A construction method for improving the bearing performance of pile foundation structures in karst dissolution and fragmentation zones

Abstract

The present invention discloses a construction method for improving the bearing performance of a pile foundation structure in a karst dissolution and fragmentation zone, which comprises the following steps: (1) planar positioning of the pile foundation structure; (2) excavating the pile hole of the pile foundation structure by using a rotary drilling rig, and adopting slurry for pile hole wall protection until the bottom elevation of the pile foundation structure; (3) cleaning the pile hole and placing the steel reinforcement cage of the pile foundation structure into the pile hole; (4) manufacturing a semi-circular opening grouting pipe, the outer sleeve of the grouting pipe is a non-woven geotextile bag, and the grouting pipes are placed at intervals around the hole wall, and the hole side of the grouting pipe is closely attached to the hole wall; (5) gradually and slowly pouring the concrete of the pile foundation structure from the bottom of the pile hole upwards; (6) after the concrete pouring of the pile foundation structure is completed and before the concrete initial sets, high-pressure grouting is carried out through the grouting pipe. The method of the present invention has the characteristics of simple construction, controllable quality, good bearing effect, economic and environmental protection, and being conducive to popularization and application, etc.

Description

Technical Field

[0001] The present invention relates to geotechnical engineering, and particularly to a construction method for improving the bearing performance of pile foundation structures in karst dissolution and fracture zones. Background Art

[0002] Karst is widely distributed in Guangxi, Guizhou, Yunnan and other places in China. Soluble rocks mainly composed of limestone and dolomite, with calcium carbonate as the main component, are gradually dissolved in water under the repeated action of groundwater and H2CO3 generated by CO2, resulting in corrosion, weathering. The soluble rocks are gradually dissolved into different forms such as soil-like and fragmented, and foundation conditions such as karst cavities and dissolution fracture zones are formed. Among them, the dissolution fracture zone is a common foundation form in soluble rock areas. The foundation of the dissolution fracture zone may also have a certain rock structure or the structure completely disappears, forming a gravel-like foundation.

[0003] When the pile foundation structure used for bearing is set in the foundation of the dissolution fracture zone, if the pile hole is formed by using mud slurry to protect the wall during the construction of the pile foundation structure, the mud slurry will have a certain impact on the fracture zone, reducing the effective friction between the pile foundation structure and the hole wall. If the steel casing is used for pipe following protection, the investment in the steel casing is very large and the construction efficiency is significantly reduced. In addition, the dissolution channels in the dissolution fracture zone are completely connected, providing convenient conditions for the infiltration, connection and further acceleration of dissolution of groundwater. Different from karst caves, the dissolution fracture zone generally does not cause karst collapse disasters, but under the continuous action of groundwater, its structural strength, frictional resistance and foundation bearing capacity are in a continuous decreasing process.

[0004] If the service life of the pile foundation structure is short or the deformation control standard of the pile foundation structure is low, the influence of the dissolution fracture zone under the action of groundwater and CO2 is small and can be ignored. However, when the service life of the pile foundation structure is longer, the importance degree is higher, and the deformation control is more strict, the influencing factors of the dissolution fracture zone under the action of groundwater should be fully considered. For example, the long-term deterioration influence of the dissolution fracture zone should be considered for high-speed railways with a service life of one hundred years and a deformation control standard of millimeter level. Summary of the Invention

[0005] The purpose of the present invention is to provide a construction method for improving the bearing performance of pile foundation structures in karst dissolution and fracture zones in view of the problems existing in the above-mentioned prior art. This method has the characteristics of simple construction, controllable quality, good bearing effect, economic and environmental protection, and is conducive to popularization and application.

[0006] The present invention is realized through the following technical solutions: A construction method for improving the bearing performance of pile foundation structures in karst dissolution and fracture zones, including the following steps:

[0007] (1) Plane positioning of the pile foundation structure;

[0008] (2)Use a rotary drilling rig to excavate the pile hole of the pile foundation structure, and use slurry for the pile hole wall protection until the elevation of the bottom of the pile foundation structure is reached;

[0009] (3)Clean the pile hole and place the steel reinforcement cage of the pile foundation structure in the pile hole;

[0010] (4)Fabricate a semi-circular perforated grouting pipe. The outer sleeve of the grouting pipe is a non-woven geotextile bag. Place the grouting pipes at intervals around the hole wall, and the side with holes of the grouting pipe is closely attached to the hole wall;

[0011] (5)Gradually and slowly pour the concrete of the pile foundation structure upward from the bottom of the pile hole;

[0012] (6)After the concrete pouring of the pile foundation structure is completed and before the concrete initial sets, perform high-pressure grouting through the grouting pipe.

[0013] Preferably, the semi-circular perforated grouting pipe described in step (4) can be fabricated using a PVC pipe with a diameter of 49 - 80 mm. Half of the PVC pipe is evenly perforated with holes having a diameter of 5 - 10 mm and a hole opening rate of 30%.

[0014] Preferably, before the concrete initial sets described in step (6), within 1 - 2 hours after the concrete pouring is completed, perform pressure grouting through the grouting pipe. The grouting pressure is 0.4 - 1.5 MPa. First, use 1.5 MPa high-pressure grouting. After the pressure on the grouting pressure gauge suddenly decreases during the grouting process, use a grouting pressure of 0.4 - 0.6 MPa for about 1 hour or stop grouting when the grouting liquid cannot be injected.

[0015] The beneficial effects of the present invention are as follows: After the pile hole of the pile foundation structure is formed, place the semi-circular perforated grouting pipes wrapped with non-woven geotextile bags at intervals around the hole wall. After the construction of the reinforced concrete of the pile foundation structure is completed, perform high-pressure grouting through the grouting pipes, which increases the strength of the karst dissolution and fragmentation zone around the pile foundation structure, significantly increases the effective friction force formed with the pile foundation structure, and significantly reduces the influence of external groundwater infiltration. Thus, the pile foundation structure has high bearing performance and good durability. Wrapping the grouting pipes with non-woven geotextile bags can prevent the slurry for wall protection from entering the grouting pipes; the semi-circular perforated grouting pipes can prevent the high-pressure grouting liquid from cutting the concrete of the pile foundation structure and affecting its quality, and are conducive to the fast and efficient construction of grouting; first use high pressure and then low pressure for grouting. The high-pressure slurry can penetrate through the non-woven geotextile bags and part of the concrete envelope outside the grouting pipes, and the low-pressure grouting can avoid slurry waste and the formation of an overly large dissolution and fragmentation zone reinforcement area. The proposed construction method effectively solves the problem that the pile side friction resistance of the pile foundation structure in the karst dissolution and fragmentation zone continuously decreases under the continuous action of groundwater and CO2, and also solves the problems of high cost and low efficiency in drilling and grouting around the pile foundation structure after the formation of the traditional pile foundation structure in the fragmentation zone. This method has the characteristics of simple and fast construction, controllable quality, good pile foundation bearing performance, economic and environmental protection, and is conducive to popularization and application. Description of the Drawings

[0016] Figure 1 It is a cross-sectional schematic diagram of a construction method for improving the bearing capacity of a pile foundation structure in a karst dissolution and fracture zone of the present invention.

[0017] Figure 2 It is a plan schematic diagram of a construction method for improving the bearing capacity of a pile foundation structure in a karst dissolution and fracture zone of the present invention.

[0018] In the figure: 1 - dissolution and fracture zone, 2 - pile foundation structure, 3 - grouting pipe, 4 - grouting reinforcement area for the dissolution and fracture zone. Specific implementation manners

[0019] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] As Figure 1-2 shown, an embodiment of the present invention is a construction method for improving the bearing capacity of a pile foundation structure in a karst dissolution and fracture zone, including the following steps:

[0021] (1) Planar positioning of the pile foundation structure 2;

[0022] (2) Using a rotary drilling rig to excavate the pile hole of the pile foundation structure 2, and using slurry for pile hole wall protection until the bottom elevation of the pile foundation structure 2;

[0023] (3) Cleaning the pile hole and placing the steel reinforcement cage of the pile foundation structure 2 in the pile hole;

[0024] (4) Making a semi-circular opening grouting pipe 3, covering the outer sleeve of the grouting pipe 3 with a non-woven geotextile bag, placing the grouting pipe 3 at intervals around the hole wall, and making the perforated side of the grouting pipe 3 close to the hole wall;

[0025] (5) Gradually and slowly pouring the concrete of the pile foundation structure 2 from the bottom of the pile hole upwards;

[0026] (6) After the concrete pouring of the pile foundation structure 2 is completed and before the concrete initial setting, high-pressure grouting is carried out through the grouting pipe 3 to form a grouting reinforcement area 4 for the dissolution and fracture zone.

[0027] Steps (1), (2), (3), and (5) are conventional operations.

[0028] In step (4), directly placing the grouting pipe 3 into the pile hole avoids the problems of high cost and low efficiency caused by the need to drill and place the traditional grouting pipe. The grouting pipe 3 has semi-circular openings, and the side with openings is closely attached to the hole wall. The slurry on the side with openings is easy to enter the dissolution and fragmentation zone 1 around the hole. The side without openings is beneficial for the high-pressure grouting liquid during grouting not to affect the concrete quality of the already cast pile foundation structure 2. A fully open grouting pipe has an impact on the concrete quality of the pile foundation structure 2, and the earlier the grouting time, the greater the impact. Wrapping the grouting pipe 3 with a non-woven geotextile bag without yarn can prevent the slurry for shaft protection from entering the grouting pipe 3. The non-woven geotextile bag without yarn has low strength, and during high-pressure grouting, the slurry is easy to pierce the geotextile bag, and the slurry can enter the dissolution and fragmentation zone 1 more conveniently.

[0029] Before the concrete begins to set, generally within 1-2 hours after the concrete pouring is completed, pressure grouting is carried out through the grouting pipe 3. The grouting pressure is generally 0.4-1.5 MPa. The grouting is first high-pressure and then low-pressure. The high-pressure slurry can penetrate through the non-woven geotextile bag without yarn and part of the cast-in-place concrete envelope outside the grouting pipe 3, and can better drive the slurry pollutants in the dissolution and fragmentation zone 1 around the pile. Due to the large pores and good connectivity of the dissolution and fragmentation zone 1, the later low-pressure slurry is mainly used to reinforce the dissolution and fragmentation zone 1 near the pile circumference to avoid waste of slurry. For an overly large reinforced area 4 of the dissolution and fragmentation zone, the improvement effect on the bearing capacity of the pile foundation structure 2 is significantly reduced. Effective grouting reinforcement is carried out on the dissolution and fragmentation zone 1 near the pile circumference. After reinforcement, the dissolution and fragmentation zone 1 has high strength, the effective friction force formed with the pile foundation structure 2 increases significantly, and the influence of external groundwater infiltration is significantly reduced. Thus, the pile foundation structure 2 has high bearing capacity and good durability. If the grouting is carried out after the concrete begins to set, the concrete wrapped outside the grouting pipe 3 will block the grouting channel, and it is necessary to increase the initial grouting pressure or even cause grouting failure.

[0030] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A construction method for improving the bearing performance of pile foundation structures in karst dissolution and fragmentation zones, characterized in that It includes the following steps: (1) Plane positioning of the pile foundation structure; (2) Using a rotary drilling rig to excavate the pile hole of the pile foundation structure, and adopting slurry for pile hole wall protection until the bottom elevation of the pile foundation structure; (3) Cleaning the pile hole and placing the steel reinforcement cage of the pile foundation structure into the pile hole; (4) Manufacturing a semi-circular opening grouting pipe, with a non-woven geotextile bag sleeved outside the grouting pipe, placing the grouting pipes at intervals around the hole wall, and the side with holes of the grouting pipe closely adhering to the hole wall; (5) Gradually and slowly pouring the concrete of the pile foundation structure upward from the bottom of the pile hole; (6) After the concrete pouring of the pile foundation structure is completed and before the concrete initial sets, high-pressure grouting is carried out through the grouting pipe; The semi-circular opening grouting pipe described in step (4) is made of a PVC pipe with a diameter of 49 - 80 mm, and half of the PVC pipe is evenly opened with holes with a pore diameter of 5 - 10 mm and an opening rate of 30%; Before the concrete initial sets in step (6), within 1 - 2 hours after the concrete pouring is completed, pressure grouting is carried out through the grouting pipe, the grouting pressure is 0.4 - 1.5 MPa, the grouting first adopts 1.5 MPa high-pressure grouting, and after the pressure of the grouting pressure gauge suddenly decreases during the grouting process, grouting is carried out at a grouting pressure of 0.4 - 0.6 MPa for 1 hour or grouting stops when the grouting liquid cannot be injected.

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