A reinforcement method for the karst cave developed behind the bottom of the cast-in-place pile

Abstract

The present invention provides a reinforcement treatment method for a karst cave developed at the bottom of a bored pile. The reinforcement treatment method comprises the following steps: S1, geological survey of the bored pile and its surroundings to obtain the size, shape and position of the karst cave; S2, drilling a hole at the center of the top of the bored pile using a coring drill, the hole extending to the bottom of the bored pile and then extending downward by 6m; S3, using a reaming drill rod to reame from the bottom of the bored pile, and the concrete debris generated by the reaming is used as the first filling material for the karst cave; S4, grouting treatment from bottom to top using high-pressure rotary spraying. By using a reaming drill to reame from the bottom of the bored pile, the concrete debris generated falls and is directly filled into the karst cave as the first filling material, which can form a more compact grouting consolidation body, provide good support for the bearing force of the bored pile bottom, make the concrete more integrated, and the core column formed by the post-casting has a step support with the bored pile, thereby ensuring that the bored pile has sufficient supporting force.

Description

Technical Field

[0001] The invention relates to the technical field of construction engineering, in particular to a method for reinforcing a karst cave developed behind the bottom of a cast-in-place pile. Background Art

[0002] Reinforced concrete bored piles are an important type of pile foundation and are widely used in foundation engineering. In specific designs, the bearing capacity of bored piles meeting the design requirements is one of the basic conditions for ensuring the safety of buildings. However, if geological caves are not clearly detected before construction or new caves develop after the construction of reinforced concrete bored piles is completed, the bearing capacity of bored piles will be affected and they need to be reinforced.

[0003] Some reinforcement methods currently used are difficult to ensure the integrity of the concrete of the post-cast part and the concrete columns constructed in the early stage, and there is a problem of unbalanced force between the repaired concrete columns and other concrete columns. For this reason, the present invention provides a reinforcement treatment method for the karst cave developed at the bottom of the cast-in-place pile. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a reinforcement treatment method for the karst caves developed at the bottom of a bored pile, which solves the problem that the current pile bottom reinforcement method is difficult to ensure the integrity of the concrete of the post-cast part and the concrete column constructed in the early stage, and there is an unbalanced force on the repaired concrete column and other concrete columns.

[0005] To achieve the above purpose, the present invention provides a method for reinforcing a bored pile with a karst cave at the bottom. The method is mainly aimed at the situation that the newly developed karst cave at the bottom of the bored pile affects the bearing capacity of the bored pile after the construction is completed. The method specifically comprises the following steps:

[0006] S1. Conduct geological survey on the cast-in-place piles and their surroundings to obtain the size, shape and location of the cave;

[0007] S2, using a coring drill to drill a hole at the center of the top of the cast-in-place pile, the hole extends to at least 6m below the bottom of the cast-in-place pile and is connected to the karst cave below the bottom of the cast-in-place pile;

[0008] S3, use the reaming drill bit to descend to the bottom of the cast-in-place pile along the borehole in step S2, and expand the hole from the bottom of the cast-in-place pile, the concrete slag produced by the expansion is used as the first filling material of the karst cave, the height a of the expansion is 1 / 3-1 / 2 of the overall length of the cast-in-place pile, and the expansion area is connected to the karst cave below the cast-in-place pile bottom;

[0009] S4, grouting the cave below the bottom of the bored pile, the expanded hole area at the bottom of the bored pile, and the central borehole of the bored pile from bottom to top by high-pressure jet grouting; during the high-pressure jet grouting process, the grouting pressure is greater than 20MPa, the grouting flow rate is 100-150L / min, the air pressure is 0.3-0.7MPa, and the lifting speed of the jet grouting reinforcement section is 10-15cm / min;

[0010] S5. 28 days after the grouting is completed, the pile static load test is used to test the pile bearing capacity. After passing the test, the reinforcement process is completed.

[0011] A further technical solution of the present invention is as follows: when a karst cave with a diameter greater than 1.5 m is detected in S1; three auxiliary boreholes of 1.0 m are drilled around the cast-in-place piles, the three auxiliary boreholes of 1.0 m are distributed in a triangle with the cast-in-place piles as the center, and the bottoms of the auxiliary boreholes extend to the karst caves; the three auxiliary boreholes of 1.0 m are all grouted from bottom to top using high-pressure rotary jetting, and the formed auxiliary foundation piles at least reach the height of the top of the cast-in-place piles.

[0012] A further technical solution of the present invention: the drill bit used for expanding the hole in step S3 is a centrifugal drill bit, which includes a drill bit body and a plurality of telescopic cutter bodies distributed on the drill bit body, the diameter of the drill bit body matches the drilling hole in step S2, a connecting male head for connecting to a drill rod is fixedly connected to the top of the drill bit body, and a cone head is fixedly connected to the bottom of the drill bit body; a cutter body mounting cavity is opened at a position of the drill bit body corresponding to each cutter body, the cutter body mounting cavity is arranged along the radial direction of the drill bit body, the cutter body is slidably mounted on the inner side of the cutter body mounting cavity, and extends out of the cutter body mounting cavity under the action of the centrifugal force of the rotation of the drill bit body.

[0013] A further technical solution of the present invention is as follows: the drill bit used for reaming in step S3 is a differential drill bit, and the differential drill bit includes a cylindrical shell and a telescopic hob structure arranged in the cylindrical shell, the diameter of the cylindrical shell matches the drilling hole in step S2, the bottom end of the cylindrical shell is fixedly connected with a bottom cutting portion, and the top end is provided with an input shaft connected with the drill rod, the bottom end of the input shaft extends into the interior of the cylindrical shell, and a first bevel gear is fixedly installed at the bottom, an extension shaft is provided at the bottom of the input shaft, and the bottom of the extension shaft is rotatably connected to the bottom of the cylindrical shell through a reduction mechanism, and under the action of the reduction mechanism, the rotation speed of the cylindrical shell is less than the rotation speed of the input shaft; the telescopic hob structure includes an annular frame and at least Two groups of chip rollers, the cylindrical shell is provided with a through hole corresponding to each group of chip rollers; the annular frame is fixedly mounted on the inner side wall of the cylindrical shell, and each group of chip rollers is mounted on the bottom of the annular frame through a mounting seat, a threaded seat is rotatably mounted on the inner side of the mounting seat, a ratchet structure is arranged between the threaded seat and the mounting seat, one end of the chip roller is fixedly connected with a threaded shaft, the threaded seat is threadedly sleeved on the threaded shaft, a transmission shaft is slidably connected to the end of the threaded shaft, a second bevel gear is fixedly mounted on the transmission shaft, and the second bevel gear is meshed with the first bevel gear; the threaded shaft on each group of chip rollers is driven to rotate by rotating the input shaft, thereby controlling at least two groups of chip rollers to extend out of the cylindrical shell along the corresponding through holes at the same time.

[0014] The preferred technical solution of the present invention is: when a fault occurs, the high-pressure rotary spraying is stopped immediately; after the fault is eliminated, the spraying is resumed, and the height of the resumed spraying is not less than 50 cm.

[0015] A preferred technical solution of the present invention is as follows: the grouting liquid cement of the high-pressure rotary spraying adopts PO 42.5 cement, and the water-cement ratio is 1:1.

[0016] A more preferred technical solution of the present invention: in the steps S2 and S3, the amount of slurry in the borehole is controlled to be less than 20%.

[0017] The preferred technical solution of the present invention is as follows: the drill body has a cylindrical structure with a diameter matching the drill hole in step S2; a plurality of cutter bodies are distributed in two layers in parallel on the middle and lower part of the drill body; each layer of cutter bodies is distributed in a ring-shaped and equidistant manner on the drill body; and a serrated portion is provided on the outer edge of each cutter body; the cutter body mounting cavity is divided into two layers and is correspondingly arranged on the drill body; a circle of annular sleeves is provided at the lower cavity opening of each layer of the cutter body mounting cavity; an annular opening is provided on the drill body corresponding to the edge of the lower cavity opening of the cutter body mounting cavity; the annular sleeve is fixedly installed in the annular opening, and a notch portion is correspondingly provided at the bottom of each cutter body; when the cutter body extends out of the cutter body mounting cavity, the annular sleeve is located on the inner side of the notch portion; and the top of the cutter body is an inclined surface.

[0018] The better technical solution of the present invention is as follows: the top end of the cylindrical outer shell is open, and an end cover is fixedly installed on the open top end of the cylindrical outer shell, the input shaft is rotatably installed with the end cover, and the top end of the input shaft is a male head connected to the drill rod; the chip roller is provided with three groups, which are evenly distributed in a ring shape on the cylindrical outer shell, and the transmission shaft is a flower shaft.

[0019] A better technical solution of the present invention: the top end of the extended shaft is fixedly connected to the bottom end of the input shaft, the reduction mechanism includes a circular groove opened on the inner bottom of the cylindrical outer shell and a wear-resistant disk arranged inside the circular groove, the bottom end of the wear-resistant disk and the inner bottom of the circular groove form a friction surface, an eccentric gear ring is rotatably installed on the top of the wear-resistant disk, a first gear is fixedly installed on the bottom end of the extended shaft, the inner ring and the outer ring of the eccentric gear ring are both provided with gear ring parts, the inner ring of the circular groove is provided with a gear ring part matching the gear ring of the outer ring of the eccentric gear ring, the first gear is meshed with the eccentric gear ring, and the eccentric gear ring is meshed with the circular groove.

[0020] The present invention has the following beneficial effects:

[0021] (1) The present invention uses a hole-reaming drill to expand the hole from the bottom of the bored pile. The concrete debris generated by the hole expansion falls directly into the cave and serves as the first filling material to increase the hard layer at the cave. It is combined with the concrete slurry injected by the subsequent high-pressure rotary jet to form a more compact grouting consolidation body, which provides good support for the bearing capacity of the bored pile bottom.

[0022] (2) The present invention forms a cavity at the bottom of the bored pile that is integrated with the cave by expanding the hole at the bottom of the bored pile. When the subsequent concrete pouring is carried out, the contact surface between the later poured concrete and the original bored pile can be increased, making the two more integrated. In addition, there is a step support between the core column formed by the later pouring and the bored pile, thereby ensuring that the bored pile has sufficient supporting force.

[0023] (3) Since the hole expansion area in the present invention is at the bottom of the bored pile, there are special requirements for the design of the drill bit. The present invention provides two types of hole expansion drill bits according to the construction method. One type uses centrifugal force to make the cutter body slide out from the drill bit body. After the hole expansion is completed, the cutter body is retracted and placed in the cutter body installation cavity, which is convenient for the drill bit to be normally removed after the hole expansion is completed; the other type controls the extension and retraction of the drill bit by gears, which can also be easily implemented by extending it in the hole expansion area and retracting it after the hole expansion is completed.

[0024] (4) The present invention adopts high-pressure rotary jet grouting from bottom to top, which can well fill the cave and make it less likely to produce a hollow structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the reinforcement treatment of the karst cave developed behind the bottom of the cast-in-place pile proposed by the present invention;

[0026] Figure 2 It is a schematic diagram of the reinforcement treatment of the karst cave developed behind the bottom of the cast-in-place pile proposed by the present invention;

[0027] Figure 3 is a three-dimensional schematic diagram of a centrifugal drill bit of the present invention;

[0028] Figure 4 is a front view of a centrifugal drill bit of the present invention;

[0029] Figure 5 is a cross-sectional view of a centrifugal drill bit of the present invention;

[0030] Figure 6 for Figure 5 A partial enlarged view in the middle;

[0031] Figure 7 is a three-dimensional schematic diagram of a drill bit in another embodiment of the present invention;

[0032] Figure 8 A front view of a drill bit in another embodiment of the present invention;

[0033] Fig. 9 is a top view of a drill bit in another embodiment of the present invention;

[0034] Fig.10 for Fig. 9 Section view of the section line at AA;

[0035] Fig.11 It is a schematic diagram of the installation of a chip drum of a drill bit in another embodiment of the present invention;

[0036] Fig.12 It is a schematic diagram of the installation of the inner bottom of the cylindrical shell of the drill bit in another embodiment of the present invention.

[0037] Among them, a, first depth; b, second depth; 1, drill bit body; 2, connecting male head; 3, cone head; 4, cutter body mounting cavity; 5, cutter body; 5c, serrated portion; 6, annular opening; 7, annular kit; 8, notch portion; 9, cylindrical shell; 10, bottom cutting portion; 11, end cover; 12, input shaft; 13, first bevel gear; 14, annular frame; 15, mounting seat; 16, threaded seat; 17, ratchet structure; 18, chip roller; 19, threaded shaft; 20, transmission shaft; 21, second bevel gear; 22, extension shaft; 23, first gear; 24, eccentric gear ring; 25, wear-resistant disk; 26, circular groove. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Embodiment 1 provides a method for reinforcing a bored pile with a karst cave at the bottom. The method is mainly aimed at the situation where the newly developed karst cave at the bottom of the bored pile affects the bearing capacity of the bored pile after the bored pile is constructed. The method specifically includes the following steps:

[0040] S1. Conduct geological survey on the cast-in-place piles and their surroundings to obtain the size, shape and location of the cave;

[0041] S2, using a coring drill to drill a hole at the center of the top of the cast-in-place pile, the hole extends to at least 6m below the bottom of the cast-in-place pile and is connected to the karst cave below the bottom of the cast-in-place pile;

[0042] S3, using a reaming drill bit to descend along the borehole in step S2 to the bottom of the bored pile, and reaming from the bottom of the bored pile, the concrete slag produced by the reaming is used as the first filling material of the karst cave, the height a of the reaming is 1 / 3-1 / 2 of the overall length of the bored pile, and the reaming area is connected to the karst cave below the bottom of the bored pile; it is specifically determined according to the size of the karst cave; after the reaming is completed, a pressure rod can also be used to insert from the top of the bored pile to pressurize the first filling material so that it is closely attached to the karst cave to block some water eyes in the karst cave;

[0043] S4, grouting treatment is performed from bottom to top on the karst cave below the bottom of the bored pile, the expansion area at the bottom of the bored pile, and the central borehole of the bored pile by high-pressure rotary jetting; the grouting liquid cement of the high-pressure rotary jetting adopts PO 42.5 cement, and the water-cement ratio is 1:1; during the high-pressure rotary jetting grouting process, the grouting pressure is greater than 20MPa, the grouting flow rate is 100-150L / min, the air pressure is 0.3-0.7MPa, and the lifting speed of the rotary jetting reinforcement section is 10-15cm / min;

[0044] S5. 28 days after the grouting is completed, the pile static load test is used to test the pile bearing capacity. After passing the test, the reinforcement process is completed.

[0045] In the embodiment, sufficient preparations are made as far as possible before high-pressure rotary spraying to ensure that it is completed in one time. If a fault occurs, the high-pressure rotary spraying is stopped immediately; after troubleshooting, the spraying is repeated, and the height of the repeated spraying is not less than 50 cm, so as to ensure that the concrete column formed by the repeated spraying and the cast-in-place pile are connected in an integrated manner to meet the requirements. If the height of the repeated spraying is less than 50 cm, secondary coring drilling can be used to ensure that the height of the repeated spraying is not less than 50 cm. In steps S2 and S3, the amount of slurry in the borehole is controlled to be less than 20%. When it exceeds 20% or there is no slurry at all, the cause should be found out and corresponding measures should be taken.

[0046] The present invention uses a hole reaming drill to expand the hole from the bottom of the bored pile, and the concrete debris generated by the hole reaming drill falls and is directly filled into the cave as the first filling material. One of its purposes is to increase the hard layer at the cave, which is combined with the concrete slurry injected by the subsequent high-pressure rotary spraying to form a denser grouting consolidation body, providing good support for the bottom bearing force of the bored pile; the second purpose is to increase the contact surface between the post-cast concrete and the original bored pile, so that the two are more integrated, and the core column formed by the post-casting and the bored pile have a step support, thereby ensuring that the bored pile has sufficient supporting force.

[0047] Reference Figure 2 In one embodiment, when a cave larger than 1.5 m is detected in S1, three auxiliary boreholes of 1.0 m are drilled around the cast-in-place pile, and the three auxiliary boreholes of 1.0 m are distributed in a triangle with the cast-in-place pile as the center, and the bottom of the auxiliary boreholes extends to the cave; the three auxiliary boreholes of 1.0 m are all grouted from bottom to top using high-pressure rotary jetting to ensure that the cave can be completely filled and the auxiliary foundation piles formed reach at least the height of the top of the cast-in-place pile.

[0048] The drill bit used for expanding the hole in step S3 in the above embodiment can be a centrifugal drill bit, such as Figures 3 to 6As shown, the centrifugal drill bit includes a drill bit body 1 and a plurality of telescopic cutter bodies 5 distributed on the drill bit body. The drill bit body 1 is a cylindrical structure with a diameter matching the drilling hole in step S2. A connecting male head 2 for connecting to a drill rod is fixedly connected to the top of the drill bit body 1, and a cone head 3 is fixedly connected to the bottom of the drill bit body 1. A cutter body mounting cavity 4 is opened at a position of the drill bit body 1 corresponding to each cutter body 5. The cutter body mounting cavity 4 is arranged along the radial direction of the drill bit body 1. The cutter body 5 is slidably mounted on the inner side of the cutter body mounting cavity 4, and extends out of the cutter body mounting cavity 4 under the action of the centrifugal force of the rotation of the drill bit body 1. A plurality of cutter bodies 5 are distributed in two layers in parallel on the middle and lower part of the drill body 1, and each layer of cutter bodies 5 is distributed in a ring-shaped and equidistant manner on the drill body 1, and a serrated portion 5c is provided on the outer edge of each cutter body 5; the cutter body mounting cavity 4 is divided into two layers and is correspondingly arranged on the drill body 1, and a circle of annular sleeves 7 are provided at the lower cavity opening of each layer of cutter body mounting cavity 4, and the drill body 1 is provided with an annular opening 6 at a position corresponding to the edge of the lower cavity opening of the cutter body mounting cavity 4, and the annular sleeve 7 is fixedly installed in the annular opening 6, and a notch portion 8 is correspondingly provided at the bottom of each cutter body 5. When the cutter body 5 extends out of the cutter body mounting cavity 4, the annular sleeve 7 is located on the inner side of the notch portion 8, and the cutter body 5 can be limited by the annular sleeve 7 to prevent the cutter body 5 from completely separating from the drill body 1.

[0049] The connecting male head 2 of the centrifugal drill bit in the embodiment corresponds to the connecting female head at the bottom end of the drill rod, so as to facilitate the fixed installation of the centrifugal drill bit and the drill rod. The bottom end of the drill bit body 1 is fixedly connected with a cone head 3 for impacting and breaking some block concrete. The side of the drill bit body 1 is provided with a cutter body installation cavity 4 for receiving and releasing the cutter body 5. The bottom of the cutter body 5 is provided with a notch 8. The top of the cutter body 5 is an inclined surface. When the top of the cutter body 5 is blocked, the cutter body 5 retracts into the inside of the cutter body installation cavity 4. When the centrifugal drill bit is in use, the drill bit body 1 is driven to rotate, and the cutter body 5 slides outward under the action of centrifugal force, and the serrated portion 5c abuts against the inner side of the hole drilled by S2 to achieve hole expansion; when the drill bit body 1 stops rotating, the position of the drill bit body 1 is adjusted in the up and down direction to achieve the opening of the hole expansion of the required height, and the inner wall of the hole expansion opened in the above manner is a roughened surface, which is in close contact with the concrete poured later.

[0050] The drill bit used for expanding the hole in step S3 in the above embodiment may also be a differential drill bit, such as Figures 7 to 11As shown, the differential drill bit includes a cylindrical housing 9 and a telescopic hob structure arranged in the cylindrical housing 9. The diameter of the cylindrical housing 9 matches the drilling hole in step S2. The bottom end of the cylindrical housing 9 is fixedly connected with a bottom cutting portion 10, and the top end is provided with an input shaft 12 connected to the drill rod. The top end of the cylindrical housing 9 is open, and an end cover 11 is fixedly installed on the open top end of the cylindrical housing 9. The end cover 11 covers the top end of the cylindrical housing 9. The input shaft 12 is rotatably installed with the end cover 11, and can be rotatably installed with a bearing. The top end of the input shaft 12 is a male head to facilitate connection with the drill rod. The bottom end of the input shaft 12 is located inside the cylindrical housing 9, and a first bevel gear 13 is fixedly installed. The telescopic hob structure includes an annular frame 14 and three groups of chip rollers 18 installed on the annular frame 14. The three groups of chip rollers 18 are evenly distributed on the cylindrical housing 9 in an annular shape. The cylindrical housing 9 is provided with a through hole corresponding to each group of chip rollers 18. The annular frame 14 is fixedly mounted on the inner wall of the cylindrical shell 9, and each group of chip rollers 18 is mounted on the bottom of the annular frame 14 through a mounting seat 15. A threaded seat 16 is rotatably mounted on the inner side of the mounting seat 15, and a ratchet structure 17 is arranged between the threaded seat 16 and the mounting seat 15. A threaded shaft 19 is fixedly connected to one end of the chip roller 18, and the threaded seat 16 is threadedly sleeved on the threaded shaft 19. A transmission shaft 20 is slidably connected to the end of the threaded shaft 19. The transmission shaft 20 is a flower shaft, and a second bevel gear 21 is fixedly mounted on the transmission shaft 20, and the second bevel gear 21 is meshed with the first bevel gear 13. The threaded shaft 19 on each group of chip rollers 18 is driven to rotate by rotating the input shaft 12, thereby controlling at least two groups of chip rollers 18 to extend out of the cylindrical shell 9 along the corresponding through holes at the same time.

[0051] The ratchet structure 17 of the differential drill bit in the embodiment enables the threaded seat 16 to rotate unidirectionally relative to the mounting seat 15. The ratchet structure 17 is specifically as follows: a ratchet structure is designed on the outer side of the threaded seat 16, and a pawl is rotatably installed on the mounting seat 15. One side of the pawl is a fixed limiting block and the other side is an elastic limiting block, so that the pawl can be rotated to one side under force, allowing the ratchet to rotate unidirectionally; one end of the chip drum 18 is fixedly connected to a threaded shaft 19, and the threaded shaft 19 is threadedly connected to the threaded seat 16. A through hole corresponding to the chip drum 18 is opened on the side of the cylindrical shell 9, and the transmission shaft 20 is a flower shaft, and one end of the transmission shaft 20 is slidably connected to the threaded shaft 19. A second bevel gear 21 is fixedly installed on the transmission shaft 20, and the second bevel gear 21 is meshed with the first bevel gear 13. Assuming that the cylindrical shell 9 does not rotate, it can be analyzed that: the input shaft 12 drives the first bevel gear 13 to rotate, and then drives the second bevel gear 21 to rotate, so that the transmission shaft 20, the threaded shaft 19, and the chip drum 18 rotate. At this time, the threaded shaft 19 and the threaded seat 16 are threadedly matched, so that the threaded shaft 19 and the chip drum 18 move laterally, so that the chip drum 18 extends out of the cylindrical shell 9 from the through hole. The end of the threaded shaft 19 has no threads. At this time, the threaded shaft 19 no longer moves laterally, and the high-speed rotating chip drum 18 can perform hole expansion operations from the bottom.

[0052] The differential drill bit in the embodiment is as follows Fig.10 and Fig.12 As shown, an extension shaft 22 is provided at the bottom of the input shaft 12, and the top of the extension shaft 22 is fixedly connected to the bottom end of the input shaft 12. A circular groove 26 is provided at the inner bottom of the cylindrical shell 9, and a wear-resistant disk 25 is provided inside the circular groove 26. The bottom end of the wear-resistant disk 25 and the inner bottom of the circular groove 26 form a friction surface, that is, the wear-resistant disk 25 can rotate relative to the circular groove 26, but during the rotation process, the wear-resistant disk 25 and the circular groove 26 generate a large friction force. An eccentric gear ring 24 is rotatably installed at the top of the wear-resistant disk 25, and a first gear 23 is fixedly installed at the bottom end of the extension shaft 22. The inner and outer sides of the eccentric gear ring 24 are provided with gear ring parts, and the inner side of the circular groove 26 is provided with a gear ring part. The first gear 23 is meshed with the eccentric gear ring 24, and the eccentric gear ring 24 is meshed with the circular groove 26. The extended shaft 22 rotates with the input shaft 12, and the extended shaft 22 drives the first gear 23 to rotate. The first gear 23 meshes with the eccentric ring gear 24, and the eccentric ring gear 24 rotates around its own center of circle. At the same time, the eccentric ring gear 24 meshes with the circular groove 26 to drive the circular groove 26 to rotate, that is, the cylindrical shell 9 rotates. In this process, the rotation of the extended shaft 22 transmitted to the cylindrical shell 9 is a decelerated rotation, that is, the rotation speed of the extended shaft 22 is greater than the rotation speed of the cylindrical shell 9.

[0053] The transmission method from the above-mentioned extended shaft 22 to the cylindrical shell 9 can be understood as follows: the first gear 23 drives the eccentric gear ring 24 to revolve, causing the wear-resistant disk 25 to rotate, and relying on the friction between the wear-resistant disk 25 and the cylindrical shell 9 to drive the cylindrical shell 9 to rotate. When the cylindrical shell 9 encounters a large resistance, the cylindrical shell 9 can stop rotating and the internal gear structures will not be damaged.

[0054] Example 2 is mainly aimed at the 4# clinker warehouse of the 4500 tons / day cement clinker production line of a cement plant in Tang County. The bored pile construction has been completed. The foundation is designed as a circular whole plate foundation with a diameter of 24m. The characteristic value of the single pile bearing capacity is 620 tons. The whole plate foundation has been completed. Before the subsequent construction, it was found that caves were developed in the limestone of the clinker warehouse foundation bearing layer.

[0055] Site geological conditions: According to the exploration, the main strata distributed within the exploration depth range of the site are described from top to bottom as follows:

[0056] ⑴Artificial fill layer

[0057] Miscellaneous fill (stratum code ①): yellowish brown, yellow, etc., loose to slightly dense.

[0058] ⑵ Quaternary Holocene slope accumulation + diluvial layer

[0059] Silty clay (stratum code ②1);

[0060] Yellowish brown, containing a small amount of angular gravel in some parts, in a slightly wet and plastic state.

[0061] Gravel contains silty clay (stratum code ②2);

[0062] Yellowish brown, with a gravel content of 50% to 70%, and is slightly wet and medium-dense.

[0063] ⑶ Archean rock strata

[0064] Quartz-bearing hornblende monzonite (stratigraphic code ③1);

[0065] Brownish yellow to gray-green, light gray, gray and gray-green.

[0066] The rock mass has a loose structure, is easily broken when struck, and produces a hoarse sound;

[0067] Joints and fissures are well developed in the rock mass, and the cut surface is stained with iron oxide, indicating a strong weathering state.

[0068] Quartz hornblende monzonite (stratigraphic code ③2);

[0069] Brownish gray to grayish white, equigranular, massive structure, and moderately weathered.

[0070] (4) The third member of the Liangjiashan Formation of the Ordovician System

[0071] Limestone (stratum code ④):

[0072] Yellowish brown, fine-grained, blocky texture.

[0073] The main forms of karst development are caves, pores and dissolution fissures, which are in a moderately weathered state.

[0074] Cave soil (stratum code ⑤)

[0075] This layer is the cave filling, mostly brown-yellow clay, containing a small amount of limestone debris, in a wet and plastic state.

[0076] This layer is distributed in the limestone (stratigraphic code ④) layer.

[0077] Monitoring of the above embodiment found that the diameter of the bored piles in the site was 2.5m to 4.9m, and there were 5 more developed karst caves at the bottom of the piles. The filling of the karst caves was soft plastic-plastic clay. Combined with the experience of foundation reinforcement treatment of similar projects, in line with the principles of cost saving and safety and reliability, the reinforcement treatment method of the present invention was adopted for this project, specifically, a coring drill bit with a diameter of 130mm was used to cooperate with a drilling rig to open a central fine hole on the bored pile. When the central fine hole reached the bottom of the bored pile, it continued to go down 6m, and then a bottom hole with a diameter of 400mm was opened using a reaming drill rod. Finally, a high-pressure rotary spraying was used for grouting treatment from bottom to top. 28 days after the treatment, such piles were selected for static load test to determine whether they met the design requirements. The next step was carried out after passing the test. After treatment, the bearing layer at the bottom of the bored pile met the bearing capacity requirements.

[0078] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for reinforcing a karst cave formed at the bottom of a cast-in-place pile, characterized in that: The reinforcement treatment method is aimed at the situation that the newly developed karst cave at the bottom of the bored pile affects the bearing capacity of the bored pile after the construction is completed, and specifically comprises the following steps: S1. Conduct geological survey on the cast-in-place piles and their surroundings to obtain the size, shape and location of the cave; S2, using a coring drill to drill a hole at the center of the top of the cast-in-place pile, the hole extends to at least 6m below the bottom of the cast-in-place pile and is connected to the karst cave below the bottom of the cast-in-place pile; S3, use the reaming drill bit to descend to the bottom of the cast-in-place pile along the borehole in step S2, and expand the hole from the bottom of the cast-in-place pile, the concrete slag produced by the expansion is used as the first filling material of the karst cave, the height a of the expansion is 1 / 3-1 / 2 of the overall length of the cast-in-place pile, and the expansion area is connected to the karst cave below the cast-in-place pile bottom; The drill bit used for expanding the hole in step S3 is a differential drill bit, the differential drill bit comprising a cylindrical housing (9) and a telescopic hob structure arranged in the cylindrical housing (9), the diameter of the cylindrical housing (9) matching the hole drilled in step S2, the bottom end of the cylindrical housing (9) is fixedly connected to a bottom end cutting portion (10), the top end of the cylindrical housing (9) is provided with an input shaft (12) connected to a drill rod, the bottom end of the input shaft (12) extends into the interior of the cylindrical housing (9), and a first bevel gear (13) is fixedly installed at the bottom, the bottom of the input shaft (12) is provided with an extension shaft (22), the bottom of the extension shaft (22) is rotatably connected to the bottom of the cylindrical housing (9) through a reduction mechanism, and under the action of the reduction mechanism, the rotation speed of the cylindrical housing (9) is less than the rotation speed of the input shaft (12); the telescopic hob structure comprises an annular frame (14) and at least two groups of chip rollers (18) mounted on the annular frame (14), the cylindrical housing (9) is provided with a plurality of chip rollers connected to each group of chip rollers. (18) corresponding through holes; the annular frame (14) is fixedly mounted on the inner side wall of the cylindrical housing (9); each group of chip rollers (18) is mounted on the bottom of the annular frame (14) through a mounting seat (15); a threaded seat (16) is rotatably mounted on the inner side of the mounting seat (15); a ratchet structure (17) is provided between the threaded seat (16) and the mounting seat (15); one end of the chip roller (18) is fixedly connected to a threaded shaft (19); the threaded seat (16) is threadedly sleeved on the threaded shaft (19); a transmission shaft (20) is slidably connected to the end of the threaded shaft (19); a second bevel gear (21) is fixedly mounted on the transmission shaft (20); the second bevel gear (21) and the first bevel gear (13) are meshed with each other; the threaded shaft (19) on each group of chip rollers (18) is driven to rotate by the rotation of the input shaft (12) at the same time, thereby controlling at least two groups of chip rollers (18) to extend out of the cylindrical housing (9) along the corresponding through holes at the same time; S4. Use high-pressure rotary grouting to grout the cave below the bottom of the bored pile, the expanded hole area at the bottom of the bored pile, and the central borehole of the bored pile from bottom to top; during the high-pressure rotary grouting process, the grouting pressure is greater than 20MPa, the grouting flow rate is 100-150L / min, the air pressure is 0.3-0.7MPa, and the lifting speed of the rotary grouting reinforcement section is 10-15cm / min; S5. 28 days after the grouting is completed, the pile static load test is used to test the pile bearing capacity. After passing the test, the reinforcement process is completed.

2. The method for reinforcing a karst cave formed at the bottom of a cast-in-place pile according to claim 1, characterized in that: When a cave with a diameter greater than 1.5 m is detected in step S1, three auxiliary boreholes of 1.0 m are drilled around the bored piles. The three auxiliary boreholes of 1.0 m are distributed in a triangle with the bored piles as the center, and the bottoms of the auxiliary boreholes extend to the caves. The three auxiliary boreholes of 1.0 m are all grouted from bottom to top using high-pressure rotary jet grouting, and the formed auxiliary foundation piles at least reach the height of the top of the bored piles.

3. The method for reinforcing a karst cave formed at the bottom of a cast-in-place pile according to claim 1, characterized in that: When a fault occurs, stop high-pressure rotary spraying immediately; resume spraying after the fault is eliminated, and the height of the re-spraying should not be less than 50cm.

4. The method for reinforcing a karst cave formed at the bottom of a cast-in-place pile according to claim 1, characterized in that: The cement used in the high-pressure rotary jet grouting liquid is PO 42.5 cement with a water-cement ratio of 1:

1.

5. The method for reinforcing a karst cave formed at the bottom of a cast-in-place pile according to claim 1, characterized in that: The top end of the cylindrical housing (9) is open, and an end cover (11) is fixedly mounted on the open top end of the cylindrical housing (9); the input shaft (12) is rotatably mounted on the end cover (11), and the top end of the input shaft (12) is a male head connected to a drill rod; the chip rollers (18) are provided in three groups, which are evenly distributed in a ring shape on the cylindrical housing (9); and the transmission shaft (20) is a flower shaft.

6. The method for reinforcing a karst cave formed at the bottom of a cast-in-place pile according to claim 1, characterized in that: The top end of the extended shaft (22) is fixedly connected to the bottom end of the input shaft (12); the reduction mechanism comprises a circular groove (26) provided at the inner bottom of the cylindrical housing (9) and a wear-resistant disc (25) arranged inside the circular groove (26); the bottom end of the wear-resistant disc (25) and the inner bottom of the circular groove (26) form a friction surface; an eccentric gear ring (24) is rotatably mounted on the top end of the wear-resistant disc (25); a first gear (23) is fixedly mounted on the bottom end of the extended shaft (22); both the inner ring and the outer ring of the eccentric gear ring (24) are provided with gear ring parts; the inner ring of the circular groove (26) is provided with a gear ring part matching the outer ring gear of the eccentric gear ring (24); the first gear (23) meshes with the eccentric gear ring (24); and the eccentric gear ring (24) meshes with the circular groove (26).

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