Deep foundation pit support structure and construction method

Abstract

The invention discloses a deep foundation pit support structure and a construction method, the deep foundation pit support structure comprises a cast-in-situ bored pile, a plain concrete diaphragm wall and a latticed column, the lower end of the latticed column is provided with a stand column pile, and the top end of the latticed column is provided with a track beam parallel to a top beam; two pile legs of the gantry crane are respectively arranged on the top beam and the track beam; the single-group first inner supporting system is horizontally arranged at the top of the foundation pit through concrete pouring, and the first inner supporting system is used for connecting the top beam and the track beam; and the second inner supporting systems are parallel to one another through concrete pouring and are horizontally arranged below the first inner supporting system, and the second inner supporting systems are used for connecting the latticed columns and the cast-in-situ bored piles. The cast-in-situ bored piles and the plain concrete diaphragm wall are combined, the light reinforcement cage is arranged in each cast-in-situ bored pile, hoisting is easy and convenient, in addition, the longitudinally-walking low-clearance gantry crane is arranged above the foundation pit, and material hoisting and unearthing operation are facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering, and in particular to a deep foundation pit retaining structure and a construction method. Background Art

[0002] At present, with the development of cities, it is becoming more and more common to implement deep foundation pits under low clearance conditions such as under viaducts and high-voltage lines.

[0003] Usually, when the ground conditions are good and there is less groundwater, piles are usually used as the retaining structure, supplemented by high-pressure rotary jetting as a water-stopping curtain; when there is more groundwater and the foundation pit is deeper, interlocking piles are used as the retaining structure; when the groundwater is abundant and the foundation pit is very deep, ground-connected walls are required as the retaining structure to achieve the ideal water-stopping and force-bearing effects.

[0004] However, for foundation pits with abundant groundwater and great depth, when working under low clearance conditions, the use of ground-anchored walls is limited due to the risks of heavy weight of the steel cage, long time for lifting in sections, great impact on the stability of the trench wall, and easy cage jam.

[0005] Therefore, it is urgent to propose a new solution to solve the above problems. Summary of the invention

[0006] The present invention provides a deep foundation pit retaining structure and a construction method to solve the problems of high risk and great implementation difficulty in deep foundation pit excavation in water-rich strata with ultra-low clearance in the prior art.

[0007] The present invention provides a deep foundation pit retaining structure, comprising:

[0008] Bored piles are vertically arranged around the foundation pit in sequence and their lower ends extend downward to below the bottom of the foundation pit. A cap beam is arranged at the top of the bored piles, and a steel cage is arranged inside each of the bored piles.

[0009] A plain concrete ground-connected wall, which is vertically arranged outside the bored piles and has its lower end extending downward to below the bottom of the foundation pit, and is used as a water-stop curtain;

[0010] A lattice column, a column pile is arranged at the lower end thereof, and a track beam parallel to the crown beam is arranged at the top end of the lattice column;

[0011] The two legs of the gantry crane are respectively set on the crown beam and the track beam;

[0012] A single set of first internal support system, which is horizontally arranged on the top of the foundation pit by pouring concrete, and the first internal support system is used to connect the crown beam and the track beam;

[0013] A plurality of groups of second inner support systems are arranged parallel to each other and horizontally below the first inner support system by pouring concrete, and the second inner support system is used to connect the lattice columns and the bored piles.

[0014] Furthermore, a retaining wall is arranged in the vertical direction at one end of the crown beam away from the gantry crane, and a side of the retaining wall away from the gantry crane is the ground after the elevation is lowered.

[0015] Furthermore, the first internal support system includes a horizontally arranged first horizontal internal support and an inclined first inclined internal support, the first horizontal internal support and the track beam are arranged perpendicular to each other, four first inclined internal supports are respectively arranged at four corners of the foundation pit, the middle lattice column is located at the lower end of the first horizontal internal support, and the outermost lattice column is located at the lower end of the first inclined internal support.

[0016] Furthermore, the second internal support system includes a horizontally arranged second horizontal internal support, an inclined second inclined internal support, a connecting beam arranged at horizontal intervals, and a waist beam arranged on the inner side of the bored pile, the waist beam is used to connect the bored pile with the second horizontal internal support or the second inclined internal support, the four second inclined internal supports are respectively inclined at the four corners of the foundation pit, the lattice column located in the middle connects a single first horizontal internal support and multiple second horizontal internal supports, the lattice column located on the outermost side connects a single first inclined internal support and multiple second inclined internal supports, and the connecting beam is used to connect two adjacent lattice columns.

[0017] Furthermore, the bored piles are connected to the waist beam via a steel bar connector, and the second horizontal inner support, the second inclined inner support and the waist beam are cast by concrete.

[0018] Furthermore, the center distance between two adjacent bored piles is 1.0 to 2.0 m.

[0019] Furthermore, the plain concrete ground-anchored wall and bored cast-in-place piles are cast by concrete, the concrete model of the plain concrete ground-anchored wall is C20, and the concrete model of the bored cast-in-place piles is C35.

[0020] Furthermore, the vertical distance between two adjacent second inner support systems is 3 to 5 m, and the vertical distance between the first inner support system and the second inner support system located at the uppermost end is 3 to 5 m.

[0021] Furthermore, after the elevation is lowered, the vertical height from the ground to the obstacle is not less than 6.5m.

[0022] The present invention also provides a construction method of a deep foundation pit retaining structure, comprising the following steps:

[0023] Carry out construction on the original ground to ensure that the vertical height of the ground from the obstacle is not less than 6.5m after the elevation is lowered;

[0024] Carry out the construction of vertical plain concrete ground-anchored walls, bored piles, column piles and lattice columns;

[0025] The horizontal crown beam, track beam and first inner support system are constructed, the lattice column is located at the lower end of the first inner support system, the crown beam and track beam are connected through the first inner support system, and then the retaining wall is constructed;

[0026] Install the gantry crane located on the crown beam and track beam;

[0027] Excavating the foundation pit downwards in sequence, installing multiple horizontal annular waist beams and the second internal support system, connecting multiple second internal support systems with a single vertically arranged lattice column, and excavating to the bottom of the foundation pit;

[0028] Backfill the foundation pit to the height of the crown beam and track beam to restore the road surface.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The deep foundation pit retaining structure of the present invention adopts the form of a combination of bored cast-in-place piles and plain concrete ground-connected walls, which is suitable for foundation pits with abundant groundwater and great depth. The plain concrete ground-connected walls do not need to be equipped with heavy steel cages, and do not have the disadvantage of segmented hoisting of heavy steel cages. The plain concrete ground-connected walls are used as foundation pit water-stop curtains. By arranging a light steel cage in each bored cast-in-place pile, the hoisting is simple and convenient, and the foundation pit retaining force system formed by the lattice columns, the first internal support system and the second internal support system can adapt to deep foundation pits. Finally, a low-clearance gantry crane with longitudinal travel is arranged above the foundation pit to facilitate material hoisting and excavation operations;

[0031] 2. The construction method of the deep foundation pit retaining structure of the present invention can be adapted to foundation pits with abundant groundwater and great foundation pit depth. By setting up a gantry crane, it can greatly improve the efficiency of hoisting and excavation under low clearance conditions and accelerate the progress of engineering construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a main structural diagram of the deep foundation pit retaining structure of the present invention;

[0033] Figure 2 It is a cross-sectional view of the deep foundation pit retaining structure of the present invention located at the first inner support system;

[0034] Figure 3 It is a cross-sectional view of the deep foundation pit retaining structure of the present invention located at the second inner support system;

[0035] Figure numerals: 1. bored cast-in-place piles; 11. cap beam; 2. plain concrete ground-connected wall; 3. lattice column; 31. track beam; 4. column piles; 5. gantry crane; 61. first internal support system; 611. first internal support system; 612. first inclined internal support; 62. second internal support system; 621. second horizontal internal support; 622. second inclined internal support; 623. connecting beam; 624. waist beam; 7. retaining wall; 81. ground after lowering the elevation; 82. original ground; 9. obstacle; 10. bottom of foundation pit. DETAILED DESCRIPTION

[0036] In order to further understand the content, features and effects of the present invention, the following embodiments are given together with the attached Figures 1 to 3 The detailed instructions are as follows.

[0037] like Figures 1 to 3 As shown, the present invention provides a deep foundation pit retaining structure, comprising:

[0038] Bored piles 1 are vertically arranged around the foundation pit in sequence and their lower ends extend downward to below the bottom of the foundation pit. A cap beam 11 is arranged at the top of the bored pile 1. A steel cage is arranged inside each of the bored piles 1.

[0039] A plain concrete ground-connected wall 2 is vertically arranged outside the bored pile 1 and has its lower end extending downward to below the bottom of the foundation pit. The plain concrete ground-connected wall 2 is used as a water-stop curtain, is not equipped with steel bars, and is not used as a load-bearing member of the foundation pit. The thickness of the plain concrete ground-connected wall 2 is 600 to 1200 mm.

[0040] A lattice column 3, a column pile 4 is arranged at the lower end thereof, and a track beam 31 parallel to the crown beam 11 is arranged at the top end of the lattice column 3;

[0041] The gantry crane 5 has two pile legs respectively arranged on the crown beam 11 and the track beam 31. In this embodiment, two sets of parallel crown beams 11 and track beams 31 are arranged, and two gantry cranes 5 are located above them. There is an obstacle 9 above the gantry cranes 5.

[0042] A single set of first internal support system 61, which is horizontally arranged on the top of the foundation pit by pouring concrete, and the first internal support system 61 is used to connect the crown beam 11 and the track beam 31;

[0043] Multiple groups of second internal support systems 62 are parallel to each other and horizontally arranged below the first internal support system 61 through concrete pouring. Multiple groups of second internal support systems 62 are arranged in parallel and spaced apart in the height direction. The second internal support systems 62 are used to connect the lattice columns 3 and the bored piles 1.

[0044] The deep foundation pit retaining structure of the present invention adopts the combination of bored cast-in-place piles and plain concrete ground-anchored walls, which is suitable for foundation pits with abundant groundwater and great depth. The plain concrete ground-anchored walls do not need to be equipped with heavy steel cages and do not have the disadvantage of segmented hoisting of heavy steel cages. The plain concrete ground-anchored walls are used as water-stop curtains for foundation pits. By arranging light steel cages in each bored cast-in-place pile, hoisting is simple and it is used for supporting force. The foundation pit retaining force system formed with the arranged lattice columns, the first internal support system and the second internal support system enables it to adapt to deep foundation pits. Finally, a low-clearance gantry crane with longitudinal travel is arranged above the foundation pit to facilitate material hoisting and excavation operations.

[0045] In this embodiment, Figure 1 As shown, a retaining wall 7 is arranged along the vertical direction at one end of the crown beam 11 away from the gantry crane 5, and a side of the retaining wall 7 away from the gantry crane 5 is the lowered ground 81, wherein the designed hoisting load of the gantry crane 5 is 15t.

[0046] In this embodiment, Figure 2 As shown, the first internal support system 61 includes a horizontally arranged first horizontal internal support 611 and an inclined first inclined internal support 612, the first horizontal internal support 611 and the track beam 31 are arranged perpendicular to each other, four first inclined internal supports 612 are respectively arranged at the four corners of the foundation pit, the ten lattice columns 3 located in the middle are located at the lower end of the first horizontal internal support 611, the two outermost lattice columns 3 are located at the lower end of the first inclined internal support 612, and the twelve lattice columns 3 are located at the intersection of the track beam 31 and the first horizontal internal support 611 or the first inclined internal support 612.

[0047] In this embodiment, Figure 3 As shown, the second internal support system 62 includes a horizontally arranged second horizontal internal support 621, an inclined second inclined internal support 622, a connecting beam 623 arranged at intervals horizontally, and a waist beam 624 arranged on the inner side of the bored pile 1, wherein the number of the second horizontal internal supports 621 is ten, and the number of the second inclined internal supports 622 is four, the waist beam 624 is used to connect the bored pile 1 with the second horizontal internal support 621 or the second inclined internal support 622, the four second inclined internal supports 622 are respectively inclinedly arranged at the four corners of the foundation pit, the lattice column 3 located in the middle connects a single first horizontal internal support 611 and multiple second horizontal internal supports 621, the lattice column 3 located on the outermost side connects a single first inclined internal support 612 and multiple second inclined internal supports 622, and the connecting beam 623 is used to connect two adjacent lattice columns 3.

[0048] In this embodiment, the bored pile 1 is connected to the waist beam 624 through a steel bar connector, and the second horizontal inner support 621, the second inclined inner support 622 and the waist beam 624 are cast by concrete.

[0049] In this embodiment, the center distance between two adjacent bored piles 1 is 1.5m, and it can also adopt other values ​​between 1.0 and 2.0m. In addition, the spacing between two adjacent bored piles 1 is 0.2 to 0.3m. The existing steel cage of the ground-connected wall is generally 6m a piece. The plain concrete ground-connected wall of the present invention does not need to be equipped with a heavy steel cage, but adopts the bored piles 1 and the light steel cage arranged therein as a whole, and its diameter is 1m, and it can also adopt other values ​​between 0.8 and 1.5m, which is more lightweight and easy to hoist.

[0050] In this embodiment, Figure 1 As shown, the plain concrete ground-anchored wall 2 and bored cast-in-place piles 1 are cast by concrete, the concrete model of the plain concrete ground-anchored wall 2 is C20, and the concrete model of the bored cast-in-place piles 1 is C35.

[0051] In this embodiment, Figure 1 As shown, the vertical distance between two adjacent second inner support systems 62 is 3 to 5 m, and the vertical distance between the first inner support system 61 and the second inner support system 62 located at the uppermost end is 3 to 5 m.

[0052] In this embodiment, Figure 1 As shown, after the elevation is lowered, the vertical height of the ground 81 from the obstacle 9 is not less than 6.5 m, so as to ensure the working space of the ground-connected wall trenching machine.

[0053] The present invention also provides a construction method of a deep foundation pit retaining structure, comprising the following steps:

[0054] S1. Construction is performed on the original ground 82 to ensure that the vertical height of the ground 81 from the obstacle 9 after the elevation is lowered is not less than 6.5m;

[0055] S2, carry out the construction of vertical plain concrete ground-connected wall 2, bored pile 1, column pile 4 and lattice column 3;

[0056] S3, construct the horizontal crown beam 11, the track beam 31 and the first inner support system 61, the lattice column 3 is located at the lower end of the first inner support system 61, the crown beam 11 and the track beam 31 are connected through the first inner support system 61, and then the retaining wall 7 is constructed;

[0057] S4, installing the gantry crane 5 on the crown beam 11 and the track beam 31;

[0058] S5, excavating the foundation pit downwards in sequence, installing multiple horizontal annular waist beams 624 and the second inner support system 62, connecting multiple second inner support systems 62 with a single vertically arranged lattice column 3, and excavating to the bottom 10 of the foundation pit;

[0059] S6. Backfill the foundation pit to the height of the crown beam 11 and the track beam 31 to restore the road surface.

[0060] The construction method of the deep foundation pit retaining structure of the present invention can be adapted to foundation pits with abundant groundwater and great foundation pit depth. By setting a gantry crane, the hoisting and excavation efficiency under low clearance conditions can be greatly improved, thereby accelerating the progress of engineering construction.

[0061] The invention described above only expresses the implementation methods of the embodiments of the present invention, and cannot be understood as limiting the scope of the invention patent, nor does it impose any form of limitation on the structure of the embodiments of the present invention. It should be pointed out that for ordinary technicians in this field, several changes and improvements can be made without departing from the concept of the embodiments of the present invention, which all belong to the protection scope of the embodiments of the present invention.

Claims

1. A deep foundation pit retaining structure, characterized in that: include: Bored cast-in-place piles (1) are vertically arranged in sequence around the foundation pit and their lower ends extend downward to below the bottom of the foundation pit. A cap beam (11) is arranged at the top of the bored cast-in-place pile (1), and a steel cage is arranged inside each of the bored cast-in-place piles (1); A plain concrete ground-connected wall (2) is vertically arranged outside the bored pile (1) and has its lower end extending downward to below the bottom of the foundation pit. The plain concrete ground-connected wall (2) is used as a water-stop curtain; A lattice column (3) having a column pile (4) at its lower end, and a track beam (31) parallel to the crown beam (11) at the top end of the lattice column (3); A gantry crane (5), two pile legs of which are respectively arranged on a crown beam (11) and a track beam (31); A single set of first internal support systems (61) is horizontally arranged on the top of the foundation pit by pouring concrete, wherein the first internal support system (61) is used to connect the crown beam (11) and the track beam (31); A plurality of groups of second internal support systems (62) are arranged parallel to each other and horizontally below the first internal support system (61) by pouring concrete, and the second internal support system (62) is used to connect the lattice column (3) and the bored pile (1).

2. A deep foundation pit retaining structure according to claim 1, characterized in that: A retaining wall (7) is arranged in the vertical direction at one end of the crown beam (11) away from the gantry crane (5); and a side of the retaining wall (7) away from the gantry crane (5) is the ground (81) after the elevation is lowered.

3. A deep foundation pit retaining structure according to claim 1, characterized in that: The first inner support system (61) comprises a first horizontal inner support (611) arranged horizontally and a first inclined inner support (612) arranged inclinedly, the first horizontal inner support (611) and the track beam (31) being arranged perpendicular to each other, four first inclined inner supports (612) being arranged at four corners of the foundation pit respectively, the middle lattice column (3) being located at the lower end of the first horizontal inner support (611), and the outermost lattice column (3) being located at the lower end of the first inclined inner support (612).

4. A deep foundation pit retaining structure according to claim 3, characterized in that: The second inner support system (62) comprises a second horizontal inner support (621) arranged horizontally, a second inclined inner support (622) arranged obliquely, a connecting beam (623) arranged horizontally at intervals, and a waist beam (624) arranged on the inner side of the bored pile (1); the waist beam (624) is used to connect the bored pile (1) with the second horizontal inner support (621) or the second inclined inner support (622); four second inclined inner supports (622) are arranged obliquely at four corners of the foundation pit respectively; the lattice column (3) located in the middle connects a single first horizontal inner support (611) and a plurality of second horizontal inner supports (621); the lattice column (3) located at the outermost side connects a single first inclined inner support (612) and a plurality of second inclined inner supports (622); and the connecting beam (623) is used to connect two adjacent lattice columns (3).

5. A deep foundation pit retaining structure according to claim 4, characterized in that: The bored pile (1) is connected to the waist beam (624) via a steel bar connector, and the second horizontal inner support (621), the second inclined inner support (622) and the waist beam (624) are cast by concrete.

6. A deep foundation pit retaining structure according to claim 1, characterized in that: The distance between the centers of two adjacent bored cast-in-place piles (1) is 1.0-2.0 m.

7. A deep foundation pit retaining structure according to claim 1, characterized in that: The plain concrete ground-anchored wall (2) and bored cast-in-place piles (1) are cast by concrete, the concrete model of the plain concrete ground-anchored wall (2) is C20, and the concrete model of the bored cast-in-place piles (1) is C35.

8. The deep foundation pit retaining structure according to claim 1, characterized in that: The vertical distance between two adjacent second inner support systems (62) is 3 to 5 m, and the vertical distance between the first inner support system (61) and the second inner support system (62) located at the uppermost end is 3 to 5 m.

9. A deep foundation pit retaining structure according to claim 2, characterized in that: After the elevation is lowered, the vertical height of the ground (81) from the obstacle (9) is not less than 6.5 m.

10. A construction method for a deep foundation pit retaining structure, characterized in that: The following steps are involved: The original ground (82) is constructed to ensure that the vertical height of the ground (81) from the obstacle (9) after the elevation is lowered is not less than 6.5m; Carrying out the construction of vertical plain concrete ground-connected walls (2), bored cast-in-place piles (1), column piles (4) and lattice columns (3); The horizontal crown beam (11), the track beam (31) and the first inner support system (61) are constructed, the lattice column (3) is located at the lower end of the first inner support system (61), the crown beam (11) and the track beam (31) are connected through the first inner support system (61), and then the retaining wall (7) is constructed; A gantry crane (5) is installed on the crown beam (11) and the track beam (31); Excavating the foundation pit downwards in sequence, installing multiple horizontal annular waist beams (624) and a second internal support system (62), connecting multiple second internal support systems (62) with a single vertically arranged lattice column (3), and excavating to the bottom of the foundation pit (10); The foundation pit is backfilled to the height of the crown beam (11) and the track beam (31) to restore the road surface.

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