Support replacement force transmission structure and construction method of staged foundation pit

Abstract

This invention relates to a phased foundation pit support structure and construction method, comprising: 1. Excavating the foundation pit to the base level, pouring ground beams, steel walers, and horizontal steel supports; 2. After the underground main structure is cured, removing the steel sections from the piles except those near the partition wall, and grouting; backfilling the trench between the basement exterior wall and the retaining structure, and constructing the above-ground structure; 3. After excavating the foundation pit to the base level, pouring the base slab and corbels; 4. After the base slab of the later-excavated foundation pit is completed, ... The construction process involves: 1. Creating openings between the steel piles of the partition wall; 2. Installing horizontal through-type steel supports; 3. Removing the horizontal steel supports, steel walers, and temporary horizontal supports of the subsequently excavated pit; 4. Constructing the basement roof slab of the subsequently excavated pit and installing horizontal through-type steel supports, removing the steel of the partition wall, and breaking the construction piles in this area down to the bottom elevation of the pit; 5. Pouring the bottom and top slabs of the area where the subsequently excavated pit meets the previously excavated pit, removing the corbels and through-type steel supports on the bottom and top slabs, and completing the construction.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering foundation pit support technology, and specifically relates to a force transmission structure for phased foundation pits and its construction method. Background Technology

[0002] In foundation pit engineering, it is common to encounter situations where two adjacent foundation pits are constructed in phases and share a common retaining wall (also known as a partition wall). The partition wall needs to be removed to connect the subsequent underground structures. When the partition wall is a diaphragm wall, the conventional approach is to directly remove the retaining wall section by section from top to bottom to achieve structural connection between the later-constructed and earlier-constructed foundation pits. However, when the partition wall is a steel-cement-soil mixing wall (commonly referred to as a construction pile), due to the large number of H-beams inserted within the retaining wall, direct removal would require cutting the steel above the pit bottom and permanently burying the steel below the bottom in the soil. This not only makes construction difficult and time-consuming but also results in poor economic efficiency. Furthermore, the foundation pits constructed sequentially experience significant horizontal earth pressure at their bottom slab elevations. If the bottom slabs on both sides fail to form an effective force transmission connection, eccentric pressure can easily occur, leading to excessive deformation or even instability of the retaining structure, or causing displacement and deformation of the main structure within the foundation pit.

[0003] Therefore, how to provide a force transfer structure and construction method for phased foundation pits is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the problems of existing technologies requiring the removal of retaining walls when adjacent foundation pits constructed sequentially share a steel-cement-soil mixing wall as a retaining structure, which leads to the inability to recycle the steel, easy disturbance of the completed structure, and difficulty in achieving effective force transmission between the bottom slabs on both sides, this paper provides a force transmission structure and construction method for phased foundation pits that enables complete steel recycling, ensures that the bottom slabs of both foundation pits share the load, controls foundation pit deformation, and ensures safe and reliable construction. This ensures that the steel is completely recycled and that the bottom slabs of both structures can reliably transmit force during structural connection.

[0005] To solve the above technical problems, the present invention includes the following technical solutions:

[0006] A method for constructing a phased foundation pit, wherein the phased foundation pits are separated by a method pile partition wall, and the phased foundation pit includes a pre-excavated foundation pit and a post-excavated foundation pit, the construction method comprising:

[0007] Step S1: First, excavate the foundation pit to the base level. When pouring the bottom slab, leave a gap at the junction with the partition wall. On the bottom slab, near the reserved gap, pour a ground beam parallel to the partition wall. On the opposite side of the ground beam, at the same elevation as the ground beam, install a steel waler, with the steel waler tightly abutting against the steel section of the adjacent partition wall. Install a horizontal steel support between the ground beam and the steel waler to transfer horizontal earth pressure to the partition wall before the bottom slab of the excavated foundation pit is connected. When constructing the basement roof slab of the excavated foundation pit, install a low wall above the capping beam on the side of the partition wall to connect with the roof slab.

[0008] Step S2: After the underground main structure is cured, remove the steel sections from the piles except those near the partition wall and fill the gaps with grout in time; leave at least two steel sections near the partition wall and do not remove them for the time being; backfill the trench between the basement exterior wall and the retaining structure, and set up a retaining wall near the partition wall to finish the edge; continue to excavate the foundation pit and construct the above-ground structure.

[0009] Step S3: The excavated foundation pit is constructed using the open-cut method. After excavating to the foundation, the bottom slab is poured, leaving a gap at the junction with the partition wall. On the bottom slab, a corbel is poured on the side near the reserved gap as a support point for subsequent through-hole force transmission.

[0010] Step S4: After the excavated foundation pit bottom slab is completed, select a location to make an opening between the construction pile steel sections of the partition wall, avoiding the positions of the steel walers and the inserted steel sections of the construction piles; install horizontal through-type steel replacement supports, with one end of the through-type steel replacement supports supported on the ground beam of the excavated foundation pit bottom slab and the other end supported on the corbel of the excavated foundation pit bottom slab; remove the horizontal steel replacement supports and steel walers on the excavated foundation pit bottom slab, remove the horizontal internal supports of the excavated foundation pit, construct the excavated foundation pit basement top slab, and install through-type steel replacement supports on both sides of the partition wall, with the two ends of the through-type steel replacement supports connected to the excavated foundation pit basement top slab and the excavated foundation pit basement top slab respectively;

[0011] Step S5: First, excavate the foundation pit and set up temporary steel columns near the partition wall area. Remove the steel of the partition wall and break the construction piles in this area down to the bottom of the pit.

[0012] Step S6: Pour the bottom and top slabs of the area where the excavated foundation pit meets the first excavated foundation pit to achieve structural connection on both sides; remove the corbels and through-type steel supports on the bottom and top slabs to complete all construction.

[0013] Furthermore, the reserved gap is 400mm to 1000mm wide, and 800mm wide can be selected.

[0014] Furthermore, before opening the hole, the area to be opened is pre-reinforced by overlapping steel sleeves or by making separate reinforcements.

[0015] Furthermore, the steel sleeve is a top-feed steel sleeve, the head of the steel sleeve is provided with cutting teeth, and the outer wall of the steel sleeve is coated with lubricating oil.

[0016] A force-transfer structure for phased excavation pits includes a partition wall, a pre-excavated pit, and a post-excavated pit. The partition wall divides the excavation pit into the pre-excavated and post-excavated pits. Reserved gaps are provided between the partition wall and the bottom slabs of the pre-excavated and post-excavated pits, respectively. The structure is characterized by a ground beam located near the reserved gap on the bottom slab of the pre-excavated pit; a steel waler located on the opposite side of the partition wall relative to the ground beam, with the steel waler and ground beam on the same horizontal plane and abutting against the partition wall; a horizontal steel brace between the ground beam and the steel waler, and the ground beam, horizontal steel brace, and steel waler interconnected; a corbel located near the reserved gap on the bottom slab of the post-excavated pit; and a through-type steel brace penetrating the partition wall, with one end of the through-type steel brace supported on the ground beam of the pre-excavated pit bottom slab and the other end supported on the corbel of the post-excavated pit bottom slab, and the ground beam, through-type steel brace, and corbel interconnected.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) The phased foundation pit construction method provided by the present invention, through the phased support and force transmission design, allows the steel in the partition wall to be completely removed and recycled after completing its retaining function, avoiding the waste caused by the traditional chiseling method of cutting the steel, resulting in significant economic benefits, realizing the complete recycling of the steel, and greatly reducing the project cost.

[0019] (2) The phased foundation pit construction method provided by the present invention effectively transfers the horizontal soil pressure borne by the first excavated foundation pit bottom plate to the second excavated foundation pit bottom plate through the combination of ground beam + temporary support and through steel + corbel support system, so as to realize the coordinated work of the two sides of the structure, avoid the excessive deformation of the retaining wall or the displacement of the main structure due to the bias pressure, thereby ensuring that the two sides of the structure are subjected to the same force and eliminating the risk of bias pressure.

[0020] (3) The phased foundation pit construction method provided by the present invention uses rebar hoop or steel sleeve to pre-reinforce the opening area, which effectively solves the problem of easy collapse and cross-section weakening of the pile opening, ensures the safety of the opening construction and the reliability of subsequent force transmission, and protects the safety of the retaining structure.

[0021] (4) The phased foundation pit construction method provided by the present invention has reasonable procedures and orderly connection. It is applicable to the configuration and combination of steel with different stiffness and can also flexibly select reinforcement methods according to site conditions, and has good engineering adaptability. Attached Figure Description

[0022] Figure 1 This is a plan view of the completed construction of a phased foundation pit according to an embodiment of the present invention;

[0023] Figures 2 to 7 This is a schematic diagram of steps S1 to S6 of a phased foundation pit construction method according to an embodiment of the present invention.

[0024] Figure 8 This is a schematic diagram of the steel sleeve structure.

[0025] 1- Excavate the foundation pit first, 2- Excavate the foundation pit later, 3- Reserved gap, 4- Partition wall, 5- Ground beam, 6- Steel waler, 7- Steel section of partition wall, 8- Horizontal steel replacement support, 9- Foundation pit bottom slab excavated first, 10- Basement top slab excavated first, 11- Foundation pit bottom slab excavated later, 12- Corbel, 13- Through steel replacement support, 14- Horizontal internal support of foundation pit excavated later, 15- Steel sleeve, 16- Basement top slab excavated later, 17- Temporary steel column, 18- Peripheral steel section of foundation pit excavated first. Detailed Implementation

[0026] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a more detailed explanation of the force transfer structure and construction method for phased foundation pits provided by the present invention. The advantages and features of the present invention will become clearer from the following description.

[0027] The following is combined with Figures 1 to 8 The construction method of the phased foundation pit of the present invention is described in detail.

[0028] Example 1

[0029] Please refer to Figures 1 to 8 A construction method for connecting phased foundation pits, wherein a method pile partition wall 4 is provided between the phased foundation pits, and the partition wall 4 is a steel-cement-soil mixing wall (also known as a method pile).

[0030] The phased excavation method includes excavating excavation pit 1 first and excavating excavation pit 2 later. The construction method includes the following steps:

[0031] Step 1: First, excavate the foundation pit 1 to the base. When pouring the bottom slab, set a reserved gap 3 with a width of 400mm~1000mm at the junction with the partition wall 4. For example, an 800mm width can be selected. On the bottom slab, near the reserved gap 3, pour a ground beam 5 parallel to the foundation pit partition wall. On the opposite side of the ground beam 5, at the same elevation as the ground beam 5, set a steel waler 6. The steel waler 6 should be tightly pressed against the steel 7 of the three adjacent partition walls. Set a horizontal steel support 8 between the ground beam 5 and the steel waler 6 to transfer horizontal earth pressure to the partition wall 4 before the foundation pit bottom slab 9 is connected. When constructing the basement top slab 10 of the foundation pit, set a low wall above the capping beam on the side of the partition wall to connect with the top slab.

[0032] Step Two: After the underground main structure is cured, excavate the foundation pit and remove the steel sections 18 on the perimeter of the foundation pit, except for the side closest to the partition wall. Grout the gaps in time to ensure water-stopping performance and control the deformation of the foundation pit. Leave at least two steel sections 7 of the partition wall on the side closest to the partition wall for temporary retaining for subsequent processes. Backfill the trench between the basement exterior wall and the retaining structure, and set up a retaining wall on the side closest to the partition wall to stop the backfilled trench soil. Continue to excavate the foundation pit and construct the above-ground structure.

[0033] Step 3: The excavated foundation pit is constructed using the open-cut method. After excavating to the foundation, the bottom slab 11 of the excavated foundation pit is poured, leaving a gap of 400mm to 1000mm at the junction with the partition wall. On the bottom slab, a corbel 12 is poured on the side near the reserved gap as a support point for subsequent through-through force transmission.

[0034] Step 4: After the excavated foundation pit bottom slab 11 is completed, select at least a few locations to make holes between the construction pile steel of the partition wall. The hole locations should avoid the locations of the steel waler 6 set in Step 1, and avoid the locations of the steel waler 6 and the inserted steel of the construction pile.

[0035] Pre-reinforcement treatment is carried out on the area to be drilled before drilling:

[0036] A self-jacking steel sleeve with a cutting edge is inserted to form a support and prevent the opening from collapsing. The head of the steel sleeve 15 has cutting teeth for jacking, and the outer wall of the steel sleeve 15 is coated with lubricating oil. Through reinforcement, it is ensured that the cement and soil do not collapse during the opening process and that the cross-section is not weakened after the opening is completed.

[0037] After reinforcement, an opening is made, and a horizontal through-type steel replacement brace 13 is installed. One end of the brace is supported on the ground beam 5 of the first excavated foundation pit bottom slab, and the other end is supported on the corbel 12 of the second excavated foundation pit bottom slab. The horizontal steel replacement brace 8 and steel waler 6 set on the first excavated foundation pit bottom slab 9 in step one are removed. The horizontal internal support 14 of the second excavated foundation pit 2 set during the foundation pit excavation construction is removed. The second excavated foundation pit basement top slab 16 is constructed. Through-type steel replacement braces 13 are set on both sides of the partition wall. That is, the two ends of the through-type steel replacement brace 13 are connected to the second excavated foundation pit basement top slab 16 and the first excavated foundation pit basement top slab 10 respectively, so as to realize the horizontal force transmission of the top slab elevation.

[0038] Step 5: First, excavate the foundation pit and set up temporary steel columns 17 near the partition wall area. Remove the steel of the partition wall and break the construction piles in this area down to the bottom of the pit.

[0039] Step Six: After pouring the concrete, pour the bottom and top slabs of the area where the excavated foundation pit meets the first excavated foundation pit to achieve structural connection on both sides; remove the corbels 12 and the through-type steel replacement supports 13 on the bottom and top slabs to complete all construction.

[0040] This embodiment also provides a support and force transmission structure for phased foundation pits, including a partition wall 4, a pre-excavated foundation pit 1, and a post-excavated foundation pit 2. The partition wall 4 divides the foundation pit into the pre-excavated foundation pit 1 and the post-excavated foundation pit 2. Reserved gaps 3 are provided between the partition wall 4 and the bottom slab 9 of the pre-excavated foundation pit and the bottom slab 11 of the post-excavated foundation pit, respectively. A ground beam 5 is provided on the bottom slab 9 of the pre-excavated foundation pit near the reserved gaps 3. A steel waler 6 is provided on the other side of the partition wall 4 opposite to the ground beam 5. The steel waler 6 and the ground beam 5 are located on the same horizontal plane and are tightly attached to each other. The partition wall 4 is supported; a horizontal steel support 8 is provided between the ground beam 5 and the steel waler 6, and the ground beam 5, the horizontal steel support 8 and the steel waler 6 are fixedly connected in sequence; a corbel 12 is provided on the bottom plate 11 of the excavated foundation pit near the reserved gap 3; a through steel support 13 is provided through the partition wall 4, one end of the through steel support 13 is supported on the ground beam 5 of the bottom plate of the excavated foundation pit, and the other end is supported on the corbel 12 of the bottom plate of the excavated foundation pit, and the ground beam 5, the through steel support 13 and the corbel 12 are fixedly connected in sequence.

[0041] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. The above embodiments only illustrate several implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for constructing a phased foundation pit, characterized in that, The phased foundation pits are separated by pile walls, and the phased foundation pits include pre-excavated pits and post-excavated pits. The construction method includes: Step S1: First, excavate the foundation pit to the base level. When pouring the bottom slab, leave a gap at the junction with the partition wall. On the bottom slab, near the reserved gap, pour a ground beam parallel to the partition wall. On the opposite side of the ground beam, at the same elevation as the ground beam, install a steel waler, with the steel waler tightly abutting against the steel section of the adjacent partition wall. Install a horizontal steel support between the ground beam and the steel waler to transfer horizontal earth pressure to the partition wall before the bottom slab of the excavated foundation pit is connected. When constructing the basement roof slab of the excavated foundation pit, install a low wall above the capping beam on the side of the partition wall to connect with the roof slab. Step S2: After the underground main structure is cured, remove the steel sections from the piles except those near the partition wall and fill the gaps with grout in time; leave at least two steel sections near the partition wall and do not remove them for the time being; backfill the trench between the basement exterior wall and the retaining structure, and set up a retaining wall near the partition wall to finish the edge; continue to excavate the foundation pit and construct the above-ground structure. Step S3: The excavated foundation pit is constructed using the open-cut method. After excavating to the foundation, the bottom slab is poured, leaving a gap at the junction with the partition wall. On the bottom slab, a corbel is poured on the side near the reserved gap as a support point for subsequent through-hole force transmission. Step S4: After the excavated foundation pit bottom slab is completed, select a location to make an opening between the construction pile steel sections of the partition wall, avoiding the positions of the steel walers and the inserted steel sections of the construction piles; install horizontal through-type steel replacement supports, with one end of the through-type steel replacement supports supported on the ground beam of the excavated foundation pit bottom slab and the other end supported on the corbel of the excavated foundation pit bottom slab; remove the horizontal steel replacement supports and steel walers on the excavated foundation pit bottom slab, remove the horizontal internal supports of the excavated foundation pit, construct the excavated foundation pit basement top slab, and install through-type steel replacement supports on both sides of the partition wall, with the two ends of the through-type steel replacement supports connected to the excavated foundation pit basement top slab and the excavated foundation pit basement top slab respectively; Step S5: First, excavate the foundation pit and set up temporary steel columns near the partition wall area. Remove the steel section of the partition wall and break the construction piles in this area down to the bottom of the pit. Step S6: Pour the bottom and top slabs of the area where the excavated foundation pit meets the first excavated foundation pit to achieve structural connection on both sides; remove the corbels and through-type steel supports on the bottom and top slabs to complete all construction.

2. The construction method according to claim 1, characterized in that, The reserved gap is 400mm to 1000mm wide.

3. The construction method according to claim 1, characterized in that, Before opening the hole, the area to be opened is pre-reinforced by overlapping steel sleeves or by making separate reinforcements.

4. The construction method according to claim 3, characterized in that, The steel sleeve is a top-feed steel sleeve, the head of the steel sleeve is provided with cutting teeth, and the outer wall of the steel sleeve is coated with lubricating oil.

5. The phased foundation pit support and force transmission structure according to any one of claims 1 to 4, comprising a partition wall, a pre-excavated foundation pit, and a post-excavated foundation pit, wherein the partition wall divides the foundation pit into a pre-excavated foundation pit and a post-excavated foundation pit, and a reserved gap is provided between the partition wall and the bottom slab of the pre-excavated foundation pit and the bottom slab of the post-excavated foundation pit, characterized in that, A ground beam is provided on the first excavated foundation pit floor slab near the reserved gap; a steel waler is provided on the other side of the partition wall opposite to the ground beam, the steel waler and the ground beam are on the same horizontal plane, and the steel waler is tightly abutted against the partition wall; a horizontal steel brace is provided between the ground beam and the steel waler, and the ground beam, the horizontal steel brace and the steel waler are interconnected; a corbel is provided on the second excavated foundation pit floor slab near the reserved gap; a through steel brace is provided through the partition wall, one end of the through steel brace is supported on the ground beam of the first excavated foundation pit floor slab, and the other end is supported on the corbel of the second excavated foundation pit floor slab, and the ground beam, the through steel brace and the corbel are interconnected.

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