Construction method of long and narrow type super deep foundation pit support

Abstract

The application discloses a long and narrow type super-deep foundation pit support construction method, which comprises trench excavation, vertical plane frame splicing and lowering, first concrete support construction, steel support axial force adjustment, next concrete support construction and lower two steel support axial force adjustment. The application can realize efficient active deformation control of a super-deep foundation pit adjacent to a protected object, ensures the safety redundancy of the foundation pit in an extreme case, reduces the foundation pit support cost through the recyclable characteristics of part of the steel supports, and has the advantages of good foundation pit deformation control efficiency and ensured construction safety of the long and narrow type super-deep foundation pit.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and underground structure engineering, and in particular to a method for supporting long and narrow ultra-deep foundation pits. Background Technology

[0002] In ultra-deep foundation pit engineering, especially in underground space development in soft soil areas or complex urban environments, diaphragm walls combined with multiple internal supports are the main form of support. Construction follows a passive sequential operation mode of "layered excavation and layered support," specifically: excavating the first layer of soil to below the elevation of the first support → constructing the first support → waiting for it to reach strength → excavating the second layer of soil to below the elevation of the second support → constructing the second support, and so on. The supports include two structural forms: concrete supports and steel supports. In foundation pits, usually only one type of support is used. The disadvantages are: using only concrete supports results in a long construction period, requiring waiting for the concrete to reach the required strength before excavation; using only steel supports leads to problems such as drastic fluctuations in axial force due to thermal expansion and contraction, significant influence from seasonal temperature differences, and a tendency to detach from the foundation pit retaining wall, resulting in poor deformation control of the retaining wall. In particular, when the first support is used as a construction platform, the steel support cannot be used as a construction platform and cannot meet the load-bearing capacity requirements. Summary of the Invention

[0003] The purpose of this invention is to provide a construction method for supporting long and narrow ultra-deep foundation pits, in order to solve the problems of long construction cycle of concrete supports, poor deformation control effect of steel supports due to displacement caused by thermal expansion and contraction and axial offset, and inability to be used as a construction platform, as well as the difficulty and long construction cycle of the formwork system of concrete supports in the foundation pit.

[0004] To solve the above-mentioned technical problems, the technical solution provided by the present invention is: a construction method for supporting a narrow and elongated ultra-deep foundation pit, comprising:

[0005] Trench excavation: Excavate several trenches at intervals along the width of the ultra-deep foundation pit to the design elevation of the bottom slab;

[0006] Vertical plane frame splicing and lowering: From top to bottom, a formwork support unit is formed by alternating arrangement of one concrete support formwork system and two steel supports. Vertical components connecting the adjacent steel supports of the formwork support unit and the steel supports with their adjacent concrete support formwork system are spliced ​​on the ground to form a vertical plane frame. Each vertical plane frame is then lowered vertically into each trench.

[0007] Construction of the first concrete support: The first concrete support is constructed using the first concrete support formwork system and connected to the foundation pit retaining wall via the capping beam;

[0008] Axial force adjustment of steel support: Excavate the soil below the first concrete support layer by layer. During the excavation process, adjust the axial force of the exposed steel support and tighten it against the foundation pit retaining wall.

[0009] Next concrete support construction: Continue excavating the soil to expose the next concrete support formwork system, construct the concrete support through this concrete support formwork system and connect it to the foundation pit retaining wall through walers;

[0010] Axial force adjustment of the two lower steel supports: Continue to excavate the soil layer by layer. During the excavation process, adjust the axial force of the two lower steel supports exposed in the soil and tighten them against the foundation pit retaining wall.

[0011] Furthermore, the construction method for supporting narrow and ultra-deep foundation pits provided by the present invention includes a concrete support formwork system comprising bottom connecting plates, support beams, middle connecting plates, and U-shaped channel formwork on all vertical members horizontally arranged on the same straight line from bottom to top; side supports horizontally arranged on the middle connecting plate and distributed on the outer side of each side formwork of the U-shaped channel formwork; and a top connecting plate horizontally arranged around the vertical members at the junction of the vertical members, the side supports, and the U-shaped channel formwork.

[0012] Furthermore, in the construction method for supporting elongated ultra-deep foundation pits provided by the present invention, the concrete support formwork system further includes diagonal bracing surrounding the vertical member and fixedly installed between the vertical member and the bottom connecting plate.

[0013] Furthermore, in the elongated ultra-deep foundation pit support construction method provided by the present invention, the support beam consists of three parallel distributed beams, two of which are distributed on both sides of all vertical members on the same straight line, and the other support beam is aligned with the axis of the vertical members.

[0014] Furthermore, in the elongated ultra-deep foundation pit support construction method provided by the present invention, the side supports consist of two beams, which are respectively aligned on the support beams on the corresponding sides.

[0015] Furthermore, in the construction method for supporting narrow and ultra-deep foundation pits provided by the present invention, before the vertical plane frame is lowered, a detachable cover plate is provided between the top connecting plates of two adjacent vertical members on the same straight line of the remaining concrete support formwork system below the first concrete support formwork system.

[0016] Furthermore, in the construction method for supporting narrow and deep foundation pits provided by the present invention, temporary top groove components are set on the outside of each support beam before the vertical plane frame is lowered. When the vertical plane frame is lowered, the verticality of the vertical plane frame is adjusted by the temporary top groove components.

[0017] Furthermore, in the elongated ultra-deep foundation pit support construction method provided by the present invention, the vertical components are connected to each steel support node through flange joints in four directions, and the servo jacks of each steel support are connected to the flange joints or to the flange joints through steel support segments.

[0018] Furthermore, the construction method for supporting narrow and ultra-deep foundation pits provided by the present invention involves reinforcing the soil within the foundation pit area before trench excavation.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention provides a construction method for supporting elongated ultra-deep foundation pits. It utilizes a combined horizontal support system consisting of one concrete support and two steel supports arranged alternately within the pit. This system integrates the adjustability and recyclability of steel supports with the high rigidity and good integrity of concrete supports, forming a support system that is both rigid and flexible, safe and economical. The steel supports provide adjustable axial force to actively control the deformation of the foundation pit retaining wall, while the concrete supports provide stable passive rigidity and integrity, achieving efficient active deformation control of the ultra-deep foundation pit adjacent to the protected object. This ensures safety redundancy for the foundation pit under extreme conditions and reduces the cost of foundation pit support through the recyclability of some steel supports.

[0021] The method for supporting long and narrow ultra-deep foundation pits provided by this invention uses a combined horizontal support system consisting of one concrete support and two steel supports arranged alternately, with the first support being a concrete support. This allows the concrete support to serve as a construction platform, material storage platform, and mechanical hoisting area, and has the advantage of strong load-bearing capacity.

[0022] The present invention provides a method for constructing support for long and narrow ultra-deep foundation pits. This method involves excavating trenches within the ultra-deep foundation pit area, and lowering vertical planar frames along each trench. These frames consist of a formwork support system and two steel supports arranged alternately, forming a formwork support unit and its connected vertical components. The vertical components provide vertical support to the foundation pit and each support. Combined with the axial force of the steel supports in the vertical planar frame, the method actively adjusts the support force. Concrete supports are installed at corresponding locations using the concrete formwork support system. This method constrains and controls the deformation of the foundation pit retaining wall in a combined active and passive manner throughout the entire process and area. It can control the foundation pit deformation within a smaller range, offering advantages such as high efficiency in controlling foundation pit deformation and ensuring the construction safety of long and narrow ultra-deep foundation pits.

[0023] The present invention provides a construction method for supporting long and narrow ultra-deep foundation pits. The vertical planar frame composed of a concrete support formwork system, steel supports, and vertical components can be spliced ​​on the ground and then lowered as a whole. This reduces the difficulty of building the concrete support formwork system, shortens the construction cycle of the concrete support formwork system, and improves the construction efficiency of the concrete support formwork system. It avoids the problems of high construction difficulty, low efficiency, and long cycle caused by limited space in the foundation pit. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the planar structure of the first layer of concrete supports;

[0025] Figure 2 This is a schematic diagram of the planar structure of the fourth concrete support arrangement;

[0026] Figure 3 It is a schematic diagram of the plan structure with the second, third, fifth, or sixth steel supports arranged.

[0027] Figure 4 It is a schematic diagram of the vertical planar frame and its elevation structure lowered into the trench;

[0028] Figure 5 It is a three-dimensional structural diagram of the connection node between the vertical component and the concrete support formwork system;

[0029] Figure 6 This is a front view structural diagram of the connection node between the vertical component and the concrete support formwork system;

[0030] Figure 7 This is a schematic diagram of the elevation structure of the trench constructed within the retaining wall area of ​​the foundation pit;

[0031] Figure 8 This is a schematic diagram of the elevation structure with each vertical planar frame lowered into each trench;

[0032] Figure 9 This is a schematic diagram of the elevation structure of the first concrete support constructed through the concrete support formwork system and its connection to the foundation pit retaining wall via the capping beam.

[0033] Figure 10 This is a schematic diagram of the elevation structure of the formwork system where the second and third steel supports are exposed during the excavation, the vertical components between the first three supports are removed, the fourth concrete support is constructed, and the concrete support formwork system at that location is removed.

[0034] Figure 11 This is a schematic diagram of the elevation structure where the fifth and sixth steel supports are exposed as the excavation continues to move the earth to the bottom of the foundation pit;

[0035] Figure 12 This is a schematic diagram of the elevation structure of the foundation slab of the underground project after the removal of the sixth steel support.

[0036] Figure 13 This is a flowchart of the construction method for supporting long and narrow ultra-deep foundation pits;

[0037] As shown in the figure:

[0038] 100. Vertical plane frame; 110. Concrete support formwork system; 111. Diagonal brace; 112. Bottom connecting plate; 113. Support beam; 114. Middle connecting plate; 115. U-shaped channel formwork; 116. Side support; 117. Top connecting plate; 118. Cover plate; 120. Steel support; 121. Servo jack; 130. Vertical component; 140. Flange joint; 150. Temporary top channel component.

[0039] 200. Excavation pit retaining wall; 201. Soil; 202. Trench; 203. Concrete support; 204. Cap beam; 205. Waler; 206. Hanging rod.

[0040] 300. Base plate. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0042] Please refer to Figures 1 to 3 and Figure 11 The elongated ultra-deep foundation pit support of this invention includes a combined horizontal support system constructed from top to bottom along the width direction of the elongated ultra-deep foundation pit, consisting of one concrete support 203 and two steel supports 120 arranged alternately, wherein the first support is the concrete support 203. Figure 11 The example of the combined horizontal support system consists of six supports, with concrete supports 203 and steel supports 120 numbered consecutively from top to bottom as the first concrete support, the second steel support, the third steel support, the fourth concrete support, the fifth steel support, and the sixth steel support. That is, the first and fourth supports are concrete supports, and the second, third, fifth, and sixth supports are steel supports 120, but not limited to six supports; it also includes vertical members 130 located in the narrow and ultra-deep foundation pit and aligned with each support.

[0043] Please refer to Figures 1 to 13 This invention provides a method for constructing a support system for a long and narrow ultra-deep foundation pit, comprising:

[0044] Step S1, trench excavation: Excavate soil at intervals along the width of the ultra-deep foundation pit 201 to form several trenches 202 up to the design elevation of the bottom slab, such as... Figure 7As shown. Before excavating trench 202, the soil 201 within the foundation pit area can be reinforced to form stable trenching conditions. Several trench positions are set, and then trenching equipment is used to excavate the trench section. The trench depth reaches the bottom elevation of the foundation pit bottom plate, and the trench section is cured.

[0045] Step S2, Vertical Plane Frame Assembly and Lowering: From top to bottom, a formwork support unit is formed by alternating arrangements of one concrete support formwork system 110 and two steel supports 120. Vertical members 130 connecting adjacent steel supports 120 within the formwork support unit, and between a steel support 120 and its adjacent concrete support formwork system 110, are assembled on the ground to form a vertical plane frame 100. One concrete support formwork system 110 and two steel supports 120 constitute a set. Each vertical plane frame 100 is then vertically lowered into each trench 202, as follows: Figure 8 and Figure 4 As shown.

[0046] Step S3, First Concrete Support Construction: Construct the first concrete support 203 using the first concrete support formwork system 110 and connect it to the foundation pit retaining wall 200 via the capping beam 204. After the first concrete support 203 reaches the strength standard, remove the concrete support formwork system 110. Figure 9 As shown. To improve the reliability of the connection, the reinforcing bars of the cap beam 204 are tied together with the reinforcing bars of the first concrete support 203. The first concrete support 203 has extremely high axial stiffness, which can firmly "hold" the top of the foundation pit like a stirrup, preventing the foundation pit retaining wall 200 from tilting or displacing into the pit. The first concrete support 203 is not sensitive to temperature. For ultra-deep foundation pits with long construction cycles, using concrete support 203 as the first support can avoid the excessive displacement of the pit top caused by temperature changes and shrinkage when using steel support 120 structure. The first support using concrete support 203 can also serve as a construction platform for material stacking and mechanical hoisting areas, with a load-bearing capacity far exceeding that of the first support formed by steel support structure.

[0047] Step S4, Steel Support Axial Force Adjustment: Excavate the soil 201 below the first concrete support 203 layer by layer. During the excavation process, adjust the axial force of the steel support 120 exposed in the soil 201 and tighten it against the foundation pit retaining wall 200. Figure 10 As shown. The axial force of the steel support 120 is adjusted via servo jacks 121 at its ends. Axial force can be applied synchronously or in stages to all steel supports 120 on the horizontal plane at each steel support 120. To improve soil excavation efficiency, after the axial force of the steel support 120 is adjusted, the vertical member 130 above it can be used.

[0048] Step S5, next concrete support construction: Continue excavating the soil 201 to expose the next concrete support formwork system 110. Construct the next concrete support 203 (i.e., the fourth concrete support) through this formwork system 110 and connect it to the foundation pit retaining wall 200 via walers 205. Figure 10 As shown. When reinforcing the waler 205, hanging bars 206 are used to anchor it to the foundation pit retaining wall 200. Once the fourth concrete support 203 reaches its design strength, the concrete support formwork system 110 is removed. When the concrete support formwork system 110 at the fourth concrete support 203 has a cover plate 118, the cover plate 118 is opened before reinforcing the waler and concrete is poured to form the fourth concrete support 203. The cover plate 118, before excavation reaches the elevation of the fourth concrete support 203, prevents soil 201 from entering the U-shaped channel formwork 115 during excavation, reducing subsequent cleaning steps for the U-shaped channel formwork 115 and preventing soil 201 from accumulating inside and causing structural deformation of the U-shaped channel formwork 115, thus affecting the construction quality of the fourth concrete support 203. The fourth layer of support uses concrete support 203, which can suppress "kickback" and deep creep. As the excavation depth increases, the stress point of the foundation pit retaining wall 200 shifts downward, and the middle part tends to "bulge" into the pit. As a high-rigidity hard support point, the fourth concrete support 203 can effectively cut off the continuous lateral pressure transmission and reduce the rheological accumulation of deep soil. As the fourth layer of support, concrete support 203 can prevent the overall instability of the foundation pit. Since servo steel supports still have the risk of multiple joints and easy instability, setting a concrete support 203 in the deep area of ​​the foundation pit is equivalent to making a "hard partition" in the middle of the foundation pit. Even if the two upper steel supports 120 fail locally, the fourth concrete support 203 can serve as the last line of defense to prevent the overall collapse of the foundation pit.

[0049] Step S6, Adjusting the Axial Force of the Next Two Steel Supports: Continue excavating the soil 201 layer by layer. During the excavation process, adjust the axial force of the next two steel supports 120 exposed in the soil 201 and tighten them against the foundation pit retaining wall 200. Figure 11 As shown, this forms a combined horizontal support system consisting of two concrete supports 203 and four steel supports 120. The first and fourth supports are concrete supports 203, while the second, third, fifth, and sixth supports are steel supports 120. This creates a structural form with an alternating arrangement of "concrete support-steel support-steel support-concrete support-steel support-steel support", but not limited to six supports, and can be adaptively adjusted according to the depth of the ultra-deep foundation pit.

[0050] During the construction of the underground structure, the last steel support was removed, and the foundation slab was constructed at 300mm. Each support was removed layer by layer upwards until the basement was completed. Figure 12 As shown.

[0051] In this embodiment, the steel support 120 is divided into three sections, comprising a standard horizontal bar, a servo jack 121 (i.e., an axial force adjustment end), and a flange joint 140. The standard horizontal bar is connected by the flange of the flange joint 140 and high-strength bolts to form a semi-rigid or rigid node. The steel support 120 compensates for displacement in real time, and the servo jack 121 can automatically adjust the axial force based on the displacement of the foundation pit retaining wall 200 or deformation monitoring data of nearby facilities (such as a subway tunnel). When the subway tunnel experiences a small displacement towards the foundation pit, the servo jack 121 of the steel support 120 increases its clamping force and actively pushes it back. The steel support 120 is installed as it is excavated, requiring no maintenance, greatly shortening the unsupported exposure time. Under conditions of high water and soil pressure at depths of 5 or 6 layers, it provides rapid support to protect the foundation pit retaining wall 200 and its adjacent facilities (subway tunnel). The optimized construction space of the base slab 300, with its small cross-section, is beneficial for improving the construction efficiency of the base slab 300.

[0052] In this embodiment, steps S1 to S3 constitute a first set of horizontal support systems consisting of one concrete support 203 and two steel supports 120, and steps S4 to S6 constitute a second set of horizontal support systems consisting of one concrete support 203 and two steel supports 120. The two sets of horizontal support systems are arranged alternately to form a combined horizontal support system, suitable for ultra-deep foundation pits exceeding 30 meters in depth. When the depth of the ultra-deep foundation pit changes, the number of alternating sets of horizontal support systems can be adjusted, and it is not limited to the alternating arrangement of two sets of horizontal support systems.

[0053] The construction method for supporting elongated ultra-deep foundation pits provided in this invention utilizes a combined horizontal support system consisting of one concrete support 203 and two steel supports 120 arranged alternately within the elongated ultra-deep foundation pit. This system integrates the adjustability and recyclability of the steel supports 120 with the high rigidity and good integrity of the concrete supports 203, forming a support system that is both rigid and flexible, safe and economical. The steel supports 120 provide adjustable axial force to actively control the deformation of the foundation pit retaining wall 200, while the concrete supports 203 provide stable passive rigidity and integrity, achieving efficient active deformation control of the ultra-deep foundation pit adjacent to the protected object. This ensures safety redundancy for the foundation pit under extreme conditions and reduces the cost of foundation pit support through the recyclability of some of the steel supports 120.

[0054] The method for supporting long and narrow ultra-deep foundation pits provided in this invention uses a combined horizontal support system consisting of one concrete support 203 and two steel supports 120 arranged alternately. The first support is the concrete support 203, which can be used as a construction platform, material stacking platform and mechanical hoisting area, and has the advantage of strong load-bearing capacity.

[0055] The method for supporting long and narrow ultra-deep foundation pits provided in this invention involves excavating trenches 202 within the ultra-deep foundation pit area, and lowering vertical planar frames 100 along each trench 202. These frames consist of formwork units formed by alternating arrangements of a concrete support formwork system 110 and two steel supports 120, along with their connected vertical components 130. The vertical components 130 provide vertical support force to the foundation pit and each support. Combined with the axial force of the steel supports 120 in the vertical planar frames 100, the method actively adjusts the force. Concrete supports 203 are installed at corresponding positions through the concrete support formwork system 110. This method constrains and controls the deformation of the foundation pit retaining wall 200 in a combined active and passive manner throughout the entire process and area. It can control the deformation of the foundation pit within a smaller range, and has the advantages of good foundation pit deformation control efficiency and ensuring the construction safety of long and narrow ultra-deep foundation pits.

[0056] Please refer to Figure 5 , Figure 6 and Figure 8 To improve the structural stability of the concrete support formwork system 110, the present invention provides a method for supporting a narrow and deep foundation pit. The concrete support formwork system 110 includes a bottom connecting plate 112, a support beam 113, a middle connecting plate 114, and a U-shaped channel formwork 115, all of which are horizontally arranged on the same straight line from bottom to top. Side supports 116 are horizontally arranged on the middle connecting plate 114 and distributed on the outside of each side formwork of the U-shaped channel formwork 115. A top connecting plate 117 is horizontally arranged around the vertical members 130 at the junction of the vertical members 130, the side supports 116, and the U-shaped channel formwork 115. The U-shaped channel formwork 115 is vertically supported by the bottom connecting plate 112, the support beam 113, and the middle connecting plate 114, improving the structural stability of the U-shaped channel formwork 115 and preventing it from falling off the vertical member 130. The side supports 116 on both sides provide lateral support for the U-shaped channel formwork 115, preventing structural deformation under stress and affecting the construction quality of the concrete support 203. The vertical member 130 can be a round steel pipe or a square steel pipe, and the support beam 113 and the side supports 116 can be H-beams or I-beams. The U-shaped channel formwork 115 can be spliced ​​from wooden formwork, welded from three steel formwork pieces, or formed by bending steel plates to create an integrated U-shaped channel structure.

[0057] Please refer to Figures 4 to 6To improve the load-bearing capacity of the bottom connecting plate 112 and its components, and to ensure the structural strength of the concrete support formwork system 110 mounted on the vertical member 130, the elongated ultra-deep foundation pit support construction method provided in this embodiment of the invention includes a diagonal brace 111 surrounding the vertical member 130 and fixedly mounted between the vertical member 130 and the bottom connecting plate 112. In this case, the bottom connecting plate 112 is mounted on the diagonal brace 111. The diagonal brace 111 can be a right-angled triangular plate or a right-angled trapezoidal plate, and the diagonal braces 111 at each node of the concrete support formwork system 110 of each vertical member 130 include, but are not limited to, four arranged in an array.

[0058] Please refer to Figures 5 to 6 To improve the load-bearing capacity of the U-shaped groove formwork 115, the present invention provides a method for supporting long and narrow ultra-deep foundation pits. In the concrete support formwork system 110, the support beams 113 are three parallel beams, two of which are distributed on both sides of all vertical members 130 on the same straight line, and the third support beam 113 is aligned with the axis of the vertical members 130. The three support beams 113 support the central connecting plate 114 and the components above it.

[0059] Please refer to Figures 5 to 6 To protect the U-shaped channel formwork 115 and prevent structural deformation during concrete pouring, the present invention provides a method for supporting long and narrow ultra-deep foundation pits. In the concrete support formwork system 110, two side supports 116 are provided, aligned with the corresponding support beams 113. The side supports 116 protect the side formwork of the U-shaped channel formwork 115, and the aligned arrangement of the side supports 116 with the support beams 113 ensures the structural stability of the concrete support formwork system 110.

[0060] The method for supporting a narrow, ultra-deep foundation pit provided in this embodiment of the invention improves the verticality of the vertical plane frame 100 when it is lowered into the trench 202. Before lowering the vertical plane frame 100, temporary top trench components 150 are installed on the outside of the support beams 113 of each concrete support formwork system 110. During the lowering of the vertical plane frame 100, the verticality of the vertical plane frame 100 is adjusted using the temporary top trench components 150. The temporary top trench components 150 can be adjustable telescopic components to accommodate different gaps and ensure the verticality of the vertical plane frame 100.

[0061] Please refer to Figure 5To prevent soil from entering the U-shaped groove formwork 115 of the subsequent concrete support formwork system 110 during excavation, the narrow and deep foundation pit support construction method provided in this embodiment of the invention involves, before lowering the vertical plane frame 100, installing a detachable cover plate 118 between the top connecting plates 117 of adjacent vertical members 130 on the same straight line of the remaining concrete support formwork systems 110 below the first concrete support formwork system 110. This allows for the removal of the cover plate 118, which is horizontally positioned on the top connecting plate 117 between adjacent vertical members 130. The detachable connection between the cover plate 118 and the top connecting plate 117 includes, but is not limited to, overlapping and hinged connections. The cover plate 118 can be a corrugated plate.

[0062] Please refer to Figure 4 The method for constructing a long and narrow ultra-deep foundation pit support according to embodiments of the present invention involves connecting the vertical members 130 and each steel support 120 node in the vertical plane frame 100 via flange joints 140 in four directions. The servo jacks 121 of each steel support 120 are connected to the flange joints 140 or connected to the flange joints 140 via steel support 120 segments. The servo jacks 121 are the servo ends of the steel supports 120. The flange joints 140 include a flange and flange bolts thereon, wherein the flange bolts are high-strength bolts. When the last steel support 120 is located at the bottom of the foundation pit, the flange joints 140 can be in three directions.

[0063] The method for supporting long and narrow ultra-deep foundation pits provided in this invention allows the vertical planar frame 100, composed of a concrete support formwork system 110, steel supports 120, and vertical components 130, to be assembled on the ground and then lowered as a whole. This reduces the difficulty of assembling the concrete support formwork system 110, shortens the construction cycle of the concrete support formwork system 110, and improves the construction efficiency of the concrete support formwork system 110. It also avoids the problems of high difficulty, low efficiency, and long cycle caused by limited space in the foundation pit.

[0064] This invention is not limited to the specific embodiments described above. Obviously, the embodiments described above are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of this invention are within the scope of protection of this invention. Those skilled in the art can make other modifications and variations to this invention. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for constructing a support system for a long and narrow ultra-deep foundation pit, characterized in that, include: Trench excavation: Excavate several trenches at intervals along the width of the ultra-deep foundation pit to the design elevation of the bottom slab; Vertical plane frame splicing and lowering: From top to bottom, a formwork support unit is formed by alternating arrangement of one concrete support formwork system and two steel supports. Vertical components connecting the adjacent steel supports of the formwork support unit and the steel supports with their adjacent concrete support formwork system are spliced ​​on the ground to form a vertical plane frame. Each vertical plane frame is then lowered vertically into each trench. Construction of the first concrete support: The first concrete support is constructed using the first concrete support formwork system and connected to the foundation pit retaining wall via the capping beam; Axial force adjustment of steel support: Excavate the soil below the first concrete support layer by layer. During the excavation process, adjust the axial force of the exposed steel support and tighten it against the foundation pit retaining wall. Next concrete support construction: Continue excavating the soil to expose the next concrete support formwork system, construct the concrete support through this concrete support formwork system and connect it to the foundation pit retaining wall through walers; Axial force adjustment of the two lower steel supports: Continue to excavate the soil layer by layer. During the excavation process, adjust the axial force of the two lower steel supports exposed in the soil and tighten them against the foundation pit retaining wall.

2. The construction method for supporting narrow, ultra-deep foundation pits according to claim 1, characterized in that, The concrete support formwork system includes bottom connecting plates, support beams, middle connecting plates, and U-shaped channel formwork on all vertical members horizontally arranged on the same straight line from bottom to top; side supports distributed on the outside of each side formwork of the U-shaped channel formwork on the middle connecting plate; and top connecting plates horizontally arranged around the vertical members at the junction of the vertical members, the side supports, and the U-shaped channel formwork.

3. The construction method for supporting narrow, ultra-deep foundation pits according to claim 2, characterized in that, The concrete support formwork system also includes diagonal bracing surrounding the vertical member and fixedly installed between the vertical member and the bottom connecting plate.

4. The construction method for supporting narrow, ultra-deep foundation pits according to claim 2, characterized in that, The support beams consist of three parallel beams, with two beams positioned on either side of all vertical members on the same straight line, and the third beam aligned with the axis of the vertical members.

5. The construction method for supporting narrow, ultra-deep foundation pits according to claim 4, characterized in that, The side supports consist of two beams, each aligned with the corresponding support beam on its respective side.

6. The construction method for supporting a long and narrow ultra-deep foundation pit according to claim 2, characterized in that, Before the vertical plane frame is lowered, a detachable cover plate is installed between the top connecting plates of two adjacent vertical members on the same straight line of the remaining concrete support formwork system below the first concrete support formwork system.

7. The construction method for supporting narrow, ultra-deep foundation pits according to claim 2, characterized in that, Before the vertical plane frame is lowered, temporary top groove components are set on the outside of each supporting beam. When the vertical plane frame is lowered, the verticality of the vertical plane frame is adjusted by the temporary top groove components.

8. The construction method for supporting a long and narrow ultra-deep foundation pit according to claim 1, characterized in that, The vertical components are connected to each steel support node via flange joints in four directions. The servo jacks of each steel support are connected to the flange joints or to the flange joints via steel support segments.

9. The construction method for supporting a long and narrow ultra-deep foundation pit according to claim 1, characterized in that, Before trench excavation, the soil within the foundation pit area is reinforced.

Images