A method for anti-collapsing hole and pipe grouting construction of water-rich pebble stratum anti-floating anchor rod

Abstract

The application discloses a hole collapse prevention and pipe following grouting construction method for anti-floating anchor rods in water-rich pebble strata and relates to the technical field of geotechnical engineering and building foundation construction technology. In order to solve the problems that the existing anti-floating anchor rods are prone to hole collapse in the construction of water-rich pebble strata, it is difficult to form a hole, and un-solidified slurry is easily washed away by passive water, thereby leading to poor anchoring quality, the following technical scheme is provided, including the following steps: S1, positioning, line laying and construction preparation, S2, pipe following drilling and hole forming, S3, hole cleaning operation, S4, anchor rod lowering, and S5, linkage dewatering and pipe following grouting. The application effectively prevents hole collapse through pipe following drilling and casing wall protection, controls the dynamic water environment through linkage dewatering to avoid slurry loss, guarantees the integrity of the anchoring body and the anti-pulling bearing capacity, and is high in construction adaptability.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering and building foundation construction technology, specifically to a method for grouting construction of anti-collapse holes and pipes for anti-buoyancy anchors in water-rich pebble strata. Background Technology

[0002] With the acceleration of urbanization, the development and utilization of urban underground space is increasing, with a large number of deep foundation pit projects such as large basements and underground parking lots emerging. In areas with high groundwater levels, anti-buoyancy anchors are usually installed over a large area to resist the enormous buoyancy force exerted by groundwater on underground structures. The construction quality of anti-buoyancy anchors directly affects the safety and stability of the entire underground structure.

[0003] Among various complex geological conditions, water-rich pebble strata (especially those containing loose to dense pebble layers, with highly developed groundwater, and even connected to surrounding river systems) pose significant challenges for the construction of anti-buoyancy anchors. Currently, existing technologies face two main technical bottlenecks when dealing with such strata: First, the borehole is extremely prone to collapse, making borehole formation extremely difficult. Traditional anti-buoyancy anchor drilling typically employs ordinary rotary drilling rigs combined with mud wall protection techniques. However, water-rich, loose gravel strata have extremely high porosity and very poor self-stabilizing ability. Traditional mud wall protection is prone to significant leakage during drilling, failing to form an effective mud cake on the borehole wall. Simultaneously, abundant groundwater further dilutes the mud. Once the drill bit is withdrawn, the unsupported gravel in the borehole wall will rapidly collapse into the hole, resulting in "every bit of drilling collapses." This not only prevents the anti-buoyancy reinforcement from being lowered to the designed depth but also easily leads to engineering accidents such as drill bit burial and stuck drill bits.

[0004] Secondly, the erosion caused by flowing water leads to grout loss and anchorage failure. Even if a hole is successfully drilled and reinforcement bars are placed, serious hidden dangers remain in the subsequent grouting process. Due to the presence of groundwater in the site, foundation pit construction is usually accompanied by dewatering operations using manholes. Manhole dewatering creates a strong groundwater seepage field (i.e., a dynamic water environment) at the bottom of the foundation pit. If conventional grouting is carried out directly without intervention, the cement grout that has just been injected into the bottom of the hole and has not yet reached its initial setting state will be carried away by the strong groundwater seepage. This not only leads to a large loss of cement grout and material waste, but more critically, it will cause a significant reduction in the effective diameter of the formed anchor body, and even the appearance of "hollow" faults. The bond strength between the anchor body and the surrounding strata, and between the anchor rod and the anchor body, will drop precipitously, making it impossible to meet the anti-buoyancy design requirements and leaving huge safety hazards for later building operation.

[0005] In summary, existing anti-buoyancy anchor construction methods lack effective technical means to prevent borehole collapse and erosion by dynamic water when dealing with water-rich gravel strata. Therefore, there is an urgent need in this field for a new type of anti-buoyancy anchor construction method that can both stably form boreholes in loose gravel strata and effectively resist groundwater erosion while ensuring the quality of grouting pile formation. Summary of the Invention

[0006] The purpose of this invention is to provide a method for grouting construction of anti-buoyancy anchor bolts in water-rich pebble formations to solve the problems of existing anti-buoyancy anchor bolts being prone to hole collapse during construction in water-rich pebble formations, leading to difficulties in hole formation, and the poor anchoring quality caused by the easy loss of uncured grout due to passive water erosion.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for constructing anti-collapse holes and casing grouting for anti-buoyancy anchors in water-rich pebble strata, comprising: S1. Positioning and Construction Preparation: Obtain the target center coordinates of the anchor hole and position the casing drilling rig according to the target center coordinates; the casing drilling rig includes a power system, casing mechanism, drill rod, drill bit and casing; S2. Casing drilling: After the casing drilling rig is in place, the power system is started to drive the drill rod and drill bit to rotate and advance downwards. At the same time, the casing mechanism is started to drive the casing to advance downwards along the same axis as the drill bit until the drill bit reaches the target hole depth, forming an anchor hole with casing in the water-rich pebble strata. S3. Hole cleaning operation: When the drill bit reaches the target hole depth, stop the downward advance of the drill rod and casing, continuously input pressurized air into the drill rod, and discharge the bottom rock cuttings at the bottom of the anchor hole through the annular gap between the casing and the drill rod to the outside of the hole until the thickness of the bottom sediment in the anchor hole is ≤50mm. S4. Lowering the anchor bar: When the thickness of the sediment at the bottom of the anchor hole is ≤50mm, stop the input of pressurized air, pull the drill rod and drill bit upward along the inner cavity of the casing to the outside of the anchor hole, and keep the casing inside the anchor hole; then lower the anti-buoyancy anchor bar with the centering support and the grouting pipe to the target hole depth inside the casing, and thus complete the lowering of the anchor bar. S5. Linked dewatering and grouting: After the anchor bars are lowered, measure the height difference between the groundwater level of the dewatering well in the area where the anchor hole is located and the bottom of the foundation pit. When the height difference is <500mm, stop the dewatering operation of the dewatering well. After the pumping operation is stopped, the grouting pump is started, and cement mortar is pumped into the bottom of the anchor hole through the grouting pipe. At the same time, the casing is pulled out of the anchor hole at a speed that meets the dynamic matching conditions until the casing is completely pulled out of the anchor hole. When the casing is completely pulled out and the cement mortar in the anchor hole reaches the initial setting state, the pumping operation is resumed.

[0008] Furthermore, in S1, after the casing drilling rig is in place, the straight-line distance deviation between the actual borehole layout center and the target center coordinates is ≤50mm; and the concentricity deviation between the central axis of the casing and the central axis of the drill bit is ≤2mm.

[0009] Furthermore, in S2, when the stratum at the depth where the drill bit is located is a soft soil layer, the downward advance speed is controlled at 2.0 m / min to 3.0 m / min; when the stratum at the depth where the drill bit is located is a rock layer or a pebble layer, the downward advance speed is controlled at 0.5 m / min to 1.0 m / min.

[0010] Furthermore, in S3, the step of continuously inputting pressurized air into the drill pipe includes: controlling the power system to keep the drill pipe idling in place, and simultaneously inputting pressurized air with a pressure of 0.4MPa to 0.7MPa into the drill pipe, with the continuous input time set to 3min to 5min.

[0011] Furthermore, in S4, the centering supports are equidistantly distributed along the axial direction of the anti-buoyancy anchor bars, and the distance between two adjacent centering supports is 1.8m to 2.0m; the difference in distance between the bottom end of the grouting pipe and the bottom end of the anti-buoyancy anchor bars is ≤100mm.

[0012] Furthermore, the preparation steps of cement mortar in S5 include: mixing cement and water at a water-cement ratio of ≤0.50, continuously mixing in a mixer for ≥5 minutes, then filtering the mixed liquid through a filter screen with a pore size of 2mm to 3mm, and inputting it into a slurry storage tank for continuous low-speed mixing to obtain cement mortar.

[0013] Furthermore, in S5, the grouting pressure at the bottom of the grouting pump is divided into two fixed intervals based on the formation density: When the stratum is a medium-dense or dense gravel layer with a standard penetration test blow count N≥10, the bottom grouting pressure is set to 3.0MPa~5.0MPa. When the stratum is soft soil or slightly dense gravel layer with a standard penetration test blow number N < 10, the grouting pressure at the bottom of the hole is set to 2.0 MPa to 3.0 MPa.

[0014] Furthermore, in S5, the dynamic matching conditions are:

[0015] in, The target lifting speed is within the range of 0.5 m / min to 1.0 m / min. This refers to the grouting flow rate per unit time. The square of the outer diameter of the casing; The filling safety factor to prevent grout interruption or diameter reduction is set between 1.15 and 1.30.

[0016] Furthermore, in S5, the horizontal straight-line distance between the dewatering well and the anchor hole is ≤15m, and the depth of the dewatering well is greater than the target hole depth.

[0017] Furthermore, after S5, once the casing is completely pulled out of the anchor hole, monitor the overflow of grout at the anchor hole opening; when the density difference between the overflowing cement mortar and the density at the time of injection is ≤0.05g / cm³, and no air bubbles emerge from the anchor hole opening for 1 minute, the grouting is deemed complete and the grouting pump is shut off; within 30 minutes after shutting off the grouting pump, pour concrete into the anchor hole opening to form a sealing layer, with a vertical thickness ≥100mm.

[0018] The present invention has the following beneficial effects: 1. This invention employs casing drilling technology, in which the casing and drill bit advance synchronously, forming a temporary protective wall in the water-rich loose gravel layer, effectively preventing hole collapse and ensuring the quality of anchor bolt hole formation.

[0019] 2. By using the "grouting and pipe pulling" process, the grout pressure and casing support are used to prevent secondary hole collapse; at the same time, a linkage mechanism with the dewatering well is established to suspend the surrounding dewatering during grouting to avoid grout loss due to water erosion, and to ensure the integrity of the anchor body and its pull-out bearing capacity.

[0020] 3. The drilling speed and grouting pressure are dynamically adjusted according to the formation density, and a formula for calculating the pipe pulling speed is introduced to achieve precise matching between grout filling degree and pipe pulling rhythm, which is suitable for complex geological conditions. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the construction process of an anti-collapse hole and pipe grouting method for an anti-buoyancy anchor rod in a water-rich pebble stratum according to an embodiment of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0023] Example As attached Figure 1 As shown in the figure, this embodiment provides a method for grouting construction of anti-collapse holes and casing for anti-buoyancy anchors in water-rich pebble strata. The specific steps are as follows: S1: Positioning and Construction Preparation. First, obtain the target center coordinates of each anchor hole according to the design drawings. Use a total station for precise layout, mark the anchor hole locations with red paint, and set fixed control points outside the anti-buoyancy zone for verification during construction.

[0024] Move the tracked hydraulic casing drilling rig to the borehole position and adjust the rig body to ensure the drill rod verticality meets design requirements. After the drilling rig is in place, perform a position check: the straight-line distance deviation between the actual borehole layout center and the target center coordinates must be strictly controlled within ≤50mm. Simultaneously, check the drill string connections to ensure the concentricity deviation between the casing's central axis and the drill bit's central axis is ≤2mm, guaranteeing that the casing and drill bit advance synchronously without deviation during drilling.

[0025] The main components of a drilling rig include the power system, casing mechanism, drill rod, drill bit, and casing.

[0026] S2: After the drilling rig is positioned and debugged, the power system is activated to drive the drill rod and drill bit to rotate and advance downwards. Simultaneously, the casing-following mechanism is activated to drive the casing to follow the drill bit downwards in the same direction. The drilling speed is dynamically adjusted according to changes in the formation. When the strata at the depth where the drill bit is located are soft soil layers (such as silty clay and silt), the downward advance speed should be controlled at 2.0 to 3.0 m / min; When the drill bit enters a pebble layer or rock layer, reduce the speed to 0.5–1.0 m / min to minimize disturbance to the borehole wall and ensure borehole quality.

[0027] During drilling, the air compressor continuously outputs high-pressure air, which blows the rock cuttings from the bottom of the hole out through the annular gap between the casing and the drill pipe via the center hole of the drill pipe, achieving dry cuttings removal and avoiding leakage problems caused by mud wall protection. When the drilling rig instruments display or the measuring rope confirms that the drill bit has reached the designed hole depth, the downward advance is stopped. At this time, the casing is still retained in the anchor hole to form a temporary wall protection.

[0028] Step S3: Hole cleaning operation. After the drill bit reaches the target hole depth, stop the downward advancement of the drill rod and casing, but keep the drill rod spinning in place. Simultaneously, continuously inject pressurized air at a pressure of 0.4–0.7 MPa into the drill rod for 3–5 minutes. The high-pressure air is ejected from the bottom of the drill bit, forcefully blowing out the remaining rock cuttings and sediment from the bottom of the hole along the annular gap between the casing and the drill rod. After hole cleaning, use a measuring rope to check the thickness of the sediment at the bottom of the hole, ensuring it is ≤50mm. If the sediment exceeds the standard, the hole cleaning operation can be repeated until it is acceptable.

[0029] Step S4: Lower the anchor bar. Once the hole is cleaned to the required standard, stop supplying pressurized air. First, slowly pull the drill rod and drill bit upwards along the inner cavity of the casing to the outside of the hole. At this time, the casing remains inside the anchor hole to continue protecting the hole wall and prevent hole collapse.

[0030] Subsequently, the pre-processed anti-buoyancy anchor bars are lowered into the casing. The anchor bars are HRB400E grade steel bars, with 2Ø25 bars in area #1 (effective length 6.7m, anchorage length 7.5m) and 2Ø25 bars in area #2 (effective length 8.0m, anchorage length 8.8m). Ø8 steel bar centering supports are welded to the steel bars at intervals not exceeding 2m (in this embodiment, the spacing between adjacent supports is 1.8~2.0m) to ensure the steel bars are centered in the anchor hole. Simultaneously, the grouting pipe (PE DN25) is tied to the steel bars, with the bottom end of the grouting pipe ≤100mm below the bottom end of the steel bar to ensure that the grout can fill from the bottom of the hole upwards.

[0031] Before lowering the anchor bolts, the quality and length of the anchor bolts must be inspected and approved. The anchors should be lowered slowly and manually to avoid collisions with the borehole wall.

[0032] Step S5: Combined Dewatering and Grouting. After the anchor bars are lowered, conduct combined dewatering before grouting. Measure the difference in elevation between the groundwater level of the dewatering well (with a horizontal distance ≤ 15m from the anchor hole and a well depth greater than the anchor hole depth) and the bottom of the foundation pit. If the difference is less than 500mm (i.e., the groundwater level is 500mm below the bottom of the foundation pit), immediately stop pumping from the dewatering well to reduce the scouring of the grout by moving water. If the difference is ≥ 500mm, grouting can proceed directly.

[0033] After stopping the pumping, start the grouting pump. First, test the pump to purge air from the pipeline and ensure it is unobstructed. The grouting slurry uses M35 cement mortar, and is prepared strictly according to the mix proportions determined by the test: water-cement ratio ≤ 0.50, mixing time ≥ 5 minutes. After mixing, filter through a 2-3 mm filter screen and pour into the slurry storage tank, stirring continuously at low speed to prevent sedimentation.

[0034] Grouting pressure is set according to the formation density: For medium-dense and dense pebble layers (standard penetration blow count N≥10), the grouting pressure at the bottom of the hole should be controlled at 3.0~5.0MPa; For soft soil or slightly dense gravel layers (N < 10), the pressure should be controlled between 2.0 and 3.0 MPa.

[0035] After grouting begins, cement mortar is pumped into the bottom of the hole through the grouting pipe, while the casing is simultaneously pulled out. The casing pulling speed needs to be dynamically matched with the grouting flow rate, calculated using the following formula:

[0036] in, The target lifting speed is within the range of 0.5 m / min to 1.0 m / min. This refers to the grouting flow rate per unit time. This is the square of the outer diameter of the casing (the space occupied by the casing in the soil is determined by its outer diameter. When the casing is pulled upwards, the cement mortar not only needs to fill the space inside the original casing, but also needs to immediately fill the outer annular gap left after the casing wall is removed). The filling safety factor to prevent grout interruption or diameter reduction is set between 1.15 and 1.30.

[0037] During casing removal, closely observe the grout return at the borehole opening. When thick grout continuously overflows from the opening, and the density difference between the overflow grout and the injected grout is ≤0.05 g / cm³, and no air bubbles emerge within 1 minute, it indicates that the grouting is dense, and grouting can be stopped. After the casing is completely removed, seal the borehole opening within 30 minutes by pouring plain concrete or cement mortar to form a sealing layer with a thickness ≥100mm, and smooth and compact it.

[0038] After grouting is completed, continue pumping from the dewatering wells until the cement mortar inside the borehole reaches its initial setting state (usually about 2 hours based on test blocks under the same conditions or field experience). After initial setting, resume pumping from the dewatering wells. When resuming, it is advisable to use intermittent startup to avoid sudden drops in water level that could cause ground subsidence.

[0039] 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.

Claims

1. A method for grouting anti-collapse holes and casing of anti-buoyancy anchors in water-rich pebble strata, characterized in that, Includes the following steps: S1. Positioning and Construction Preparation: Obtain the target center coordinates of the anchor hole, and position the casing drilling rig according to the target center coordinates; the casing drilling rig includes a power system, casing mechanism, drill rod, drill bit and casing; S2. Casing drilling: After the casing drilling rig is in place, the power system is started to drive the drill rod and drill bit to rotate and advance downwards. At the same time, the casing mechanism is started to drive the casing to advance downwards along the same axis as the drill bit until the drill bit reaches the target hole depth, forming an anchor hole with the casing in the water-rich pebble stratum. S3. Hole cleaning operation: When the drill bit reaches the target hole depth, stop the downward advance of the drill rod and casing, continuously input pressurized air into the drill rod, and discharge the bottom rock cuttings at the bottom of the anchor hole through the annular gap between the casing and the drill rod to the outside of the hole until the thickness of the bottom sediment in the anchor hole is ≤50mm. S4. Lowering the anchor bar: When the thickness of the sediment at the bottom of the anchor hole is ≤50mm, stop the input of pressurized air, pull the drill rod and drill bit upward along the inner cavity of the casing to the outside of the anchor hole, and keep the casing inside the anchor hole; then lower the anti-buoyancy anchor bar with centering support and the grouting pipe to the target hole depth inside the casing, thereby completing the lowering of the anchor bar; S5. Linked dewatering and grouting: After the anchor bars are lowered, measure the height difference between the groundwater level of the dewatering well in the area where the anchor hole is located and the bottom of the foundation pit. When the height difference is <500mm, stop the pumping operation of the dewatering well. After the pumping operation is stopped, the grouting pump is started, and cement mortar is pumped into the bottom of the anchor hole through the grouting pipe. At the same time, the casing is pulled out of the anchor hole at a speed that meets the dynamic matching conditions until the casing is completely pulled out of the anchor hole. When the casing is completely pulled out and the cement mortar in the anchor hole reaches the initial setting state, the pumping operation is resumed.

2. The method for grouting construction of anti-collapse holes and casings for anti-buoyancy anchors in water-rich pebble strata according to claim 1, characterized in that, In step S1, after the casing drilling rig is in place, the straight-line distance deviation between the actual borehole layout center and the target center coordinates is ≤50mm; and the concentricity deviation between the central axis of the casing and the central axis of the drill bit is ≤2mm.

3. The method for grouting the anti-collapse hole of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, In step S2, when the stratum at the depth where the drill bit is located is a soft soil layer, the downward advancing speed is controlled to be 2.0 m / min to 3.0 m / min; when the stratum at the depth where the drill bit is located is a rock layer or a pebble layer, the downward advancing speed is controlled to be 0.5 m / min to 1.0 m / min.

4. The method for grouting the anti-collapse hole and casing of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, In step S3, the step of continuously inputting pressurized air into the drill pipe includes: controlling the power system to keep the drill pipe idling in place, and simultaneously inputting pressurized air with a pressure of 0.4MPa to 0.7MPa into the drill pipe, and setting the continuous input time to 3min to 5min.

5. The method for grouting the anti-collapse hole of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, In step S4, the centering supports are equidistantly distributed along the axial direction of the anti-buoyancy anchor bars, and the distance between two adjacent centering supports is 1.8m to 2.0m; the distance difference between the bottom end of the grouting pipe and the bottom end of the anti-buoyancy anchor bars is ≤100mm.

6. The method for grouting the anti-collapse hole and casing of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, The preparation steps of the cement mortar in S5 include: mixing cement and water at a water-cement ratio of ≤0.50, continuously mixing in a mixer for ≥5 minutes, then filtering the mixed liquid through a filter screen with a pore size of 2mm to 3mm, and inputting it into a slurry storage tank for continuous low-speed mixing to obtain the cement mortar.

7. The method for grouting the anti-collapse hole and casing of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, In step S5, the grouting pressure at the bottom of the grouting pump is divided into two fixed intervals based on the formation density: When the stratum is a medium-dense or dense pebble layer with a standard penetration blow count N≥10, the grouting pressure at the bottom of the hole is set to 3.0MPa~5.0MPa; When the stratum is soft soil or slightly dense gravel layer with a standard penetration test blow count N < 10, the grouting pressure at the bottom of the hole is set to 2.0 MPa to 3.0 MPa.

8. The method for grouting the anti-collapse hole and casing of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, In S5, the dynamic matching condition is: in, The target lifting speed is within the range of 0.5 m / min to 1.0 m / min. This refers to the grouting flow rate per unit time. The square of the outer diameter of the sleeve; The filling safety factor to prevent grout interruption or diameter reduction is set between 1.15 and 1.

30.

9. The method for grouting the anti-collapse hole and casing of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, In step S5, the horizontal straight-line distance between the dewatering well and the anchor hole is ≤15m, and the depth of the dewatering well is greater than the target hole depth.

10. The method for grouting the anti-collapse hole of the anti-buoyancy anchor bolt in water-rich pebble strata according to claim 1, characterized in that, After step S5, once the casing is completely pulled out of the anchor hole, monitor the overflow of grout at the anchor hole opening. When the density difference between the overflowing cement mortar and the density during injection is ≤0.05g / cm³, and no air bubbles emerge from the anchor hole opening for 1 minute, the grouting is deemed complete and the grouting pump is shut off. Within 30 minutes after shutting off the grouting pump, pour concrete into the anchor hole opening to form a sealing layer, the vertical thickness of which is ≥100mm.

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