Support conversion method for realizing synchronous construction of deep foundation pits in open cut adjacent sections

Abstract

The invention discloses a support conversion method for realizing synchronous construction of deep foundation pits in open cut adjacent sections, and relates to the technical field of civil construction. Comprising the steps that a first-layer support changing system is installed below a first-layer inclined strut system of a first foundation pit, the first-layer inclined strut system is replaced with the first-layer support changing system, adjacent foundation pit earthwork is symmetrically excavated from the middle to the two sides, the earthwork close to the middle of a plug wall is firstly unloaded, then the earthwork close to fender posts on the two sides is unloaded, and finally the remaining earthwork is unloaded. The first layer of inclined strut system of the first foundation pit is dismantled, operation is repeated till the nth layer of inclined strut system of the first foundation pit is converted into the nth layer of support changing system, meanwhile, the plug wall is dismantled, nth excavation is completed in the adjacent foundation pit, and the nth layer of straight strut system is installed; according to the method, inclined support replacement is replaced with straight support replacement, earthwork behind a plug wall is unloaded in a partitioned and segmented jump support mode, the purpose of support replacement is achieved through load conversion, and synchronous construction can be achieved on the basis that the safety of a foundation pit is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of civil construction, and in particular to a support conversion method for realizing synchronous construction of adjacent sections of deep foundation pits in open excavation. Background Art

[0002] For stations or sections that adopt the open-cut method, due to the constraints of land acquisition and demolition, traffic diversion, underground pipeline relocation or process, the long foundation pit is usually divided into several sections and constructed in stages. The usual method is to arrange diagonal braces on the plugging wall of foundation pit one, which transfers the passive earth pressure at the plugging wall to the retaining structures on the left and right sides of the foundation pit to form an internal balance state. The adjacent foundation pits two and three must be completed after the main structure of foundation pit one is constructed, and the steel diagonal braces on the plugging wall side are removed layer by layer before the adjacent foundation pits can be excavated, which will inevitably lead to an increase in cost, construction period, safety, progress and traffic pressure.

[0003] The current support replacement method is only for the same section of the same foundation pit and the same structural construction section. It is mainly during the structural construction stage, which will affect the horizontal internal straight support of the structural construction support on the retaining piles or ground-connected walls; by changing the height position, the support is on the constructed inner lining wall, which is convenient for the construction of the middle plate or top plate at the internal support position, generally replacing the straight support with the straight support. The force direction of the support remains unchanged, but the force magnitude of a single support changes. Before and after the support replacement, it is still an independent force balance system, which cannot form a joint effect with the adjacent foundation pit support system. In this way, in the process of foundation pit excavation in the previous stage, the overall force balance of the support system between the adjacent foundation pits was not established, so that the adjacent foundation pits did not have the conditions for synchronous construction, resulting in a waste of working surface, leading to an increase in cost, construction period, safety, progress and traffic pressure. Summary of the invention

[0004] The present invention is to solve the technical problem that the current support replacement method is only for the same foundation pit, the overall force balance of the support system between adjacent foundation pits is not established, and the adjacent foundation pits do not have the conditions for synchronous construction. The purpose is to provide a support conversion method for realizing the synchronous construction of open excavation adjacent sections of deep foundation pits, by successively replacing the oblique supports of the plugging wall of foundation pit one with straight supports, and excavating the adjacent foundation pits on the other side of the plugging wall in a plane partitioning, symmetrical from the middle to both sides, jump support, and step-by-step unloading manner, so that the force transmitted to the steel oblique support by the plugging wall is gradually weakened, and the steel straight support of foundation pit one bears the active earth pressure on both sides, so as to achieve the purpose of using straight supports instead of oblique supports, establish the overall force balance of the support system between adjacent foundation pits, and make the adjacent foundation pits have the conditions for synchronous construction.

[0005] The present invention is achieved through the following technical solutions:

[0006] A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation, wherein a deep foundation pit is divided into multiple foundation pits for regional construction by a plugging wall, retaining piles are set for a certain foundation pit that has been constructed first, and a support system is set in layers, wherein the support system includes a straight support system connected to the retaining piles and an inclined support system connected to the plugging wall, and after the foundation pit has been excavated to a certain stage, support conversion is performed, comprising the following steps:

[0007] S1. Install the first layer of replacement bracing system below the first layer of diagonal bracing system of foundation pit 1, wherein the replacement bracing system includes steel replacement straight bracing connected to the retaining piles;

[0008] S2. Apply axial prestress to the first-layer replacement support system in stages, so that the first-layer replacement support system can fully bear the axial load;

[0009] S3, excavation of adjacent foundation pits, excavation height to the support system layer and the next layer support system, excavation method is to excavate symmetrically from the middle to both sides, first unload the soil near the middle of the plug wall, then unload the soil near the retaining piles on both sides, and finally unload the remaining soil;

[0010] S4. Remove the first layer of diagonal bracing system of foundation pit 1 and completely transfer the load of the diagonal bracing system to the first layer of replacement bracing system;

[0011] S5, repeating steps S1-S4, converting the second-layer diagonal bracing system of foundation pit 1 into the second-layer replacement bracing system, while dismantling the plugging wall to the excavation height of the adjacent foundation pit, retaining the top crown beam of the plugging wall and the pile foundation in the plugging wall as the first-layer straight bracing system of the adjacent foundation pit, and installing the second-layer straight bracing system;

[0012] S6. Repeat step S5 until the conversion of the n-th layer of diagonal support system is completed in foundation pit 1, the n-th excavation is completed in the adjacent foundation pit, and the n-th layer of straight support system is installed.

[0013] Furthermore, the replacement support system includes multiple steel replacement straight supports, connecting beam three and replacement support steel lattice columns. Both ends of the steel replacement straight supports are fixed to the retaining piles through steel surrounding purlin one. The replacement support steel lattice columns are vertically arranged in the foundation pit. Connecting beam three are installed on both sides of the replacement support steel lattice columns, and the steel replacement straight supports are fixed on the connecting beam three.

[0014] Furthermore, the end of the steel vertical support is hung on the top of the steel perimeter purlin through an L-shaped steel plate, and the steel vertical support is connected to a crown beam of the foundation pit through a steel wire rope.

[0015] Furthermore, the steel straight support is fixed to the connecting beam three through a U-shaped channel steel.

[0016] Furthermore, the end of the steel support is also provided with an automatic axial force compensation device.

[0017] Furthermore, the support system of foundation pit one is connected to the retaining piles through steel retaining purlin two, and the support system of the adjacent foundation pit is connected to the retaining piles through steel retaining purlin three.

[0018] Furthermore, the straight support system includes steel straight supports, straight support steel lattice columns and connecting beams. The two ends of the steel straight supports are fixed to the retaining piles through steel purlins. The straight support steel lattice columns are vertically arranged in the foundation pit. Connecting beams are installed on both sides of the straight support steel lattice columns, and the steel straight supports are fixed on the connecting beams.

[0019] Furthermore, the diagonal bracing system includes a steel diagonal brace, a second connecting beam and a diagonal brace steel lattice column. One end of the steel diagonal brace is fixed to the retaining pile through a steel purlin, and the other end is connected to the end wall. The diagonal brace steel lattice column is vertically arranged in the foundation pit. Two connecting beams are installed on both sides of the diagonal brace steel lattice column, and the steel diagonal brace is fixed on the two connecting beams.

[0020] Furthermore, the axial prestressing is applied to the first layer of the replacement support system in three stages:

[0021] 40% of the designed axial force is applied for the first time, 70% of the designed axial force is applied for the second time, and 100% of the designed axial force is applied for the third time.

[0022] Furthermore, after the blocking wall is removed to the excavation height of the adjacent foundation pit, the steel purlin three of the adjacent foundation pit needs to be connected with the steel purlin two of the foundation pit one, and then the straight support system of the adjacent foundation pit is installed.

[0023] Furthermore, the steel perimeter purlins corresponding to the second to nth layer replacement support systems are installed using a balanced counterweight method.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. The present invention adopts steel-for-vertical bracing to replace the steel diagonal bracing of the same cross section in the height direction in foundation pit one, replaces the diagonal bracing of the plugging wall of foundation pit one with straight bracing in sequence, and excavates the adjacent foundation pit on the other side of the plugging wall in a plane partitioning, symmetrical from the middle to both sides, jump bracing, and step-by-step unloading manner, so that the force transmitted to the steel diagonal bracing by the plugging wall is gradually weakened, and the active soil pressure on both sides is borne by the steel-for-vertical bracing of foundation pit one, so as to achieve the purpose of replacing diagonal bracing with straight bracing, establish the overall force balance of the support system between adjacent foundation pits, and enable the adjacent foundation pits to have the conditions for synchronous construction.

[0026] 2. The traditional method of sequential construction of adjacent foundation pits has a small number of single foundation pit working surfaces, and each type of work can only be constructed in sequence according to the process. The types of work that are not within the time range of the process will be idle, increasing costs. After adopting the method of the present invention, when the foundation pit of the previous stage is still in earth excavation, the adjacent foundation pit can be excavated to create a new working surface, and various types of work can be constructed in a continuous manner, reducing idle work, improving the utilization efficiency of construction resources, reducing construction costs, speeding up progress, and reducing the municipal traffic pressure and investment waste caused by the phased traffic diversion.

[0027] 3. The prestressing of the steel brace of the present invention is applied in stages according to 0→40%→70%→100% of the designed axial force value, and an automatic axial force compensation device is installed at the movable end of the steel brace to automatically compensate for the axial force when the excavated earth in the adjacent foundation pit is unloaded, and dynamic correction is performed to ensure the designed prestressing value of the steel brace and the safety of the foundation pit.

[0028] 4. The present invention unloads the earth behind the plugging wall by using jump braces in sections and segments, thereby realizing step-by-step unloading of the active earth pressure on the plugging wall, gradually weakening the force transmitted from the steel perimeter purlin to the steel diagonal brace, and re-establishing a stable and balanced force system between the foundation pit and the adjacent foundation pit at the end. After the earth is unloaded step by step, the steel perimeter purlin is no longer subject to the active earth pressure, and the diagonal brace can be easily removed, thereby realizing load conversion and achieving the purpose of brace replacement.

[0029] 5. When the plugging wall is excavated and cut layer by layer, the present invention leaves a pile foundation in the middle of the span of the top crown beam on the top of the plugging wall, so that the compressive stability of the top crown beam is ensured when it is transformed into the first layer of steel straight support.

[0030] 6. After the plugging wall is cut into layers, the present invention immediately pulls through and connects the steel purlins between adjacent foundation pits to form a whole. If the spacing is larger than the designed steel straight support spacing, it is necessary to add a steel straight support near the plugging wall to form an effective unified support as a whole to ensure the stability of the overall structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0032] Figure 1 It is the plan layout of foundation pit 1 and adjacent foundation pits;

[0033] Figure 2 The plan layout of the replacement support system for foundation pit 1;

[0034] Figure 3This is a cross-sectional view of the installation of the first layer of the replacement support system for foundation pit 1;

[0035] Figure 4 It is a schematic diagram of the connection structure between the retaining piles and the replacement support system;

[0036] Figure 5 It is a schematic diagram of the connection structure between the steel straight support and the third connecting beam;

[0037] Figure 6 It is the unloading zoning map of the adjacent foundation pits;

[0038] Figure 7 This is a longitudinal section of foundation pit 1 and the adjacent foundation pit after the first layer of support replacement is completed;

[0039] Figure 8 This is the cross-section diagram of the foundation pit after the first layer of support replacement is completed;

[0040] Fig. 9 Cross-section diagram of the installation of the second layer of the replacement support system for foundation pit 1;

[0041] Fig.10 This is a longitudinal section of foundation pit 1 and the adjacent foundation pit after the second layer of support replacement is completed;

[0042] Fig.11 This is a cross-sectional view of the second-layer replacement support system completed for foundation pit 1;

[0043] Fig.12 This is the cross-section diagram after the second excavation of foundation pit 2;

[0044] Fig.13 It is a longitudinal section of foundation pit 1 and adjacent foundation pit after the nth layer of support replacement is completed;

[0045] Fig.14 This is a cross-sectional view of the nth layer of the replacement support system for foundation pit 1;

[0046] Fig.15 This is the cross-section diagram of the foundation pit after the nth excavation.

[0047] Marks and corresponding parts names in the attached drawings:

[0048] 1-guard piles, 2-straight bracing system, 21-steel straight bracing, 22-straight bracing steel lattice column, 23-connection beam one, 3-diagonal bracing system, 31-steel diagonal bracing, 32-connection beam two, 33-diagonal bracing steel lattice column, 4-replacement bracing system, 41-steel replacement straight bracing, 42-connection beam three, 43-replacement bracing steel lattice column, 44-L-shaped steel plate, 45-U-shaped channel steel, 5-blocking wall, 501-top crown beam, 6-axial force automatic compensation device, 7-steel perimeter purlin one, 8-steel perimeter purlin two, 9-crown beam of foundation pit one, 10-steel wire rope, 11-steel perimeter purlin three, 12-pile foundation. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are clearly and completely described below in combination with the embodiments and drawings. Obviously, the schematic implementation modes of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0050] Example 1

[0051] For the first foundation pit of the subway open excavation, which is in the condition of earth excavation, this embodiment adopts steel straight supports 21 to replace each layer of reinforced concrete diagonal supports or steel diagonal supports 31 in the depth direction of the foundation pit, and cooperates with the adjacent foundation pit to be excavated synchronously to adopt an excavation method of symmetrically from the middle to both sides, skipping supports, and step-by-step unloading of earth on the other side of the plugging wall 5, so as to achieve the purpose of replacing diagonal supports with straight supports and synchronous excavation of adjacent foundation pits.

[0052] The specific implementation process is described in detail below with reference to the accompanying drawings.

[0053] Example 1

[0054] This embodiment 1 describes the structure of the support system and the support replacement system 4 involved in the present invention. Figure 1-5 shown.

[0055] The deep foundation pit is divided into multiple foundation pits by the damming wall 5 for easy construction in different areas. The top of the damming wall 5 is provided with a damming wall 5 top crown beam 501, in which a pile foundation 12 is retained. One of the foundation pits excavated in advance is set as foundation pit one. The supporting system of foundation pit one and the adjacent foundation pit are the same. The supporting system of foundation pit one is connected to the retaining pile 1 through the steel retaining purlin 2 8, and the supporting system of the adjacent foundation pit is connected to the retaining pile 1 through the steel retaining purlin 3 11.

[0056] The straight support system 2 includes steel straight supports 21, straight support steel lattice columns 22 and connecting beams 23. The two ends of the steel straight supports 21 are fixed to the retaining piles 1 through steel surrounding purlins 8. The straight support steel lattice columns 22 are vertically arranged in the foundation pit. Connecting beams 23 are installed on both sides of the straight support steel lattice columns 22. The steel straight supports 21 are fixed on the connecting beams 23. The connecting beams 23 connect multiple steel straight supports 21 into one, and are connected to the steel straight supports 21 at 90 degrees.

[0057] The diagonal brace system 3 includes a steel diagonal brace 31, a connecting beam 32 and a diagonal brace steel lattice column 33. One end of the steel diagonal brace 31 is fixed to the retaining pile 1 through a steel purlin 7, and the other end is connected to the end wall 5. The diagonal brace steel lattice column 33 is vertically arranged in the foundation pit. Connecting beams 32 are installed on both sides of the diagonal brace steel lattice column 33. The steel diagonal brace 31 is fixed on the connecting beam 32. The connecting beam 32 connects multiple steel diagonal braces 31 into one, and is connected to the steel diagonal braces 31 at 90°.

[0058] The replacement support system 4 includes a plurality of steel replacement straight supports 41 , a third connecting beam 42 and replacement support steel lattice columns 43 .

[0059] The two ends of the steel replacement straight brace 41 are fixed to the retaining pile 1 through a steel retaining purlin 1 7, and the steel retaining purlin 1 7 is installed under the steel retaining purlin 2 8 of the first layer of diagonal bracing system 3, and the prestress of the steel replacement straight brace 41 is transferred to the retaining piles 1 on both sides or the ground-connected wall through the steel retaining purlin to achieve force balance.

[0060] The steel replacement straight brace 41 needs to be installed in multiple pieces, directly bear the active soil pressure on both sides during the replacement process, and is installed under the steel diagonal brace 31. In the process of applying prestress in stages, the force on the diagonal brace is reduced until it is zero, so as to achieve the purpose of replacing the diagonal brace. In the limited space near the plug wall 5, the number of steel replacement straight braces 41 is usually equal to the number of steel diagonal braces 31.

[0061] The flange plate at the end of the steel replacement straight support 41 is welded with an L-shaped steel plate 44 and hung on the top of the steel surrounding purlin 7, and the anti-falling measure adopts a φ16 steel wire rope 10 and a pre-buried steel ring of the foundation pit crown beam 9 to tighten; the end of the steel replacement straight support 41 is also provided with an automatic axial force compensation device 6, which can automatically supplement the prestress loss to the design value at any time.

[0062] The replacement support steel lattice column 43 is vertically arranged in the foundation pit and pre-anchored with bored piles to transfer the vertical weight of the connection beam 3 42 and the steel replacement straight support 41 to the foundation.

[0063] The two sides of the replacement brace steel lattice column 43 are welded with connecting beams three 42, and the steel replacement straight brace 41 is fixed on the connecting beam three 42 by U-shaped channel steel 45. The U-shaped channel steel 45 constrains the steel replacement straight brace 41, which can reduce the span of the steel replacement straight brace 41 to maintain compressive stability, and at the same time transfer the weight of the steel replacement brace to the replacement brace steel lattice column 43.

[0064] It should be noted that, for the sake of convenience in distinction and explanation, in the present invention, the connecting beams of the steel straight brace 21 are uniformly referred to as connecting beam one 23, the connecting beams of the steel diagonal brace 31 are uniformly referred to as connecting beam two 32, and the connecting beams of the steel replacement straight brace 41 are uniformly referred to as connecting beam three 42; the steel perimeter purlins of the replacement brace system 4 in foundation pit one are uniformly referred to as steel perimeter purlin one 7, the steel perimeter purlins of the support system are uniformly referred to as steel perimeter purlin two 8, and the steel perimeter purlins of the adjacent foundation pits are uniformly referred to as steel perimeter purlin three 11.

[0065] Example 2

[0066] A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation, such as Figure 6-15 As shown, the deep foundation pit is divided into multiple foundation pits for construction in different areas by a plugging wall 5. For a foundation pit that has been constructed in advance, retaining piles 1 (or ground-connected walls) are set up and a support system is set up in layers. The support system includes a straight support system 2 connected to the retaining piles 1 and a diagonal support system 3 connected to the plugging wall 5.

[0067] When the excavation of foundation pit 1 has reached a certain stage and the external factors restricting the construction of the adjacent foundation pit have ceased, the adjacent foundation pit can construct the retaining pile 1 and the first layer of support system. At this time, in order to achieve synchronous excavation of the foundation pit, the following method is used for support conversion, which specifically includes the following steps:

[0068] S1. Install the first layer of replacement support system 4 below the first layer of diagonal support system 3 of foundation pit 1. Figure 3 shown.

[0069] S11. After the first layer of concrete support of the adjacent foundation pit is completed, the first layer of steel purlin 17 and angle steel corbels are installed under the crown beam of the foundation pit. A φ16 steel wire rope 10 and a basket bolt are installed between the first layer of steel purlin 17 and the crown beam to prevent falling and tighten them. C25 quick-setting fine stone concrete is used to compact the steel purlin 17 and the retaining pile 1 (or ground-connected wall). The angle steel corbels (L125×12mm) are arranged at a spacing of 2m along the mileage direction and fixed to the bite pile or ground-connected wall with steel expansion bolts M20L=285.

[0070] S12. Install the connecting beam 3 42 (2[40C channel steel) for fixing the steel vertical support 41 on both sides of the steel lattice column 43 and under the first layer of steel vertical support 41, and weld the connecting beam 3 42 and both sides of the steel lattice column 43.

[0071] S2. Replace the first layer diagonal support system 3 of foundation pit 1 with the first layer replacement support system 4, and unload the soil of the adjacent foundation pit.

[0072] S21. Install the first layer of steel replacement straight braces 41 under the first layer of diagonal bracing system 3 of foundation pit 1, and apply axial prestressing to the first layer of steel replacement straight braces 41 in stages, from 0→40%→70%→100% to the most unfavorable working condition value, so that the steel replacement straight braces 41 can fully bear the Y-direction load.

[0073] S22, excavation of adjacent foundation pits, excavation height from the original ground to the middle of the first layer support system and the second layer support system, the excavation method is symmetrical from the middle to both sides, jump support excavation, such as Figure 6 As shown, the earthwork in area ① is unloaded first, then the earthwork in area ②, and finally the earthwork in area ③. When unloading the load in the X direction, the axial force automatic compensation device 6 installed at the axial end of the first layer of steel straight support 41 can automatically supplement the prestress loss to the design value at any time.

[0074] S23, dismantle the first layer of steel diagonal braces 31, the second connecting beam 32, and the second steel perimeter purlin 8 of the foundation pit, and completely transfer the load of the steel diagonal braces 31 to the second layer of steel replacement straight braces 41, and then cut off the diagonal brace steel lattice column 33 from the bottom of the first layer of steel diagonal braces 31 to the top of the second layer of steel diagonal braces 31, so as to achieve the purpose of replacing the diagonal braces with straight braces. The structure of the foundation pit after completing the first layer of replacement braces is shown in the figure Figure 7and Figure 8 shown.

[0075] S3, replace the second layer of inclined support system 3 of foundation pit one with the second layer of replacement support system 4, continue to unload the earthwork of the adjacent foundation pit, connect foundation pit one and the adjacent foundation pit and install the second layer of straight support system 2.

[0076] S31, install the second layer of the support replacement system 4 according to steps S1-S21. Fig. 9 As shown, the second layer of diagonal bracing system 3 of foundation pit 1 is then replaced;

[0077] S32, excavation of adjacent foundation pits, the excavation height is from the first excavation height to the middle of the second support system and the third support system, the excavation method is the same as step S22.

[0078] S33, dismantle the second layer of steel diagonal braces 31, the second connecting beam 32, and the second steel perimeter purlin 8 of the foundation pit 1, and completely transfer the load of the steel diagonal braces 31 to the second layer of steel replacement straight braces 41, and then cut off the diagonal brace steel lattice columns 33 from the bottom of the second layer of steel diagonal braces 31 to the top of the third layer of steel diagonal braces 31. The structure of the foundation pit 1 after completing the second layer of replacement braces is as follows: Figure 10-11 shown.

[0079] S34, use a rope saw to cut and remove the plugging wall 5, the cutting height is the height from the bottom of the top beam 501 of the plugging wall 5 to the second excavation height of the adjacent foundation pit, such as Fig.12 As shown, the top crown beam 501 and the pile foundation 12 of the plugging wall 5 are retained as the first support layer straight support at this position, and the second layer steel perimeter purlin 3 11 of the adjacent foundation pit is connected with the second layer steel perimeter purlin 1 7 of the foundation pit to form a whole. If the spacing between the steel replacement straight supports 41 and the steel straight supports 21 between the adjacent foundation pits is greater than the designed spacing, it is necessary to add a steel replacement straight support 41 near the plugging wall 5 to form an effective unified support as a whole to ensure the stability of the overall structure.

[0080] S35. Install the second layer of straight support system 2 on the adjacent foundation pit.

[0081] S4, repeat the second layer of support replacement operation until the foundation pit completes the nth layer of straight to inclined conversion, the adjacent foundation pit completes the nth earthwork unloading and installs the nth layer of straight support system 2. Figure 13-15 described.

[0082] It should be noted that the excavation height of adjacent foundation pits is between the support system and the next support system. If the nth excavation is carried out, the excavation height is between the heights of the nth support system and the n+1th support system.

[0083] Among them, the steel perimeter purlin 7 corresponding to the second to nth layer replacement support system 4 is installed by the balanced counterweight method.

[0084] Finally, it should be noted that the above specific embodiments are only used to explain in detail the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific implementation method of the present invention and is not used to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the above specific embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions recorded in the above embodiments, or to replace or improve some or all of the technical features therein. These modifications, equivalent replacements and improvements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation, wherein a deep foundation pit is divided into a plurality of foundation pits for construction in different areas by means of a plugging wall (5), a retaining pile (1) is set for a certain foundation pit constructed in advance, and a support system is set in layers, wherein the support system comprises a straight support system (2) connected to the retaining pile (1) and an inclined support system (3) connected to the plugging wall (5), and is characterized in that: After the foundation pit has been excavated to a certain stage, support conversion is carried out, including the following steps: S1, installing a first-layer replacement support system (4) below the first-layer diagonal support system (3) of foundation pit 1, wherein the replacement support system (4) comprises steel replacement straight supports (41) connected to the retaining piles (1); S2, applying axial prestress to the first-layer replacement support system (4) in stages, so that the first-layer replacement support system (4) can fully bear the axial load; S3, excavating the adjacent foundation pits to a height between the current support system and the next support system. The excavation method is to excavate symmetrically from the middle to both sides, first unloading the soil near the middle of the plug wall (5), then unloading the soil near the retaining piles (1) on both sides, and finally unloading the remaining soil; S4, dismantling the first layer of the diagonal bracing system (3) of the foundation pit 1, and completely transferring the load of the diagonal bracing system (3) to the first layer of the replacement bracing system (4); S5, repeating steps S1-S4, converting the second layer of the inclined support system (3) of the foundation pit 1 into the second layer of the replacement support system (4), while dismantling the plugging wall (5) to the excavation height of the adjacent foundation pit, retaining the top crown beam (501) of the plugging wall (5) and the pile foundation (12) in the plugging wall (5) as the first layer of the straight support system (2) of the adjacent foundation pit, and installing the second layer of the straight support system (2); S6, repeat step S5 until the conversion of the n-th layer of diagonal support system (3) is completed in foundation pit 1, and the n-th excavation of the adjacent foundation pit is completed and the n-th layer of straight support system (2) is installed.

2. A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1, characterized in that: The replacement support system (4) comprises a plurality of steel replacement supports (41), a third connecting beam (42) and a replacement support steel lattice column (43). Both ends of the steel replacement supports (41) are fixed to the retaining piles (1) through a first steel purlin (7). The replacement support steel lattice column (43) is vertically arranged in the foundation pit. A third connecting beam (42) is installed on both sides of the replacement support steel lattice column (43). The steel replacement support (41) is fixed on the third connecting beam (42).

3. A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 2, characterized in that: The end of the steel replacement straight support (41) is hung on the top of the steel surrounding purlin (7) through an L-shaped steel plate (44), and the steel replacement straight support (41) is connected to the foundation pit crown beam (9) through a steel wire rope (10).

4. A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 2, characterized in that: The steel straight support (41) is fixed to the third connecting beam (42) via a U-shaped channel steel (45).

5. A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 2, characterized in that: The end of the steel straight support (41) is also provided with an automatic axial force compensation device (6).

6. The support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1 is characterized in that: The support system of the foundation pit one is connected to the retaining piles (1) via the steel retaining purlin two (8), and the support system of the adjacent foundation pit is connected to the retaining piles (1) via the steel retaining purlin three (11).

7. The support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1 is characterized in that: The straight bracing system (2) comprises a steel straight brace (21), a straight brace steel lattice column (22) and a connecting beam (23); both ends of the steel straight brace (21) are fixed to the retaining pile (1) through a second steel purlin (8); the straight brace steel lattice column (22) is vertically arranged in the foundation pit; connecting beams (23) are installed on both sides of the straight brace steel lattice column (22); and the steel straight brace (21) is fixed to the connecting beam (23).

8. The support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1 is characterized in that: The diagonal bracing system (3) comprises a steel diagonal brace (31), a second connecting beam (32) and a diagonal brace steel lattice column (33); one end of the steel diagonal brace (31) is fixed to the retaining pile (1) through a first steel purlin (7), and the other end is connected to the end wall (5); the diagonal brace steel lattice column (33) is vertically arranged in the foundation pit; the second connecting beam (32) is installed on both sides of the diagonal brace steel lattice column (33); and the steel diagonal brace (31) is fixed to the second connecting beam (32).

9. The support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1 is characterized in that: The stepwise application of axial prestress to the first-layer replacement support system (4) is specifically carried out in three steps: 40% of the design axial force is applied for the first time, 70% of the design axial force is applied for the second time, and 100% of the design axial force is applied for the third time.

10. The support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1, characterized in that: After the blocking wall (5) is removed to the height of the adjacent foundation pit excavation, the steel purlin 3 (11) of the adjacent foundation pit needs to be connected with the steel purlin 2 (8) of the foundation pit 1, and then the vertical support system (2) of the adjacent foundation pit is installed.

11. A support conversion method for realizing synchronous construction of adjacent deep foundation pits in open excavation according to claim 1, characterized in that: The steel purlins (7) corresponding to the second to nth layer replacement support systems (4) are installed by using the balanced counterweight method.

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