders 20 are also assembled by plugging the watertight male head and the watertight female head.

[0104] S5. Use auxiliary devices such as wellhead tools and pulling ropes, and adopt a step-by-step installation method to assemble and sink the multi-stage digital piezometric probe assembly 10 and the multi-stage seepage isolation cylinder assembly 2 into the monitoring hole 1. Specifically, 1) Select one seepage isolation cylinder 20 as the lower sealing layer, tie it with a pulling rope, and then sink it into the hole, leaving its end above the hole opening, and fix it with a wellhead tool. The pulling rope is used to assist in installation, prevent the structure from falling into the hole, and facilitate pulling out the equipment when the hole is blocked. 2) Use the watertight joint assembly 30 to threadedly connect and fix the seepage isolation cylinder 20 and the first-stage digital piezometric probe assembly 10 (including the first-stage vibrating wire pore water pressure gauge, as Figure 4 shown) with the fastening screw 33. 3) Slowly lower the pulling rope and sink the first-stage digital piezometric probe assembly 10 into the monitoring hole 1, leaving its end above the hole opening, and fix it with a hole opening tool. 4) Connect the watertight joint assembly 30 to the first-stage digital piezometric probe assembly 10 and connect it to the next-stage seepage isolation cylinder assembly 2, then perform threaded connection and fix it tightly with the fastening screw 33, and sink the connected next-stage seepage isolation cylinder assembly 2 into the monitoring hole 1, leaving its port at the hole opening, and fix it with a hole opening tool. 5) Continue to assemble the second-stage digital piezometric probe assembly 10 (including the second-stage vibrating wire pore water pressure gauge). The multi-core cables 40 in the adjacent digital piezometric probe assemblies 10 and the multi-core cables 40 in the central pipes 21 of the seepage isolation cylinders 20 are assembled by plugging the watertight male head and the watertight female head.

[0105] In sequence, until the last-stage digital piezometric probe assembly 10 (including the last-stage vibrating wire pore water pressure gauge, as Figure 4 shown), the multi-stage seepage isolation cylinder assembly 2, and the watertight joint assembly 30 are sunk into the hole.

[0106] S6. Install the ground acquisition station 100, debug and detect the working status of each level of probe and the integrity of data transmission to ensure that each probe works normally and the data transmission and clock synchronization are accurate.

[0107] S7. Pull out the casing from the hole and fill the hole with water. Through the water absorption and expansion material 24 expanding in volume when encountering water, a sealing layer is formed between each level of digital piezometric probe assembly 10 to complete the isolation of the water pressure of the formation where each level of digital piezometric probe assembly 10 is located, and there is no vertical connection and mutual leakage between each level of pore water pressure gauge assembly 12.

[0108] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A multi-level pore water pressure observation device with the same hole, characterized in that, Comprising: A plurality of digital piezometric probe assemblies (10) arranged at intervals from bottom to top in the monitoring hole (1), a stage interval permeable cylinder assembly (2) connected between two adjacent digital piezometric probe assemblies (10), and a watertight joint assembly (30) for connecting adjacent digital piezometric probe assemblies (10) and the stage interval permeable cylinder assembly (2); Each of the digital piezometric probe assemblies (10) includes a long and hollow permeable cylinder (11), a pore water pressure gauge assembly (12) arranged in the permeable cylinder (11), a highly permeable material (13) filled in the gap between the inner wall of the permeable cylinder (11) and the pore water pressure gauge assembly (12), and a water-permeable geotextile (14) wrapping the highly permeable material (13); A multi-core cable (40) is electrically connected between adjacent pore water pressure gauge assemblies (12), and the multi-core cable (40) passes through the stage interval permeable cylinder assembly (2) between adjacent pore water pressure gauge assemblies (12); The stage interval permeable cylinder assembly (2) includes one section of impermeable cylinder (20) or multiple sections of impermeable cylinders (20) connected in series; Each of the impermeable cylinders (20) includes a central tube (21) and a grille cage (22) concentrically arranged from inside to outside, and a water-absorbing and swelling material (24) wrapped by a water-soluble film (23) is filled between the central tube (21) and the grille cage (22); The multi-core cable (40) extends out from both ends of the central tube (21) and is respectively connected to two adjacent pore water pressure gauge assemblies (12).

2. The multi-level pore water pressure observation device with the same hole according to claim 1, characterized in that, A plurality of water-permeable holes (111) are provided on the side wall of the permeable cylinder (11), cylinder covers (112) are provided at the upper and lower ends of the permeable cylinder (11), and joint pipes (113) for connecting one end of the watertight joint assembly (30) are provided on the cylinder covers (112); The multi-core cable (40) connected to the pore water pressure gauge assembly (12) passes through the joint pipe (113) and extends into the stage interval permeable cylinder assembly (2), and potting glue is provided on the inner wall of the joint pipe (113).

3. The multi-level pore water pressure observation device with the same hole according to claim 2, characterized in that The watertight joint assembly (30) includes a threaded sleeve (31) and a silicone rubber gasket (32) with upper and lower openings; A transverse plate (311) that divides the threaded sleeve (31) into upper and lower chambers is provided inside the threaded sleeve (31), and a central hole is provided in the transverse plate (311) for the multi-core cable (40) to pass through; The silicone rubber gaskets (32) are respectively laid on both sides of the transverse plate (311), and the chambers on both sides of the transverse plate (311) are respectively used for threadedly connecting the joint pipe (113) and the stage interval permeable cylinder assembly (2).

4. The multi-level pore water pressure observation device with the same hole according to claim 1, characterized in that, The pore water pressure gauge assembly (12) includes a sealed housing (121), a small lock nut (122), a large lock nut (123), a data acquisition circuit board (124), a pore water pressure sensor (125) electrically connected to the data acquisition circuit board (124) and its signal line (126), and a probe multi-core cable (127) electrically connected to the data acquisition circuit board (124); The multi-core cable (127) of the probe, the signal line (126), and the acquisition circuit board (124) are all located inside the encapsulation housing (121). The small locknut (122) is used to seal the place where the signal line (126) extends out of the encapsulation housing (121), and the large locknut (123) is used to seal the place where the multi-core cable (127) of the probe extends out of the encapsulation housing (121).

5. The same-hole multi-stage pore water pressure observation device according to claim 4, characterized in that The acquisition circuit board (124) includes: An MCU microcontroller integrated with a storage module; An excitation frequency sweep module, a signal processing module, and a temperature acquisition module that are all electrically connected to the MCU microcontroller; A bus communication module and a power supply module that are all electrically connected to the MCU microcontroller; A pore water pressure sensor (125) that is electrically connected to the excitation frequency sweep module, the signal processing module, and the temperature acquisition module.

6. The multi-level pore water pressure observation device with the same hole according to claim 4, characterized in that The highly permeable material (13) is medium coarse sand, the water-absorbing and swelling material (24) is water-absorbing and swelling resin, and the acquisition circuit board (124) is externally sealed and coated with epoxy resin.

7. The same-hole multi-stage pore water pressure observation device according to any one of claims 1 to 6, characterized in that, The multiple digital piezometric probe assemblies (10), the seepage isolation cylinder (20), and the watertight joint assembly (30) are all integrally prefabricated.

8. The multi-level pore water pressure observation device with the same hole according to claim 3, characterized in that, When the stage seepage isolation cylinder assembly (2) includes multiple sections of seepage isolation cylinders (20) connected in series, the watertight joint assembly (30) is connected between each seepage isolation cylinder (20); The watertight joint assembly (30) further includes a fastening screw (33), and the threaded sleeve (31) is provided with a threaded hole corresponding to the fastening screw (33).

9. A method for installing a multi-level pore water pressure observation device with the same hole, which is used for the multi-level pore water pressure observation device with the same hole according to any one of claims 1 to 8, characterized in that, Including steps: According to the observation design requirements, dispatch a drilling rig to construct a borehole at the site to be measured, and use a drilling casing to protect the wellbore. The drilling depth reaches a position deeper than the design depth by the length of one section of the seepage isolation cylinder (20). Pull out the drill rod, and build a temporary working platform near the wellhead to prepare the equipment and materials required for installing the multi-stage pore water pressure observation device in the same borehole; Transport the corresponding number of each digital piezometric probe assembly (10), each section of seepage isolation cylinder (20), and each watertight joint assembly (30) to the site according to the monitoring design requirements; Before burial, soak all the digital piezometric probe assemblies (10) in clean water for more than 24 hours to discharge the air in the probes inside the digital piezometric probe assemblies (10); Before burial, assemble each seepage isolation cylinder (20) in the stage seepage isolation cylinder assembly (2) on the ground. First, connect two adjacent seepage isolation cylinders (20) through the watertight joint assembly (30); Using auxiliary devices such as wellhead tools and ropes, adopt a step-by-step installation method to place the stage seepage isolation cylinder assembly (2) of the first stage into the monitoring hole (1) and connect the digital piezometric probe assembly (10) of the first stage through the watertight joint assembly (30) at the upper end; then place the stage seepage isolation cylinder assembly (2) of the second stage into the monitoring hole (1) and connect the upper end of the digital piezometric probe assembly (10) of the first stage through the watertight joint assembly (30); in this sequential order until all the digital piezometric probe assemblies (10), stage seepage isolation cylinder assemblies (2), and watertight joint assemblies (30) sink into the hole; Install the ground acquisition station (100), debug and detect the working status of the probes of each digital piezometric probe assembly (10) and the integrity of data transmission, ensuring that the probes of each digital piezometric probe assembly (10) work properly and the data transmission and clock synchronization are accurate and error-free; Pull the casing out of the hole and fill the hole with water. Through the volume expansion of the water-absorbing and swelling material (24) when it meets water, a hole-sealing layer is formed between each digital piezometric probe assembly (10), completing the isolation of the water pressure of the formation where each digital piezometric probe assembly (10) is located, and there is no vertical connection and mutual leakage between each pore water pressure gauge assembly (12).

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