A deep-hole construction method for karst development areas under pebble coverings

Abstract

The present invention relates to the field of pile foundation hole construction methods, and specifically discloses a deep hole construction method for a karst development area under a pebble covering layer, including: S1, drilling a pilot hole; S2, reinforcing the pebble layer; S3, jet grouting a retaining wall structure; S4, drilling a pile hole; S5, excavating a sedimentation tank; S6, installing a vibrating screen; S7, installing a slurry pump; S8, lowering a conduit; S9, lowering an adjustment pipe; S10, circulating and filtering; S11, adjusting and optimizing, etc. By drilling a pilot hole with a large aperture at the pebble layer and injecting nano-silicate waterproof agent into the hole wall of the pilot hole, the bonding force and structural strength of the pebble layer can be improved. Then, a retaining wall structure is sprayed on the hole wall of the pilot hole by the jet grouting method to form a reinforcement layer. The rotating jet grouting method of the branch pipe structure and the conduit can lift the large particle sediment at the bottom and corners of the deep hole. The adjustment pipe can increase the lifting force when the large particle sediment surges back. After the large particle sediment is discharged, the mud concentration is adjusted to protect the retaining wall structure and ensure the stability of the hole wall.

Description

Technical Field

[0001] The invention belongs to the field of pile foundation hole construction, and in particular relates to a deep hole construction method in a karst development area under a pebble covering layer. Background Art

[0002] When carrying out railway construction in Guangdong and Guangxi, there will be some terrains with complex construction conditions, especially in northern Guangxi, where the geology has the characteristics of developed caves, widespread distribution of pebble layers, and interlaced dissolution fissures. The thickness of the pebble layer is usually 10-25 meters underground, and even 30-55 meters deep in some riverbed areas. The drilling depth of the pile foundation hole must exceed 20 meters from the bottom of the pebble layer to achieve the expected strength. The final total length of the hole is greater than 40 meters. In the field of railway roadbed construction, pile foundation holes with a depth of more than 40 meters are usually considered deep holes. The pebble layer is mainly composed of gravel and pebbles of varying particle sizes. There is a lack of effective cementation between particles, the porosity is as high as 25%-40%, and the permeability coefficient is about 1×10 -2 This loose structure makes the hole wall very easy to become unstable during the drilling process, resulting in collapse, shrinkage and other problems. In serious cases, it may even cause drill jamming or drill burial accidents, leading to delays in construction and increased construction costs.

[0003] The traditional construction method uses mud wall protection and casing follow-up. However, when constructing in the pebble layer, grouting reinforcement causes slurry loss due to the difference in porosity of the pebbles, making it difficult to form a uniform reinforcement layer. Therefore, the mud wall protection has problems such as low wall strength, unstable effect, long drilling cycle, and complex equipment. In addition, there will be a large amount of sediment at the bottom of the hole after drilling. Due to the large drilling depth required by the strongly developed landform, the traditional method uses a grouting pipe to flush the bottom of the hole to cause the mud to surge back, which will cause large particles of sediment to fall back midway and fall off the hole wall, resulting in incomplete slag cleaning and affecting the final drilling quality.

[0004] A method for drilling and re-drilling concrete retaining walls for rock-embedded piles in karst areas is disclosed in a patent document with application number "CN2016100943052". The method mainly comprises: constructing a plain concrete bored pile composed of a retaining concrete thin-walled barrel pile and a coring concrete solid pile located in the retaining concrete thin-walled barrel pile in the overlying soil layer. The diameter of the plain concrete bored pile is larger than the diameter of the pile hole of the underlying bedrock embedded rock pile. The pile length is the depth from the natural ground to the top surface of the underlying bedrock. When the age of the pile body concrete reaches 3 to 7 days, a rotary drilling rig is used to core the plain concrete bored pile, and the coring concrete solid pile is taken out. A re-drilled concrete retaining wall structure is formed by the retaining concrete thin-walled barrel pile, and then the underlying bedrock is exposed and the underlying bedrock embedded rock pile drilling construction is carried out in the bedrock stratum. The method still deviates from the traditional mud retaining wall, and therefore there are still problems such as the difficulty in forming a uniform reinforcement layer, the long drilling cycle and the unstable reinforcement of the traditional retaining wall.

[0005] A method for cleaning sediment at the bottom of a deep-hole pile is disclosed in the patent document with the application number "CN2018103862677", which includes the following steps: A. First, obtain a sediment cleaning bucket with the following structure. A casing mechanism is coaxially arranged in the middle of the sediment cleaning bucket. The bottom of the sediment cleaning bucket is a filter screen through which mud can flow, and the aperture of the filter screen is smaller than the minimum diameter of the debris to be cleaned. A lifting lug for connecting a lifting rope is also arranged on the sediment cleaning bucket. B. During use, pass a grouting conduit through the casing mechanism and vertically extend the grouting conduit to the bottom of the hole. Connect the lifting lug of the sediment cleaning bucket to the lifting rope of a hoisting device and lower it to the bottom of the hole. Inject mud into the bottom of the pile hole through the grouting conduit, so that the mud drives the debris at the bottom of the hole to rise above the sediment cleaning bucket and then sink into the sediment cleaning bucket. Then, lift the sediment cleaning bucket with the lifting rope to clean the sediment. And the comparative document also discloses an adjacent sedimentation tank and a mud tank, as well as a mud pump arranged in the mud tank. The outlet of the mud pump is connected through a pipeline to a grouting conduit for vertically extending into the bottom of the hole. Although this comparative document can perform a certain sediment cleaning function on the bottom of the deep hole of the pile foundation through the sediment cleaning bucket, and also has a sedimentation tank and a mud tank, which can play a role in filtering and circulating the mud, the gap between the sediment cleaning bucket and the hole wall is too small to allow large-particle pebble sediment to pass through. It is still not applicable to the structure under a thick pebble covering layer, and sediment can still leak through the gap outside the sediment cleaning bucket, resulting in incomplete sediment cleaning.

[0006] The disclosure of the above background technical content is only used to assist in understanding the inventive concept and technical solution of the present invention, and it does not necessarily belong to the prior art of this patent application. Without clear evidence indicating that the above content was publicly available on the filing date of this patent application, the above background art should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0007] The purpose of the present invention is to provide a deep-hole construction method for a karst development area under a pebble covering layer, so as to overcome the defects that when the traditional method is used for construction in a geological area with strong karst development under a thick pebble covering layer, there are problems such as low retaining wall strength, difficulty in forming a uniform reinforcement layer, large-particle sediment existing at the bottom of the pile hole after hole formation, and poor hole formation quality.

[0008] To achieve the above purpose, the present invention provides a deep-hole construction method for a karst development area under a pebble covering layer, including the following steps:

[0009] S1. Drill a guide hole: Determine the position of the thick pebble layer according to geological exploration conditions, drill a guide hole, the diameter of the guide hole is larger than the diameter of the pile hole, the center of the guide hole coincides with the center of the pile hole, and the lower end of the guide hole is lower than the bottom of the pebble layer;

[0010] S2. Reinforce the pebble layer: Inject nano-silicate waterproof agent from the hole wall of the guide hole into the voids of the pebble layer through a high-pressure grouting pump connected to a grouting pipe, vibrate and solidify;

[0011] S3. Jet grouting retaining wall structure: The jet grouting pipe is connected to the high-pressure mud pump and extends into the pilot hole. The high-pressure triple-tube jet grouting method is used to make the jet grouting pipe jet grout onto the hole wall of the pilot hole, forming a retaining wall structure on the hole wall of the pilot hole. The thickness of the retaining wall structure is not less than 20 cm.

[0012] S4. Drill the pile hole: Continue to drill the pile hole downward at the bottom of the pilot hole until the predetermined position is reached.

[0013] Preferably, in the above technical solution, the following steps are further included:

[0014] S5. Dig the sedimentation tank: Dig the sedimentation tank, which is partitioned into a mud tank and a sediment tank. Install a return mud pump in the mud tank and connect it with a return mud pipe.

[0015] S6. Install the vibrating screen: Install the vibrating screen above the sedimentation tank. The coarse material outlet and the fine material outlet of the vibrating screen correspond to the sediment tank and the mud tank respectively.

[0016] S7. Install the slurry pumping pump: A buffer tank is formed between the mouth of the pilot hole and the top end of the retaining wall structure. A pump installation groove is dug on the outer periphery of the buffer tank. Install a slurry pumping pump in the pump installation groove. The slurry pumping pump is connected to the feed inlet of the vibrating screen through a delivery hose.

[0017] S8. Insert the conduit: Insert the conduit into the pile hole. The upper end of the conduit is connected to the return mud pipe, and the diameter of the lower end of the conduit gradually decreases.

[0018] S9. Insert the regulating pipe: The upper end of the regulating pipe is connected to the regulating tank through a regulating pump. The regulating tank can move independently. Mud or clear water is filled in the regulating tank. The bottom end of the regulating pipe extends into the gap between the outer wall of the conduit and the inner wall of the pile hole.

[0019] S10. Circulating filtration: Add mud to the mud tank, turn on the return mud pump to pump the mud into the conduit. The mud is accelerated and sprayed towards the bottom of the pile hole through the conduit, flushing up the sediment and mixing it with the mud in the pile hole, and then surging back towards the hole mouth. Turn on the slurry pumping pump to pump the surging mud to the vibrating screen for screening. The large-particle sediment enters the sediment tank, and the fine-particle sediment passes through the screen and enters the mud tank. The mud in the mud tank continues to be pumped into the conduit by the return mud pump, forming a cycle.

[0020] S11. Adjustment and optimization: Inject mud through the regulating pipe. When the sediment in the surging mud decreases, inject clear water into the regulating pipe or close the regulating pipe, and reduce the working power of the return mud pump.

[0021] Preferably, in the above technical solution, in step S1, the distance between the lower end of the pilot hole and the bottom of the pebble layer is not less than 20 cm.

[0022] Preferably, in the above technical solution, the jet grouting pipe sinks to the bottom of the guide hole. After the pressure of the high-pressure mud pump increases to the construction design value, the jet grouting pipe sprays cement slurry at the bottom of the guide hole for 30 s, while spraying slurry and rotating, and at the same time, it is lifted at the lifting speed determined by the design and test piles. When the jet grouting pipe is lifted 20 cm above the top surface of the pebble layer, it is repeatedly sunk and lifted for slurry spraying.

[0023] Preferably, in the above technical solution, the bottom of the lower pump tank is lower than the top of the retaining wall structure.

[0024] Preferably, in the above technical solution, in step S9, the number of the regulating tanks is more than two. One of the regulating tanks is connected to the return slurry pipe, the regulating pumps are respectively arranged in each regulating tank, and the regulating pumps are connected to the upper end of the regulating pipe through branch pipes and branch valves.

[0025] Preferably, in the above technical solution, in step S8, an automatic sensor is further included. The automatic sensor includes a fixed block and a movable block. The fixed block is fixedly connected to the outer side wall of the conduit, the movable block is connected to the fixed block in a slidable manner, and a pressure sensor is installed between the fixed block and the movable block.

[0026] Preferably, in the above technical solution, in step S8, the diameter of the conduit is d. The diameter of the conduit gradually decreases to d / 2 starting from 2 m away from the lower end of the conduit, so as to form an inverted conical surface. A branch pipe is arranged on the inverted conical surface, and the outlet of the branch pipe extends downward and laterally of the conduit.

[0027] Preferably, in the above technical solution, in step S10, the conduit is rotated to make the outlet of the branch pipe rotate and spray slurry towards the bottom of the pile hole.

[0028] Preferably, in the above technical solution, the diameter at the outlet of the branch pipe gradually decreases.

[0029] Compared with the existing technology, the present invention has the following beneficial effects:

[0030] 1. The deep hole construction method in the karst development area under the pebble covering layer in the present invention can improve the bonding force and structural strength of the pebble layer by opening a large-diameter guide hole at the pebble layer and injecting nano-silicate waterproof agent into the hole wall of the guide hole, and then spraying a retaining wall structure on the hole wall of the guide hole by the jet grouting method, thus solving the problems of low retaining wall strength and difficulty in forming a reinforcement layer in the construction under this geological condition, preventing the collapse and sedimentation of the pebble layer during drilling, and ensuring the hole-forming quality.

[0031] 2. Steps S5 to S11 in the present invention can further remove the sediment in the hole after hole formation to ensure the hole formation quality. The conduit with a necking structure can increase the jet velocity during sediment cleaning, and combined with the branch pipe and the rotating slurry spraying method, large particle sediments at the bottom and corners of the deep hole can be flushed up simultaneously and gush back from the pile opening. The regulating pipe can assist in increasing the lifting force of the gushing-back slurry when the large particle sediments rise, making it easier to discharge the large particle sediments. After the large particle sediments are discharged, the regulating pipe can be closed or clean water can be injected to reduce the concentration of the gushing-back slurry, and the working power of the return slurry pump can be reduced to protect the retaining wall structure; reducing the concentration of the gushing-back slurry is also beneficial for the vibrating screen to screen the slurry.

[0032] 3. In the present invention, nano-silicate waterproof agent is injected into the pebble covering layer and then consolidated to form a reinforced pebble layer. After curing, the compressive strength can reach 15 - 20 MPa, significantly improving the bonding force between pebbles, and having water resistance, corrosion resistance and erosion resistance, thereby reducing the probability of hole collapse caused by the instability of the hole wall.

[0033] 4. The retaining wall structure is formed by multi-layer spraying through the jet grouting method, which can prevent the damage of the pilot hole structure during spraying, further improving the stability. And the bottom of the pilot hole and the retaining wall extends 20 cm below the bottom of the pebble layer, and the top of the retaining wall extends 20 cm above the top surface of the pebble layer, which can further prevent the collapse at the junction of the pebble layers and further improve the stability.

[0034] 5. The pilot hole in the present invention can not only play the role of reaming to facilitate grouting into the gaps of the pebble layer, but also form a buffer groove with the top of the retaining wall structure after the jet grouting retaining wall structure. A lower pump groove is dug on the outer periphery of the buffer groove, and the bottom of the lower pump groove is lower than the top of the buffer groove, which is convenient for placing the slurry pump and storing the large particle sediments after gushing back, thereby further preventing the sediment from falling back. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flowchart of a deep hole construction method in a karst development area under a pebble covering layer of the present invention.

[0036] Figure 2 is a schematic diagram of the pilot hole and the retaining wall structure.

[0037] Figure 3 is a schematic diagram of the structure in the orifice direction of the pilot hole.

[0038] Figure 4 is an installation schematic diagram of the vibrating screen and the sedimentation tank.

[0039] Figure 5 is the front view of the conduit.

[0040] Figure 6 is the top view of the conduit.

[0041] Description of main reference numerals:

[0042] 100 - support platform, 120 - support plate;

[0043] 200 - conduit, 210 - inverted conical surface;

[0044] 300 - loop buckle;

[0045] 400 - branch pipe;

[0046] 500 - adjusting pipe;

[0047] 700 - vibrating screen, 710 - mud pit, 720 - sediment pit, 730 - fixed frame;

[0048] 910 - guide hole, 920 - retaining wall structure, 930 - pile hole, 940 - pebble layer, 950 - buffer groove, 960 - pump - down groove. Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0050] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "top part", "bottom part", "top surface", "bottom surface", "inner", "outer", "inner side", "outer side", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention.

[0051] In the description of the present invention, the meaning of "several" is one or more, the meaning of "multiple" is two or more, understandings such as "greater than", "less than", "exceeding" do not include the present number, and understandings such as "above", "below", "within" include the present number. If there are descriptions of the terms "first", "second", "third", they are only for the purpose of description and distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0052] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", "linkage", and "setting" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The embodiments of the present invention will be described below according to its overall structure.

[0053] As Figures 1 to 6 shown, the deep-hole construction method for the karst development area under the pebble covering layer in this embodiment includes the following steps:

[0054] S1. Drilling a pilot hole: Determine the position of the thick pebble layer 940 according to the geological exploration situation, drill a pilot hole 910 with a hole diameter value enlarged by 50 cm compared to the diameter value of the pile hole 930. The center of the pilot hole 910 coincides with the center of the pile hole 930, and the lower end of the pilot hole 910 is 20 cm below the bottom of the pebble layer 940;

[0055] S2. Reinforcing the pebble layer: Insert a grouting pipe into the pilot hole 910. A plurality of slurry passing holes are provided on the side wall of the grouting pipe. Inject nano-silicate waterproof agent from the hole wall of the pilot hole 910 into the voids of the pebble layer 940 through a high-pressure grouting pump. The grouting pressure is controlled at 0.5 - 1.0 MPa. After the grouting is completed, let it stand for 5 minutes. Wait until the slurry initially penetrates into the pores, lower a vibrating rod, adjust the amplitude of the vibrating rod to 2 - 4 mm, the frequency to 50 - 60 Hz, continuously vibrate for 3 - 5 minutes, and reciprocally lift and lower the vibrating rod to solidify the slurry;

[0056] S3. Spiral jetting a retaining wall structure: Connect the upper end of the spiral jetting pipe to a high-pressure mud pump. The lower end of the spiral jetting pipe extends into the pilot hole. Use the high-pressure triple-tube spiral jetting method to make the spiral jetting pipe jet cement slurry onto the hole wall of the pilot hole 910. The spiral jetting pipe sinks to the bottom of the pilot hole 910. After the pressure of the high-pressure mud pump increases to the construction design value, the spiral jetting pipe jets cement slurry at the bottom of the pilot hole 910 for 30 s, while jetting slurry and rotating, and at the same time lift the spiral jetting pipe at the lifting speed determined by the design and test piles. When the spiral jetting pipe is lifted 20 cm above the top surface of the pebble layer, repeatedly sink and lift for jetting slurry; to form a retaining wall structure 920 on the hole wall of the pilot hole 910, and the thickness of the retaining wall structure 920 is not less than 20 cm;

[0057] S4. Drilling the pile hole: Use a drill bit to continue drilling the pile hole 930 downward from the bottom of the pilot hole 910 until reaching the predetermined position;

[0058] S5. Excavate the sedimentation tank: Excavate a sedimentation tank around the pile hole 930 area, partition the sedimentation tank area into two independent areas, namely the slurry tank 710 and the sediment tank 720. Install a number of slurry return pumps in the slurry tank 710 and connect them with slurry return pipes;

[0059] S6. Install the vibrating screen: Build a fixed frame 730 above the sedimentation tank, install a vibrating screen 700 on the fixed frame 730, align the coarse material outlet of the vibrating screen 700 with the mouth of the sediment tank 720, and align the fine material outlet of the vibrating screen 700 with the mouth of the slurry tank 710. The mesh aperture of the screen mesh of the vibrating screen 700 is 5 mm, the vibration frequency is adjusted to 45 - 50 Hz, and the amplitude is 0 - 2 mm;

[0060] S7. Install the slurry pumping pump: A buffer tank 950 is formed between the mouth of the guide hole 910 and the top end of the retaining wall structure 920. An under - pump groove 960 is dug on the outer periphery of the buffer tank 950, and a slurry pumping pump is installed in the under - pump groove 960. The slurry pumping pump is connected to the feed inlet of the vibrating screen 700 through a delivery hose;

[0061] S8. Lower the conduit: Build a support platform 100 at the mouth of the pile hole 930, open an installation hole on the support platform 100, install a conduit 200 in the installation hole. The diameter of the conduit 200 is d. The top end of the conduit 200 is connected to the slurry return pipe. The lower end of the conduit 200 extends towards the bottom of the pile hole and an automatic sensor is installed on its side wall. The diameter of the conduit 200 gradually decreases to d / 2 starting from 2 meters away from the lower end of the conduit 200, thus forming an inverted conical surface 210. A branch pipe 400 is welded at the inverted conical surface 210, and the outlet of the branch pipe 400 extends towards the lower side of the conduit 200. The diameter at the outlet of the branch pipe 400 gradually decreases;

[0062] S9. Lower the adjustment pipe: The top end of the adjustment pipe 500 is connected to the adjustment tank through an adjustment pump. The number of adjustment tanks is two or more and they can be independently moved. Slurry or clear water is filled in each adjustment tank respectively. The adjustment tank filled with slurry is connected to a slurry return pipe. The adjustment pumps are installed in each adjustment tank respectively. Each adjustment pump is connected to the upper end of the adjustment pipe 500 through a branch pipe and a branch valve. The bottom end of the adjustment pipe 500 extends into the gap between the outer wall of the conduit 200 and the inner wall of the pile hole;

[0063] S10. Circulating filtration: First, add a portion of mud into the mud pit 710, turn on the return slurry pump. After the mud is accelerated by the conduit 200, it is sprayed into the pile hole. At the same time, rotate the conduit 200 so that the mud is accelerated and ejected from the lower end of the conduit 200 and the branch pipe 400 to lift the sediment at the bottom of the pile hole and mix it with the mud, then the mixture surges back into the buffer tank 950. Turn on the slurry pumping pump to send the surging mud into the inlet of the vibrating screen 700 for screening. Large particles (with a diameter greater than 5 mm) of pebbles and some coarse sand are intercepted by the screen and flow into the sediment pond 720 from the coarse material outlet. Fine particles (with a diameter less than or equal to 5 mm) of sediment pass through the screen and flow into the mud pit 710. The mud in the mud pit 710 is continuously pumped into the conduit 200 by the return slurry pump to form a cycle;

[0064] S11. Adjusting and optimizing: Turn on the regulating pump in the regulating tank filled with mud to inject mud into the regulating pipe 500. Then, the automatic sensor can sense the shear force during the mud flow. When the measured value and fluctuation amount of the shear force are large, it indicates that there is still sediment remaining in the hole, and the flow rate of the return slurry pipe or the flow rate of the mud injected into the regulating pipe 500 can be increased; when the measured value and fluctuation amount of the shear force are small, it indicates that the sediment in the hole has been basically cleared, and the working power of the return slurry pump and the flow rate of the return slurry pipe can be reduced. At the same time, close the regulating pipe 500. When the mud density at the feed inlet of the vibrating screen 700 is large, clean water can be injected by switching the regulating pipe 500 to reduce the scouring force on the pile hole wall and prevent collapse. At the same time, the concentration of the surging mud can also be reduced to improve the screening effect.

[0065] More specifically, the automatic sensor in step S8 includes a fixed block and a movable block. The fixed block is fixedly connected to the outer side wall of the conduit 200. The movable block is connected to the fixed block in a slidable manner and can slide along the axial direction of the conduit 200. A pressure sensor is installed between the movable block and the fixed block. When the mud surges in the gap between the conduit 200 and the pile hole, it can impact the movable block, so that the shear force can be detected through the pressure sensor. When the movable block is impacted by larger sediment particles, the fluctuation amplitude of the real-time pressure measurement value of the pressure sensor is large and irregular. After the large particle sediment is cleared, the fluctuation amplitude of the real-time pressure measurement value of the pressure sensor is small and tends to be stable.

[0066] More specifically, the viscosity of the nano-silicate waterproofing agent slurry in step S2 is 0.05 - 0.1 Pa·s, which can quickly penetrate into the pores of the pebble layer, with a filling rate of more than 90%. By adding a retarder or an accelerator, the initial setting time can be accurately controlled within 10 - 15 minutes to meet the rapid reinforcement requirements; after curing, the compressive strength reaches 15 - 20 MPa, significantly improving the bonding force between pebbles, and having corrosion resistance and anti-scouring performance; the proportion of the nano-silicate waterproofing agent slurry needs to be optimized according to on-site tests. The typical proportion is: nano-silicate solution (main agent) 60%, water 35%, regulator (retarder / accelerator) 5%.

[0067] More specifically, the support platform 100 is of a cubic frame structure. A support plate 120 is provided at the top of the support platform 100. Among them, two support plates 120 near the middle can be opened towards each other. Semi-circular holes are respectively formed at the edges of the two openable and closable support plates 120. When the two semi-circular holes are combined, an installation hole can be formed. An outwardly protruding ring buckle 300 is provided on the outer wall of the upper end of the conduit 200. The ring buckle 300 can be stuck above the installation hole, so as to position and install the conduit 200, limit the downward movement of the conduit 200 along its own axis direction, and enable the conduit 200 to rotate around the axis of the conduit 200 itself.

[0068] In summary, the deep-hole construction method for the karst development area under the pebble covering layer in this embodiment can improve the bonding force and structural strength of the pebble layer 940 by opening a large-diameter pilot hole 910 at the pebble layer 940 and injecting nano-silicate waterproof agent into the hole wall of the pilot hole 910. Then, the shaft protection structure 920 is sprayed on the hole wall of the pilot hole 910 by the jet grouting method, thus solving the problems of low shaft protection strength and difficulty in forming a reinforcement layer during construction under this geological condition; and the conduit 200 with a reduced diameter structure can increase the jetting speed during slag cleaning, and combined with the branch pipe 400 and the rotating slurry spraying method, the large-particle sediment at the bottom and corners of the deep hole can be simultaneously flushed up and gushed back from the pile mouth. The regulating pipe 500 can assist in increasing the lifting force of the gushing-back slurry when the large-particle sediment rises, making it easier to discharge the large-particle sediment. When the large-particle sediment is discharged, the regulating pipe can be closed or clean water can be injected to reduce the concentration of the gushing-back slurry, and the working power of the slurry return pump can be reduced to protect the shaft protection structure 920.

[0069] The foregoing description of the specific exemplary embodiments of the present invention is for the purposes of illustration and exemplification. These descriptions are not intended to limit the present invention to the precise forms disclosed, and it is obvious that many changes and variations can be made in accordance with the above teachings. Although the embodiments of the present invention have been shown and described, the specific embodiments are merely explanations of the present invention and are not limitations of the invention. The specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical applications, so that those skilled in the art can, after reading this specification, make modifications, substitutions, variations, and various different selections and changes that do not make creative contributions to the embodiments as needed, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A deep-hole construction method for a karst development area under a pebble covering layer, characterized in that It includes the following steps: S1. Drilling a guide hole: Determine the position of the thick pebble layer according to geological exploration conditions, drill a guide hole, the diameter of the guide hole is larger than that of the pile hole, the center of the guide hole coincides with that of the pile hole, and the lower end of the guide hole is lower than the bottom of the pebble layer; S2. Reinforcing the pebble layer: Connect a grouting pipe through a high-pressure grouting pump and inject nano-silicate waterproof agent into the voids of the pebble layer from the hole wall of the guide hole, vibrate and solidify; S3. Spiral jetting a retaining wall structure: Connect a spiral jetting pipe with a high-pressure mud pump and extend it into the guide hole. Use the high-pressure triple-tube spiral jetting method to make the spiral jetting pipe jet cement slurry onto the hole wall of the guide hole, and form a retaining wall structure on the hole wall of the guide hole, and the thickness of the retaining wall structure is not less than 20 cm; S4. Drilling the pile hole: Continue to drill the pile hole downward at the bottom of the guide hole until reaching the predetermined position; S5. Digging a sedimentation tank: Dig a sedimentation tank, which is partitioned into a mud tank and a sediment tank. Install a reverse slurry pump in the mud tank and connect it with a reverse slurry pipe; S6. Installing a vibrating screen: Install a vibrating screen above the sedimentation tank, and the coarse material outlet and the fine material outlet of the vibrating screen correspond to the sediment tank and the mud tank respectively; S7. Installing a slurry pumping pump: A buffer tank is formed between the mouth of the guide hole and the top of the retaining wall structure. A pump installation groove is dug on the outer periphery of the buffer tank, and a slurry pumping pump is installed in the pump installation groove. The slurry pumping pump is connected to the feed inlet of the vibrating screen through a conveying hose; S8. Inserting a conduit: Insert a conduit into the pile hole, the upper end of the conduit is connected to the reverse slurry pipe, and the diameter of the lower end of the conduit gradually decreases; S9. Inserting an adjusting pipe: The upper end of the adjusting pipe is connected to an adjusting tank through an adjusting pump. The adjusting tank can move independently. Mud or clear water is filled in the adjusting tank, and the bottom end of the adjusting pipe extends into the gap between the outer wall of the conduit and the inner wall of the pile hole; S10. Circulating filtration: Add mud to the mud tank, turn on the reverse slurry pump to pump the mud into the conduit. The mud is accelerated and sprayed towards the bottom of the pile hole through the conduit, and the sediment is washed up and mixed with the mud in the pile hole and then surges back towards the hole mouth. Turn on the slurry pumping pump to pump the surging mud to the vibrating screen for screening. The large-particle sediment enters the sediment tank, and the fine-particle sediment passes through the screen and enters the mud tank. The mud in the mud tank continues to be pumped into the conduit by the reverse slurry pump to form a cycle; S11. Adjusting and optimizing: Inject mud through the adjusting pipe. When the sediment in the surging mud decreases, inject clear water into the adjusting pipe or close the adjusting pipe, and reduce the working power of the reverse slurry pump.

2. The deep hole construction method for the karst development area under the pebble covering layer according to claim 1, characterized in that In step S1, the distance between the lower end of the guide hole and the bottom of the pebble layer is not less than 20 cm.

3. The deep hole construction method for the karst development area under the pebble covering layer according to claim 2, characterized in that The spiral jetting pipe sinks to the bottom of the guide hole. After the pressure of the high-pressure mud pump increases to the construction design value, the spiral jetting pipe sprays cement slurry at the bottom of the guide hole for 30 s, spraying and rotating at the same time, and lifting at the lifting speed determined according to the design and test pile. When the spiral jetting pipe is lifted 20 cm above the top surface of the pebble layer, it sinks and lifts repeatedly for spraying.

4. The deep hole construction method for the karst development area under the pebble covering layer according to claim 1, characterized in that The bottom of the pump installation groove is lower than the top of the retaining wall structure.

5. The deep hole construction method for the karst development area under the pebble covering layer according to claim 1, characterized in that, In step S9, the number of the adjusting tanks is more than two. One of the adjusting tanks is connected to the reverse slurry pipe. The adjusting pumps are respectively arranged in each adjusting tank, and the adjusting pumps are connected to the upper end of the adjusting pipe through branch pipes and branch valves.

6. The deep-hole construction method for a karst development area under a pebble covering layer according to claim 1, characterized in that In step S8, an automatic sensor is further included. The automatic sensor includes a fixed block and a movable block. The fixed block is fixedly connected to the outer side wall of the conduit. The movable block is connected to the fixed block in a slidable manner. A pressure sensor is installed between the fixed block and the movable block.

7. The deep-hole construction method for the karst development area under the pebble covering layer according to claim 1, characterized in that In step S8, the diameter of the conduit is d. The diameter of the conduit gradually decreases to d / 2 starting from 2 meters away from the lower end of the conduit, thereby forming an inverted conical surface. A branch pipe is provided on the inverted conical surface, and the outlet of the branch pipe extends downward and to the side of the conduit.

8. The deep hole construction method for the karst development area under the pebble covering layer according to claim 7, characterized in that, In step S10, rotate the conduit so that the outlet of the branch pipe rotates and sprays slurry towards the bottom of the pile hole.

9. The deep-hole construction method for a karst development area under a pebble covering layer according to claim 8, characterized in that, The diameter at the outlet of the branch pipe gradually decreases.

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