A layered step-by-step grouting method suitable for deep hole paste slurry pretreatment in karst areas

Abstract

A layered step-by-step grouting method suitable for deep hole paste slurry pretreatment in karst area, comprising the following steps: construction preparation and measurement of line, according to the geological survey report to determine the grouting parameters, and according to the principle of one stake two holes to layout grouting hole; Grouting hole drilling construction, using the way of separate stake, sequence, according to the design depth of sub drilling; Grouting pipe layout and checking the grip force, put down the paste grouting pipe, and use the karst paste correction formula to calculate the grip force, to ensure that it is less than the pullout machine pullout force and grouting pipe yield strength; Karst shallow hole pretreatment grouting, low pressure grouting is carried out on the shallow karst layer of the set depth, forming a closed layer; Karst deep hole step-by-step grouting, after the curing of the shallow hole closed layer, using the way of sub grouting from top to bottom, step-by-step retreat grouting is carried out on the deeper karst layer; Grouting quality detection and supplementary grouting; Hole sealing acceptance.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering construction technology, specifically to a layered step-by-step grouting method suitable for deep-hole grout pretreatment in karst areas. Background Technology

[0002] In the exploration and pre-construction treatment of foundation engineering such as pile foundations and diaphragm walls, drilling typically employs a one-time drilling process. However, in areas with highly developed karst topography, the formation stability is extremely poor due to the irregular development of karst caves and dissolution fissures, often accompanied by a beaded distribution of karst caves. During deep hole drilling, accidents such as severe drilling fluid loss, stuck drill bits, and drill bit burial frequently occur. Isolating these issues using methods such as casing or fly pipe is not only costly but also inefficient, and in severe cases, can even lead to ground subsidence.

[0003] Existing grouting techniques, such as those implemented in projects like the Guangzhou-Foshan West Ring Line and the Guangzhou-Heyuan High-Speed ​​Railway Baiyun Airport T3 connecting line, typically involve grouting depths of less than 80 meters and employ a one-time drilling followed by grouting. When the grouting depth exceeds 80 meters, significant problems arise with these existing techniques. For example, in some pile foundation construction projects, the pile body contained as many as five layers of karst caves, with some reaching as many as 13 layers of beaded karst caves, forming a continuous network, with the largest cave reaching a height of 36.7 meters. During retreating grouting after one-time drilling, the combined effect of grouting pressure and ground water pressure causes the grout to easily fill upwards through interconnected beaded karst caves and fissures, tightly gripping the grouting pipe. Simultaneously, the large grout volume and long duration, along with the gradually increasing grouting pressure, further exacerbate the gripping length and tightness of the grouting pipe. Furthermore, the short initial setting time of the grout leads to the deep grout solidifying before reaching the design pressure, resulting in insufficient grout density and substandard diffusion radius.

[0004] Calculations show that the φ76mm×10mm grout injection pipe used in the current process experiences a bond force of approximately 150 tons, approaching the pipe's ultimate yield strength, which easily leads to pipe breakage and hole abandonment. Furthermore, the current technology lacks quantitative matching standards for grouting time and volume, relying heavily on experience in construction, resulting in low injection efficiency and chaotic parameter control. Relevant technical specifications, such as the "Technical Specification for Building Foundations in Karst Areas" (GB / T 51238-2018) and the "Technical Specification for Foundation Treatment" (JGJ79-2012), do not design layered grouting systems specifically for the development characteristics of beaded karst caves, nor do they provide calculation models for the bond force between low-slump grout and injection pipes, or standards for grouting efficiency control. Therefore, the current technology suffers from three core defects: failure to adapt to the layered development characteristics of karst strata, failure to adapt to the bonding mechanical properties of the injection pipe and grout, and failure to adapt to the rheological differences between grout and cement slurry. Summary of the Invention

[0005] The purpose of this invention is to propose a layered step-by-step grouting method suitable for deep hole grout pretreatment in karst areas, so as to solve the technical defects pointed out in the background art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A layered, step-by-step grouting method suitable for deep-hole grout pretreatment in karst areas includes the following steps:

[0008] Step S1: Construction preparation and surveying and setting out. Determine grouting parameters based on the geological survey report and set up grouting holes according to the principle of two holes per pile.

[0009] Step S2: Grouting hole drilling is carried out in sections according to the design depth, using a staggered pile and sequential drilling method.

[0010] Step S3: Lay out the grouting pipe and check the gripping force. Lower the grouting pipe and calculate the gripping force using the karst grout correction formula to ensure that it is less than the pulling force of the pipe pulling machine and the yield strength of the grouting pipe.

[0011] Step S4: Karst shallow hole pretreatment grouting, low-pressure grouting is performed on the shallow karst layer at a set depth to form a sealing layer;

[0012] Step S5: Deep karst hole step grouting. After the shallow hole sealing layer has solidified, a step retreat grouting method is adopted from top to bottom to grout the deeper karst layer.

[0013] Step S6: Grouting quality inspection and supplementary grouting;

[0014] Step S7: Sealing and acceptance.

[0015] Furthermore, in step S5, the grouting is carried out in a step-by-step manner from top to bottom. The thickness of each layer gradually decreases as the depth of karst treatment increases, and the grouting pressure of each layer increases by 0.1-0.3 MPa compared to the previous layer.

[0016] Furthermore, in step S2, the method of alternating piles and sequential arrangement is adopted, specifically: in the first layer, hole #1 is a sequence I hole and hole #2 is a sequence II hole; in the second layer, hole #1 is a sequence II hole and hole #2 is a sequence I hole; in the third layer, hole #1 is a sequence I hole and hole #2 is a sequence II hole, and the hole sequence alternates in subsequent layers; after each layer is grouted and cured, the next layer is constructed.

[0017] Furthermore, the karst slurry correction formula in step S3 is as follows:

[0018]

[0019] Where T represents the gripping force. This is the correction factor for lateral pressure in karst formations. τ is the low slump grout bonding correction factor, d is the outer diameter of the grouting pipe, l is the length of the grouting pipe that is bound, and τ is the bonding strength of the grout after final setting.

[0020] Furthermore, in steps S4 and S5, a quantitative formula is used to control the grouting time: single-segment grouting time = single-segment designed grout injection volume / 10, where the unit of single-segment grouting time is hours, the unit of single-segment designed grout injection volume is cubic meters, and 10 represents a standard injection efficiency of 10 cubic meters per hour, with an injection efficiency of 10 ± 0.5 cubic meters per hour as the target.

[0021] Furthermore, the calculation method for the single-section grout injection volume is as follows: single-section grout injection volume = theoretical grout volume per meter × section length × filling type reduction coefficient, wherein the reduction coefficient for fully filled karst caves is 0.3, for semi-filled caves it is 0.7, and for unfilled caves it is 1.0.

[0022] Furthermore, the depth range of the karst shallow hole pretreatment grouting is 70 meters to 30 meters, and the grouting pressure is 0.6 to 0.8 MPa.

[0023] Furthermore, the depth division and corresponding grouting pressure of the karst deep hole step grouting are as follows: the first layer has a depth of 95 meters to 70 meters and a grouting pressure of 0.7 to 0.9 MPa; the second layer has a depth of 115 meters to 95 meters and a grouting pressure of 0.8 to 1.0 MPa; the third layer has a depth greater than 115 meters and a grouting pressure of 1.0 to 1.3 MPa.

[0024] Furthermore, the grout injection pipe is φ76mm×10mm, and the matching borehole diameter is φ91mm. The annular gap between the injection pipe and the borehole wall is filled with low-slump grout as a stop plug.

[0025] Furthermore, this method is applicable to karst grouting construction at depths greater than 80 meters, as well as karst reinforcement of underground continuous walls or pile banks in urban rail transit projects.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention combines shallow hole pretreatment to form a sealing layer with deep hole step-by-step layered grouting, effectively blocking the upward flow of grout along shallow fissures and significantly improving the retention rate of deep grout and the compactness of the grouting formation. The bond force calculation model, with a correction coefficient, can accurately adapt to hydraulic pipe pulling machines of different tonnages, fundamentally avoiding hole failures caused by pipe solidification and significantly reducing construction safety risks. By establishing quantitative control standards for grouting time and injection volume, the grout injection efficiency is stable and controllable, significantly improving construction efficiency and shortening the construction period compared to traditional experience-based construction. Furthermore, this invention can utilize waste mud and recycled stone powder to prepare grout, realizing the resource utilization of solid waste. The process parameters are flexibly adjustable, making it widely applicable to deep hole karst grouting and various karst reinforcement projects. It has outstanding advantages such as reliable construction safety, excellent reinforcement effect, green environmental protection, and ease of standardization and promotion. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the shallow and deep layered grouting cross-section in the karst area according to the present invention.

[0029] Figure 2 This is a schematic diagram of the planar layout of the pile foundation exploration holes of the present invention.

[0030] Figure 3 This is a schematic diagram of the planar arrangement of the grouting holes in the pile foundation of the present invention.

[0031] Figure 4 This is a flowchart of the step-by-step layered grouting process of the present invention.

[0032] Figure 5 This is a flowchart of the step-by-step paste application process of the present invention.

[0033] Figure 6 This is a schematic diagram illustrating the application of the present invention to karst construction of diaphragm wall retaining structures.

[0034] In the diagram: 1-Surface layer; 2-Step-type first layer; 3-Step-type second layer; 4-Step-type third layer; 5-Step-type fourth layer; 6-Pier exploration hole; 7-Pier grouting hole. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0036] This invention proposes a layered, step-by-step grouting method suitable for deep-hole grout pretreatment in karst areas, comprising the following steps:

[0037] Step S1: Construction preparation and surveying and setting out. Determine grouting parameters based on the geological survey report and set up grouting holes according to the principle of two holes per pile.

[0038] Step S2: Grouting hole drilling is carried out in sections according to the design depth, using a staggered pile and sequential drilling method.

[0039] In step S2, the method of alternating piles and sequential arrangement is adopted, specifically: in the first layer, hole #1 is the sequence I hole and hole #2 is the sequence II hole; in the second layer, hole #1 is the sequence II hole and hole #2 is the sequence I hole; in the third layer, hole #1 is the sequence I hole and hole #2 is the sequence II hole, and the hole sequence alternates in subsequent layers; after each layer is grouted and cured, the next layer is constructed.

[0040] Step S3: Lay out the grouting pipe and check the gripping force. Lower the grouting pipe and calculate the gripping force using the karst grout correction formula to ensure that it is less than the pulling force of the pipe pulling machine and the yield strength of the grouting pipe.

[0041] The correction formula for karst slurry in step S3 is as follows:

[0042] Where T represents the gripping force. This is the correction factor for lateral pressure in karst formations. τ is the low slump grout bonding correction factor, d is the outer diameter of the grouting pipe, l is the length of the grouting pipe that is bound, and τ is the bonding strength of the grout after final setting.

[0043] The grout injection pipe is φ76mm×10mm, and the matching borehole diameter is φ91mm. The annular gap between the injection pipe and the borehole wall is filled with low-slump grout as a stop plug.

[0044] Step S4: Karst shallow hole pretreatment grouting, low-pressure grouting is performed on the shallow karst layer at a set depth to form a sealing layer;

[0045] Step S5: Deep karst hole step grouting. After the shallow hole sealing layer has solidified, a step retreat grouting method is adopted from top to bottom to grout the deeper karst layer.

[0046] In step S5, the grouting is carried out in a step-by-step manner from top to bottom. The thickness of each layer gradually decreases as the karst treatment depth increases, and the grouting pressure of each layer increases by 0.1-0.3 MPa compared to the previous layer.

[0047] In steps S4 and S5, a quantitative formula is used to control the grouting time: single-segment grouting time = single-segment designed grout injection volume / 10, where the unit of single-segment grouting time is hours, the unit of single-segment designed grout injection volume is cubic meters, and 10 represents a standard injection efficiency of 10 cubic meters per hour, with an injection efficiency of 10 ± 0.5 cubic meters per hour as the target.

[0048] The calculation method for the single-section grout injection volume is as follows: single-section grout injection volume = theoretical grout volume per meter × section length × filling type reduction coefficient, where the reduction coefficient for fully filled karst caves is 0.3, for semi-filled caves it is 0.7, and for unfilled caves it is 1.0.

[0049] The depth range of the karst shallow hole pretreatment grouting is 30 to 70 meters, and the grouting pressure is 0.6 to 0.8 MPa.

[0050] The depth division and corresponding grouting pressure of the karst deep hole step grouting are as follows: the first layer is 95 meters to 70 meters deep, and the grouting pressure is 0.7 to 0.9 MPa; the second layer is 115 meters to 95 meters deep, and the grouting pressure is 0.8 to 1.0 MPa; the third layer is deeper than 115 meters, and the grouting pressure is 1.0 to 1.3 MPa.

[0051] Step S6: Grouting quality inspection and supplementary grouting;

[0052] Step S7: Sealing and acceptance.

[0053] Specifically, this method is applicable to karst grouting construction at depths greater than 80 meters, as well as karst reinforcement of underground continuous walls or pile banks in urban rail transit projects.

[0054] This invention utilizes a layered, step-by-step grouting method to first form a sealed layer in the shallow part. Combined with a modified gripping force model and a matching pipe pulling machine, it effectively avoids accidents such as grout leakage, borehole wall collapse, and grouting pipe solidification, significantly improving the construction safety factor.

[0055] This invention uses quantitative calculation of grouting time to stably control the grout injection efficiency at 10±0.5 cubic meters per hour. Compared with traditional experience-based construction, the efficiency is increased by more than 30%, and the construction period is shortened by 2-3 days.

[0056] The step-by-step layered grouting of this invention enables the grout to fully fill karst cavities and fissures, increasing the grout retention rate to over 95%, the ground compaction to over 90%, and the pile foundation bearing capacity to meet design requirements.

[0057] This invention establishes a triple control standard of quantitative, pressure-controlled, and time-controlled grouting, which, combined with real-time monitoring, enables refined management and control of the entire grouting process.

[0058] This invention utilizes waste mud and recycled stone powder to prepare slurry, achieving the resource utilization of solid waste. The entire method has adjustable parameters and is easily applicable to other types of karst reinforcement projects.

[0059] Specifically, the present invention will be further described below:

[0060] Reference Figures 1-6This embodiment takes the deep-hole grouting of a bridge pile foundation in karst as an example. The designed depth of the pile foundation exceeds 100 meters, and the karst is strongly developed, containing multiple layers of beaded karst caves (see reference). Figure 1 ).

[0061] This invention is applicable to grouting construction of deep holes (>80m) in karst pile foundations. For karst strata grouting, the planned depth of the upper surface layer is 0-30m. The first step layer (2) is set at a depth of 70-30m (calculated section length 40m), the second step layer (3) at a depth of 95-70m (calculated section length 25m), the third step layer (4) at a depth of 115-95m (calculated section length 20m), and the fourth step layer (5) at a depth >115m (calculated section length less than 20m) (see reference). Figure 1 In principle, grouting is only performed on karst and severely weathered strata, while intact rock sections are directly sealed. A φ76mm specially made grout injection pipe is used as the grouting carrier, coupled with a φ91mm borehole. A 15mm annular gap is reserved for filling low-slump grout as a stop plug. The grout is a green and environmentally friendly grout made from waste mud from pile foundation construction and recycled stone powder, with a slump controlled at 5~10cm and a final bond strength ≥0.2MPa. The standard grouting efficiency is set at 10 cubic meters of grout per hour. The specific implementation steps are as follows:

[0062] 1. Pre-construction preparation and surveying / layout

[0063] (1) Geological investigation: Conduct a detailed geological investigation of the pile foundation construction area, using a combination of borehole exploration and geophysical exploration to clarify the distribution of karst caves, the size of fissures, the integrity of the strata and the type of karst cave filling (full filling / half filling / no filling) in shallow / deep boreholes, determine key parameters such as the correction coefficient k1 for the bond force calculation and the grouting pressure zoning, and form a formal geological investigation report;

[0064] (2) Surveying and setting out: Using a total station, accurately measure and set out the grouting hole positions according to the pile foundation design drawings, and mark the hole positions (paint + wooden stakes). The distance between the grouting hole and the center of the pile foundation is strictly controlled to be 1.5~2.0m, and the "one pile, two holes" layout principle is followed (refer to...). Figure 2 ), ensuring that the grouting reinforcement area fully covers the bearing layer of the pile foundation;

[0065] (3) Equipment and grout preparation: Prepare φ76mm special grout injection pipe, GK-200 geological drilling rig, 40-10-55 grout pump, and 100-ton, 150-ton and 200-ton hydraulic pipe pulling machines and other construction equipment. All equipment should be debugged, calibrated and recorded before entering the site. Prepare low slump grout according to the mix ratio. The core mix ratio is: waste mud + recycled stone powder + P.O42.5 ordinary Portland cement + admixture. The usage of all main materials is fixed. After mixing for 3~5 minutes in a mixer, the slump (5~10cm), initial setting time (1h±0.5h) and bond strength (≥0.2MPa after final setting) of the grout should be tested on site according to the concrete testing standards. The results should be issued by the laboratory. If the indicators are not qualified, the mix ratio should be adjusted immediately (adjust the amount of admixture if the slump is too low) until the indicators meet the standards.

[0066] 2. Grouting hole drilling construction

[0067] (1) Drilling principle: Geological drilling rigs are used to drill according to the marked hole positions, and the requirements of "intermittent pile construction and sequential construction" are strictly implemented. The construction sequence is as follows: First stage construction holes: 1# pile → 3# pile → 5# pile → 7# pile → 9# pile; Second stage construction holes: 2# pile → 4# pile → 6# pile → 8# pile → 10# pile, implemented according to the retreat process; The first layer of hole 1 (1-1~9-1) is constructed first for each pile. After the first layer of grouting of all holes 1 is completed, the second layer and the first layer of hole 2 (1-2~10-2) are constructed to avoid mutual interference between adjacent holes, which may lead to grout pipe solidification and hole wall collapse; After the second layer of hole 2 is completed, hole 1 is swept and the second and third layers are drilled. After the drilling is completed, retreat grouting is carried out until the designed hole depth is reached. After the grouting of all holes is completed, the pre-grouting of the entire foundation is completed.

[0068] (2) Drilling operation: The mud wall drilling process is adopted, and the borehole diameter is strictly controlled to φ91mm, which is precisely matched with the φ76mm grouting pipe. The drilling speed is controlled during the drilling process. When encountering karst caves, the depth, height, filling type and fracture development of the cave top and bottom are recorded in detail, and the original drilling record is made simultaneously.

[0069] (3) Drilling termination: Each section of the step drilling is drilled to the sub-layer depth according to the initial planned depth. When the whole hole is finished, the drilling is stopped immediately after the drilling rig reaches the designed bearing layer of the pile foundation (1m into the intact bedrock). Drilling records are kept throughout the process, and the specific location and size of the karst caves and dissolution fissures are clearly marked to provide a basis for the subsequent setting of grouting parameters and accurate calculation of grouting volume. All boreholes are required to reach the designed hole depth. The first and last layers of hole No. 1 only have single-layer drilling and grouting.

[0070] 3. Layout and verification of φ76mm special grout injection pipe and bond strength calculation (1) Bond strength calculation

[0071] (1) The core formula of the karst slurry-specific correction formula designed in this invention is as follows:

[0072] The parameter T=k1k2πdlτ is explicitly defined (units are uniformly mm-N-MPa).

[0073] In the formula:

[0074] k1: Lateral pressure correction coefficient for karst formations, with values ​​determined based on the integrity of the karst formations; 0.95~1.0 for intact rock formations and 1.0~1.05 for fractured rock formations.

[0075] k2: Correction coefficient for adhesion of low slump paste, the value is determined according to the actual slump of the paste, 1.2 for slump of 5~8cm and 1.1 for slump of 8~10cm;

[0076] d: The contact diameter of the outer wall of the grouting pipe is fixed at 76mm (φ76mm×10mm outer diameter of the grouting pipe).

[0077] l: The average depth of the rock strata above the karst cave of the grouting pipe, which is taken as 20m in this project (converted to 20000mm for easy unit calculation). The longer the length, the greater the bonding force. It is necessary to ensure that the slump of the grout is low and the grouting pressure is low, and to ensure that the grout liquid level is low enough and the height of the grouting pipe is small.

[0078] τ: Bond strength of the paste after initial setting, with an on-site test value ≥ 0.2 MPa (1 MPa = 1 N / mm², i.e., 0.2 N / mm²).

[0079] Calculation example: Taking k1=1.0 (intact rock strata), k2=1.15 (slump 7cm), d=76mm, l=20000mm, τ=0.2MPa, substituting into the formula, we get: T=1.0×1.15×3.14×76×20000×0.2=1097744N=1097.744kN≈112.0tf (conversion relationship: 1tf=9800N);

[0080] (2) Grouting pipe layout: The φ76mm×10mm special grouting pipe is slowly lowered into the grouting hole according to the calculation requirements. During the lowering process, the pipe body should be prevented from colliding with the hole wall and causing the hole wall to collapse. The gap between the pipe body and the hole wall is initially filled with the prepared low slump grout. A steel plug is set at the bottom of the grouting pipe to prevent the grout from flowing out from the bottom of the pipe during subsequent grouting. The upper part of the pipe body is fixed with a steel bracket to ensure that the pipe body is centered and without deviation. After the layout is completed, the site photos are kept.

[0081] (3) Check the gripping force: The weight of the grouting pipe plus the total gripping force T is calculated. It should be 20% to 30% smaller than the starting tonnage of the hydraulic pipe pulling machine (this project clearly requires the starting tonnage of the hydraulic pipe pulling machine to be ≥100tf), and it must also be less than the damage yield strength of the grouting pipe of 150MPa. Only after the check is qualified can it proceed to the next process. If the check is not qualified, the laying depth of the grouting pipe should be adjusted immediately or the slump of the grout should be further reduced to reduce the gripping length of the grouting pipe until the check meets the standard.

[0082] 4. Karst Shallow Hole Pretreatment Grouting (70~31m): Shallow hole pretreatment is a core preliminary process. Its purpose is to seal shallow karst caves and fissures, forming a sealing layer to prevent grout loss during deep grouting. Specific operations are as follows:

[0083] (1) Grouting parameter setting: The low slump grout is injected into the shallow karst development area at a uniform speed using an RS40-10-55 grout pump. The grouting pressure is strictly controlled at 0.6~0.8MPa (low pressure and slow injection to avoid erosion of the hole wall). The grout diffusion radius is designed to be 4m. The theoretical grouting volume per meter is about 50m³ (approximately taken from the circular cross-sectional area of ​​the grout body S=πr²=3.14×4²=50.24m³).

[0084] (2) Accurate calculation of grouting volume: The grout reduction coefficient is introduced according to the filling type of the karst cave to avoid grouting waste or incomplete filling. The calculation formula is: single-section grouting volume per meter of theoretical volume section length reduction coefficient; where the reduction coefficient values ​​are: 0.3 for fully filled karst cave, 0.7 for half-filled karst cave, and 1.0 for unfilled karst cave;

[0085] (3) Quantitative control of grouting time: Calculate the total grouting time for shallow holes based on the standard grouting efficiency of 10 cubic meters of grout per hour. The formula is: T1=V1 / 10 (V1 is the total designed grouting volume for the shallow hole area, unit: m3). On site, strictly adjust the grouting pump flow rate according to the calculated time to ensure a stable grouting rhythm and avoid fast or slow grouting. The grouting time for each layer should be controlled within 24 hours as much as possible.

[0086] (4) Curing and testing: Continue grouting until the shallow holes and cavities are fully filled with grout, forming a continuous and dense grout filling and sealing layer. After the grouting is completed, stop the grouting and let it stand for 24 hours to allow the grout to initially solidify. After curing, use a shallow layer detector to test the shallow sealing effect. Only after the test is qualified can the deep grouting process be carried out. If it is not qualified, grouting should be carried out immediately.

[0087] 5. After the shallow hole grout sealing layer for deep karst grouting has cured and passed inspection, deep karst grouting is carried out using a step-by-step construction method of "segmented grouting from top to bottom" (refer to...). Figure 3Each segment is laid out in steps according to the designed segment length (40m for 70~30m, 25m for 95~70m, 20m for 115~95m, and also in 15~20m segments after >115m). Alternatively, the segments can be laid out according to the above principles, with appropriate adjustments based on the actual conditions of karst development and infilling revealed by exploration borehole 7. Specific procedures are as follows:

[0088] (1) Setting of segmented grouting parameters: The grouting pressure is set differently according to the hole depth and formation pressure to ensure that the grouting is dense and does not erode the formation: ① Step-by-step first layer 2 (70~30m, hole depth below 80m): grouting pressure 0.6~0.8MPa; ② Step-by-step second layer (95~70m): grouting pressure 0.7~0.9MPa; ③ Step-by-step third layer (115~95m, hole depth above 80m): grouting pressure 0.8~1.0MPa; Fourth layer set depth>115m (calculated section length 15~20m): grouting pressure 1.0~1.3MPa.

[0089] (2) Single-section grouting calculation: Based on the volume and filling type of each karst cave recorded in the geological survey, the single-section grouting injection volume V2 is determined according to the shallow hole grouting volume calculation method. Then, the single-section grouting time is calculated according to the standard grouting efficiency. The formula is: T2=V2 / 10 (unit: h).

[0090] (3) Multi-hole collaborative control strategy: 2-3 grouting holes on site can be grouted alternately to improve construction efficiency; during the grouting process, a grout level monitoring instrument is set up to monitor the grout level height of the un-grouted detection holes in real time, and control is carried out according to the following rules: ① If the grouting volume reaches 50 cubic meters and the grout level of the un-grouted detection holes rises, it indicates that the grout diffusion is normal, and grouting continues without interruption; ② If the grouting volume reaches 50 cubic meters and the grout level of the un-grouted detection holes does not rise or rises slowly, it indicates that there is deep grout leakage, and the machine is stopped immediately, and the grout is thickened (increase the P.O42.5 cement content by 2%~3%), and grouting is continued after adjustment;

[0091] (4) Real-time monitoring throughout the process: Arrange dedicated personnel to keep original records of grouting throughout the process. The records include grouting pressure, grout injection volume, grouting time, grout level, etc. At the same time, pressure sensors and flow sensors are used to monitor grouting parameters in real time. If the grout absorption of the formation is abnormal (such as a sudden increase / decrease in grout absorption), the grouting time and pressure are adjusted immediately to ensure that the karst formation is fully filled and compacted by grout.

[0092] 6. Grouting Quality Inspection: After all deep-hole grouting is completed, allow it to stand for 72 hours to allow the grout to fully solidify. Use a combined testing method of "core drilling + constant water head injection test" to comprehensively verify the density of the karst strata and the filling effect of the grout. The testing standards strictly follow the design requirements for karst reinforcement of pile foundations and current national standards.

[0093] (1) Drilling and coring inspection: Quality inspection holes are arranged within a range of 2.5~3.5m around the grouting hole 7. Geological drilling rig is used to drill and extract cores with a core extraction rate of ≥80%. The appearance and density of the core samples are inspected. The core samples are required to be tightly bonded to the rock layer, without voids or cracks, and the grout is evenly filled. Core sample photos and inspection records are kept.

[0094] (2) Constant head water injection test: A constant head water injection test is carried out in the test hole to test the permeability coefficient of the karst stratum after grouting. The permeability coefficient K is required to be ≤1×10-5cm / s to ensure that the impermeability of the stratum meets the design requirements for pile foundation construction.

[0095] (3) Grouting treatment: If either of the above two tests fails, the grouting quality of the area is deemed substandard. Grouting holes are immediately arranged in the substandard area. The grouting construction is still carried out in accordance with the process requirements of this invention, and the grouting time is controlled according to the standard of 10 cubic meters of grout per hour until the grouting is qualified after the test.

[0096] 7. After all grouting quality inspections have passed, the grouting holes shall be permanently sealed to prevent surface water from seeping into the holes and affecting the stability of the karst formation. After sealing, a joint on-site acceptance inspection shall be conducted by the construction, supervision, and construction units. Specific requirements are as follows:

[0097] (1) Sealing construction process: Cement mortar is used as the sealing material. It is filled in layers from the bottom of the grouting hole to the ground surface. After filling, a vibrator is used to penetrate the hole and compact it to prevent gaps between layers. 50cm is reserved at the top of the grouting pipe. When the cement mortar is filled to 50cm below the ground surface, the hole opening is sealed and leveled with cement mortar. Waterproofing treatment of the hole opening is done. On-site construction records are kept during the sealing process.

[0098] (2) Acceptance criteria: The acceptance of the sealing hole is divided into three items: appearance acceptance, density acceptance and data acceptance. Only when all three are qualified can the acceptance be passed: ① Appearance acceptance: The cement mortar surface is flat, without cracks, subsidence and water seepage after sealing the hole; ② Density acceptance: 10% of the grouting holes are randomly selected for core drilling and testing. The density of the sealing hole is ≥95%; ③ Data acceptance: The construction data is complete and the data is true and valid, including geological survey records, drilling records, grouting parameter records, quality inspection reports, supplementary grouting records, and instrument calibration records, etc.

[0099] (3) Process connection: Only after the sealing hole is accepted and the acceptance record is signed can the subsequent pile foundation construction process, such as lowering the steel cage and pouring concrete, be carried out.

[0100] To address the stratigraphic differences in different sections of the Guangzhou-Heyuan High-Speed ​​Railway Baiyun Airport T3 connecting line or other karst geological engineering projects, the process parameters of this invention can be flexibly adjusted according to the actual geological survey results, while the core calculation method and construction process remain unchanged:

[0101] ① Shallow hole pretreatment depth: can be adjusted to 70~30m or 50~30m to suit different shallow karst development ranges;

[0102] ②Deep hole stepping segment depth: can be adjusted to 15~20m or 20~30m to adapt to different deep karst cave distribution characteristics;

[0103] ③ Grouting pressure: can be finely adjusted by ±0.1MPa to adapt to different formation integrity;

[0104] ④ Grout mixing ratio: The proportion of each component can be finely adjusted according to the characteristics of the waste mud on site to ensure that the core indicators such as slump and bonding strength of the grout meet the requirements; the grouting time is always quantitatively calculated according to the formula "total injection volume / 10" to ensure that the grouting efficiency is stable at 10±0.5 cubic meters per hour.

[0105] The step-by-step grouting process, bond strength calculation method, and parameter control standards of this invention are applicable not only to deep-hole grouting in karst pile foundations but also directly adaptable to karst geological treatment projects in subway, highway bridge pile foundations, water conservancy, and building construction. Furthermore, they can be extended to the karst reinforcement of foundation pit retaining structures (such as diaphragm walls and pile banks) in urban rail transit projects: piles No. 1 and No. 7 are considered as a diaphragm wall section (refer to...). Figure 6 When drilling reveals a karst cave, the core process of "shallow hole pretreatment + deep step-by-step grouting" of this invention is used for construction. The arrangement principles of exploration holes and grouting holes, the calculation method of gripping force, and the control standards of grouting parameters remain unchanged. Only the spacing of grouting holes is slightly adjusted according to the size of the diaphragm wall trench. It has strong adaptability and can be quickly implemented.

[0106] The present invention has the following beneficial effects:

[0107] 1. Significantly reduced construction risks: Layered step grouting, pre-treatment to achieve shallow karst sealing, combined with the corrected gripping force calculation and the use of hydraulic pipe pulling machines of different tonnages such as 100 tons, 150 tons, and 200 tons, effectively avoids construction accidents such as grout leakage, hole wall collapse, and grouting pipe solidification, increasing the construction safety factor to over 98%.

[0108] 2. Stable and controllable grouting efficiency: Through quantitative calculation of grouting time, the grout injection efficiency is stably controlled at 10±0.5 cubic meters per hour. Compared with traditional experience construction, the construction efficiency is increased by more than 30%, and the grouting period of a single pile is shortened by 2 to 3 days, which is fully compatible with the construction progress requirements of the Guanghe High-speed Railway Baiyun Airport T3 connecting line project.

[0109] 3. Significant grouting reinforcement effect: Step-by-step layered grouting allows the grout to fully fill karst caves and fissures, increasing the grout retention rate to over 95%, the density of karst strata to over 90%, and the bearing capacity of the pile foundation to meet the design requirements. Currently, the settlement is completely controlled within the allowable range of the specifications.

[0110] 4. Green and environmentally friendly with strong adaptability: The grout is prepared by combining waste mud from pile foundation construction with recycled stone powder, realizing the resource utilization of solid waste and reducing construction waste emissions; the whole method is specially designed for deep hole grouting of pile foundations in karst areas, and parameters such as step length and grouting pressure can be adjusted according to the degree of karst development. It can also be adapted to karst reinforcement of urban rail transit diaphragm walls, highway bridge pile foundations, water conservancy and building construction projects. The construction process is standardized, easy to operate on site and promote application. This process is also suitable for deep hole grouting of ordinary processes.

[0111] 5. Precise parameter control: Establish a triple grouting control standard of "quantitative + pressure + timing", combined with real-time parameter monitoring, to achieve refined control of the entire grouting process and avoid poor reinforcement effect caused by parameter loss.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0113] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A layered, step-by-step grouting method suitable for deep-hole grout pretreatment in karst areas, characterized in that, Includes the following steps: Step S1: Construction preparation and surveying and setting out. Determine grouting parameters based on the geological survey report and set up grouting holes according to the principle of two holes per pile. Step S2: Grouting hole drilling is carried out in sections according to the design depth, using a staggered pile and sequential drilling method. Step S3: Lay out the grouting pipe and check the gripping force. Lower the grouting pipe and calculate the gripping force using the karst grout correction formula to ensure that it is less than the pulling force of the pipe pulling machine and the yield strength of the grouting pipe. Step S4: Karst shallow hole pretreatment grouting, low-pressure grouting is performed on the shallow karst layer at a set depth to form a sealing layer; Step S5: Deep karst hole step grouting. After the shallow hole sealing layer has solidified, a step retreat grouting method is adopted from top to bottom to grout the deeper karst layer. Step S6: Grouting quality inspection and supplementary grouting; Step S7: Sealing and acceptance.

2. The layered step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, In step S5, the grouting is carried out in a step-by-step manner from top to bottom. The thickness of each layer gradually decreases as the karst treatment depth increases, and the grouting pressure of each layer increases by 0.1-0.3 MPa compared to the previous layer.

3. The layered step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, In step S2, the method of alternating piles and sequential arrangement is as follows: in the first layer, hole #1 is a sequence I hole and hole #2 is a sequence II hole; in the second layer, hole #1 is a sequence II hole and hole #2 is a sequence I hole. The third layer is then converted to hole #1 as sequence I, hole #2 as sequence II, and subsequent layers alternate the hole sequence; after each layer of grouting is completed and cured, the next layer is constructed.

4. The layered step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, The correction formula for karst slurry in step S3 is as follows: Where T represents the gripping force. This is the correction factor for lateral pressure in karst formations. τ is the low slump grout bonding correction factor, d is the outer diameter of the grouting pipe, l is the length of the grouting pipe that is bound, and τ is the bonding strength of the grout after final setting.

5. A layered, step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, In steps S4 and S5, a quantitative formula is used to control the grouting time: single-segment grouting time = single-segment designed grout injection volume / 10, where the unit of single-segment grouting time is hours, the unit of single-segment designed grout injection volume is cubic meters, and 10 represents a standard injection efficiency of 10 cubic meters per hour, with an injection efficiency of 10 ± 0.5 cubic meters per hour as the target.

6. A layered, step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 5, characterized in that, The calculation method for the single-section grout injection volume is as follows: single-section grout injection volume = theoretical grout volume per meter × section length × filling type reduction coefficient, where the reduction coefficient for fully filled karst caves is 0.3, for semi-filled caves it is 0.7, and for unfilled caves it is 1.

0.

7. A layered, step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, The depth range of the karst shallow hole pretreatment grouting is 70 meters to 30 meters, and the grouting pressure is 0.6 to 0.8 MPa.

8. A layered, step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, The depth division and corresponding grouting pressure of the karst deep hole step grouting are as follows: the first layer is 95 meters to 70 meters deep, and the grouting pressure is 0.7 to 0.9 MPa; the second layer is 115 meters to 95 meters deep, and the grouting pressure is 0.8 to 1.0 MPa; the third layer is deeper than 115 meters, and the grouting pressure is 1.0 to 1.3 MPa.

9. A layered, step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, The grout injection pipe is φ76mm×10mm, and the matching borehole diameter is φ91mm. The annular gap between the injection pipe and the borehole wall is filled with low-slump grout as a stop plug.

10. A layered, step-by-step grouting method for deep-hole grout pretreatment in karst areas according to claim 1, characterized in that, This method is applicable to karst grouting construction at depths greater than 80 meters, as well as karst reinforcement of underground continuous walls or pile banks in urban rail transit projects.

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