Steel trestle construction method for deep foundation pit engineering using cover-excavation reverse construction method

Abstract

The invention discloses a steel trestle construction method for deep foundation pit engineering of cover-excavation reverse construction method, comprising: drilling holes in soil layer; lowering steel cage and pouring concrete; inserting steel pipe column into cast-in-place pile; excavating soil layer downward to construct the first underground floor; excavating soil layer downward, constructing platform section based on each steel pipe column exposed by excavation, and welding steel support at the same time; constructing the next underground floor at the previous depth position, and then continue to excavate soil layer downward, construct the next platform section based on each steel pipe column exposed by excavation, and weld steel support at the same time until all platform sections are completed; continue to excavate soil layer downward to the bottom of the pit, construct the structural foundation bottom plate at the bottom of the pit, and weld steel support; the construction of steel trestle is completed. The invention constructs steel trestle section by section as the cover-excavation reverse construction is carried out layer by layer downward, and the construction between steel trestle and underground structure does not conflict, thereby improving construction efficiency and reducing construction cost.

Description

Technical Field

[0001] The invention relates to a trestle structure, in particular to a steel trestle construction method for deep foundation pit engineering using a cover-excavation reverse construction method. Background Art

[0002] Deep foundation pit engineering using the cover-and-excavation reverse construction method has been widely used in underground structure construction. Due to its unique reverse construction sequence, it is necessary to reserve a construction channel in advance to ensure that the earthwork can be smoothly transported out during the construction process and that personnel and mechanical equipment can easily enter and exit the site.

[0003] At present, there are mainly two traditional ways to reserve construction channels:

[0004] One is the earth road, which means that during the earthwork excavation, part of the soil is reserved and not excavated, but left as a passage. This type of earth road does not require the use of other materials (such as steel), does not require additional construction processes, and is easy to construct. However, during the construction of the earth road, the integrity of the reserved soil cannot be guaranteed, and usually a second excavation is required, and the soil needs to be reinforced multiple times. In addition, the construction of the earth road and the underground structure cannot be carried out simultaneously. Only after the earth road is demolished can the underground structure at that location be constructed. It can be seen that the construction period is greatly affected, and the construction of the earth road is time-consuming and labor-intensive, with high labor costs.

[0005] The other is the Bailey steel temporary bridge, which is constructed by first constructing steel pipe piles on the soil layer, and then splicing the pre-assembled bridge abutments with the steel pipe piles. Compared with the above-mentioned earth horse road, this steel temporary bridge reduces the time for soil reinforcement and secondary excavation, but its load-bearing performance is poor, the labor cost is high, and it conflicts with the construction of underground structures and cannot be carried out simultaneously, which affects the construction period and has low construction efficiency. Summary of the invention

[0006] The purpose of the present invention is to provide a steel trestle construction method for deep foundation pit engineering of cover-excavation reverse construction method, in which the steel trestle is constructed section by section as the cover-excavation reverse construction is carried out layer by layer, and the construction of the steel trestle and the underground structure does not conflict, thereby improving the construction efficiency and reducing the construction cost.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A steel trestle construction method for deep foundation pit engineering using a cover-excavation reverse construction method, characterized in that it comprises the following steps:

[0009] 1) Drill holes in the soil layer to be constructed;

[0010] 2) lowering the steel cage to the bottom of the borehole obtained by drilling a hole on the soil layer, and then pouring concrete into the borehole to form a cast-in-place pile;

[0011] 3) Before the concrete solidifies, the steel pipe column is inserted into the cast-in-place pile, wherein: the lower part of the steel pipe column is in the steel cage, and the top of the steel pipe column is lower than the top surface of the soil layer;

[0012] 4) Excavating the soil layer downward to a first depth, and constructing a first underground floor slab at the first depth;

[0013] 5) excavating the soil layer downward to a second depth, constructing a first platform section of the steel trestle based on the steel pipe columns exposed by the excavation, and welding steel supports between the steel pipe columns below the first platform section;

[0014] 6) Construct the next underground floor at the previous depth, then continue to excavate the soil layer downward to the next depth, and construct the next platform section based on the steel pipe columns exposed by the excavation. This platform section is continuous with the previous platform section of the steel trestle, and at the same time, weld steel supports between the steel pipe columns below this platform section;

[0015] 7) Repeat step 6) until all platform sections are completed;

[0016] 8) Continue to excavate the soil layer downward to the bottom of the pit, construct the structural foundation floor at the bottom of the pit, make the structural foundation floor continuous with the last platform section of the steel trestle, and weld steel supports between the steel pipe columns exposed by the excavation;

[0017] 9) Construction of steel trestle completed.

[0018] The advantages of the present invention are:

[0019] 1. The steel trestle construction method of the present invention is particularly suitable for deep foundation pit projects using the cover-excavation reverse construction method. The steel trestle is constructed and formed section by section as the cover-excavation reverse construction is carried out layer by layer, and the construction of the steel trestle and the underground structure can be carried out simultaneously without conflicting with each other, thereby shortening the construction period, greatly reducing the construction cost, and improving the transportation efficiency during the cover-excavation reverse construction process.

[0020] 2. The steel trestle construction method based on the present invention has high construction efficiency, low construction difficulty, low cost, and guaranteed quality of the steel trestle. Further, on the one hand, the steel pipe columns of the steel trestle use inserted cast-in-place piles as a support foundation, on the other hand, the main longitudinal beams of the steel trestle are connected to the pre-buried connectors on the underground floor slab, and on the other hand, as the soil is excavated downward, steel supports are welded between the steel pipe columns of the steel trestle in time for reinforcement. It can be seen that at any stage of earth excavation and underground structure construction, the steel trestle constructed based on the steel trestle construction method of the present invention has good overall structural stability, good load-bearing performance, safety and reliability, and the overall strength and rigidity meet the transportation requirements, creating efficient access conditions for construction vehicles and large-scale machinery and equipment, and avoiding a series of safety hazards and efficiency problems caused by poor construction channels at the construction site. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of inserting steel pipe columns into cast-in-place piles.

[0022] Figure 2 yes Figure 1 An enlarged schematic diagram of a single steel pipe column inserted into a cast-in-place pile.

[0023] Figure 3 This is the schematic diagram of the first downward excavation and construction of the first underground floor.

[0024] Figure 4 This is a schematic diagram of the second downward excavation and construction of the first platform section.

[0025] Figure 5 This is a schematic diagram of the construction of the second underground floor and the third downward excavation of earth and the construction of the second platform section (the first platform section and the first underground floor are not shown).

[0026] Figure 6 It is a schematic diagram of excavating earth downwards to the bottom of the pit and constructing the foundation slab of the structure.

[0027] Figure 7 It is a schematic diagram of the connection structure between the longitudinal beam of the steel trestle and the underground floor. DETAILED DESCRIPTION

[0028] The present invention proposes a steel trestle construction method for deep foundation pit engineering using the cover-excavation reverse construction method. Figures 1 to 7 To understand, it includes the following steps:

[0029] 1) drilling holes in the soil layer 10 to be constructed;

[0030] 2) lowering the steel cage 21 to the bottom of the borehole 11 drilled on the soil layer 10, and then pouring concrete 40 into the borehole 11 to form a cast-in-place pile 20, wherein: the concrete should be slow-setting concrete so that the steel pipe column 30 can be smoothly inserted below;

[0031] 3) Before the concrete 40 solidifies, the steel pipe column 30 is inserted into the cast-in-place pile 20, wherein: the lower part of the steel pipe column 30 is in the steel cage 21, and the top of the steel pipe column 30 should be lower than the top surface of the soil layer 10 (such as Figure 1 , Figure 2 As shown), the concrete overflowing from the borehole 11 should be cleaned up at this time;

[0032] 4) Excavate the soil layer downward to the first depth (such as Figure 3 ), constructing the first underground floor at the first depth;

[0033] 5) Dig the soil layer 10 downward to a second depth (such as Figure 4), constructing the first platform section of the steel trestle based on the steel pipe columns 30 exposed by excavation, and welding steel supports 90 between the steel pipe columns 30 below the first platform section;

[0034] 6) Construct the next underground floor at the previous depth, and then continue to excavate the soil layer 10 downward to the next depth (such as Figure 5 The third depth shown in the figure), based on the steel pipe columns 30 exposed by the excavation, the next platform section is constructed so that this platform section is continuous with the previous platform section of the steel trestle, and at the same time, steel supports 90 are welded between the steel pipe columns 30 located below this platform section;

[0035] 7) Repeat step 6) until all platform sections are completed;

[0036] 8) Continue to excavate the soil layer 10 downward to the pit bottom 12 (the pit bottom 12 is slightly higher than the top of the cast-in-place pile 20), and construct the structural foundation bottom plate 100 at the pit bottom 12, so that the structural foundation bottom plate 100 is continuous with the last platform section of the steel trestle, such as Figure 6 As shown, steel supports 90 are welded between the steel pipe columns 30 exposed by excavation to enhance the supporting performance;

[0037] 9) The construction of the steel trestle has been completed and is waiting to be put into use in subsequent projects.

[0038] like Figure 2 The steel cage 21 is formed by binding the longitudinal reinforcement 211 and the stirrups 212, and the steel pipe column 30 is a round steel pipe.

[0039] In actual implementation, in step 3), the tops of the steel pipe columns 30 inserted into the soil layer 10 are at different heights, such as Figure 1 In practice, the height of the top of each steel pipe column 30 after being inserted into the soil layer 10 should be reasonably designed according to the inclination of the first platform section of the steel trestle.

[0040] Furthermore, the depth of the steel pipe column 30 inserted into the steel cage 21 should be at least 3.5 m to ensure the stability of the steel trestle.

[0041] During the construction of the underground floor, connectors are pre-buried on the underground floor. Then, for the platform section to be constructed, longitudinal beams and transverse beams are hoisted and welded on the steel pipe columns 30. The longitudinal beams include main longitudinal beams and secondary longitudinal beams. Then, steel supports 90 are welded between the steel pipe columns 30. Finally, the platform plate (such as steel plate, not shown in the figure) is installed and welded, wherein: the main longitudinal beams in the longitudinal beams are connected to the connectors pre-buried on the underground floor, while the secondary longitudinal beams in the longitudinal beams do not need to be connected to the connectors.

[0042] In the present invention, the longitudinal beams are arranged along the length direction of the steel trestle, and the transverse beams are arranged along the direction perpendicular to the length direction of the steel trestle.

[0043] In addition, when constructing the platform section and installing the steel support 90, the top and side walls of the steel pipe column 30 can be cut accordingly according to actual needs.

[0044] In actual construction, the underground floor should be used as a turning platform between the upper and lower continuous platform sections to solve the problem that the slope caused by the large height difference cannot meet the requirements for safe vehicle driving.

[0045] Specifically, when constructing an underground floor, the steel bars are first tied, and the connectors are embedded while the steel bars are tied. Then, a formwork (not shown in the figure) is set up and concrete is poured to form an underground floor, wherein: the main longitudinal beam is an I-beam, the web of the I-beam is welded and fixed to the connector, and the upper and lower flange plates of the I-beam are welded to the connector by single-sided cutaway pad welding.

[0046] Figure 7 The figure shows the situation that the connecting piece 61 is embedded in the first underground floor slab 60 and the connecting piece 61 is connected to the main longitudinal beam 51. The specific situation of the embedding of the connecting piece and the connection with the main longitudinal beam of the underground floor slabs of other layers can be referred to Figure 7 Come to understand.

[0047] In addition, a gap (eg, a 100 mm wide gap) should be left between the underground floor and the steel pipe column 30.

[0048] In actual application, the steel trestle can be composed of multiple inclined platform sections. The lowest platform section of the steel trestle is used to connect the structural foundation bottom plate 100 with the lowest underground floor, and the remaining platform sections of the steel trestle are used to connect the upper and lower underground floors. Each platform section is composed of a longitudinal beam, a cross beam and a platform plate. The structure of the platform section is well-known in the art and is not limited. For example, the platform section may also include protective plates on both sides. Each platform section is supported by a plurality of steel pipe columns 30 from high to low.

[0049] In the present invention, the steel support 90 is mostly a diagonal support, but can also be a horizontal support (such as Figure 6 ), not limited. When installing steel support 90, it is usually installed with a hand chain hoist.

[0050] In actual implementation, the structural foundation slab 100 is formed by tying steel bars, setting up formwork and pouring concrete, which is a well-known technique in the art.

[0051] The present invention reasonably designs the single excavation depth according to the earth excavation progress (layered excavation), and it is suitable to carry out excavation in three or more times, and the single excavation depth is preferably 3 meters to 4 meters.

[0052] like Figures 1 to 6, the figure shows the construction of two underground floors 60, 80 and a steel trestle consisting of two platform sections 50, 70. During construction, holes are drilled in the soil layer 10, a steel cage 21 is lowered, concrete 40 is poured to form a cast-in-place pile 20, and a steel pipe column 30 is inserted before the concrete 40 solidifies. Then, the soil layer 10 is excavated downward to a first depth, such as Figure 3 As shown, a first underground floor slab (such as a B1 floor slab) 60 is constructed at a first depth, and then the soil layer 10 is excavated downward to a second depth, such as Figure 4 As shown, the first platform section 50 of the steel trestle is constructed based on the steel pipe columns 30 exposed by excavation, and steel supports 90 are welded between the steel pipe columns 30 below the first platform section 50. Then, the second underground floor slab (such as the B2 floor slab) 80 is constructed at the second depth position, and then the soil layer 10 is excavated downward to the third depth, such as Figure 5 As shown, the second platform section 70 is constructed based on the steel pipe columns 30 exposed by excavation, and this platform section 70 is continuous with the upper platform section 50 of the steel trestle, and steel supports 90 are welded between the steel pipe columns 30 below this platform section 70. Then, the soil layer 10 is excavated downward to the pit bottom 12 (the pit bottom 12 is slightly higher than the top of the cast-in-place pile 20), and the structural foundation bottom plate 100 is constructed at the pit bottom 12, so that the structural foundation bottom plate 100 is continuous with the second platform section 70, as shown in FIG. Figure 6 As shown, steel supports 90 are welded between the steel pipe columns 30 exposed by excavation to enhance the supporting performance. The steel trestle construction is then completed, and the structural foundation bottom plate 100 is connected to the second underground floor 80 and the first underground floor 60 via the steel trestle, so that personnel, construction vehicles and large machinery and equipment can move freely between the three.

[0053] The invention is particularly suitable for implementation on deep foundation pits with poor bearing capacity geological characteristics such as water-rich sand layers, soft soil, thicker fill layers or weak foundations.

[0054] The above are preferred embodiments of the present invention and the technical principles used therein. For those skilled in the art, any obvious changes such as equivalent transformations, simple replacements, etc. based on the technical solution of the present invention, without departing from the spirit and scope of the present invention, are within the scope of protection of the present invention.

Claims

1. A steel trestle construction method for deep foundation pit engineering using a cover-excavation reverse construction method, characterized in that: It includes the steps: 1) Drill holes in the soil layer to be constructed; 2) lowering the steel cage to the bottom of the borehole obtained by drilling a hole on the soil layer, and then pouring concrete into the borehole to form a cast-in-place pile; 3) Before the concrete solidifies, the steel pipe column is inserted into the cast-in-place pile, wherein: the lower part of the steel pipe column is in the steel cage, and the top of the steel pipe column is lower than the top surface of the soil layer; 4) Excavating the soil layer downward to a first depth, and constructing a first underground floor slab at the first depth; 5) excavating the soil layer downward to a second depth, constructing a first platform section of the steel trestle based on the steel pipe columns exposed by the excavation, and welding steel supports between the steel pipe columns below the first platform section; 6) construct the next underground floor at the previous depth, then continue to excavate the soil layer downward to the next depth, and construct the next platform section based on the steel pipe columns exposed by the excavation. This platform section is continuous with the previous platform section of the steel trestle, and steel supports are welded between the steel pipe columns below this platform section. The underground floor serves as a turning platform between the upper and lower continuous platform sections; 7) Repeat step 6) until all platform sections are completed; 8) Continue to excavate the soil layer downward to the bottom of the pit, construct the structural foundation floor at the bottom of the pit, make the structural foundation floor continuous with the last platform section of the steel trestle, and weld steel supports between the steel pipe columns exposed by the excavation; 9) Construction of steel trestle completed.

2. The steel trestle construction method for deep foundation pit engineering using the cover-excavation reverse construction method according to claim 1, characterized in that: In step 3), the tops of the steel pipe columns inserted into the soil layer are at different heights.

3. The steel trestle construction method for deep foundation pit engineering using the cover-excavation reverse construction method as claimed in claim 2, characterized in that: The depth of the steel pipe column inserted into the steel cage is at least 3.5m.

4. The steel trestle construction method for deep foundation pit engineering using the cover-excavation reverse construction method according to claim 1, characterized in that: During the construction of the underground floor, connectors are pre-buried on the underground floor, and then the longitudinal beams and transverse beams are hoisted and welded on the steel pipe columns for the platform section to be constructed, and then the steel supports are welded between the steel pipe columns, and finally the platform plate is installed and welded, wherein the main longitudinal beams in the longitudinal beams are connected to the connectors pre-buried on the underground floor.

5. The steel trestle construction method for deep foundation pit engineering using the cover-excavation reverse construction method as claimed in claim 4, characterized in that: When constructing the underground floor, the steel bars are first tied, and the connecting parts are pre-buried while tying the steel bars. Then the formwork is set up and concrete is poured to form the underground floor, wherein: the main longitudinal beam is an I-beam, the web of the I-beam is welded and fixed to the connecting parts, and the upper and lower flange plates of the I-beam are welded and connected to the connecting parts by single-sided cutaway pad welding.

6. The steel trestle construction method for deep foundation pit engineering using the cover-excavation reverse construction method as claimed in claim 4, characterized in that: A gap is left between the underground floor and the steel pipe column.

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