Immersible microprobe electrode for electrophysical monitoring in loose soils

Abstract

FIELD: soil monitoring.SUBSTANCE: invention relates to devices for electrophysical monitoring of loose soils. The essence: the device contains outer insulating shell (1), inside which insulated copper wires (3) are placed, from the bent ends of which electrodes (2) are made. Outer insulating shell (1) is placed in thin-walled pipe (5). Thin-walled pipe (5) is equipped with detachable conical tip (6) at the bottom and handles (7) at the top for immersing the device in loose soil.EFFECT: increasing the contact area of the electrodes with the soil surface.1 cl, 1 dwg

Description

[0001] The invention relates to electrical exploration and can be used in monitoring the processes of formation of zones in near-surface massifs of loose soils that are anomalous in electrical conductivity properties, using methods based on the propagation of electric current.

[0002] Electrodes for surface sounding and exploratory well logging are used in electrical exploration. Rod electrodes, which are pointed metal rods driven into the outcrop surface, are used for direct and alternating current sounding. Electrodes for borehole logging and cross-well sounding provide pressure on the contact elements of the borehole surface using spring and lever devices of various designs (see Komarov, S.G., Geophysical Methods of Well Research. 2nd edition, revised and supplemented. Moscow: Nedra, 1973. pp. 116-118).

[0003] The main disadvantage of these devices is the insufficient contact area of ​​the electrode with the borehole surface, which leads to an increase in the density of the probing current and a decrease in the accuracy of measurements. This disadvantage is eliminated by using a number of devices. For example, in a device for grounding power circuits (see patent no. 306406, IPC G01V 3 / 20, priority 12.08.1968), the electrodes are made in the form of flexible ribbed elements located longitudinally on the surface of an elastic hydraulic chamber. In the sensor of a downhole tool (see patent no. 438964, IPC G01V3 / 08, priority 20.09.1972), the cylindrical electrodes are made split and fixed on an elastic shell enclosing the body. In the device for electric well logging (see patent application No. 1040449C1, MKIG01V3 / 20, priority 20.12.1983), the housing is made of two parts placed symmetrically relative to the elastic chamber.Automatic pressure regulation in the body parts ensures a tighter pressure of the electrode against the borehole surface when it is curved.

[0004] During deep rock surveys, individual electrodes (sensors) are structurally combined to form probes, which constitute a specialized logging device. For example, the simplest four-electrode probe for borehole logging includes a dielectric rod to which spring-type electrodes are attached. These electrodes can be moved along the rod and the spring contact diameter adjusted by varying the distance between the electrode bushings (see V. A. Hämäläinen et al., Geoelectric Control of Rock Fracture and Injection Hardening. Moscow: Nedra 1996, pp. 75-76).

[0005] The described devices have the following disadvantages, which prevent their use in the study of loose soil massifs.

[0006] 1. Their installation deep within the massif requires the drilling of boreholes. Loose soils have low strength, so the borehole cannot be maintained without casing due to soil subsidence. Probing through a pipe (metal or dielectric) is impossible.

[0007] 2. These devices contain elements (lever, pneumatic, hydraulic, etc.), which complicate their design and increase the cost of manufacture. When studying the physical condition (density, moisture, ecotoxicant content, etc.) of near-surface soil layers using methods based on the propagation of electric current, a stationary sensor system is often installed at a depth of up to 2 m below the ground surface. In this case, it is advisable to use submersible microprobe electrodes of a simplified design.

[0008] These shortcomings are partially eliminated in the design of a four-electrode sensor-probe for measuring the electrical resistance of water-saturated clay soils (see Prostov S. M., Electrochemical Soil Stabilization. - Tomsk: Tomsk University Press, 2011. - pp. 129-130). The sensor includes an outer insulating sheath, insulated copper conductors placed inside it, microprobe electrodes made of copper conductors with stripped insulation, and a connector in the form of an insulating plate with contacts. The use of a standard four-wire copper cable in its manufacture significantly simplified the design of this device and reduced its cost.

[0009] To install this device at a geomonitoring point, simply drill a hole of the appropriate diameter to the required depth in the loose soil being studied, insert the microprobe electrode, and then connect it to the measuring network via a connector. After monitoring is complete, the microprobe can be removed for reuse.

[0010] We choose this device as a prototype, since it has the greatest coincidence of features with the declared one.

[0011] The disadvantages of the prototype are as follows.

[0012] 1. The outer shell of the microprobe is not rigid enough to ensure its axis remains straight. When inserting the microprobe into a hole drilled in the ground, it is likely to become jammed on any curvatures. Furthermore, the lower part of the microprobe, where the electrodes are located, is not protected from mechanical damage, which could lead to failure. For this reason, as practice has shown, the immersion depth of the prototype microprobe does not exceed 0.7 m, and its reusability is minimal.

[0013] 2. Additional cavities may form at the electrode-ground interface at the bottom of the microprobe due to incomplete immersion. These cavities disrupt the electrical contact, leading to reduced measurement accuracy or even compromising the ability to monitor, necessitating reinstallation of the microprobe.

[0014] The purpose of the invention is to increase the immersion depth of the microprobe electrode, increase the contact area of ​​the microelectrodes with the soil surface and increase the service life of the device.

[0015] The stated objective is achieved by the fact that in the known device of the electrode-microprobe, containing an outer insulating shell, insulated copper cores placed inside it, electrodes made of copper cores with the insulation removed, the outer insulating shell is placed in a removable thin-walled pipe with a wall thickness of 0.8 - 1.0 mm and a gap of no more than 1.0 mm, equipped in the lower part with a detachable conical tip, and in the upper part - with handles for immersion into loose soil to the required depth and subsequent removal after installation of the device.

[0016] Fig. 1 shows the structure of a submersible electrode-microprobe for electrophysical monitoring in loose soils and explains the procedure for its installation.

[0017] The device consists of an outer insulating shell 1, inside which four insulated copper cores 3 are placed, from the bent ends of which electrodes 2 are made by removing the insulation. The outer insulated shell 1, together with the electrodes 2 and the insulated copper cores 3, is placed in a removable thin-walled tube 5 with a wall thickness of 0.8 - 1.0 mm, while the gap between the elements should be no more than 1.0 mm. The outer edges of the electrodes 2 are at the level of the outer insulating shell 1. The distance between adjacent electrodes 2 can vary in the range of 1 - 10 cm. Element 4 and the lower electrode 2 with their shell freely rest in the detachable conical tip 6. The extractable thin-walled tube 5 in the upper part is equipped with two handles 7. The terminals of the insulated copper wires 3 are connected to a connector 8, which is closed by a cover 9. Cable 11, connecting the electrode-microprobe with the measuring equipment (in Fig.1 not shown). When installing the device in the ground, a sending rod 10 is used.

[0018] The immersion electrode microprobe for electrophysical monitoring in loose soils is installed as follows.

[0019] The assembled device (Fig. 1, pos. a) is installed vertically or at an angle on the ground surface. The operator, applying downward force to the handles 7, lowers the device to the required depth, wherein the detachable conical tip 6 facilitates overcoming the soil resistance and protects the electrodes 2 from deformation. In case of compacted soils, it is advisable to drill a hole at the installation site of the device to the full depth with a diameter equal to 0.5 - 0.8 of the diameter of the thin-walled pipe 5 being extracted. After lowering the device to the required depth, the operator, applying upward force to the handles 7, extracts the element 5, wherein the sending rod 10, resting on the cover 9, holds the outer insulating shell 1 and the contacts 2 in the lower position resting on the detachable conical tip 6 (Fig. 1, pos. b). After the element 5 has been completely extracted, it and the sending rod 10 can be used to immerse the next device, and the detachable conical tip 6 remains in the ground.After removing cover 9 and connecting cable 11 to connector 8, the device is ready for monitoring (Fig. 1, pos. c). Once monitoring is complete, the main elements of the device—1, 2, and 3—are removed from the ground using simple grips and devices.

[0020] When the device is driven into the ground, the detachable conical tip 6 and the extractable thin-walled tube 5 absorb the soil resistance. Therefore, the primary elements 1, 2, and 3 are completely preserved. When the extractable thin-walled tube 5 is moved upward, the gaps between elements 1 and 5 minimize the negative mechanical impact on the primary elements 1, 2, and 3. When these elements are removed after monitoring, the friction between the soil wall and the outer insulating shell 1 is significantly lower than during immersion. This increases the maximum immersion depth of the microprobe electrode in loose soils to at least 2.0 m and significantly (at least an order of magnitude) increases its service life.

[0021] After element 5 is removed, the soil undergoes reverse elastic deformation, ensuring its tight adherence to electrodes 2. In addition, soil particles separated during the lifting of element 5 accumulate in the cavity above the detachable conical tip 6. This ensures an increase in the contact area of ​​electrodes 2 with the soil surface.

[0022] Thus, the object of the invention is achieved.

Claims

An immersion electrode-microprobe for electrophysical monitoring in loose soils, comprising an outer insulating shell, insulated copper conductors placed inside it, electrodes made of copper conductors with the insulation removed, characterized in that the outer insulating shell is placed in a removable thin-walled tube with a wall thickness of 0.8 - 1.0 mm and a gap of no more than 1.0 mm, equipped in the lower part with a detachable conical tip, and in the upper part - with handles for immersion into loose soil to the required depth and subsequent removal after installation of the device.

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