Construction method of pile foundation penetrating through underwater concealed hole

Abstract

The invention relates to the technical field of pile foundation construction, and particularly discloses a construction method of a pile foundation penetrating through an underwater concealed hole, which comprises the following steps: forming holes by stages through a punching pile driver, welding section by section, lowering a steel casing, puncturing a karst cave top plate, and pouring underwater concrete. The design of the steel casing comprises a reinforcing hoop and a hanging support accessory. The pile casing is connected through double-groove welding and a connecting assembly. A ball pulling method is adopted for concrete pouring, the first batch of concrete amount is calculated and determined through a formula, and the pouring height is monitored in real time. And after final setting, continuously forming the hole to the designed height. The invention aims to solve the problem of stability in the environment that the steel casing passes through the flowing water blind hole.

Description

Technical Field

[0001] The present invention relates to the technical field of pile foundation construction, and particularly relates to a construction method for a pile foundation passing through an underwater blind hole. Background Art

[0002] During the construction of cast-in-place piles in karst areas, geological problems such as karst caves and underground rivers are easily encountered, resulting in the connection between the drilled hole and the underground cavity, causing excessive loss of concrete and difficulty in forming the pile body. Traditional methods use yellow mud and broken stones for plugging or low-strength concrete backfilling, but there are problems such as incomplete filling of large-volume cavities, low efficiency of repeated plugging, and poor sealing, resulting in material waste, increased costs, and unstable pile foundation quality.

[0003] The utility model patent authorization number CN214530672U discloses a construction structure for a karst cave pile foundation, including a formation, in which there is a karst cave, and further including: a pile hole connecting the surface of the formation and the karst cave; a casing disposed at the upper orifice of the pile hole along the axial direction of the pile hole; a retaining wall disposed in the karst cave, and the retaining wall is filled and disposed on the periphery of the pile hole. The bottom of the casing of the present utility model is provided with cutting teeth, which can be used to penetrate hard formations, concrete, and other obstacles. By arranging the casing and the retaining wall on the periphery of the pile hole, the present utility model can protect the mud and underwater concrete in the pile hole from leaking, ensure the quality of hole formation and pile formation, prevent slurry leakage during the process of hole formation and underwater concrete pouring, is suitable for various drilling technologies of drills in karst cave areas, and has the advantages of improving the construction efficiency of pile foundations and saving raw materials.

[0004] The invention patent publication number CN118441671A discloses a construction method for a rotary drilled pile passing through an underground karst cave or an underground river. A construction method for a rotary drilled pile passing through an underground karst cave or an underground river includes the following steps: performing a drilling operation at a preset position until the first preset height position at the top of the karst cave or underground river space is reached to form a preliminary hole; placing a casing in the preliminary hole as a retaining wall; continuing the drilling operation at the preset position through the casing until the second preset height position at the bottom of the karst cave or underground river space is reached; continuing the drilling operation until the third preset height position at the bottom of the karst cave or underground river space is reached; hoisting a steel reinforcement cage into the casing and pouring concrete into the steel reinforcement cage to form a rotary drilled pile. The present invention sets a clamping hoop at the ground position, clamps the position of the casing on the ground through the clamping hoop, and then the clamping hoop abuts against the ground, thereby realizing the fixation of the casing. This construction method for a rotary drilled pile passing through an underground karst cave or an underground river overcomes the problem that the traditional scheme cannot fill the large-volume karst cave or underground river to form a complete hole, has good engineering economy during the implementation process, low construction difficulty, is stable and effective in dealing with hole formation under the geological conditions of karst caves or underground rivers, can form a hole quickly, and can well meet the design strength of pile foundations under poor geological conditions.

[0005] The invention patent publication number CN113006117A discloses a pile foundation structure and pile forming process for karst strata, belonging to the technical field of pile foundation construction. It includes a drill hole opened in the karst strata and a casing placed in the drill hole. The drill hole vertically penetrates through the roof and wall of the karst cave and extends into the bottom rock mass of the karst cave. The length of the casing is greater than the height of the karst cave cavity. The top end of the casing is placed in the drill hole of the karst cave roof, and the bottom end of the casing is placed in the drill hole of the bottom rock mass of the karst cave, and concrete is poured into the steel casing. In the present invention, the casing is tied with wire to make the casing shrink to a state where it is close to the reinforcement cage, and then a support ring is welded on the reinforcement cage to make the casing abut against the support ring. By arranging a casing in the cavity of the karst cave, a retaining wall is formed at the position of the karst cave cavity by the casing. When pouring concrete, the concrete is blocked by the casing and is not easy to flow into the karst cave cavity, so as to ensure that the pouring volume of the concrete is consistent with the designed volume, and a large amount of concrete waste will not be caused due to the existence of the karst cave, and the quality of the pile foundation after forming is correspondingly improved.

[0006] The above-mentioned prior art uses a casing or a casing to penetrate through the karst cave area, optimizes the traditional construction method of filling karst caves, and uses the casing or the casing as a concrete pouring formwork, solving the problem of unstable quality of pile foundations passing through the karst cave area.

[0007] However, the casings or casings of the prior art are mainly designed for static underwater environments and do not consider the stability problems brought by continuous scouring of flowing water. The water flow may cause the casing to shift or the seal to fail, thereby causing concrete loss or mud leakage. Summary of the Invention

[0008] Aiming at the deficiencies of the prior art, the technical problem solved by the present invention is to provide a construction method for pile foundations passing through underwater dark caves, and solve the stability problem of steel casings passing through the environment of flowing water dark caves.

[0009] To solve the above problems, the technical solution adopted by the present invention is: a construction method for pile foundations passing through underwater dark caves, including the following steps:

[0010] Step 1, forming a hole with a punching pile driver;

[0011] Step 2, lowering the first section of the steel casing;

[0012] Step 3, the punching pile driver continues to form a hole;

[0013] Step 4, welding and lengthening the middle section of the steel casing and lowering the steel casing;

[0014] Step 5, the punching pile driver forms a hole to penetrate the roof of the dark cave;

[0015] Step 6, welding and lengthening the last section of the steel casing and lowering the steel casing to the first preset height;

[0016] Step 7: Pour underwater concrete. When the height of the concrete reaches the second preset height, lift the steel casing to the third preset height and continue pouring the concrete until the bottom end of the steel casing.

[0017] Step 8: Lower the steel casing to the second preset height before the concrete begins to set.

[0018] Step 9: After the concrete has finally set, continue to drill the hole into the bearing stratum with the punching rig.

[0019] Step 10: First hole cleaning.

[0020] Step 11: Fabricate the steel reinforcement cage.

[0021] Step 12: Second hole cleaning.

[0022] Step 13: Pour the underwater concrete pile foundation.

[0023] The first preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the blind tunnel, and the specific value is 0 m.

[0024] The second preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the blind tunnel, and the specific value is 1.0 m.

[0025] The third preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the blind tunnel, and the specific value is 2.0 m.

[0026] Compared with the prior art, the beneficial effects of this solution are as follows: 1. Lower the steel casing for the second time before the concrete begins to set, and utilize the plastic state of the concrete to combine with the steel casing to form an overall anchoring effect to resist the lateral thrust of the water flow on the steel casing; 2. By welding and lengthening the steel casing in sections and gradually lowering it, the construction risk of a single lowering is reduced, and the structure is strengthened in sections, which is suitable for the complex geological conditions of the blind tunnel.

[0027] Furthermore, the first section and the intermediate sections of the steel casing include a reinforcing hoop fixed in the middle of the steel casing by welding and a suspension support fitting fixed by welding 500 mm from the upper end of the steel casing. A round hole is opened in the middle of the suspension support fitting, and its shape is a right trapezoid, and the "waist" with a right angle is welded and fixed to the steel casing; the suspension support fittings are symmetrically welded and fixed in the same radial direction of the steel casing; for the last section of the steel casing, another set of suspension support fittings is welded and fixed 1 m directly below the existing suspension support fittings of the first section and the intermediate sections of the steel casing.

[0028] Furthermore, the reinforcing hoop is made of a steel plate with a thickness of 10 mm and a width of 300 mm, and is fixedly connected to the steel casing by fillet welding. The reinforcing hoop is welded in the middle of the steel casing to enhance the overall bending stiffness of the steel casing through circumferential reinforcement, and the reinforcing hoop can effectively disperse the lateral impact load of the flowing water on the steel casing.

[0029] Furthermore, the hanging support fitting is made of a 20-mm-thick steel plate, and the edge of the hole flap is not less than twice the diameter of the round hole. The hanging support fitting combines the functions of a lifting lug and a bearing support. When welding and extending the middle or end section of the steel casing, the symmetrical positions of the hanging support fittings can be used as the reference points for aligning the upper and lower sections of the casing, ensuring that the axes of each section of the steel casing are consistent and reducing the risk of misalignment.

[0030] Furthermore, after the preliminary fixed connection between the steel casings is carried out by double-sided groove welding, the connection is further strengthened by a connection assembly; the connection assembly includes longitudinal stiffeners and stiffening steel plates. Twelve longitudinal stiffeners are evenly welded and fixed along the outer periphery of the steel casing, and the stiffening steel plates are welded and fixed between the longitudinal stiffeners. The longitudinal stiffeners extend along the axis direction of the steel casing to form a circumferential reinforcement framework, enhancing the overall bending resistance of the steel casing; the stiffening steel plates welded between the longitudinal stiffeners form a grid-like support structure, filling the weak areas between the longitudinal stiffeners and enhancing the bending resistance of the side wall of the steel casing; in a flowing water environment, the grid-like reinforcement design of the connection assembly can reduce the impact of water flow on the connection part.

[0031] Furthermore, the underwater concrete pouring in step 7 is carried out by the ball-pulling method, and the diameter D of the selected conduit is determined by the following energy conservation formula:

[0032]

[0033] Parameter meaning and unit description:

[0034] Initial kinetic energy term: where ρ c is the density of concrete, unit kg / m 3 ; is the initial flow velocity of the concrete when it enters the conduit, unit m / s;

[0035] Gravitational potential energy term: ρ c gh0, where g is the acceleration due to gravity, ≈9.81 m / s 2 ; h0 is the vertical height difference of the concrete pouring, that is, the vertical distance from the conduit inlet to the outlet, unit m;

[0036] Friction loss term: where f is the friction coefficient, dimensionless, related to the inner wall roughness of the conduit and the flow state; L is the length of the conduit, unit m; D is the inner diameter of the conduit, unit m; v is the average flow velocity of the concrete in the conduit, unit m / s;

[0037] Flow water resistance: where C d is the resistance coefficient of water to the flow of concrete, dimensionless, related to the shape and surface roughness of the concrete flow; ρ w is the density of water, approximately equal to 1000 kg / m3 ;

[0038] The buoyancy loss term ρ w gh1: where h1 is the preset height of the concrete to be poured underwater, in meters. Select an ideal conduit diameter through the energy conservation formula, optimize the energy conversion and loss during the concrete flow process, and balance kinetic energy and resistance to maximize the conversion of potential energy into effective kinetic energy; ensure that the kinetic energy of the concrete per unit time is greater than the work required to overcome the water pressure, so that the concrete can be smoothly poured underwater.

[0039] Furthermore, during the process of pouring underwater concrete described in Step 7 and Step 13, the pouring height of the concrete is measured in real time by the plumb bob method and / or the steel pipe sampling box method.

[0040] Furthermore, the diameter of the further drilled hole in Step 9 is smaller than the inner diameter of the steel casing, and the center of the further drilled hole is aligned with the center of the steel casing. To ensure that there is a support platform at the bottom of the steel casing. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a sectional view of the pile foundation hole forming of the present invention.

[0042] Figure 2 It is a perspective view of the steel casing of the present invention.

[0043] Figure 3 It is a front view of the steel casing of the present invention.

[0044] Figure 4 It is a perspective view of the connecting assembly of the present invention.

[0045] Figure 5 It is the present invention in Figure 3 Sectional view 1-1.

[0046] Figure 6 It is the present invention in Figure 3 Sectional view 2-2.

[0047] Figure 7 It is the pre-unfolding structure diagram of the waterproof cloth cylinder of the present invention.

[0048] Figure 8 It is the unfolded diagram of the waterproof cloth cylinder after the connection line is broken.

[0049] Figure 9 It is the unfolded diagram of the waterproof cloth cylinder after the sewing thread is broken.

[0050] The reference numerals in the accompanying drawings of the specification include: 1. Reinforcing hoop; 2. Suspension brace fitting; 3. Connecting assembly; 31. Longitudinal stiffening rib; 32. Stiffening steel plate; 4. Support member; 8. Steel casing; 9. Concrete; 10. Underwater cavity; 11. Bearing stratum; 12. Sewing thread; 13. Annular flange; 14. Connection line. Detailed implementation manners

[0051] The following is a further detailed description through specific implementation manners:

[0052] Example 1

[0053] As shown in the Figures 1-6 accompanying drawings, a construction method for a pile foundation passing through an underwater dark hole includes the following steps:

[0054] Step 1, forming a hole with a punching pile driver;

[0055] Step 2, lowering the first section of the steel casing 8;

[0056] Step 3, the punching pile driver continues to form a hole;

[0057] Step 4, welding and lengthening the middle section of the steel casing 8 and lowering the steel casing 8;

[0058] Step 5, the punching pile driver forms a hole to penetrate the top plate of the dark hole;

[0059] Step 6, welding and lengthening the last section of the steel casing 8 and lowering the steel casing 8 to a first preset height;

[0060] Step 7, pouring underwater concrete. When the height of the concrete reaches a second preset height, the steel casing is lifted to a third preset height, and the concrete is continuously poured to the bottom end of the steel casing;

[0061] Step 8, lowering the steel casing 8 to the second preset height before the concrete 9 starts to set;

[0062] Step 9, after the concrete 9 has finally set, the punching pile driver continues to form a hole into the bearing stratum 11;

[0063] Step 10, the first hole cleaning;

[0064] Step 11, fabricating the steel reinforcement cage;

[0065] Step 12, the second hole cleaning;

[0066] Step 13, pouring the underwater concrete 9 pile foundation;

[0067] The first preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the dark hole, and the specific value is 0 meters;

[0068] The second preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the dark hole, and the specific value is 1.0 meter;

[0069] The third preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the dark hole, and the specific value is 2.0 meters.

[0070] The first and middle steel casing sections 8 include a reinforcing hoop 1 fixedly welded in the middle of the steel casing 8 and a suspension support fitting 2 fixedly welded 500 mm from the upper end of the steel casing 8. A round hole is provided in the middle of the suspension support fitting 2, and its shape is a right trapezoid with the "waist" having a right angle welded and fixed to the steel casing 8; the suspension support fittings 2 are symmetrically welded and fixed in the same radial direction of the steel casing 8;

[0071] For the last steel casing section 8, another set of suspension support fittings 2 is welded and fixed 1 m directly below the existing suspension support fittings 2 of the first and middle steel casing sections 8.

[0072] Furthermore, the reinforcing hoop 1 is made of a steel plate with a thickness of 10 mm and a width of 300 mm, and is fixedly connected to the steel casing 8 by fillet welding.

[0073] Furthermore, the suspension support fitting 2 is made of a 20-mm-thick steel plate, and the hole rib margin is not less than 2 times the diameter of the round hole.

[0074] Furthermore, after the steel casings 8 are preliminarily fixedly connected by double-sided groove welding, they are further strengthened and connected by a connection assembly 3; the connection assembly 3 includes longitudinal stiffeners 31 and stiffening steel plates 32. Twelve longitudinal stiffeners 31 are evenly welded and fixed along the outer periphery of the steel casing 8, and the stiffening steel plates 32 are welded and fixed between the longitudinal stiffeners 31.

[0075] Furthermore, the underwater concrete 9 in step 7 is poured by the "ball-pulling method", and the diameter D of the selected conduit is determined by the following energy conservation formula:

[0076]

[0077] Parameter meaning and unit description:

[0078] Initial kinetic energy term: where ρ c is the density of the concrete 9, with the unit kg / m 3 ; is the initial flow velocity of the concrete 9 when it enters the conduit, with the unit m / s;

[0079] Gravitational potential energy term: ρ c gh0, where g is the acceleration due to gravity, ≈9.81 m / s 2 ; h0 is the vertical height difference of the concrete 9 pouring, i.e., the vertical distance from the conduit inlet to the outlet, with the unit m;

[0080] Friction loss term: where L is the friction coefficient, dimensionless, related to the inner wall roughness and flow state of the conduit; L is the length of the conduit, with the unit m; D is the inner diameter of the conduit, with the unit m; v is the average flow velocity of the concrete 9 in the conduit, with the unit m / s;

[0081] Flow water resistance: Among them, C d is the resistance coefficient of water to the flow of concrete, dimensionless, related to the shape and surface roughness of the flow of concrete; ρ w is the density of water, approximately equal to 1000 kg / m 3 ;

[0082] Buoyancy loss term ρ w gh1: where h1 is the preset height of the concrete to be poured underwater, in meters.

[0083] Furthermore, during the process of pouring underwater concrete described in Step 7 and Step 13, the pouring height of the concrete is measured in real time by the plumb bob method and / or the steel pipe sampling box method.

[0084] Furthermore, the diameter of the continued hole forming in Step 9 is smaller than the inner diameter of the steel casing 8, and the center of the continued hole forming is aligned with the center of the steel casing 8.

[0085] The impact pile driver described in Step 1 uses a 9.5T impact hammer. While the drill is driving the hammer to impact, a mud pump is used to transport mud into the hole. The flushing fluid that flushes the bottom of the hole and carries the drill cuttings rises along the outer ring space between the wire rope and the hole wall, and flows back from the hole mouth to the mud pit to form a slag discharge system. At the same time, the pressure of the mud in the hole is used to balance the hole wall pressure and the water pressure, and the mud plays a role in protecting the hole wall.

[0086] The steel casing 8 described in Step 2 includes a reinforcing hoop 1 fixed in the middle of the steel casing 8 by welding and a suspension support fitting 2 fixed by welding 0.5 m from the upper end of the steel casing 8. A round hole is opened in the middle of the suspension support fitting 2, and its shape is a right trapezoid, and the "waist" with a right angle is welded and fixed to the steel casing 8; the suspension support fittings 2 are symmetrically welded and fixed on both sides of the steel casing 8.

[0087] The steel casing 8 is made of a 10-mm-thick steel plate rolled and welded. The casing is lifted by a 25t crane. The crane wire rope passes through the round hole of the suspension support fitting 2 to lift the steel casing 8, and the steel casing 8 is lowered while being aligned with the center of the pile hole.

[0088] The reinforcing hoop 1 is made of a 10-mm-thick and 300-mm-wide steel plate and is fixedly connected to the steel casing 8 by fillet welding.

[0089] The suspension support fitting 2 is made of a 20-mm-thick steel plate, and the hole collar edge is not less than twice the hole diameter. The suspension support fitting 2 has both the functions of a lifting lug and bearing support.

[0090] After the steel casing 8 is lowered, the suspension support fitting 2 is placed on two support members 4 composed of channel steels with their openings facing each other.

[0091] After the middle steel casing 8 in Step 4 is aligned with the first steel casing 8, it is preliminarily fixedly connected by double-sided groove welding, and then reinforced and connected by the connecting component 3. The connecting component 3 includes longitudinal stiffeners 31 made of channel steel 8A and stiffening plates 32 made of 10-mm-thick steel plates. Twelve longitudinal stiffeners 31 are uniformly welded and fixed along the outer circumference of the steel casing 8, and the stiffening plates 32 are welded and fixed between the longitudinal stiffeners 31.

[0092] Repeat Step 3 and Step 4 until reaching Step 5.

[0093] On the basis of the steel casing 8 in Step 2, another set of suspension support fittings 2 is welded and fixed at a distance of 1 m directly below the suspension support fittings 2 in Step 2 for the end steel casing 8 in Step 6. The suspension support fittings 2 below the end steel casing 8 are placed on the support member 4 by a crane, so that the lowering depth of the steel casing 8 reaches the first preset height.

[0094] The first preset height is the vertical distance from the lower end of the first steel casing 8 to the bottom surface of the underwater blind hole 10, and the specific value is 0 m.

[0095] For the underwater concrete 9 pouring in Step 7, the "conduit method" is adopted for pouring. The conduit method for pouring is a method of underwater concrete 9 pouring in which the concrete 9 mixture enters the bottom of the initially poured concrete 9 through the lower opening of the conduit, and the newly poured concrete 9 jacks up the initially poured concrete 9 and spreads it to the periphery.

[0096] The slump of the underwater poured concrete 9 is 200 mm;

[0097] For the initially poured concrete 9, the ball-pulling method is adopted for pouring. The core steps of the ball-pulling method are as follows: Place a separation ball at the bottom of the conduit. After fixing the conduit by hoisting, quickly pour a sufficient amount of concrete 9 into the conduit, and then remove the separation ball. At this time, the concrete 9 quickly rushes out of the conduit under the action of its own weight, forming a continuously falling concrete 9 flow. Using its impact force, the water in the steel casing 8 is displaced and the bottom of the conduit is sealed to prevent water from flowing back and mixing in, ensuring the compactness and integrity of the concrete 9 at the bottom of the pile foundation.

[0098] When pouring by the ball-pulling method, the filling quantity of the first batch of poured concrete 9 is determined by the following formula:

[0099]

[0100] The meanings of the letters in the formula are as follows:

[0101] V: The quantity of the first batch of concrete 9 required, unit m 3 ;

[0102] d: The inner diameter of the conduit, unit m;

[0103] h1: The height required for the concrete column in the conduit to balance the water or mud pressure outside the conduit, in m, i.e.,

[0104]

[0105] Where: H w : The depth of water or mud above the concrete surface, in m;

[0106] γ w : The unit weight of water or mud, in kN / m 3 ;

[0107] γ c : The unit weight of the concrete, in kN / m 3 ;

[0108] D: The diameter of the steel casing, in m;

[0109] H c : The height from the bottom of the steel casing to the bottom of the underwater cavity when pouring the first batch of concrete, in m, i.e.,

[0110] H c ≥h2 + h3

[0111] Where: h2: The initial embedment depth of the conduit (in m), not less than 1 m;

[0112] h3: The distance from the bottom end of the conduit to the bottom of the cavity, about 0.5 m;

[0113] After pouring the first batch of concrete, continuous pouring shall be maintained without interruption. When the concrete height reaches the second preset height, the steel casing is lifted to the third preset height, and concrete is continuously poured until the bottom of the steel casing and the already poured concrete are in contact and reach the third preset height, and then immediately enter step 8; during the entire pouring process, the embedment depth of the conduit in the concrete is not less than 1 m.

[0114] The second preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom of the underwater cavity, and the specific value is 1.0 m.

[0115] The third preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom of the underwater cavity, and the specific value is 2.0 m.

[0116] Step 8 is, after the concrete is poured to the third preset height, placing the suspension fitting 2 above the last section of the steel casing on the support member 4 by a crane, so that under the action of gravity, the steel casing is lowered to the second preset height, allowing the concrete to wrap the steel casing, thereby fixing the lower end of the steel casing.

[0117] Step 9: After the concrete 9 described in step 7 has finally set, a punching pile driver is used to continue drilling holes in the steel casing 8. To ensure that there is a supporting platform at the bottom of the steel casing 8, the diameter of the hole is 100 mm smaller than the inner diameter of the steel casing 8. The center of the hole is aligned with the center of the steel casing 8, and the hole is continued to be drilled into the bearing layer 11.

[0118] The first hole cleaning described in step 10 adopts the "slurry replacement method" to clean the hole. On the one hand, the mud pump of the drilling rig is used to pump slurry to discharge the mud and drill cuttings mixture at the bottom of the hole out of the hole, and on the other hand, the mud purified by the mud pool is added into the hole to clean the drill cuttings at the bottom of the hole.

[0119] The steel cage described in step 11 is made using the "long line method", in which each section is tied and connected to form a shape, and then separated from the joints, the reference steel bars are marked, and stored for later use.

[0120] The second hole cleaning described in step 12 adopts the "slurry replacement method" to clean the hole and replace the new slag produced at the bottom of the hole. After the thickness of the sediment at the bottom of the hole is re-measured and found to be within the design range, the hole cleaning is completed and underwater concrete 9 pile foundation pouring is immediately carried out.

[0121] The underwater concrete 9 pile foundation pouring described in step 13 adopts the "catheter method" to pour the underwater concrete 9.

[0122] During the pouring process of concrete 9, the pouring height of concrete 9 is measured in real time by using a hammer method and / or a steel pipe sampling box method.

[0123] Hammer method: A heavy hammer is hung into the steel casing 8 with a rope, so that it stays on the surface of the concrete 9. The depth of the hammer shown by the measuring rope is used to calculate the pouring depth of the concrete 9. The weight is conical, the weight of the hammer is not less than 4kg, and the measuring rope is light, strong in tension, does not shrink when exposed to water, and is marked with a scale.

[0124] Steel pipe sampling box method: Use multiple sections of 1m to 2m long steel pipes to tighten and connect them. An iron box is set at the bottom of the steel pipe, with a movable cover tied with a thin rope and led upward with the steel pipe. When the poured concrete 9 reaches a preset height, insert the steel pipe sampling box into the mixture, pull the thin rope to open the movable cover, the mixture enters the box, and then take out the steel pipe to identify whether the content in the box is concrete 9 or mud residue, thereby determining the exact position of the concrete 9 surface.

[0125] Example 2

[0126] As attached Figures 7-9 As shown, before pouring concrete in step 7, a waterproof cloth tube is placed at the bottom of the steel casing. The waterproof cloth tube is folded into a tube by the waterproof cloth and is shaped by the stitches 12; the stitches 12 have a lower tensile strength than the stitches 12 of the waterproof cloth. When the tension caused by the diffusion of concrete on the stitches 12 of the waterproof cloth tube exceeds the tensile strength of the stitches 12, the stitches 12 break, causing the waterproof cloth tube to unfold into a conical cylindrical structure.

[0127] The upper opening diameter of the conical structure matches the inner diameter of the steel casing. The lower diameter of the fully expanded conical structure is 4 - 5 times the upper opening diameter. The edge of the lower diameter folds inward to form a circular flange 13. The inner diameter of the circular flange 13 is smaller than the upper opening diameter. A number of connecting lines 14 are evenly arranged on the circular flange 13. The connecting lines 14 are distributed circumferentially along the bottom of the cone and connect the circular flange 13 into a whole. The connecting lines 14 are made of cotton threads with a tensile strength lower than that of the waterproof cloth, and their natural length is less than the bottom circumference of the cone after being fully expanded. When the waterproof cloth cylinder expands outward under internal pressure, the connecting lines 14 are stretched and broken due to insufficient length, causing the circular flange 13 to be released from restraint, and the lower opening to fully expand to fit the bottom surface of the blind hole.

[0128] The height of the waterproof cloth cylinder is greater than the third preset height.

[0129] After lowering the steel casing 8 to the first preset height in step 6, the waterproof cloth cylinder is lowered to the inner bottom of the steel casing 88. Enter step 7 to pour underwater concrete 9. When the height of the concrete 9 reaches the second preset height, the poured concrete 9 gives the waterproof cloth cylinder lateral pressure under gravity. However, since the outside of the waterproof cloth cylinder is restricted by the steel casing 8 at this time, the waterproof cloth cylinder will not expand. And because the inner diameter of the circular flange 13 is smaller than the upper opening diameter, the poured concrete 9 will press on the circular flange 13 to position the waterproof cloth cylinder. During the process of lifting the steel casing 8 to the third preset height, the lower part of the waterproof cloth cylinder loses the lateral pressure protection of the steel casing 8. The concrete 9 inside the waterproof cloth cylinder diffuses outward under gravity. At this time, the waterproof cloth cylinder expands outward under internal pressure, and the connecting lines 14 are stretched and broken due to insufficient length, causing the circular flange 13 on the side of the waterproof cloth cylinder to be released from restraint, and the lower end of the waterproof cloth cylinder begins to expand. Continue to pour concrete 9. The amount of concrete 9 inside the waterproof cloth cylinder increases, and the height of the concrete 9 extends upward. When the tension caused by the internal diffusion of the concrete 9 on the side stitches 12 of the waterproof cloth cylinder exceeds the tensile strength of the stitches 12, the stitches 12 break, causing the waterproof cloth cylinder to gradually expand from bottom to top into a conical structure.

[0130] Until the height of the poured concrete 9 reaches the third preset height, enter step 8.

[0131] During this process, the staged breaking of the low-strength stitches 12 and the connecting lines 14 ensures that the waterproof cloth cylinder unfolds as needed, while achieving rapid adaptive sealing and wrapping the diffused concrete 9 inside the waterproof cloth cylinder.

[0132] The conical structure and the flange design enhance the adaptability to the irregular bottom surface of the blind hole and improve the sealing effect of the concrete.

[0133] The above are only embodiments of the present invention, and common knowledge such as specific structures and characteristics known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope claimed in this application shall be subject to the content of its claims, and the specific implementation manners and the like described in the specification can be used to interpret the content of the claims.

Claims

1. A construction method for pile foundations passing through underwater hidden caves, characterized in that: It includes the following steps: Step 1, forming a hole with a punching pile driver; Step 2, lowering the first section of the steel casing; Step 3, the punching pile driver continues to form a hole; Step 4, welding and extending the middle section of the steel casing and lowering the steel casing; Step 5, the punching pile driver forms a hole to penetrate the top plate of the hidden hole; Step 6, welding and extending the last section of the steel casing and lowering the steel casing to the first preset height; Step 7, pouring underwater concrete. When the height of the concrete reaches the second preset height, the steel casing is lifted to the third preset height, and the concrete is continuously poured to the bottom end of the steel casing; Step 8, lowering the steel casing to the second preset height before the concrete initial sets; Step 9, after the concrete final sets, the punching pile driver continues to form a hole into the bearing stratum; Step 10, the first hole cleaning; Step 11, fabricating the steel reinforcement cage; Step 12, the second hole cleaning; Step 13, pouring the underwater concrete pile foundation; The first preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the hidden hole, and the specific value is 0 m; The second preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the hidden hole, and the specific value is 1.0 m; The third preset height is the vertical distance from the lower end of the first section of the steel casing to the bottom surface of the hidden hole, and the specific value is 2.0 m.

2. The construction method of a pile foundation for crossing an underwater dark hole according to claim 1, characterized in that: The first section and the middle section of the steel casing include a reinforcing hoop fixed in the middle of the steel casing by welding and a suspension support fitting fixed by welding 500 mm from the upper end of the steel casing. A round hole is opened in the middle of the suspension support fitting, and its shape is a right trapezoid with the "waist" with a right angle welded and fixed to the steel casing; the suspension support fittings are symmetrically welded and fixed on the same radial direction of the steel casing; for the last section of the steel casing, another set of suspension support fittings is welded and fixed 1 m directly below the existing suspension support fittings of the first section and the middle section of the steel casing.

3. The construction method of a pile foundation for crossing an underwater dark hole according to claim 2, wherein: The reinforcing hoop is made of a steel plate with a thickness of 10 mm and a width of 300 mm, and is fixedly connected to the steel casing by fillet welding.

4. The construction method of a pile foundation for crossing an underwater dark hole according to claim 2, characterized in that: The suspension support fitting is made of a steel plate with a thickness of 20 mm, and the hole edge is not less than 2 times the diameter of the round hole.

5. The construction method of a pile foundation for crossing an underwater hidden cave according to claim 1, characterized in that: After the preliminary fixed connection between the steel casings is made by double-sided groove welding, the connection is further strengthened by a connection component; the connection component includes longitudinal stiffeners and stiffening steel plates. 12 longitudinal stiffeners are evenly welded and fixed along the outer circumference of the steel casing, and the stiffening steel plates are welded and fixed between the longitudinal stiffeners.

6. The construction method of a pile foundation for crossing an underwater dark hole according to claim 1, characterized in that: In step 7, the pouring of the underwater concrete adopts the ball-pulling method, and the diameter D of the selected conduit is determined by the following energy conservation formula: Parameter meaning and unit description: Initial kinetic energy term: where ρ c is the density of concrete, in kg / m 3 ; is the initial flow velocity of concrete when it enters the conduit, in m / s; Gravitational potential energy term: ρ c gh0, where g is the acceleration due to gravity, ≈9.81 m / s 2 ; h0 is the vertical height difference of concrete pouring, that is, the vertical distance from the inlet to the outlet of the conduit, in m; Frictional loss term: where f is the friction coefficient, dimensionless, related to the inner wall roughness of the conduit and the flow state; L is the length of the conduit, in m; D is the inner diameter of the conduit, in m; v is the average flow velocity of the concrete in the conduit, in m / s; Flow water resistance: where C d is the resistance coefficient of water to the flow of concrete, dimensionless, related to the shape and surface roughness of the concrete flow; ρ w is the density of water, approximately equal to 1000 kg / m 3 ; Buoyancy loss term ρ w gh1, where h1 is the preset height of the concrete to be poured underwater, in m.

7. A construction method for a pile foundation passing through an underwater dark hole, according to claim 1, wherein: During the pouring of the underwater concrete in steps 7 and 13, the pouring height of the concrete is measured in real time by the sounding weight method and / or the steel pipe sampling box method.

8. A construction method for a pile foundation passing through an underwater dark hole, as described in claim 1, characterized in that: The diameter of the hole formed continuously in step 9 is smaller than the inner diameter of the steel casing, and the center of the continuously formed hole is aligned with the center of the steel casing.

9. The construction method of a pile foundation passing through an underwater dark hole according to claim 1, characterized in that: Before pouring the concrete in step 7, place a waterproof cloth tube at the bottom of the steel casing.

10. A construction method for a pile foundation passing through an underwater dark hole, as claimed in claim 9, wherein: The waterproof cloth tube is formed by folding the waterproof cloth into a tube shape and fixed by stitches; the stitches are made of threads with a tensile strength lower than that of the waterproof cloth. When the tension caused by the concrete diffusion on the waterproof cloth tube exceeds the tensile strength of the stitches, the stitches break, causing the waterproof cloth tube to unfold into a conical tube structure; the upper opening diameter of the conical tube structure matches the inner diameter of the steel casing, and the lower end diameter of the fully unfolded conical tube structure is 4-5 times the upper opening diameter; the edge of the lower opening is folded inward to form an annular flange, and the inner diameter of the annular flange is smaller than the upper opening diameter. A number of connecting threads are evenly arranged on the annular flange; the connecting threads are distributed circumferentially along the bottom of the conical tube, connecting the annular flange into a whole; the connecting threads are made of cotton threads with a tensile strength lower than that of the waterproof cloth, and their natural length is less than the bottom circumference of the fully unfolded conical tube; when the waterproof cloth tube expands outward due to internal pressure, the connecting threads are stretched and broken due to insufficient length, causing the annular flange to be released from the restraint, and the lower opening is fully unfolded to fit the bottom surface of the blind hole.

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