Limestone stratum soft filling large karst cave combined grouting reinforcement method

Abstract

The invention belongs to the technical field of karst cave treatment, and particularly relates to a limestone stratum soft filling large karst cave combined grouting reinforcement method. Aiming at the pure mud filling karst cave or the cohesive soil filling karst cave, the karst cave is reinforced in a combined mode of high-pressure rotary spraying and segmented grouting, high-pressure rotary spraying holes are formed in the edge of the karst cave, and segmented grouting holes are formed between the high-pressure rotary spraying holes; high-pressure jet grouting reinforcement is carried out firstly, and segmented grouting reinforcement is carried out after the high-pressure jet grouting reinforcement structure stands still and is stable; the homogenization of a filling body is realized through high-pressure jet grouting pretreatment, micro gaps are filled through grouting reinforcement, the uniformity and compactness of a consolidated body are remarkably improved, and the bearing capacity and the impermeability are superior to those of a single method; the problems that slurry is prone to layering when the karst cave is filled with pure slurry and soil of the karst cave filled with cohesive soil is difficult to break are solved, the uniformity of a consolidated body is improved, and the requirement for stability of a shield tunnel face is met. And the reinforcing effect (bearing capacity and impermeability) and the construction efficiency are both considered.

Description

Technical Field

[0001] This invention belongs to the field of karst cave treatment technology, specifically relating to a combined grouting reinforcement method for filling large karst caves in weak limestone strata. Background Technology

[0002] Pure mud-filled karst caves and clay-filled karst caves are common complex geological conditions, especially in karst-developed areas. These two types of caves are the core risk sources for shield tunneling. Shield tunneling relies on face pressure balance, synchronous grouting behind the segments, and stable cutting by the cutterhead. Unreinforced pure mud / clay-filled karst caves can easily lead to multiple construction accidents. Pure mud filling the cave: When the shield cutterhead is cutting, the highly fluid mud can easily break through the sealing structure of the tunnel face and flow into the shield chamber, causing a sudden drop in pressure inside the chamber, destruction of the tunnel face balance system, and in turn triggering ground collapse.

[0003] Clay filling karst caves: Clay particles have strong cohesion and easily form "mud cakes" on the surface of the shield cutterhead and roller cutters, which leads to a decrease in cutting efficiency and a surge in cutterhead torque. In severe cases, it can cause cutter jamming and machine shutdown. Moreover, the clay is tightly bonded to the karst cave wall, which can easily cause local spalling of the karst cave wall during shield advancement, resulting in uneven stress on the cutterhead, causing shield attitude yaw, and increasing the difficulty of subsequent correction.

[0004] In existing technologies, although high-pressure jet grouting can forcibly mix soil and grout, it has problems such as high grout leakage rate, incomplete coverage of large karst caves, and high construction costs when filling karst caves with pure mud / cohesive soil. Although grouting has a wide range of applications, it has defects such as uneven mixing, low strength of the consolidated body, and poor impermeability. Using either method alone cannot meet the dual requirements of shield tunneling for "short-term stability (face collapse resistance) + long-term bearing capacity (segment support)" of the strata, nor can it balance reinforcement effect, construction efficiency, and cost control. There is an urgent need for a targeted combined construction scheme. Summary of the Invention

[0005] This invention aims to solve the problems of easy slurry stratification when reinforcing karst caves filled with pure mud and the difficulty in breaking up the soil when reinforcing karst caves filled with cohesive soil.

[0006] This invention provides the following technical solution: a method for combined grouting reinforcement of large karst caves filled with weak limestone strata. For karst caves filled with pure mud or cohesive soil, a combination of high-pressure jet grouting and segmented grouting is used to reinforce the karst caves. High-pressure jet grouting holes are arranged at the edge of the karst cave, and segmented grouting holes are arranged between the high-pressure jet grouting holes. High-pressure jet grouting reinforcement is performed first, and segmented grouting reinforcement is performed after the high-pressure jet grouting reinforced structure has been statically stabilized.

[0007] Furthermore, the spraying ranges of adjacent high-pressure jet grouting holes overlap, and the segmented grouting holes are located within the overlapping spraying range between the high-pressure jet grouting holes.

[0008] Furthermore, the high-pressure jet grouting reinforcement construction steps are as follows: S1; Drilling, drilling to the final hole 1-2 meters below the bottom of the cave, with casing installed for wall protection during the drilling process; S2: High-pressure rotary jetting, the rotary jetting pipe with a three-phase injection channel is lowered into the bottom of the casing, and the three-phase medium of fine sand, air and water is simultaneously injected into the borehole through the rotary jetting pipe. The rotary jetting pipe is rotated and raised at the same time as the casing. S3: Stabilizes after standing. For karst caves filled with pure mud, let stand for 2 hours; or for karst caves filled with cohesive soil, let stand for 3-4 hours.

[0009] Furthermore, for filling karst caves with pure mud slurry, the parameters for high-pressure jet grouting are: water pressure 25-30MPa, air pressure 0.6-0.8MPa, fine sand particle size 0.1-0.3mm, injection rate 30-50kg / m, jet grouting speed 15-20r / min, and lifting speed 8-12cm / min.

[0010] Furthermore, for filling karst caves with cohesive soil, the parameters for high-pressure jet grouting are: water pressure 30-35 MPa, air pressure 0.8-1.0 MPa, fine sand particle size 0.2-0.5 mm, injection rate 40-60 kg / m, jet grouting speed 20-25 r / min, lifting speed 5-8 cm / min, and dispersant added to the water at a volume ratio of 0.3%-0.5%.

[0011] Furthermore, the grouting holes for segmented grouting are drilled to a final depth of 0.5 meters below the bottom of the karst cave; after the grouting pipe for segmented grouting is inserted 0.5 meters below the top of the karst cave, grouting begins in segments downwards, with each segment being 1-1.5 meters high and the grouting pressure being 0.5-1.5 MPa. Grouting in that hole is stopped when the grouting volume reaches 90% of the design volume or the grout return concentration at the borehole opening is ≥80% of the design grout concentration.

[0012] Furthermore, the grouting material for segmented grouting is silicate cement slurry of grade 42.5 or higher; for filling karst caves with pure mud slurry, the water-cement ratio of silicate cement slurry is 0.8:1-1:1; for filling karst caves with cohesive soil, the water-cement ratio of silicate cement slurry is 1:1-1.2:1.

[0013] Furthermore, a geological survey is conducted before the cave is reinforced to clarify the cave's boundaries, filling type, and surrounding geological conditions; the physical parameters of the filling material are measured, including water content, porosity, and cohesion.

[0014] Furthermore, after all the grouting of a single segmented grouting hole is completed, it is left to stand for 12 hours before secondary grouting is applied to the settlement area at the hole opening.

[0015] Furthermore, the karst caves filled with pure mud or cohesive soil must have a diameter of 3 to 10 meters, be not connected in series, and have a burial depth of ≤80 meters.

[0016] Compared with the prior art, the advantages of the present invention are: This invention provides a combined grouting reinforcement method for filling large karst caves in weak limestone strata. It adopts a combined construction method of high-pressure jet grouting with simultaneous injection of fine sand-air-water three-phase medium pretreatment and segmented grouting reinforcement. The high-pressure jet grouting pretreatment realizes the homogenization of the filling body, and the grouting reinforcement fills the tiny voids. The uniformity and density of the consolidated body are significantly improved, and the bearing capacity and impermeability are better than those of the single method.

[0017] It solves the problems of easy slurry stratification and difficulty in breaking the soil in karst caves filled with cohesive soil, which are caused by pure mud filling. It improves the uniformity of the consolidated body and meets the stability requirements of the shield tunnel face. It takes into account the reinforcement effect (bearing capacity and impermeability) and construction efficiency, and is suitable for pure mud / cohesive soil filling karst caves of different sizes (diameter 3-10 meters) to ensure the stability of the shield tunneling posture.

[0018] High-pressure jet grouting employs a three-phase medium synergistic crushing and mixing process combined with segmented grouting, which can achieve a solidified body compressive strength ≥2.5MPa and a permeability coefficient ≤1×10⁻⁶. -6 cm / s, suitable for karst caves with diameters of 3-10 meters, balancing reinforcement effectiveness and economy, and the construction process is controllable.

[0019] High-pressure jet grouting simultaneously injects a three-phase medium of fine sand, air, and water. The fine sand acts as a framework, reducing grout loss during segmented grouting (loss rate reduced by 30%-50%). Segmented grouting uses 20%-30% less grout compared to single-stage grouting. High-pressure jet grouting is only used for pretreatment, avoiding the high costs of separate construction. Overall, the cost is reduced by 40%-50% compared to single-stage high-pressure jet grouting. This reduces grout loss, lowers construction costs, and meets the time requirements of "rapid reinforcement and efficient tunneling" in shield tunneling. Attached Figure Description

[0020] Figure 1 This is a diagram showing the layout of high-pressure jet grouting holes and segmented grouting holes; Figure 2 This is a cross-sectional view of the high-pressure jet grouting construction. Figure 3 This is a cross-sectional view of the segmented grouting construction.

[0021] In the diagram: 1-High-pressure jet grouting hole; 2-Segmented grouting hole; 3-Cave; 4-Casing; 5-Jet grouting pipe; 6-Grouting pipe; 7-Jet grouting zone; 8-Jet grouting overlap zone; R-Jet grouting radius. Detailed Implementation

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] like Figure 1 , Figure 2 , Figure 3 As shown: A combined grouting reinforcement method for filling large karst caves in weak limestone strata, which is suitable for karst caves filled with pure mud or cohesive soil with a diameter of 3 to 10 meters, no interconnection between karst caves, and a burial depth of ≤80 meters.

[0024] The combined grouting reinforcement method includes the following steps: S1: Preliminary preparation and geological exploration; through drilling exploration, ultrasonic testing and ground-penetrating radar, the boundaries (diameter, height, burial depth), filling type (pure mud / cohesive soil) and surrounding geological conditions (whether there are fissures, groundwater flow) of cave 3 are determined; the physical parameters of the filling body are measured, including water content, void ratio and cohesion.

[0025] S2: High-pressure jet grouting reinforcement. High-pressure jet grouting holes 1 are arranged at the edge of the karst cave 3, and the jet grouting ranges of adjacent high-pressure jet grouting holes 1 overlap. High-pressure jet grouting reinforcement includes the following construction steps: S2.1; Drilling, the diameter of the drill hole is determined according to the model of the jet grouting pipe 5 (Φ108-Φ159mm), drill to the final hole 1~2 meters below the bottom of the cave 3, and insert the casing 4 to protect the wall during the drilling process; The inner diameter of casing 4 is slightly larger than the outer diameter of jet nozzle 5, and its length covers the entire borehole section, ensuring that the entire borehole (from the surface to the stable stratum below the cave 3) is protected by casing 4, especially avoiding the collapse of the borehole wall in the cave section due to loose filling material (pure mud) or strong cohesion (cohesive soil). S2.2: High-pressure jet grouting: The jet grouting pipe 5 with three-phase injection channels (fine sand channel, air channel, and water channel) is lowered into the bottom of the casing 4. Fine sand, air, and water three-phase medium are simultaneously injected into the borehole through the jet grouting pipe 5. The jet grouting pipe 5 is rotated and raised while the casing 4 is raised simultaneously. The overlap width of the jet grouting solidified body of adjacent high-pressure jet grouting holes 1 is ≥20cm to form a uniform mixing system. S2.3: Static stabilization. For pure mud filling karst caves, allow to stand for 2 hours; for cohesive soil filling karst caves, allow to stand for 3-4 hours. This static stabilization allows the "fine sand-crushed filler-water" mixture formed by high-pressure jet grouting pretreatment to fully settle and compact, preventing fine sand from becoming suspended or unevenly distributed, forming a stable skeletal structure, and reducing grout loss during subsequent grouting. Pure mud has high fluidity, and 2 hours of static stabilization is sufficient for settlement; cohesive soil particles have strong cohesion, and 3-4 hours of static stabilization allows the crushed soil and fine sand to fully integrate, preventing medium loss during subsequent grouting.

[0026] S3: Segmented grouting reinforcement. The segmented grouting hole 2 is located within the overlapping range of the high-pressure jet grouting holes 1. The grouting holes for segmented grouting are drilled to a final depth of 0.5 meters below the bottom of the karst cave 3. After the grouting pipe 6 for segmented grouting is inserted 0.5 meters below the top of the karst cave 3, segmented grouting begins downwards. Each segment is 1-1.5 meters high, and the grouting pressure is 0.5-1.5 MPa (lower value for pure mud filling of karst caves, higher value for cohesive soil filling of karst caves). Grouting of the hole is stopped when the grouting volume reaches 90% of the design volume or the grout return concentration at the hole opening is ≥80% of the design grout concentration. After stabilizing the pressure for 3-5 minutes, the hole is moved to the next hole.

[0027] S4: Quality inspection. The reinforcement effect is verified by core sampling, ultrasonic testing and penetration test 28 days after the grouting is completed. After the test is qualified, the hole is sealed. The quality inspection standards are as follows: the consolidated body should be free of voids and interlayers; compressive strength ≥2.5MPa (pure mud filling karst caves), ≥3.0MPa (cohesive soil filling karst caves); sonic velocity ≥2500m / s; and impermeability coefficient ≤1×10⁻⁶. -6 cm / s.

[0028] In high-pressure jet grouting, construction parameters are adjusted according to the different types of karst cave filling, and the characteristics of pure mud slurry and cohesive soil filling karst caves are adapted accordingly, solving the core pain points of pure mud slurry stratification and the difficulty in breaking up cohesive soil. For pure mud slurry filling karst caves, the parameters of high-pressure jet grouting are: water pressure 25-30MPa, air pressure 0.6-0.8MPa, fine sand particle size 0.1-0.3mm, injection rate 30-50kg / m, jet grouting speed 15-20r / min, and lifting speed 8-12cm / min.

[0029] For filling karst caves with cohesive soil, the parameters for high-pressure jet grouting are: water pressure 30-35 MPa, air pressure 0.8-1.0 MPa, fine sand particle size 0.2-0.5 mm, injection rate 40-60 kg / m, jet grouting speed 20-25 r / min, lifting speed 5-8 cm / min, and dispersant added to the water at a volume ratio of 0.3%-0.5%. The dispersant is a naphthalene-based water-reducing agent, whose main function is to reduce the water-cement ratio of the filling material in the karst cave, improving its fluidity and cohesiveness, and facilitating subsequent grouting construction.

[0030] The grouting material for segmented grouting is silicate cement slurry of grade 42.5 or higher. For filling karst caves with pure mud slurry, the water-cement ratio of silicate cement slurry is 0.8:1-1:1. For filling karst caves with cohesive soil, the water-cement ratio of silicate cement slurry is 1:1-1.2:1. Bentonite can be added to silicate cement slurry at a volume ratio of 5%-10% to improve impermeability.

[0031] After all the grouting of a single segmented grouting hole 2 is completed, let it stand for 12 hours, and then perform secondary grouting on the settlement area at the hole opening.

[0032] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for reinforcing large karst caves in weak limestone strata using a combined grouting technique, characterized in that: For karst caves filled with pure mud or cohesive soil, a combination of high-pressure jet grouting and segmented grouting is used to reinforce the karst cave (3). High-pressure jet grouting holes (1) are arranged at the edge of the karst cave (3), and segmented grouting holes (2) are arranged between the high-pressure jet grouting holes (1). High-pressure jet grouting reinforcement is carried out first, and segmented grouting reinforcement is carried out after the high-pressure jet grouting reinforced structure has been statically stabilized.

2. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 1, characterized in that: The spraying ranges of adjacent high-pressure jet grouting holes (1) overlap, and the segmented grouting holes (2) are located within the overlapping spraying range between the high-pressure jet grouting holes (1).

3. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 1, characterized in that, The high-pressure jet grouting reinforcement construction steps are as follows: S1; Drill a hole to the bottom of the cave (3) 1-2 meters below the final hole. During the drilling process, insert a casing (4) to protect the wall. S2: High-pressure rotary jetting, the rotary jetting pipe (5) with a three-phase injection channel is lowered into the bottom of the casing (4), and fine sand, air and water three-phase medium are simultaneously injected into the borehole through the rotary jetting pipe (5). The rotary jetting pipe (5) is rotated and lifted while the casing (4) is lifted simultaneously. S3: Stabilizes after standing. For karst caves filled with pure mud, let stand for 2 hours; or for karst caves filled with cohesive soil, let stand for 3-4 hours.

4. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 3, characterized in that: For filling karst caves with pure mud slurry, the parameters for high-pressure jet grouting are: water pressure 25-30MPa, air pressure 0.6-0.8MPa, fine sand particle size 0.1-0.3mm, injection rate 30-50kg / m, jet grouting speed 15-20r / min, and lifting speed 8-12cm / min.

5. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 3, characterized in that: For filling karst caves with cohesive soil, the parameters for high-pressure jet grouting are: water pressure 30-35MPa, air pressure 0.8-1.0MPa, fine sand particle size 0.2-0.5mm, injection rate 40-60kg / m, jet grouting speed 20-25r / min, lifting speed 5-8cm / min, and dispersant added to the water at a volume ratio of 0.3%-0.5%.

6. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 1, characterized in that: The grouting hole for segmented grouting is drilled to a depth of 0.5 meters below the bottom of the karst cave (3). The grouting pipe (6) for segmented grouting is inserted 0.5 meters below the top of the karst cave (3) and then grouting is started in segments. Each segment is 1-1.5 meters high and the grouting pressure is 0.5-1.5 MPa. Grouting in the hole is stopped when the grouting volume reaches 90% of the design volume or the grout return concentration at the hole opening is ≥ 80% of the design grout concentration.

7. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 6, characterized in that: The grouting material for segmented grouting is silicate cement slurry of grade 42.5 or above; for filling karst caves with pure mud slurry, the water-cement ratio of silicate cement slurry is 0.8:1-1:1; for filling karst caves with cohesive soil, the water-cement ratio of silicate cement slurry is 1:1-1.2:

1.

8. The method for combined grouting reinforcement of weak limestone strata and large karst caves according to claim 1, characterized in that: Before reinforcing the karst cave (3), a geological survey is conducted to clarify the boundaries, filling type and surrounding geological conditions of the karst cave (3); the physical parameters of the filling are measured, including water content, porosity and cohesion.

9. A method for reinforcing weak limestone strata with combined grouting and filling of large karst caves according to claim 2, characterized in that: After all the grouting of a single segmented grouting hole (2) is completed, let it stand for 12 hours and then perform secondary grouting on the settlement part of the hole opening.

10. The method for combined grouting reinforcement of large karst caves in weak limestone strata according to claim 1, characterized in that: For karst caves filled with pure mud or cohesive soil, the diameter must be 3 to 10 meters, there must be no connection between the karst caves, and the burial depth must be ≤80 meters.

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