Deepwater composite cofferdam system suitable for complex embankment area of tidal river channel

Abstract

The utility model discloses a deepwater composite cofferdam system suitable for a tidal river complex embankment area, which comprises a Larsen steel sheet pile cofferdam system, a cast-in-situ bored pile support system and a concrete steering block, and the Larsen steel sheet pile cofferdam system comprises U-shaped Larsen steel sheet piles and an inner support system; the cast-in-situ bored pile supporting system is arranged between the Larsen steel sheet pile cofferdam system and the flood control wall and is a pipe gallery composed of a plurality of soil retaining and supporting cast-in-situ bored piles. The end parts of two side arms of the U-shaped Larsen steel sheet pile are correspondingly sealed with the two ends of the cast-in-situ bored pile support system respectively; and the cast-in-situ bored pile supporting system is connected with the enclosing purlins into a whole through concrete steering blocks at the positions as high as the enclosing purlin supports. Therefore, the utility model can effectively prevent the surrounding soil body of the flood control wall from collapsing towards the quay wall in the main pier construction operation process, ensure the safety of the main pier construction operation, and improve the construction economy of the deepwater composite cofferdam system.

Description

Technical Field

[0001] The utility model relates to a deep-water composite cofferdam system suitable for complex embankment areas of tidal rivers, belonging to the technical field of bridge engineering structure design. Background Art

[0002] When designing the super-large bridge across Fenghua River in Section IV of the Yinzhou Avenue Expressway (Airport Road-Yinheng Line) project in Ningbo, Zhejiang, the main pier on the east side was designed in the embankment area of ​​the main stream of Fenghua River based on the following considerations:

[0003] ① The Yinzhou Avenue Expressway adopts a split structure of upper and lower sections when crossing the Fenghua River, that is, river crossing passages are set up on both sides of the existing Yinzhou Bridge, so the elevated road is bifurcated;

[0004] ② The main bridge is a steel truss, which should be kept as straight as possible to reduce bending, so the total length of the main bridge should not exceed 400m;

[0005] ③ The main span crosses the Fenghua River, the west side span crosses the Hengba River, and the east side span crosses the Xiku River. The main span is not less than 150m due to flood control and navigation requirements, and the main pier is aligned with the old bridge pier as much as possible; the side span is not more than 80% of the main span, not less than 60% of the main span, and try to keep a gap of 3~4m with the old bridge - considering that the span of the old bridge is only 100m, if the west main pier is aligned with the old bridge, the east main pier will be in the Xiku River, and the east side span bend will overlap with the existing bridge, which is unacceptable.

[0006] Note: The elevated route cannot be adjusted to either side because the south side is permanent farmland and the north side involves 110kV power pipelines.

[0007] The embankment of the main stream of Fenghua River is different from that of ordinary river channels. The embankment conditions in this section are extremely complex (see Appendix Figure 1 ), which is reflected in the following 6 points:

[0008] 1) The mainstream of Fenghua River is a typical tidal river channel with a high-tidal and low-tidal level difference of up to 3.74m. Therefore, when constructing a cofferdam in this area, the load state of the cofferdam varies greatly;

[0009] 2) The Fenghua River embankment is a typical embankment separation structure, and the distance between embankments is small, less than 5.0m;

[0010] 3) Due to architectural design requirements, the main pier is located outside the flood control embankment, and 1 / 2 of the main pier is located in the mainstream, and 1 / 2 is located in the river bank, so the target abutment of the main pier coincides with the existing bank wall. Therefore, the existing embankment structure must be cleared before the pier is implemented;

[0011] 4) The bank wall is located in the scour area and has been built many times, including riprap to squeeze out silt, pine piles, etc.;

[0012] 5) The flood control wall must not be damaged during the construction period, especially the inclination caused by foundation settlement, otherwise it will not meet the requirements of water conservancy flood control - during the obstacle clearing stage, it may cause the flood control embankment to slide (the flood control embankment adopts an expanded foundation and has extremely poor lateral resistance);

[0013] 6) Complex geological conditions, such as Figure 2 As shown in the figure, the surface layer of 10m is silty clay, which is a typical soft soil layer; 18m~22m below the riverbed is a medium-weathered rock layer, which is not only inaccessible to temporary steel sheet piles or lock-mouth steel pipe piles (which means that the cofferdam is only set 18~22m below the riverbed), but also difficult for GPS drilling rigs to enter the rock - if impact drilling rigs are used, the construction efficiency will be greatly reduced, the construction cost will be greatly increased, and it is not suitable for the existing retaining support structure. In the riverbank area, cement mixing piles are used in some areas due to the need for previous embankment construction.

[0014] In order to ensure the completion of the construction of the main pier cap and columns under the above conditions, the conventional steel box cofferdam solution was adopted. With the help of the steel box cofferdam's own bearing capacity and rigidity, the coordination site faced many difficulties and challenges:

[0015] 1. Conventional steel casing operations require the use of completed bored piles (steel casing) to achieve sinking. Because the main pier cap overlaps with the existing embankment, the bored piles cannot be implemented without clearing the existing embankment.

[0016] 2. The steel box cofferdam is usually divided into several sections along the height direction, and the height of a single section is usually 4.0m~7.5m. If calculated based on 4.0m, the weight of a single section exceeds 65 tons, and the operating radius is 21m, a 500-ton crawler crane is required for lifting (the waterfront section is a scouring area with frequent ship traffic, so a floating crane cannot be used);

[0017] 3. Before the existing bank wall is cleaned, it is affected by riprap, pine piles, etc., so a long-arm excavator is required to clear and sink at the same time;

[0018] 4. The existing abutment has Fenghua River channel on one side, Yinzhou Bridge on the other, park road between flood control wall and bank wall (only for long-arm excavator operation, not capable of 500-ton crawler crane), and flood control wall and Xiku River on one side. Crawler crane can only rely on trestle (across Xiku River and terminate at flood control wall) as operating platform. At present, there is no trestle in China that meets the 170-ton single pile bearing capacity operation requirements.

[0019] In summary, it is necessary to develop a new support system to meet the actual needs of engineering construction. Utility Model Content

[0020] The utility model aims to provide a deep-water composite cofferdam system suitable for complex embankment areas of tidal rivers, so as to assist the viaduct in carrying out main pier construction in complex embankment areas of tidal rivers, and can effectively prevent the surrounding soil of the flood control wall from collapsing toward the bank wall during the main pier construction, thereby ensuring the safety of the main pier construction and improving the economy of the deep-water composite cofferdam system construction.

[0021] In order to achieve the above technical objectives, the utility model will adopt the following technical solutions:

[0022] A deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers is used to assist the main pier construction of bridges in complex embankment areas of tidal rivers. The complex embankment areas of tidal rivers are provided with quay walls and flood control walls. The deepwater composite cofferdam system includes a Larsen steel sheet pile cofferdam system, a bored cast-in-place pile support system and a concrete turning block, wherein:

[0023] The Larsen steel sheet pile cofferdam system includes an inner support system and U-shaped Larsen steel sheet piles arranged in a semi-enclosed shape outside the inner support system; the inner support system is arranged in the upper area inside the U-shaped Larsen steel sheet piles, including a purlin and a purlin support system, the purlin is rectangular, and the purlin support system is arranged in the purlin, with at least one layer;

[0024] The bored cast-in-place pile support system is arranged between the Larsen steel sheet pile cofferdam system and the flood control wall. It is a pipe gallery composed of several retaining support bored cast-in-place piles.

[0025] The closed end of the U-shaped Larsen steel sheet pile is arranged on the water side of the complex embankment area of ​​the tidal river channel, and the two side arms of the U-shaped Larsen steel sheet pile point to the bored pile support system, and the ends of the two side arms of the U-shaped Larsen steel sheet pile are respectively sealed with the two ends of the bored pile support system;

[0026] Each retaining support bored cast-in-place pile of the bored cast-in-place pile support system is connected to the purlin through a concrete turning block at a position at the same height as the purlin support system.

[0027] Preferably, each layer of the purlin support system includes four purlin supports, and both ends of each purlin support are integrally connected to a group of corresponding adjacent edges of the purlin through purlin reinforcements.

[0028] Preferably, two adjacent bored cast-in-place retaining piles are spliced ​​into one piece by concrete grouting on the side adjacent to the purlin, and are connected by high-pressure jet grouting piles on the bank side.

[0029] Preferably, the concrete turning block comprises a pre-buried steel cage, one end of which is provided with a first connecting bar for each retaining support bored pile; the pre-buried steel cage is connected to the retaining support bored pile at the corresponding position through the first connecting bar.

[0030] Preferably, both side arm ends of the U-shaped Larsen steel sheet pile are sealed to the bored pile support system through a water-stop curtain.

[0031] Preferably, the ends of the two side arms of the U-shaped Larsen steel sheet pile extend 1-2 steel sheet piles outward after intersecting with the bored pile support system to form the water-stop curtain.

[0032] Preferably, the outer side of the water-stop curtain is connected to the retaining support bored piles at the end of the bored pile support system through corner reinforcement piles.

[0033] Preferably, the top and bottom elevations of the high-pressure jet grouting piles are consistent with the top and bottom elevations of the retaining support bored cast-in-place piles.

[0034] Preferably, the pile tops of the soil retaining and supporting bored cast-in-place piles are spliced ​​into one piece through a cap beam.

[0035] Based on the above technical objectives, compared with the prior art, the utility model has the following advantages:

[0036] The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers described in the utility model, on the one hand, is provided with a bored cast-in-place pile support system between the Larsen steel sheet pile cofferdam system and the flood control wall, and the bored cast-in-place pile support system is a pipe gallery formed by evenly arranging a number of retaining support bored cast-in-place piles, and on the other hand, it also optimizes the existing Larsen steel sheet pile cofferdam system, so that the bored cast-in-place pile support system and the Larsen steel sheet pile cofferdam system are structurally integrated into a cofferdam and support complex. It can be seen that the utility model effectively supports the soil around the flood control wall by arranging the deepwater composite cofferdam system, prevents the soil around the flood control wall from collapsing toward the cofferdam construction position during the excavation of the Larsen steel sheet pile cofferdam system, improves the safety of cofferdam construction, and ensures the safety of construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a common example of complex embankment in tidal rivers;

[0038] Figure 1 Middle: 1-flood control wall; 2-railing; 3-bank wall; 4-long pine piles; 5-ground beam; 6-riprap accumulation area;

[0039] Figure 2 It is a common geological cross-section structural map of riverbank areas;

[0040] Figure 2 Middle: 1-flood control wall; 2-railing; 3-bank wall; 4-long pine pile; 5-ground beam; 6-riprap accumulation area; 71, miscellaneous fill layer; 72, plain fill layer; 73, silty clay layer; 74, silty clay layer; 75, moderately weathered silty mudstone;

[0041] Figure 3 It is a vertical structural diagram of a deep-water composite cofferdam system (foundation pit excavation stage) suitable for complex embankment areas of tidal rivers described in the utility model;

[0042] Figure 4 It is a vertical structural diagram of a deep-water composite cofferdam system (column construction stage) suitable for complex embankment areas of tidal rivers described in the utility model;

[0043] Figure 5 It is a plan view of the deep-water composite cofferdam system suitable for the complex bank area of ​​tidal river channels described in the utility model;

[0044] Figure 6 It is an enlarged structural schematic diagram of the concrete turning block between the perimeter purlin support and the bored pile support system;

[0045] Figure 3-6 Middle: 81-U-shaped Larsen steel sheet pile; 82-peripheral purlin; 821-peripheral purlin reinforcement; 822-corner reinforcement; 83-peripheral purlin support system; 84-main pier column; 85-main pier bored pile; 86-main pier cap; 87-cap bottom cushion; 9-bored pile support system; 91-retaining support bored pile; 92-high-pressure jet grouting pile; 93-concrete caulking; 101-corner reinforcement pile; 102-concrete turning block; 103-first connecting bar. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means any restriction on the utility model and its application or use. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model. Unless otherwise specified, the relative arrangement, expressions and numerical values ​​of the components and steps described in these embodiments do not limit the scope of the utility model. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but in appropriate cases, the techniques, methods and equipment should be regarded as part of the specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, not as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0047] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations).

[0048] like Figures 3 to 6 As shown, the deepwater composite cofferdam system suitable for the complex embankment area of ​​the tidal river described in the utility model is used to assist the main pier construction of the bridge in the complex embankment area of ​​the tidal river. The complex embankment area of ​​the tidal river is provided with a quay wall and a flood control wall. The deepwater composite cofferdam system includes a Larsen steel sheet pile cofferdam system, a bored cast-in-place pile support system 91 and a concrete turning block 102, wherein:

[0049] The Larsen steel sheet pile cofferdam system is arranged on the water side (i.e., the river side, adjacent to the river) of the complex embankment area of ​​the tidal river channel. In fact, based on the actual construction drawings, the Larsen steel sheet pile cofferdam system is designed at the location of the quay wall in the complex embankment area of ​​the tidal river channel, and the bored cast-in-place pile support system 91 is arranged between the Larsen steel sheet pile cofferdam system and the flood control wall.

[0050] The purpose of arranging the bored cast-in-place pile support system 91 in the utility model is to ensure the overall stability of the existing flood control wall when clearing obstacles in the pier area.

[0051] To this end, the bored pile support system 91 needs to meet the following functional requirements:

[0052] 1) It has sufficient bearing capacity to resist the uneven lateral earth pressure on both sides of the bored pile support system 91 and to bear the lateral earth pressure generated by the operating machinery on the side of the flood control wall;

[0053] 2) It has sufficient rigidity to ensure that the lateral displacement of the flood control wall is no more than 5mm, avoiding the cracking and damage of the original concrete flood control wall caused by foundation deviation, and maintaining the original flood control function;

[0054] 3) The construction of bored pile support system 91 has little impact on the existing flood control wall, and the ground acceleration during construction should not exceed 5m / s 2 . Reduce the vibration damage of acceleration to the original concrete flood control wall.

[0055] Based on the above functional requirements, the utility model transforms the bored cast-in-place pile support system 9 into a pipe gallery composed of a plurality of retaining support bored cast-in-place piles 91 .

[0056] Since the utility model arranges a bored cast-in-place pile support system 9 used as retaining support between the Larsen steel sheet pile cofferdam system and the existing flood control wall, the limitation of the construction site on the construction of the deepwater cofferdam system is basically broken through. However, in view of the geological conditions of the construction site itself (such as the small bedrock depth and poor geological conditions of the overburden), how to ensure that the bored cast-in-place pile support system 9 formed by the construction meets the above functional requirements is a technical problem that the utility model needs to solve.

[0057] Based on the construction site where the utility model is located, without considering the influence of the Larsen steel sheet pile cofferdam system, the boundary conditions of the bored pile support system 9 are determined, mainly including the following points:

[0058] 1) Determine the design elevation of the top of the bored pile 91 for retaining support:

[0059] The top design elevation of the bored cast-in-place pile 91 for retaining support is +2.60m, 80cm higher than the navigation water level elevation +1.83m (to resist the influence of astronomical tides, not floods), and is set according to the requirements of "bank wall";

[0060] 2) Determine the ground elevation of the bored pile support system 9:

[0061] The ground elevation of the bored pile support system 9 is the existing ground elevation, calculated as +3.50m, that is, no soil is unloaded or piled, and the original state is maintained;

[0062] 3) Determine the construction location of the bored pile support system 9:

[0063] The bored cast-in-place pile support system 9 is arranged as close as possible to the construction area of ​​the Larsen steel sheet pile cofferdam system and away from the existing flood control wall. During actual construction, the net distance between the bored cast-in-place pile support system 9 and the Larsen steel sheet pile cofferdam system can be set to 0.5m.

[0064] 4) Determine the downstream bottom elevation of the bored pile support system 9:

[0065] According to the preliminary exploration data, the bottom elevation of the original shore wall structure layer is about -0.50m. Considering the over-excavation effect of the construction work, the downstream bottom elevation of the bored pile support system 9 is calculated as -0.70m.

[0066] 5) Determine the lowest water level in tidal rivers:

[0067] The lowest water level in the tidal river channel is about -1.76m, and if it is unfavorable, it will be calculated as -1.8m.

[0068] Based on the boundary conditions of the bored pile support system 9, it can be seen that the pile length of the retaining support bored pile 91 described in the utility model is limited. Therefore, when designing the bored pile support system 9, the following contents need to be paid attention to:

[0069] 1) Pile diameter and spacing of bored cast-in-place piles 91 for retaining support:

[0070] The larger the diameter of bored piles, the higher the bearing capacity and stiffness of a single pile, and the larger the corresponding spacing (lateral earth pressure within the subordinate width range); conversely, the smaller the pile diameter, the lower the bearing capacity and stiffness of a single pile, and the spacing needs to be reduced to reduce the lateral earth pressure allocated to a single pile. Therefore, while meeting the functional requirements, economic indicators (concrete volume and corresponding steel bar usage, where the steel bar configuration must simultaneously meet the bored pile's own bearing capacity requirements and crack width limit requirements) are key factors in evaluating technical solutions.

[0071] Preliminary analysis shows that the overall stability of the Φ0.8m@1.5m type, Φ1.0m@2.0m type, Φ1.2m@2.5m type, and Φ1.5m@3.3m type is relatively close. After carrying capacity evaluation and economic analysis of these four types of layouts, the pile diameter and spacing of the bored cast-in-place retaining piles 91 are selected as follows:

[0072] The single pile diameter of the retaining bored cast-in-place pile 91 is 1.5m, the pile spacing is 3.3m, the pile top elevation is +2.60m, the pile bottom elevation is -19.4m, and the single pile length is 22m.

[0073] 2) Retaining problems of 91 bored piles:

[0074] Due to the need for a certain distance between bored piles in the hole-making process to prevent the soil layer on the side of the hole from collapsing, it is inevitable that there will be a certain distance between bored piles. After the bored piles reach the designed strength, the soil layer behind the pile body will flow into the foundation pit along the gap between the bored piles. For this reason, high-pressure rotary jet piles 92 are installed between the bored piles to prevent the soil layer from flowing and to stop water.

[0075] The retaining support bored pile 91 is 2.25m away from the cap near the river channel, that is, assuming that the width of the Larsen steel sheet pile cofferdam system is 0.75m, the inner edge of the Larsen steel sheet pile cofferdam system is 1.0m away from the edge of the cap. A 0.5m gap is reserved between the retaining support bored pile 91 and the outer edge of the cofferdam.

[0076] A high-pressure jet grouting pile 92 with a diameter of 0.6 m and a depth of 22 m is driven between the retaining support bored piles 91 . The top and bottom elevations of the high-pressure jet grouting pile 92 are consistent with those of the retaining support bored piles 91 .

[0077] In the present invention, after the end of the U-shaped Larsen steel sheet pile 81 is sealed with the bored pile support system 91 , a corner reinforcement pile 101 is arranged outside the sealing position between the U-shaped Larsen steel sheet pile 81 and the bored pile support system 91 .

[0078] In order to ensure that the end of the U-shaped Larsen steel sheet pile 81 is sealed with the bored pile support system 91, the utility model adds 1 to 2 steel sheet piles as a water-stop curtain outside the intersection of the end of the U-shaped Larsen steel sheet pile 81 and the bored pile support system 91.

[0079] 3) The integrity of the bored cast-in-place piles 91 for retaining support. The utility model arranges a cap beam on the top layer of each bored cast-in-place pile 91 for retaining support, so that each bored cast-in-place pile 91 for retaining support is connected to form a whole. The design basis of the cap beam includes: ① The top elevation should be flush with the original soil elevation at the existing bank wall, that is, the top elevation of the retaining support system should not be higher than the original ground elevation at the existing bank wall, because it is useless and wasteful; ② The bottom elevation should depend on the seepage effect of the highest tidal water level during the construction period (the highest water level of the tidal river channel within 30 days is different), that is, during the construction stage of the cap beam (excavation of the working surface, removal of the pile head, steel bar binding, formwork support, concrete pouring, etc.), the working surface should be kept dry; ③ The width of the cap beam is usually "extended 200mm~250mm on both sides of the pile diameter" - in essence, the cap beam is only a structural requirement, and its calculation and design requirements are relatively low, so the determination of its bottom elevation is particularly critical. According to calculations, the width of the crown beam is 2.0m, the height is 1.5m, and the bottom elevation of the crown beam is +1.10m, which can meet the seepage stability requirements.

[0080] In addition, the present invention also connects the two adjacent earth retaining support bored cast-in-place piles 91 to the purlin 82 on one side adjacent to the purlin 82 through concrete caulking 93, thereby solving the integrity of the connection between the Larsen steel sheet pile cofferdam system and the bored cast-in-place pile support system 9.

[0081] After the above-mentioned bored cast-in-place pile support system 91 is completed, the construction machinery can operate at the rear side of the retaining support bored cast-in-place piles 91, clear the obstacles within the target foundation range, and then deploy a conventional drilling operation platform, using a conventional positive cycle rotary drilling process to complete the operation of 9 1.5m main pier bored cast-in-place piles 85.

[0082] Since the Larsen steel sheet pile has a low rigidity, the Larsen steel sheet pile cofferdam system itself cannot transmit tidal water pressure. Therefore, it is necessary to optimize the existing Larsen steel sheet pile cofferdam system so that it can be integrated with the bored cast-in-place pile support system 91 to form an integral structure. Specifically:

[0083] The Larsen steel sheet pile cofferdam system described in the utility model includes a U-shaped Larsen steel sheet pile 81 and an internal support system, that is, the utility model changes the existing rectangular Larsen steel sheet pile into a U-shaped Larsen steel sheet pile 81, so that the closed end of the U-shaped Larsen steel sheet pile 81 is arranged on the water side of the complex embankment area of ​​the tidal river channel, and the two side arms of the U-shaped Larsen steel sheet pile 81 point to the bored cast-in-place pile support system 9, and the two side arm ends of the U-shaped Larsen steel sheet pile 81 are respectively sealed with the two ends of the bored cast-in-place pile support system 91. It can be seen that the Larsen steel sheet pile cofferdam system described in the utility model cancels the Larsen steel sheet pile on the side adjacent to the bored cast-in-place pile support system 91, and is only supported by three sides of Larsen steel sheet piles, and together with the retaining support bored cast-in-place pile 91 support system 9, it constitutes the cofferdam body. The structure of the internal support system is similar to that of the internal support system in the existing Larsen steel sheet pile cofferdam system, which is arranged on the inner side of the U-shaped Larsen steel sheet pile 81 and located in the upper area of ​​the U-shaped Larsen steel sheet pile 81, including the purlin 82 and the purlin support system 83; the purlin support system 83 and the purlin 82 are connected as a whole through the purlin reinforcement 821. The number of purlin support systems 83 can be one (one layer) or two (layers). When the number of purlin support systems 83 is two, the two purlin support systems correspond to the first and second purlin support systems, and the first purlin support system is located above the second purlin support system, that is, the second purlin support system is adjacent to the main pier cap 86. Each purlin support system 83 includes four purlin supports, and both ends of each purlin support are connected to a group of corresponding adjacent edges of the purlin through purlin reinforcements 821 to form a whole.

[0084] In order to achieve the transmission of tidal water pressure, the bored cast-in-place pile support system 91 described in the utility model is connected to the purlin through a concrete turning block 102 at a position at the same height as the purlin support system 83. The concrete turning block 102 is set by the "rebar embedding method". Specifically, the concrete turning block 102 includes a pre-embedded steel cage and concrete cast into one piece with the pre-embedded steel cage, and a pre-embedded steel plate is arranged at the end of the purlin support to serve as a supporting point for the purlin. The pre-embedded steel cage is arranged between the pre-embedded steel plate and the retaining support bored cast-in-place pile 91, and a first connecting rib 103 is arranged at one end of the pre-embedded steel cage to connect with the retaining support bored cast-in-place pile 91 at the corresponding position through the first connecting rib 103, and then the concrete can be poured to form the concrete turning block 102 to connect the purlin support and the retaining support bored cast-in-place pile 91 into one piece.

[0085] The purlin 82 is rectangular in shape as a whole and is connected at the corners by corner stiffeners 822 .

[0086] There is usually a module mismatch at the junction (intersection) of the side arm end of the U-shaped Larsen steel sheet pile 81 and the retaining support bored pile 91 - even if the matching is perfect in the design stage, the coupling between the side arm end of the U-shaped Larsen steel sheet pile 81 and the retaining support bored pile 91 is difficult to fit perfectly. Considering that the length of the retaining support bored pile 91 exceeds the side arm end of the U-shaped Larsen steel sheet pile 81, 1~2 Larsen steel sheet piles are added outside the corner point formed by the intersection of the side arm end of the U-shaped Larsen steel sheet pile 81 and the retaining support bored pile 91 as a water-stop curtain. It should be noted that the load at the corner point is shared by the purlin and the purlin support, and the focus is on preventing leakage.

[0087] The main pier is constructed in the area enclosed by the Larsen steel sheet pile cofferdam system and the bored cast-in-place pile support system 91, including the main pier bored cast-in-place piles 85, the main pier cap 86 arranged above the top of the main pier bored cast-in-place piles 85, and the main pier columns 84 arranged above the main pier cap 86; the main pier cap 86 is connected to each side of the U-shaped Larsen steel sheet pile 81 by a first temporary plate support, and is connected to the bored cast-in-place pile support system 91 by a second temporary plate support.

[0088] The design principles of the Larsen steel sheet pile cofferdam system in the preliminary design (not considering the influence of the retaining support system for the time being, and considering it as a conventional cofferdam system) specifically include the following:

[0089] 1) Consider the highest tidal water level without considering the flood control water level, that is, it is assumed that the Larsen steel sheet pile cofferdam system is submerged during floods. Specifically, the design water level of the Larsen steel sheet pile cofferdam system is calculated as high tide water level + 2.00m, and the cofferdam top elevation is calculated as + 2.5m.

[0090] 2) Considering the conventional Larsen steel sheet pile cofferdam system, the base elevation is -3.80m, the maximum excavation depth is 6.6m, the ratio of embedment depth to excavation depth in the preliminary design stage is 2:1, and the total height of the cofferdam is allowed to be 18m.

[0091] 3) A clear distance of 1.0m is reserved between the inner wall of the cofferdam and the main pier cap 86 as working space for the cap construction;

[0092] 4) Two inner support systems and one bottom concrete are set in a single Larsen steel sheet pile cofferdam system, and the average distance between the two inner support systems is about 2.5m. The bottom concrete can form the main pier cap cushion 87.

[0093] 5) Larsen steel sheet piles use Larsen IV type steel sheet piles.

[0094] In the actual construction process, the retaining support bored pile 91 has three use conditions:

[0095] 1) Working condition 1 (first construction stage): the state after the original bank wall is removed and before the cofferdam is constructed. At this time, the fill elevation behind the bored pile support system 91 is +2.60m, that is, the fill elevation on the shore side of the bored pile support system 91 is +2.60m, and the soil layer elevation after the excavation in front of the bored pile support system 91 is -0.70m, that is, the soil layer elevation on the water side of the bored pile support system 91 is -0.70m. Therefore, the cantilever length of the bored pile support system 91 is 3.3m.

[0096] 2) Working condition 2 (second construction stage): the cofferdam is excavated to the bottom layer (the bottom elevation of the bottom concrete is -4.10m at this time), and before the bottom concrete is poured, the nominal excavation depth of the bored pile support system 91 reaches 6.6m. At this time, the first and second internal support systems exist in the Larsen steel sheet pile cofferdam system;

[0097] 3) Working condition three (third construction stage): After the construction of the main pier column 84 is completed and the internal support system is removed, although the nominal excavation depth of the bored pile support system 91 remains basically unchanged at 6.3m (bottom concrete top elevation -3.80m), only the bottom concrete remains at this stage and the second internal support has been removed.

[0098] Based on the analysis of the above three operating conditions, it can be seen that:

[0099] 1) The retaining height on the side of the bored pile support system 91 is much greater than the retaining height on the side of the Larsen steel sheet pile cofferdam system;

[0100] 2) The bored cast-in-place pile support system 91 has already borne the active earth pressure of the first stage (working condition 1) before the Larsen steel sheet pile cofferdam system is subjected to stress; in the second stage (working condition 2), the active earth pressure borne by the bored cast-in-place pile support system 91 increases accordingly due to the increase in the support height;

[0101] 3) The soil pressure increment borne by the bored cast-in-place pile support system 91 in the second stage is lower than the soil pressure increment on the Larsen steel sheet pile cofferdam system side. The reason is that the soil pressure increment of the bored cast-in-place pile support system 91 comes from the part from -0.70m (soil layer elevation after the bank wall is removed) to -4.1m (bottom elevation of the bottom concrete seal in the cofferdam), while the soil pressure increment of the Larsen steel sheet pile cofferdam system comes from the part from +2.00m (high tide water level elevation) to -4.1m (bottom elevation of the bottom concrete seal in the cofferdam).

[0102] Based on the above analysis, in order to ensure that the bored pile support system 91 meets the required stability requirements, the coupling effect of the Larsen steel sheet pile cofferdam system and the bored pile support system 91 must be considered during the implementation of the Larsen steel sheet pile cofferdam system. In other words, the design load of the bored pile support system 91 should be mainly in the first stage, and the increment in the second stage should be balanced by the increment on the Larsen steel sheet pile cofferdam system side.

Claims

1. A deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers, used to assist the main pier construction of bridges in complex embankment areas of tidal rivers, where embankment walls and flood control walls are provided, characterized in that: The deepwater composite cofferdam system includes a Larsen steel sheet pile cofferdam system, a bored pile support system and a concrete turning block, wherein: The Larsen steel sheet pile cofferdam system includes an inner support system and U-shaped Larsen steel sheet piles arranged in a semi-enclosed shape outside the inner support system; the inner support system is arranged in the upper area inside the U-shaped Larsen steel sheet piles, including a purlin and a purlin support system, the purlin is rectangular, and the purlin support system is arranged in the purlin, with at least one layer; The bored cast-in-place pile support system is arranged between the Larsen steel sheet pile cofferdam system and the flood control wall. It is a pipe gallery composed of several retaining support bored cast-in-place piles. The closed end of the U-shaped Larsen steel sheet pile is arranged on the water side of the complex embankment area of ​​the tidal river channel, and the two side arms of the U-shaped Larsen steel sheet pile point to the bored pile support system, and the ends of the two side arms of the U-shaped Larsen steel sheet pile are respectively sealed with the two ends of the bored pile support system; Each retaining support bored cast-in-place pile of the bored cast-in-place pile support system is connected to the purlin through a concrete turning block at a position at the same height as the purlin support system.

2. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 1 is characterized in that: Each layer of the perimeter purlin support system includes four perimeter purlin supports, and both ends of each perimeter purlin support are connected to a group of corresponding adjacent edges of the perimeter purlin through perimeter purlin reinforcements to form an integral whole.

3. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 2 is characterized in that: Two adjacent bored cast-in-place retaining piles are spliced ​​with the purlin on the side adjacent to the purlin by concrete grouting, and are connected by high-pressure jet grouting piles on the bank side.

4. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 3 is characterized in that: The concrete turning block comprises a pre-buried steel cage, one end of which is provided with a first connecting bar for each retaining support bored pile; the pre-buried steel cage is connected to the retaining support bored pile at the corresponding position through the first connecting bar.

5. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 4 is characterized in that: The ends of both side arms of the U-shaped Larsen steel sheet pile are sealed with the bored pile support system through a water-stop curtain.

6. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 5 is characterized in that: The ends of the two side arms of the U-shaped Larsen steel sheet pile extend 1-2 steel sheet piles outward after intersecting with the bored pile support system to form the water-stop curtain.

7. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 5, characterized in that: The outer side of the water-stop curtain is connected to the retaining support bored piles at the end of the bored pile support system through the corner reinforcement piles.

8. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 3, characterized in that: The top and bottom elevations of high-pressure jet grouting piles are consistent with the top and bottom elevations of bored cast-in-place piles for retaining support.

9. The deepwater composite cofferdam system suitable for complex embankment areas of tidal rivers according to claim 3, characterized in that: The tops of the bored cast-in-place piles of each retaining support are spliced ​​into one piece through a crown beam.

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