Fine particle tailings sand layer exploration borehole hole forming control method

Abstract

The application provides a fine-grained tailings soil layer exploration drilling hole forming control method. The control method is mainly for the control in the drilling exploration process of the soil layer formed by the accumulation of fine-grained tailings, specifically, before the initial water level is found, dry drilling is performed, after water is found, casing is used for wall protection, after the water level observation is stable, slurry wall protection drilling is used; when the particle size composition of the accumulation is mainly tail silt and tail silt soil, ordinary bentonite mud slurry is used for slurry wall protection drilling; when the particle size composition of the accumulation is mainly tail silty clay and tail clay, the slurry wall protection uses the Kalil chemical mud slurry; in the drilling process, for the accumulation body within the hole depth of 60m, the drilling speed is not higher than 285-295r / min; for the accumulation body with the depth of 60-120m, low-speed drilling is performed at 142r / min, and the drilling pressure is adjusted in real time. Through the selection of different particle size wall protection methods and the quantitative control of key operation procedures, the drilling and coring efficiency can be greatly improved, and the hole accidents and production costs can be reduced.

Description

Technical Field

[0001] This invention relates to the field of mine tailings dump exploration, specifically a borehole control method for drilling in fine-grained tailings sand layers. Background Technology

[0002] In recent years, with the rapid development of the national economy, the demand for mineral products has increased, the scale of mining development has become larger and larger, and the particle size of mining and beneficiation has become finer, resulting in a large amount of fine particulate solid waste being dumped in the reservoir area. In order to grasp and verify its stability, in accordance with the regulations on mine safety management, it is necessary to conduct dam body exploration and evaluation regularly.

[0003] Existing geological exploration methods primarily rely on drilling. Drilling rigs are used to obtain physical parameters of the underground rock strata for geological analysis and to generate exploration results. However, due to the complex sedimentary characteristics of tailings deposits, poor regularity of interbedded sand and soil, generally heavy intergranular material, poor consolidation, and high water content making them prone to disturbance, drilling exploration in tailings pond areas is more challenging than in typical fluvial sedimentary areas. Drilling exploration typically relies heavily on personnel experience and operational skills. However, engineering practice shows that when the deposit thickness exceeds 30m, inadequate drilling procedures and improper borehole protection methods can easily lead to borehole narrowing and collapse; beyond 60m, risks of drill bit entrapment and drill bit seizing are high; and beyond 100m, drilling becomes difficult or "borrowed holes" may be abandoned, causing significant difficulties for on-site operations, especially in deeper sections beyond 60m. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a borehole control method for exploration of fine-grained tailings sand layers. The control method, through the selection of different particle size wall protection methods and the quantitative control of key operation procedures, can significantly improve drilling and coring efficiency, reduce borehole accidents and production costs, and effectively alleviate the current situation of no regulations in the field of fine-grained deep borehole exploration in the mining tailings dam sector. It has strong practicality.

[0005] To achieve the above-mentioned technical objectives, this invention provides a method for controlling borehole formation in the exploration of fine-grained tailings sand layers. This method primarily targets the control of borehole formation during exploration of soil layers composed of fine-grained tailings sand, and is particularly suitable for tailings piles containing fine, silty, and colloidal particles with particle sizes between and less than 0.075 mm. The method specifically includes the following steps:

[0006] S1. After the drilling rig is in place and ready, drilling will begin. Before the initial water level is reached, dry drilling will be carried out using the drilling rig. After water is reached, casing will be used for wall protection. The casing will be inserted 1-3m below the initial water level. After standing for 25-35 minutes, the water level will be observed to stabilize. The total depth of the casing should not exceed 65m to avoid excessive side friction and difficulty in pulling it out smoothly when the hole is closed.

[0007] S2. After stabilizing the water level, switch to slurry drilling for wall protection. When the sediment particle size distribution is mainly tailings silt and tailings clay, ordinary bentonite mud is used for slurry drilling for wall protection. Ordinary bentonite mud is prepared from bentonite powder, which is a relatively abundant supply of calcium-based bentonite. When the sediment particle size distribution is mainly tailings silty clay and tailings clay, CLEAR chemical mud is used for slurry drilling for wall protection. CLEAR chemical mud is either a directly purchased finished product or prepared from purchased CLEAR chemical mud powder. CLEAR chemical mud has a large molecular weight and strong adsorption and cementing capacity, which allows drill cuttings to settle quickly. Compared to bentonite mud, it is more suitable for wall protection in cohesive soil layers.

[0008] S3. During drilling, for Class III and lower embankments with a depth of less than 60m, the drilling speed should not exceed 285-295 r / min (level 2); for Class II and higher embankments with a depth of 60-120m, drilling should be carried out at a low speed of 142 r / min (level 1); the vertical shaft feed pressure at each depth should be calculated and applied according to formula ①, and adjusted in real time. P=0.0095 rh-0.07L ①, Where: P - drilling pressure, unit kPa; r - tailings layer unit weight, unit kN / m 3 h - Drilling depth, in meters; L - Drill pipe length, in meters;

[0009] S4. During the drilling process, when the hole depth is within 60m, core sampling and in-situ testing shall be carried out at intervals of 1.50m, and the advance per cycle shall not exceed 1.5m; when the hole depth is greater than 60m, core sampling and in-situ testing shall be carried out at intervals of 3m, and the advance per cycle shall not exceed 1.0m.

[0010] S5. If grout leakage occurs during drilling, immediately stop the machine, lift the drill, pour in a sufficient amount of air-dried clay balls into the hole, compact them by reversing the drill bit to seal the leak, and then continue drilling. The diameter of the air-dried clay balls can be 20mm.

[0011] A further technical solution of the present invention: The amount of air-dried clay balls added in step S5 is calculated according to the following formula: G=KrAh ②, In the above formula, G represents the amount of air-dried clay balls added, in kg; r represents the density of the air-dried clay balls, in kN / m³. 3 A - Drilling area, in m² 2 h - length of the sealing section per cycle, in meters; K - backfill coefficient.

[0012] The preferred technical solution of the present invention is as follows: In step S1, fine-grained tailings sand refers to tailings fine sand, tailings silt, tailings silt soil and tailings silty clay with a discharge sediment particle size between and less than 0.075 mm.

[0013] The preferred technical solution of this invention is as follows: When using ordinary bentonite mud in step S2, the mud concentration is 75-100 kg / m³ when the drilling depth is within 60 m. 3 Simultaneously add 0.50–1.0 kg of hydroxypropyl methylcellulose and 1.75–3.0 kg of soda ash; when the drilling depth is greater than 60 m and less than 120 m, the mud concentration is 125–150 kg / m. 3 Simultaneously, 1.25–1.5 kg of hydroxypropyl methylcellulose and 3.5–4.25 kg of soda ash are added per cubic meter of mud. The amount of hydroxypropyl methylcellulose and soda ash added is controlled to ensure that the pH value of the slurry is not lower than 8, the viscosity is not lower than 21, and the sediment at the bottom of the borehole does not exceed 15 cm. The hydroxypropyl methylcellulose is a cold water-soluble type. When the viscosity value of the bentonite slurry is low, it can be added to quickly increase the viscosity value of the bentonite slurry and reduce water loss. The soda ash (caustic soda) has the functions of adjusting the pH value, enhancing dispersibility, and improving fluidity.

[0014] When using Kelier chemical mud in step S2, the mud is prepared using Kelier chemical mud powder, with a concentration of 0.30–0.40 kg / m³. 3 The pH value is adjusted by adding 0.20-0.30 kg of caustic soda per cubic meter of mud, controlling the pH value of the slurry to be no lower than 9, the viscosity to be no lower than 19, and the sediment at the bottom of the hole to be no more than 10 cm.

[0015] The preferred technical solution of the present invention is as follows: In step S4, ensure that the thickness of the floating scum at the bottom of the hole is not greater than 10cm, and when taking the core, use a split ring cutter for core taking.

[0016] The preferred technical solution of this invention is as follows: The drilling equipment is an XY-150 or XY-200 high-speed hydraulic drilling rig, with two S1105 high-efficiency diesel engines on its base to ensure sufficient power output for the traction and rotation systems; the drill rod specification is Ф50x6.5mm, which increases the transmission torque compared to a typical Φ42mm drill rod, reducing the risk of rod disengagement; the high-speed hydraulic drilling rig frame is available in both crawler and tripod types, with the crawler type suitable for dam areas and the tripod type being more suitable for riverbanks facing water due to its lighter weight; the casing diameter is selected according to the borehole diameter, using Ф127mm, Ф108mm, and Ф89mm, and a reasonable combination of two or three diameters is adopted according to the water level and burial depth; the bottom 1-3m section of the casing is designed as a perforated pipe, using 150-200g / m³ steel. 2 The non-woven geotextile wrapping facilitates continuous monitoring of the water level using an electronic water level gauge.

[0017] The preferred technical solution of this invention is as follows: When performing drilling pressure calculations for preliminary borehole exploration, the unit weight of the tailings layer is taken based on existing reports. When no data is available for reference, the unit weight of the tailings layer in various states is taken as follows: The unit weight of the loose tailings layer is taken as 16 kN / m³. 3 In a slightly denser state, the strength is taken as 17 kN / m. 3 In medium-dense conditions, the value is taken as 18.5 kN / m. 3 20 kN / m in dense state 3 The tailings silty clay was taken as 18.5 kN / m. 3 The pore pressure was adjusted after the actual density of each layer was determined by on-site testing.

[0018] The preferred technical solution of this invention is as follows: During the drilling process, each drill should be completed in one go without interruption. When encountering resistance during drilling, the drill should not be released abruptly. When encountering jamming during drilling, it should not be pulled forcefully. Instead, the drill should be released when the resistance is above and lifted when the resistance is below, and the drill should be moved up and down in the direction of rotation to release the jam.

[0019] The preferred technical solution of the present invention is as follows: during the drilling process, the drum lifting speed is 0.5 to 1.0 m / s when the drill is started, and the core tube is quickly supported when it is brought to the hole opening to prevent negative pressure from forming at the bottom of the drill bit.

[0020] The preferred technical solution of this invention is as follows: the density r of the air-dried clay ball used for sealing leaks is 1.45 × 10⁻⁶. 3 kg / m 3 The backfill coefficient K is set to 2.0.

[0021] In this invention, the water used to prepare the slurry can be recycled water from the mining area after being treated by a recovery pumping station, as long as the indicators such as fluoride, sulfide, thallium, lead, and chromium meet the standards; the specific gravity of the slurry is tested using a hydrometer, the viscosity is measured using a Marshall funnel meter, the pH value is tested using test paper, and the thickness of the sediment is calculated using the plumb bob method.

[0022] The present invention has the following effects:

[0023] This invention employs different mud slurry methods for wall protection based on different filler layers during drilling, enhancing the wall protection effect. It also utilizes different rotation speeds based on different hole depths to prevent significant vibration from high-speed rotation, which could excessively disturb the surrounding soil and rock, ensuring that the tailings sand is appropriately cut and minimizing disturbance to the hole wall. Furthermore, the drilling pressure at each depth is calculated and adjusted in real-time based on the drilling depth to avoid problems such as hole collapse due to excessive drilling pressure. Through the selection of different particle size wall protection methods and the quantitative control of key operational procedures, this invention can significantly improve drilling and coring efficiency, reduce in-hole accidents and production costs, and effectively alleviate the current lack of regulations in fine-grained deep-hole exploration in the field of mine tailings dams, demonstrating strong practicality. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the construction process of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments; the technical solutions shown in the embodiments are specific solutions of the embodiments of the present invention and are not intended to limit the scope of the claimed invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In the following embodiments, the drilling equipment is an XY-150 or XY-200 high-speed hydraulic drilling rig, with drill rod specifications of Ф50x6.5mm; the casing diameter is selected according to the borehole diameter, using Ф127mm, Ф108mm, or Ф89mm, and a reasonable combination of two or three diameters is adopted according to the water level and burial depth; the bottom 1-3m section of the protective casing is set as a perforated pipe, and uses 150-200g / m 2 Wrapped with non-woven geotextile. When pulling up the drill string, the drum lifting speed is 0.5 to 1.0 m / s. When the core tube is brought up to the borehole opening, it is quickly supported to prevent negative pressure from forming at the bottom of the drill bit.

[0027] In the following embodiments, the vertical shaft feed pressure at each depth is calculated and applied according to formula ①, and adjusted in real time: P=0.0095 rh-0.07L ①, Where: P - drilling pressure, unit kPa; r - tailings layer unit weight, unit kN / m 3 h - Drilling depth, in meters; L - Drill pipe length, in meters;

[0028] The amount of air-dried clay balls to be added is calculated using the following formula: G=KrAh ②, In the above formula, G represents the amount of air-dried clay balls added, in kg; r represents the density of the air-dried clay balls, in kN / m³. 3 A - Drilling area, in m² 2 h - length of the sealing section per cycle, in meters; K - backfill coefficient.

[0029] Implementation 1: For borehole Z9# in a reservoir dam area, the drilling area mainly consists of tailings silty sand interbedded with tailings silt, with a designed borehole depth of 60.0m. During the drilling process, the method described in this invention was used for borehole control of Z9#, as follows:

[0030] S1. Drilling rig in position and drilling; first, control the drilling speed at 285 (295) r / min (2nd gear) to avoid the high-speed rotation of the machine body causing the sand and soil on the hole wall to collapse; the drilling pressure is calculated using the above formula ① and applied by reading the middle or whole scale of the bottom pressure indicator. Since the dial scale value is an integer, it is difficult to read the decimal. On site, it is generally convenient to read the middle or whole scale value for control (the final actual value in the following examples is taken according to this rule). The calculation results and the actual drilling pressure value are shown in Table 1 below; the advance per cycle is controlled at a interval of 1.50m, and the drilling speed is controlled at 1.0m / s.

[0031] Table 1 shows the drilling pressure for different hole depths below 10m in the first implementation.

[0032]

[0033] S2. When the borehole reaches 9.2m, the water level is initially observed. A single layer of Ф127mm casing is installed for wall protection. The casing length is 10.5m, and the bottom 1.0m is a perforated pipe. After standing for 30 minutes, the stable water level is observed.

[0034] S3. After stabilizing the water level, continue drilling using ordinary bentonite slurry for wall protection; the initial slurry concentration is based on past experience, using 50 kg / m³ of bentonite powder. 3 At the same time, add 1 kg / m³ of soda ash. 3 The initial configuration was unsatisfactory, with severe sedimentation requiring repeated hole washing. It was then replaced with bentonite powder at 75 kg / m³. 3 Soda ash 2Kg / m 3 At the same time, 0.5 g / m³ of hydroxypropyl methylcellulose was added. 3 The drilling progress gradually returned to normal. After reaching a depth of 30m, the sand content of the drilling mud gradually increased again. To ensure the quality of sampling and testing at 1.5m intervals and to avoid borehole collapse during prolonged operation, the drilling mud concentration was adjusted to 100 kg / m³ of bentonite powder. 3 3.0 kg / m³ of soda ash 3 Hydroxypropyl methylcellulose 1.0 kg / m 3 After adjustment, the slurry return was normal. The drill bit passed through the tailings layer at 57.4m and entered the lower natural soil layer. The drilling speed was controlled at 285 (295) r / min (level 2) throughout the process. The drilling pressure was calculated using the above formula ① and applied by reading the pressure indicator at the middle or whole scale. Since the dial scale value is an integer and the decimal is difficult to read, it is generally easier to control by reading the middle or whole scale value on site (the final actual value in the following examples is taken according to this rule). The calculation results and the actual drilling pressure values ​​are shown in Table 2 below. The drilling speed was controlled at 1.0m / s.

[0035] Table 2 shows the drilling pressure for different hole depths from 10 to 60 m in Example 1.

[0036]

[0037] The performance of the aforementioned wall-protecting mud was tested, and the test results are shown in Table 3 below.

[0038] Table 3 Performance indicators of the wall-protecting mud in Example 1

[0039]

[0040] S4. For minor grout leakage at the top, promptly seal with air-dried clay balls. The amount of clay balls used is calculated according to formula ② above, and the calculation results are shown in Table 4 below:

[0041] Table 4 shows the amount of clay balls used for backfilling in Example 1.

[0042]

[0043] Example 2: Hole Z14# in a reservoir dam, mainly composed of tailings silty sand interbedded with tailings silt, with a designed depth of 95m. During the drilling process, the method described in this invention was used for drilling control of hole Z9#, as follows:

[0044] S1. Drilling rig positioning and hole drilling. The procedures before the initial water level is reached are the same as step S1 in Example 1.

[0045] At an initial water level of 2.12.6m, casing drilling was adopted, with a single layer of Ф127mm casing for wall protection. The casing length was 13.5m, and the bottom 1m was a perforated casing. After standing for 30 minutes, the stable water level was observed.

[0046] S3. After stabilizing the water level, continue drilling using bentonite slurry for wall protection. The process for the 13–65m depth section is the same as step 3 in S1 of Example 1; after 65m, to ensure sampling and testing quality at 1.0m intervals and to avoid borehole collapse during low-speed drilling, the slurry concentration is set at 125 kg / m³ of bentonite powder. 3 Soda ash 4Kg / m 3 Hydroxypropyl methylcellulose 1.25 kg / m 3 Adjustments were made, and the mud return was normal. The drill bit passed through the tailings layer at 94.3m and entered the lower natural soil layer. The drilling speed was controlled at 142 r / min (level 1) throughout the entire process. The drilling pressure was estimated using formula ①, as shown in Table 5, and the actual applied value was obtained from the bottom hole pressure indicator. The actual value was taken according to the rules in Example 1. The drilling speed was controlled at 0.5 m / s. The mud performance indicators are shown in Table 6 below.

[0047] Table 5. Drill pressure for different hole depths (60m to 95m) in Implementation 2

[0048]

[0049] Table 6 Performance Indicators of the Wall Protection Slurry in Implementation 2

[0050]

[0051] S4. Immediately seal any abnormal depths of slurry return in the upper part. Estimate the amount of clay balls using formula ② and then apply them as shown in Table 7.

[0052] Table 7 shows the amount of clay balls used for backfilling in Example 2.

[0053]

[0054] Implementation 3: Hole Z19# in a sedimentary beach of a reservoir area mainly consists of alternating layers of tailings silt, tailings silt, and tailings silty clay, with a designed depth of 31m. During the drilling process, the method described in this invention was used for borehole control of hole Z9#, as follows:

[0055] S1. Position the drilling rig (tripod type) and begin drilling. Before initially encountering the water level, control the drilling speed at 142 r / min (level 1). Calculate the drilling pressure using formula ① and apply it in conjunction with the actual value obtained from the bottom hole pressure indicator. The actual value is taken according to the rules in Example 1. The calculated and actual pressure values ​​are shown in Table 7, and the actual value is also taken according to the rules in Example 1. Control the drill pulling speed at 0.5 m / s. Control the advance per pass at 1.50 m intervals, and control the drill pulling speed at 1.0 m / s.

[0056] Table 7. Drill pressure for different hole depths from 1m to 5m in Implementation 3

[0057]

[0058] When the initial water level was reached at S2.3.2m, casing drilling was adopted, with a single layer of Ф127mm casing for wall protection. The casing length was 4.5m, and the bottom 1.5m was a perforated pipe. After standing for 60 minutes, the stable water level was observed.

[0059] S3. With the water level stabilized, continue drilling using Kelier chemical drilling mud for wall support. Initially, follow the instructions to apply 0.1 kg / m of Kelier chemical drilling mud dry powder. 3 Soda ash is 0.05 kg / m³. 3 When added to water, the wall-protecting effect is not significantly better than that of bentonite slurry, and slight shrinkage and drill bit sticking occur. The dry powder concentration was adjusted to 0.35 kg / m³. 3 The soda ash concentration is 0.25 kg / m³. 3The drilling progressed smoothly, reaching 30.3m through the tailings layer and entering the lower natural soil layer. The drilling speed was controlled at 142 r / min (level 1) throughout the process. The drilling pressure was calculated using formula ① and applied based on the actual value obtained from the bottom hole pressure indicator. The actual value was taken according to the rules in Example 1, and the calculated and actual pressure values ​​are shown in Table 8. The hoisting speed was controlled at 1.0 m / s. The mud performance indicators are shown in Table 9 below.

[0060] Table 8. Drill pressure for different hole depths from 5m to 30m in Implementation 3

[0061]

[0062] Table 9 Performance indicators of the wall-supporting mud in Implementation 3

[0063]

[0064] Through the operation of the three embodiments described above, it can be seen that compared with the current operation, after adopting the new process for comprehensive control, the operation time for a 60m deep hole is shortened from 6-8.5 days to 3-3.5 days, and the problem of difficult exploration of 60-120m deep holes is overcome, significantly reducing the risks of high cost and easy drill bit burial in deep holes. It has been tested and applied in the exploration projects of fine-grained tailings sand and soil layers in multiple tailings pond areas in Hubei and Jiangxi, and has a very strong practical effect.

[0065] In the three embodiments described above, different mud slurry is used for wall protection according to different filler layers during the drilling process. By selecting different particle size wall protection methods and quantitatively controlling key operation procedures, drilling and core sampling efficiency is greatly improved and in-hole accidents are reduced.

Claims

1. A method for controlling borehole formation in exploration of fine-grained tailings sand layers, characterized in that: The control method mainly targets the control during drilling exploration of soil layers formed by fine-grained tailings sand and soil deposits, and specifically includes the following steps: S1. After the drilling rig is in place and ready, drilling will begin. Before the initial water level is reached, dry drilling will be carried out using the drilling rig. After water is reached, casing will be used for wall protection. The casing will be inserted 1-3m below the initial water level. After standing for 25-35 minutes, the water level will be stabilized and observed. S2. After stabilizing the water level, switch to slurry wall drilling; when the particle size composition of the deposit is mainly tailings silt and tailings soil, ordinary bentonite mud is used for slurry wall drilling; when the particle size composition of the deposit is mainly tailings silty clay and tailings clay, Kelier chemical mud is used for slurry wall drilling. S3. During drilling, for Class III and lower embankments with a depth of less than 60m, the drilling speed should not exceed 285-295 r / min; for Class II and higher embankments with a depth of 60-120m, drilling should be carried out at a low speed of 142 r / min; the vertical shaft feed drilling pressure at each depth should be calculated and applied according to formula ①, and adjusted in real time. P=0.0095 rh-0.07L ① Where: P - drilling pressure, unit kPa; r - tailings layer unit weight, unit kN / m 3 ; h - Drilling depth, in meters; L - Drill pipe length, in meters; S4. During the drilling process, when the hole depth is within 60m, core sampling and in-situ testing shall be carried out at intervals of 1.50m, and the advance per cycle shall not exceed 1.5m; when the hole depth is greater than 60m, core sampling and in-situ testing shall be carried out at intervals of 3m, and the advance per cycle shall not exceed 1.0m. S5. If grout leakage occurs during drilling, immediately stop the machine, lift the drill, pour in a sufficient amount of air-dried clay balls into the hole, compact them by reversing the drill bit to seal the leak, and then continue drilling.

2. The method for controlling borehole formation in fine-grained tailings sandy soil exploration according to claim 1, characterized in that: The amount of air-dried clay balls added in step S5 is calculated according to the following formula: G=KrAh ② In the above formula, G represents the amount of air-dried clay balls added, in kg; r represents the density of the air-dried clay balls, in kN / m³. 3 ; A - Drilling area, in meters 2 h - length of the sealing section per cycle, in meters; K - backfill coefficient.

3. The method for controlling borehole formation in fine-grained tailings sand layer exploration according to claim 1, characterized in that: In step S1, fine-grained tailings sand refers to tailings fine sand, tailings silt, tailings silt, and tailings silty clay with a discharge sediment particle size between and less than 0.075 mm.

4. The borehole formation control method for fine-grained tailings sand layer exploration according to claim 1, characterized in that: When using ordinary bentonite mud in step S2, the mud concentration should be 75–100 kg / m³ when the borehole depth is within 60 m. 3 Simultaneously, 0.50–1.0 kg of hydroxypropyl methylcellulose and 1.75–3.0 kg of soda ash are added per cubic meter of drilling mud; when the drilling depth is greater than 60 m and less than 120 m, the mud concentration is 125–150 kg / m³. 3 At the same time, add 1.25-1.5 kg of hydroxypropyl methylcellulose and 3.5-4.25 kg of soda ash; the amount of hydroxypropyl methylcellulose and soda ash added should be controlled so that the pH value of the slurry is not lower than 8, the viscosity is not lower than 21, and the sediment at the bottom of the hole is not more than 15 cm. When using Kelier chemical mud in step S2, the mud is prepared using Kelier chemical mud powder, with a concentration of 0.30–0.40 kg / m³. 3 The pH value is adjusted by adding 0.20-0.30 kg of caustic soda per cubic meter of mud, controlling the pH value of the slurry to be no lower than 9, the viscosity to be no lower than 19, and the sediment at the bottom of the hole to be no more than 10 cm.

5. The method for controlling borehole formation in fine-grained tailings sandy soil exploration according to claim 1, characterized in that: In step S4, ensure that the thickness of the scum at the bottom of the hole is no more than 10cm. When core sampling, use a split-ring cutter for core sampling.

6. The method for controlling borehole formation in fine-grained tailings sand layer exploration according to claim 1, characterized in that: The drilling equipment is an XY-150 or XY-200 high-speed hydraulic drilling rig, with drill rod specifications of Ф50x6.5mm; the casing diameter is selected according to the borehole diameter, using Ф127mm, Ф108mm, or Ф89mm, and a reasonable combination of two or three diameters is adopted according to the water level and burial depth; the bottom 1-3m section of the protective casing is set as a perforated pipe, and uses 150-200g / m 2 Wrapped with non-woven geotextile.

7. The method for controlling borehole formation in fine-grained tailings sand layer exploration according to claim 1, characterized in that: When performing drilling pressure calculations for preliminary borehole exploration, the unit weight of the tailings layer is taken based on existing reports. In the absence of reference data, the unit weight of tailings layers in various states is taken as follows: For loose tailings layers, the unit weight is taken as 16 kN / m³. 3 In a slightly denser state, the strength is taken as 17 kN / m. 3 In medium-dense conditions, the value is taken as 18.5 kN / m. 3 20 kN / m in dense state 3 The tailings silty clay was taken as 18.5 kN / m. 3 The pore pressure was adjusted after the actual density of each layer was determined by on-site testing.

8. The borehole control method for exploration of fine-grained tailings sand layers according to claim 1, characterized in that: During drilling, drill to the bottom in one go without stopping. If you encounter resistance while drilling down, do not release the drill bit abruptly. If you encounter a stuck hole when lifting the drill bit, do not pull it forcefully. Instead, release the drill bit when it encounters resistance at the top and lift it when it encounters resistance at the bottom, and move it up and down in the direction of rotation to release the stuck hole.

9. The borehole formation control method for fine-grained tailings sand layer exploration according to claim 1, characterized in that: During drilling, the drum lifting speed is 0.5 to 1.0 m / s when starting the drill. When the core tube is brought up to the borehole opening, it is quickly supported to prevent negative pressure from forming at the bottom of the drill bit.

10. The method for controlling borehole formation in fine-grained tailings sand layer exploration according to claim 2, characterized in that: The density r of the air-dried clay balls used for sealing leaks is taken as 1.45 × 10⁻⁶. 3 kg / m 3 The backfill coefficient K is set to 2.0.

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