A method applicable to the prevention and control of ground karst collapse

Abstract

The present invention discloses a method suitable for preventing and controlling ground karst collapse, which comprises the following steps: a. Determine the horizontal curtain range and curtain height; b. Set curtain lines at a specified line distance within the horizontal curtain range, and arrange grouting holes on each curtain line; c. The grouting holes on each curtain line are constructed in three sequences. The first-sequence holes are evenly distributed, the second-sequence holes are centered and arranged between adjacent first-sequence holes, and the third-sequence holes are centered and arranged between adjacent first-sequence holes and second-sequence holes; d. When the grouting hole drills to the curtain roof, lower a geological casing, and fill and consolidate the gap between the casing and the borehole wall with cement slurry, and conduct a water pressure test to check the water-stop effect; e. The grouting hole is drilled and grouted in sections; f. Repeat steps d and e to complete the construction of all grouting holes within the horizontal curtain range. Aiming at the root cause of karst collapse, the problem of preventing and controlling collapse is fundamentally solved. Constructing vertical grouting holes on the ground is simple in construction, small in investment, and high in water-blocking rate. The suspended horizontal curtain saves the investment cost to the greatest extent.

Description

Technical Field

[0001] The present invention relates to the field of geological disaster prevention and control, and particularly to a method suitable for preventing and controlling ground karst collapse. Background Art

[0002] Karst is particularly developed in limestone strata. When extracting underground water resources and ore resources, as the groundwater level drops below the bedrock surface or surface water infiltration changes the geotechnical stress balance, the soil layer gradually collapses from bottom to top, forming hidden soil caves, and then continues to collapse, eventually leading to surface subsidence.

[0003] To prevent surface subsidence during underground resource extraction, the prevention and control methods of high-pressure jet grouting piles and drilling grouting reinforcement are usually adopted.

[0004] High-pressure jet grouting piles are an effective method for strengthening soft soil layers. It cuts cohesive soil or sandy soil layers through high-pressure water, and cement slurry fills the voids formed by high-pressure water cutting to form a cement slurry cementation body, which can greatly improve the mechanical properties of the Quaternary soft layer and keep itself stable without collapse, but the construction cost is high.

[0005] The drilling grouting reinforcement method is to fill and reinforce the Quaternary system and the underlying karst-developed rock stratum in the subsidence area by constructing a certain number of grouting holes on the ground surface. However, the traditional grouting method has a poor reinforcement effect on the Quaternary system, and the fissures in limestone have good connectivity, often causing a large amount of waste of slurry and increasing the treatment cost. Summary of the Invention

[0006] The purpose of the present invention is to provide a prevention and control method that can fundamentally prevent ground karst collapse in view of the deficiencies of the prior art.

[0007] The prevention and control method suitable for ground karst collapse provided by the present invention includes the following steps:

[0008] a. Determine the horizontal curtain range and curtain height;

[0009] b. Set curtain lines at a specified line distance within the horizontal curtain range, and arrange grouting holes on each curtain line;

[0010] c. The grouting holes on each curtain line are constructed in three sequences. The first-sequence holes are evenly distributed, the second-sequence holes are centered and arranged between adjacent first-sequence holes, and the third-sequence holes are centered and arranged between adjacent first-sequence holes and second-sequence holes;

[0011] d. When the grouting hole drills to the curtain roof, lower a geological casing, and fill and consolidate the gap between the casing and the borehole wall with cement slurry, and conduct a water pressure test to check the water-stop effect;

[0012] e. Drill and grout the grouting hole in sections;

[0013] f. Repeat steps d and e to complete the construction process of all grouting holes within the horizontal curtain range.

[0014] When the above method is implemented, in step (a), the area to be treated that has experienced historical collapses is determined as the horizontal curtain range. The starting position of the curtain is the bedrock surface, and the calculation formula for the curtain height H is:

[0015]

[0016] In the above formula, M is the thickness of the Quaternary system above the bedrock surface, with the unit of m; K is the safety factor; P is the hydrostatic pressure borne by the roof of the curtain, with the unit of mPa; K P is the shear strength of the Quaternary system, with the unit of mPa. When the Quaternary system contains multiple layers of rock and soil, it is determined by the weighted calculation method.

[0017] When the above method is implemented, the value of K in the above calculation formula is 2 - 5.

[0018] When the above method is implemented, when the calculated value of the curtain height is less than 20m, it is taken as 20m; when it is greater than 20m, it is taken as the calculated value.

[0019] When the above method is implemented, in step (b), the curtain lines are set at a line spacing of 8 - 10m within the horizontal curtain range on the ground surface. Grouting holes are arranged at a hole spacing of 8 - 10m on each curtain line and are staggered in a plum blossom shape.

[0020] When the above method is implemented, in step (c), the spacing between the first - order holes is 32 - 40m.

[0021] When the above method is implemented, in step (d), the opening diameter of the grouting hole is not less than φ110mm, the final hole diameter is not less than φ91mm, the water - solid ratio of the cement slurry is 0.5:1, and the pressure water test pressure is 2 times the hydrostatic pressure.

[0022] When the above method is implemented, in step (e), the requirements for segmenting the grouting holes are considered in the following three cases:

[0023] 1) In the karst cave development area, all the flushing fluid is lost, and the grouting section length is 5 - 10m;

[0024] 2) When encountering a karst cave larger than 1m, stop drilling and start grouting;

[0025] 3) In the section where karst fissures are not developed, that is, part or all of the drilling flushing fluid returns, and the lithology is intact, the section length does not exceed 20m.

[0026] When the above method is implemented, in step (e), the grouting material is cement - clay slurry, the water - solid ratio is 1.2:1 - 0.8:1, and the admixture of the cement - clay slurry is 2% - 5% of the solid material quality.

[0027] When the above method is implemented, in step (e), when the last grouting section reveals a karst cave and the height of the bottom plate of the karst cave is lower than the bottom plate of the horizontal curtain, grouting shall be carried out according to the following steps:

[0028] 1), First, gravel with a particle size of 5%-10% of the borehole diameter is put into the hole mouth. During the putting process, water is injected through a high-pressure water pump to transport the gravel and sand-gravel to the bottom of the borehole and fill it to a height of 1-2 m above the bottom plate of the horizontal curtain;

[0029] 2), High-concentration cement-clay slurry is used to grout in a self-flowing manner until the slurry fills the hole mouth;

[0030] 3), After waiting for 8-12 hours of setting, the hole is reamed to the position of the filling height of the gravel and sand-gravel;

[0031] 4), Pressurized grouting. On the premise of ensuring that the slurry does not spread into the karst cave in large quantities, high-pressure grouting of cement-clay slurry is carried out for the fissures within the height of the horizontal curtain section to ensure the grouting effect.

[0032] The present invention is a new prevention and control method that constructs vertical grouting holes on the ground surface, grouts and fills the karst fissures at a certain height below the bedrock surface, and the slurry stone body is cemented with the rock mass to form an integral horizontal hanging curtain, blocking the vertical infiltration of the Quaternary pore water into the underground mining area, maintaining the stability of the Quaternary rock and soil mass, and preventing the ground karst collapse caused by underground resource mining. Compared with the prior art, the present invention has the following advantages: aiming at the root cause of karst collapse, fundamentally solving the problem of collapse prevention and control once and for all. Constructing vertical grouting holes on the ground surface, the construction is simple, the investment is small, and the water blocking rate is high. Using a suspended horizontal curtain, the investment cost is saved to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic plan view of the layout of horizontal curtain grouting holes in an embodiment of the present invention.

[0034] Figure 2 is Figure 1 The schematic sectional view of the layout of the grouting hole A-A in.

[0035] Figure 3 It is a schematic diagram of the grouting construction when the bottom plate of the horizontal curtain reveals a karst cave in this embodiment.

[0036] The marks shown in the figure and the corresponding component names are:

[0037] 1, Horizontal curtain range; 2, Curtain line; 3, First-order grouting hole; 4, Second-order grouting hole; 5, Third-order grouting hole; 6, Geological casing; 7, Curtain roof; 8, Curtain bottom plate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] From Figure 1 and Figure 2It can be seen that the method for preventing and controlling ground karst collapse disclosed in this embodiment includes the following steps:

[0039] a. Determine the horizontal curtain range 1 and the curtain height H

[0040] Determine the area to be treated where historical collapses occurred as the horizontal curtain range 1. The starting position of the horizontal curtain is the bedrock surface. The calculation formula for the curtain height H is:

[0041]

[0042] In the above formula, M is the thickness of the Quaternary system above the bedrock surface, with the unit of m; K is the safety factor, taking a value of 2 - 5; P is the hydrostatic pressure borne by the curtain roof 7, with the unit of mPa; K P is the shear strength of the Quaternary system, with the unit of mPa. When the Quaternary system contains multiple layers of rock and soil, it is determined by the weighted calculation method.

[0043] When the curtain height calculated by the above formula is less than 20m, take 20m; when it is greater than 20m, take the calculated value.

[0044] b. Within the horizontal curtain range 1, set the curtain lines 2 at a line distance of 10m ( Figure 1 L1 in Figure 1 ), and arrange the grouting holes on each curtain line 2 at a hole distance of 10m ( L2 in

[0045]

[0046] ), and arrange them in a staggered plum blossom pattern.

[0047] c. All the grouting holes on each curtain line 2 are constructed in three sequences. The spacing between the first - sequence holes 3 is 40m. The second - sequence holes 4 are arranged centrally between two adjacent first - sequence holes 3, and the third - sequence holes 5 are arranged centrally between an adjacent first - sequence hole 3 and a second - sequence hole 4.

[0048] d. When the grouting hole drills to the curtain roof 7, lower the geological casing 6, and fill and consolidate the gap between the casing and the borehole wall with cement slurry, and conduct a water pressure test to check the water - stopping effect.

[0049] The opening diameter of the grouting hole is not less than φ110mm, and the final hole diameter is not less than φ91mm. The water - solid ratio of the cement slurry is 0.5:1, and the water pressure test pressure is 2 times the hydrostatic pressure.

[0050] e. The grouting holes are drilled and grouted in sections. The section requirements are considered in the following three cases:

[0051] 1) In the karst cave development area, all the flushing fluid is lost, and the grouting section length is 5 - 10m;

[0050] 2) When encountering a karst cave larger than 1m, stop drilling immediately and conduct grouting;

[0051] 3) In the section where karst fissures are not well-developed, that is, part or all of the drilling flushing fluid returns to the surface, and the lithology is intact, and the section length does not exceed 20 m;

[0052] The grouting material is cement-clay slurry, the water-solid ratio is 1.2:1 to 0.8:1, and the admixture of the cement-clay slurry is 2% - 5% of the solid material quality.

[0053] f. When the last grouting section reveals a karst cave and the height of the bottom plate of the karst cave is lower than the bottom plate of the curtain by 8, the grouting is carried out according to the following steps:

[0054] 1) First, put gravel with a particle size of 5% - 10% of the borehole diameter into the hole mouth. During the putting process, water is injected through a high-pressure water pump to transport the gravel and sand-gravel to the bottom of the borehole and fill it to a height of 1 m above the bottom plate of the curtain;

[0055] 2) Use high-concentration cement-clay slurry to grout in a self-flowing manner until the hole mouth is filled with slurry;

[0056] 3) After waiting for 8 - 12 hours of setting, ream the hole to the position of the filling height of the gravel and sand-gravel;

[0057] 4) Grout under pressure. On the premise of ensuring that the slurry does not spread largely into the karst cave, inject high-pressure cement-clay slurry into the fissures within the height of the curtain section to ensure the grouting effect;

[0058] g. Repeat steps d, e, and f to complete the construction process of all grouting holes within the horizontal curtain range.

[0059] Generally speaking, the present invention is a new prevention and control method that constructs vertical grouting holes on the ground surface, grouts and fills the karst fissures at a certain height below the bedrock surface, and the slurry stone body and the rock mass are cemented to form an integral horizontal suspended curtain, blocking the vertical infiltration of the Quaternary pore water into the underground mining area, maintaining the stability of the Quaternary rock and soil body, and preventing the ground karst collapse caused by underground resource mining. Compared with the prior art, the present invention has the following advantages: aiming at the root cause of karst collapse, fundamentally solving the prevention and control problem of collapse once and for all. Constructing vertical grouting holes on the ground surface, with simple construction, small investment, and high water-blocking rate. Adopting a suspended horizontal curtain to save the investment cost to the greatest extent. In short, the present invention grouts and fills the karst cave fissures causing collapse through a certain number of grouting holes to form a horizontal water-proof curtain with a certain thickness, which can fundamentally solve the ground collapse problem and has a low treatment cost.

Claims

1. A method applicable to the prevention and control of ground karst collapse, characterized in that It includes the following steps: a. Determine the horizontal curtain range and curtain height; b. Set curtain lines within the horizontal curtain range at a specified line spacing, and arrange grouting holes on each curtain line; c. The grouting holes on each curtain line are constructed in three sequences. The first-sequence holes are evenly distributed, the second-sequence holes are centered and arranged between adjacent first-sequence holes, and the third-sequence holes are centered and arranged between adjacent first-sequence and second-sequence holes; d. When the grouting hole drills to the curtain roof, lower a geological casing, and fill and consolidate the gap between the casing and the borehole wall with cement slurry, and conduct a water pressure test to check the water-stopping effect; e. Drill and grout the grouting holes in sections; f. Repeat steps d and e to complete the construction process of all grouting holes within the horizontal curtain range; In step (a), the area to be treated where historical collapses occurred is determined as the horizontal curtain range. The starting position of the curtain is the bedrock surface. The calculation formula for the curtain height H is as follows: ; in the above formula, M is the thickness of the Quaternary system above the bedrock surface, with the unit of m; K is the safety factor; P is the hydrostatic pressure borne by the curtain roof, with the unit of MPa; is the shear strength of the Quaternary system, with the unit of MPa. When the Quaternary system contains multiple layers of rock and soil, it is determined by the weighted calculation method; When the calculated value of the curtain height is less than 20m, take 20m; when it is greater than 20m, take the calculated value; In step (e), the requirements for sectioning the grouting holes are considered according to the following three situations: 1) In the karst cave developed area, all the flushing fluid is lost, and the grouting section length is 5 - 10m; 2) When encountering a karst cave larger than 1m, stop drilling immediately and conduct grouting; 3) In the section where the karst fissures are not developed, that is, part or all of the flushing fluid of the drilling returns, and the lithology is complete, the section length does not exceed 20m; In step (e), when the last grouting section reveals a karst cave and the bottom height of the karst cave is lower than the bottom of the horizontal curtain, grouting is carried out according to the following steps: 1). First, put gravel with a particle size of 5% - 10% of the borehole diameter into the hole mouth. During the putting process, inject water through a high-pressure water pump to transport the gravel and sand-gravel to the bottom of the borehole and fill it to a height of 1 - 2m above the horizontal curtain bottom; 2). Use high-concentration cement-clay slurry to grout in a self-flowing manner until the slurry fills the hole mouth; 3). After waiting for 8 - 12 hours of setting, ream the hole to the position of the gravel and sand-gravel filling height; 4). Apply pressure grouting. On the premise of ensuring that the slurry does not spread largely into the karst cave, high-pressure grout the cement-clay slurry into the fissures within the height of the horizontal curtain section to ensure the grouting effect.

2. The method according to claim 1, wherein The value of K is 2 - 5.

3. The method according to claim 1, wherein In step (b), curtain lines are set within the surface horizontal curtain range at a line spacing of 8 - 10m, and grouting holes are arranged on each curtain line at a hole spacing of 8 - 10m and are staggered in a plum blossom shape.

4. The method according to claim 1, wherein In step (c), the spacing between the first-sequence holes is 32 - 40m.

5. The method according to claim 1, wherein In step (d), the opening diameter of the grouting hole is not less than φ110mm, the final hole diameter is not less than φ91mm, the water-solid ratio of the cement slurry is 0.5:1, and the water pressure test pressure is 2 times the hydrostatic pressure.

6. The method according to claim 1, characterized in that, In step (e), the grouting material is cement-clay slurry, the water-solid ratio is 1.2:1 - 0.8:1, and the cement-clay slurry admixture is 2% - 5% of the solid material quality.

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