Locking steel pipe pile-cast-in-situ bored pile supporting composite cofferdam system

Abstract

The utility model discloses a fore shaft steel pipe pile-cast-in-situ bored pile supporting composite cofferdam system which is used for assisting main pier construction operation in a complex embankment area of a tidal river channel and comprises a fore shaft steel pipe pile cofferdam system and a soil retaining supporting cast-in-situ bored pile system which are independent from each other. A quay wall and a flood control wall are arranged in the complex embankment area of the tidal river channel, the fore shaft steel pipe pile cofferdam system is arranged on the water facing side of the complex embankment area of the tidal river channel, and the soil retaining support cast-in-situ bored pile system is arranged between the fore shaft steel pipe pile cofferdam system and the flood control wall and is arranged adjacent to the fore shaft steel pipe pile cofferdam system. The cast-in-situ bored pile supporting system is a pipe gallery composed of a plurality of soil retaining and supporting cast-in-situ bored piles, and the pile tops of the soil retaining and supporting cast-in-situ bored piles are connected through a top beam. Therefore, the anti-collapse structure can effectively prevent the soil body around the flood control wall from collapsing towards the cofferdam construction position in the excavation process of the fore shaft steel pipe pile cofferdam system, and the construction safety is guaranteed.

Description

Technical Field

[0001] The utility model relates to a design method for a locking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system, which is suitable for complex embankment areas of tidal river channels. 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 to 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 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 conventional 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 main stream 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, pinewood 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 to 22m below the riverbed is a medium-weathered rock layer, which is not only impossible for temporary steel sheet piles or lock-mouth steel pipe piles to invade (which means that the setting depth of the cofferdam is only 18 to 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 to 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 on one side (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 composite cofferdam system supported by a locking steel pipe pile and bored cast-in-place piles, so as to assist the viaduct in carrying out main pier construction in the complex embankment area of ​​a tidal river channel, 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.

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

[0022] A composite cofferdam system supported by interlocking steel pipe piles and bored cast-in-place piles is used to assist the main pier construction in the complex embankment area of ​​a tidal river channel. The complex embankment area of ​​the tidal river channel is provided with a quay wall and a flood control wall, including an independent interlocking steel pipe pile cofferdam system and a retaining support bored cast-in-place pile system; wherein:

[0023] The interlocking steel pipe pile cofferdam system is arranged on the water side of the complex embankment area of ​​the tidal river channel, while the retaining support bored pile system is arranged between the interlocking steel pipe pile cofferdam system and the flood control wall and is arranged close to the interlocking steel pipe pile cofferdam system.

[0024] The bored cast-in-place pile support system is a pipe gallery composed of a number of retaining bored cast-in-place piles, the tops of the retaining bored cast-in-place piles are connected by a cap beam, and a temporary retaining steel plate is arranged on the outer side of the upper area of ​​each retaining bored cast-in-place pile close to the pile top;

[0025] The distance between each locking steel pipe pile of the locking steel pipe pile cofferdam system and each retaining support bored cast-in-place pile of the bored cast-in-place pile support system shall not be less than 0.5m.

[0026] Preferably, the locking steel pipe pile cofferdam system includes a cofferdam body and an internal support system;

[0027] The cofferdam body is enclosed by a number of locking steel pipe piles;

[0028] The internal support system is arranged in the upper area of ​​the cofferdam body, including the purlin and the purlin support; the purlin support is arranged in the purlin and connected with the purlin through the purlin reinforcement to form an integral whole.

[0029] Preferably, there are two purlin supports, corresponding to the first and second purlin supports, and the first purlin support is located above the second purlin support.

[0030] Preferably, two adjacent locking steel pipe piles are connected by a CO lock or a CT lock to form a whole.

[0031] Preferably, the width of the temporary retaining steel plate is greater than the spacing between two adjacent retaining support bored cast-in-place piles, and the height is not less than the height difference between the pile top elevation of the retaining support bored cast-in-place piles and the cofferdam excavation surface.

[0032] Preferably, the main pier is constructed in the area enclosed by the locking steel pipe pile cofferdam system, including the main pier bored cast-in-place piles, the main pier cap arranged above the top of the main pier bored cast-in-place piles, and the main pier columns arranged above the main pier cap; the main pier cap and each side of the locking steel pipe pile cofferdam system are connected by temporary plate supports.

[0033] Preferably, the earth retaining support bored piles are arranged at equal intervals.

[0034] Preferably, the interlocking steel pipe pile cofferdam system is arranged at the location of the quay wall.

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

[0036] The locking steel pipe pile-bored cast-in-place pile support composite cofferdam system described in the utility model has a retaining support bored cast-in-place pile system arranged between the locking steel pipe pile cofferdam system and the flood control wall. The retaining support bored cast-in-place pile system is a pipe gallery formed by a number of retaining support bored cast-in-place piles evenly arranged, which can effectively support the soil around the flood control wall, prevent the soil around the flood control wall from collapsing toward the cofferdam construction position during the excavation of the locking steel pipe pile cofferdam system, and ensure the safety of the 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 structural schematic diagram of the locking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system described in the utility model;

[0042] Figure 4 yes Figure 3 The elevation structure diagram of the locking steel pipe pile-bored cast-in-place pile support composite cofferdam system shown (foundation pit excavation stage).

[0043] Figure 5 yes Figure 3The elevation structure diagram of the locking steel pipe pile-bored cast-in-place pile support composite cofferdam system shown (column construction stage).

[0044] Figure 6 yes Figure 3 The plan view of the interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system shown;

[0045] Figure 3-6 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;

[0046] 81. Main pier columns; 82. Main pier cap; 83. Locking steel pipe piles; 84. Main pier bored piles; 85. Peripheral purlin support; 86. Temporary plate support; 87. Peripheral purlin reinforcement; 881. Peripheral purlin; 882. Peripheral purlin corner reinforcement; 9. Earth retaining support bored pile system; 91. Cap beam; 92. Temporary earth retaining steel plate; 93. Earth retaining support bored piles; 10. Original soil between piles. DETAILED DESCRIPTION

[0047] 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.

[0048] 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).

[0049] like Figures 3 to 6 As shown, the locking steel pipe pile-bored cast-in-place pile support composite cofferdam system described in the utility model is arranged in the complex embankment area of ​​the tidal river channel to assist the main pier construction work in the complex embankment area of ​​the tidal river channel. The complex embankment area of ​​the tidal river channel is provided with a quay wall 3 and a flood control wall 1. The locking steel pipe pile-bored cast-in-place pile support composite cofferdam system includes a mutually independent locking steel pipe pile cofferdam system and a retaining support bored cast-in-place pile system 9; wherein:

[0050] The locking steel pipe pile cofferdam system is arranged on the water side (i.e., the river side, adjacent to the river channel) of the complex embankment area of ​​the tidal river channel. In the present utility model, the locking steel pipe pile cofferdam system happens to be arranged at the location of the shore wall 3. The retaining support bored pile system 9 is arranged between the locking steel pipe pile cofferdam system and the flood control wall 1 and is arranged adjacent to the locking steel pipe pile cofferdam system. Specifically, the bored pile support system is a pipe gallery formed by evenly arranging a number of retaining support bored piles 93. The tops of the retaining support bored piles 93 are connected by a crown beam 91, and each retaining support bored pile 93 is arranged with a temporary retaining steel plate 92 on the outer side of the upper area close to the top of the pile; the spacing between each locking steel pipe pile 83 of the locking steel pipe pile cofferdam system and each retaining support bored pile 93 of the bored pile support system is not less than 0.5m. That is, there is a pile-to-pile original soil 10 with a thickness of not less than 0.5m between the locking steel pipe pile cofferdam system and the bored cast-in-place pile support system, that is, the net distance between the locking steel pipe pile cofferdam system and the bored cast-in-place pile support system is not less than 0.5m. In fact, the net distance D should be as small as possible in principle, but to prevent excessive soil compression and deformation, resulting in direct contact between the locking steel pipe pile cofferdam system and the bored cast-in-place pile support system, a limit value of 0.5m is set.

[0051] The purpose of arranging the bored cast-in-place pile support system in the utility model is to ensure the overall stability of the existing flood control wall 1 when clearing obstacles in the pier area.

[0052] To this end, the bored pile support system must meet the following functional requirements:

[0053] 1) It has sufficient bearing capacity to resist the uneven lateral earth pressure on both sides of the bored pile support system, and at the same time bear the lateral earth pressure generated by the operating machinery on the side of the flood control wall 1;

[0054] 2) It has sufficient rigidity to ensure that the lateral displacement of the flood control wall 1 is no more than 5 mm, avoiding the cracking and damage of the original concrete flood control wall 1 caused by the foundation deviation, and maintaining the original flood control function;

[0055] 3) The construction of bored pile support system has little impact on the existing flood control wall 1, and the ground acceleration during construction should not exceed 5m / s 2 . Reduce the vibration damage of the original concrete flood control wall 1 caused by acceleration.

[0056] Based on the above functional requirements, the utility model selects the bored cast-in-place pile support system as a bored cast-in-place pile support system. The bored cast-in-place pile support system includes a plurality of retaining support bored cast-in-place piles 93, the pile tops of each retaining support bored cast-in-place pile 93 are connected by a cap beam 91, and each retaining support bored cast-in-place pile 93 is connected between the upper areas close to the pile tops by a temporary retaining steel plate 92.

[0057] Since the utility model arranges a bored cast-in-place pile support system between the locking steel pipe pile cofferdam system and the existing flood control wall 1, it basically breaks through the restrictions on the construction of the locking steel pipe pile cofferdam system at the construction site. 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 formed by the construction meets the above functional requirements is a technical problem that the utility model needs to solve.

[0058] Based on the construction site where the utility model is located, without considering the influence of the locking steel pipe pile cofferdam system, the boundary conditions of the bored pile support system are determined, mainly including the following points:

[0059] 1) Determine the design elevation of the top of the bored pile 93 for retaining support:

[0060] The top design elevation of the bored pile 93 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 3";

[0061] 2) Determine the ground elevation of the bored pile support system:

[0062] The ground elevation of the bored cast-in-place pile support system is the existing ground elevation, calculated as +3.50m, that is, no soil unloading or soil piling, and the original state is maintained;

[0063] 3) Determine the construction location of the bored pile support system:

[0064] The bored cast-in-place pile support system shall be arranged as close as possible to the construction area of ​​the locking steel pipe pile cofferdam system and away from the existing flood control wall 1; during actual construction, the net distance between the bored cast-in-place pile support system and the locking steel pipe pile cofferdam system can be set to 0.5m.

[0065] 4) Determine the downstream bottom elevation of the bored pile support system:

[0066] According to preliminary exploration data, the bottom elevation of the original quay wall 3 structural layer is about -0.50m. Considering the over-excavation effect of construction work, the downstream bottom elevation of the bored pile support system is calculated as -0.70m.

[0067] 5) Determine the lowest water level in tidal rivers:

[0068] 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.

[0069] Based on the boundary conditions of the bored pile support system, it can be seen that the pile length of the retaining support bored pile 93 described in the utility model is limited. Therefore, when designing the bored pile support system, the following contents need to be paid attention to:

[0070] 1) Pile diameter and spacing of bored cast-in-place piles 93 for retaining support:

[0071] The larger the bored pile diameter, the higher the single pile bearing capacity and stiffness, and the corresponding larger spacing (lateral earth pressure within the subordinate width range); conversely, the smaller the pile diameter, the lower the single pile bearing capacity and stiffness, and the spacing needs to be reduced to reduce the lateral earth pressure allocated to the single pile. Therefore, under the condition of meeting the functional requirements, economic indicators (concrete volume and corresponding steel bar usage, where the steel bar configuration must meet both the bored pile's own bearing capacity requirements and crack width limit requirements) are the key factors in evaluating technical solutions.

[0072] 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 93 are selected as follows:

[0073] The single pile diameter of the retaining bored cast-in-place pile 93 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.

[0074] 2) Retaining problems of 93 bored piles:

[0075] It is only applicable to the part above the excavation boundary. A pluggable retaining structure needs to be set up on the flood wall side to control the loss of soil on the support side. The larger the spacing of the bored piles 93, the larger the span of the bored pile support system, and the higher the mechanical requirements. Usually, the pluggable retaining structure is preferably a temporary retaining steel plate 92. When the spacing of the bored piles 93 is large, the thickness of the temporary retaining steel plate 92 is increased to meet the requirements. Taking the application case as an example, the top surface elevation of the bored piles 93 is +2.60m, the maximum excavation elevation of the first phase is -0.70m, and the height difference is 3.3m, so only the local support of this part of the soil needs to be considered.

[0076] The thickness of the temporary retaining steel plate 92 is 20 mm, and the plug-and-pull mode is adopted. The plug-and-pull operation is performed by a 200-type excavator without a vibrating hammer. In addition, the width of the temporary retaining steel plate 92 is greater than the spacing between two adjacent retaining support bored cast-in-place piles 93, and the height is not less than the height difference between the top elevation of the retaining support bored cast-in-place piles 93 and the cofferdam excavation surface.

[0077] The retaining support bored pile 93 is 2.25m away from the pedestal on the river channel side, that is, assuming that the width of the locking steel pipe pile cofferdam system is 0.75m, the inner edge of the locking steel pipe pile cofferdam system is 1.0m away from the edge of the pedestal, and 0.5m is reserved between the outer edges of the retaining support bored pile 93 and the locking steel pipe pile cofferdam system.

[0078] 3) The integrity problem between the earth retaining support bored cast-in-place piles 93. The utility model arranges a cap beam 91 on the top layer of each earth retaining support bored cast-in-place pile 93, so that each earth retaining support bored cast-in-place pile 93 is connected to form a whole. The design basis of crown beam 91 includes: ① The top elevation should be flush with the original soil elevation at three locations of the existing bank wall, that is, the top elevation of the bored pile support system should not be higher than the original ground elevation at three locations of the existing bank wall, because it is useless and wasteful if it is higher; ② The bottom elevation should depend on the seepage effect of the highest tidal level during the construction period (the highest water level of the tidal river channel is different within 30 days), that is, during the construction stage of crown beam 91 (excavation of the working surface, removal of pile heads, steel bar binding, formwork support, concrete pouring, etc.), the working surface should be kept dry; ③ The width of crown beam 91 is usually "extended 200mm to 250mm on both sides of the pile diameter" - in essence, crown beam 91 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 crown beam 91 is 2.0m and the height is 1.5m. The bottom elevation of crown beam 91 + 1.10m can meet the seepage stability requirements.

[0079] After the above-mentioned bored pile support system is completed, the construction machinery can operate on the rear side of the retaining support bored piles 93, clear the obstacles within the target foundation range, and then deploy a conventional drilling operation platform, using the conventional positive cycle rotary drilling process to complete the operation of 9 1.5m retaining support bored piles 93.

[0080] The locking steel pipe pile cofferdam system described in the utility model is as follows: Figure 3-6 As shown, the structure is similar to the conventional locking steel pipe pile cofferdam system as a whole, including the cofferdam body and the internal support system. The cofferdam body is enclosed by a number of locking steel pipe piles 83, and two adjacent locking steel pipe piles are connected by CO locks or CT locks to form a whole; the internal support system is arranged in the upper area of ​​the cofferdam body, including a purlin 881 and a purlin support 85; the purlin 881 is provided with a purlin corner reinforcement 882 at the corner position, and the purlin support 85 is arranged in the purlin 881 and connected to the purlin 881 through the purlin reinforcement 87. The purlin support 85 can be one or two. When there are two purlin supports 85, they correspond to the first and second purlin supports, and the first purlin support is located above the second purlin support.

[0081] The main pier is constructed within the area enclosed by the locking steel pipe pile cofferdam system, including the main pier bored cast-in-place piles 84, the main pier cap 82 arranged above the top of the main pier bored cast-in-place piles 84, and the main pier columns 81 arranged above the main pier cap 82; the main pier cap 82 and the side surfaces of the locking steel pipe pile cofferdam system are connected by temporary plate supports 86.

[0082] The design principles of the lock-mouth steel pipe pile cofferdam system in the preliminary design (not considering the influence of the bored pile support system for the time being, and considering it as a conventional cofferdam system) specifically include the following:

[0083] 1) Consider the highest tidal water level without considering the flood control water level, that is, it is assumed that the lock-mouth steel pipe pile cofferdam system is submerged during the flood. Specifically, the design water level of the lock-mouth steel pipe pile cofferdam system is calculated as +2.00m, and the cofferdam top elevation is calculated as +2.5m.

[0084] 2) According to the conventional cofferdam system, the elevation of the bottom of the pedestal is -3.80m, the maximum excavation depth is 6.6m, the ratio of the embedded depth to the excavation depth in the preliminary design stage is 2:1, and the total height of the cofferdam is allowed to be 18m.

[0085] 3) A clear distance of 1.0m is reserved between the inner wall of the cofferdam and the main pier cap 82 as working space for the cap construction;

[0086] 4) Two purlin supports 85 and one bottom concrete are set for a single cofferdam, and the average support spacing is about 2.5m.

[0087] 5) The locking steel pipe pile 83 adopts Φ630 steel pipe.

[0088] In the actual construction process, there are three working conditions for the bored pile support system:

[0089] 1) Working condition 1: The state after the original bank wall 3 is removed and before the cofferdam is constructed. At this time, the fill elevation behind the bored pile support system is +2.60m, the soil elevation behind the excavation in front of the bored pile support system is -0.70m, and the cantilever length is 3.3m.

[0090] 2) Working condition 2: When the cofferdam is excavated to the lowest layer (-4.10m, the bottom elevation of the bottom concrete), and before the bottom concrete is poured, the nominal excavation depth of the bored pile support system reaches 6.6m - at this stage, the cofferdam has the first and second purlin supports;

[0091] 3) Working condition 3: After the construction of main pier column 81 is completed and the purlin support is removed, although the nominal excavation depth of the retaining structure remains basically unchanged at 6.3m (bottom concrete top elevation -3.80m), only the bottom concrete remains at this stage and the second purlin support has been removed.

[0092] Based on the analysis of the above three operating conditions, it can be seen that:

[0093] 1) The retaining height on the side of the bored pile support system is much greater than the retaining height on the side of the lock-mouth steel pipe pile cofferdam system;

[0094] 2) The bored cast-in-place pile support system has already borne the active earth pressure of the first stage (working condition 1) before the lock-mouth steel pipe pile cofferdam system is stressed; in the second stage (working condition 2), due to the increase in the support height of the bored cast-in-place pile support system, the active earth pressure it bears increases accordingly;

[0095] 3) The soil pressure increment borne by the bored cast-in-place pile support system in the second stage is lower than the soil pressure increment on the side of the locking steel pipe pile cofferdam system. The reason is that the soil pressure increment of the bored cast-in-place pile support system comes from the part from -0.70m (the soil layer elevation after the removal of the bank wall 3) to -4.1m (the bottom elevation of the bottom concrete seal in the cofferdam), while the soil pressure increment of the locking steel pipe pile cofferdam system comes from the part from +2.00m (high tide water level elevation) to -4.1m (the bottom elevation of the bottom concrete seal in the cofferdam).

[0096] Based on the above analysis, in order to ensure that the bored cast-in-place pile support system meets the required stability requirements, the coupling effect of the locked steel pipe pile cofferdam system and the bored cast-in-place pile support system must be considered during the implementation of the locked steel pipe pile cofferdam system. In other words, the design load of the bored cast-in-place pile support system should be based on the first stage, and the increment of the second stage should be balanced by the increment on the locked steel pipe pile cofferdam system side.

Claims

1. A composite cofferdam system supported by a locking steel pipe pile and bored cast-in-place piles, used to assist the main pier construction in a complex embankment area of ​​a tidal river, where a quay wall and a flood control wall are provided, characterized in that: It includes independent interlocking steel pipe pile cofferdam system and retaining support bored pile system; among which: The interlocking steel pipe pile cofferdam system is arranged on the water side of the complex embankment area of ​​the tidal river channel, while the retaining support bored pile system is arranged between the interlocking steel pipe pile cofferdam system and the flood control wall and is arranged close to the interlocking steel pipe pile cofferdam system. The bored cast-in-place pile support system is a pipe gallery composed of a number of retaining bored cast-in-place piles, the tops of the retaining bored cast-in-place piles are connected by a cap beam, and a temporary retaining steel plate is arranged on the outer side of the upper area of ​​each retaining bored cast-in-place pile close to the pile top; The distance between each locking steel pipe pile of the locking steel pipe pile cofferdam system and each retaining support bored cast-in-place pile of the bored cast-in-place pile support system shall not be less than 0.5m.

2. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 1 is characterized in that: The lock-mouth steel pipe pile cofferdam system includes the cofferdam body and the internal support system; The cofferdam body is enclosed by a number of locking steel pipe piles; The internal support system is arranged in the upper area of ​​the cofferdam body, including the purlin and the purlin support; the purlin support is arranged in the purlin and connected with the purlin through the purlin reinforcement to form an integral whole.

3. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 2 is characterized in that: There are two purlin supports, corresponding to the first and second purlin supports, and the first purlin support is located above the second purlin support.

4. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 1 is characterized in that: Two adjacent locking steel pipe piles are connected by CO locks or CT locks to form a whole.

5. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 1 is characterized in that: The width of the temporary retaining steel plate is greater than the spacing between two adjacent retaining support bored cast-in-place piles, and the height is not less than the height difference between the pile top elevation of the retaining support bored cast-in-place pile and the cofferdam excavation surface.

6. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 1 is characterized in that: The main pier is constructed in the area enclosed by the interlocking steel pipe pile cofferdam system, including the main pier bored cast-in-place piles, the main pier cap arranged above the top of the main pier bored cast-in-place piles, and the main pier columns arranged above the main pier cap; the main pier cap and the side surfaces of the interlocking steel pipe pile cofferdam system are connected by temporary plate supports.

7. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 1 is characterized in that: The retaining and supporting bored piles are arranged at equal intervals.

8. The interlocking steel pipe pile-bored cast-in-place pile supporting composite cofferdam system according to claim 1 is characterized in that: The interlocking steel pipe pile cofferdam system is arranged at the location of the quay wall.

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