Deep water bare rock low pile cofferdam platform in karst development area and construction method thereof

Abstract

This invention discloses a low-pile cofferdam platform for deep-water exposed rock in karst development areas and its construction method. The cofferdam platform includes pile foundations, piers, a cofferdam, and multi-layer internal support components. The pile foundation includes piles, a reinforced concrete cushion layer, and a pile cap. The cofferdam is assembled from multiple interlocking steel pipe piles, with the lower end of each interlocking steel pipe pile extending into a pilot hole groove. The groove wall is sealed to the cofferdam through a sand layer. Each layer of internal support components includes multiple walers, multiple corbels, and multiple steel columns. Each waler is installed on the inner wall of the cofferdam via corbels, and each end of each steel column is fixedly installed on a waler. The reinforced concrete cushion layer includes a concrete structure and multiple reinforcing cages. The end of each reinforcing cage near the cofferdam is welded to the interlocking steel pipe piles of the cofferdam. The interlocking steel pipe piles of this invention can be installed quickly and accurately. The sand layer formed by chemical grouting into the sand grains enhances the overall sealing of the cofferdam, while the reinforced concrete cushion layer reduces the amount of exposed rock excavation.

Description

Technical Field

[0001] This invention belongs to the field of bridge engineering, and more specifically, relates to a low-pile cofferdam platform for deep-water bare rock in karst development areas and its construction method. Background Technology

[0002] In bridge construction, cofferdams, as temporary or permanent water-retaining structures, play an indispensable role in the construction of foundations such as pier caps in underwater environments. The main function of a cofferdam is to block water flow, providing a dry working environment for pier cap construction and ensuring the safety, stability, and efficiency of the construction process. Under different geological conditions and aquatic environments, the design and construction of cofferdams face diverse challenges and difficulties.

[0003] Karst development zones refer to areas where soluble rocks (such as carbonate rocks and gypsum) are distributed and have formed significant karst landforms due to long-term water erosion. Groundwater dissolves rocks over a long period, creating complex geological structures such as caves, fissures, and underground rivers. Underwater bare rock refers to rocks on the bottom of rivers, lakes, or oceans, typically composed of volcanic rocks, coral reefs, or continental extensions. These rocks are often uncovered by vegetation or clay and are commonly found in areas of frequent geological activity. In bridge construction, areas with a water depth exceeding 6 meters are generally considered deep water. This geological condition further increases the difficulty of cofferdam construction in deep-water environments and with low pile foundations (where the pile cap is relatively low). The higher water pressure in deep-water areas places higher demands on the strength, stability, and seepage prevention of the cofferdam structure.

[0004] In deep-water bare rock environments within karst development zones, traditional cofferdam construction methods typically require deep excavation of the bare rock within the cofferdam to ensure the stability and sealing of the constructed foundation, preventing karst water from entering the cofferdam through rock fissures or caves. However, this extensive excavation not only increases construction difficulty and cost but may also damage the geological structure of karst areas, triggering new geological problems.

[0005] Furthermore, the geological characteristics of karst development areas present numerous challenges to cofferdam construction: 1) The rock surface in karst areas is uneven. The bare rock surface has many uneven areas, increasing the difficulty of sealing between the cofferdam and the rock surface. Traditional cofferdam structures and construction techniques struggle to achieve a good seal, easily leading to water and sand leakage, thus reducing the cofferdam's water-blocking effect. 2) Karst water is highly mobile and its water level fluctuates greatly. The groundwater system in karst areas is complex and hydraulically interconnected. During cofferdam construction, karst water may connect with external water bodies through rock fissures or caves, making it difficult to effectively control the water level within the cofferdam, and even causing large-scale water inrush, affecting the dry construction environment of the foundation pit.

[0006] Furthermore, existing cofferdam construction techniques have the following shortcomings when dealing with deep-water bare rock in karst development areas: First, the installation accuracy and speed of the cofferdam are difficult to guarantee. On deep-water bare rock, the positioning and verticality control of steel pipe piles are challenging. Traditional construction methods lack effective guiding and correction measures, leading to the steel pipe piles easily tilting, affecting the integrity of the cofferdam and the construction progress. Second, when sealing the lower part of the cofferdam, concrete is generally used in the trench. To ensure the accurate assembly and verticality of the interlocking steel pipe piles, the trench is usually excavated to a considerable size, resulting in a large amount of concrete being used and significant material waste. Summary of the Invention

[0007] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a low-pile cofferdam platform for deep-water bare rock in karst development areas and its construction method. The interlocking steel pipe piles can be installed quickly and accurately, and the sand layer formed by chemical grouting into the sand grains can enhance the overall sealing of the cofferdam. At the same time, the reinforced concrete cushion layer can reduce the amount of bare rock excavation, making construction safer and faster.

[0008] To achieve the above objectives, according to one aspect of the present invention, a low-pile cofferdam platform for deep-water bare rock in karst development areas is provided, characterized in that it comprises pile foundations, piers, a cofferdam, and multi-layered internal support components arranged vertically, wherein: The pile foundation includes piles, a reinforced concrete cushion layer, and a pile cap. Multiple piles are installed in pile holes drilled from underwater bare rock. The reinforced concrete cushion layer is installed in the space chiseled out from the underwater bare rock. The reinforced concrete cushion layer is fixedly connected to the top of each pile. The pile cap is installed at the top of the reinforced concrete cushion layer, and the pier is installed at the top of the pile cap. The cofferdam surrounds the pile foundation. The cofferdam is assembled from multiple interlocking steel pipe piles. The lower end of each interlocking steel pipe pile extends into the pilot hole groove. The pilot hole groove consists of four channels excavated from the underwater bare rock and distributed on the four sides of a rectangle. The walls of the pilot hole groove are sealed to the cofferdam with a layer of sand. Each layer of the internal support assembly includes multiple walers, multiple corbels, and multiple steel columns. Each waler is installed on the inner wall of the cofferdam via corbels, and each end of each steel column is fixedly installed on a waler. The reinforced concrete cushion layer includes an integrally formed concrete structure and multiple reinforcing cages, with each reinforcing cage having its end near the cofferdam welded to the interlocking steel pipe piles of the cofferdam.

[0009] Preferably, the sand layer is formed by a mixture of medium and coarse sand, and the interior of each interlocking steel pipe pile is also filled with sand to improve the strength of the interlocking steel pipe pile.

[0010] Preferably, each of the locking steel pipe piles is connected to the waler through a force transmission plate. The surface of the force transmission plate that contacts the waler is flat to fit against the side of the waler. The surface of the force transmission plate that contacts the locking steel pipe pile is an arc-shaped surface that matches the outer diameter of the locking steel pipe pile.

[0011] Preferably, the seepage points on the cofferdam are sealed with waterproof filler, which includes cement, bentonite, sawdust, and water, and the weight ratios of cement, bentonite, sawdust, and water are as follows: Cement: Bentonite: Sawdust: Water = (0.8-1.2): (2.5-3.5): (0.5-1.5): (0.8-1.2).

[0012] According to another aspect of the present invention, a construction method for a low-pile cofferdam platform for deep-water bare rock in karst development areas is also provided, characterized by comprising the following steps: S1. Construct a trestle bridge and a temporary piling platform. Drill pile holes in the underwater bare rock using a drilling rig on the temporary piling platform. Then construct the pile columns in the pile holes. After the pile column construction is completed, dismantle the temporary piling platform. S2. Use a rotary drilling rig on the trestle to excavate a pilot hole trench on the underwater bare rock, and then fill the pilot hole trench with sand. S3. Multiple interlocking steel pipe piles are assembled in sequence and inserted into the sand grains. These interlocking steel pipe piles enclose and form a cofferdam. S4. Chemical grouting is performed on the sand particles in the pilot hole groove to achieve a seal between the cofferdam and the groove wall of the pilot hole. S5. Drain some of the water from the cofferdam so that the water level inside the cofferdam is below the inner support assembly to be installed. Weld multiple brackets onto the cofferdam and install multiple walers on these brackets. Then connect multiple steel columns to the walers. The brackets, walers, and steel columns together form an inner support assembly. S6. Check if there are any leaks on the cofferdam. If so, seal the leaks with waterproof filler. If not, proceed to step S7. S7. Repeat steps S5 and S6 until the installation of the bottommost inner support component is completed. S8. Drain the water in the cofferdam to form a foundation pit. Clean the foundation pit to expose the bare rock inside. Then check if there are any seepage points on the cofferdam. If there are, seal the seepage points with waterproof filler. If not, proceed to step S9. S9. Clean the foundation pit and use sonar to detect whether there are interconnected karst caves inside the bare rock below the foundation pit. If there are interconnected karst caves, grout them to seal them; otherwise, proceed to step S10. S10. On the bare rock in the foundation pit, the bare rock is blasted by pre-splitting blasting, and the rock blocks produced by the blasting are removed by excavator. In this way, a space for constructing a reinforced concrete cushion layer is formed on the bare rock, and the top of each pile is exposed in the space formed. S11. Place multiple steel cages in the space carved out on the bare rock, and weld the end of each steel cage near the cofferdam to the cofferdam. Then pour concrete on the steel cages. The concrete is fixedly connected to each of the piles. The steel cages and the concrete together form the reinforced concrete cushion layer of the pile foundation. S12. Construct the pile cap of the pile foundation on the reinforced concrete cushion, and then construct the pier column on the pile cap.

[0013] Preferably, in step S2, the pilot hole groove is formed by rotary drilling with a first rotary drill bit of diameter D1 and a second rotary drill bit of diameter D2, and D1 is greater than D2, as detailed below: S2.1 The first rotary drilling bit drills multiple circular holes in the underwater bare rock. Any two adjacent circular holes A are tangent to each other. These circular holes are distributed on the four sides of a rectangle. S2.2 For any two adjacent circular holes at their tangent points, the second rotary drilling bit performs rotary drilling with the tangent point as the center. In this way, four continuous channels are formed on the four sides of the rectangle. These four continuous channels together form the pilot hole groove.

[0014] Preferably, on any channel, the rotary drilling point of the second rotary drill bit forms four vertical lines. Two vertical lines along the length of the channel are distributed on plane A, and the other two vertical lines along the length of the channel are distributed on plane B. Each of the locking steel pipe piles is located between plane A and plane B.

[0015] Preferably, step S4 includes the following steps: S4.1. The guide frame and the positioning seat are fixedly connected to the trestle. The guide frame is rectangular and is located directly above the guide hole groove. The positioning plate installed on the guide frame is located above or below the positioning seat. The positioning plate is provided with an arc-shaped surface for contacting the outer wall of the locking steel pipe pile, and the arc-shaped surface of the positioning plate is provided with a notch groove to accommodate the locking buckle on the outer wall of the locking steel pipe pile. S4.2 Each of the aforementioned interlocking steel pipe piles is welded together from multiple column segments; Insert the locking mechanism of the first locking steel pipe pile into the notch groove of the positioning plate, so that the outer wall of the first locking steel pipe pile contacts the arc surface of the positioning plate and the outer wall of the first locking steel pipe pile contacts the positioning seat. Through the cooperation of the notch groove, the positioning seat and the positioning plate, the first locking steel pipe pile is kept vertical. Then, the first locking steel pipe pile is driven into the bottom of the pilot hole groove. S4.3 After completing the connection of a row of interlocking steel pipe piles, remove the guide frame on the trestle to prevent it from affecting the installation of the remaining interlocking steel pipe piles. S4.4. Assemble the remaining interlocking steel pipe piles in sequence to complete the construction of the cofferdam.

[0016] Preferably, in steps S6 and S8, the waterproof filler includes cement, bentonite, sawdust, and water, and the weight ratio is cement:bentonite:sawdust:water = (0.8-1.2):(2.5-3.5):(0.5-1.5):(0.8-1.2).

[0017] Preferably, the specific method of step S10 is as follows: S10.1 Draw grid lines on the bare rock in the foundation pit, drill holes at each intersection of the grid lines, and place pre-splitting agent in each hole; S10.2. Allow the pre-splitting agent in each hole to explode inside the hole, thereby creating multiple cracks in the bare rock. S10.3. Use an excavator inside the foundation pit to remove one layer of bare rock; S10.4 Repeat steps S10.1 to S10.3 until the set depth is reached; S10.5 Drill multiple rings of protective holes on the bare rock. Each ring of protective holes consists of multiple protective holes distributed circumferentially. Each ring of protective holes is arranged around the top of one of the piles to protect the piles. Then, proceed with steps S10.1 to S10.3. S10.6 Repeat step S10.5 until a space for constructing a reinforced concrete cushion layer is formed on the bare rock.

[0018] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1) This invention discloses a low-pile cofferdam platform for deep-water exposed rock in karst development areas. Through the organic combination of pile foundations, piers, a cofferdam, and multi-layered internal support components, a stable and reliable construction platform structure is formed. The piles are embedded in the underwater exposed rock, and a reinforced concrete cushion layer is fixedly connected to the top of the piles and placed on the top of the pier cap, providing a solid support foundation for the piers. The cofferdam is assembled from interlocking steel pipe piles, with its lower end extending into the pilot hole groove. The pilot hole groove and the cofferdam are sealed with a sand layer, effectively preventing water flow into the cofferdam and ensuring a dry construction environment inside. The multi-layered arrangement of the internal support components enhances the overall stability of the cofferdam, enabling it to withstand external forces such as water pressure in deep-water environments. The welded reinforced concrete cushion layer to the interlocking steel pipe piles further strengthens the integrity and connection strength of the cofferdam platform, giving the entire platform sufficient load-bearing capacity and stability to meet the needs of engineering activities such as bridge foundation construction under complex geological conditions such as deep-water exposed rock in karst development areas.

[0019] 2) This invention relates to a low-pile cofferdam platform for deep-water exposed rock in karst development areas. Each reinforcing cage of the reinforced concrete cushion layer is welded to a locking steel pipe pile at its end near the cofferdam. This welding connection method makes the reinforced concrete cushion layer and the locking steel pipe piles form a unified whole. When the cofferdam is subjected to external forces such as water pressure and construction loads, the locking steel pipe piles can transfer the force to the reinforced concrete cushion layer through the welding points, and then the reinforced concrete cushion layer evenly transfers the force to the piles, thereby achieving effective load distribution. The connection between the reinforced concrete cushion layer and the locking steel pipe piles not only enhances the cofferdam's bending and shear resistance but also improves its overall rigidity. This integrity allows the cofferdam to better resist the impact of water pressure in deep-water environments, reducing deformation and stress concentration in the cofferdam and reinforced concrete cushion layer, and effectively preventing karst water and water from outside the cofferdam from entering the cofferdam.

[0020] 3) The present invention provides a low-pile cofferdam platform for deep-water bare rock in karst development areas. The reinforced concrete cushion layer is connected to the piles and interlocking steel pipe piles respectively, and the whole has high strength and rigidity, providing sufficient bearing capacity with a relatively small thickness. This means that during construction, only a relatively shallow space needs to be chiseled out on the surface of the bare rock to install the reinforced concrete cushion layer, without the need for deep excavation of the bare rock as in traditional methods, thus reducing the excavation depth and greatly reducing the amount of excavation work.

[0021] 4) This invention provides a low-pile cofferdam platform for deep-water exposed rock in karst development areas. Addressing the challenges of highly mobile karst water and significant water level fluctuations, the platform utilizes a sand layer sealing system combined with interlocking steel pipe piles to effectively block karst water seepage paths, reducing the difficulty of water level control within the foundation pit and ensuring a dry working environment. The cofferdam structure improves sealing performance and reduces water and sand leakage through a tight fit between the sand and rock layers. In deep-water, low-pile environments, multi-layered internal support components enhance the cofferdam's resistance to water pressure, ensuring construction safety. The reinforced concrete cushion layer reduces the amount of exposed rock excavation, minimizing damage to the geological environment while accelerating construction progress and improving project efficiency. This provides a feasible and efficient cofferdam solution for bridge construction in complex geological areas, demonstrating significant engineering application value and promising prospects for wider application. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the low-pile cofferdam platform for deep-water bare rock in karst development areas according to the present invention; Figure 2 This is a schematic diagram illustrating how the guide frame and positioning plate guide the locking steel pipe pile in this invention. Figure 3 This is a schematic diagram of one of the channels of the through-hole groove in this invention; Figure 4 This is a schematic diagram of the waler being installed on the locking steel pipe pile via a force transmission plate in this invention; Figure 5 This is a schematic diagram of the force transmission plate in this invention; Figure 6 This is a schematic diagram showing two adjacent interlocking steel pipe piles connected together by interlocking. Figure 7 This is a schematic diagram of the grid lines drawn and the protective holes drilled during pre-splitting blasting operations on bare rock.

[0023] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. Pier; 2. Foundation; 3. Steel pipe pile; 4. Pre-hole trench; 5. Steel column; 6. Waler; 7. Reinforced concrete cushion; 8. Replacement support concrete; 9. Pile column; 10. Guide frame; 11. Positioning plate; 12. Circular hole; 13. Second rotary drilling bit; 14. Force transmission plate; 15. Rubber pad; 16. Locking buckle; 17. Plane A; 18. Plane B; 19. Protective hole. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Reference Figures 1-6 A low-pile cofferdam platform for deep-water bare rock in karst development areas includes pile foundations, piers 1, cofferdam, and multi-layer internal support components arranged vertically.

[0026] The pile foundation includes piles 9, reinforced concrete cushion 7, and pile cap 2. Multiple piles 9 are installed in pile holes drilled from underwater bare rock. The reinforced concrete cushion 7 is installed in the space chiseled from the underwater bare rock. The reinforced concrete cushion 7 is fixedly connected to the top of each of the piles 9. The pile cap 2 is installed at the top of the reinforced concrete cushion 7. The pier 1 is installed at the top of the pile cap 2.

[0027] The cofferdam surrounds the pile foundation. The cofferdam is assembled from multiple interlocking steel pipe piles 3. The lower end of each interlocking steel pipe pile 3 extends into a pilot hole groove 4. The pilot hole groove 4 consists of four channels excavated from underwater bare rock, distributed along the four sides of a rectangle. The groove wall of the pilot hole groove 4 is sealed to the cofferdam with a layer of sand. The interlocking steel pipe pile 3 is a conventional interlocking steel pipe pile structure, consisting of a pile pipe and interlocking clips 16 mounted on the outer wall of the pile pipe. Any two adjacent interlocking steel pipe piles 3 are tightly connected together by interlocking clips 16. The assembly of the interlocking steel pipe piles 3 of the cofferdam can refer to the assembly of existing cofferdams.

[0028] Each layer of the inner support assembly includes multiple walers 6, multiple corbels, and multiple steel columns 5. Each waler 6 is installed on the inner wall of the cofferdam via corbels, and each end of each steel column 5 is fixedly installed on the waler 6.

[0029] The reinforced concrete cushion layer 7 includes an integrally formed concrete structure and multiple reinforcing cages, with the end of each reinforcing cage near the cofferdam welded to the interlocking steel pipe piles 3 of the cofferdam.

[0030] This invention is applicable to construction in deep water areas of 15 to 20 meters underwater.

[0031] Furthermore, the sand layer is formed by a mixture of medium and coarse sand, and the interior of each of the interlocking steel pipe piles 3 is also filled with sand to enhance the strength of the interlocking steel pipe piles 3.

[0032] The sand layer formed by the mixture of medium and coarse sand has better particle size distribution and density, which can better fill the gap between the borehole groove 4 and the cofferdam, enhance the sealing performance, and prevent karst water from seeping between the cofferdam and the wall of the borehole groove 4. At the same time, the sand filling inside the interlocking steel pipe pile 3 can improve the strength of the interlocking steel pipe pile 3, making it more stable and capable of bearing water pressure and construction loads, further ensuring the reliability of the cofferdam structure, helping to resist the large water pressure in deep water environment and various impact loads that may occur during construction, extending the service life of the cofferdam, and reducing the frequency of maintenance and replacement. Furthermore, each of the interlocking steel pipe piles 3 is connected to the waler 6 via a force transmission plate 14. The surface of the force transmission plate 14 in contact with the waler 6 is flat, fitting snugly against the side of the waler 6. The surface of the force transmission plate 14 in contact with the interlocking steel pipe pile 3 is an arc-shaped surface consistent with the outer diameter of the interlocking steel pipe pile 3. This design enables effective connection and uniform force transmission between the inner support components of the cofferdam and the interlocking steel pipe piles 3. When the cofferdam is subjected to external forces such as water pressure, the inner support components smoothly transmit the force to the interlocking steel pipe piles 3 through the force transmission plate 14, thereby distributing it throughout the entire cofferdam structure, avoiding local stress concentration, ensuring balanced stress on the cofferdam structure, and improving its overall stability and load-bearing capacity.

[0033] By rationally designing the shape and contact surface of the force transmission plate 14, the force transmission path between the internal support components and the cofferdam is improved, reducing the risk of structural damage caused by stress concentration. In complex construction environments, this ensures the stability and safety of the cofferdam under long-term exposure to complex loads such as water pressure. It also helps improve the installation accuracy and construction efficiency of the cofferdam during construction, facilitating the connection and assembly of various components. Furthermore, the force transmission plate 14 includes a plate body and a rubber pad layer 15 disposed on the plate body. The plate body is provided with an arc-shaped surface, and an arc-shaped rubber pad layer 15 is disposed on the arc-shaped surface. The rubber pad layer 15 is in contact with the locking steel pipe pile 3.

[0034] Furthermore, a replacement support concrete 8 is provided on the reinforced concrete cushion layer, and the bottommost internal support component is embedded in the replacement support concrete 8. The replacement support concrete 8 can effectively connect the internal support component and the cofferdam. It is closely integrated with the internal support system composed of walers, corbels, and steel columns, forming a whole, thereby enhancing the cofferdam's resistance to external forces such as water pressure and construction loads in deep water environments, ensuring the stability of the cofferdam structure, and preventing deformation or instability of the cofferdam due to external forces.

[0035] Furthermore, the seepage points on the cofferdam are sealed with waterproof filler, which includes cement, bentonite, sawdust powder and water, and the weight ratio is cement:bentonite:sawdust powder:water = (0.8-1.2):(2.5-3.5):(0.5-1.5):(0.8-1.2).

[0036] Cement, as a cementing material, plays a crucial role in the bonding and hardening of waterproof fillers. A cement ratio of 0.8-1.2 ensures the filler has sufficient strength and hardness to form a robust sealing structure at the leakage points of the cofferdam, resisting the impact and seepage of water. If too little cement is used, the filler will lack strength and be unable to effectively seal leaks; if too much cement is used, it may reduce the filler's plasticity, hindering construction.

[0037] Bentonite possesses unique water absorption and swelling properties, as well as good plasticity. Its high proportion (2.5-3.5%) in the mix effectively increases the compactness and stability of the filler. When used to seal leaks, bentonite absorbs moisture and expands, filling pores and cracks, enhancing the bond between the filler and the cofferdam structure, and improving waterproofing. Simultaneously, bentonite improves the workability of the filler, making it easier to apply and fill complex leakage areas.

[0038] Sawdust can increase the volume and plasticity of fillers. An appropriate amount of sawdust makes the filler easier to handle and shape, facilitating its application to cracks and fissures in leaks. It also improves the filler's adhesion and crack resistance to some extent. Adding sawdust can reduce the overall cost of the filler, achieving a balance between economic benefits and performance; however, excessive sawdust will reduce the filler's strength.

[0039] Water is an essential component for activating cementitious materials such as cement and bentonite. Appropriate amounts of water give the filler good fluidity and plasticity, facilitating construction and filling even the smallest leaks. However, the amount of water needs strict control. Too much water will make the filler too thin, reducing its strength and making it prone to shrinkage cracks; too little water will make the filler too dry and hard, making it difficult to apply and fill completely.

[0040] After sealing, the waterproof filler hardens rapidly to form a waterproof layer with a certain strength and stability, adapting to water level changes and water flow impacts. The materials in the above-mentioned proportions, when mixed, can reach a certain strength in a short time, meeting the waterproofing requirements during construction, effectively reducing the difficulty of water level control within the foundation pit, and ensuring a dry working environment.

[0041] In deep-water environments, cofferdams are subjected to significant water pressure. The formulation of waterproof filler material needs to ensure good adhesion and compressive strength during underwater construction, enabling it to firmly adhere to the cofferdam structure, form an effective waterproof barrier, resist water pressure in deep-water environments, prevent karst water leakage, and ensure a dry construction environment inside the cofferdam.

[0042] According to another aspect of the present invention, a construction method for a low-pile cofferdam platform for deep-water bare rock in a karst development area is also provided, comprising the following steps: S1. Construct a trestle bridge and a temporary piling platform. Drill pile holes in the underwater bare rock using a drilling rig on the temporary piling platform. Then construct the pile column 9 in the pile hole. After the pile column 9 is completed, dismantle the temporary piling platform. S2. Using a rotary drilling rig on the trestle, excavate the pilot hole groove 4 on the underwater bare rock, and then fill the pilot hole groove 4 with sand. S3. Multiple interlocking steel pipe piles 3 are assembled in sequence and inserted into the sand grains. These interlocking steel pipe piles 3 enclose and form a cofferdam. S4. Chemical grouting is performed on the sand particles in the pilot hole groove 4 to achieve a seal between the cofferdam and the groove wall of the pilot hole groove 4. S5. Drain some of the water from the cofferdam so that the water level inside the cofferdam is below the inner support assembly to be installed. Weld multiple brackets onto the cofferdam and install multiple walers 6 on these brackets. Then connect multiple steel columns 5 to the walers 6. The brackets, walers 6 and steel columns 5 together form an inner support assembly. S6. Check if there are any leaks on the cofferdam. If so, seal the leaks with waterproof filler. If not, proceed to step S7. S7. Repeat steps S5 and S6 until the installation of the bottommost inner support component is completed. S8. Drain the water in the cofferdam to form a foundation pit. Clean the foundation pit to expose the bare rock inside. Then check if there are any seepage points on the cofferdam. If there are, seal the seepage points with waterproof filler. If not, proceed to step S9. S9. Clean the foundation pit and use sonar to detect whether there are interconnected karst caves inside the bare rock below the foundation pit. If there are interconnected karst caves, grout them to seal them, preferably using two-liquid grouting; if not, proceed to step S10. S10. On the bare rock in the foundation pit, the bare rock is blasted by pre-splitting blasting, and the rock blocks produced by the blasting are removed by excavator. In this way, a space for constructing the reinforced concrete cushion layer 7 is formed on the bare rock, and the top of each pile 9 is exposed in the formed space. S11. Place multiple steel cages in the space carved out on the bare rock, and weld the end of each steel cage near the cofferdam to the cofferdam. Then pour concrete on the steel cages. The concrete is fixedly connected to each of the piles 9. The steel cages and concrete together form the reinforced concrete cushion layer 7 of the pile foundation. S12. Construct the pile cap 2 on the reinforced concrete cushion 7, and then construct the pier column 1 on the pile cap 2.

[0043] The construction method of this invention, which involves first constructing pile foundations and then building the cofferdam, and then installing multi-layer internal support components within the cofferdam before pumping out water to form the foundation pit, fully considers the complexity of geological conditions in karst development areas, effectively reducing construction risks and ensuring construction safety. Furthermore, measures such as chemical grouting sealing, sealing leak points with waterproof fillers, and chiseling space out of the bare rock further enhance the sealing, stability, and adaptability of the cofferdam, improving the overall quality of the cofferdam platform. Finally, this construction method emphasizes the treatment of karst geological features, such as using sonar to detect and grout-seal karst caves within the bare rock below the foundation pit, effectively preventing problems such as cofferdam instability caused by karst caves, and providing reliable technical support for bridge construction in karst development areas. Furthermore, in step S2, the pilot hole groove 4 is formed by rotary drilling using a first rotary drill bit with a diameter of D1 and a second rotary drill bit 13 with a diameter of D2, where D1 is greater than D2, as detailed below: S2.1 The first rotary drilling bit drills out multiple circular holes 12 on the underwater bare rock. Any two adjacent circular holes 12A are tangent to each other. These circular holes 12 are distributed on the four sides of a rectangle. S2.2 For any two adjacent circular holes 12, the second rotary drilling bit 13 performs rotary drilling with the tangent point as the center, thereby forming four continuous channels distributed on the four sides of the rectangle. These four continuous channels together form the pilot hole groove 4.

[0044] This rotary drilling method can more precisely control the shape, size and position of the pre-hole trench 4, ensuring that it meets the installation requirements of the locking steel pipe pile 3, and laying a good foundation for the stable installation of the cofferdam.

[0045] The precisely drilled pilot hole groove 4 fits more tightly with the interlocking steel pipe pile 3, which helps to enhance the connection strength and stability between the cofferdam and the rock surface. Connecting the circular holes 12 together using the second rotary drill bit 13, instead of creating discontinuous holes 12, allows the interlocking steel pipe piles 3 to be arranged closely together. This method of drilling with two different diameter rotary drill bits effectively saves on the amount of sand material used between the interlocking steel pipe piles 3 and the pilot hole groove 4, compared to the conventional method of drilling only continuous tangential circular holes.

[0046] Furthermore, on any given trench, the second rotary drilling bit forms four vertical lines at its drilling point. Two of these vertical lines, along the length of the trench, are distributed on plane A17, and the other two are distributed on plane B18. Each of the interlocking steel pipe piles 3 is located between plane A17 and plane B18. This ensures that the interlocking steel pipe piles 3 are installed in the correct position.

[0047] Furthermore, step S4 includes the following steps: S4.1. The guide frame 10 and the positioning seat (not shown in the figure) are fixedly connected to the trestle. The guide frame 10 is rectangular and is located directly above the guide hole slot 4. The positioning plate 11 installed on the guide frame 10 is located above or below the positioning seat. The positioning plate 11 has an arc-shaped surface for contacting the outer wall of the locking steel pipe pile 3, and a notch is provided on the arc-shaped surface of the positioning plate 11 to accommodate the locking buckle 16 on the outer wall of the locking steel pipe pile 3. The positioning seat is preferably made of I-beam, and the plate at the end of the I-beam contacts the outer wall of the locking steel pipe pile 3. The positioning plate 11 is preferably snapped onto the guide frame 10 for easy disassembly. Since the notch and arc surface on the positioning plate 11 only positions one part of the locking steel pipe pile 3, the positioning plate 11 needs to cooperate with the positioning seat to position the upper and lower parts of the locking steel pipe pile 3 to ensure the verticality of the locking steel pipe pile 3.

[0048] S4.2 Each of the aforementioned locking steel pipe piles 3 is welded from multiple column segments; Insert the locking 16 of the first locking steel pipe pile 3 into the notch groove of the positioning plate 11, so that the outer side wall of the first locking steel pipe pile 3 contacts the arc surface of the positioning plate 11 and the outer side wall of the first locking steel pipe pile 3 contacts the positioning seat. Through the cooperation of the notch groove, the positioning seat and the positioning plate 11, the first locking steel pipe pile 3 is kept vertical. Then, the first locking steel pipe pile 3 is driven into the bottom of the pilot hole groove 4. S4.3 After assembling a row of interlocking steel pipe piles 3, remove the guide frame 10 on the trestle to prevent affecting the installation of the remaining interlocking steel pipe piles 3. Since the first interlocking steel pipe pile 3 is vertical, the interlocking links of the other interlocking steel pipe piles 3 are connected sequentially, facilitating the connection of these interlocking steel pipe piles 3. The distribution of the interlocking links on each interlocking steel pipe pile 3 should ensure that any two adjacent interlocking steel pipe piles 3 are connected by interlocking links 16.

[0049] S4.4. Assemble the remaining interlocking steel pipe piles 3 in sequence to complete the construction of the cofferdam.

[0050] The first interlocking steel pipe pile 3 was precisely positioned and driven using positioning plates 11 and positioning seats, providing effective guidance and correction for the installation of each interlocking steel pipe pile 3. This ensured the verticality and installation accuracy of each interlocking steel pipe pile 3, allowing it to be accurately inserted into the pilot hole slot 4, thus guaranteeing the construction quality and stability of the cofferdam. This positioning method effectively solved the problem of positioning and verticality control of steel pipe piles 3 on deep-water bare rock. The cofferdam structure formed by the precisely installed interlocking steel pipe piles 3 has higher quality and can better resist external forces such as water pressure, reducing the risk of overall tilting and deformation of the cofferdam. At the same time, it improved construction efficiency and reduced construction delays caused by repeated adjustments to the position and angle of the steel pipe piles 3.

[0051] Furthermore, in steps S6 and S8, the waterproof filler includes cement, bentonite, sawdust, and water, and is prepared by weight in the ratio of cement:bentonite:sawdust:water = (0.8-1.2):(2.5-3.5):(0.5-1.5):(0.8-1.2). Accurate proportioning of the waterproof filler ensures its waterproof performance. Cement, as the primary cementitious material, provides the strength and hardness of the grouting material. Under the influence of water, it undergoes a chemical reaction, gradually hardening and forming a stable structure. Bentonite increases the plasticity and malleability of the grouting material, making it easier to inject into cracks and pores. It also improves the density and stability of the material, helping to prevent water penetration. Sawdust, as a filler, increases the volume of the grouting material, providing a certain strength and structural stability. It also improves the fluidity and workability of the material, making it easier to construct. Water acts as a medium to activate the cementitious materials such as cement and bentonite, mixing them with the aforementioned materials.

[0052] The bentonite, sawdust, cement, and water mixed in the prescribed proportions can form a uniform and dense waterproof layer, which can better fill the pores and cracks of leakage points, and tightly integrate with the cofferdam structure, thereby improving the waterproof reliability and durability of the cofferdam, effectively preventing karst water leakage, and ensuring a dry construction environment inside the foundation pit.

[0053] Furthermore, in step S11, the reinforced concrete cushion layer 7 has wet joints. The design of wet joints improves the construction quality of the reinforced concrete cushion layer 7, enabling it to evenly transfer loads to each pile 9 under stress, reducing local stress concentration, and enhancing the overall bearing capacity of the pile foundation. Under complex karst geological conditions, good connection and force transmission performance help the cofferdam platform resist various external forces, reduce the risk of structural damage, and ensure construction safety and quality.

[0054] Furthermore, refer to Figure 7 The specific method for step S10 is as follows: S10.1 Draw grid lines on the bare rock in the foundation pit, drill holes at each intersection of the grid lines, and place pre-splitting agent in each hole; S10.2. Allow the pre-splitting agent in each hole to explode inside the hole, thereby creating multiple cracks in the bare rock. S10.3. Use an excavator inside the foundation pit to remove one layer of bare rock; S10.4 Repeat steps S10.1 to S10.3 until the set depth is reached; S10.5) Drill multiple rings of protective holes in the bare rock. Each ring of protective holes consists of multiple protective holes 19 distributed circumferentially. Each ring of protective holes 19 is arranged around the top of one of the piles to protect the pile. Then, proceed with steps S10.1) to S10.3). S10.6) Repeat step S10.5) until a space for constructing the reinforced concrete cushion layer 7 is formed on the bare rock.

[0055] By employing a grid-based perforation system, pre-splitting agent blasting, and layered excavation, the bare rock was peeled off layer by layer. Compared to traditional one-time blasting methods, this phased, layered controlled blasting method significantly reduces the impact and disturbance on the cofferdam structure, piles, and surrounding rock mass, effectively avoiding the risk of deformation, loosening, or leakage of the cofferdam structure due to blasting vibrations. It is particularly suitable for construction scenarios in deep-water environments where structural stability requirements are extremely high.

[0056] By arranging pre-crack agent holes in a grid pattern on the bare rock surface, directional crack propagation is achieved, causing the bare rock to fracture along a predetermined path, greatly improving excavation accuracy. Compared with traditional mechanical rock drilling, this method not only reduces the difficulty of mechanical operation on hard bare rock, but also significantly shortens the construction cycle and improves overall construction efficiency. It is especially suitable for deep-water bare rock areas with hard, undulating rock surfaces where direct mechanical operation is difficult.

[0057] Multiple protective holes are arranged around the top of each pile to form a "circular isolation zone," effectively preventing the transfer of blast energy to the pile and avoiding damage to the top of the pile due to blast impact. This design significantly improves construction safety, ensuring that the pile structure maintains its integrity and load-bearing capacity during blasting, and avoiding subsequent reinforcement or rework due to accidental damage during construction.

[0058] Because the blasting process is carried out in a layered, small-scale, and controlled manner, it avoids large-scale rock loosening, reduces the risk of connection between karst fissures or caves and external water bodies, and effectively controls the possibility of sudden karst water inrush. This characteristic is particularly important in karst development areas, significantly improving the stability and safety of the dry working environment within the cofferdam.

[0059] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A deep water bare rock low-pile cofferdam platform in a karst development area, characterized in that, Includes pile foundations, piers, cofferdams, and multi-layered internal support components arranged vertically, wherein: The pile foundation includes piles, a reinforced concrete cushion layer, and a pile cap. Multiple piles are installed in pile holes drilled from underwater bare rock. The reinforced concrete cushion layer is installed in the space chiseled out from the underwater bare rock. The reinforced concrete cushion layer is fixedly connected to the top of each pile. The pile cap is installed at the top of the reinforced concrete cushion layer, and the pier is installed at the top of the pile cap. The cofferdam surrounds the pile foundation. The cofferdam is assembled from multiple interlocking steel pipe piles. The lower end of each interlocking steel pipe pile extends into the pilot hole groove. The pilot hole groove consists of four channels excavated from the underwater bare rock and distributed on the four sides of a rectangle. The walls of the pilot hole groove are sealed to the cofferdam with a layer of sand. Each layer of the internal support assembly includes multiple walers, multiple corbels, and multiple steel columns. Each waler is installed on the inner wall of the cofferdam via corbels, and each end of each steel column is fixedly installed on a waler. The reinforced concrete cushion layer includes an integrally formed concrete structure and multiple reinforcing cages, with each reinforcing cage having its end near the cofferdam welded to the interlocking steel pipe piles of the cofferdam.

2. The karst development area deep water bare rock low pile cofferdam platform according to claim 1, characterized in that, The sand layer is formed by a mixture of medium and coarse sand, and the interior of each interlocking steel pipe pile is also filled with sand to enhance the strength of the interlocking steel pipe pile.

3. The karst development area deep water bare rock low-pile cofferdam platform of claim 1, characterized in that, Each of the interlocking steel pipe piles is connected to the waler through a force transmission plate. The surface of the force transmission plate that contacts the waler is flat, so as to fit against the side of the waler. The surface of the force transmission plate that contacts the interlocking steel pipe pile is an arc-shaped surface that is consistent with the outer diameter of the interlocking steel pipe pile.

4. The low-pile cofferdam platform for deep-water bare rock in karst development areas according to claim 1, characterized in that, The seepage points on the cofferdam are sealed with waterproof filler, which includes cement, bentonite, sawdust and water, and the weight ratio is cement:bentonite:sawdust:water = (0.8-1.2):(2.5-3.5):(0.5-1.5):(0.8-1.2).

5. A construction method for a low-pile cofferdam platform in deep-water bare rock in a karst development area, characterized in that, Includes the following steps: S1. Construct a trestle bridge and a temporary piling platform. Drill pile holes in the underwater bare rock using a drilling rig on the temporary piling platform. Then construct the pile columns in the pile holes. After the pile column construction is completed, dismantle the temporary piling platform. S2. Use a rotary drilling rig on the trestle to excavate a pilot hole trench on the underwater bare rock, and then fill the pilot hole trench with sand. S3. Multiple interlocking steel pipe piles are assembled in sequence and inserted into the sand grains. These interlocking steel pipe piles enclose and form a cofferdam. S4. Chemical grouting is performed on the sand particles in the pilot hole groove to achieve a seal between the cofferdam and the groove wall of the pilot hole. S5. Drain some of the water from the cofferdam so that the water level inside the cofferdam is below the inner support assembly to be installed. Weld multiple brackets onto the cofferdam and install multiple walers on these brackets. Then connect multiple steel columns to the walers. The brackets, walers, and steel columns together form an inner support assembly. S6. Check if there are any leaks on the cofferdam. If so, seal the leaks with waterproof filler. If not, proceed to step S7. S7. Repeat steps S5 and S6 until the installation of the bottommost inner support component is completed. S8. Drain the water in the cofferdam to form a foundation pit. Clean the foundation pit to expose the bare rock inside. Then check if there are any seepage points on the cofferdam. If there are, seal the seepage points with waterproof filler. If not, proceed to step S9. S9. Clean the foundation pit and use sonar to detect whether there are interconnected karst caves inside the bare rock below the foundation pit. If there are interconnected karst caves, grout them to seal them; otherwise, proceed to step S10. S10. On the bare rock in the foundation pit, the bare rock is blasted by pre-splitting blasting, and the rock blocks produced by the blasting are removed by excavator. In this way, a space for constructing a reinforced concrete cushion layer is formed on the bare rock, and the top of each pile is exposed in the space formed. S11. Place multiple steel cages in the space carved out on the bare rock, and weld the end of each steel cage near the cofferdam to the cofferdam. Then pour concrete on the steel cages. The concrete is fixedly connected to each of the piles. The steel cages and the concrete together form the reinforced concrete cushion layer of the pile foundation. S12. Construct the pile cap of the pile foundation on the reinforced concrete cushion, and then construct the pier column on the pile cap.

6. The construction method of a low-pile cofferdam platform for deep-water bare rock in a karst development area according to claim 5, characterized in that, In step S2, the pilot hole groove is formed by rotary drilling with a first rotary drill bit of diameter D1 and a second rotary drill bit of diameter D2, where D1 is greater than D2, as detailed below: S2.1 The first rotary drilling bit drills multiple circular holes in the underwater bare rock. Any two adjacent circular holes A are tangent to each other. These circular holes are distributed on the four sides of a rectangle. S2.2 For any two adjacent circular holes at their tangent points, the second rotary drilling bit performs rotary drilling with the tangent point as the center. In this way, four continuous channels are formed on the four sides of the rectangle. These four continuous channels together form the pilot hole groove.

7. The construction method of a low-pile cofferdam platform for deep-water bare rock in a karst development area according to claim 6, characterized in that, On any channel, the rotary drilling point of the second rotary drill bit forms four vertical lines. Two vertical lines along the length of the channel are distributed on plane A, and the other two vertical lines along the length of the channel are distributed on plane B. Each of the locking steel pipe piles is located between plane A and plane B.

8. The construction method of a low-pile cofferdam platform for deep-water bare rock in a karst development area according to claim 7, characterized in that, Step S4 includes the following steps: S4.

1. The guide frame and the positioning seat are fixedly connected to the trestle. The guide frame is rectangular and is located directly above the guide hole groove. The positioning plate installed on the guide frame is located above or below the positioning seat. The positioning plate is provided with an arc-shaped surface for contacting the outer wall of the locking steel pipe pile, and the arc-shaped surface of the positioning plate is provided with a notch groove to accommodate the locking buckle on the outer wall of the locking steel pipe pile. S4.2 Each of the aforementioned interlocking steel pipe piles is welded together from multiple column segments; Insert the locking mechanism of the first locking steel pipe pile into the notch groove of the positioning plate and make the outer side wall of the first locking steel pipe pile contact the arc surface of the positioning plate. Then make the outer side wall of the first locking steel pipe pile contact the positioning seat. Through the cooperation of the notch groove, the positioning seat and the positioning plate, the first locking steel pipe pile is kept vertical. Then drive the first locking steel pipe pile into the bottom of the pilot hole groove. S4.3 After assembling a row of interlocking steel pipe piles, remove the guide frame on the trestle to prevent it from affecting the installation of the remaining interlocking steel pipe piles. S4.

4. Assemble the remaining interlocking steel pipe piles in sequence to complete the construction of the cofferdam.

9. The construction method of a low-pile cofferdam platform for deep-water bare rock in a karst development area according to claim 5, characterized in that, In steps S6 and S8, the waterproof filler comprises cement, bentonite, sawdust, and water, and the weight ratios of the cement, bentonite, sawdust, and water are as follows: Cement: Bentonite: Sawdust: Water = (0.8-1.2): (2.5-3.5): (0.5-1.5): (0.8-1.2).

10. The construction method of a low-pile cofferdam platform for deep-water bare rock in a karst development area according to claim 5, characterized in that, The specific method for step S10 is as follows: S10.1 Draw grid lines on the bare rock in the foundation pit, drill holes at each intersection of the grid lines, and place pre-splitting agent in each hole; S10.

2. Allow the pre-splitting agent in each hole to explode inside the hole, thereby creating multiple cracks in the bare rock. S10.

3. Use an excavator inside the foundation pit to remove one layer of bare rock; S10.4 Repeat steps S10.1 to S10.3 until the set depth is reached; S10.5 Drill multiple protective holes in the bare rock. Each group of protective holes consists of multiple protective holes distributed circumferentially. Each group of protective holes is arranged around the top of one of the piles to protect the piles. Then, proceed with steps S10.1 to S10.

3. S10.6 Repeat step S10.5 until a space for constructing a reinforced concrete cushion layer is formed on the bare rock.

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