Cast-in-place pile treatment quicksand soil retaining wall and karst cave treatment method

Abstract

The invention discloses a cast-in-place pile quicksand soil retaining wall treatment and karst cave treatment method, and relates to the technical field of pile foundation construction, and the method comprises the steps of drilling identification, positioning preparation, high-pressure water cutting disturbance, directional grouting, drill bit rotary lifting synchronous grouting, equipment exiting, curing maintenance, secondary hole forming and the like. Through combined operation of high-pressure water cutting and chemical slurry, a flow state structure is effectively destroyed, filling and consolidation are synchronously carried out, the stratum stability is improved, the used slurry has good fluidity and rapid curing characteristics, a high-strength consolidation body can be formed within 24-48 hours, and the method can be widely applied to cast-in-place pile construction in complex areas containing karst caves, quicksand, powder stratums and the like, and has wide application prospects. And the pore-forming success rate and the engineering quality are obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering construction, in particular to a method for treating quicksand soil wall and karst cave with cast-in-place piles. Background Art

[0002] When constructing bored piles in karst or other geologically challenging areas, quicksand-like soil and hidden caves are common. Traditional retaining wall methods, such as conventional slurry retaining walls and steel casing retaining walls, struggle to maintain stable operation in formations where drilling is impossible or where there is severe collapse. This can lead to retaining wall failure, heavy bottom sedimentation, or even drilling interruptions. Construction becomes even more challenging when encountering interspersed strata with powdery quicksand and cave formations. Therefore, we propose a bored pile retaining wall method for quicksand and cave treatment. Summary of the Invention

[0003] In order to solve the above technical deficiencies, the present invention adopts a modified technical solution, a method for treating quicksand soil retaining walls and caves with cast-in-place piles, and the specific steps include the following:

[0004] S1, drilling identification: Use a rotary pile driver to drill into the quicksand soil or karst cave area, and stop drilling when the drilling resistance suddenly drops or the hole collapses severely;

[0005] S2, Positioning Preparation: The tower pile driver is adjusted to the position directly above the pile hole, and the drill is started to drill down to the suspected cave area for the second time;

[0006] S3, high-pressure water cutting: After the drill bit enters the fluidized filling, the high-pressure pump is started to perform circumferential cutting at a water pressure of 8-12 MPa to fully disturb and fluidize the loose soil around the cave;

[0007] S4, directional grouting: simultaneous high-pressure injection of pre-prepared chemical slurry through the drill pipe. The slurry has fluidity and fast curing properties.

[0008] S5, drill bit lifting: lift the drill rig at a constant speed of 0.3-0.5m / min while rotating the drill bit to evenly fill, wrap and consolidate the surrounding caves and quicksand areas with slurry;

[0009] S6, termination of grouting: when the drill bit is lifted to the top of the cave layer, grouting is stopped and the high-pressure pump is turned off;

[0010] S7, curing stage: After grouting is completed, it is left to stand for 24-48 hours to allow the slurry to react chemically with the soil to form a consolidated body;

[0011] S8, secondary drilling: After the slurry is solidified and formed, the rotary drilling equipment is put into place and drilled again, successfully passing through the original cave or quicksand layer to reach the bearing layer.

[0012] As a further preferred embodiment of the present invention, the slurry comprises the following components in percentage by mass: curing agent: 20-30%; flow aid: 10-15%; composite bentonite: 5-10%; and water: balanced.

[0013] As a further preferred embodiment of the present invention, in step S1, a rotary drilling rig equipped with a drill bit of Φ800mm or above is used to start drilling from the surface. When the drilling depth reaches the abnormally weak or hollow layer area indicated in the design and survey report, the following indicators are monitored in real time to identify whether the problem formation has been entered: the drilling torque drops sharply by more than 30%; the drilling footage suddenly deepens rapidly or becomes unstable; the slag return in the borehole is significantly reduced and the water inflow increases abnormally. If any of the indicators appears, the drilling operation is stopped immediately, the current hole depth, time, and drilling parameters are recorded, and it is determined that the fluid filling or hollow area has been entered.

[0014] As a further preferred embodiment of the present invention, step S2 includes withdrawing the rotary drilling rig from the hole mouth, shifting the high tower pile driver or long spiral drilling rig to a position directly above the center of the target hole, using a centering device to ensure that the verticality error of the drill rod is ≤1%, restarting the drill bit to slowly drill down, entering the quicksand or suspected cave area to a depth of about 1-1.5m, and forming a closed grouting control space.

[0015] As a further preferred embodiment of the present invention, in step S3, the high-pressure water pump is turned on, the output water pressure range is 30-40 MPa, and the surrounding fluidized soil and cave wall are subjected to 360° rotational cutting disturbance through the drill nozzle. The cutting time is controlled at 3-6 minutes / meter and adjusted according to the density of the formation; the drill bit is kept slightly oscillating ±3° during the cutting process to enhance the disturbance radius; the cutting depth is 1-2 m below the drill bit.

[0016] As a further preferred embodiment of the present invention, in step S4, step 4: directional grouting, stop high-pressure water cutting, switch the slurry channel, start the high-pressure grouting pump, working pressure: 40MPa, inject the self-prepared chemical slurry into the cave area through the inside of the drill pipe, while maintaining the drill bit to rotate slowly, the speed is 10-15rpm, the slurry components are stirred evenly on site according to the set ratio, and the slurry specific gravity is controlled at 1.5-1.6g / mm³; the grouting rate is controlled at 15-25L / min. During the grouting period, ensure that the slurry diffuses symmetrically along the axis of the borehole to fill and wrap the cave boundary.

[0017] As a further preferred embodiment of the present invention, in step S5, the drill bit is lifted and grouting is performed synchronously. During the grouting process, the drilling rig is started and the drill bit is slowly lifted while being rotated to realize a composite operation mode of rotating, lifting and grouting: the lifting rate is controlled at 0.3-0.5 m / min, and the rotation is maintained at 10-15 rpm; if the slurry refluxes severely or the pressure drops suddenly, the lifting is suspended to find out the cause of the blockage or crack leakage; and the grouting is stopped when the grouting reaches 0.5 m from the top of the cave layer.

[0018] As a further preferred embodiment of the present invention, in step S7, after the grouting is completed, it is allowed to stand for 24-48 hours to allow the slurry to fully react and consolidate with the original soil of the cave. The ambient temperature should be controlled at 10-35°C. If it is lower than 10°C, heating measures should be taken. CO2 carbonization curing is used to enhance the surface density. The parameters are 20% concentration, 0.8 MPa air pressure, and 46 hours. After the curing period expires, the strength of the consolidated body is tested using static probing or standard penetration test to ensure that it reaches 1.0-1.5 MPa or above.

[0019] As a further preferred embodiment of the present invention, in step S8, after confirming that the consolidation effect meets the requirements, the rotary drilling rig is re-positioned for secondary drilling operations: the initial drilling depth is 0.5m below the top of the grouting area, and the drilling speed is controlled at 20-30cm / min; during the drilling process, it is recorded whether there is abnormal backflow of slag, collapse of the hole wall, or torque change.

[0020] Beneficial effects

[0021] The present invention provides a method for treating quicksand soil retaining walls and karst caves with cast-in-place piles. It has the following beneficial effects:

[0022] Accurate identification and real-time response: By monitoring parameters such as drilling torque, footage rate, and slag return, abnormal formations such as caves or quicksand can be quickly identified, enabling real-time intervention and significantly improving construction safety and identification accuracy.

[0023] Bidirectional disturbance grouting mechanism: adopts high-pressure water cutting and chemical slurry synergistic injection mechanism to effectively destroy the flow structure and simultaneously fill and consolidate, improve slurry permeability and reinforcement efficiency, and form a continuous, dense and stable wrapping layer.

[0024] Multi-parameter adjustable control process: grouting pressure, lifting speed, rotation speed, slurry composition, CO2 carbonization concentration, etc. can be flexibly adjusted according to different formation conditions, enhancing process adaptability and material utilization.

[0025] Rapid consolidation to form a stable retaining wall: High-efficiency chemical grouting materials combined with disturbance diffusion technology can form a consolidated body with a strength of 1.0-1.5MPa within 24-48 hours, providing reliable protection for subsequent secondary drilling and significantly improving the qualified rate of pile foundation drilling.

[0026] Reduced project costs and risks: This approach avoids rework and accidents caused by hole wall collapse, slurry loss, or pile foundation failure, shortens construction cycles, and reduces labor and material costs, resulting in significant economic benefits. Applicable to a variety of construction scenarios: This method can be used for bridge and high-rise building pile foundations, as well as for strengthening karst caves or weak strata in specialized engineering areas such as tunnel pilot tunnels and subway deep foundation pits, making it highly applicable. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] The present invention provides a technical solution: a method for treating quicksand soil retaining walls and karst caves with cast-in-place piles, the specific steps of which include the following:

[0029] Step 1: Drilling Identification

[0030] Use a rotary drilling rig equipped with a drill bit of Φ800mm or larger to start drilling from the surface. When the drilling depth reaches the abnormally weak or hollow layer (such as caves or quicksand) indicated in the design survey report, monitor the following indicators in real time to identify whether you have entered the problematic stratum:

[0031] The drilling torque dropped by more than 30%;

[0032] The drilling footage suddenly increases rapidly or becomes unstable;

[0033] The amount of slag returned in the borehole has been significantly reduced and the amount of water gushing has increased abnormally.

[0034] If any of the above indicators appears, stop drilling operation immediately, record the current hole depth, time, drilling parameters, and determine whether it has entered the fluid filling or cavity area.

[0035] Step 2: Positioning Preparation

[0036] Withdraw the rotary drilling rig from the hole and position the high-tower pile driver or long auger directly above the center of the target hole. Use a centering device to ensure the drill pipe verticality error is ≤1%. Restart the drill bit and slowly lower it into the quicksand or suspected cave area to a depth of approximately 1-1.5 meters to create a closed grouting control space.

[0037] Step 3: High-pressure water cutting

[0038] Turn on the high-pressure water pump, with an output water pressure range of 30-40MPa, and use the drill nozzle to perform 360° rotating cutting disturbance on the surrounding fluidized soil and cave wall.

[0039] The cutting time is controlled at 3-6 minutes / meter and adjusted according to the density of the formation;

[0040] The drill bit is kept in a slight swing (±3°) during the cutting process to enhance the disturbance radius;

[0041] The cutting depth is generally 1-2m below the drill bit.

[0042] The purpose is to:

[0043] Destroy the structure of debris deposits in the cave;

[0044] Increase the permeability channel of grouting medium;

[0045] Expand grouting coverage volume.

[0046] Step 4: Directional Grouting

[0047] Stop high-pressure water cutting, switch the slurry channel, start the high-pressure grouting pump (working pressure: 40MPa), and inject the self-prepared chemical slurry into the cave area through the drill pipe, while maintaining slow rotation of the drill bit (speed 10-15rpm).

[0048] The slurry components are mixed evenly on site according to the set ratio (such as 25% agent A, 40% slag powder, water, etc.), and the viscosity is controlled at 12-18s (Marsh funnel method);

[0049] The grouting rate is controlled at 15-25L / min, and the maximum grouting volume can be adjusted according to the volume of the cave, generally 100-300L.

[0050] During grouting, ensure that the slurry spreads symmetrically along the axis of the drill hole to fill and wrap the boundaries of the cave.

[0051] Step 5: Drill bit lifting and synchronous grouting

[0052] During the grouting process, start the drilling rig and slowly lift the drill bit while keeping it rotating to achieve a composite operation mode of "rotating, lifting and grouting":

[0053] The lifting speed is controlled at 0.3-0.5m / min and the rotation is maintained at 10-15rpm;

[0054] If slurry reflux is serious or pressure drops suddenly, stop lifting and find out the cause of blockage or crack leakage;

[0055] Stop grouting when it reaches 0.5m from the top of the cave layer.

[0056] This process enables the slurry to form a continuous consolidation body and wall protection layer, avoiding uneven strength or missing cavities caused by single-point pouring.

[0057] Step 6: Termination of grouting and equipment withdrawal

[0058] After grouting to the designed depth, turn off the high-pressure pump and stirring system, and stop the rotation and lifting actions;

[0059] Clean the residual slurry in the drill pipe to avoid solidification and clogging of the equipment;

[0060] Remove the grouting hose and connecting joints and move out the drilling rig.

[0061] At this time, the entire cave or quicksand area in the hole has been initially filled with slurry and entered the curing reaction stage.

[0062] Step 7: Maintenance Phase

[0063] After the grouting is completed, it is left to stand for 24-48 hours to allow the slurry to fully react and consolidate with the original soil of the cave.

[0064] The ambient temperature should be controlled at 10-35°C. If it is lower than 10°C, heating measures should be taken.

[0065] Based on design requirements, CO2 carbonization curing can be used to enhance surface density, such as at a 20% concentration and 0.8 MPa pressure for 46 hours. After the curing period, the strength of the consolidated mass can be tested using a cone penetration test (CPT) or standard penetration test (SPT), which should reach above 1.0-1.5 MPa.

[0066] Step 8: Secondary Hole Forming

[0067] After confirming that the consolidation effect meets the requirements, re-position the rotary drilling rig for secondary drilling operations:

[0068] The initial drilling depth is 0.5m below the top of the grouting area, and the drilling speed is controlled at 20-30cm / min;

[0069] During the drilling process, record whether there is abnormal backflow of soil, hole wall collapse, torque change, etc.

[0070] After successfully passing through the consolidation section, it entered the normal bearing layer section and completed subsequent construction according to standard technology.

[0071] This treatment method ensures that the karst caves and quicksand sections that were originally unable to be drilled have stable, pressure-bearing wall protection capabilities, effectively improving the engineering drilling rate.

[0072] Optimized parameters

[0073] High pressure pump pressure: 30-40MPa;

[0074] Water cutting time: 3-6 minutes / meter;

[0075] Grouting flow rate: 15-25 L / min;

[0076] Lifting speed: 0.3-0.5m / min;

[0077] Slurry initial setting time: ≤4h, final setting time ≤8h;

[0078] Consolidated body compressive strength: ≥1.2MPa;

[0079] Slurry composition (mass percentage):

[0080] Agent A (curing agent): 20-30%;

[0081] Agent B (glidant): 10-15%;

[0082] Composite bentonite: 5-10%;

[0083] Water: Balance and replenishment.

[0084] Example 1

[0085] Karst interlayer reinforcement pile construction

[0086] In a subway project, a bored pile with a designed diameter of Φ1200mm encountered a cave when it was drilled to 14.2m. Drilling was immediately stopped and the following treatment procedures were initiated:

[0087] High-pressure water cutting disturbance for 3 minutes, with the water pressure controlled at 30 MPa;

[0088] Inject 300L of self-mixed slurry, control the slurry viscosity to 16s, and the grouting pressure to 9MPa;

[0089] Grouting rate: 20L / min, drill bit rotation speed 0.4m / min;

[0090] Curing time: 48 hours, CO2 carbonization concentration: 20%, curing time: 6 hours;

[0091] After drilling, the pile body is intact and the strength of the consolidated body reaches 1.4MPa after standard penetration test.

[0092] Example 2:

[0093] Pile foundation wall consolidation in quicksand layer

[0094] In the Coastal Expressway Interchange Bridge Project, bored piles entered the fine sand layer at a depth of 9.6m and were accompanied by water seepage:

[0095] High-pressure water disturbance for 5 minutes, water pressure 30MPa;

[0096] After starting the grouting pump, 260 L of slurry was injected at a flow rate of 22 L / min;

[0097] The slurry composition contains 30% slag powder and 12% flow aid;

[0098] The lifting speed is 0.3m / min and the rotation is maintained at 12rpm;

[0099] After 36 hours of static curing, the thickness of the consolidated layer reached 1.1m, and subsequent drilling went smoothly.

[0100] Example 3

[0101] Ultra-deep pile foundation treatment in cave section

[0102] In a certain viaduct deep foundation pile project, the pile diameter was Φ1500mm and the pile was drilled to a depth of 21.7m into a large karst cave with a span of 1.8m:

[0103] Use directional disturbance of 4 minutes / meter and high-pressure water pressure of 30MPa;

[0104] The grouting slurry is 25% curing agent, 18% bentonite, 2% NaOH activator, and 55% water;

[0105] Grouting volume 420L, pressure 10MPa;

[0106] Increase the rotation speed to 0.5m / min and the rotation speed to 14rpm;

[0107] After the grouting is completed, CO2 curing is carried out for 48 hours, and the solidified body is detected to be 1.6MPa.

[0108] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be regarded as illustrative and non-restrictive in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all changes that come within the meaning and range of equivalents of the claims be included therein.

[0109] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for treating quicksand soil retaining walls and karst caves with cast-in-place piles, characterized by: The specific steps include the following, S1, drilling identification: Use a rotary pile driver to drill into the quicksand soil or karst cave area, and stop drilling when the drilling resistance suddenly drops or the hole collapses severely; S2, Positioning Preparation: The tower pile driver is adjusted to the position directly above the pile hole, and the drill is started to drill down to the suspected cave area for the second time; S3, high-pressure water cutting: After the drill bit enters the fluidized filling, the high-pressure pump is started to perform circumferential cutting at a water pressure of 30-40 MPa to fully disturb and fluidize the loose soil around the cave; S4, directional grouting: simultaneous high-pressure injection of pre-prepared chemical slurry through the drill pipe. The slurry has fluidity and fast curing properties. S5, drill bit lifting: lift the drill rig at a constant speed of 0.3-0.5m / min while rotating the drill bit to evenly fill, wrap and consolidate the surrounding caves and quicksand areas with slurry; S6, termination of grouting: when the drill bit is lifted to the top of the cave layer, grouting is stopped and the high-pressure pump is turned off; S7, curing stage: After grouting is completed, it is left to stand for 24-48 hours to allow the slurry to react chemically with the soil to form a consolidated body; S8, secondary drilling: After the slurry is solidified and formed, the rotary drilling equipment is put into place and drilled again, successfully passing through the original cave or quicksand layer to reach the bearing layer.

2. A method for treating quicksand soil retaining walls and karst caves with bored piles according to claim 1, characterized in that: The mass percentages of the slurry include: curing agent: 20-30%; Flow aid: 10-15%; compound bentonite: 5-10%; Water: Balance and replenishment.

3. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: In step S1, a rotary drilling rig equipped with a drill bit of Φ800mm or above is used to start drilling from the surface. When the drilling depth reaches the abnormally weak or hollow layer area indicated in the design and survey report, the following indicators are monitored in real time to identify whether the problem formation has been entered: the drilling torque drops by more than 30%; the drilling footage suddenly deepens rapidly or becomes unstable; the return slag in the borehole is significantly reduced or the water inflow increases abnormally. If any of the indicators appears, the drilling operation is stopped immediately, the current hole depth, time, and drilling parameters are recorded, and it is determined whether the fluid filling or hollow area has been entered.

4. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: Step S2 includes withdrawing the rotary drilling rig from the hole mouth, moving the high tower pile driver or long spiral drilling rig to the position just above the center of the target hole, using a centering device to ensure that the verticality error of the drill rod is ≤1%, restarting the drill bit and slowly drilling into the quicksand or suspected cave area at a depth of about 1-1.5m to form a closed grouting control space.

5. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: In step S3, the high-pressure water pump is turned on, and the output water pressure range is 30-40 MPa. The surrounding fluidized soil and cave wall are subjected to 360° rotational cutting disturbance through the drill nozzle. The cutting time is controlled at 3-6 minutes / meter and adjusted according to the density of the formation. During the cutting process, the drill bit is kept slightly oscillating ±3° to increase the disturbance radius. The cutting depth is 1-2 meters below the drill bit.

6. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: In step S4, directional grouting is performed, high-pressure water cutting is stopped, the slurry channel is switched, and the high-pressure grouting pump is turned on with a working pressure of 40 MPa. The self-prepared chemical slurry is injected into the cave area through the inside of the drill pipe, while the drill bit is kept rotating slowly at a speed of 10-15 rpm. The slurry components are mixed evenly on-site according to the set ratio, and the slurry specific gravity is controlled at 1.5-1.6 g / mm³; the grouting rate is controlled at 15-25 L / min. During the grouting process, the slurry is ensured to spread symmetrically along the axis of the borehole to fill and wrap the cave boundary.

7. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: In step S5, the drill bit is lifted and grouting is performed synchronously. During the grouting process, the drilling rig is started and the drill bit is slowly lifted while being rotated to realize a composite operation mode of rotating, lifting and grouting: the lifting rate is controlled at 0.3-0.5 m / min, and the rotation is maintained at 10-15 rpm; if the slurry reflux is serious or the pressure drops suddenly, the lifting is suspended to find out the cause of the blockage or crack leakage; the grouting is stopped when the lifting reaches 0.5 m from the top of the cave layer.

8. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: In step S7, after the grouting is completed, it is left to stand for 24-48 hours to allow the slurry to fully react and consolidate with the original soil of the cave. The ambient temperature should be controlled at 10-35°C. If it is lower than 10°C, heating measures should be taken. Carbonation curing enhances surface density with parameters of 20% concentration, 0.8 MPa air pressure, and 46 hours. After the curing period, static penetration or standard penetration test is used to detect the strength of the consolidated body, which should reach above 1.0-1.5 MPa.

9. The method for treating quicksand soil retaining wall and karst cave with bored piles according to claim 1, characterized in that: In step S8, after confirming that the consolidation effect meets the requirements, the rotary drilling rig is re-positioned for secondary drilling operations: the initial drilling depth is 0.5m below the top of the grouting area, and the drilling speed is controlled at 20-30cm / min; during the drilling process, it is recorded whether there is abnormal backflow of debris, collapse of the hole wall, or torque change.