Dissolved geology river-crossing bridge foundation construction method

Abstract

The invention provides a dissolved geology river-crossing bridge foundation construction method, which relates to the technical field of bridge foundation construction, and comprises the steps of pile foundation hole forming and cleaning, anchor rod hole site measurement lofting and drilling, hollow anchor rod installation and grouting preparation, pressure grouting, reinforcement cage lowering, pile body concrete pouring and the like. The foundation bearing capacity can be remarkably improved, meanwhile, pile foundation deformation is restrained, and horizontal resistance is enhanced.

Description

Technical Field

[0001] This invention relates to the field of bridge foundation construction technology, specifically a method for constructing bridge foundations for karst river crossings. Background Technology

[0002] Currently, when bridge engineering needs to traverse karst rock layers, fill karst caves, and water-rich strata, it often faces four major challenges: First, poor stability during the drilling process, mud loss, and ground subsidence; second, collapse of the borehole after drilling through karst caves, deformation of the reinforcing cage, and excessive concrete volume; third, groundwater infiltration alters the mix ratio, and karst caves may lead to quality defects such as broken piles and mud inclusions; fourth, the loose filling strata have insufficient bearing capacity and may experience brittle failure under load, and the development of rock fissures around the piles leads to a significant reduction in side friction, resulting in excessive or uneven settlement of the pile foundation under the design load. Summary of the Invention

[0003] In view of the above-mentioned prior art, the present invention proposes a construction method for bridge foundations in karst geological conditions.

[0004] The present invention provides a method for constructing a bridge foundation in karst terrain, comprising the following steps: Step 1, Drilling and cleaning of pile foundation holes: After drilling, check the hole diameter and verticality. The pile hole diameter deviation should be ≤ ±50mm and the hole inclination should be ≤1%. After cleaning the hole, control the thickness of sediment at the bottom of the hole to be ≤50mm. Step 2, Anchor Bolt Hole Position Measurement and Drilling: In the pile hole after cleaning, mark out the designed hole position of each hollow anchor bolt. The anchor bolts are evenly distributed along the circumference of each layer in a quincunx pattern. Drill holes into the outer rock layer of the pile foundation according to the design angle. Step 3, Hollow Anchor Installation and Grouting Preparation: Drill holes in the sidewall of the pile hole, insert the hollow anchor into the drilled hole. The hollow anchor has multiple overflow holes. Install grout stop plugs, washers and nuts at the hole opening to seal the hollow anchor with the drilled hole wall. Connect all the grouting ports of the hollow anchor to the grouting equipment through grouting pipes. Step 4, Pressure Grouting: Start the grouting equipment and perform grouting; Step 5: Lowering the reinforcing cage and pouring the pile concrete: After the grout has initially set and formed sufficient strength, lower the reinforcing cage according to the conventional process; use the tremie method to continuously pour the pile concrete to the design elevation.

[0005] Preferably, in step 2, the drilling depth is 2-3 times the pile diameter, and a geotextile filter is wrapped around the outside of the hollow anchor rod.

[0006] Preferably, in step 4, the grouting equipment is a two-liquid grouting machine, which prepares cement-water glass two-liquid grout according to the ratio determined by the experiment.

[0007] Preferably, in step 4, the grouting process is divided into three stages: Initial low-pressure infiltration stage: The initial pressure is 0.5-1.0 MPa. When slurry is continuously discharged from the exhaust pipe, it indicates that the shallow cavities have been basically filled and the conditions for pressurization are met. Gradual pressure escalation and fracturing stage: After confirming the penetration and filling effect, gradually increase the pressure to the design final pressure in increments of 0.2-0.3 MPa per cycle; Pressure stabilization and compaction stage: After reaching the final design pressure, maintain the pressure stable for a period of time.

[0008] Compared to existing technologies, the beneficial effects of this invention are as follows: This invention provides a construction method for karst bridge foundations across rivers. After the pile foundation is drilled and before the reinforcing cage is lowered, hollow grouting anchors are driven into the surrounding karst strata at a specific angle along the pile sidewall. This is similar to implanting a directional three-dimensional skeleton into the rock mass around the pile, precisely reinforcing the key areas around the pile. Through grouting, the grout penetrates, splits, and fills the pre-reserved holes in the anchors and the original fracture network of the rock mass, forming a composite reinforcement zone of conglomerate with the pile hole as the core and spreading outward. This significantly improves the bearing capacity of the foundation, while restraining pile deformation and enhancing horizontal resistance.

[0009] Furthermore, the pre-designed hollow anchor rod has its inner end anchored to the subsequently poured pile concrete, while its outer end is fixed in the deep, stable rock mass with grout. This structure makes the anchor rod a force transmission link between the pile and the distant stable rock layer, efficiently and accurately transferring and distributing part of the load borne by the pile to deeper, more stable rock layers. The pile, anchor rod, and reinforced body together form a root-like deep foundation system, combining the advantages of friction piles and end-bearing piles, significantly optimizing the stress characteristics of the pile foundation. Attached Figure Description

[0010] Figure 1 This is a construction diagram illustrating the construction method for a river-crossing bridge foundation in karst terrain, as described in this embodiment of the invention.

[0011] Figure 2 This is a schematic diagram of the hollow anchor rod in an embodiment of the present invention. Detailed Implementation

[0012] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0013] Example: Figure 1-2 The method for constructing a bridge foundation in karst terrain includes the following steps: Step 1, Drilling and cleaning of pile foundation holes: After drilling, check the hole diameter and verticality. The pile hole diameter deviation should be ≤ ±50mm and the hole inclination should be ≤1%. After cleaning the hole, control the thickness of sediment at the bottom of the hole to be ≤50mm.

[0014] Step 2: Anchor Bolt Hole Measurement and Drilling: Within the cleaned pile hole, surveyors precisely mark the designed hole positions for each hollow anchor bolt. Anchor bolts are evenly distributed along the circumference of each layer in a quincunx pattern. Using a specialized geological drilling rig, boreholes are drilled into the outer rock strata of the pile foundation at the designed angle, typically 15°-30° to the pile sidewall, adjusted according to the direction of the main fissures. Drilling depth is a key technical parameter; it should penetrate the main loosened zone and dense fissure zone around the pile, reaching into relatively intact bedrock. The drilling depth is 2-3 times the pile diameter. For example, with a pile diameter of 1.8m, the anchor bolt length is 5.4m. Geotextile mesh is wrapped around the hollow anchor bolts to prevent grout backflow. The specific depth is determined through calculation and testing, and the borehole diameter matches the selected hollow anchor bolt specifications.

[0015] Step 3, Hollow Anchor Installation and Grouting Preparation: A small pneumatic drilling rig is used to drill holes in the sidewall of the pile hole. The prefabricated hollow anchor rods are slowly sent into the drilled holes. The hollow anchor rods have multiple overflow holes. Grout stop plugs, washers, and nuts are installed at the hole openings to ensure that the hollow anchor rods are effectively sealed to the borehole wall. The grouting ports of all hollow anchor rods are connected to the grouting equipment through grouting pipes, which serve as grouting channels and load-bearing skeletons to directionally transmit grouting pressure and ensure that the grout fills and disperses the voids.

[0016] Step 4, Pressure Grouting: Start the grouting equipment, which uses a two-component grouting machine. The two-component grout is prepared according to the experimentally determined ratio, for example, the cement-water glass two-component grout water-cement ratio is 0.8:1-1:1, the water glass concentration is 35%, and the two-component volume ratio is 1:0.3-1:0.5. The two-component grout sets rapidly, with an initial setting time of 30-60 seconds, which can block the seepage of solution water and avoid diluting the subsequent concrete. Grouting is then carried out, and the grouting process is divided into three stages: Initial low-pressure infiltration stage: The initial pressure is 0.5-1.0MPa. The cement-water glass double liquid grout can slowly infiltrate along the tiny solution gaps (width <5mm) to avoid direct splitting by high pressure and grout channeling. When it is observed that the vent pipe continuously discharges grout (the discharge concentration is consistent with the injection concentration), it indicates that the shallow solution gaps have been basically filled and the conditions for pressurization are met. Gradual pressure escalation and fracturing stage: After confirming the penetration and filling effect, the pressure is gradually increased to the design final pressure in increments of 0.2-0.3 MPa / time, usually 3-5 MPa, and adjusted according to the formation strength; Under high pressure, the grout can fracture medium and large solution fissures (width > 5 mm) or loose fillings, forming dendritic diffusion channels and expanding the reinforcement range; Pressure stabilization and compaction stage: After reaching the final design pressure, maintain the pressure for 30 minutes. During the pressure stabilization process, the grout can further compact the loose particles in the pores, expel residual air, improve the density of the stone body, and prevent the grout from flowing back and forming voids due to a sudden drop in pressure.

[0017] Step 5: Lowering the reinforcing cage and pouring the pile concrete: After the grout has initially set and formed sufficient strength, lower the reinforcing cage according to the conventional process; at this time, the inner end of the pre-embedded hollow anchor rod is naturally inserted into the inside of the reinforcing cage; then, the pile concrete is continuously poured to the design elevation using the tremie pipe method; when vibrating the concrete, care should be taken to avoid the anchor rod to ensure the bonding quality between it and the concrete.

[0018] This embodiment proposes an innovative combined pile foundation reinforcement technology using hollow anchor grouting and pile foundation co-construction. Its core innovation lies in shifting from passive treatment to active reinforcement and optimizing independent components into a holistic system. The main procedures occur within the window period after drilling and before lowering the reinforcing cage, as detailed below: ① After the pile foundation borehole is formed and before the reinforcing cage is lowered, hollow grouting anchors are driven into the surrounding karst strata at a specific angle along the pile sidewall. This is similar to implanting a directional three-dimensional skeleton into the rock mass around the pile, precisely reinforcing the key areas around the pile. Through grouting, the grout penetrates, splits, and fills the pre-reserved holes in the anchors and the original fracture network of the rock mass, forming a composite reinforcement zone of concretion with the pile hole as the core and spreading outward. This significantly improves the bearing capacity of the foundation, while restraining pile deformation and enhancing horizontal resistance.

[0019] ② The cement-water glass double-liquid grout is injected by a grouting machine. The double-liquid grout solidifies quickly, which can block the seepage of solution water and avoid diluting the subsequent concrete.

[0020] ③ Overall Coordinated Force-Bearing Principle: The pre-designed hollow anchor rod has its inner end anchored inside the subsequently poured pile concrete, while its outer end is fixed in the deep, stable rock mass with the help of grout. This structure makes the anchor rod a force-transferring link between the pile and the distant stable rock layer, efficiently and accurately transferring and distributing part of the load borne by the pile to deeper, more stable rock layers. The pile, anchor rod, and reinforced body together form a root-like deep foundation system, combining the advantages of friction piles and end-bearing piles, significantly optimizing the stress characteristics of the pile foundation.

[0021] This embodiment utilizes innovative processes and designs to form an integrated stress-bearing system between the anchor bolts and the pile foundation, thereby achieving the purpose of reinforcing the strata and realizing the synergistic optimization of karst strata reinforcement and pile foundation stress, fundamentally improving the overall working performance of the pile foundation.

[0022] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent solutions made using the contents of the present invention specification, whether directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of the present invention.

Claims

1. A method of constructing a ground-hugging geotechnical river-crossing bridge foundation, characterized by, It comprises the following steps: Step 1, pile hole forming and hole cleaning: after drilling the hole, check the hole diameter and hole verticality, the pile hole diameter deviation is ≤±50 mm, the hole inclination is ≤1%, after hole cleaning, the hole bottom sediment thickness is controlled to be ≤50 mm; Step 2, anchor hole position measurement and drilling: in the pile hole after hole cleaning, the design hole position of each hollow anchor rod is laid out, the anchor rods are evenly distributed along the circumference at each layer, and are arranged in a plum blossom shape; drill holes to the rock layer outside the pile foundation according to the design angle; Step 3, hollow anchor rod installation and grouting preparation: drill holes in the side wall of the pile hole, send the hollow anchor rod into the drilled hole, the rod body of the hollow anchor rod is provided with a plurality of grout overflow holes, install a grout stopper, a pad and a nut at the hole mouth to seal between the hollow anchor rod and the drilled hole wall; connect the grouting ports of all hollow anchor rods to the grouting equipment through the grouting pipeline; Step 4, pressure grouting: start the grouting equipment and perform grouting; Step 5, lowering the steel reinforcement cage and pouring the pile body concrete: after the grouting body is initially cured to form sufficient strength, lower the steel reinforcement cage according to the conventional process; Pour the pile body concrete continuously to the design elevation by using the duct method.

2. The method of constructing a ground improvement river-crossing bridge foundation according to claim 1, wherein In step 2, the drilling depth is 2-3 times of the pile diameter, and a geotextile filter screen is wrapped outside the hollow anchor rod.

3. The method of constructing a ground-based river-crossing bridge foundation according to claim 1 or 2, characterized in that, In step 4, the grouting equipment uses a double-liquid grouting machine, which prepares cement-silicate double-liquid slurry according to the mixing ratio determined by the test.

4. The method of constructing a ground-based river-crossing bridge pier according to claim 1 or 2, wherein In step 4, the grouting process is divided into three stages: Initial low-pressure penetration stage: the initial pressure is 0.5-1.0 MPa, when continuous grout is observed from the exhaust pipe, it indicates that the shallow dissolution fissure has been basically filled, and the pressure is ready to be raised; Gradually increasing pressure splitting stage: after confirming the penetration and filling effect, gradually increase the pressure by 0.2-0.3 MPa per time to the design final pressure; Stable pressure compaction stage: after reaching the design final pressure, keep the pressure stable for a period of time.

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