Deep foundation pit pit and construction method

Abstract

The present application relates to a kind of deep foundation pit pit-in-pit and construction method, using the structure of pile head cutting device of cast-in-place pile, by setting safety fixing device and telescopic pile head cutting saw, effectively improve the stability and efficiency of pile head cutting;Using the structure of hoisting cage of cast-in-place pile pile head holding, through the pile head holding cylinder and press lock in the pile head holding device, realize the quick holding of cast-in-place pile pile head, use crane to quickly lift out of field the cast-in-place pile pile head in the pile head holding device;Using the template in the elevator shaft pit inside formwork upper press down pull anti-floating structure, pull down lengthening steel bottom welding cast-in-place pile main reinforcement, top passes through reserved hole and is connected with bracing horizontal steel pipe welding, bracing horizontal steel pipe is transversely fixed template in the elevator shaft pit by supporting fixing device, upper pressure weight is placed in the elevator shaft, to form the template in the elevator shaft pit inside formwork upper press down pull anti-floating structure, effectively ensure the smooth construction of elevator shaft.

Description

Technical Field

[0001] This invention belongs to the field of deep foundation pit engineering technology, and particularly relates to a deep foundation pit with a pit-within-a-pit and a construction method. Background Technology

[0002] In the construction of deep soft soil foundation pits, due to the characteristics of the building structure or functional requirements, secondary and multiple excavations are often required within the original foundation pit, creating a pit-within-a-pit within the foundation pit project. This pit-within-a-pit excavation in deep soft soil foundations generates significant internal stress on the surrounding large foundation pit, leading to deformation and affecting the overall stability and safety of the foundation pit. Therefore, it is crucial to ensure the quality of pit-within-a-pit construction techniques. To make rational use of urban land resources, various urban buildings often include basements of varying lengths, and especially to meet functional needs, deep pits such as elevator shafts are also included, i.e., pit-within-a-pits. The construction of these pit-within-a-pits is generally complex and has a certain impact on the overall construction progress of underground engineering. This is especially true for pit-within-a-pits in water-rich strata, which further increases the construction difficulty. Improper groundwater treatment may also lead to the risk of localized leakage later on. Furthermore, the construction of deep foundation pits in deep soft soil foundations presents challenges such as difficulties in cutting and transporting pile heads for cast-in-place piles. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a deep foundation pit with a pit-within-a-pit construction method.

[0004] This construction equipment for deep foundation pits includes: elevator shafts, pile head cutting devices for cast-in-place piles, pile head holding and hoisting cage structures, upper and lower tension anti-buoyancy structures for formwork inside the elevator shaft pit, and foundation pit retaining elevator shaft structures.

[0005] The pile head cutting device for cast-in-place piles is fixed to the pile head of the cast-in-place pile by a safety fixing device. The lower part of the pile head cutting device is equipped with a telescopic pile head cutting saw facing the pile head of the cast-in-place pile.

[0006] The pile head holding and hoisting cage structure for cast-in-place piles includes a pile head holding device, which encloses the cast-in-place pile head cut by the pile head cutting device through a pile head holding cylinder.

[0007] The anti-buoyancy structure of the elevator shaft pit formwork includes the pit formwork and the downward extension steel bars. The pit formwork of the elevator shaft is fixed with the cross-bracing steel pipes. The two ends of the downward extension steel bars are respectively welded to the main reinforcement of the cast-in-place pile and the cross-bracing steel pipes at the top of the cast-in-place pile. The upper part of the elevator shaft is placed with a heavy object.

[0008] Preferably, the pile head cutting device for cast-in-place piles includes a pile head cutting tool and a pile head cutting frame. The pile head cutting tool is placed on the pile head cutting frame, and the pile head cutting frame is fixed to the pile head of the cast-in-place pile by a safety fixing device. The pile head of the cast-in-place pile is located at the top of the cast-in-place pile, and a telescopic pile head cutting saw is installed at the bottom of the pile head cutting frame.

[0009] Preferably, the pile head holding device includes a first unit block and a second unit block. The first unit block and the second unit block are connected and closed by four pile head holding devices pressing and locking buckles to form a pile head holding cylinder. The pile head holding cylinder wraps the cut pile head. Two lifting rings are symmetrically welded and installed on the upper part of the pile head holding device.

[0010] Preferably, the pit formwork is installed on the side and bottom of the elevator shaft. The bottom of the pit formwork has pre-drilled holes. The pit formwork is horizontally fixed with a support and fixing device. A pull-down extension steel bar is inserted into the pre-drilled hole. The bottom of the pull-down extension steel bar is welded to the main reinforcement of the cast-in-place pile above the pile. The top of the pull-down extension steel bar is welded to the pull-down extension steel bar. The pull-down extension steel bars are reinforced by the pull-down vertical steel pipes.

[0011] This method of constructing a deep foundation pit within a pit includes the following steps:

[0012] Step 1: Construct the water-stop curtain around the foundation pit;

[0013] Step 2: Construct the cast-in-place piles and column piles, and construct steel lattice columns on top of the column piles;

[0014] Step 3: The pile head cutting device is fixed to the pile head of the cast-in-place pile through a safety fixing device, and the telescopic pile head cutting saw is extended to start cutting the pile head.

[0015] Step 4: The pile head holding device is closed to form a pile head holding cylinder that wraps the cut pile head. The pile head holding device is then lifted off the field using a crane.

[0016] Step 5: Construct a cushion layer on top of the cast-in-place pile, and install a water-stop steel plate above the cushion layer;

[0017] Step 6: The upper part of the steel lattice column is connected to the concrete support. The capping beam, concrete support, cast-in-place piles near the water-stop curtain and steel lattice column are connected to each other to form an integral structure.

[0018] Step 7: Construct the base slab, foundation, and raft slab on the subbase. Use an anti-buoyancy structure with upper and lower pressure on the formwork inside the elevator shaft to install the formwork inside the shaft and construct the elevator shaft.

[0019] As a preferred option, in step one, a water-retaining sill is installed on the water-stop curtain, and a drainage ditch is constructed on the outside of the water-stop curtain.

[0020] As a preferred embodiment, in step four, two lifting rings are symmetrically welded and installed on the upper part of the pile head holding device. The crane pulls up the lifting rope, which is connected to the hook, and the hook pulls the lifting ring.

[0021] As a preferred embodiment, in step seven, the slope protection in the raft slab is made of fine stone concrete with built-in steel mesh, and a plain concrete replacement layer is provided between the cast-in-place piles near the water-stop curtain and the bottom slab on its inner side.

[0022] The deep foundation pit within a pit is obtained by any of the methods described above.

[0023] The beneficial effects of this invention are:

[0024] 1) The present invention adopts a pile head cutting device structure for cast-in-place piles. By setting up a safety fixing device and a telescopic pile head cutting saw, the stability and efficiency of pile head cutting are effectively improved.

[0025] 2) This invention adopts a cage structure for holding and hoisting the pile head of the cast-in-place pile. Through the pile head holding cylinder and pressing lock in the pile head holding device, the pile head of the cast-in-place pile is quickly placed and then lifted out of the field by a crane.

[0026] 3) This invention adopts an anti-buoyancy structure of upper pressure and lower pull for the formwork in the elevator shaft pit. The bottom of the lower pull-up extended steel bar is welded with the main reinforcement of the cast-in-place pile, and the top passes through the reserved hole and is welded to the horizontal steel pipe of the support. The horizontal steel pipe of the support is horizontally fixed to the formwork in the elevator shaft pit through the support and fixing device. The upper part of the elevator shaft is placed with a heavy object, thereby forming an anti-buoyancy structure of upper pressure and lower pull for the formwork in the elevator shaft pit, which effectively ensures the smooth construction of the elevator shaft. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the elevator shaft structure in the foundation pit retaining wall;

[0028] Figure 2 This is a schematic diagram of the pile head cutting device for cast-in-place piles;

[0029] Figure 3 This is a schematic diagram of the structure of the hoisting cage for holding the pile head of a cast-in-place pile;

[0030] Figure 4 This is a schematic diagram of the anti-buoyancy structure of the template inside the elevator shaft, which is subjected to pressure and tension.

[0031] In the diagram: 1-Cast-in-place pile, 2-Cast-in-place pile head, 3-Pile head cutting tool, 4-Pile head cutting frame, 5-Extendable pile head cutting saw, 6-Safety fixing device, 7-Pile head holding device, 8-First unit block of pile head holding device, 9-Second unit block of pile head holding device, 10-Pile head holding cylinder, 11-Pile head holding device pressing lock, 12-Lifting ring, 13-Lifting hook, 14-Lifting rope, 15-Cranial crane, 16-Main reinforcement of cast-in-place pile, 17-Pulley extension reinforcement, 18-Elevator shaft, 19-Bottom 20-Pit formwork, 21-Horizontal steel pipe for bracing, 22-Support fixing device, 23-Vertical steel pipe for bracing, 24-Reserved hole, 25-Top weight, 26-Column pile, 27-Steel lattice column, 28-Waterstop steel plate, 29-Top beam, 30-Waterstop curtain, 31-Water retaining sill, 32-Drainage ditch, 33-Subbase, 34-Plain concrete replacement layer, 35-Bottom slab, 36-Pile cap, 37-Raft slab, 38-Fine aggregate concrete slope protection with built-in steel mesh, 39-Concrete support. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0033] Example 1

[0034] As one example, the main construction process of this deep foundation pit-within-a-pit is as follows:

[0035] Step 1, Construction of the water-stop curtain 30: First, construct the water-stop curtain 30 around the foundation pit. Set up a water-retaining sill 31 on the water-stop curtain 30. Then, construct a drainage ditch 32 on the outside of the water-stop curtain 30.

[0036] Step 2, Construction of cast-in-place pile 1 and column pile 26: After the construction of the water-stop curtain 30 is completed, the construction of cast-in-place pile 1 and column pile 26 will be carried out. During the construction of column pile 26, the steel lattice column 27 will be constructed on the upper part.

[0037] Step 3, Construction of pile head 2 of cast-in-place pile: The pile head cutting tool 3 is placed on the pile head cutting frame 4. The pile head cutting frame 4 is fixed to the pile head 2 of the cast-in-place pile by the safety fixing device 6. The pile head 2 of the cast-in-place pile is located at the top of the cast-in-place pile 1. The lower part of the pile head cutting frame 4 is equipped with a telescopic pile head cutting saw 5. The telescopic pile head cutting saw 5 is extended to start cutting the pile head 2 of the cast-in-place pile.

[0038] Step 4, hoisting construction of the pile head 2: The pile head holding device 7 is composed of the first unit block 8 and the second unit block 9 of the pile head holding device, which are connected by four pile head holding device pressing locks 11. The first unit block 8 and the second unit block 9 of the pile head holding device are closed to form a pile head holding cylinder 10 to wrap the cut pile head 2 of the cast-in-place pile. Two lifting rings 12 are symmetrically welded and installed on the upper part of the pile head holding device 7. The lifting hook 13 pulls the lifting ring 12, the lifting rope 14 is connected to the lifting hook 13, and the crane 15 pulls the lifting rope 14. The crane 15 is used to hoist the pile head 2 placed in the pile head holding device 7 out of the field.

[0039] Step 5, Construction of cushion layer 33 and waterstop steel plate 28: After the pile head 2 of the cast-in-place pile is cut, cushion layer 33 is constructed on the top of the cast-in-place pile 1, and waterstop steel plate 28 is installed above the cushion layer 33.

[0040] Step 6, Construction of capping beam 29 and concrete support 39: The upper part of steel lattice column 27 is connected to concrete support 39. The capping beam 29, concrete support 39, cast-in-place pile 1 near water-stop curtain 30 and steel lattice column 27 are interconnected to form a stable overall structure.

[0041] Step 7: Construction of base slab 35, pile cap 36, and raft slab 37: The base slab 35, pile cap 36, and raft slab 37 are constructed on the foundation layer 33. The slope protection in the raft slab 37 uses fine aggregate concrete slope protection 38 with built-in steel mesh. Plain concrete replacement layer 34 is used between the cast-in-place pile 1 near the water-stop curtain 30 and its inner base slab 35. The formwork 20 inside the elevator shaft 18 construction pit adopts an upper-pressure, lower-tension anti-buoyancy structure. After the base slab reinforcement 19 is installed, the pit formwork 20 is installed on the sides and bottom of the elevator shaft 18. The bottom surface of the inner formwork 20 has a pre-reserved hole 24. The bottom of the pull-down extended steel bar 17 is welded to the main reinforcement bar 16 of the cast-in-place pile 1. The top of the pull-down extended steel bar 17 passes through the pre-reserved hole 24 and is welded to the horizontal support steel pipe 21. The horizontal support steel pipe 21 is horizontally fixed to the inner formwork 20 of the elevator shaft 18 through the support fixing device 22. The vertical support steel pipe 23 is reinforced to connect the horizontal support steel pipe 21. The upper weight 25 is placed on the upper part of the elevator shaft 18 to form an upper pressure and lower pull anti-buoyancy structure for the inner formwork 20 of the elevator shaft 18.

[0042] Example 2

[0043] As another embodiment, the deep foundation pit construction device used in the method of embodiment one includes: a pile head 2 cutting device, a pile head 2 hoisting cage structure, an elevator shaft 18 pit formwork 20 upper pressure and lower pull anti-buoyancy structure, and a foundation pit retaining elevator shaft 18 structure.

[0044] The pile head cutting device for cast-in-place piles is fixed to the pile head 2 of the cast-in-place pile by a safety fixing device 6. The lower part of the pile head cutting device is provided with a telescopic pile head cutting saw 5 facing the pile head 2 of the cast-in-place pile.

[0045] The pile head holding and hoisting cage structure includes a pile head holding device 7, which encloses the pile head 2 cut by the pile head cutting device through a pile head holding cylinder 10.

[0046] The anti-buoyancy structure of the elevator shaft pit formwork includes the pit formwork 20 and the downward extension steel bar 17. The pit formwork 20 of the elevator shaft 18 is fixed with a cross-bracing steel pipe 21. The two ends of the downward extension steel bar 17 are respectively welded to the main reinforcement 16 of the cast-in-place pile 1 and the cross-bracing steel pipe 21. The upper part of the elevator shaft 18 is placed with a top weight 25.

[0047] The pile head 2 cutting device for cast-in-place piles is characterized in that it includes: a pile head cutting tool 3 is placed on a pile head cutting frame 4, the pile head cutting frame 4 is fixed to the pile head 2 of the cast-in-place pile by a safety fixing device 6, the pile head 2 of the cast-in-place pile is located at the top of the cast-in-place pile 1, and a telescopic pile head cutting saw 5 is installed at the lower part of the pile head cutting frame 4, and the telescopic pile head cutting saw 5 is extended to start cutting the pile head 2 of the cast-in-place pile.

[0048] The aforementioned cage structure for holding and hoisting the pile head 2 of the cast-in-place pile is characterized in that it includes: a pile head holding device 7, which is formed by connecting a first unit block 8 and a second unit block 9 of the pile head holding device through four pile head holding device pressing locks 11. The first unit block 8 and the second unit block 9 of the pile head holding device are closed to form a pile head holding cylinder 10 to enclose the cut cast-in-place pile head 2. Two lifting rings 12 are symmetrically welded and installed on the upper part of the pile head holding device 7. A hook 13 pulls the lifting rings 12, and a lifting rope 14 is connected to the hook 13. A crane 15 pulls the lifting rope 14, and the crane 15 is used to hoist the cast-in-place pile head 2 placed in the pile head holding device 7 out of the field.

[0049] The aforementioned anti-buoyancy structure of the inner formwork 20 in the elevator shaft 18 is characterized by comprising: after the bottom plate reinforcement 19 is installed, the inner formwork 20 is installed on the side and bottom of the elevator shaft 18; the bottom surface of the inner formwork 20 has a pre-reserved hole 24; the bottom of the pull-down extension reinforcement 17 is welded with the main reinforcement 16 of the upper part of the cast-in-place pile 1; the top of the pull-down extension reinforcement 17 passes through the pre-reserved hole 24 and is welded to the horizontal support steel pipe 21; the horizontal support steel pipe 21 is horizontally fixed to the inner formwork 20 in the elevator shaft 18 by the support fixing device 22; the vertical support steel pipe 23 is reinforced to connect the horizontal support steel pipe 21; and a top weight 25 is placed on the upper part of the elevator shaft 18 to form the anti-buoyancy structure of the inner formwork 20 in the elevator shaft 18.

[0050] The aforementioned foundation pit retaining elevator shaft 18 structure is characterized by comprising: firstly, constructing a water-stop curtain 30 around the foundation pit, setting a water-retaining sill 31 on the water-stop curtain 30, constructing a drainage ditch 32 on the outside of the water-stop curtain 30, then constructing cast-in-place piles 1 and column piles 26, with the upper part of the cast-in-place piles 1 near the water-stop curtain 30 connected to the capping beam 29, and a steel lattice column 27 set on the upper part of the column piles 26, the upper part of the steel lattice column 27 connected to the concrete support 39, and the structure constructed via the capping beam 29, concrete support 39, and... The cast-in-place piles 1 and steel lattice columns 27 near the water-stop curtain 30 are connected to form a stable overall structure. After the pile head 2 of the cast-in-place pile is cut, the cushion layer 33 is constructed on the top of the cast-in-place pile 1. The water-stop steel plate 28 is installed above the cushion layer 33. The base plate 35, the pile cap 36 and the raft slab 37 are constructed on the cushion layer 33 respectively. The slope protection in the raft slab 37 adopts the fine stone concrete slope protection 38 with built-in steel mesh. The cast-in-place pile 1 near the water-stop curtain 30 and its inner base plate 35 adopt the plain concrete replacement layer 34.

[0051] It should be noted that the parts in this embodiment that are the same as or similar to those in Embodiment 1 can be referred to each other, and will not be repeated in this application.

[0052] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

Claims

1. A deep foundation pit in-pit construction method using a construction device of a deep foundation pit in-pit, characterized by, The construction device comprises a bored pile head cutting device, a bored pile head containing and hoisting cage structure, and an anti-floating structure of pressing the formwork in the elevator shaft pit from above and pulling it from below. The bored pile head cutting device is fixed on the bored pile head by a safety fixing device, and a telescopic pile head cutting saw is arranged at the lower part of the bored pile head cutting device and faces the bored pile head. The bored pile head containing device comprises a pile head containing device, which wraps the bored pile head cut by the bored pile head cutting device. The anti-floating structure of pressing the formwork in the elevator shaft pit from above and pulling it from below comprises a pit formwork and a pulling and lengthening steel bar, the pit formwork in the elevator shaft is fixed with a supporting transverse steel pipe, and the pulling and lengthening steel bar is welded with the bored pile main reinforcement at the upper part of the bored pile and the supporting transverse steel pipe at two ends, respectively, and a heavy object is placed at the upper part of the elevator shaft. The construction method comprises the following steps. Step one: construction of the water stop curtain outside the foundation pit is performed. Step two: construction of the bored pile and the column pile is performed, and a steel lattice column is constructed at the upper part of the column pile. Step three: the bored pile head cutting device is fixed on the bored pile head by the safety fixing device, and the telescopic pile head cutting saw is stretched out to start cutting the bored pile head. Step four: the pile head containing device is folded to form a pile head containing cylinder to wrap the cut bored pile head, and the pile head containing device is hoisted out of the site by a crane. Step five: a cushion layer is constructed at the top of the bored pile, and a water stop steel plate is arranged at the upper part of the cushion layer. Step six: the upper part of the steel lattice column is connected with the concrete support, the compression roof beam, the concrete support, the bored pile close to the water stop curtain, and the steel lattice column are connected to form an integral structure. Step seven: the bottom plate, the pile cap, and the raft are constructed on the cushion layer, the pit formwork is installed by using the anti-floating structure of pressing the formwork in the elevator shaft pit from above and pulling it from below, and the elevator shaft is constructed.

2. The deep excavation pit-in-pit construction method using the construction device for deep excavation pit-in-pit according to claim 1, characterized in that, The deep foundation pit pit-in-pit construction device comprises a pile head cutting device and a pile head cutting frame, the pile head cutting device is arranged on the pile head cutting frame, the pile head cutting frame is fixed on the bored pile head by a safety fixing device, the bored pile head is located at the top of the bored pile, and a telescopic pile head cutting saw is arranged at the lower part of the pile head cutting frame.

3. The deep excavation pit-in-pit construction method using the construction device for deep excavation pit-in-pit according to claim 1, characterized in that, The deep foundation pit pit-in-pit construction device comprises a pile head containing device first unit block and a pile head containing device second unit block, the pile head containing device first unit block and the pile head containing device second unit block are connected and folded to form a pile head containing cylinder by four pile head containing device pressing locks, the pile head containing cylinder wraps the cut bored pile head, and two lifting rings are symmetrically welded and arranged at the upper part of the pile head containing device.

4. The deep excavation pit-in-pit construction method using the construction device for deep excavation pit-in-pit according to claim 1, characterized in that, The deep foundation pit pit-in-pit construction device comprises a pit formwork installed on the side and bottom of the elevator shaft, a reserved hole is arranged at the bottom of the pit formwork, a supporting transverse steel pipe is fixed in the pit formwork by a supporting fixing device, a pulling and lengthening steel bar is arranged in the reserved hole, the pulling and lengthening steel bar is welded with the bored pile main reinforcement at the upper part of the bored pile at the bottom, the pulling and lengthening steel bar is welded with the supporting transverse steel pipe at the top, and the supporting transverse steel pipes are reinforced by a supporting vertical steel pipe.

5. The deep excavation pit-in-pit construction method using the construction device for deep excavation pit-in-pit according to claim 1, characterized in that, In step one, a water retaining ridge is arranged on the water stop curtain, and a drainage ditch is constructed outside the water stop curtain.

6. The deep excavation pit-in-pit construction method using the construction device for deep excavation pit-in-pit according to claim 1, wherein, In step four, two lifting rings are symmetrically welded on the upper part of the pile head containing device, a lifting rope is pulled on the crane, the lifting rope is connected with a lifting hook, and the lifting hook pulls the lifting ring.

7. The deep excavation pit-in-pit construction method using the construction device for deep excavation pit-in-pit according to claim 1, characterized in that, In step seven, the slope protection in the raft is made of fine stone concrete slope protection with built-in steel mesh, and plain concrete layers are arranged between the cast-in-place pile close to the water stop curtain and the bottom plate on the inner side.

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