CN114660371A - Shallow electrode construction method for long-term observation of fracture electric field - Google Patents

Abstract

The invention relates to a shallow electrode construction method for long-term observation of a fracture electric field, which comprises the following steps: selecting at least two shallow electrode embedding points in a fourth loose layer or a bedrock weathering crust of a broken disc on the same side of a broken zone; when the depth of the fourth loose layer or the bedrock weathering crust is smaller than the preset depth, excavating a soil pit at a shallow electrode embedding point, placing the shallow electrode in the soil pit, backfilling and compacting the soil pit, wherein backfilling materials for backfilling the soil pit are soil or coke; and when the depth of the fourth series of unconsolidated formations or bedrock weathering crust is greater than the preset depth, drilling by a drill bit with the diameter greater than that of the shallow electrode, wherein the drilling depth is below the annual average pore water submergence surface, placing the shallow electrode at the bottom of a drilling hole, and sealing the hole opening by a protective material. Compared with the prior art, the invention can ensure that the shallow electrode is arranged in the diffusion electric field and can improve the stability of the shallow electrode.

Description

Shallow electrode construction method for long-term observation of fracture electric field

technical field

The invention relates to the technical field of fractured electric fields, in particular to a shallow electrode construction method for long-term observation of fractured electric fields.

Background technique

The natural electric field method is currently the mainstream natural electric field observation technology. The traditional natural electric field method, also known as the land electric method, was one of the means of collective defense in my country in the 1960s and 1970s. It took the superficial earth current as the observation object. The principle of the land electric method is to invert the natural electric field by observing the real-time change of the potential difference between the two electrodes on the measuring track. The electrode layout technology of the land electric method is to arrange a pair of electrodes in a specified direction according to a certain distance. The electrodes mainly use the method of digging holes in the superficial soil layer, and each pair of electrodes is a measurement channel. A number of measurement tracks are set up in the area to observe the changes of the natural electric field in the soil layer (Xu Shijian, 1979; Qiu Yonghai, 1995, 2008).

In recent years, some scholars have improved this method so that it can seamlessly observe all directions in the area. This technique is called omnidirectional natural electric field observation method. The omnidirectional natural electric field observation method is also an improved land electric observation technology, which improves the shortcomings of the original measurement channel layout in the land electric observation. The electrode layout technology of this method is to set the central observation point in the area to be observed as the reference point, and arrange multiple directions (not less than 8) within a range of 360° around the reference point. By measuring the electrodes arranged in each corresponding direction The natural electric field component between the center point electrode and the center point electrode, and the omnidirectional variation map of the natural electric field is drawn to observe the variation of the regional natural electric field (Xi Jilou, Song Yanru, Hu Mingchao, etc., 2013). To sum up, the natural electric field method does not involve the geological unit that can induce tectonic earthquakes—faults, and its observation method is equivalent to the shallow natural electric field scanning of the whole area.

The fracture electric field specifically refers to the natural electric field distributed in the fractured zone formed by piezoelectric and rock battery effects caused by uneven stress in the deep fractured fracture zone of the crust. It belongs to a kind of natural electric field (Chen Z and Chen G.N., 2021, DOI: 10.21203/rs.3.rs-42860/v1). When the fault fracture zone extends to the shallow part and contacts with loose layers containing pore water (including water-bearing sedimentary rock layers, Quaternary overburden layers, etc., collectively referred to as loose layers), the above-mentioned fault electric field existing in the fault can be perpendicular to the fault trend. The shallow cap layer diffuses, creating a secondary effect like "leakage". The latter is also known as the fracture diffusion electric field. It can be seen from the physical principle that the equipotential line on the plane of the fracture diffusion electric field existing in the loose layer is basically balanced with the fracture trend, and on the plane, the farther the vertical distance is from the fracture zone, the smaller the electric field strength. Please refer to FIG. 1, which is a schematic diagram of the electrode arrangement of a fracture electric field observation method. One electrode is placed in the fracture zone as a common electrode, and a plurality of electrodes are placed in the deposition layer as shallow electrodes. The external electrode and the common electrode are connected by an observation instrument to form a plurality of measurement channels, and the values between the measurement channels are compared to effectively observe the existence of the fracture electric field.

However, in order to achieve a better observation effect through this fracture electric field observation method, there are certain requirements for the layout of the electrodes. First, it is necessary to ensure that the electrodes can be placed in the diffusion electric field; higher stability. How to make the electrode meet the observation requirements during the electrode construction is of great significance for the fracture electric field observation method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and to provide a shallow electrode construction method for long-term observation of the fractured electric field, which can ensure that the electrode is placed in the diffusion electric field and the electrode has high stability.

The present invention is achieved through the following technical solutions: a shallow electrode construction method for long-term observation of a fractured electric field, comprising the steps of:

Select at least two shallow electrode burying points in the Quaternary loose layer or bedrock weathering crust on the same side of the fault fracture zone;

When the depth of the Quaternary loose layer or the bedrock weathering crust is less than the preset depth, excavate the soil pit at the shallow electrode burying point, place the shallow electrode in the soil pit, and dig the soil pit. The soil pit is backfilled and compacted, and the backfill material used for backfilling the soil pit is soil or coke;

When the depth of the Quaternary loose layer or the bedrock weathering crust is greater than the preset depth, drilling is carried out with a drill bit with a diameter larger than the diameter of the shallow electrode, and the drilling depth is below the perennial average pore water phreatic surface, and the shallow electrode is drilled. The bottom of the drilling hole is placed, and the hole of the drilling hole is fixedly sealed with a protective material.

Compared with the prior art, the present invention provides a shallow electrode construction method for long-term observation of a fractured electric field. Different burying methods are selected according to the depth of the Quaternary loose layer or bedrock weathering crust. When the depth of the rock weathering crust is shallow, the shallow electrode is buried by the soil pit method, and the construction cost and maintenance cost are small; when the depth of the Quaternary loose layer or the bedrock weathering crust is deep, the shallow drilling method is used. By burying the shallow electrode, the shallow electrode can be surrounded by sufficient pore water to ensure the accuracy of the observation data. By wrapping the shallow electrode with the backfill material or pore water, it can ensure that the shallow electrode is placed in the diffusion electric field, and the backfill material or the solid sealing of the drill hole can fix and protect the shallow electrode and improve the stability of the shallow electrode.

Further, a common electrode is provided in the fractured zone, and at least two shallow electrode burying points are selected, including the step of: on the same vertical plane as the common electrode, the vertical plane and the direction of the fractured zone At least two shallow electrode burying points are selected at positions that are vertical and equal to the projected distance of the common electrode on the ground surface;

When placing the shallow electrodes in the soil pit, or placing the shallow electrodes at the bottom of the drilling hole, each of the shallow electrodes is set at the same depth.

Further, when placing the shallow electrode in the soil pit, or placing the shallow electrode into the bottom of the drilling hole, the step includes: placing the shallow electrode vertically in the soil pit or in the drilled hole.

Further, before the borehole is sealed with a protective material, the method includes the step of backfilling the borehole, and the backfill material used for backfilling the borehole is soil or coke.

Further, when backfilling the soil pit or the borehole with the coke, the method includes the step of: grinding the coke to a granular shape with fine particle size and then backfilling.

Further, after backfilling and compacting the soil pit, the step includes: sealing the surface of the soil pit with cement or asphalt.

Further, when the depth of the Quaternary loose layer or bedrock weathering crust is less than the preset depth, the shallow electrode is a polarized electrode; when the depth of the Quaternary loose layer or bedrock weathering crust is greater than the preset depth , the shallow electrode is a non-polarized electrode.

Further, the non-polarized electrode is a solid long cylindrical lead rod with a certain thickness;

Before placing the non-polarized electrode into the bottom of the drilling hole, the step includes: performing passivation treatment on the surface of the non-polarized electrode with dilute sulfuric acid.

Further, the drilling depth is at most above the fresh bedrock surface.

Further, the shallow electrode is connected with a cable, including the steps of: sheathing a PVC pipe or a stainless steel pipe on the cable; burying the cable while burying the shallow electrode, so that the PVC pipe or stainless steel pipe Place vertically on the pit or hole and have the section of PVC or stainless steel pipe outside the pit or borehole.

For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings.

Description of drawings

1 is a schematic diagram of electrode arrangement of a fracture electric field observation method in the background technology;

2 is a schematic flowchart of a shallow electrode construction method for long-term observation of a fractured electric field in an embodiment;

FIG. 3 is a schematic diagram of an exemplary electrode arrangement in the embodiment;

Fig. 4 is the schematic flow chart of burying shallow electrode by soil pit method in the embodiment;

Fig. 5 is the schematic diagram of the shallow electrode burying of the soil pit method in the embodiment;

6 is a schematic flow chart of a shallow drilling method for burying a shallow electrode in an embodiment;

FIG. 7 is a schematic diagram of burying a shallow electrode in a shallow drilling method in an embodiment.

Detailed ways

Please refer to FIG. 2 , which is a schematic flowchart of the construction method of the shallow electrode for long-term observation of the fractured electric field according to the present embodiment. The method includes:

Step 1: Select at least two shallow electrode burying points in the Quaternary loose layer or bedrock weathering crust on the same side of the fault fracture zone.

Since the existence of the fracture electric field needs to be judged according to the change characteristics of the data obtained by the two measurement channels, when the data obtained by the two measurement channels changes synchronously, that is, the values of the two measurement channels are different in magnitude but the change trend is the same, the fracture can be judged. Electric field exists. Therefore, when arranging the shallow electrodes, it is necessary to ensure that at least two shallow electrodes are placed on the same broken disk on the same side of the fracture, that is, the same upper disk or the same lower disk.

In a preferred embodiment, a linear interpolation method is used to obtain the increment of the electric field change per unit distance: read the data of two measurement channels, and divide the difference between the observation data of the two measurement channels by the shallowness of the two measurement channels. If the distance between the external electrodes is determined, the increment of the electric field change per unit distance can be obtained. In order to facilitate the interpolation of the equipotential lines on the plane through the data between the two measurement tracks in the later stage, when selecting the buried point of the shallow electrode in step 1, set the projection distance of the common electrode and the shallow electrode on the surface to be equal, and the common electrode and The shallow electrodes are located on the same vertical plane, and the vertical plane is perpendicular to the direction of the fractured zone at the same time, and the shallow electrodes are arranged at the same depth. Please refer to FIG. 3 , which is an exemplary schematic diagram of electrode layout. Among them, A is the common electrode buried in the deep fracture zone. The vertical projection position of the common electrode A on the surface is O. B and C are the shallow electrodes respectively, and the shallow electrode B is farther from the fracture zone than the shallow electrode. C. Then the horizontal distance between the projection position O and the shallow electrode C is set to be equal to the horizontal distance between the shallow electrode C and the shallow electrode B. A straight line, and the straight line on the plane is perpendicular to the strike of the fracture zone.

Step 2: According to the depth of the Quaternary loose layer or the bedrock weathering crust, the shallow electrode is buried by the soil pit method or the shallow drilling method.

Specifically, when the depth of the Quaternary loose layer or the bedrock weathering crust is less than the preset depth, the soil pit method is used to bury the shallow electrode. Please refer to FIG. 4 and FIG. 5. FIG. 4 is a schematic flowchart of burying the shallow electrode by the soil pit method. FIG. 5 is a schematic diagram of the shallow electrode burying by the soil pit method. The burying of the shallow electrode by the soil pit method includes:

Step 211 : excavate the soil pit at the shallow electrode burying point. The excavation depth can be determined according to the conditions of the construction site. In this embodiment, the excavation depth is set to 3-5m.

Step 212 : Place the shallow electrode in the excavated soil pit, and the placement mode of the shallow electrode may be vertical placement, lying flat, or inclined placement. In a preferred embodiment, the vertical placement is chosen to better induce changes in the electric field.

Step 213 : backfill and compact the soil pit where the shallow electrode is placed. The backfill material used for backfilling the soil pit can be soil stripped when the soil pit is excavated, or coke. Among them, the semiconducting properties of coke can ensure the continuity of the diffusion electric field, and inhibit the redox effect when the shallow electrode is in contact with the soil layer, so as to achieve the purpose of protecting the shallow electrode. In a preferred embodiment of using coke as the backfill material, the coke can be further ground into fine-grained particles before backfilling, so that the coke can fully contact the shallow electrode.

In order to further protect the shallow electrode, in a preferred embodiment, the soil pit method further includes step 214 : sealing the surface of the soil pit with cement or asphalt.

When the depth of the Quaternary loose layer or bedrock weathering crust is greater than the preset depth, the shallow drilling method is used to bury the shallow electrode. Please refer to FIG. 6 and FIG. 7 , FIG. 6 is a schematic flow chart of burying a shallow electrode by the shallow drilling method, and FIG. 7 is a schematic diagram of burying the shallow electrode by the shallow drilling method. The burying of the shallow electrode by the shallow drilling method includes:

Step 221: Drill with a drill bit with a diameter larger than the diameter of the shallow electrode. The drilling depth is below the perennial average pore water phreatic surface. When the thickness of the Quaternary loose layer or bedrock weathering crust in the construction area is moderate, the drilling depth can reach the fresh foundation. on the rock face. It should be noted that the drilling depth should not exceed the depth of the common electrode placed in the fracture zone.

Step 222: Place the shallow electrode into the bottom of the drilling hole, in a preferred embodiment, the shallow electrode is placed vertically in the hole.

When the pore water in the borehole is sufficient, there is no need to backfill the borehole, and the wrapping of the pore water can completely place the shallow electrode in the diffusion electric field; when the pore water in the borehole is insufficient, go to step 223: place the Drilling into the shallow electrode is backfilled, and the backfill material used for backfilling the drilled hole can be the core obtained by drilling, or it can be coke.

Step 224: Seal the drill hole with a protective material to protect the shallow electrode. The protective material can be cement or the like.

In step 2, care should be taken to protect the cable connected to the shallow electrode when burying the shallow electrode. The casing can be made of PVC or stainless steel, and the interfaces of the casing can be bonded by glue or connected by series joints; when burying the shallow electrode, bury the cable, so that the casing is placed vertically in the pit or hole, and reserved Partially outside of pits or boreholes. In this embodiment, the buried depth of the cable is greater than 1 m, and warning signs must be installed along the line after burying.

In this embodiment, the shallow electrodes may be polarized electrodes or non-polarized electrodes. Preferably, when the shallow electrode is buried by the soil pit method, a polarized electrode is selected as the shallow electrode; when the shallow electrode is buried by the shallow drilling method, a non-polarized electrode is selected as the shallow electrode, and the non-polarized electrode is selected to have Solid long cylindrical lead rod of sufficient thickness. This is because the polarized electrode has strong anti-interference ability, which is conducive to the long-term observation of the fractured diffusion electric field, but the electrolyte in the polarized electrode will be consumed during the observation process and needs to be replenished regularly, and the buried cost of the shallow drilling method is Compared with the soil pit method, if the polarized electrode is used in the shallow drilling method, it will cause a higher maintenance cost, and the non-polarized electrode does not require regular replenishment of electrolyte, which is more suitable for the quaternary loose layer or bedrock weathering crust. In the case of greater depth.

In a preferred embodiment, before burying the non-polarized electrode, the surface of the non-polarized electrode is passivated with dilute sulfuric acid, so as to improve the anti-interference performance of the non-polarized electrode.

In the fracture electric field observation method, the electrodes and the observation instrument are mainly connected by cables. One end of the cable is connected to an electrode, and the other end is connected to the observation instrument for reading, thereby constructing a measurement channel. Please refer to Fig. 3 again, where the measurement traces A-C and A-B are used to observe the fracture electric field, and the measurement traces B-C are used to observe the regional background natural electric field, so as to understand the changes of the surface electric field and its interference on the fracture electric field measurement results.

Compared with the prior art, the construction method of the shallow electrode of the present invention selects different shallow electrodes according to the depth of the Quaternary loose layer or bedrock weathering crust, and selects different burying methods, and selects different shallow electrodes according to the depth of the Quaternary loose layer or bedrock weathering crust. When the depth of the rock weathering crust is shallow, the shallow electrode is buried by the soil pit method, and the construction cost and maintenance cost are small, and the polarized electrode with strong anti-interference can be used at a low cost by the soil pit method. When the depth of the loose layer or bedrock weathering crust is relatively deep, the near-surface area may lack pore water due to drought, resulting in low humidity in the soil pit and an increase in the resistivity of the shallow electrode, thus affecting the observation data. Burying the shallow electrode by drilling method can make the shallow electrode surrounded by sufficient pore water to ensure the accuracy of the observation data. By wrapping the shallow electrode with the backfill material or pore water, it can ensure that the shallow electrode is placed in the diffusion electric field, and the backfill material or the solid sealing of the drill hole can fix and protect the shallow electrode and improve the stability of the shallow electrode.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be pointed out that, for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims (10)

1. A shallow electrode construction method for long-term observation of a fracture electric field is characterized by comprising the following steps:

selecting at least two shallow electrode embedding points in a fourth loose layer or a bedrock weathering crust of a broken disc on the same side of a broken zone;

when the depth of the fourth series of unconsolidated formations or bedrock weathering crust is smaller than the preset depth, excavating a soil pit at the shallow electrode embedding point, placing the shallow electrode in the soil pit, backfilling and compacting the soil pit, wherein backfilling substances for backfilling the soil pit are soil or coke;

and when the depth of the fourth series of unconsolidated formations or bedrock weathering crust is greater than the preset depth, drilling by a drill bit with the diameter greater than that of the shallow electrode, wherein the drilling depth is below the annual average pore water submergence surface, placing the shallow electrode at the bottom of a drilling hole, and sealing the hole opening by a protective material.

2. The method of claim 1, wherein a common electrode is disposed in the fracture and fragmentation zone, and wherein the step of selecting at least two shallow electrode burial points comprises the steps of: selecting at least two shallow electrode embedding points at the position which is on the same vertical plane with the common electrode, is vertical to the trend of the fracture zone and is equal to the projection distance of the common electrode on the ground surface;

and placing the shallow electrodes in the soil pits, or placing the shallow electrodes at the bottoms of the drilled holes, and enabling each shallow electrode to be arranged at the same depth.

3. The method of claim 1, wherein placing the shallow electrode in the earth pit or into the bottom of a drilled borehole comprises: placing the shallow electrode vertically in the earth pit or the borehole.

4. The method of claim 1, comprising, prior to sealing the drilling opening with a protective material, the steps of: and backfilling the drilled hole, wherein the backfilling material for backfilling the drilled hole is soil or coke.

5. The method of claim 4, comprising, in backfilling the earth pit or the borehole with the coke, the steps of: and grinding the coke into granules with fine particle size, and backfilling.

6. The method of claim 1, wherein after backfilling and compacting the pit, comprising the steps of: and sealing the surface of the soil pit by cement or asphalt.

7. The method of claim 1, wherein: when the depth of the fourth series unconsolidated formation or bedrock weathering crust is less than the preset depth, the shallow electrode is a polarized electrode; the shallow electrode is a non-polarizing electrode when the depth of the fourth series unconsolidated layer or bedrock weathering crust is greater than a predetermined depth.

8. The method of claim 7, wherein the non-polarizing electrode is a solid long cylindrical lead rod having a thickness;

placing said non-polarized electrode in front of the bottom of a drilled borehole, comprising the steps of: and passivating the surface of the non-polarized electrode by using dilute sulfuric acid.

9. The method of claim 1, wherein: the drilling depth is up to above the fresh bedrock face.

10. The method of claim 1, the shallow electrode having a cable attached thereto, comprising the steps of: a PVC pipe or a stainless steel pipe is sleeved on the cable; and burying the cable while burying the shallow electrode, so that the PVC pipe or the stainless steel pipe is vertically placed at the pithead or the orifice, and the part of the PVC pipe or the stainless steel pipe is positioned outside the soil pit or the drilled hole.

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