CN116289979A - Construction Method of Deep Foundation Pit Supporting Underground Simultaneous Construction - Google Patents

Abstract

The deep foundation pit supporting construction method of underground forward and reverse simultaneous construction of the present invention is aimed at the problem that when the basement roof and the ground are not located on the same horizontal plane, it is necessary to set transverse supports in the foundation pit to strengthen the support, which reduces the construction efficiency. The steps are as follows: use the straight method to construct the central island area in advance, excavate the soil in the central island area to the level below the second structural beam slab in the basement, and pour the central part of the second structural beam slab in the basement; The second structural beams and slabs are arranged at intervals and fixed with multiple diagonal throwing braces; the surrounding area of the foundation pit is excavated and the second structural beams and slabs of the basement are poured. After the second structural beams and slabs of the basement reach the required strength, they are removed Diagonal throwing bracing, using the sequential method to construct the underground structure and the structures of the above-ground layers, simultaneously excavating the soil below the second structural beam slab in the basement and using the reverse method to construct the underground structures in sequence.

Description

Construction Method of Deep Foundation Pit Supporting Underground Simultaneous Construction

technical field

The invention relates to the technical field of geotechnical engineering foundation pit support, in particular to a deep foundation pit support construction method for underground forward and reverse simultaneous construction.

Background technique

In recent years, with the acceleration of urbanization, the development and utilization of underground space has been increasing, the depth of foundation pits has become deeper and deeper, and the construction space of support structures has become more and more limited. The forward method is simple in operation, fast in speed, low in cost, simple in the supporting structure, easy to grasp the construction period, and easy to control the project quality, but it will cause great damage to the surrounding environment; the reverse method uses the beams, slabs, and columns of the main underground structure as the retaining wall Lateral support can greatly shorten the construction period, reduce the amount of earthwork, and improve the safety of construction, but the quality of concrete bonding of wall columns in underground structures is difficult to control.

At present, in construction projects with simultaneous forward and reverse construction, the basement roof is usually used as the first support. When it is not at the same level as the ground, the roof of the basement cannot provide support as an enclosure structure. During the excavation of the foundation pit, the enclosure structure will deform due to the excessively long cantilever. It is necessary to set up horizontal supports in a large area in the foundation pit. Strengthening the support reduces the construction efficiency and increases the engineering cost.

Contents of the invention

When the roof of the basement is not at the same level as the ground, it is necessary to set up a large area of lateral support in the foundation pit to strengthen the support, which reduces the construction efficiency and increases the project cost. The object of the invention is to provide a deep foundation pit support construction method for underground forward and reverse simultaneous construction.

The technical solution adopted by the present invention to solve the technical problem is: a deep foundation pit support construction method of underground forward and reverse synchronous construction, the steps are as follows:

S1: Construct the foundation pit enclosure structure. Vertically connected column piles and lattice piles are used as vertical supports in the foundation pit. The method is to construct the central island area in advance. The soil in the central island area is sloped and excavated to below the level of the second structural beam and slab in the basement, and the central part of the second structural beam and slab in the basement is poured. Part of the lattice pile for structural column construction, so that the top of the lattice pile is located at the bottom of the second structural beam slab in the basement;

S2: Set and fasten multiple diagonal braces at intervals between the top beam and the central part of the second structural beam slab in the basement, and cut off some lattice piles that affect the installation of diagonal braces;

S3: Excavate the reserved soil slope in the surrounding area of the foundation pit and continue to pour the second structural beam slab in the basement. After the second structural beam slab in the basement reaches the strength required by the design, remove the oblique struts and use the straight method to construct the first underground structure. Layer structure and the structure of each layer above the ground, the soil below the second structural beam slab in the basement is excavated simultaneously, and the structure of each underground layer is constructed sequentially by using the reverse method.

In the deep foundation pit support construction method of underground forward and reverse simultaneous construction of the present invention, firstly, the underground layer of foundation pit soil is divided into a central island area and surrounding areas, the central island area is constructed in advance by the forward method, and the underground is excavated by sloping. A layer of soil and pouring the central part of the second structural beam slab in the basement, installing diagonal throw braces between the top beam and the second structural beam slab in the basement, and then excavating the reserved soil slope around the foundation pit and completing the basement For the pouring construction of the second structural beam and slab, after the second structural beam and slab of the basement reaches the strength required by design, the oblique throwing braces will be removed and the structure of the first basement and its upper floors will be constructed by the sequential method, and the second basement will be excavated simultaneously. The soil mass under the beam slab of the road structure and the structure of each underground layer are sequentially constructed by using the reverse method; the deep foundation pit support construction method of the underground forward and backward simultaneous construction of the present invention has at least the following beneficial effects:

1. Different from the existing top-down method, which uses the first structural beam and slab of the basement as the first horizontal support, this construction method constructs the center island area in advance and pours the center part of the second structural beam and slab in the basement. Diagonal braces are added between the beams and slabs of the road structure, so that the enclosure structure, diagonal braces, lattice piles and part of the main structure are connected to each other to form a complete supporting structure force system to resist surrounding water and soil pressure and construction loads, etc. , the support structure in the foundation pit can be simplified, which not only improves the construction efficiency, shortens the construction period, but also avoids the disadvantages of long construction period and environmental pollution caused by the erection and removal of horizontal supports in conventional construction. Dismantle, recycle and reuse, effectively saving the project cost and realizing green construction;

2. Since the second structural beam slab in the basement is used as the first horizontal support of the top-down method, that is, the up-and-down simultaneous construction is carried out below the ground, which reduces the number of layers of upside-down construction, reduces the construction difficulty, and shortens the construction time. The time spent waiting for the structural beam and slab to reach the design strength is shortened, the construction efficiency is accelerated, and the project cost is reduced;

3. The existing upside-down method uses the first structural beam and slab in the basement as the first horizontal support. In order to meet the vertical bearing capacity requirements of one column and one pile, the cross-sectional size of the lattice pile is often larger than the structural column in the basement, resulting in that the structural column cannot contain In the case of lattice piles, this technical solution uses the second structural beam slab in the basement as the first support, the vertical bearing capacity of one column and one pile becomes smaller, and the cross-sectional size of the lattice piles is also reduced accordingly, which is convenient for the structural columns to enclose The lattice column realizes the reliable connection between the two, avoiding the situation that the structural column cannot cover the lattice pile with a large cross-sectional size.

Preferably, in the step S1, the construction method of the foundation pit enclosure structure is as follows: install three-axis cement-soil mixing piles on both sides of the groove section where the underground diaphragm wall is located to reinforce the groove wall, and use large-diameter high-pressure rotary grouting The pile seals the water at the joints of the underground diaphragm wall, and an "L"-shaped concrete guide wall is formed on the top of the three-axis cement-soil mixing pile located on the outside. One end of the concrete guide wall is set inside the three-axis cement-soil mixing pile. The other end is located on the top of the three-axis cement-soil mixing pile, and a top beam is constructed on the top of the underground diaphragm wall and a reserved main reinforcement is provided.

Preferably, in the step S1, the surrounding area of the soil body of the basement layer of the foundation pit is excavated in such a way that the width of the grading platform is ≥ 3m, and the grading slope is not greater than 1:1.5. Reinforced mesh, with anchor bars and insert bars inside for slope protection.

Preferably, the concrete support is fixed at the intersection between the edge top of the center part of the second structural beam slab in the basement and the structural column, the steel support is riveted to the side of the top beam, and one end of the slanting brace is welded on the steel support , the other end of which is riveted to the concrete support through the anchor plate.

Preferably, the construction joints at the ends of the central part of the second structural beam slab in the basement are provided with reserved main reinforcement, and the reserved main reinforcement is connected with the structural main reinforcement of the second structural beam slab in the surrounding area of the later construction.

Description of drawings

Fig. 1 is the schematic diagram of excavation in the central island area of an embodiment of the deep foundation pit support construction method of underground forward and reverse synchronous construction of the present invention;

Fig. 2 is a schematic diagram of the installation of diagonal braces between the first structural beam slab and the top beam in the basement in an embodiment of the deep foundation pit support construction method of underground forward and reverse simultaneous construction according to the present invention.

Fig. 3 is a schematic diagram of forward and reverse simultaneous construction of an embodiment of the deep foundation pit support construction method of underground forward and reverse simultaneous construction according to the present invention.

The numbers in the figure are as follows:

Column pile 1; lattice pile 2; concrete panel 3; inserting reinforcement 4; anchor reinforcement 5; underground diaphragm wall 11; triaxial cement-soil mixing pile 12; The main reinforcement 17 is left; the first structural beam slab 21 of the basement; the second structural beam slab 22 of the basement; the structural column 25; the concrete support 26; the steel support 27;

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that all the drawings are in very simplified form and use inaccurate scales, and are only used to facilitate and clearly assist the purpose of illustrating the embodiments of the present invention. For the convenience of description, the "up" and "down" described below are consistent with the directions of up and down in the drawings, but this should not be a limitation of the technical solution of the present invention.

In this embodiment, the basement roof (i.e., the first structural beam slab 21 of the basement) is located above the leveled ground, and the deep foundation pit support construction method of the present invention will be described below in conjunction with Fig. 1 to Fig. 3 . Proceed as follows:

S1: As shown in Figure 1, the foundation pit enclosure structure is constructed, and vertically connected column piles 1 and lattice piles 2 (that is, one column and one pile) are used as vertical supports in the foundation pit, and the underground layer of soil is divided into For the central island area and the surrounding area enclosed by it, the central island area is constructed in advance using the straight method. The area marked by the dotted line in Figure 1 is the central island area. The soil in the central island area is sloped and excavated to the second basement. Below the elevation of the first structural beam slab 22, pour the central part of the second structural beam slab 22 in the basement, as shown in Figure 2, cut off some lattice piles 2 that affect the construction of the second structural beam slab 22 and structural column 25 in the basement, namely In Fig. 2, part of lattice pile 2 filled with dotted frame line and oblique line makes the top of lattice pile 2 be located at the bottom of the second structural beam slab 22 in the basement;

S2: As shown in Figure 2, a plurality of slanting struts 28 are arranged and fixed at intervals between the top beam 16 and the central part of the second structural beam slab 22 in the basement, and part of the lattice piles that affect the setting of the slanting struts 28 are cut off 2;

S3: As shown in Figure 3, excavate the reserved soil slope in the surrounding area of the foundation pit and continue to pour the second structural beam 22 in the basement. After the second structural beam 22 in the basement reaches the strength required by the design, remove the oblique casting Brace 28, use the straight method to construct the structure of the first basement and its upper layers, simultaneously excavate the soil below the second structural beam slab 22 in the basement, and use the reverse method to sequentially construct the second underground structure, the third underground structure, etc. layers of structure.

In the deep foundation pit support construction method of underground forward and reverse simultaneous construction of the present invention, firstly, the underground layer of foundation pit soil is divided into a central island area and surrounding areas, the central island area is constructed in advance by the forward method, and the underground is excavated by sloping. A layer of soil is poured into the central part of the second structural beam slab 22 in the basement, and a diagonal brace 28 is installed between the top beam 16 and the second structural beam slab 22 in the basement. Then, the reserved soil in the surrounding area of the foundation pit is excavated Slope and complete the pouring construction of the second structural beam slab 22 in the basement. After the second structural beam slab 22 in the basement reaches the strength required by the design, remove the oblique throwing braces 28 and adopt the sequential method to construct the structure of the first floor of the basement and its upper floors. , synchronously excavate the soil below the second structural beam slab 22 in the basement and adopt the reverse method to construct the underground layers in sequence; the deep foundation pit support construction method of underground forward and backward simultaneous construction of the present invention has at least the following beneficial effects:

1. Unlike the existing top-down method, which uses the first structural beam 21 in the basement as the first horizontal support, this construction method constructs the central island area in advance and pours the central part of the second structural beam 22 in the basement, and the top beam 16 and Diagonal throwing braces 28 are added between the second structural beams and slabs 22 of the basement, so that the enclosure structure, diagonal throwing braces 28, lattice piles 2 and part of the main structure are connected to each other to form a complete supporting structure stress system to resist Surrounding water and soil pressure and construction load, etc., the supporting structure in the foundation pit is simplified, which not only improves the construction efficiency, shortens the construction period, but also avoids the long construction period and environmental pollution caused by the erection and removal of horizontal supports in conventional construction. Moreover, the oblique throw brace 28 can be dismantled and recycled in the later stage, which effectively saves the project cost and realizes green construction;

2. Since the second structural beam slab 22 in the basement is used as the first horizontal support of the upside-down method, that is, the up-and-down simultaneous construction is carried out below the ground, which reduces the number of layers of upside-down construction, reduces the difficulty of construction, and It shortens the waiting time for the structural beam and slab to reach the design strength, speeds up the construction efficiency and reduces the project cost;

3. The existing upside-down method uses the first structural beam 21 in the basement as the first horizontal support. In order to meet the vertical bearing capacity requirements of one column and one pile, the cross-sectional size of the lattice pile 2 is often larger than the structural column 25 in the basement, resulting in structural The column 25 cannot enclose the lattice pile 2. In this technical solution, since the second structural beam 22 in the basement is used as the first support, the vertical bearing capacity of one column and one pile becomes smaller, and the section size of the lattice pile 2 is correspondingly The shrinkage makes it easier for the structural column 25 to enclose the lattice column 2 to achieve reliable connection between the two, and avoids the situation that the structural column 2 cannot enclose the lattice column 2 with a large cross-sectional size.

As shown in Figure 1, the construction method of the foundation pit enclosure structure in this embodiment, the steps are as follows: install three-axis cement-soil mixing piles 12 on both sides of the groove section where the underground diaphragm wall 11 is located to reinforce the groove wall, so as to ensure the continuous underground The wall 11 is grooved safely, and the joints of the underground diaphragm wall 11 are water-stopped through RJP large-diameter high-pressure jet grouting piles 14; "L"-shaped concrete pouring is formed on the top of the three-axis cement-soil mixing pile 12 located on the outside Guide wall 15, one end of concrete guide wall 15 is set inside the triaxial cement-soil mixing pile 12, and the other end is located at the top of the triaxial cement-soil mixing pile 12, and the top beam 16 is constructed on the top of the underground diaphragm wall 11 and the main reinforcement 17 is reserved for It is connected with the main reinforcement of the basement exterior wall in the later construction.

Please continue to refer to Figure 1. The ground floor of the foundation pit is excavated with a grading platform width ≥ 3m and a grading slope of no more than 1:1.5. The 80mm thick C20 concrete panel 3 is laid on the slope surface, and the concrete panel 3 is equipped with 6.5 @200×200 reinforcement mesh (not shown in the figure), and φ48×3.5 anchor reinforcement 5 and φ20 insertion reinforcement 4 are installed inside for slope protection.

As shown in Figure 2, the concrete support 26 is fixed on the junction between the edge top of the center part of the second structural beam slab 22 in the basement and the structural column 25, the steel support 27 is riveted to the side of the top beam 16, and the oblique cast support 28 One end is welded on the steel support 27, and the other end is riveted to the concrete support 26 through the anchor plate.

The main reinforcement 17 is reserved at the construction joint at the end of the central part of the second structural beam slab 22 in the basement, so as to facilitate connection with the structural main reinforcement of the second structural beam slab in the surrounding area of the later construction.

A construction operation space greater than or equal to 1m is reserved between the construction joints of the second structural beam slab 22 of the basement and the bottom of the slope.

The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention. Any changes and modifications made by those of ordinary skill in the field of the present invention based on the above disclosures shall fall within the scope of the claims.

Claims (5)

1. The deep foundation pit supporting construction method for underground forward and reverse synchronous construction is characterized by comprising the following steps:

s1: constructing a foundation pit enclosure structure, wherein vertical column piles and lattice piles which are vertically connected are adopted in a foundation pit as vertical supports, a layer of soil body in the ground is divided into a central island area and a peripheral area enclosed on the outer side of the central island area, the soil body in the central island area is excavated to the lower part of the elevation of a second structural beam slab of the basement in a forward construction method in advance, the central part of the second structural beam slab of the basement is poured, and part of the lattice piles which influence the construction of the second structural beam slab and the structural columns of the basement are cut off, so that the top of the lattice piles are positioned at the bottom of the second structural beam slab of the basement;

s2: a plurality of inclined throwing supports are arranged at intervals between the top beam and the central part of a second structural beam plate of the basement, and partial lattice piles influencing the arrangement of the inclined throwing supports are cut off;

s3: and excavating a soil slope in the peripheral area of the foundation pit, continuing pouring and constructing a second structural beam slab of the basement, dismantling the inclined throwing support after the second structural beam slab of the basement reaches the strength required by design, constructing a layer of underground structure and all layers of above-ground structure by adopting a forward method, synchronously excavating soil below the second structural beam slab of the basement, and constructing all layers of underground structure in sequence by adopting a reverse method.

2. The deep foundation pit supporting construction method for simultaneous underground forward and reverse construction according to claim 1, wherein in the step S1, the construction method of the foundation pit supporting structure is as follows: the two sides of the groove section where the underground diaphragm wall is positioned are provided with triaxial cement mixing piles for groove wall reinforcement, water is stopped at the joint of the underground diaphragm wall through large-diameter high-pressure jet grouting piles, an L-shaped integrally-poured concrete guide wall is formed at the top of the triaxial cement mixing piles located on the outer side, one end of the concrete guide wall is arranged on the inner side of the triaxial cement mixing piles, the other end of the concrete guide wall is located at the top of the triaxial cement mixing piles, a capping beam is constructed at the top of the underground diaphragm wall, and reserved main ribs are arranged.

3. The deep foundation pit supporting construction method for underground forward and reverse synchronous construction according to claim 1, wherein the method comprises the following steps: in the step S1, the peripheral area of a layer of soil body under the foundation pit is excavated in a mode that the width of a slope-placing platform is more than or equal to 3m, the slope-placing gradient is not more than 1:1.5, a concrete panel is paved on the slope, a reinforcing steel bar net is arranged in the concrete panel, and anchor bars and dowel bars are arranged in the concrete panel to protect the slope.

4. The deep foundation pit supporting construction method for underground forward and reverse synchronous construction according to claim 1, wherein the method comprises the following steps: the concrete support is fixedly connected to the joint part between the top of the edge of the central part of the second structural beam slab of the basement and the structural column, the steel support is riveted on the side surface of the top beam, one end of the inclined throwing support is welded on the steel support, and the other end of the inclined throwing support is riveted on the concrete support through an anchor plate.

5. The deep foundation pit supporting construction method for underground forward and reverse synchronous construction according to claim 1, wherein the method comprises the following steps: and a reserved main rib is arranged at the end construction joint of the central part of the second structural beam slab of the basement and is connected with the structural main rib of the second structural beam slab of the peripheral area of the later construction.

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