Cantilever side wall self-stabilizing system for deep foundation pit support and construction method thereof

Abstract

The application discloses a cantilever type side wall self-stabilizing system applied to deep foundation pit support and a construction method thereof, which comprises two water-stopping curtains, support piles, concrete slope protection, a plurality of soil nails arranged in the concrete slope protection, a corbel arranged at the top of the support piles, and a wet lean concrete layer arranged at the inner side of the support piles, further comprises a box culvert of a lower passageway, a plurality of rows of additional support steels arranged at intervals are arranged in the structural steel of the box culvert of the lower passageway, and the box culvert of the lower passageway comprises a lower passageway bottom plate, a lower passageway top plate and two lower passageway side walls; one end of the additional support steel is inserted into the lower passageway side wall, the other end of the additional support steel is arranged through the vertical side wall section of the lower passageway bottom plate, and is bent and inserted into the horizontal bottom wall section of the lower passageway bottom plate, so as to ensure the bending bearing capacity of the lower passageway bottom plate; thus, the existing technology of the inverted support structure can be replaced, the pressure of the side wall panel is smaller, the rigidity and the anti-seismic capacity of the overall structure are improved, and the construction period can be obviously shortened.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation pit support, in particular to a cantilever type side wall self-stabilizing system for deep foundation pit support and a construction method thereof, which is especially suitable for the foundation pit support operation of the deep foundation pit with a depth of no more than 8 meters, complex surrounding geology, many underground pipelines and internal support. BACKGROUND

[0002] The foundation pit engineering is to excavate a underground space from the ground, and a vertical enclosure structure is arranged around the underground space, and a certain depth of an inserted plate (or pile) wall structure is arranged under the excavation surface.

[0003] At present, the inverted support structure is often used for the foundation pit support to reduce the deformation of the enclosure structure and control the wall bending moment, but the inverted support directly supports the inner surface of the side wall panel, so that the stress area of the side wall panel is very small, and the side wall panel is prone to deformation and damage.

[0004] In addition, the box culvert structure of each section is generally provided with 9 inverted supports, and the inverted support of each section needs to be repeatedly installed and removed, which is time-consuming and labor-consuming. SUMMARY

[0005] Therefore, the present application provides a cantilever type side wall self-stabilizing system for deep foundation pit support and a construction method thereof, which can replace the inverted support structure of the prior art, the pressure of the side wall panel is smaller, the rigidity and the anti-seismic ability of the overall structure are improved, and the construction period can be obviously shortened.

[0006] To achieve the above-mentioned purpose, the technical scheme provided by the present application is as follows:

[0007] The present application provides a cantilever type side wall self-stabilizing system for deep foundation pit support, which comprises two waterproof curtains, a support pile arranged between the waterproof curtains, a concrete slope arranged between the waterproof curtains and the support pile, a plurality of soil nails arranged in the concrete slope, a corbel arranged at the top of the support pile, a wet lean concrete layer arranged at the inner side of the support pile, and a lower passage box culvert arranged between the two wet lean concrete layers; a plurality of additional support steels are arranged in the structure steel of the lower passage box culvert in the form of rows at intervals, and the lower passage box culvert comprises a lower passage bottom plate, a lower passage top plate and two lower passage side walls arranged between the lower passage bottom plate and the lower passage top plate; one end of the additional support steel is inserted into the lower passage side wall, the other end of the additional support steel penetrates through the vertical side wall section of the lower passage bottom plate, and is bent and inserted into the horizontal bottom wall section of the lower passage bottom plate, so as to ensure the bending bearing capacity of the lower passage bottom plate.

[0008] Further, at least 4 additional support steels are arranged in the side wall of the lower passage box culvert per meter.

[0009] Further, the diameter of the additional support steel bars is 28 mm, and the spacing therebetween is 25 mm.

[0010] Further, the additional support steel bars comprise vertical segments and elbow segments, one end of the vertical segments is inserted into the side wall of the lower passage, the other end of the vertical segments is inserted into the vertical side wall segment of the bottom plate of the lower passage, and the elbow segments are inserted into the horizontal bottom wall segment of the bottom plate of the lower passage.

[0011] Further, the lengths of the vertical segments and the elbow segments are equal.

[0012] The present application provides a construction method of the cantilever type side wall self-stabilizing system for deep foundation pit support, comprising the following steps: S1, leveling the construction site, then constructing a water stop curtain, carrying out slope excavation between two water stop curtains, then constructing at least three soil nails to form slope support, and then sequentially carrying out shotcrete slope protection and driving support piles; S2, after the underground water in the construction site is pumped and drained, excavating the soil body on the top of the support piles, constructing a corbel on the top of the support piles, and constructing a reinforced concrete support between two corbels; after the concrete strength of the corbel and the reinforced concrete support meets the design requirements, continuing to excavate the lower earthwork, and erecting a steel enclosing purlin and a steel support to form a deep foundation pit; S3, respectively arranging the structural steel bars of the side wall of the lower passage and the bottom plate of the lower passage on both sides and the bottom of the deep foundation pit according to the pre-design, and arranging the structural steel bars at intervals with the support piles, then arranging additional support steel bars, and then pouring the bottom plate of the lower passage; after the concrete strength of the bottom plate of the lower passage meets the design requirements, backfilling wet lean concrete in the fat groove between the support piles and the bottom plate of the lower passage; S4, after the wet lean concrete in S3 meets the design requirements, sequentially removing the steel support and the steel enclosing purlin, and then pouring the side wall of the lower passage; after the concrete strength of the side wall of the lower passage meets the design requirements, backfilling wet lean concrete in the fat groove between the support piles and the side wall of the lower passage; S5, after the wet lean concrete in S4 meets the design requirements, removing the reinforced concrete support, then erecting a disc-type full-frame scaffold, then constructing the top plate of the lower passage above the disc-type full-frame scaffold; after the concrete strength of the bottom plate of the lower passage meets the design requirements, backfilling wet lean concrete in the fat groove between the support piles and the top plate of the lower passage; S6, after the wet lean concrete in S5 meets the design requirements, integrally pulling the disc-type full-frame scaffold to the working face of the next section through a pulling moving device, and repeating S2 to S5 until the lower passage box culvert is obtained.

[0013] Further, at least 4 additional support steel bars are additionally arranged in the side wall of the lower passage box culvert per meter.

[0014] Further, the diameter of the additional supporting steel bars is 28mm, and the interval is 25mm.

[0015] Further, in S2, the over-excavation depth of each supporting frame is not more than 0.5m.

[0016] Further, S7 is further included; in S7, the earthwork is backfilled and compacted in layers above the top plate of the underpass.

[0017] The technical scheme provided by the application has the following beneficial effects:

[0018] The underpass box culvert of the application is a beam-column-free structure, and compared with the inverted strut structure of the prior art, the side wall panel of the application is subjected to smaller pressure under the same earth pressure, and the integrity and safety of the side wall structure are higher, so that the application can not only effectively replace the inverted strut structure, but also improve the rigidity and seismic capacity of the overall structure, strengthen the concrete crack resistance, and improve the safety of the redundant structure, thereby ensuring that the underpass is in a safe use state for a long time.

[0019] The application does not need to install and remove the inverted strut structure of the prior art, so the application can also significantly shorten the construction period, effectively save the construction cost, and improve the construction efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 Fig. 1 shows a schematic diagram of the underpass box culvert in the embodiment;

[0021] Figure 2 Fig. 2 shows a reinforcement diagram of the underpass box culvert in the embodiment;

[0022] Figure 3 Fig. 3 shows a cross-sectional view of A-A in Fig. 1; Figure 2

[0023] Figure 4 Fig. 4 shows a state schematic diagram of step S1 of the construction method in the embodiment;

[0024] Figure 5 Fig. 5 shows a state schematic diagram of step S2 of the construction method in the embodiment;

[0025] Figure 6 Fig. 6 shows a state schematic diagram of step S3 of the construction method in the embodiment;

[0026] Figure 7 Fig. 7 shows a state schematic diagram of step S4 of the construction method in the embodiment;

[0027] Figure 8 Fig. 8 shows a state schematic diagram of step S5 of the construction method in the embodiment;

[0028] ​Figure 9 The diagram shown is a state diagram of step S6 of the construction method in the embodiment. Detailed Implementation

[0029] To further illustrate the various embodiments, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention and are mainly used to illustrate the embodiments, and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementations and the advantages of the present invention. Components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0030] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0031] Reference Figures 1 to 9 As shown, this embodiment provides a cantilevered sidewall self-stabilizing system (hereinafter referred to as the cantilevered sidewall self-stabilizing system) used in deep foundation pit support, including as follows: Figure 9 The two water-stop curtains 2 shown, the support piles 1 set between the water-stop curtains 2, and the concrete slope protection 3 set between the water-stop curtains 2 and the support piles 1 are provided. Three soil nails 31 are provided in the concrete slope protection 3. A cap beam 5 is provided on the top of the support piles 1, and a wet lean concrete layer 7 is provided on the inner side of the support piles 1.

[0032] The cantilevered sidewall self-stabilizing system in this embodiment also includes a system such as one disposed between the two wet and lean concrete layers 7. Figure 1 The underpass box culvert 8 shown has multiple rows of additional supporting steel bars 9 arranged at intervals within its structural steel reinforcement, and includes an underpass bottom slab 81, an underpass top slab 83, and two underpass sidewalls 82 located between the underpass bottom slab 81 and the underpass top slab 83.

[0033] One end of the additional supporting steel bar 9 is inserted into the side wall 82 of the underpass, and the other end passes through the vertical side wall section 811 of the underpass bottom plate 81, and is bent and inserted into the horizontal bottom wall section 812 of the underpass bottom plate 81 to ensure the bending bearing capacity of the underpass bottom plate 81.

[0034] In this embodiment, four additional supporting steel bars 9 are added per linear meter inside the side wall of the underpass box culvert 8, and the diameter of the additional supporting steel bars 9 is 28mm, and their spacing is 25mm.

[0035] More specifically, such as Figure 1 , Figure 2 and Figure 3As shown, the additional support steel bars 9 include a vertical segment 91 and an elbow segment 92, the upper end of the vertical segment 91 is inserted into the lower passage side wall 82, the lower end of the vertical segment 91 is inserted into the vertical side wall segment 811 of the lower passage floor 81, and the elbow segment 92 is inserted into the horizontal bottom wall segment 812 of the lower passage floor 81, at this time, the vertical segment 91 and the elbow segment 92 are crossed at 90 degrees, and the lengths of the vertical segment 91 and the elbow segment 92 are equal.

[0036] In particular implementation, the construction method described below is used to construct the cantilever side wall self-stabilizing system of the embodiment, and includes the following specific steps:

[0037] As shown in Figure 4 Step S1, the construction site is leveled to a site level of 12.0 m, then the water stop curtain 2 is constructed, and then the site is excavated with a slope between the two water stop curtains 2, that is, the site is excavated with a slope on the ground of the site level of 12.0 m to 6.1 m (such as miscellaneous fill, silty clay, etc.), and the earthwork is excavated to a level of 7.0 m, then the slope top guardrail 12 is set, then at least three soil nails 31 are constructed to form a slope support, and then the shotcrete slope protection 3 and the support pile 1 are successively driven.

[0038] As shown in Figure 5 Step S2, the underground water in the construction site is pumped out to dryness when the bottom of the foundation pit is at a level of 0.5 m, then the soil on top of the support pile 1 is excavated, and the corbel 5 is constructed on top of the support pile 1, then the reinforced concrete support 61 is constructed between the two corbels 5, and the top of the reinforced concrete support 61 is at a level of 7.0 m; after the concrete strength of the corbel 5 and the reinforced concrete support 61 meets the design requirements, the lower part of the earthwork is continuously excavated, and the steel enclosing purlin 63 and the steel support 62 are erected, the top of the steel support 62 is at a level of 3.5 m, to form a deep foundation pit, and the overbreak depth of each support during erection does not exceed 0.5 m.

[0039] As shown in Figure 6 Step S3, the structural steel bars of the lower passage side wall and the lower passage floor are respectively arranged on both sides and the bottom of the deep foundation pit according to the pre-design, and are arranged at intervals with the support pile 1, then the additional support steel bars 9 are arranged in a binding manner, then the lower passage floor 81 is poured, the lower passage floor 81 includes the vertical side wall segment 811 and the horizontal bottom wall segment 812, and is provided with a cushion layer and a waterproof layer, at this time, the vertical side wall segment 811 is part of the side wall structure, and the top of the vertical side wall segment 811 is at a level of 2.45 m; after the concrete strength of the lower passage floor 81 meets the design requirements, the wet lean concrete is backfilled in the fat groove between the support pile 1 and the lower passage floor 81.

[0040] As shown in Figure 7As shown, in step S4, after the strength of the wet lean concrete in step S3 meets the design requirements, the steel support 62 and the steel waler 63 are removed in sequence, and then the underpass side wall 82 is poured. At this time, the top elevation of the two underpass side walls 82 is 5.5m. After the concrete strength of the underpass side wall 82 meets the design requirements, the wet lean concrete is backfilled into the trench between the support pile 1 and the underpass side wall 82.

[0041] like Figure 8 As shown, in step S5, after the strength of the wet lean concrete in step S4 meets the design requirements, the reinforced concrete support 61 is removed, and then a disc-lock full-span scaffold 11 is erected. Then, the underpass top slab 83 is constructed above the disc-lock full-span scaffold 11. After the concrete strength of the underpass bottom slab 81 meets the design requirements, the wet lean concrete is backfilled into the trench between the support pile 1 and the underpass top slab 83.

[0042] like Figure 9 As shown, in step S6, after the strength of the wet lean concrete in step S5 meets the design requirements, the entire disc-lock full-span scaffold 11 is pulled to the working surface of the next segment using the traction and moving device of utility model patent CN215564490U, and steps S2 to S5 are repeated until the entire underpass box culvert 8 at the construction site is completed.

[0043] Step S7: Backfill and compact the soil in layers above the top slab 83 of the underpass, starting from an elevation of 8.9m above the top slab 83 and continuing until the site level reaches 12.0m. A waterproof layer and a protective layer are also installed above the top slab 83 of the underpass.

[0044] After all construction is completed, the side walls of the underpass box culvert 8 bear earth pressure loads, and its bottom bears uniformly distributed loads (mainly from the self-weight of the structure and the loads from the finishing surface). At this time, the bending moment at the connection between the side walls and the bottom of the underpass box culvert 8 is relatively large. Therefore, the bent section 92 of the additional supporting steel bar 9 is extended to the transverse bottom wall section 812 of the underpass bottom slab 81 to serve as additional steel bars at the bottom of the underpass box culvert 8, thereby increasing the reinforcement ratio and thus increasing its bottom bending bearing capacity.

[0045] Furthermore, in this embodiment, the underpass bottom slab 81 is 1.2m thick, the underpass sidewall 82 is 3.8m high, the retaining wall is 5.0m high, and the back soil density of the retaining wall is taken as 20KN / m³. 3, the static earth pressure coefficient is 1-sin30°, then the reinforcement calculation and multiple field data tests are carried out to determine that 4 additional supporting steels 9 are added in the sidewall of the underpass box culvert 8 per meter, the vertical segment 91 length of the additional supporting steel 9 is 4.9m, the elbow length of the additional supporting steel 9 is 4.9m, and the material of the additional supporting steel 9 is HRB400 steel, so that the maximum crack width of the cantilever sidewall self-stabilizing system of the embodiment is less than 0.2mm, so as to meet the crack control requirement.

[0046] In summary, the underpass box culvert 8 of the embodiment is a beam-column structure, and compared with the inverted strut structure of the prior art, the sidewall panel of the embodiment is subjected to smaller pressure under the action of the same earth pressure, and the integrity and safety of the sidewall structure are higher, so that the embodiment not only can effectively replace the inverted strut structure, but also can improve the rigidity and seismic capacity of the overall structure, and can strengthen the concrete crack resistance and improve the safety of the redundant structure, so as to ensure that the underpass is in a safe use state for a long time.

[0047] In addition, Table 1 as shown below is the construction days of the inverted strut of the prior art, and Table 2 as shown below is the construction days of the cantilever sidewall self-stabilizing system of the embodiment.

[0048] Table 1: Construction days of the inverted strut of the prior art

[0049]

[0050] Table 2: Construction days of the cantilever sidewall self-stabilizing system of the embodiment

[0051]

[0052] According to Tables 1 and 2, the embodiment does not need to install and remove the inverted strut structure of the prior art, so the embodiment can also significantly shorten the construction period, effectively save the construction cost and improve the construction efficiency.

[0053] Although the present application is specifically shown and described in connection with preferred embodiments, those skilled in the art should understand that various changes in form and details can be made to the present application without departing from the spirit and scope of the present application defined in the appended claims.

Claims

1. A construction method for a cantilevered sidewall self-stabilizing system used in deep foundation pit support, characterized in that, Includes the following steps: The cantilevered sidewall self-stabilizing system includes two water-stop curtains, support piles set between the water-stop curtains, and a concrete slope protection set between the water-stop curtains and the support piles. The concrete slope protection is provided with multiple soil nails. The top of the support piles is provided with a cap beam, and the inner side of the support piles is provided with a wet and lean concrete layer. It also includes an underpass box culvert set between the two wet and lean concrete layers. The underpass culvert has multiple rows of additional supporting steel bars spaced apart within its structural steel reinforcement, and includes an underpass bottom slab, an underpass top slab, and two underpass sidewalls located between the underpass bottom slab and the underpass top slab. One end of each additional supporting steel bar is inserted into the underpass sidewall, and the other end passes through the vertical sidewall section of the underpass bottom slab, and is bent and inserted into the transverse bottom wall section of the underpass bottom slab to ensure the bending bearing capacity of the underpass bottom slab. S1. Level the construction site, then construct the water-stop curtain, excavate the slope between the two water-stop curtains, then construct at least three soil nails to form slope support, and then carry out shotcrete slope protection and drive in support piles in sequence. S2. After draining the groundwater in the construction site, excavate the soil at the top of the support piles and construct a capping beam at the top of the support piles. Concrete reinforcement supports are constructed between the two capping beams. After the concrete strength of the capping beams and reinforced concrete supports meets the design requirements, continue to excavate the lower soil and erect steel walers and steel supports to form a deep foundation pit. S3, the structural steel bars of the underpass sidewalls and the underpass bottom slab are set on both sides and the bottom of the deep foundation pit according to the pre-design, and are set at intervals with the support piles. Then, additional support steel bars are set, and then the underpass bottom slab is poured. After the concrete strength of the underpass bottom slab meets the design requirements, wet lean concrete is backfilled in the trench between the support piles and the underpass bottom slab. S4. After the strength of the wet lean concrete in S3 meets the design requirements, the steel supports and steel walers are removed in sequence, and then the side wall of the underpass is poured. After the concrete strength of the side wall of the underpass meets the design requirements, the wet lean concrete is backfilled into the trench between the support piles and the side wall of the underpass. S5. After the strength of the wet lean concrete in S4 meets the design requirements, the reinforced concrete support is removed, and then a disc-lock full-span scaffold is erected. Then, the top slab of the underpass is constructed above the disc-lock full-span scaffold. After the concrete strength of the bottom slab of the underpass meets the design requirements, the wet lean concrete is backfilled into the trench between the support piles and the top slab of the underpass. S6. After the wet lean concrete in S5 meets the design requirements, the entire disc-lock full-span scaffold is pulled to the working face of the next segment by the traction and moving device, and S2 to S5 are repeated until the underpass box culvert is obtained.

2. The construction method of the cantilever sidewall self-stabilizing system for deep foundation pit support according to claim 1, characterized in that: At least four additional supporting steel bars are added to the side wall of the underpass box culvert for every meter of length.

3. The construction method of the cantilever sidewall self-stabilizing system for deep foundation pit support according to claim 2, characterized in that: The additional supporting steel bars have a diameter of 28mm and a spacing of 25mm.

4. The construction method of the cantilever sidewall self-stabilizing system for deep foundation pit support according to claim 1, characterized in that: In S2, the over-excavation depth during the erection of each support shall not exceed 0.5m.

5. The construction method of the cantilever sidewall self-stabilizing system for deep foundation pit support according to claim 1, characterized in that: It also includes S7; in S7, compacted earth is backfilled in layers above the top slab of the underpass.

6. The construction method of the cantilever sidewall self-stabilizing system for deep foundation pit support according to claim 1, characterized in that: The additional supporting steel bars include a vertical section and a bent section. One end of the vertical section is inserted into the side wall of the underpass, and the other end of the vertical section is inserted into the vertical side wall section of the bottom plate of the underpass. The bent section is inserted into the horizontal bottom wall section of the bottom plate of the underpass.

7. The construction method of the cantilever sidewall self-stabilizing system for deep foundation pit support according to claim 6, characterized in that: The vertical section and the elbow section are configured with equal lengths.

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