Karst stratum pile-forming construction method

Abstract

The application provides a karst stratum pile-forming construction method, comprising the following steps: S1, performing geological survey on a construction area; S2, determining the depth of a steel casing according to the geological condition of a pile hole position and burying the steel casing; S3, drilling to form a first pile hole and cleaning the first pile hole until a sedimentation requirement is reached; S4, drilling to form a second pile hole and simultaneously hoisting a reinforcement cage in the first pile hole; S5, performing reverse pressure plugging on the second pile hole and concrete pouring on the first pile hole; S6, performing secondary drilling on the second pile hole and cleaning the second pile hole until the sedimentation requirement is reached; S7, hoisting the reinforcement cage in the second pile hole, pouring concrete and simultaneously drilling the next pile hole. The construction method performs reverse pressure plugging on the second pile hole, so that when the first pile hole is poured with concrete, the concrete slurry can only fill karst fissures connecting the second pile hole and the first pile hole and is difficult to enter the second pile hole, thereby avoiding hole connection between adjacent pile holes.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of karst stratum pile foundation construction methods, in particular to a karst stratum pile forming construction method. BACKGROUND

[0002] In pile foundation engineering, a large number of karst strata often exist within the scope of the project. For the construction of bored piles in complex karst areas, the existing karst treatment methods in the pile forming process mainly include concrete backfilling method, steel casing following method, and grouting method. The cement mortar or concrete backfilling method has high treatment cost and is difficult to handle twice. The steel casing following method has high cost, complex construction technology, and poor applicability in hard rock geology. The grouting method has poor operability and is not economical due to the wide distribution of fissures and the difficulty of detection, and cannot adapt to strata with close pile spacing, wide fissure distribution, and serious local karst development.

[0003] A karst stratum pile foundation construction method is disclosed in Chinese patent application No. CN201911409994.1. This method requires that a group of pile holes connected by karst caves be drilled uniformly to the bottom of the karst cave, uniformly backfilled, and fully compacted between each other. This construction method has the following problems: on the one hand, there is a high probability of connection between most pile holes in the same area, and uniform hole forming and backfilling cannot meet the requirements of the highway bridge and culvert construction technical specification (JTG / T 3650-2020) for pile foundation skip hole operation, and the construction has obvious limitations. On the other hand, karst strata generally have wide fissures, and small caves and karst fissures are difficult to fully explore, making it difficult to solve the problems of easy leakage and hole connection in karst strata. SUMMARY

[0004] The present application aims to overcome the defects of the prior art and provide a karst stratum pile forming construction method.

[0005] The present application provides a karst stratum pile forming construction method, comprising the following steps:

[0006] S1, geological survey of the construction area;

[0007] S2, determine the depth of the steel casing according to the geological conditions of the pile hole position and bury the steel casing;

[0008] S3, drill a first pile hole and clean the first pile hole until the sedimentation requirement is met;

[0009] S4, drill a second pile hole and simultaneously lower a reinforcement cage into the first pile hole;

[0010] S5, back pressure sealing of the second pile hole and concrete pouring of the first pile hole;

[0011] S6. Drill the second pile hole a second time and clean the second pile hole until the sediment requirements are met.

[0012] S7. The steel cage is lowered into the second pile hole and concrete is poured in, while drilling of the next pile hole is carried out simultaneously.

[0013] This construction method involves back-pressure sealing of the second pile hole, ensuring that when concrete is poured into the first pile hole, the concrete slurry can only fill the karst fissures connecting the second and first pile holes, preventing it from entering the second pile hole. This avoids cement slurry or concrete flowing through the narrow karst fissures into the second pile foundation under construction, thus preventing cross-hole between adjacent pile holes. It solves the problem of not being able to fully explore or treat small karst caves and fissures, and reduces the loss of cement slurry or water in the poured concrete, ensuring that the concrete mix ratio is largely unaffected, resulting in better pile foundation quality. Furthermore, the drilling and backfilling of the first pile hole can be carried out simultaneously with the pile formation of the second pile hole, accelerating the construction progress.

[0014] Furthermore, in step S5, the second pile hole is sealed with back pressure using drill cuttings.

[0015] By reusing drill cuttings, the space required for temporary drill cuttings storage is reduced, thus minimizing resource waste and environmental impact in traditional pile foundation construction methods, as well as energy consumption and carbon emissions during construction. Furthermore, using drill cuttings to backfill the second borehole facilitates secondary drilling and accelerates construction speed.

[0016] Furthermore, in step S5, large-diameter drill cores are removed from the drill cuttings, and a mixture of clay, stone chips, and boulders from the drill cuttings is used to back-pressure seal the second pile hole until the hole opening is reached.

[0017] Because the mixture of clay, stone chips, and boulders is easy to mix evenly, using the mixture of clay, stone chips, and boulders from the drill cuttings to apply counter-pressure to seal the second pile hole improves the sealing effect on karst fissures and helps to avoid cross-hole between adjacent pile holes.

[0018] Furthermore, in step S5, when the second pile hole is backfilled with back pressure, it is compacted section by section using drill bit pressure to ensure the sealing effect.

[0019] When performing counter-pressure sealing on the second pile hole, the method of backfilling and compacting section by section can further improve the sealing effect on karst fissures.

[0020] Furthermore, if the second pile hole is drilled using wet drilling and there are large karst fissures between the first and second pile holes, the first pile hole should be cleaned again before concrete pouring until the sediment requirements are met.

[0021] In the process of wet drilling, in order to prevent the mud from carrying the sediment in the second pile hole into the first pile hole and affecting the pile quality of the first pile hole, the first pile hole can be cleaned again to avoid the above problem.

[0022] Furthermore, if the borehole collapses, the steel casing becomes partially suspended, or the steel casing shifts during the drilling process, the steel casing is lifted, the borehole is backfilled with a mixture of drill cuttings and cement, the steel casing is re-installed, and drilling resumes.

[0023] When backfilling pile holes, drill cuttings can be used as part of the backfill material. The main advantage over backfilling with concrete is that it is cheaper and secondary drilling is not constrained by the strength of the backfill material. This solves the problem of ground collapse at the borehole opening and also allows for faster construction.

[0024] Furthermore, if a large cavity is discovered during the drilling process to form the pile hole, the cavity is backfilled with concrete, and drilling is carried out again after the concrete reaches the design strength.

[0025] If an unexplored cavity is discovered during drilling, the cavity should be backfilled before constructing the pile hole.

[0026] Furthermore, step S1 includes: using advanced drilling and ground-penetrating radar to determine the location, diameter, and depth of the karst cave.

[0027] Furthermore, the diameter of the large-diameter drill core is greater than 20 cm.

[0028] The maximum size of large-diameter drill cores can reach 2 to 3 meters, while the minimum should be controlled to be above 20 cm.

[0029] Furthermore, the width of large-sized karst fissures is greater than 2 cm.

[0030] Large karst fissures must be at least 2cm in size, and the fissures must be at least 2cm in size along the entire connecting path for cross-holes to affect sedimentation.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention uses drill cuttings to back-pressure the second pile hole to seal karst fissures, which allows for rapid construction and solves the problem that it is difficult to fully explore or treat small karst caves and fissures using conventional methods. It also avoids the problem that concrete can directly enter the second pile hole through karst fissures when pouring the first pile hole.

[0033] 2. This invention ensures that the mix proportion of the grouting concrete is basically unaffected, and that the secondary drilling of the drill cuttings is not constrained by the strength of the backfill material, thus ensuring that the construction quality is not affected.

[0034] 3. This invention reduces the space required for temporary storage of drill cuttings by reusing the drilling cuttings, thereby reducing resource waste and environmental impact in traditional pile foundation construction methods, and reducing energy consumption and carbon emissions during construction.

[0035] 4. This invention can meet the requirements of dry and wet methods for pile foundation construction in karst geology, expands the treatment methods for easily collapsible sections of the strata at the borehole opening, and is especially suitable for dry construction of pile foundations in karst geology. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure during the drilling of the first pile hole according to the present invention;

[0037] Figure 2 This is a schematic diagram of the structure after concrete has been poured into the first pile hole of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure during re-drilling after the second pile hole is sealed by back pressure according to the present invention;

[0039] Figure 4 This is a schematic diagram of the structure after concrete has been poured into the second pile hole of the present invention.

[0040] Attached reference numerals: 1. Steel casing; 2. First pile hole; 3. Second pile hole; 4. Drill cuttings; 5. Karst fissure; 6. Rotary drilling rig. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0042] Currently, conventional karst treatment methods are limited by the accuracy and cost of geological exploration, and only consider treating the larger cavities discovered during the drilling process of each pile foundation. This approach fails to address the problem of cross-hole issues between piles caused by the widespread distribution of karst geological fissures during simultaneous construction of multiple piles. Furthermore, it cannot prevent cement slurry or even concrete from flowing through narrow karst fissures into piles under construction on the other side, affecting construction quality and efficiency. Due to the complex distribution of small cavities and fissures in karst areas, the bearing capacity of the strata beneath the pile foundation construction platform is uncertain. In addition, the drilling process causes significant disturbance to the strata, especially the strata at the borehole opening, which can easily lead to instability or collapse of the upper strata. Traditional treatment methods such as concrete backfilling are difficult to address quickly and efficiently.

[0043] This embodiment proposes a pile construction method in karst formations, including the following steps:

[0044] S1. Use advanced drilling, ground-penetrating radar and other methods to determine the location, diameter and depth of the karst cave.

[0045] S2. Construct the pile foundation operation platform, determine a reasonable drilling sequence and number it, determine the depth of the steel casing 1 according to the geological conditions of the pile hole location, and bury the steel casing 1 at the opening of the pile hole; the burial depth of the steel casing 1 should be determined according to the design requirements or the hydrogeological conditions of the pile location, not less than 1.0m in clay, not less than 1.5m in sandy soil, and generally the burial depth should be 2 to 4m. The steel casing 1 can ensure the smooth progress of drilling and concrete pouring.

[0046] S3. Drilling is carried out using a rotary drilling rig 6. The drilling rig drills a hole in the ground according to the design requirements to form the first pile hole 2. The first pile hole 2 is cleaned until the sediment requirements are met. The sediment requirements are: 1. For end-bearing piles, the sediment thickness should not exceed 50mm; 2. For friction piles, the sediment thickness should not exceed 100mm; 3. For pull-out and horizontal force-resistant piles, the sediment thickness should not exceed 200mm. Drill cuttings 4 are reserved during the drilling process. Excessively large drill cores are removed using excavators, cranes, etc., retaining a mixture of clay, stone chips, and boulders. Large-diameter drill cores are promptly transported to the designated spoil disposal site using transport vehicles. Figure 1 As shown, the diameter and height of some drill cores in hard rock geological drilling cuttings can reach several meters. In order to avoid the inability of excessively large drill cores to mix evenly with clay, stone chips, etc., and affect the effect of subsequent backfilling, it is necessary to remove drill cores with excessively large diameters in advance. Generally, drill cores with a diameter or height of 20cm or more can be removed.

[0047] S4. Move the drilling rig to the position of the second pile hole 3 and start drilling to form the second pile hole 3. At the same time, hoist the reinforcing cage into the first pile hole 2 and install a reinforcing cage lowering frame to assist in lowering the reinforcing cage into the first pile hole 2. Similarly, leave the drill cuttings 4 from the drilling process. Use excavators, cranes, etc. to remove drill cores with excessive particle size, and retain the mixture of clay, stone chips and boulders.

[0048] If the second pile hole 3 is drilled using wet drilling and there is a large karst fissure 5 between the first pile hole 2 and the second pile hole 3, the cement slurry during the drilling of the second pile hole 3 may carry sediment into the first pile hole 2 through the karst fissure 5, making the first pile hole 2 unable to meet the sediment requirements. Therefore, before pouring concrete into the first pile hole 2, the thickness of the sediment in the first pile hole 2 needs to be checked. If it does not meet the sediment requirements, the first pile hole 2 needs to be cleaned again until the sediment requirements are met, thereby ensuring the quality of the pile foundation in the first pile hole 2. The size of the aforementioned large karst fissure 5 depends on whether concrete and cement slurry can penetrate the karst fissure 5 and cause cross-hole formation. Specifically, it is closely related to the concrete concentration. Generally, the large karst fissure 5 needs to reach a size of 2 cm or more, and the fissures along the entire connecting line need to reach this size for cement slurry and fine debris to cross-hole formation and affect the sediment. Dry drilling will not cause the above phenomenon.

[0049] It should be noted that if a large-sized cavity is found during the drilling of the first pile hole 2 and the second pile hole 3, the cavity will be backfilled with concrete. Drilling will resume after the concrete has reached the design strength. Generally, cavities with a diameter of more than one meter need to be treated.

[0050] S5, such as Figure 2 As shown, the second pile hole 3 is sealed by back pressure using a mixture of clay, stone chips, and boulders screened from the drill cuttings 4. The backfilling and compaction are carried out in sections, that is, a section is backfilled and compacted with the drill bit before the next section is backfilled. After the back pressure sealing of the second pile hole 3 is completed, concrete is poured into the first pile hole 2. The concrete injected into the first pile hole 2 will flow into the karst fissures 5. Since the second pile hole 3 has been sealed by the drill cuttings 4, the concrete cannot flow into the second pile hole 3, thus avoiding cross-hole formation and improving the pile quality of the first pile hole 2.

[0051] The specific proportions of the clay, stone chips, and boulders mixture should be determined based on achieving the best sealing effect.

[0052] Figure 2 The diagram only shows the karst fissure 5 connecting the first pile hole 2 and the second pile hole 3. Although some of the concrete injected into the first pile hole 2 will flow to other karst fissures 5, the fluidity of the concrete is limited, and the amount of concrete flowing into other karst fissures 5 is small, so the impact on the first pile hole 2 is small.

[0053] S6, such as Figure 3 As shown, a drilling rig is used to drill a second hole 3, and the second hole 3 is cleaned until the sediment requirements are met.

[0054] S7. The reinforcing cage is lowered into the second pile hole 3, while the third pile hole is being drilled simultaneously. After the third pile hole is drilled and sealed with counter-pressure, concrete is poured into the second pile hole 3. Figure 4 As shown. Similarly, during the drilling of the third pile hole, drill cuttings 4 were left in advance.

[0055] Repeat the above steps until all pile hole work is completed.

[0056] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for pile construction in karst formations, characterized in that: Includes the following steps: S1. Conduct geological surveys of the construction area; S2. Determine the depth of the steel casing (1) based on the geological conditions at the location of the pile hole and install the steel casing (1); S3. Drill to form the first pile hole (2), and clean the first pile hole (2) until the sediment requirements are met; S4. Drill a hole to form the second pile hole (3), and at the same time, hang the steel cage in the first pile hole (2); S5. The second pile hole (3) is sealed with counter-pressure, and the first pile hole (2) is filled with concrete. S6. Drill the second pile hole (3) a second time and clean the second pile hole (3) until the sediment requirements are met; S7. The steel cage is hoisted into the second pile hole (3) while the drilling of the next pile hole is carried out simultaneously.

2. The method for pile construction in karst formations according to claim 1, characterized in that: In step S5, the drill cuttings (4) are used to seal the second pile hole (3) with back pressure.

3. The method for pile construction in karst formations according to claim 2, characterized in that: In step S5, large-diameter drill cores are removed from the drill cuttings (4), and a mixture of clay, stone chips and boulders in the drill cuttings (4) is used to back-pressure seal the second pile hole (3) until the hole opening.

4. The method for pile construction in karst formations according to claim 2 or 3, characterized in that: In step S5, when the second pile hole (3) is backfilled with back pressure, it is compacted by using the pressure of the drill bit to ensure the sealing effect.

5. The method for pile construction in karst formations according to claim 1, characterized in that: If the second pile hole (3) is formed by wet drilling and there is a large karst fissure (5) between the first pile hole (2) and the second pile hole (3), the thickness of the sediment in the first pile hole (2) should be checked before concrete pouring. If the sediment requirement is not met, the first pile hole (2) should be cleaned again until the sediment requirement is met.

6. The method for pile construction in karst formations according to claim 1, characterized in that: If the borehole collapses, the steel casing (1) is partially suspended, or the steel casing (1) is displaced during the drilling process, the steel casing (1) is lifted, the pile hole is backfilled with a mixture of drilling slag (4) and cement, the steel casing (1) is re-buried, and the hole is drilled again.

7. The method for pile construction in karst formations according to claim 1, characterized in that: If a large cavity is found during the drilling process to form the pile hole, the cavity is backfilled with concrete, and drilling is carried out again after the concrete reaches the design strength.

8. The method for pile construction in karst formations according to claim 1, characterized in that: Step S1 includes: using advanced drilling and ground-penetrating radar to determine the location, diameter, and depth of the karst cave.

9. The method for pile construction in karst formations according to claim 3, characterized in that: The diameter of the large-diameter drill core is greater than 20 cm.

10. The method for pile construction in karst formations according to claim 5, characterized in that: The width of the large-sized karst fissure (5) is greater than 2 cm.

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