Cast-in-place pile construction method in complex karst cave stratum

Abstract

The invention relates to a cast-in-place pile construction method for a complex karst cave stratum, and relates to the technical field of cast-in-place piles. The cast-in-place pile construction method comprises the following steps that S1, the position and depth of an underground karst cave are determined through a geological exploration instrument; s2, a process hole is drilled to the karst cave through a drilling machine; s3, injecting flow-state solidified soil to seal the karst cave; s4, after the flow-state solidified soil is solidified, a pile grouting hole is drilled; and S5, filling pile construction is conducted on the filling pile holes. By adopting the construction method, all explored karst caves can be treated, the vacancy of the karst caves is filled, and the treatment is simple and easy; when the cast-in-place pile is constructed, no matter whether a pile casing is used or not, solidified soil blocks solidified in a karst cave can support the pile casing or the cast-in-place pile in an all-around mode, and stability is improved; the solidified layer is formed by pouring cement mortar in advance, gaps and holes of the karst cave are blocked, and waste of the fluid solidified soil is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of bored piles, and in particular to a method for constructing bored piles in complex karst strata. Background Art

[0002] The karst strata are mainly soluble arch caves. On the one hand, the karst caves and cracks cause the incompleteness of the rock structure and form local instability. On the other hand, they provide sufficient space conditions for accommodating collapsed materials and groundwater. If the karst strata perforated cast-in-place piles are constructed using conventional perforation construction methods, it is difficult to build walls in unstable strata, resulting in construction quality and safety issues.

[0003] The invention patent application with the existing announcement number CN104674780A discloses a stabilizing structure for karst formations, which is used for the construction of bored piles. The bored piles pass through at least one cave in the karst formation from top to bottom. The hole wall treatment structure includes a casing buried to a certain depth in the karst formation at the location of the bored piles to be constructed and a certain height above the surface of the karst formation before the construction of the cave roof, a pile hole of the bored pile concentric with the casing and with a diameter smaller than the casing diameter, a water neutralizing layer in the cracks of the pile hole wall, and a closed, dense and impermeable mud protective layer of the cave wall and the pile hole wall after the cave roof is penetrated. The thickness of the mud protective layer is greater than 20 mm, and it is squeezed into the hole wall under the impact of the hammer, and the mud protective layer forms a dense and impermeable structure.

[0004] Regarding the above-mentioned related technologies, the inventors believe that although the casing is used to increase the stability of the bored pile, the space vacancy caused by the cave next to the casing still exists. This part cannot support the casing and the bored pile, and there is a problem of insufficient stability. Summary of the invention

[0005] The present application provides a method for constructing bored piles in complex karst strata, which can provide all-round support for the bored piles and improve stability by injecting fluidized solidified soil to seal the karst caves.

[0006] The present application provides a method for constructing cast-in-place piles in complex karst strata, which adopts the following technical solution: A method for constructing cast-in-place piles in complex karst strata, comprising the following steps: Step S1: Determine the location and depth of the cave under the surface by using geological survey instruments; Step S2: Drilling a technical hole to the cave using a drilling rig; Step S3: injecting fluidized solidified soil to seal the cave; Step S4: After the fluidized solidified soil solidifies, drilling pile holes; Step S5: performing cast-in-place pile construction on the pile hole.

[0007] By adopting the above technical solution, fluidized solidified soil is injected to fill the gaps in the cave. During the construction of cast-in-place piles, regardless of whether casing is used or not, the solidified soil blocks in the cave can provide all-round support for the casing or cast-in-place piles, thereby improving stability.

[0008] Optionally, the pile hole is drilled on the basis of the process hole, and the diameter of the process hole is less than half of the diameter of the pile hole.

[0009] By adopting the above technical solution, the size of the process hole is small, and a small drilling rig is used to drill into the cave, which makes the construction speed fast, flexible and convenient; the grouting hole is drilled on the basis of the existing hole, and the drilling of the pile hole is simpler and more efficient.

[0010] Optionally, before step S3, a hose is inserted into the process hole, with the lower end of the hose inserted into the cave and the upper end of the hose located on the ground; during step S3, fluidized solidified soil is injected into the cave through the hose.

[0011] By adopting the above technical solution, injection is carried out through a hose, and the smooth and regular shape of the inner wall of the hose can make the fluidized solidified soil flow smoothly, and when the sand on the inner wall of the process hole is peeled off, it will not block the injection channel.

[0012] Optionally, an air outlet pipe is fixed to the outer wall of the hose; after the hose is inserted into the process hole, the lower end of the air outlet pipe is inserted into the cave, and the upper end of the air outlet pipe is located on the ground.

[0013] By adopting the above technical solution, the air outlet pipe provides a channel for the discharge of air in the cave, making the injection of cement mortar and fluidized solidified soil smoother.

[0014] Optionally, a pull wire is passed through the air outlet pipe, and the lower end of the pull wire passes through the air outlet pipe and is fixed with a blocking cover; when the hose is lowered, force is applied to the upper end of the pull wire so that the blocking cover covers the lower end of the hose and the air outlet pipe.

[0015] By adopting the above technical solution, the height position of the blocking cover is maintained by pulling the wire, and during the process of lowering the hose, the blocking cover can prevent sand and gravel debris on the inner wall of the process hole from entering the hose and the air outlet pipe.

[0016] Optionally, the top surface of the baffle cover is a concave arc surface, the baffle cover is fixed with a guide rod, and the bottom end of the hose is provided with a guide hole for the guide rod to slide; before step S3, thickened cement mortar is injected into the cave through the hose, and the cement mortar hits the top surface of the baffle cover and splashes to the inner wall of the cave, and forms a solidified layer after solidification.

[0017] By adopting the above technical solution, the thickened cement mortar can seal gaps and holes under tension due to its viscous characteristics, and form a solidified layer after solidification. In this way, in the subsequent pouring process, the fluidized solidified soil will not flow directly through the holes, thereby reducing the waste of fluidized solidified soil.

[0018] Optionally, during the process of injecting cement mortar, the height of the retaining cover is gradually lowered by pulling a wire.

[0019] By adopting the above technical solution, the inner wall of the cave can be covered with cement mortar.

[0020] Optionally, a thickener and an early strength agent are added to the cement mortar, wherein the thickener accounts for 3-5% of the total weight of the cement mortar, and the early strength agent accounts for 1%-2% of the total weight of the cement mortar.

[0021] By adopting the above technical solution, the viscosity of cement mortar is increased by adding a higher proportion of thickener to improve the sealing effect of holes and gaps. The early strength agent is used to increase the strength of cement mortar in the early stage of solidification and reduce waiting time.

[0022] Optionally, the fluidized solidified soil includes the following formula components in parts by weight: 15-20 parts of slag, 7-9 parts of water, 1.5-2.5 parts of cement, 5-7 parts of pottery sand, and 0.5-1 part of curing agent.

[0023] By adopting the above technical solution, the raw materials of fluidized solidified soil are simple and easy to obtain, and the cost is low.

[0024] Optionally, the slag comes from soil excavated from the construction site.

[0025] By adopting the above technical solution, the soil and mud generated during construction can be digested on site to avoid external transportation.

[0026] In summary, the present application includes at least one of the following beneficial technical effects: 1. This construction method can be used to treat all the explored caves and fill the gaps in the caves, and the treatment is simple and easy; 2. During the construction of cast-in-place piles, whether or not casing is used, the solidified soil blocks in the cave can provide all-round support for the casing or cast-in-place piles, thus improving stability; 3. By pre-pouring cement mortar to form a solidified layer, the gaps and holes in the cave are sealed to reduce the waste of fluid solidified soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a cave and a process hole of an embodiment; Figure 2 is a cross-sectional view of a hose and a blocking cover of an embodiment; Figure 3 yes Figure 2 A magnified image of point A; Figure 4 is a three-dimensional diagram of a hose and a blocking cover of an embodiment; Figure 5Schematic diagram of cement mortar forming a solidified layer in an embodiment; Figure 6 Schematic diagram of pouring fluidized solidified soil in an embodiment; Figure 7 Schematic diagram of the pile hole in the embodiment.

[0028] Explanation of the reference numerals: 1. cave; 2. process hole; 3. pile hole; 4. hose; 41. air outlet pipe; 42. pull wire; 5. cover; 51. guide rod; 43. guide hole; 11. cement mortar; 12. solidification layer; 13. fluidized solidified soil; 14. solidified soil block. DETAILED DESCRIPTION

[0029] The present application is further described in detail below in conjunction with the accompanying drawings.

[0030] This embodiment discloses a method for constructing cast-in-place piles in complex karst strata, comprising the following steps: Step S1: Determine the location and depth of the cave 1 under the surface by using geological survey instruments.

[0031] Step S2: Refer to Figure 1 , use a drilling rig to drill a process hole 2 to the cave 1; the diameter of the process hole 2 is small, and the diameter of the process hole 2 is less than half of the diameter of the pile hole 3. A small drilling rig is used to drill into the cave 1, and the construction speed is fast, flexible and convenient.

[0032] Reference Figures 2 to 4 , insert the hose 4 into the process hole 2, and fix the air outlet pipe 41 on the outer wall of the hose 4, which can be fixed by gluing or by a cable tie. A pull wire 42 is passed through the air outlet pipe 41, and the lower end of the pull wire 42 passes through the air outlet pipe 41 and is fixed with a baffle 5. The top surface of the baffle 5 is a concave arc surface, and the baffle 5 is fixed with a guide rod 51. The bottom end of the hose 4 is provided with a guide hole 43 for the guide rod 51 to slide. The baffle 5 and the guide rod 51 are both made of plastic. There are two guide rods 51, and the guide rod 51 allows the baffle 5 to slide only vertically to prevent the baffle 5 from swinging. After the hose 4 is inserted into the process hole 2, the lower end of the hose 4 is inserted into the cave 1, and the upper end of the hose 4 is located on the ground. The lower end of the air outlet pipe 41 is inserted into the cave 1, and the upper end of the air outlet pipe 41 is located on the ground. When lowering the hose 4 , force is applied to the upper end of the pull wire 42 to cover the lower end of the hose 4 and the air outlet pipe 41 . The cover 5 can prevent sand and gravel debris on the inner wall of the process hole 2 from entering the hose 4 and the air outlet pipe 41 .

[0033] Reference Figure 5, inject thickened cement mortar 11 into the cave 1 through the hose 4, and use a pump for injection. Thickener and early strength agent are added to the cement mortar 11, wherein the thickener accounts for 3-5% of the total weight of the cement mortar 11, and the early strength agent accounts for 1%-2% of the total weight of the cement mortar 11. By adding a higher proportion of thickener, the viscosity of the cement mortar 11 is increased, and the early strength agent increases the strength of the cement mortar 11 in the early stage of solidification, thereby reducing the waiting time. After the cement mortar 11 impacts the top surface of the retaining cover 5, due to the concave arc shape of the top surface of the retaining cover 5, the cement mortar 11 will splash to the inner wall of the cave 1. In the process of injecting the cement mortar 11, the height of the retaining cover 5 is gradually lowered by the pull wire 42, so that the inner wall of the cave 1 can be covered by the cement mortar 11, and the cement mortar 11 forms a solidified layer 12 after solidification.

[0034] In complex karst strata, there may be cracks or holes in the cave 1 that connect to other caves 1. If other caves 1 are not in the construction area, the amount of injection will increase, resulting in waste. If it is connected to other wide spaces, it may not be fully filled. Due to its viscous characteristics, the thickened cement mortar 11 can seal cracks and holes under tension and form a solidified layer 12 after solidification. The role of the thickened cement mortar 11 is to seal cracks and holes. Even if it cannot be completely sealed, reducing the size of the holes is also a purpose. In this way, in the subsequent injection process, the fluidized solidified soil 13 can avoid directly flowing through the holes by virtue of its own poor fluidity, thereby reducing the waste of the fluidized solidified soil 13.

[0035] Step S3: Refer to Figure 6 , inject the fluidized solidified soil 13 into the cave 1 through the hose 4, and inject the fluidized solidified soil 13 to seal the cave 1. The fluidized solidified soil 13 includes the following formula components in parts by weight: 15-20 parts of slag, 7-9 parts of water, 1.5-2.5 parts of cement, 5-7 parts of pottery sand, and 0.5-1 part of curing agent. The slag comes from the soil excavated at the construction site, and the mud produced during construction is digested on site to avoid external transportation. The strength range of the fluidized solidified soil 13 is 0.3MPa~5.0MPa, and the range of selection of proportion strength is large. Different strengths of fluidized solidified soil 13 can be mixed according to the needs of the site. For example, low-strength solidified soil can be selected for the cave 1 on the pile side, and high-strength solidified soil can be used for the cave 1 at the bottom of the pile.

[0036] The injection is carried out through the hose 4. The smooth and regular shape of the inner wall of the hose 4 can make the cement mortar 11 and the fluidized solidified soil 13 flow smoothly, and when the sand and soil on the inner wall of the process hole 2 peels off, it will not block the injection channel. The air outlet pipe 41 provides a channel for the discharge of air in the cave 1, making the injection of cement mortar 11 and the fluidized solidified soil 13 smoother.

[0037] After the injection is completed, the hose 4 and the air outlet pipe 41 are taken out, and the blocking cover 5 can be left in the cave 1 without affecting the stability of the structure and subsequent construction. A new blocking cover 5 is used when constructing another cave 1.

[0038] Step S4: Refer to Figure 7 After the fluidized solidified soil 13 solidifies, a solidified soil block 14 is formed, and then a pile hole 3 is drilled on the ground; the drilling of the pile hole 3 is carried out on the basis of the process hole 2.

[0039] Step S5: performing cast-in-place pile construction on the pile hole 3. This is a conventional cast-in-place construction method and will not be described in detail.

[0040] The implementation principle of the embodiment of the present application is as follows: When a conventional cast-in-place pile encounters a karst cave 1, usually only the karst cave 1 that has been drilled through is processed, and the karst cave 1 around the pile foundation is difficult to process, which brings potential safety hazards to the project. This construction method can process all the explored karst caves 1 and fill the vacancies of the karst caves 1, and the processing is simple and easy. During the construction of cast-in-place piles, regardless of whether a casing is used, the solidified soil blocks 14 in the karst cave 1 can provide all-round support for the casing or cast-in-place piles to improve stability.

[0041] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for constructing cast-in-place piles in complex karst strata, characterized by: The following steps are involved: Step S1: Determine the location and depth of the cave (1) under the surface by using geological survey instruments; Step S2: using a drilling rig to drill a process hole (2) to the cave (1); Step S3: injecting fluidized solidified soil (13) to seal the cave (1); Step S4: After the fluidized solidified soil (13) solidifies, drilling a pile hole (3); Step S5: performing cast-in-place pile construction on the pile hole (3).

2. A method for constructing cast-in-place piles in complex karst cave formations according to claim 1, characterized in that: The pile-casting hole (3) is drilled on the basis of the process hole (2), and the diameter of the process hole (2) is less than half of the diameter of the pile-casting hole (3).

3. The method for constructing a cast-in-place pile in a complex karst cave formation according to claim 1, characterized in that: Before step S3, a hose (4) is inserted into the process hole (2), the lower end of the hose (4) is inserted into the cave (1), and the upper end of the hose (4) is located on the ground; during step S3, fluidized solidified soil (13) is injected into the cave (1) through the hose (4).

4. A method for constructing cast-in-place piles in complex karst cave formations according to claim 3, characterized in that: An air outlet pipe (41) is fixed to the outer wall of the hose (4); after the hose (4) is inserted into the process hole (2), the lower end of the air outlet pipe (41) is inserted into the cave (1), and the upper end of the air outlet pipe (41) is located on the ground.

5. A method for constructing cast-in-place piles in complex karst cave formations according to claim 4, characterized in that: A pull wire (42) is inserted into the air outlet pipe (41), and the lower end of the pull wire (42) passes out of the air outlet pipe (41) and is fixed with a blocking cover (5); during the process of lowering the hose (4), force is applied to the upper end of the pull wire (42) so that the blocking cover (5) covers the outside of the hose (4) and the lower end of the air outlet pipe (41).

6. A method for constructing cast-in-place piles in complex karst cave formations according to claim 5, characterized in that: The top surface of the blocking cover (5) is an inwardly concave arc surface, a guide rod (51) is fixed to the blocking cover (5), and a guide hole (43) for the guide rod (51) to slide is provided at the bottom end of the hose (4); before step S3, thickened cement mortar (11) is injected into the cave (1) through the hose (4), and the cement mortar (11) impacts the top surface of the blocking cover (5) and splashes onto the inner wall of the cave (1), and forms a solidified layer (12) after solidification.

7. A method for constructing cast-in-place piles in complex karst cave formations according to claim 6, characterized in that: During the process of injecting cement mortar (11), the height of the blocking cover (5) is gradually lowered by pulling the wire (42).

8. The method for constructing cast-in-place piles in complex karst cave formations according to claim 6, characterized in that: A thickener and an early strength agent are added to the cement mortar (11), wherein the thickener accounts for 3-5% of the total weight of the cement mortar (11), and the early strength agent accounts for 1%-2% of the total weight of the cement mortar (11).

9. The method for constructing cast-in-place piles in complex karst cave formations according to claim 1, characterized in that: The fluidized solidified soil (13) comprises the following formula components in parts by weight: 15-20 parts of slag soil, 7-9 parts of water, 1.5-2.5 parts of cement, 5-7 parts of pottery sand, and 0.5-1 part of a curing agent.

10. A method for constructing cast-in-place piles in complex karst cave formations according to claim 9, characterized in that: The slag comes from the soil excavated from the construction site.

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