Construction method for combined steel sheet pile cofferdam of river blocking section bearing platform deep foundation pit

Abstract

The invention discloses a combined steel sheet pile cofferdam construction method for a river blocking section bearing platform deep foundation pit, relates to the technical field of cofferdam construction, and has the advantage that steel sheet piles can still be constructed when the distance between adjacent bearing platforms is small. Meanwhile, steel sheet pile inserting and driving positions are arranged at the positions 1-1.1 m away from the outer sides of the bearing platform foundation side lines, the steel sheet piles are directly inserted and driven, lofting is conducted on the side lines of the steel sheet piles before inserting and driving, the steel sheet piles are driven one by one on the premise that the steel sheet piles are perpendicular, and pier position bearing platforms are marked and classified as one bearing platform combination, two bearing platform combinations, three bearing platform combinations... N bearing platform combinations, according to an outer frame of the combination, steel sheet piles are arranged at the positions, 1-1.1 m away from the outer sides of the side lines of the adjacent bearing platform foundations, of the positions without interference along the positions 1-1.1 m away from the outer sides of the side lines of the bearing platform foundations, and the rear portions of the parts with interference are excavated together to be communicated in the same combination foundation pit.

Description

TECHNICAL FIELD

[0001] The present application relates to the cofferdam construction technical field, specifically to a kind of river section pile cap deep foundation pit combined steel sheet pile cofferdam construction method. BACKGROUND

[0002] In the construction of city viaduct bridge pile cap deep foundation pit in river section, steel sheet pile cofferdam, as temporary water retaining structure, provides water-free construction environment for lower structure, and is often used as foundation pit supporting method.Steel sheet pile cofferdam has the advantages of high strength, good toughness, good waterproof performance, stable and safe support, high recycling rate, etc.

[0003] After cofferdam pumping and old bridge demolition, lime soil replacement treatment is carried out on river bottom silt, and the site is compacted after construction.

[0004] Pile cap is located on the top of pile foundation, and is the force transmission platform between pile and pier column or pier body.It connects multiple piles into a whole to form pile foundation, and uniformly distributes the load from pier body or column to each pile top to avoid single pile overload, and transmits the load to deep foundation to reduce settlement risk.Each pile cap is surrounded by steel sheet pile before construction.

[0005] However, due to the limitation of site size, the distance between adjacent pile caps is small, and steel sheet pile cannot be constructed.

[0006] Therefore, the applicant has developed a new technical solution in the actual production process to solve the above technical problems. SUMMARY

[0007] In view of the above technical deficiencies, the present application aims to provide a kind of river section pile cap deep foundation pit combined steel sheet pile cofferdam construction method, which has the advantage of enabling the distance between adjacent pile caps to be small and still enabling steel sheet pile to be constructed.

[0008] To solve the above technical problems, the present application adopts the following technical solutions: The present application provides a kind of river section pile cap deep foundation pit combined steel sheet pile cofferdam construction method, including the following processes: Steel sheet pile positioning→steel sheet pile setting→initial excavation→steel enclosing purlin installation→steel support plate installation→secondary excavation→pad construction→pile cap construction→backfilling after completion→removal of steel support plate and steel enclosing purlin→removal of steel sheet pile; Steel sheet pile positioning and steel sheet pile setting: after marking the pile cap position and verifying that it is correct, steel sheet pile insertion position is placed at a distance of 1-1.1 meters from the outer side of the pile cap foundation line.Steel sheet pile is inserted directly, and the steel sheet pile line is laid out before insertion.Under the premise of vertical steel sheet pile, steel sheet pile is inserted one by one; The pier position bearing platform is marked with a classification: one bearing platform combination, two bearing platform combinations, three bearing platform combinations, and N bearing platform combinations. The outer frame of the combination is that: the positions without interference of 1-1.1 meters outside the adjacent bearing platform foundation boundary are respectively provided with steel sheet piles along the 1-1.1 meters outside the adjacent bearing platform foundation boundary, and the positions with interference are excavated together and connected in the same combined foundation pit.

[0009] By adopting the above technical scheme, the positions without interference of 1-1.1 meters outside the adjacent bearing platform foundation boundary are respectively provided with steel sheet piles along the 1-1.1 meters outside the adjacent bearing platform foundation boundary, and the positions with interference are excavated together and connected in the same combined foundation pit, so that there is one bearing platform or two or three in the same combined foundation pit, thereby reducing the limitation of the size of the site, and enabling the adjacent bearing platforms to have a small distance and still be able to construct the steel sheet piles.

[0010] Preferably, the excavation of the earthwork is vertically divided into two layers from top to bottom, that is, primary excavation: the first layer of soil is excavated to a position 0.5 m below the steel support plate, an ordinary excavator is used for excavation, and the earthwork is directly transported out by a dump truck; after the first layer of soil is excavated to the position, steel enclosing purlins and steel support plates are constructed, after the steel support plate construction is completed, a long-arm excavator is used for secondary excavation of the second layer of soil, that is, secondary excavation, after excavation to the pit bottom elevation, concrete cushion pouring is immediately performed, and after the concrete strength of the concrete cushion reaches the requirement, subsequent pile head removal and bearing platform construction can be performed.

[0011] Preferably, the steel enclosing purlins and the steel support plates are installed: the steel enclosing purlin bottom elevation position is measured and marked on the exposed steel sheet pile in the primary excavation, and a bracket is welded; the steel enclosing purlin is hoisted to the bracket and welded, at this time, the steel enclosing purlin is distributed around the inner wall of the steel sheet pile, steel support plates are additionally installed between adjacent and perpendicular steel enclosing purlins, and the two ends of the steel support plate are respectively welded on the steel enclosing purlin.

[0012] Preferably, the bearing platform construction includes bearing platform steel bar binding on the concrete cushion, pre-connecting the pier body steel bar and the bearing platform steel bar, and then supporting the formwork connected with each other around the bearing platform steel bar and pouring the bearing platform.

[0013] Preferably, the formwork includes a steel plate on the side facing the bearing platform steel bar and a plurality of vertically distributed vertical plates provided on the side of the steel plate away from the bearing platform steel bar, the upper end of the vertical plate extends out of the upper end of the steel plate, the vertical columns on the opposite two steel plates are connected by being pulled tight by the tension steel, and the adjacent two steel plates are connected by the angle steel, the angle steel is distributed along the height direction of the steel plate, and is connected with the side surface of each steel plate by the bolt.

[0014] Preferably, when the steel sheet pile on one side of the bearing platform is driven to a position less than 1 meter from the outer side of the bearing platform foundation line and less than the thickness of the steel sheet pile, the formwork at this position is replaced by a structure comprising a plurality of foam boards closely fitted between the steel sheet pile and the bearing platform reinforcement, each of the foam boards being vertically distributed and arranged along the length direction of the bearing platform, one side of each foam board abutting against the steel sheet pile, and the other side having two end faces each abutting against the steel plate on the adjacent formwork, and the vertical plate on the formwork corresponding to the foam board being provided with an abutting rod horizontally abutting against the side face of the steel sheet pile.

[0015] Preferably, each of the vertical plates comprises two mounting plates connected to the plate face of the steel plate and having a U-shaped cross section, the U-shaped openings of the two mounting plates being distributed away from each other, and one of the opposite vertical side edges of the mounting plate being detachably connected to the steel plate by a screw, and there being a gap between the two mounting plates of each vertical plate for the passage of the tie bar; and each of the two mounting plates being provided with an adjusting member for adjusting the position of the tie bar.

[0016] Preferably, the adjusting member comprises a horizontal plate placed on the vertical side walls of each of the two mounting plates, the horizontal plate being located above the steel plate and used for supporting the tie bar, a pressing plate being placed on the vertical side walls of each of the two mounting plates, the pressing plate and the horizontal plate being located on the two sides of the vertical side walls of the mounting plate respectively, and the horizontal plate being provided with a prism on the side facing the pressing plate, a threaded rod being coaxially provided on the prism, a through hole being formed in the pressing plate for the passage of the threaded rod, the threaded rod being threadedly connected with a locking block abutting against the pressing plate after passing through the pressing plate, and an insertion slot being formed in the upper end face of the pressing plate for the insertion of the tie bar, the tie bar abutting against the upper end face of the horizontal plate when the tie bar has not been straightened and inserted into the insertion slot, the two end outer walls of the tie bar being provided with threads and being threadedly connected with a screwing block located on the side of the pressing plate away from the horizontal plate.

[0017] Preferably, the vertical plate provided with the abutting rod has one mounting plate, and the height of the foam board is greater than the height of the bearing platform, the side of the foam board facing the steel sheet pile being provided with a plurality of vertically inserted vertical plates, the side edges of the two vertical plates farthest apart being provided with extension plates extending in the direction of the formwork, one end of the steel plate of the adjacent formwork extending into the extension plate, and the plate face of the steel plate abutting against one side of the foam board.

[0018] Preferably, the steel enclosing purlin and the steel support plate are symmetrically and spacedly removed to reduce the local deformation and cracking caused by the excessive release of the instantaneous pre-stress. When the steel enclosing purlins are close to each other in the same combined foundation pit, triangular thick steel backing plates are welded between them.

[0019] The beneficial effect of the present application is that the positions 1-1.1 meters outside the side lines of the adjacent pile caps are not interfered, and the steel sheet piles are arranged along the positions 1-1.1 meters outside the side lines of the respective pile caps, and the positions with interference are excavated together and connected in the same combined foundation pit, so that one pile cap or two or three pile caps are arranged in the same combined foundation pit, thereby reducing the limitation of the size of the site, and enabling the adjacent pile caps to be arranged at a small distance and still be able to be constructed with steel sheet piles. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 It is a structural schematic diagram of the present embodiment; Figure 2 It is a structural schematic diagram of the present embodiment for embodying double-row water-stop steel sheet piles; Figure 3 It is a structural schematic diagram of the present embodiment for embodying a same combined foundation pit of one pile cap combination; Figure 4 and Figure 5 It is a structural schematic diagram of the present embodiment for embodying a same combined foundation pit of two pile cap combinations; Figure 6 It is a structural schematic diagram of the present embodiment for embodying a same combined foundation pit of three pile cap combinations; Figure 7 It is a structural schematic diagram of the present embodiment for embodying a formwork during pile cap pouring; Figure 8 It is Figure 7 an enlarged structural schematic diagram of part A in FIG. 6; Figure 9 It is Figure 7 an enlarged structural schematic diagram of part B in FIG. 6; Figure 10 It is a structural schematic diagram of the present embodiment for embodying an adjusting member; Figure 11 It is a structural schematic diagram of the present embodiment for embodying a threaded rod; Figure 12 It is a structural schematic diagram of the present embodiment for embodying a foam board; Figure 13 It is a structural schematic diagram of the present embodiment for embodying a longitudinal section of a pile cap cofferdam.

[0022] Explanation of reference signs: Fig. 1: 1, steel sheet pile; 11, bearing platform; 111, cushion layer; 12, steel surrounding purlin; 121, thick steel cushion plate; 13, same group of combined foundation pit; 14, steel support plate; 15, pier body; 16, steel plate; 161, opposite-pulling steel bar; 162, angle steel; 163, contact rod; 164, mounting plate; 17, foam plate; 18, cross plate; 181, compression plate; 182, prism; 183, threaded rod; 184, locking block; 185, slot; 186, screwing block; 19, vertical plate; 191, extension plate; 2, double-row water-stopping steel sheet pile; 21, steel temporary bridge. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0024] As Figure 2 , the following construction is the construction of the applicant in the Jinxi Bridge old bridge demolition reconstruction project. The south and north side steel sheet pile cofferdams of the Jinxi Bridge old bridge are demolished before the old bridge is demolished. After the cofferdams are pumped out and the old bridge is demolished, the silt at the river bottom is treated by lime soil replacement. After compaction, the site elevation is 2.0 m. The underwater bearing platform is converted into a land bearing platform for construction. After the Jinxi Bridge old bridge is demolished, a new elevated bridge is built over the river section, and then a ground bridge is reconstructed. It is planned to construct the lower structures of the two bridges together. Therefore, the bearing platforms in the lower river are dense, the number is large, the spacing is small, and two bridges are involved.

[0025] The south and north side cofferdams are both double-row water-stopping steel sheet piles 2, which are located outside the scope of the newly built Jinxi Bridge. The double-row water-stopping steel sheet piles 2 are of Larsen type IV, with a pile length of 12 m and a spacing of 1 m between the two rows. The clear distance from the two sides of the steel temporary bridge is 2 m. The river channel of the Jinxi Bridge has a normal water level elevation of 2.0 m, a river bed bottom elevation of -1.9 m, and a water depth of 3.9 m. The double-row water-stopping steel sheet piles 2 are designed to have a pile top elevation of 3.0 m and a pile bottom elevation of -9.0 m. According to the survey report, the thickness of the silt layer is 1.0-1.4 m, and the effective soil penetration depth of the double-row water-stopping steel sheet piles is 5.7-6.1 m. The double-row water-stopping steel sheet piles 2 in the above process are mainly used to block the water flow under the old bridge, facilitating the subsequent bearing platform construction; In addition, steel temporary bridges 21 can also be laid in the south and north side double-row water-stopping steel sheet piles, facilitating the normal passage of social vehicles and pedestrians.

[0026] A construction method of a combined steel sheet pile cofferdam for a river section bearing platform deep foundation pit, as Figure 1 and Figure 3 , comprises the following processes: Steel sheet pile positioning → steel sheet pile setting → initial excavation → steel surrounding purlin installation → steel support plate installation → secondary excavation → cushion construction → pile cap construction → complete backfilling → removal of steel support plate and steel surrounding purlin → removal of steel sheet pile; the method is used for non-flood season construction.

[0027] Steel sheet pile 1 positioning and setting: after the pier position pile cap 11 is marked and no error is found after rechecking, the steel sheet pile 1 insertion position is placed at a position 1-1.1 meters outside the foundation edge line of the pile cap 11, the steel sheet pile 1 is directly inserted, the steel sheet pile 1 edge line is laid out before insertion, and the steel sheet pile 1 is inserted into the ground under the premise of verticality; As Figure 3 and Figure 4 and Figure 5 and Figure 6 The pier position pile cap 11 is marked for classification: one pile cap 11 combination, two pile cap 11 combinations, three pile cap 11 combinations, …, N pile cap 11 combinations, the outer frame of the combination: the part without interference at the position 1-1.1 meters outside the foundation edge line of each pile cap 11 is set with steel sheet pile 1 along the position 1-1.1 meters outside the foundation edge line of each pile cap 11, and the part with interference is excavated together later to be connected in the same combination foundation pit 13; The part without interference refers to the position 1-1.1 meters outside the foundation edge line of the pile cap 11 which will not form interference with the position 1-1.1 meters outside the foundation edge line of the adjacent pile cap 11; The part with interference refers to the position 1-1.1 meters outside the foundation edge line of the pile cap 11 which will form interference with the position 1-1.1 meters outside the foundation edge line of the adjacent pile cap 11, and the interference part is excavated through; The same combination foundation pit 13 is a closed loop formed by surrounding steel sheet piles, i.e. a pile cap cofferdam. For example, when there is one pile cap 11 combination, the same combination foundation pit 13 is in the shape of a rectangle, when there are two pile cap 11 combinations, the same combination foundation pit 13 is in the shape of Z or a rectangle, and so on.

[0028] As Figure 3 and Figure 4 and Figure 5 and Figure 6 The part without interference at the position 1-1.1 meters outside the foundation edge line of the adjacent pile cap 11 is set with steel sheet pile 1 along the position 1-1.1 meters outside the foundation edge line of each pile cap 11, and the part with interference is excavated together later to be connected in the same combination foundation pit 13, so that there is one pile cap 11 or two or three pile caps 11 in the same combination foundation pit 13, thereby reducing the limitation of the size of the site, and enabling the construction of steel sheet pile 1 even when the distance between adjacent pile caps 11 is small.

[0029] As Figure 3 and Figure 4 and Figure 5 and Figure 6, the excavation of earthwork is divided into two layers from top to bottom, namely the initial excavation: the first layer of soil is excavated to the position 0.5m below the steel support plate 14, and an ordinary excavator is used for excavation. The earthwork is directly transported out by a soil transport vehicle. During construction, the farther the ordinary excavator is from the foundation pit, the better, so as to reduce the dynamic load at the edge of the foundation pit; after the first layer of soil is excavated in place, the steel purlin 12 and the steel support plate 14 are constructed. After the construction of the steel support plate 14 is completed, a long-arm excavator is used to excavate the second layer of soil, namely the secondary excavation. After excavation to the pit bottom elevation, the concrete cushion layer 111 is poured immediately. After the concrete cushion layer is poured, After the concrete strength of layer 111 meets the requirements, the subsequent pile head can be chiseled out and the foundation 11 can be constructed; before pouring the concrete cushion layer 111, a plastic film is laid on the inner wall of the steel sheet pile 1, and then the concrete cushion layer 111 is poured. At this time, the concrete is poured all over the bottom of the foundation pit. Since there is a plastic film between the steel sheet pile 1 and the concrete, it does not affect the subsequent extraction of the steel sheet pile 1. At this time, the cushion layer 111 is poured all over the bottom of the foundation pit to achieve the purpose of sealing the bottom of the foundation pit, which is convenient for forming a working surface for subsequent construction. In addition, the cushion layer 111 also supports the steel sheet pile 1, thereby increasing the stability of the foundation pit enclosure.

[0030] Pile head chiseling refers to the pile body that was previously driven into the ground and located below the pedestal 11. The pile head is located above the concrete cushion layer 111. In addition to chiseling the concrete at the pile head, the exposed steel bars are to be located inside the pedestal 11. According to the design of this project implementation plan, 15m deep Larsen IV steel sheet piles 1 are used for support, and 400×400H-shaped steel is used as steel purlins 12 and steel support plates 14.

[0031] like Figure 3 and Figure 4 and Figure 5 and Figure 6 Installation of the steel purlins 12 and steel support plates 14: Measure and mark the bottom elevation of the steel purlins 12 on the exposed steel sheet piles 1 during the initial excavation, and weld a corbel to it. Lift the steel purlins 12 onto the corbel and spot weld them. At this point, the steel purlins 12 are circumferentially distributed around the inner wall of the steel sheet piles 1 and form a closed ring, i.e., the steel purlins 12 are distributed around the edge of the same combined foundation pit 13. Steel support plates 14 are installed between adjacent and mutually perpendicular steel purlins 12. Steel support plates 14 can also be installed between adjacent and mutually parallel steel purlins 12, thereby increasing the support force of the steel purlins 12 and steel support plates 14 on the steel sheet piles 1. The two ends of the steel support plates 14 are spot welded to the steel purlins 12. The purpose of spot welding is to facilitate the subsequent use of existing technologies such as thermal cutting and chemical demolition to separate the welds, thereby facilitating the removal of the steel purlins 12 and steel support plates 14.

[0032] The dimensions in the above construction include but are not limited to the following examples: Figure 13, the site elevation at the pier cap is 2.0m, the design bottom elevation of the cap 11 is -4.641~ -3.817m, the top elevation is -2.141~ -0.817m, the scheme arrangement is to drive a 15m long Larsen IV type water stop steel sheet pile 1 (top elevation 2.3m, bottom elevation -12.7m) at 1m~1.1m outside the base line of the cap 11, vertically set 1 row of steel surrounding purlin 12 and steel support plate 14, the steel surrounding purlin 12 and steel support plate 14 are both set at 1.80m below the top of the steel sheet pile 1 using 400x400 H-shaped steel, and a 15cm thick C15 concrete cushion is provided at the bottom of the cap.

[0033] As Figure 3 and Figure 4 and Figure 5 and Figure 6 , the cap 11 construction includes steel reinforcement binding on the concrete cushion 111, then pre-connecting the pier body 15 steel reinforcement with the cap 11 steel reinforcement, i.e. implementing the step of pre-burying the pier body 15 steel reinforcement, and supporting the formwork connected with each other around the cap 11 steel reinforcement, and pouring the cap 11.

[0034] As Figure 7 and Figure 8 and Figure 9 , the formwork includes a steel plate 16 facing the side of the cap 11 steel reinforcement and a plurality of vertical distribution of vertical plates provided on the side of the steel plate 16 away from the cap 11 steel reinforcement, at this time the cap 11 is rectangular, the steel plate 16 around the periphery of the cap 11 is in the shape of a rectangle, the upper end of the vertical plate extends out of the upper end of the steel plate 16, the vertical columns on the opposite two steel plates 16 are connected by tensioning the tie steel 161, the purpose is to facilitate providing stable tension to the opposite two formworks, at this time the vertical columns on the opposite two steel plates 16 are both provided with tie steel 161, so that the tie steel 161 has two layers of tie steel 161 distributed vertically and horizontally above the cap 11, for example: the lower layer is longitudinal tie steel 161, and the upper layer is transverse tie steel 161, the adjacent two steel plates 16 are connected by angle steel 162, the angle steel 162 is distributed along the height direction of the steel plate 16, and is connected with the side surface of each steel plate 16 by bolts, thereby fixing the steel plate 16 in the shape of a rectangle.

[0035] In addition, in order to increase the strength of the steel plate 16, a transversely distributed horizontal rib can also be provided on the side of the steel plate 16 away from the cap 11, the horizontal rib is distributed along the length direction of the steel plate 16, and the vertical plate is provided on the horizontal rib.

[0036] As Figure 12When the steel sheet pile 1 on one side of the bearing platform 11 is driven to a position less than 1 meter from the outer side of the bearing platform 11 and less than the thickness of the steel plate 16 and the vertical plate, the above-mentioned situation is caused by the deviation of the driving or the hard block in the riverbed, etc., which can only be avoided. The formwork at this position is replaced by the following structure: a plurality of foam boards 17 closely attached to each other between the steel sheet pile 1 and the reinforcement of the bearing platform 11, each foam board 17 is vertically distributed and arranged along the length direction of the bearing platform 11, one side of each foam board 17 abuts against the steel sheet pile 1, and the other side has two end faces abutting against the steel plate 16 on the adjacent formwork. At this time, the steel plate 16 abuts the foam board 17 against the steel sheet pile 1, and the height of the foam board 17 is greater than the height of the steel plate 16. The vertical plate on the formwork corresponding to the foam board 17 is provided with an abutting rod 163 abutting against the side surface of the steel sheet pile 1. At this time, the abutting rod 163 provides support force to the formwork connected with the abutting rod 163, so that the position of the formwork is stable during the pouring of the bearing platform 11. The arrangement of each foam board 17 facilitates the disassembly and reuse of other formworks after the pouring and forming of the bearing platform 11. Since the foam board 17 is located between the steel sheet pile 1 and the bearing platform 11, it cannot be disassembled, and a separation surface is formed between the bearing platform 11 and the steel sheet pile 1, which facilitates the subsequent pulling out of the steel sheet pile 1.

[0037] As Figure 8 and Figure 9 Each vertical plate includes two mounting plates 164 connected with the plate surface of the steel plate 16 and having a U-shaped cross section. The U-shaped openings of the two mounting plates 164 are distributed away from each other, i.e., the two opposite vertical sides of the mounting plate 164 are distributed away from the vertical sides on the other mounting plate 164, and one of the two opposite vertical sides of the mounting plate 164 is detachably connected with the steel plate 16 by a screw. At this time, the vertical sides of the two mounting plates 164 are in contact with the steel plate 16. There is a gap between the two mounting plates 164 of each vertical plate, and the tensioning reinforcement 161 passes through the gap.

[0038] As Figure 8 and Figure 9 and Figure 10 and Figure 11, the adjusting member comprises a horizontal plate 18 placed on the vertical side walls of each two mounting plates 164, the horizontal plate 18 is located above the steel plate 16 and is used for supporting the tensioned steel bar 161, a pressing plate 181 is placed on the vertical side walls of each two mounting plates 164, the pressing plate 181 and the horizontal plate 18 are located on the two sides of the mounting plate 164 respectively, the horizontal plate 18 is provided with a prism 182 on the side facing the pressing plate 181, the prism 182 is located in the gap between the two mounting plates 164, a threaded rod 183 is coaxially arranged on the prism 182, the pressing plate 181 is provided with a through hole through which the threaded rod 183 passes, the threaded rod 183 is threadedly connected with a locking block 184 which is in contact with the pressing plate 181 after passing through the pressing plate 181, the pressing plate 181 is provided with an insertion groove 185 at the upper end surface for the tensioned steel bar 161, the groove opening of the insertion groove 185 extends out of the upper end surface of the pressing plate 181, the groove bottom is used for the insertion of the tensioned steel bar 161, when the tensioned steel bar 161 has not been straightened and inserted into the insertion groove 185, the tensioned steel bar 161 is in contact with the upper end surface of the horizontal plate 18, the outer wall of the two ends of the tensioned steel bar 161 is provided with a thread, and a screwing block 186 located on the side of the pressing plate 181 away from the horizontal plate 18 is connected through the thread. The specific structure of the tensioned steel bar 161 can be round steel, and the two ends of the round steel in the length direction are both welded with screw rods.

[0039] As Figure 8 and Figure 9 and Figure 10 and Figure 11 , the working process of the adjusting member: after the bearing platform 11 formwork is installed, when the tensioned steel bar 161 needs to be installed, the first step is to install the horizontal plate 18 and the pressing plate 181 from top to bottom in the two mounting plates 164, at this time, the horizontal plate 18 and the pressing plate 181 are respectively located on the two sides of the opposite vertical side edges of the two mounting plates 164, the horizontal plate 18 is located above the steel plate 16, which is convenient for supporting the subsequent tensioned steel bar 161, the prism 182 and the threaded rod 183 enter the gap between the two mounting plates 164, when the horizontal plate 18 and the pressing plate 181 are moved into position, the locking block 184 is rotated to gradually reduce the distance between the horizontal plate 18 and the pressing plate 181, so that the horizontal plate 18 and the pressing plate 181 are respectively in contact with the two vertical side edges of the mounting plate 164, at this time, the groove opening of the insertion groove 185 is distributed upward; The second step is to lay the tensioned steel bar 161 between the two opposite steel plates 16, at this time, the tensioned steel bar 161 between the two steel plates 16 is called longitudinal steel bar, the two ends of the longitudinal steel bar are respectively placed in the gap between the two mounting plates 164, at this time, the end of the tensioned steel bar 161 also enters the insertion groove 185, and the tensioned steel bar 161 is placed on the upper end surface of the horizontal plate 18; Third step: after the longitudinal reinforcement is laid, the rotating block 186 is located on the side of the pressing plate 181 away from the horizontal plate 18, and the user rotates the rotating block 186 to move the rotating block 186 close to the pressing plate 181, at this time the rotating block 186 is pressed on the pressing plate 181, and as the rotating block 186 rotates, the tensioning force is generated on the tensioning reinforcement 161, and then the longitudinal reinforcement is straightened, at this time one person can perform tensioning, the rotating block 186 on one steel plate 16 can be rotated first, so that one end of the tensioning reinforcement 161 is rotated out, and then the rotating block 186 on the steel plate 16 corresponding to the tensioning reinforcement 161 is rotated, until the tensioning reinforcement 161 is straightened; in addition, two people can rotate the rotating blocks 186 at both ends of the tensioning reinforcement 161 at the same time; the construction and installation method is mostly used, and the use range is increased. Fourth step: after the lower longitudinal reinforcement is straightened, the upper horizontal reinforcement is laid on the other two opposite steel plates 16, so that the horizontal reinforcement is laid on the longitudinal reinforcement, and the two ends of the horizontal reinforcement enter between the two mounting plates 164 and are laid on the horizontal plate 18, at this time the height of the horizontal plate 18 is greater than the height of the horizontal plate 18 on which the longitudinal reinforcement is installed, and then the rotating block 186 is rotated to straighten the horizontal reinforcement. At this time, the horizontal reinforcement is close to the longitudinal reinforcement.

[0040] This completes the installation of the tensioning reinforcement 161. As Figure 8 And Figure 9 And Figure 10 And Figure 11 The horizontal plate 18 and the pressing plate 181 are connected through the threaded rod 183 and the prism 182, so that the horizontal plate 18 and the pressing plate 181 abut on the mounting plate 164, and then the height position of the horizontal plate 18 and the pressing plate 181 is changed, and the installation position of the longitudinal reinforcement and the horizontal reinforcement is adjusted.

[0041] In addition, a lower tensioning reinforcement can be provided inside the opposite formwork according to selection. The two ends of the tensioning reinforcement extend out of the formwork and are locked by the nut.

[0042] As Figure 12The vertical plate provided with the abutting rod 163 has a mounting plate 164, at this time, the mounting plate 164 has high versatility, and the height of the foam plate 17 is greater than the height of the bearing platform 11, and the side of the foam plate 17 facing the steel sheet pile 1 is provided with a plurality of vertical plates 19 which are inserted into each other, the vertical plate 19 can be a wooden plate, the plate surfaces of the vertical plates 19 are flush, and the adjacent vertical plates 19 are installed through the cooperation of the plug and the slot, the purpose of this design is to increase the flatness of the foam plate 17 and the steel sheet pile 1, so as to facilitate the pouring and forming of the bearing platform 11, the side edges of the two vertical plates 19 farthest apart are provided with extension plates 191 extending in the direction of the formwork, one end of the steel plate 16 of the adjacent formwork extends into the extension plate 191, and the plate surface of the steel plate 16 abuts against one side of the foam plate 17, at this time, the design of the extension plate 191 facilitates the entry of the steel plate 16 and the abutment against the foam plate 17, so that the steel plate 16 on the formwork provides a limiting force to the two vertical plates 19 farthest apart, and after the formwork is pulled out upward after the pouring and forming of the bearing platform 11, there is a gap between the extension plate 191 and the foam plate 17, and the height of each vertical plate 19 is greater than the height of the foam plate 17, which facilitates the upward lifting of each vertical plate 19, so that there is a gap between the foam plate 17 and the steel sheet pile 1, which is more convenient for pulling out the steel sheet pile 1 later.

[0043] As Figure 3 and Figure 4 and Figure 5 and Figure 6 The steel enclosing purlin 12 and the steel supporting plate 14 are symmetrically and intervally removed, so as to reduce the local deformation and cracking caused by the excessive release of instantaneous pre-stress. The steel enclosing purlin 12 in the same combined foundation pit 13 is welded with a thick steel pad plate 121 in a triangular shape when the relative distance of the steel enclosing purlin 12 is close.

[0044] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application belong to the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A method for constructing a combined steel sheet pile cofferdam for a deep foundation pit in a river dam section, characterized in that: The following processes are included: Steel sheet pile positioning → steel sheet pile driving → initial excavation → steel purlin installation → steel support plate installation → secondary excavation → cushion layer construction → foundation pile construction → backfilling after completion → removal of steel support plates and steel purlins → removal of steel sheet piles; Positioning and driving of steel sheet piles: After marking the pier cap and verifying that they are correct, the steel sheet pile driving position is set out at a distance of 1m to 1.1m from the outer edge of the cap foundation. The steel sheet piles are driven directly. Before driving, the edge of the steel sheet piles is set out and the steel sheet piles are driven one by one under the premise that they are vertical. The pier caps are marked and classified as follows: one cap combination, two cap combinations, three cap combinations...N cap combinations, and the outer frame of the combination: the steel sheet piles are driven 1 meter to 1.1 meters outside the adjacent cap foundation edges at the position without interference, and the parts with interference are excavated together and connected in the same combined foundation pit.

2. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section according to claim 1, characterized in that: The excavation of earthwork is divided into two layers from top to bottom, namely the initial excavation: the first layer of soil is excavated to 0.5m below the steel support plate, using ordinary excavators for excavation, and the earthwork is directly transported out by earthmoving trucks; After the first layer of soil is excavated, the steel purlin and steel support plate are constructed. After the steel support plate is constructed, a long-arm excavator is used to excavate the second layer of soil, i.e., secondary excavation. After excavation to the pit bottom elevation, the concrete cushion layer is poured immediately. After the concrete strength of the concrete cushion layer reaches the requirement, the subsequent pile head removal and foundation foundation construction can be carried out.

3. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section as claimed in claim 2, characterized in that: Installation of steel perimeter purlins and steel support plates: Measure and mark the bottom elevation of the steel perimeter purlins on the exposed steel sheet piles during the initial excavation, and weld the corbels; hoist the steel perimeter purlins onto the corbels and weld them. At this time, the steel perimeter purlins are distributed around the inner wall of the steel sheet piles and are closed in a ring. Steel support plates are installed between adjacent and mutually perpendicular steel perimeter purlins, and the two ends of the steel support plates are welded to the steel perimeter purlins.

4. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section according to claim 2, wherein: The foundation cap construction includes tying foundation cap steel bars on a concrete cushion layer, pre-connecting the pier body steel bars with the foundation cap steel bars, and then setting up interconnected formwork around the foundation cap steel bars and casting the foundation cap.

5. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section as claimed in claim 4, characterized in that: The formwork includes a steel plate facing the side of the base reinforcement and a plurality of vertically distributed vertical plates arranged on the side of the steel plate away from the base reinforcement. The upper end of the vertical plate extends out of the upper end of the steel plate. The columns on the two opposite steel plates are tightened and connected by tensioning steel bars. The adjacent steel plates are connected by angle steels. The angle steels are distributed along the height direction of the steel plates and are connected to the sides of each steel plate by bolts.

6. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section according to claim 5, characterized in that: When the steel sheet piles on one side of the pedestal are driven into a position less than 1 meter away from the outside of the edge of the pedestal foundation and the distance is less than the thickness of the steel plate plus the vertical plate, the formwork at this location is replaced by the following structure: it includes a plurality of foam boards that fit tightly together between the steel sheet piles and the pedestal steel bars, each of the foam boards is vertically distributed and arranged along the length direction of the pedestal, one side of each foam board is in contact with the steel sheet pile, and both end faces of the other side are in contact with the steel plate on the adjacent formwork, and the vertical plates on the formwork corresponding to the foam boards are provided with contact rods that horizontally contact the side faces of the steel sheet piles.

7. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section according to claim 6, characterized in that: Each of the vertical plates includes two mounting plates connected to the surface of the steel plate and having a U-shaped cross section, the U-shaped openings of the two mounting plates being arranged in opposite directions, and one of the two opposite vertical sides of the mounting plate is detachably connected to the steel plate by screws, and a gap is provided between the two mounting plates of each vertical plate for the tension steel bars to pass through; Each of the two mounting plates is provided with an adjusting piece for adjusting the position of the tensioning steel bars.

8. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section according to claim 7, characterized in that: The adjusting member includes a horizontal plate placed on the vertical side walls of each two mounting plates, the horizontal plate being located above the steel plate and used to support the tensioned steel bars, and a pressure plate being placed on the vertical side walls of each two mounting plates, the pressure plate and the cross plate being respectively located on both sides of the vertical side walls of the mounting plates relative to each other, and the cross plate is provided with a prism on the side facing the pressure plate, a threaded rod being coaxially provided on the prism, a through hole for the threaded rod to pass through being provided on the pressure plate, the threaded rod being threadedly connected to a locking block that contacts the pressure plate after passing through the pressure plate, a placement groove for the tensioned steel bars to be placed on the upper end face of the pressure plate, when the tensioned steel bars have not been straightened and placed in the placement groove, the tensioned steel bars contact the upper end face of the cross plate, the outer walls of both ends of the tensioned steel bars are provided with threads, and are threadedly connected to a tightening block located on the side of the pressure plate away from the cross plate.

9. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section according to claim 7, wherein: The vertical plate provided with the interference rod has a mounting plate, and the height of the foam plate is greater than the height of the base. The side of the foam plate facing the steel sheet pile is provided with a number of vertical plates connected to each other, and the two sides of the vertical plates farthest away are provided with extension plates extending toward the template. One end of the steel plate of the adjacent template extends into the extension plate, and the plate surface of the steel plate interferes with one side of the foam plate.

10. The method for constructing a combined steel sheet pile cofferdam for a deep foundation pit of a river dam section as claimed in claim 3, characterized in that: Removal of steel purlins and steel support plates: Steel purlins and steel support plates should be removed at symmetrical intervals to reduce local deformation and cracking caused by excessive instantaneous prestress release; When the steel purlins are in the same combined foundation pit and are close to each other, triangular thick steel pads are welded between them.

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