Deep foundation pit pier foundation cofferdam and foundation pit construction method thereof

Abstract

The invention discloses a deep foundation pit pier foundation cofferdam and a foundation pit construction method thereof.The cofferdam comprises a set of lock catch steel pipe piles and a reinforced concrete enclosing purlin structure, the set of lock catch steel pipe piles are connected to form an annular steel pipe pile cofferdam structure, and the reinforced concrete enclosing purlin structure is located on the inner side of the annular steel pipe pile cofferdam structure; the reinforced concrete enclosing purlin structure is an annular enclosing purlin structure matched with the lock catch steel pipe piles in shape. The circular foundation pit support mainly bears radial pressure, and no additional bending moment exists in the enclosing purlin under the condition that the surrounding stress is balanced; and under the condition that the compression resistance of the enclosing purlin structure meets the requirement, structures such as diagonal bracings and diagonal bracings are not arranged, so that the construction space is enlarged while materials are saved, and subsequent mechanical operation is facilitated. Compared with a steel structure under the same economic input condition, the annular enclosing purlin is higher in bearing capacity and smaller in deformation in terms of structural bearing capacity. And the cast-in-place concrete structure has better adaptability to the cofferdam lock catch pile, the integrally poured concrete is in full contact with the lock catch pile, and the overall stress of the enclosing purlin is more uniform.

Description

Technical Field

[0001] This invention relates to the field of bridge foundation technology, and more specifically, to a method for supporting and constructing a cofferdam with a circular overall outline. Background Technology

[0002] During bridge foundation construction, to meet the needs of flood control or planned river dredging, the abutments within the river channel are buried relatively deep. Currently, deep foundation pits are mostly protected by interlocking steel pipe piles or steel sheet pile cofferdam structures. In order to improve the stability of the steel pipe pile (steel sheet pile) cofferdam, the inner side of the cofferdam is equipped with frame structure walers and internal supports, which are complex structures and occupy the inner construction space.

[0003] For example, patent CN217378962U discloses a cofferdam structure, including: interlocking steel pipe piles, positioning piles, and walers; the number of interlocking steel pipe piles and positioning piles is multiple; the multiple interlocking steel pipe piles are evenly arranged in a circle around the periphery of the bridge pier to form the cofferdam body; the multiple positioning piles are evenly arranged in a circle around the periphery of the bridge pier to form a positioning pile group, which is used to install the walers; the positioning pile group is located inside the cofferdam structure, and the positioning pile group, the cofferdam body, and the bridge pier are coaxially arranged; the overall structure of the walers formed is a frame structure, which occupies a relatively large space. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a deep foundation pit pier cofferdam and its foundation pit construction method, aiming to save materials while expanding construction space.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A deep foundation pit pier cofferdam includes a set of interlocking steel pipe piles connected to form a ring-shaped steel pipe pile cofferdam structure. It also includes a reinforced concrete waler structure located inside the ring-shaped steel pipe pile cofferdam structure. The reinforced concrete waler structure is a ring-shaped waler structure that matches the shape of the interlocking steel pipe piles.

[0007] The annular steel pipe pile cofferdam structure is connected to the annular reinforced concrete waler structure to form a combined support system for the overall structure.

[0008] The reinforced concrete waler structure includes annular waler reinforcement bars, which are segmented connection structures. The concrete is poured integrally on site, and the cast-in-place concrete fills the gap between the waler and the steel pipe to form an integral structure.

[0009] The reinforced concrete waler structure includes a multi-layered annular waler structure with upper and lower intervals.

[0010] The inner side of the steel pipe pile is welded with a hanging bracket, and the annular waler structure is suspended on the bracket.

[0011] The reinforced concrete waler structure is equipped with a set of sensors that can collect and analyze waler temperature and stress data in real time.

[0012] A circumferential water jet pipe is installed above the reinforced concrete waler structure, forming a waler temperature control system through a set of sensors and the circumferential water jet pipe.

[0013] The bottom of the foundation pit inside the cofferdam is equipped with a dewatering well structure, which includes a drainage well pipe, a water meter, a suppression valve, and a drainage pipe. The drainage well pipe and the drainage pipe are connected, and the water meter and the suppression valve are installed on the drainage pipe.

[0014] A method for constructing a foundation pit includes the following steps:

[0015] Step 1: Level the site, remove obstacles, set up construction safety barriers and drainage facilities;

[0016] Step 2: First, test drive the interlocking steel pipes to clarify the parameters of the pile driving equipment, and then carry out continuous construction until the construction is completed;

[0017] Step 3: Harden the area around the foundation pit, excavate the soil inside the foundation pit, and excavate to the bottom elevation of the first waler;

[0018] Step 4: Lay the bottom formwork at the corresponding position of the waler, hoist the waler steel reinforcement segments, and weld the steel reinforcement segments together on site;

[0019] Step 5: Weld the triangular hanging brackets above the waler. The brackets are connected to the waler through pre-embedded steel plates and pre-embedded reinforcing bars. The top surface of the pre-embedded parts is flush with the top surface of the waler concrete.

[0020] Step 6: Install the side formwork for the walers, pour and cure the waler concrete;

[0021] Step 7: After the first waler is cured, continue to excavate the soil in the foundation pit, excavating in layers to the bottom elevation of each concrete waler. Repeat steps 4 to 6 to complete the installation of each concrete waler. After the last waler is installed and cured, continue to excavate the soil to the design bottom elevation of the foundation pit.

[0022] Step 8: Construct the bottom sealing concrete and plain concrete cushion layer of the foundation pit, ensuring the thickness and flatness of the cushion layer. Set up drainage wells on the side of the foundation pit according to the plan drawing.

[0023] Step 9: After the foundation layer is cured, the layered pouring construction of the foundation is carried out. After the foundation is cured, the construction of the upper tower or pier is carried out. When the height of the tower or pier is higher than the flat ground and the highest design water level, the backfilling of the foundation pit and the removal of the walers are considered according to the site requirements.

[0024] Step 10: When backfilling the soil in the foundation pit, first seal the dewatering pipe well, then use silty sand to backfill and compact the foundation pit. When backfilling to the lower part of the fourth waler, use a wire saw to cut the waler. After the waler is removed, remove the triangular bracket in time.

[0025] Step 11: After the fourth waler is removed, the second, third and fourth backfilling work is carried out in the foundation pit. The third, second and first concrete walers are removed in sequence. After the first waler is removed, the soil backfilling in the foundation pit continues until the soil in the foundation pit is level with the surrounding ground.

[0026] Step 12: After the soil in the foundation pit is backfilled, the locking steel pipe piles are removed using equipment.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) The design of the cofferdam for the deep foundation pit is reasonable. The circular foundation pit is better supported than the square foundation pit. The cofferdam mainly bears the radial pressure. Under the condition of balanced force around the perimeter, there is no additional bending moment in the waler. If the compressive strength of the waler structure meets the requirements, it is not necessary to set up structures such as bracing or diagonal bracing, which saves materials and expands the construction space, making it easier for subsequent mechanical operations.

[0029] (2) Using reinforced concrete structures for ring walers has a stronger load-bearing capacity and less deformation than steel structures under the same economic investment conditions. In addition, cast-in-place concrete structures are more adaptable to the interlocking piles of the cofferdam, and the overall cast-in-place concrete is in full contact with the interlocking piles, resulting in a more uniform stress distribution on the waler. Attached Figure Description

[0030] The following is a brief explanation of the contents of each of the accompanying drawings and the markings in the drawings:

[0031] Figure 1 This is a schematic diagram of the cofferdam plan of the foundation pit of the present invention.

[0032] Figure 2 This is a schematic diagram of the foundation pit elevation of the present invention.

[0033] Figure 3 This is a schematic diagram of the dewatering well pipe structure of the present invention.

[0034] Figure 4 This is a partially enlarged schematic diagram of the cofferdam of the present invention.

[0035] Figure 5 This is a schematic diagram of the cofferdam waler suspension of the present invention.

[0036] Figure 6 This is a diagram of the reinforcing steel bars for the waler of this invention.

[0037] Figure 7 This is a sensor arrangement diagram of the present invention.

[0038] Figures 8 to 17 This is a schematic diagram of the construction steps for the foundation pit according to the present invention.

[0039] In the picture:

[0040] 1. Construction access road; 2. Reinforced concrete circumferential waler; 201. Integral pouring of filling concrete and waler; 3. Locking steel pipe pile; 4. Foundation; 5. Hanging bracket; 6. Bottom sealing and cushion layer; 7. Engineering pile; 8. Dewatering well structure; 801. Drainage well pipe; 802. Clay ball; 803. Gravel; 804. Water meter; 805. Inhibition valve; 806. Drainage pipe; 9, 10. Embedded anchor plate; 11. Waler main reinforcement; 12. Waler stirrups; 13. Sensor. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and through the description of the examples.

[0042] like Figures 1 to 17 As shown, the deep foundation pit pier cofferdam includes a set of interlocking steel pipe piles 3 and a reinforced concrete waler structure; the set of interlocking steel pipe piles are connected to form a ring-shaped steel pipe pile cofferdam structure, and the reinforced concrete waler structure is located inside the ring-shaped steel pipe pile cofferdam structure. The reinforced concrete waler structure is a ring-shaped waler structure; the ring-shaped steel pipe pile cofferdam structure is connected to the ring-shaped reinforced concrete waler structure to form a combined system support structure.

[0043] The waler and interlocking piles are matched in shape, forming a ring structure. The waler is composed of main reinforcement bars 10, stirrups 11, and concrete. The waler reinforcement skeleton composed of main reinforcement bars 10 and stirrups 11 is manufactured in sections at the back-end and connected in sections on site.

[0044] The filling concrete 201 between the waler and the interlocking steel pipe pile is poured together with the waler concrete, and the same concrete grade is used; it is integrally formed, the structure is stable and reliable, and the construction is simple.

[0045] A layer of reinforced concrete walers is set at intervals of 3 to 5 meters in height. The ring steel pipe pile cofferdam structure and the multi-layer waler structure form a three-dimensional integrated support structure, which is stable and reliable. There is no need to set up bracing or diagonal bracing inside the cofferdam.

[0046] A hanging bracket 5 is welded to the inner side of the steel pipe pile, and the annular waler is suspended on the bracket structure. The bracket structure is connected to the waler through a pre-embedded anchor plate 9, and the top surface of the pre-embedded anchor plate is flush with the top surface of the waler concrete.

[0047] A set of sensors 12 is installed inside the reinforced concrete waler structure to collect and analyze waler temperature and stress data in real time. A circumferential water jet pipe is installed above the reinforced concrete waler structure, forming a waler temperature control system through temperature sensors and the circumferential water jet pipe. Temperature sensors are symmetrically embedded at equal intervals in each waler to monitor waler temperature changes during pit operation, controlling the temperature difference between the waler's center and the pit's bottom temperature under high-temperature conditions to not exceed 15 degrees Celsius. Furthermore, to ensure sufficient exposure time for the walers and reduce the possibility of temperature rise, backfilling or grouting can be carried out after the main pier body is poured to ensure stable waler temperature.

[0048] The bottom of the foundation pit inside the cofferdam is equipped with a dewatering well structure 8; the dewatering well structure includes a drainage well pipe 801, a water meter 804, a suppression valve 805, and a drainage pipe 806. The drainage well pipe and the drainage pipe are connected, and the water meter and the suppression valve are installed on the drainage pipe.

[0049] The dewatering wells are drilled using the impact method to avoid using thick mud and prevent clogging of the filter channels. Water pumped from the wells is discharged directly into the external drainage system through pipes, and sewage is strictly prohibited from being discharged directly into rivers. The well pipes can be made of steel or PVC; if steel pipes are used, the wall thickness should not be less than 4mm. The filter pipe sections are perforated with an opening rate of not less than 20-30%, and three layers of 60-mesh filter screen are wrapped along the well pipe. The well pipe connections are reliably sealed, and the pipes are centered with a deviation of no more than 1cm. The filter media is 2.0-10.0mm continuously graded gravel 803. The filter media is added when the water is flowing, and it must be compacted. When adding clay balls 802 for water stopping, they should be compacted and not left loose.

[0050] In the example, the pier cap 4 is an octagonal structure, the cofferdam is circular, and a space is formed between each side of the main pier cap and the cofferdam. A dewatering well structure is set for each space, and the drainage and pressure reduction at the bottom of the pit are stable and reliable.

[0051] The foundation pit construction method of the present invention includes the following steps:

[0052] Step 1: Level the site, remove obstacles, set up construction safety barriers and drainage facilities;

[0053] Step 2: First, test drive the interlocking steel pipes to clarify the parameters of the pile driving equipment, and then carry out continuous construction until the construction is completed;

[0054] Step 3: Harden the area around the foundation pit, excavate the soil inside the foundation pit, and excavate to the bottom elevation of the first waler;

[0055] Step 4: Lay the bottom formwork at the corresponding position of the waler, hoist the waler steel reinforcement segments, and weld the steel reinforcement segments together on site;

[0056] Step 5: Weld the triangular hanging brackets above the waler. The brackets are connected to the waler through pre-embedded steel plates and pre-embedded reinforcing bars. The top surface of the pre-embedded parts is flush with the top surface of the waler concrete.

[0057] Step 6: Install the side formwork for the walers, pour and cure the waler concrete;

[0058] Step 7: After the first waler is cured, continue to excavate the soil in the foundation pit, excavating in layers to the bottom elevation of each concrete waler. Repeat steps 4 to 6 to complete the installation of each concrete waler. After the last waler is installed and cured, continue to excavate the soil to the design bottom elevation of the foundation pit.

[0059] Step 8: Construct the bottom sealing concrete and plain concrete cushion layer of the foundation pit, ensuring the thickness and flatness of the cushion layer. Set up drainage wells on the side of the foundation pit according to the plan drawing.

[0060] Step 9: After the foundation layer is cured, the layered pouring of the foundation is carried out. After the foundation is cured, the construction of the upper tower (pier) is carried out. When the height of the tower (pier) is higher than the flat ground and the highest design water level, the backfilling of the foundation pit and the removal of the walers are considered in combination with the site requirements.

[0061] Step 10: When backfilling the soil in the foundation pit, first seal the dewatering pipe well, then use silty sand to backfill and compact the foundation pit. When backfilling to the lower part of the fourth waler, use a wire saw to cut the waler. After the waler is removed, remove the triangular bracket in time.

[0062] Step 11: After the fourth waler is removed, the second, third and fourth backfilling work is carried out in the foundation pit. The third, second and first concrete walers are removed in sequence. After the first waler is removed, the soil backfilling in the foundation pit continues until the soil in the foundation pit is level with the surrounding ground.

[0063] Step 12: After the soil in the foundation pit is backfilled, the locking steel pipe piles are removed using equipment.

[0064] This invention presents a rationally designed deep foundation pit cofferdam and its construction method. Utilizing the radial stress characteristics of a circular structure, it employs a combined support system of steel pipe pile cofferdam and reinforced concrete walers. This fully leverages the compressive strength of the waler concrete, allowing the circular walers to replace complex bracing and diagonal bracing structures, saving materials while expanding construction space and facilitating subsequent mechanical operations. Furthermore, in the construction of a circular structure, concrete, compared to steel, better adapts to changes in the cofferdam's curvature and accommodates localized deformation. The integrally cast concrete maintains full contact with the interlocking piles, resulting in more uniform stress distribution across the walers.

[0065] The above description is merely an illustration of preferred embodiments of the present invention, and the above technical features can be arbitrarily combined to form multiple embodiments of the present invention.

[0066] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the concept and technical solution of the present invention, or the direct application of the concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A deep foundation pit pier cofferdam, comprising a set of interlocking steel pipe piles, wherein the set of interlocking steel pipe piles are connected to form a ring-shaped steel pipe pile cofferdam structure, characterized in that: It also includes a reinforced concrete waler structure, which is located inside the annular steel pipe pile cofferdam structure. The reinforced concrete waler structure is an annular waler structure that matches the shape of the interlocking steel pipe piles.

2. The deep foundation pit pier cofferdam as described in claim 1, characterized in that: The annular steel pipe pile cofferdam structure is connected to the annular reinforced concrete waler structure to form a combined support system for the overall structure.

3. The deep foundation pit pier cofferdam as described in claim 2, characterized in that: The reinforced concrete waler structure includes annular waler reinforcement bars, which are segmented connection structures. The concrete is poured integrally on site, and the cast-in-place concrete fills the gap between the waler and the steel pipe to form an integral structure.

4. The deep foundation pit pier cofferdam as described in claim 2, characterized in that: The reinforced concrete waler structure includes a multi-layered annular waler structure with upper and lower intervals.

5. The deep foundation pit pier cofferdam as described in claim 2, characterized in that: The inner side of the steel pipe pile is welded with a hanging bracket, and the annular waler structure is suspended on the bracket.

6. The deep foundation pit pier cofferdam as described in claim 2, characterized in that: The reinforced concrete waler structure is equipped with a set of sensors that can collect and analyze waler temperature and stress data in real time.

7. The deep foundation pit pier cofferdam as described in claim 6, characterized in that: A circumferential water jet pipe is installed above the reinforced concrete waler structure, forming a waler temperature control system through a set of sensors and the circumferential water jet pipe.

8. The deep foundation pit pier cofferdam as described in claim 1, characterized in that: The bottom of the foundation pit inside the cofferdam is equipped with a dewatering well structure, which includes a drainage well pipe, a water meter, a suppression valve, and a drainage pipe. The drainage well pipe and the drainage pipe are connected, and the water meter and the suppression valve are installed on the drainage pipe.

9. A method for constructing a foundation pit, characterized in that: The foundation pit construction method includes the following steps: Step 1: Level the site, remove obstacles, set up construction safety barriers and drainage facilities; Step 2: First, test drive the interlocking steel pipes to clarify the parameters of the pile driving equipment, and then carry out continuous construction until the construction is completed; Step 3: Harden the area around the foundation pit, excavate the soil inside the foundation pit, and excavate to the bottom elevation of the first waler; Step 4: Lay the bottom formwork at the corresponding position of the waler, hoist the waler steel reinforcement segments, and weld the steel reinforcement segments together on site; Step 5: Weld the triangular hanging brackets above the waler. The brackets are connected to the waler through pre-embedded steel plates and pre-embedded reinforcing bars. The top surface of the pre-embedded parts is flush with the top surface of the waler concrete. Step 6: Install the side formwork for the walers, pour and cure the waler concrete; Step 7: After the first waler is cured, continue to excavate the soil in the foundation pit, excavating in layers to the bottom elevation of each concrete waler. Repeat steps 4 to 6 to complete the installation of each concrete waler. After the last waler is installed and cured, continue to excavate the soil to the design bottom elevation of the foundation pit. Step 8: Construct the bottom sealing concrete and plain concrete cushion layer of the foundation pit, ensuring the thickness and flatness of the cushion layer. Set up drainage wells on the side of the foundation pit according to the plan drawing. Step 9: After the foundation layer is cured, the layered pouring construction of the foundation is carried out. After the foundation is cured, the construction of the upper tower or pier is carried out. When the height of the tower or pier is higher than the flat ground and the highest design water level, the backfilling of the foundation pit and the removal of the walers are considered according to the site requirements. Step 10: When backfilling the soil in the foundation pit, first seal the dewatering pipe well, then use silty sand to backfill and compact the foundation pit. When backfilling to the lower part of the fourth waler, use a wire saw to cut the waler. After the waler is removed, remove the triangular bracket in time. Step 11: After the fourth waler is removed, the second, third and fourth backfilling work is carried out in the foundation pit. The third, second and first concrete walers are removed in sequence. After the first waler is removed, the soil backfilling in the foundation pit continues until the soil in the foundation pit is level with the surrounding ground. Step 12: After the soil in the foundation pit is backfilled, the locking steel pipe piles are removed using equipment.

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