Variable steel casing pile group structure in complex water and soil environment and construction method thereof

Abstract

The invention discloses a variable steel casing pile group structure in a complex water and soil environment and a construction method thereof. A cast-in-situ bored pile is sleeved with a steel casing; the fixing piece comprises a crescent-shaped steel ring sleeve and a top butt joint fixing block. The crescent-shaped steel ring sleeves are evenly distributed on the outer wall of the steel casing, the steel piles penetrate through the crescent-shaped steel ring sleeves, the top ends of the steel piles are connected with the lower sides of the top butt joint fixing blocks, jacks are arranged on the upper sides of the top fixing blocks to jack the steel piles into the soil in place, and the top fixing blocks are welded to fix the steel piles to the outer wall of the steel casing; the grouting pipe is mounted on the inner wall of the steel pile; the steel casing strain gauge is arranged on the outer side wall of the steel casing; the steel pile strain gauge is arranged on the outer side wall of the steel pile, and a flower hole round hole is formed in the lower section of the steel pile. The method is easy to operate, steel members can be prefabricated on the ground, the soil penetration depth and the grouting area of the steel piles can be adjusted in time according to geological and stress testing conditions, soft soil layers around the driven steel piles are reinforced, and the horizontal bearing capacity and durability of the steel casing pile group structure are effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of underwater pile foundation engineering and control technologies, and more specifically, to a variable steel casing group pile structure in a complex water and soil environment and a construction method thereof. Background Art

[0002] When applying bored cast-in-place piles in an underwater environment, using a steel casing to construct a cofferdam can determine the position of the pile body, prevent water from entering the borehole, and effectively protect the pile body. Through research, it has been found that after the steel casing is sunk to a specific depth, the structure formed by combining the steel casing and the bored cast-in-place pile can fully exert the bearing performance of the pile and reduce the displacement of the pile, thereby determining the position of the pile.

[0003] However, when constructing the steel casing of a composite pile in a water area environment, due to the complex geological conditions in each place and the different depths of soft soil layers, the construction difficulty increases. It is difficult to accurately reinforce the soil layer around the bored cast-in-place pile, and connection reliability problems frequently occur. Research shows that if the connection between composite piles is unreliable, a severe axial force mutation will occur at the connection, and the pile-soil interaction is obvious, easily causing the pile body to tilt. In a deep water environment, horizontal loads such as water flow and earthquake have a greater impact on pile foundations with a smaller cross-section. The pile body part in the soft soil layer is difficult to fully exert its bearing effect. In addition, considering the rise of the soft floating slurry layer with poor quality at the top of underwater concrete, especially at the change of the pile hole cross-section diameter, a situation that is not conducive to the quality control of concrete will occur, resulting in poor concrete quality within a certain range around the pile. For the safety and stability of composite piles in a water area environment, it is necessary to build an adjustable monitoring system to cope with sudden changes in loads such as water flow in a complex environment, so as to control the safety of the composite group pile structure in the water area environment.

[0004] Therefore, in a complex water and soil environment, it is necessary to design a steel pile structure with variable length to adapt to different depths of soft soil layers, thereby improving the pile-forming quality of bored cast-in-place piles and an underwater composite pile that can improve the horizontal bearing capacity of the pile body. The composite pile should be characterized by convenient construction, and at the same time be able to strengthen the soft soil layer and establish a control technology solution to effectively solve the above technical problems. Summary of the Invention

[0005] Technical problem: The present invention aims to provide a variable steel casing group pile structure and its construction method in a complex water and soil environment, aiming to specifically solve the related problems such as precise and reliable connection, different depths of soft soil layers, water flow, and seismic horizontal loads mentioned in the background technology. Through the application of this structure and its construction method, not only can the pile forming quality be improved, but also the soft soil layer where the pile body is located can be reinforced, further achieving the purpose of reinforcing the pile body and improving the bearing capacity of the pile body. If systematic analysis finds that the bearing efficiency of this combined group pile structure does not meet the expected standard, further optimization measures can be initiated to make the structural stress tend to be evenly distributed and controlled within a preset limit range.

[0006] Technical solution: To solve the technical problem, the present invention provides a variable steel casing group pile structure and its construction method in a complex water and soil environment. This steel casing group pile structure includes the following components: steel casing, fixing piece, steel pile, grouting pipe, bored cast-in-place pile, perforated round hole, steel casing strain gauge, steel pile strain gauge, movable rubber piston; among them, the steel casing surrounds the outside of the bored cast-in-place pile, the fixing piece is on the outer wall of the steel casing, the fixing piece is composed of a crescent-shaped steel ring sleeve and a top docking fixing block, the steel pile passes through the crescent-shaped steel ring sleeve, the lower end of the top docking fixing block is connected to the top of the steel pile, and the upper end is connected to a jack to press the steel pile into the soil. Finally, the steel pile is welded to the outer wall of the steel casing through the top fixing block to achieve limit. The grouting pipe is installed inside the steel pile, and perforated round holes are provided in the lower section of the steel pile; the steel casing strain gauge is arranged on the side wall of the steel casing, and the steel pile strain gauge is arranged on the side wall of the steel pile.

[0007] The inner diameter of the steel casing is 200 - 350 mm larger than the designed diameter of the bored cast-in-place pile.

[0008] The crescent-shaped steel ring sleeves are distributed on the outer wall of the steel casing. Specifically, the number arranged along the longitudinal position is 2 - 5, and the number arranged along the transverse direction is 3 - 6; the lower end of the top docking fixing block is connected to the top of the steel pile, and the upper end is connected to a jack to press the steel pile into the soil. Finally, the top docking fixing block is welded to the outer wall of the steel casing using a cross buckle, thereby fixing the position of the steel pile.

[0009] The crescent-shaped steel ring sleeve is made of a steel ring sleeve with a thickness of 50 - 100 mm; a steel pile sleeve ring is arranged at the lower end of the top docking fixing block to connect the steel pile, and a component connected to the jack is arranged at the upper end. This jack connection component is adjusted accordingly according to the type of the on-site jack; the top docking fixing block is semi-circular cake-shaped, with a thickness of 50 - 100 mm, and a circular hole for inserting the grouting pipe is left in the middle, and the diameter of this hole is 30 - 60 mm.

[0010] The steel pile is designed with a hollow structure, and its bottom is in the shape of a conical pointed head. A movable rubber piston is arranged on the inner middle and lower side of the steel pile. The movable rubber piston can closely fit the inner wall of the steel pile, thus effectively preventing external water flow from pouring into the inside of the steel pile and creating a relatively dry and stable internal environment for subsequent construction. The grouting pipe accurately passes through the movable rubber piston and is fixed inside the steel pile. The steel pile is divided into an initial steel pile and continuous steel pile segments. According to the geological exploration situation, the continuous steel pile segments are welded to the initial steel pile to adjust the total length of the steel pile, and the lengths of the steel piles at each position can be different.

[0011] The grouting pipe is made of a steel circular pipe material, and its bottom end is in the shape of a conical pointed head to facilitate insertion and fixation. The grouting pipe is vertically installed and fixed inside the steel pile, and its length increases synchronously with the increase of the continuous steel pile segments. In the lower 1 / 2 range of the side wall of the initial steel pile, two rows of perforated round holes are opened to achieve a specific grouting function.

[0012] The diameters of the initial steel pile and the continuous steel pile segments in the steel pile are both 50 - 150 mm, and the diameter of the grouting pipe is 20 - 45 mm.

[0013] The diameter of the perforated round holes is 5 - 10 mm, and the spacing is 20 - 50 cm.

[0014] The steel casing strain gauges are arranged in the middle 1 / 3 - 2 / 3 range of the side wall of the steel casing; the steel pile strain gauges are arranged in the middle 1 / 3 - 2 / 3 range of the side wall of the steel pile, and the spacing is evenly distributed according to the engineering conditions and controlled to be 50 - 100 cm.

[0015] The construction method of the variable steel casing group pile structure under complex water and soil environment of the present invention is as follows: Step S1: Prefabricate the steel casing and the steel pile, install a crescent-shaped steel ring sleeve on the side wall of the steel casing, and install a top docking fixing block on the top of the steel pile; set steel casing strain gauges on the outer wall of the steel casing and steel pile strain gauges on the outer wall of the steel pile; vertically install and fix the grouting pipe on the inner wall of the steel pile. Step S2: Conduct a positioning operation on the construction site to accurately determine the construction position; install a cage-type guide frame, hammer the steel casing into the ground until it reaches the predetermined elevation, ensure that the water level inside the steel casing is always higher than that outside the casing, and pump the prepared slurry into the steel casing. Step S3: Along the position of the crescent-shaped steel ring sleeve fixed axially, use a ground jack to press the top docking fixing block to drive the steel pile in, connect the continuous steel pile segments to the initial steel pile according to the geological conditions to adjust the length of the steel pile; use a cross buckle to weld and fix the top fixing block on the side wall of the steel casing. Step S4: Under the stable enclosure of the steel casing, lower the drilling rig to the designated position, start the drilling operation process, and at the same time start the mud circulation system to carry out the drilling cuttings generated during the drilling process; when the drilling depth reaches the design requirements, transfer to the hole cleaning link to remove the residual sediment at the bottom of the hole; after the hole cleaning is completed, hoist the concrete conduit to ensure that the conduit is accurately positioned, vertical and stable, and then carry out secondary hole cleaning; Step S5: Inject underwater concrete into the hole through the concrete conduit. During the pouring process, monitor the rising height and flow state of the concrete, and continue the operation until the top surface of the concrete touches the top design elevation of the steel casing, completing the construction of the bored pile; Step S6: Use the grouting pipe installed on the inner wall of the steel pile to inject cement slurry into the soft soil layer around the steel pile through the perforated round holes to achieve the reinforcement treatment of the soft soil layer; after the cement slurry injection operation of the grouting pipe is completed, carry out the cement slurry pouring operation inside the steel pile, and continue to fill until the cement slurry reaches the pile top position and reaches the pre-set design elevation of the steel pile, completing the construction task of the underwater group piles; Step S7: During the operation of the steel casing group pile structure, use high-precision strain gauges to measure the dynamic change of the axial force of the underwater combined group pile structure under the actual load condition, and transmit the collected stress and strain signals to the ground management system; if the system analysis finds that the bearing capacity of the combined group pile structure does not meet the expected standard, start optimization measures, including removing the top docking fixing block and appropriately lengthening the length of the steel pile to strengthen the support force of the pile foundation, and continuing to grout around or inside the steel pile to adjust the interaction between the soil and the pile body, so that the structural stress tends to be evenly distributed and controlled within the pre-set limit range.

[0016] Beneficial effects: Compared with the prior art, the technical advantages of the present invention are: 1. The present invention proposes a variable steel casing group pile structure and its construction method under complex water and soil environments. Compared with traditional composite piles, the present invention can weld steel collar rings on the steel casing in the ground environment, and then the steel collar rings and the steel casing sink together to the predetermined position. By jacking the top docking fixing block on the ground, the driving operation of the steel pile can be realized. According to the geological conditions, continuous steel pile segments can be welded to the initial steel pile to adjust the length of the steel pile, and at the same time, a detachable steel pipe cross buckle is used to fix the top fixing block on the side wall of the steel casing. This construction method is simple and feasible, and can effectively solve the problem of poor connection reliability of traditional composite piles.

[0017] 2. The present invention provides a variable steel casing group pile structure and its construction method in a complex water and soil environment. By welding steel collar rings on the steel casings and driving steel piles, an extended steel pile support function is given to the traditional composite piles. This operation greatly improves the overall stiffness of the steel casings, reverses the cross-section mutation situation of the traditional composite piles, and further optimizes the stress condition of the pile body. The surrounding group piles not only serve as the retaining structure for pile hole formation but also play the role of a guiding structure, and cooperate with the steel casings to form a "group pile" structure, further enhancing the horizontal stiffness of the piles. Compared with the traditional bored cast-in-place piles, the composite steel casing structure provided by the present invention has greater bearing capacity and higher stiffness.

[0018] 3. The present invention provides a variable steel casing group pile structure and its construction method in a complex water and soil environment. By measuring the axial force change of the steel casing structure with axial force strain gauges arranged on the steel casings, synchronously and real-time measuring the stress information of the steel piles, and outputting the signal to the ground system. The stress change of the steel casing is converted and calculated into the change of the side friction resistance of the steel pile, and strictly controlling the difference of the axial force and the difference of the side friction resistance measured by each steel pile within 30%. If the difference exceeds this control range, it indicates that the side friction resistance of the steel pile is not fully exerted. At this time, the grouting effect of the steel pile can be controlled, and according to the specific geological conditions, the top fixing block can be disassembled and the length of each steel pile in each direction can be appropriately lengthened for adjustment. Under different geological conditions and engineering requirements, steel piles with different lengths can flexibly adapt to different depths of soft soil layers, making the distribution of the axial force and the side friction resistance of the steel pile structure uniform, and further effectively controlling the reasonable sharing of loads in all directions by the composite steel casing group pile structure, and fully realizing the stability and effectiveness of the structure.

[0019] 4. The variable steel casing group pile structure and its construction method provided by the present invention in a complex water and soil environment. Aiming to solve the situation that in the construction of traditional bored cast-in-place piles, complex geological conditions are often faced, and the depths of soft soil layers are different, which greatly increases the construction difficulty and it is difficult to accurately reinforce the soil layers around the bored cast-in-place piles. In response to this situation, after the bored cast-in-place pile is poured, the grouting pipe on the inner wall of the steel pile sprays cement slurry into the soft soil layer around the steel pile through the perforated round holes to reinforce the soil body. After the grouting is completed, due to the consolidation of the external surrounding soil, as the cement slurry is continuously injected, the cement slurry will gradually fill the space inside the steel pile. After a period of solidification, the cement slurry will form a solid filling body inside the steel pile. When facing different depths of soft soil layers, the length of the steel pile in the variable steel casing group pile structure can be adjusted accordingly. If the soft soil layer is relatively shallow, a shorter steel pile length can be used, which can not only meet the bearing requirements but also reduce the construction cost; if the soft soil layer is relatively deep, a longer steel pile length is selected to ensure that the steel pile can penetrate into the stable bearing layer, fully exert its bearing capacity, effectively reinforce the soil layer around the composite steel casing, and further improve the horizontal bearing capacity of the composite steel casing group pile structure. Brief Description of the Drawings

[0020] Figure 1 This is the structural elevation view after the implementation of the present invention.

[0021] Figure 2 This is the schematic diagram of the structural section and the soil layer grouting reinforcement area after the implementation of the present invention.

[0022] Figure 3 This is the structural plan view after the implementation of the present invention.

[0023] Figure 4 This is the schematic diagram of the steel pile detail and the grouting pipe after the implementation of the present invention. Among them, Figure 4 Figure (a) therein is the schematic diagram of the grouting pipe inside the steel pile, Figure 4 Figure (b) therein is the schematic diagram of the initial steel pile and the continuous steel pile section, Figure 4 Figure (c) therein is the schematic diagram of the final combined steel pile.

[0024] Figure 5 This is the schematic diagram of the steel pile grouting and subsequent construction process after the implementation of the present invention.

[0025] Figure 6 This is the schematic diagram of the detail of the fixing part after the implementation of the present invention.

[0026] In the figure: steel casing 1, fixing part 2, crescent-shaped steel ring sleeve 21, top butt fixing block 22, steel pile 3, initial steel pile 31, continuous steel pile section 32, grouting pipe 4, bored cast-in-place pile 5, perforated round hole 6, steel casing strain gauge 71, steel pile strain gauge 72, movable rubber piston 8. Specific embodiments

[0027] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all the embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0028] Please refer to Figure 1-6, the present invention provides a variable steel casing group pile structure and its construction method in a complex water and soil environment. The combined steel casing structure includes: a steel casing 1, a fixing member 2, a steel pile 3, a grouting pipe 4, a bored cast-in-place pile 5, a perforated round hole 6, a steel casing strain gauge 71, a steel pile strain gauge 72, and a movable rubber piston 8; the steel casing 1 is arranged outside the bored cast-in-place pile 5. The fixing member 2 is arranged on the outer wall of the steel casing 1, and the fixing member 2 includes a crescent-shaped steel ring sleeve 21 and a top docking fixing block 22. The steel pile 3 passes through and is fixed in the crescent-shaped steel ring sleeve 21. The lower end of the top docking fixing block 22 is connected to the top of the steel pile 3, and the upper end is connected to a jack to press the steel pile 3 into the soil. Finally, the steel pile 3 is welded to the outer wall of the steel casing 1 through the top docking fixing block 22 to achieve positioning. The grouting pipe 4 is installed inside the steel pile 3, and a perforated round hole 6 is provided in the lower section of the steel pile 3. The steel casing strain gauge 71 is arranged on the side wall of the steel casing 1, and the steel pile strain gauge 72 is arranged on the side wall of the steel pile 3. The steel casing 1 is driven into the riverbed mud surface to a certain depth, and its top elevation is higher than the water level. In the present invention, the fixing member 2 plays the role of fixing the position of the limiter and transmitting the load, and can be adjusted accordingly according to the on-site construction conditions. The crescent-shaped steel ring sleeve 21 can be fixed at the bottom and middle of the vertical steel track on the steel casing 1, distributed axially along the outer wall of the steel casing. The longitudinal position can be arranged in 2 - 5, and the transverse direction can be arranged in 3 - 6. The top docking fixing block 22 is arranged at the top of the steel pile 3, connected to a jack to press the steel pile 3 to control the penetration depth, and finally the top docking fixing block 22 is welded to the outer wall of the steel casing 1 to fix the position of the steel pile 3. The grouting pipe 4 is installed inside the steel pile 3, and its bottom elevation is located between the soft soil layers below the mud surface, and the top elevation is higher than the steel pile 3. In the present invention, the steel pile 3 is determined by the steel sleeve ring system, effectively breaking the characteristics that the pile body is vulnerable to the influence of water flow and has insufficient horizontal bearing capacity in the soft soil layer, and effectively improving the stability of the overall combined structure; when pouring the concrete of the cast-in-place pile, it can also avoid abnormal conditions at the cross-section change of the soft layer at the top of the underwater concrete.

[0029] The inner diameter of the steel casing 1 is 300 - 400 mm larger than the designed diameter of the bored cast-in-place pile 5 to ensure that the drill does not collide with the steel casing when drilling under its protection. For small-diameter bored cast-in-place piles, the wall thickness of the steel casing 1 is 1 / 150 - 1 / 100 of the diameter; for large-diameter extra-long cast-in-place piles, the wall thickness of the steel casing 1 is 15 - 25 mm. This thickness setting is aimed at ensuring that the steel casing does not deform during the construction process. It should be noted that the wall thickness of the steel casing is closely related to the diameter, penetration depth, etc., and its thickness selection should be combined with the actual project. The deviation of the center plane position of the steel casing 1 from the center of the bored cast-in-place pile 5 is not more than 50 mm to achieve positioning and anti-offset. The top elevation is 1 - 2 m higher than the maximum water level line to prevent surface water from entering the borehole; the bottom elevation is lower than the riverbed top surface, and it is driven into a non-soft soil layer with high bearing capacity and low permeability to ensure the structural stability and prevent mud loss.

[0030] The fixing member 2 is welded to the outer wall of the steel casing. The crescent steel ring sleeve 21 is made of a crescent-shaped steel ring with a thickness in the range of 50 - 100 mm. The crescent steel ring sleeve 21 is axially distributed along the outer wall of the steel casing 1. 2 to 5 can be arranged in the longitudinal position and 3 to 6 can be arranged transversely, and it can be flexibly adjusted according to the on-site construction conditions. The lower end of the top docking fixing block 22 is connected to the top of the steel pile 3. A jack is used to connect the top docking fixing block 22 to jack up the steel pile 3 to a predetermined position. After cross-buckling and fixing the top of the steel pile, the steel pile 3 is welded and fixed through the top docking fixing block 22. The fixing member 2 can effectively ensure the stability of the connection between the driven steel pile 3 and the structure, enabling the steel pile 3 to effectively exert the horizontal bearing capacity, thereby improving the stability of the overall composite structure.

[0031] The steel pile 3 is a drilled steel pile with a tapered pointed bottom end. The diameter of the steel pile is 20 - 50 mm. It is driven into the riverbed according to the position of the crescent steel ring sleeve 21. Its top elevation is higher than that of the steel casing 1, and the bottom elevation is located between the soft soil layers below the mud surface. Two rows of symmetrically arranged perforated round holes 6 are opened within the lower 1 / 3 range of the steel pile 3. The diameter of the perforated round holes 6 is 5 - 8 mm, and the spacing is 15 cm. The perforated round holes 6 are sealed with tape. A movable rubber piston 8 is arranged on the lower side inside the steel pile 3. The grouting pipe 4 is inserted, and the movable rubber piston 8 isolates the outside water from entering the steel pile 3. The steel pile 3 is divided into an initial steel pile 31 and a continuous steel pile section 32. According to the geological exploration situation, the continuous steel pile section 32 is welded to the initial steel pile 31 to adjust the total length of the steel pile 3. After the crescent steel ring sleeve 21 is driven into place, the weak soil at the position can be reinforced by injecting cement slurry through the grouting pipe 4 to improve the soil layer stability. After the injection is completed, due to the consolidation of the surrounding soil outside, as the cement slurry is continuously injected, the cement slurry will gradually fill the space inside the steel pile. After a period of solidification, the cement slurry will form a solid filling body inside the steel pile (3).

[0032] The grouting pipe 4 is made of a steel round pipe material with a tapered pointed bottom end to facilitate insertion and fixation. The grouting pipe is vertically installed and fixed inside the steel pile 3, and its length can increase synchronously with the increase of the continuous steel pile section 32. Two rows of perforated round holes 6 are opened within the lower 1 / 2 range of the side wall of the initial steel pile 31 to achieve a specific grouting function.

[0033] The steel casing strain gauge 71 is arranged within the middle 1 / 3 - 2 / 3 range of the side wall of the steel casing 1; the steel pile strain gauge 72 is arranged within the middle 1 / 3 - 2 / 3 range of the side wall of the steel pile 3, and the spacing can be considered to be evenly distributed at 50 - 100 cm according to the engineering conditions.

[0034] The following describes the specific implementation steps of the present invention: Step S1: Prefabricate the steel casing 1 and the steel pile 3. Install the crescent-shaped steel ring sleeve 21 on the side wall of the steel casing 1, and install the top docking fixing block 22 on the top of the steel pile 3. Install the steel casing strain gauge 71 on the outer wall of the steel casing 1 and the steel pile strain gauge 72 on the outer wall of the steel pile 3. Vertically install and fix the grouting pipe 4 on the inner wall of the steel pile 3.

[0035] Step S2: Conduct the positioning operation at the construction site to accurately determine the construction location. Install the cage-type guide frame, and hammer the steel casing 1 into the ground until the predetermined elevation is reached, ensuring that the water level inside the steel casing 1 is always higher than that outside the casing. Pump the prepared mud into the steel casing 1.

[0036] Step S3: At the position of the crescent-shaped steel ring sleeve 21 fixed axially, use the ground jack to press the top docking fixing block 22 into the steel pile 3. The continuous steel pile section 32 can be connected to the initial steel pile 31 according to the geological conditions to adjust the length of the steel pile 3. Use the cross buckle to weld and fix the top docking fixing block 22 on the side wall of the steel casing 1.

[0037] Step S4: Under the stable enclosure of the steel casing 1, lower the drill to the designated position, start the drilling operation process, and at the same time start the mud circulation system to carry out the drill cuttings generated during drilling. When the drilling depth reaches the design requirements, transfer to the hole cleaning link to remove the residual sediment at the bottom of the hole. After the hole cleaning is completed, hoist the concrete conduit to ensure that the conduit is accurately positioned, vertical and stable, and then carry out secondary hole cleaning.

[0038] Step S5: Inject the underwater concrete into the hole through the concrete conduit. During the pouring process, monitor the rising height and flow state of the concrete, and continue the operation until the top surface of the concrete touches the top design elevation of the steel casing 1 to complete the construction of the bored cast-in-place pile 5.

[0039] Step S6: Use the grouting pipe 4 installed on the inner wall of the steel pile 3 to inject cement slurry into the soft soil layer around the steel pile 3 through the perforated round holes 6 to achieve the reinforcement treatment of the soft soil layer. After the cement slurry injection operation of the grouting pipe 4 is completed, carry out the cement slurry perfusion operation inside the steel pile 3, and continuously fill until the cement slurry reaches the pile top position and reaches the pre-set design elevation of the steel pile 3 to complete the construction task of the underwater group piles.

[0040] Step S7: During the operation of the engineering system, use high-precision strain gauges to measure the dynamic changes in the axial force of the underwater combined group pile structure under actual load-bearing conditions, and transmit the collected stress-strain signals to the ground management system; if the system analysis finds that the load-bearing efficiency of the combined group pile structure does not meet the expected standard, start optimization measures, including removing the top docking fixing block 22 and moderately lengthening the length of the steel pile 3 to strengthen the support force of the pile foundation, and continuing to grout around or inside the steel pile 3 to adjust the interaction force between the soil and the pile body, so as to make the structural stress tend to be evenly distributed and controlled within the preset limit range.

[0041] The working principle of the present invention is described below: In the present invention, a steel sleeve ring is welded on the steel casing and a steel pile is driven in, endowing the traditional combined pile with the extended steel pile support function. This operation greatly improves the overall stiffness of the steel casing, reverses the cross-section mutation situation of the traditional combined pile, and then optimizes the stress condition of the pile body. The surrounding group piles not only serve as the retaining structure for pile hole formation but also play the role of a guiding structure, and together with the steel casing, they form a structure similar to a "group pile", further enhancing the horizontal stiffness of the pile. When facing different depths of soft soil layers, the length of the steel pile in the variable steel casing group pile structure can be adjusted accordingly. If the soft soil layer is relatively shallow, a shorter steel pile length can be used, which can not only meet the load-bearing requirements but also reduce the construction cost; if the soft soil layer is relatively deep, a longer steel pile length is selected to ensure that the steel pile can penetrate into the stable bearing layer, fully exert its bearing capacity, effectively reinforce the soil layer around the combined steel casing, and further improve the horizontal bearing capacity of the combined steel casing group pile structure.

[0042] I. Horizontal bearing capacity Existing research shows that the properties of the soil on the surface layer where the traditional bored cast-in-place pile enters the soil are mostly poor, and the stiffness difference between the pile and the soil layer is large, resulting in low horizontal resistance of the soil around the pile. In the water area environment, affected by horizontal loads such as water flow and earthquake, the pile body is prone to tilt.

[0043] For the design value of the horizontal bearing capacity of the group pile foundation It can be calculated according to the following formula: , Among them, is the characteristic value of the horizontal bearing capacity of a single pile, which can be determined by the horizontal static load test of a single pile or calculated according to the method recommended by relevant specifications. For example, for a pile with a pile diameter of and a pile length of , under the limit of the horizontal displacement coefficient at the ground surface, according to the flexural rigidity of the pile body and the proportional coefficient of the horizontal resistance coefficient m of the foundation soil, it is calculated using the formula: , Among them, , is the calculated width of the pile shaft, is the horizontal displacement coefficient at the pile top, is the allowable value of the horizontal displacement at the pile top corresponding to the horizontal bearing capacity of a single pile; is the flexural stiffness, is the comprehensive coefficient of group pile effect, which considers the influence of the interaction between piles in the group on the horizontal bearing capacity. Its calculation formula is: , where, is the coefficient of mutual influence of piles, which is related to factors such as the pile spacing , the pile diameter etc.; is the coefficient of pile top restraint effect, which is related to the connection method between the pile top and the cap (rigid connection or hinged connection), etc.; is the coefficient of lateral soil resistance effect of the cap, which is related to the properties of the soil on the side of the cap, etc.; is the lateral displacement coefficient of the group pile foundation, which is related to the overall stiffness of the group pile, etc.

[0044] Compared with a single pile with the same length and a constant cross-section pile with a diameter equal to the pile top diameter, the advantages of the composite steel casing group pile system are: 1. In terms of the flexural stiffness of the pile shaft ( ) For a constant cross-section pile, its flexural stiffness ( is the elastic modulus of the pile shaft material, is the moment of inertia of the cross-section, is the pile diameter). In the composite steel casing group pile system, compared with a constant cross-section pile, the peripheral steel piles are equivalent to expanding the cross-section of the steel casing, which is equivalent to enlarging the cross-section of the pile shaft. The combined moment of inertia of the cross-section will increase, and the flexural stiffness of the combined system will be significantly improved due to the increase in the moment of inertia of the cross-section, thereby increasing the horizontal bearing capacity of the composite steel casing group pile.

[0045] 2. In terms of group pile effect ( ) The composite steel casing group pile system forms a structure similar to a "group pile", which changes the interaction between the pile and the soil. In the comprehensive coefficient of group pile effect : Coefficient of mutual influence of piles : The steel casing makes the pile spacing equivalent to increase to a certain extent because it provides additional space constraints and changes in soil stress distribution. Compared with a constant cross-section pile, the mutual adverse effects between piles in the group pile (such as the stress superposition of the soil between piles leading to premature yield of the soil, etc.) will be reduced, which is more conducive to improving the horizontal bearing capacity.

[0046] Coefficient of pile top restraint effect : The socket connection and top welding between the steel casing and the surrounding steel piles can change the restraint conditions at the pile top. If the steel casing is tightly connected to the tops of each steel pile, it is equivalent to enhancing the restraint at the pile top, making increase, which is beneficial to resisting horizontal loads.

[0047] Coefficient of lateral soil resistance effect of the cap : The steel casing can be used as a special "lateral strengthening structure of the cap" to enhance the lateral soil resistance of the cap. Because the presence of the steel casing in the soil changes the stress state of the soil around the cap, making increase, thus having a positive impact on the horizontal bearing capacity.

[0048] Lateral displacement coefficient of pile group foundation : When facing different depths of soft soil layers, the length of the steel piles in the variable steel casing pile group structure can be adjusted accordingly. The grouting pipes are used to effectively reinforce the soft soil layers at different depths. The improvement of the overall stiffness of the steel casing pile group system optimizes the lateral displacement coefficient of the pile group foundation. Under the action of horizontal loads, the overall lateral displacement of the pile group decreases, thus improving the horizontal bearing capacity of the pile group system.

[0049] In summary, from the two key factors of the horizontal bearing capacity of a single pile and the comprehensive coefficient of pile group effect : The steel casing pile group system improves the flexural stiffness of the pile body by increasing the cross-section and optimizes the pile group effect at the same time. The synergistic effect of these two aspects enables the steel casing pile group system to have a significant advantage in improving the horizontal bearing capacity compared with the equal-section pile with the same length and diameter as the pile top diameter in resisting horizontal loads. This advantage can effectively reduce problems such as pile body inclination in the case of significant horizontal loads (such as water flow, earthquake, etc.) in the water area environment, improving the safety and stability of the structure.

[0050] II. Real-time monitoring and control scheme Measure the axial force change of the steel casing structure through the axial force strain gauges of the steel casing, synchronously and real-time measure the stress information of the steel pile, and output the signal into the ground system; convert the stress change of the steel casing into the change of the side friction resistance of the steel pile, and control the axial force difference and the side friction resistance difference measured by each steel pile within 30%. For the difference exceeding the control range, it indicates that the side friction resistance of the steel pile is not fully exerted. The reasons are that the depths of the soft soil layers are different and the connection reliability problems occur frequently, making it difficult to accurately grout and reinforce the soil layer around the bored cast-in-place pile. By controlling the grouting degree of the steel pile and appropriately adjusting the lengths of the steel piles in each direction according to the specific geological conditions, it can flexibly adapt to different depths of soft soil layers. If the soft soil layer is relatively shallow, shorter steel pile lengths can be used, which can not only meet the bearing requirements but also reduce the construction cost; if the soft soil layer is relatively deep, longer steel pile lengths are selected to ensure that the steel pile can penetrate into the stable bearing layer, fully exert its side friction resistance, effectively reinforce the soil layer around the combined steel casing, and further improve the horizontal bearing capacity of the combined steel casing group pile structure.

[0051] According to the existing research, the mutual slip between the side of the composite pile and the soil around the pile restricts the exertion degree of the side friction resistance of the pile. From the axial force change of the steel casing structure and the axial force information of the steel pile, it can be obtained that: , , In the formula: ——The axial force value on the side of a certain steel casing; ——The axial force value of the adjacent certain steel casing; ——The side friction resistance value per unit area of the pile; ——The pile perimeter value; ——The pile length distance value from point 1 to point 2; ——The strain value measured by the strain gauge at a certain place; ——The elastic modulus of the material; ——The unit area where the strain gauge is located.

[0052] It can be seen from the formula that through the axial force change of the steel casing, the side friction resistance value per unit area of the pile can be obtained, so as to effectively control the reasonable sharing of each load direction by the combined steel casing and fully realize the structural stability and effectiveness.

[0053] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacements for some of the technical features. Any modifications, replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A variable steel casing pile group structure in a complex water and soil environment, characterized by: The steel casing pile group structure comprises the following components: a steel casing (1), a fixing member (2), a steel pile (3), a grouting pipe (4), a bored pile (5), a flower eye circular hole (6), a steel casing strain gauge (71), a steel pile strain gauge (72), and a movable rubber piston (8); wherein the steel casing (1) surrounds the outside of the bored pile (5), the fixing member (2) is located on the outer wall of the steel casing (1), the fixing member (2) is composed of a crescent-shaped steel ring sleeve (21) and a top butt fixing block (22), and the steel pile (3) passes through A crescent-shaped steel ring sleeve (21), the lower end of the top docking fixing block (22) is connected to the top of the steel pile (3), and the upper end is connected to a jack to press the steel pile (3) into the soil. Finally, the steel pile (3) is welded to the outer wall of the steel casing (1) through the top docking fixing block (22) to achieve position limiting. The grouting pipe (4) is installed on the inner wall of the steel pile (3), and a flower eye circular hole (6) is provided at the lower section of the steel pile (3); the steel casing strain gauge (71) is arranged on the side wall of the steel casing (1), and the steel pile strain gauge (72) is arranged on the side wall of the steel pile (3).

2. The variable steel casing pile group structure in complex water and soil environment according to claim 1 is characterized by: The inner diameter of the steel casing (1) is 200-350 mm larger than the designed diameter of the bored pile (5).

3. The variable steel casing pile group structure in complex water and soil environment according to claim 1 is characterized by: The crescent-shaped steel ring sleeves (21) are distributed on the outer wall of the steel casing (1). Specifically, 2 to 5 of them are arranged in the longitudinal direction, and 3 to 6 of them are arranged in the transverse direction. The lower end of the top docking fixing block (22) is connected to the top of the steel pile (3), and the upper end is connected to a jack to press the steel pile (3) into the soil. Finally, the top docking fixing block (22) is welded to the outer wall of the steel casing (1) using a cross buckle, thereby fixing the position of the steel pile (3).

4. The variable steel casing pile group structure in complex water and soil environment according to claim 3 is characterized by: The crescent-shaped steel ring sleeve (21) is made of a steel ring sleeve with a thickness of 50-100 mm; a steel pile ring is provided at the lower end of the top docking fixing block (22) to connect the steel pile (3), and a component connected to the jack is provided at the upper end, and the jack connection component is adjusted accordingly according to the type of the on-site jack; the top docking fixing block (22) is semicircular and has a thickness of 50-100 mm, with a circular hole in the middle for inserting the grouting pipe (4), and the diameter of the hole is 30-60 mm.

5. The variable steel casing pile group structure in complex water and soil environment according to claim 1 is characterized by: The steel pile (3) is designed with a hollow structure, and its bottom is in the shape of a conical tip. A movable rubber piston (8) is arranged on the inner middle lower side of the steel pile (3). The movable rubber piston can fit tightly against the inner wall of the steel pile (3), thereby effectively preventing external water from flowing into the interior of the steel pile, thereby creating a relatively dry and stable internal environment for subsequent construction. The grouting pipe (4) accurately passes through the movable rubber piston (8) and is fixed inside the steel pile (3). The steel pile (3) is divided into an initial steel pile (31) and a continuous steel pile section (32). According to geological exploration conditions, the continuous steel pile section (32) is welded to the initial steel pile (31) to adjust the total length of the steel pile (3), and the lengths of the steel piles (3) at different positions can be different.

6. The variable steel casing pile group structure in complex water and soil environment according to claim 1 is characterized by: The grouting pipe (4) is made of a steel round tube, and the bottom end is in a conical tip shape to facilitate insertion and fixation. The grouting pipe is vertically installed and fixed inside the steel pile (3), and its length increases synchronously with the increase of the continuous steel pile section (32); two rows of flower eye circular holes (6) are opened in the lower 1 / 2 range of the side wall of the initial steel pile (31) to achieve a specific grouting function.

7. The variable steel casing pile group structure in complex water and soil environment according to claim 6 is characterized by: The diameters of the initial steel pile (31) and the continuous steel pile section (32) in the steel pile (3) are both 50-150 mm, and the diameter of the grouting pipe (4) is 20-45 mm.

8. The variable steel casing pile group structure in complex water and soil environment according to claim 6 is characterized by: The diameter of the eyelet circular holes (6) is 5-10 mm, and the spacing is 20-50 cm.

9. The variable steel casing pile group structure in complex water and soil environment according to claim 1 is characterized by: The steel casing strain gauge (71) is arranged within the range of 1 / 3 to 2 / 3 of the middle part of the side wall of the steel casing (1); the steel pile strain gauge (72) is arranged within the range of 1 / 3 to 2 / 3 of the middle part of the side wall of the steel pile (3), and the spacing is controlled to be uniformly distributed at 50 to 100 cm according to engineering conditions.

10. A construction method for a variable steel casing pile group structure in a complex soil and water environment as claimed in claim 1, characterized in that The construction method is: Step S1: prefabricate a steel casing (1) and a steel pile (3), install a crescent-shaped steel ring (21) on the side wall of the steel casing (1), and install a top docking fixing block (22) on the top of the steel pile (3); install a steel casing strain gauge (71) on the outer wall of the steel casing (1), and install a steel pile strain gauge (72) on the outer wall of the steel pile (3); and vertically install and fix a grouting pipe (4) on the inner wall of the steel pile (3); Step S2: performing a point positioning operation at the construction site to accurately determine the construction location; installing a cage guide frame, hammering the steel casing (1) into the ground until it reaches a predetermined elevation, ensuring that the horizontal surface inside the steel casing (1) is always higher than that outside the casing, and pumping the prepared mud into the steel casing (1); Step S3: along the axially fixed position of the crescent-shaped steel ring sleeve (21), use a ground jack to press the top docking fixing block (22) to drive the steel pile (3), and connect the continuous steel pile section (32) to the initial steel pile (31) according to the geological conditions to adjust the length of the steel pile (3); use a cross buckle to weld and fix the top docking fixing block (22) to the side wall of the steel casing (1); Step S4: Under the stable protection of the steel casing (1), the drilling rig is lowered to the designated position, the drilling process is started, and the mud circulation system is started to carry out the drill cuttings generated during the drilling process; when the drilling depth reaches the design requirement, the hole cleaning process is started to remove the sediment remaining at the bottom of the hole; after the hole cleaning is completed, the concrete guide tube is hoisted to ensure that the guide tube is accurately positioned, vertically and stably, and then the second hole cleaning is carried out; Step S5: inject underwater concrete into the hole through the concrete conduit. During the pouring process, monitor the rising height and flow state of the concrete and continue the operation until the top surface of the concrete touches the top design elevation of the steel casing (1), thus completing the construction of the bored pile (5); Step S6: using the grouting pipe (4) provided on the inner wall of the steel pile (3), cement slurry is injected into the soft soil layer around the steel pile (3) through the eyelet circular hole (6) to achieve reinforcement of the soft soil layer; after the cement slurry injection operation of the grouting pipe (4) is completed, cement slurry is poured into the interior of the steel pile (3), and the filling is continued until the cement slurry reaches the pile top position and reaches the pre-set design elevation of the steel pile (3), thereby completing the underwater pile group construction task; Step S7: During the operation of the steel casing pile group structure, a high-precision strain gauge is used to measure the dynamic change of the axial force of the underwater composite pile group structure under the actual load-bearing condition, and the collected stress-strain signal is transmitted to the ground management system; If the system analysis finds that the bearing performance of the combined pile group structure does not meet the expected standard, optimization measures are initiated, including removing the top docking fixing block (22) to appropriately lengthen the length of the steel pile (3) to strengthen the supporting force of the pile foundation, and continuing to inject grout around or inside the steel pile (3) to adjust the interaction force between the soil and the pile body, so as to promote the structural stress to be evenly distributed and controlled within a pre-set limit range.

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