A pile foundation construction method based on karst geological structure distribution

Abstract

The present application relates to the field of grouting construction, in particular to a pile foundation construction method based on distributed karst geological structure, step 1: drill several pile holes in the karst area, the spacing between adjacent pile holes is 2m-3m; step 2: inject concrete into the pile hole and make it solidify into a friction pile; step 3: within 7-8h after the concrete solidifies into a friction pile, use high-pressure water to dredge the grouting pipe; step 4: after all the friction piles are formed and the strength of the friction pile reaches more than 70%, carry out grouting operation; when grouting, the grouting holes at the same position are alternately and equally grouted, when no grouting pressure is detected, intermittent grouting is adopted, and the intermittent grouting time at the pile end is 5-6h; step 5: when the total amount of grouting and grouting pressure both meet the design requirements, the grouting can be terminated; step 6: after the friction pile load detection meets the standard, pour raft on the top of all friction piles in the same karst area. Through the implementation of the present application, the problem of settlement of friction piles located in the karst area is solved.

Description

Technical Field

[0001] This invention relates to the field of grouting construction, and more specifically to a pile foundation construction method based on karst geological structures. Background Technology

[0002] During the structural exploration for the building construction, the applicant discovered large karst caves in the soil beneath some of the structural load-bearing walls. These caves were filled with karst material, and the soil above them was red clay, primarily composed of cohesive soil. Furthermore, due to the low-lying terrain of the site, plain fill was used to raise the elevation to the required level during initial construction. This fill layer consisted of muddy, gravelly soil, and multiple boreholes at the site failed to reveal any rock strata. Therefore, directly pouring concrete piles in this area using traditional methods would pose a significant risk of settlement. Thus, a concrete pile construction method that minimizes this risk is needed. Summary of the Invention

[0003] The present invention aims to provide a pile foundation construction method based on karst geological structures to solve the problem of settlement of friction piles located in karst areas.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a pile foundation construction method based on karst geological structures, comprising the following construction steps:

[0005] Step 1: Drill several pile holes in the karst area, with a spacing of 2m-3m between adjacent pile holes. Weld auxiliary supports horizontally around the circumference of the reinforcing cage and tie the grouting pipe to the auxiliary supports so that the distance between the grouting pipe and the outer wall of the friction pile is less than 25mm. Set grouting holes at the pile end and pile side of the grouting pipe. Except for the grouting hole located in the backfill layer at the top of the pile, the other grouting holes are arranged in the middle of the red clay layer.

[0006] Step 2: Lower the steel cage with the grouting pipe tied to it into the bottom pile hole, and inject concrete into the pile hole to solidify it into a friction pile.

[0007] Step 3: Within 7-8 hours after the concrete has solidified into a friction pile, use high-pressure water to clear the grouting pipe.

[0008] Step 4: After all friction piles in the same karst area are completed and the strength of the friction piles reaches more than 70%, grouting operation is carried out. During grouting, the grouting holes at the same location are grouted in turn with equal amounts. When no grouting pressure is detected, intermittent grouting is adopted, and the intermittent grouting time at the pile end is 5-6 hours.

[0009] Step 5: Grouting can be terminated when both the total grouting volume and grouting pressure meet the design requirements, or when the total grouting volume has reached 75% of the design value and the grouting pressure exceeds 3MPa.

[0010] Step 6: After the friction pile load test meets the standard, pour a raft slab on top of all friction piles in the same karst area.

[0011] The principle and advantages of this scheme are as follows: Due to the loose soil and lack of a rock layer for bearing capacity in this area, the risk of settlement is relatively high. This scheme employs post-grouting treatment at the pile tips and sides of the friction piles to reinforce the soil structure at the bottom and around the piles, thereby increasing the bearing capacity of the pile tips and the frictional resistance of the pile sides. Simultaneously, a group pile bearing method is used in the karst area. This involves designing multiple friction piles and installing raft foundations on them to connect them into a unified structure, allowing them to share the load and further reducing the risk of friction pile settlement.

[0012] However, during the grouting pipe clearing process, the inventors discovered that when grouting the same batch of friction piles, some of the grouting holes could not be cleared, leading to grouting failure. Since the grouting holes were deeply buried inside the already formed friction piles, it was very difficult to find the real cause of the blockage. After a long period of analysis of the problem, the inventors concluded that the grouting holes might be located in the red clay area, and the distance between the grouting holes and the outer wall of the friction pile was too far, causing the blockage to occur because the grouting holes could not break through the side wall of the friction pile during the clearing process.

[0013] After identifying the cause of the blockage, a contradiction arose in the actual solution: if the diameter of the reinforcing cage was increased to a suitable range (i.e., the range that allows for unblocking the grouting hole), the reinforcing cage would be too close to the outer wall of the friction pile, affecting the overall bearing capacity of the friction pile. Therefore, to address this problem, the inventors welded auxiliary supports for binding the grouting pipes transversely along the circumference of the reinforcing cage, ensuring that the distance between the grouting pipes and the outer wall of the friction pile is less than 25mm. This ensures both the bearing capacity of the friction pile and, with the help of the auxiliary supports, allows the grouting pipes to be closer to the outer wall of the friction pile. Therefore, during the unblocking process, pressurized water can more easily break through the side wall of the friction pile, achieving the desired unblocking effect.

[0014] After resolving the issue of unblocking the grouting pipe, a new problem arose during the grouting process: the grouting pressure at the pile tip remained low. Initial analysis suggested that the pile tip might be sitting on karst filler, where the high permeability caused grout loss. The grout was thickened, but the grouting pressure still wouldn't rise. Intermittent grouting was then considered. Initially, the grouting pressure reached 0.4 MPa, but it disappeared again after one hour. After multiple analyses and considerations, the spacing between adjacent pile holes was adjusted to 2-3 meters, and the grouting interval was set at 5-6 hours. After this, the grouting pressure at the pile tip stabilized within the normal range.

[0015] Preferably, as an improvement, in step 4, the intermittent grouting method is as follows: when there is no grouting pressure at the pile end, the first grouting volume is 1.5t per grouting pipe, with an appropriate amount of early strength agent added; the second grouting volume is 1.5t per grouting pipe; when there is no grouting pressure on the pile side, the first grouting volume is 1t per grouting pipe, with an appropriate amount of early strength agent added; the second grouting volume is 1t per grouting pipe.

[0016] Preferably, as an improvement, the grouting at the pile tip can be terminated when the grouting pressure at the pile tip reaches 0.5-2 MPa.

[0017] Preferably, as an improvement, in step 4, the water-cement ratio of the grout is 0.4, and the grouting flow rate is controlled at 30-40 L / min during grouting.

[0018] Preferably, as an improvement, a layer of stone is laid at the bottom of the pile hole before step 2.

[0019] Preferably, as an improvement, a sealing unit is provided on the outer wall of the grouting pipe at the grouting hole. The sealing unit includes a positioning layer, a plugging layer and a sealing layer from the inside to the outside. The plugging layer includes a plurality of plugging parts inserted into each grouting hole.

[0020] Preferably, as an improvement, the plugging component includes an arc-shaped cap and an insert connected to the concave surface of the cap, the arc of which matches the arc of the sidewall of the grouting pipe.

[0021] Preferably, as an improvement, in step 6, the thickness of the raft foundation is 1m, a 100mm thick concrete pad is set under the raft foundation, and the top surface elevation of the raft foundation is -1.35m. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the installation of the auxiliary support in Example 1.

[0023] Figure 2 for Figure 1 Enlarged view of point B in the middle.

[0024] Figure 3 for Figure 2 A bottom view showing the auxiliary support and grouting pipe tied together.

[0025] Figure 4 This is a schematic diagram of the grouting pipe in Example 1 (the plugging component is not shown on the left).

[0026] Figure 5 for Figure 4 Enlarged sectional view at point A in the middle.

[0027] Figure 6 for Figure 5Top view of the plug hole component. Detailed Implementation

[0028] The following detailed description illustrates the specific implementation method:

[0029] The reference numerals in the accompanying drawings include: friction pile 1, reinforcing cage 2, pile hole 3, grouting pipe 4, auxiliary support 5, fixed pipe 6, movable rod 7, bolt 8, grouting hole 9, binding component 10, cap 11, plug 12, protrusion 13.

[0030] Example 1

[0031] A pile foundation construction method based on karst geological structures includes the following construction steps:

[0032] Step 1: Drill 12 pile holes 3 with a diameter of 800mm and a depth of 22m in the karst area. The pile holes 3 are arranged in a matrix with an adjacent hole spacing of 2.4m. This hole spacing is optimal, effectively preventing cross-hole problems between two pile holes 3 during the subsequent grouting process, and better ensuring the overall bearing capacity of the friction piles 1 in this area. On one side of the 12 matrix pile holes 3, drill 4 pile holes 3 with a diameter of 1200mm and a depth of 40m in the karst area. The 4 pile holes 3 are distributed in a rhomboid pattern. Lay a layer of stone at the bottom of the pile holes 3 to reduce the risk of grouting hole blockage.

[0033] like Figure 1 As shown, at least two rows of auxiliary supports 5 are welded horizontally around the circumference of the reinforcing cage 2, with at least two auxiliary supports in each row. The auxiliary supports 5 in each row are located on the same straight line and parallel to the axis of the reinforcing cage 2, ensuring the grouting pipe 4 is vertically straight to facilitate smooth grouting. The grouting pipe 4 is then vertically tied to the auxiliary supports 5, with a distance of 5mm between the grouting pipe 4 and the outer wall of the friction pile 1. Grouting holes 9 are installed at the pile end and on the pile side of the grouting pipe 4. For an 800mm friction pile 1, grouting holes 9 are installed at the pile end, 5m from the pile end, and 5.5m below the pile top along the pile side. For a 1200mm friction pile 1, grouting holes 9 are installed at the pile end, 7m, 14m, and 28m from the pile end, and 5.5m below the pile top along the pile side. Except for the grouting hole 9 located in the backfill layer at the top of the pile, the other grouting holes 9 are arranged in the red clay layer.

[0034] Step 2: Lower the steel cage with the grouting pipe to the bottom pile hole, and inject concrete into the pile hole 3, and let it solidify into friction pile 1.

[0035] Step 3: Within 7-8 hours after the concrete has solidified into friction pile 1, use high-pressure water to clear the grouting pipe 4.

[0036] Step 4: Grouting is performed after all friction piles 1 in the same karst area are completed and the strength of friction pile 1 reaches more than 70%. First, the four diagonally opposite piles are constructed, then the outer piles are constructed, and finally the two middle piles are constructed. During grouting, grouting holes 9 at the same location are grouted alternately with equal amounts. For example, two symmetrically arranged pile-side grouting pipes 4 on a friction pile 1 are grouted alternately to the left and right grouting holes 9 at the same height. When no grouting pressure is detected, intermittent grouting is used, specifically:

[0037] When there is no grouting pressure at the pile tip, the water-cement ratio is controlled at 0.4:1 and the grouting flow rate is 40L / min. The first grouting volume at the pile tip is 41.5t per grouting pipe, and an appropriate amount of early strength agent is added. The second grouting volume is 41.5t per grouting pipe, and the interval between each grouting is 5-6 hours.

[0038] When there is no grouting pressure on the pile side, the water-cement ratio is controlled at 0.4:1 and the grouting flow rate is 35L / min. The first grouting volume is 41t per grouting pipe, and an appropriate amount of early strength agent is added. The second grouting volume is 41t per grouting pipe, and the interval between each grouting is 30-50min.

[0039] By adjusting the spacing between adjacent 800mm pile holes 3 to 2.4m, controlling the water-cement ratio at 0.4:1, and designing the grouting intervals at the pile tip and pile side within the above range, the grouting success rate at the pile tip and pile side is better, the grouting pressure at the pile tip is stable at 0.5-1MPa, and the grouting pressure at the pile side is stable at 0.8-1.5MPa.

[0040] Step 5: Grouting can be terminated when both the total grouting volume and grouting pressure meet the design requirements, or when the total grouting volume has reached 75% of the design value and the grouting pressure exceeds 3MPa.

[0041] Step 6: After the load test of friction pile 1 meets the standard, pour a raft slab on the top of the 12 800mm friction piles 1 and pour a raft slab on the top of the 4 1200mm friction piles 1. The thickness of the raft slab is 1m. A 100mm thick concrete pad layer is set under the raft slab. The top surface elevation of the raft slab is -1.35m.

[0042] Example 2

[0043] During the grouting pipe unblocking process, some grouting holes were found to be blocked. Analysis suggested that the sealing structure used to seal the grouting holes was not thick enough, causing some grouting holes to become blocked during the concrete pouring and pile formation process. Later, the sealing structure was strengthened, but another problem arose: the water pressure could not break through the sealing structure, causing the grouting holes to become blocked as well.

[0044] Therefore, in response to the above problems, such as Figure 4-6 As shown, the sealing structure in this embodiment includes a positioning layer, a plugging layer, and a sealing layer from the inside out. The positioning layer and sealing layer can be made of tape or plastic wrap (not shown in the figure). The plugging layer includes multiple plugging components for sealing each grouting hole 9. Each plugging component seals one grouting hole 9. The plugging component includes an arc-shaped cap 11 and an insert 12 connected to the concave surface of the cap 11. The insert 12 is welded to the center of the cap 11. In this solution, the diameter of the insert 12 is smaller than the diameter of the grouting hole 9, and the curvature of the cap 11 matches the curvature of the side wall of the grouting pipe 4. To further ensure that each grouting hole 9 can be smoothly unclogged during the grouting process, a protrusion 13 is integrally formed on the side of the cap 11 away from the insert 12. The protrusion 13 is located in the center of the cap 11, and the top of the protrusion 13 is conical, preferably a rounded cone, to prevent the protrusion 13 from puncturing the sealing layer under non-external force.

[0045] Specifically, the process involves: first, wrapping the grouting pipe with grouting holes with tape to form a positioning layer; then, inserting plugs into the positioning layer corresponding to the positions of each grouting hole; finally, wrapping tape around the perimeter of the grouting pipe 4 with plugs to ensure the sealing of the grouting pipe 4. During the unblocking process of the grouting pipe 4, clean water is injected into it. Because the cap 11 of the plug has an outwardly convex arc-shaped structure, the water pressure pushes the plug outward a certain distance, concentrating the impact on the cap 11 to enhance the outward pushing force on the plug, effectively improving the effect of the plug breaking through the sealing layer and detaching from the grouting hole 9. Simultaneously, through the structural design of the protrusion 13, when the plug is under water pressure and utilizes the stress concentration of the protrusion 13 on the sealing layer, the plug can quickly and effectively break through the sealing layer and the side wall of the friction pile 1 to unblock the grouting hole 9.

[0046] Example 3

[0047] Considering the influence of geographical environment and other factors during the actual grouting process, the length of the auxiliary support 5 is designed to be adjustable, such as... Figure 1-3 As shown, the auxiliary support 5 includes a fixed tube 6 and a movable rod 7 slidably connected inside the fixed tube 6. The fixed tube 6 is a steel pipe with a wall thickness of 0.2-0.3cm. One end of the fixed tube 6 is welded to the reinforcing cage 2. A locking mechanism for locking the movable rod 7 is provided between the fixed tube 6 and the movable rod 7. The locking mechanism includes a threaded hole opened on the fixed tube 6 and a bolt 8 threadedly connected to the threaded hole. When the movable rod 7 slides out to the specified length, the bolt 8 is tightened to press against the movable rod 7 to achieve the purpose of locking the movable rod 7.

[0048] In addition, to facilitate the binding of the grouting pipe 4 to the auxiliary support 5, a binding member is fixedly connected to the end of the movable rod 7 away from the fixed pipe 6. In this embodiment, the binding member is preferably a strip-shaped binding member 10. The setting direction of the strip-shaped binding member 10 is parallel to the axis of the reinforcing cage 2, so that the binding member and the grouting pipe 4 are in the same direction, which is conducive to binding the grouting pipe 4 to the binding member 10 with steel wire.

[0049] Meanwhile, for greater precision and speed, a scale value is provided on the movable rod 7. This ensures that the lengths of each auxiliary support 5 are consistent, thereby ensuring that the grouting pipe 4 remains in a straight line and that grouting is smooth. It also helps to improve the efficiency of length adjustment.

[0050] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for pile foundation construction based on karst geological structure distribution, characterized in that: The method comprises the following steps: Step 1: drilling a plurality of pile holes in a karst area, the distance between adjacent pile holes is 2-3 m, and auxiliary supports are transversely welded on the circumference of the reinforcement cage, the length of the auxiliary support is designed to be adjustable, the auxiliary support comprises a fixed tube and a movable rod slidably connected in the fixed tube, one end of the fixed tube is welded on the reinforcement cage, a locking mechanism for locking the movable rod is arranged between the fixed tube and the movable rod, a grouting pipe is bound to the auxiliary support, so that the distance between the grouting pipe and the outer wall of the friction pile is less than 25 mm, and grouting holes are arranged at the pile end and the pile side of the grouting pipe, except for the grouting hole located in the pile top backfill layer, the other grouting holes are arranged in the red clay layer; Step 2: lowering the reinforcement cage with the bound grouting pipe into the pile hole, pouring concrete into the pile hole, and allowing the concrete to solidify into a friction pile; Step 3: dredging the grouting pipe with high-pressure water within 7-8 hours after the concrete solidifies into a friction pile; Step 4: after all the friction piles in the same karst area are formed and the strength of the friction piles reaches more than 70%, grouting is performed, the grouting holes at the same position are alternately and equally grouted, when no grouting pressure is detected at the pile end, intermittent grouting is adopted, and the intermittent grouting time at the pile end is 5-6 hours; Step 5: when the total amount of grouting and the grouting pressure both meet the design requirements, the grouting can be terminated, or when the total amount of grouting has reached 75% of the design value and the grouting pressure exceeds 3 MPa, the grouting can be terminated; Step 6: after the load detection of the friction pile meets the requirements, a raft is poured on the top of all the friction piles in the same karst area.

2. The method for pile construction based on karst geological structure distribution according to claim 1, characterized in that: In step 4, the intermittent grouting mode is that when there is no grouting pressure at the pile end, the first grouting amount is 1.5 t per grouting pipe, and early strength agent is appropriately added; the second grouting amount is 1.5 t per grouting pipe; when there is no grouting pressure at the pile side, the first grouting amount is 1 t per grouting pipe, and early strength agent is appropriately added; the second grouting amount is 1 t per grouting pipe.

3. The method according to claim 2, wherein: When the grouting pressure at the pile end reaches 0.5-2 MPa, the grouting at the pile end can be terminated.

4. The method according to claim 3, wherein: In step 4, the water-cement ratio of the grout is 0.4, and the grouting flow rate is controlled at 30-40 L / min.

5. The method for pile construction based on karst geological structure distribution according to claim 4, characterized in that: Before step 2, a layer of stone is laid at the bottom of the pile hole.

6. The method for pile construction based on distribution of karst geological structure according to claim 5, characterized in that: A plugging unit is arranged on the outer wall of the grouting pipe at the grouting hole, the plugging unit comprises a positioning layer, a hole plugging layer and a sealing layer from inside to outside, the hole plugging layer comprises a plurality of hole plugging pieces inserted into the grouting holes.

7. The method according to claim 6, wherein: The hole plugging piece comprises an arc-shaped cover and a plug connected to the concave surface of the cover, and the curvature of the cover matches the curvature of the side wall of the grouting pipe.

8. A method of pile construction based on the distribution of karst geological structures according to claim 7, characterized in that: In step 6, the thickness of the raft is 1 m, a 100 mm thick concrete cushion layer is arranged under the raft, and the top surface elevation of the raft is -1.35 m.

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