Rapid construction method for overwater large cofferdam applied to geology with impervious layer at bottom

Abstract

The invention discloses a rapid construction method for an overwater large cofferdam applied to a geology with an impervious layer at the bottom, aiming at the characteristic that the geology with the impervious layer at the bottom, a locking steel pipe pile cofferdam is adopted as a structural form of the overwater large cofferdam, and excavation construction of the overwater large cofferdam is carried out by applying a dry excavation method. Meanwhile, rapid installation of the inner support of the overwater large cofferdam is achieved through the method of layered water pumping and dry digging and layer-by-layer overall lowering of the inner support through a hanging system; according to the method, the base of the overwater large cofferdam is constructed in a block interval dry digging in-place and cushion concrete pouring mode, pit bottom upheaval and sudden gushing are effectively avoided, and rapid installation of the overwater large cofferdam is achieved. Due to the fact that the cofferdam is in a water-free environment, compared with a double-wall steel / steel sheet pile cofferdam and underwater excavation method adopted in traditional overwater large cofferdam construction, the method is higher in construction speed, higher in construction efficiency, better in construction quality, free of slurry pollution, economical and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the field of construction of cofferdams for bridge engineering pile caps, and particularly to a rapid construction method for large-scale waterborne cofferdams applied to geological conditions with an impervious layer at the bottom. Background Art

[0002] With the continuous advancement of domestic infrastructure construction, the scale of cofferdams for pile caps in bridge engineering has been constantly breaking records. The traditional construction method for large-scale waterborne pile cap cofferdams uses the "double-wall steel / steel sheet pile cofferdam + underwater excavation method", which has the disadvantages of low underwater excavation efficiency, difficult control of excavation quality, and relatively large mud pollution. As a result, the construction period of large-scale waterborne pile cap cofferdams is long, the construction cost is high, and the large mud pollution cannot meet the requirements of rapid construction and green construction of modern bridges.

[0003] If the excavation of the cofferdam is carried out in a waterless environment, the above problems can be avoided. However, the prerequisite conditions for dry excavation construction of large-scale waterborne cofferdams are: ① The bottom of the large-scale waterborne cofferdam contains geological conditions with an impervious layer; ② The large-scale waterborne cofferdam has high flexural resistance, large driving depth, and high overall strength. Since the existing construction methods for waterborne cofferdams do not have the above prerequisite conditions, for actual construction needs, it is urgent to develop a rapid construction method for large-scale waterborne cofferdams applied to geological conditions with an impervious layer at the bottom. Summary of the Invention

[0004] The purpose of the present invention is to provide a rapid construction method for large-scale waterborne cofferdams applied to geological conditions with an impervious layer at the bottom. When there is an impervious layer geological condition at the bottom of the large-scale waterborne cofferdam, a lock-pile steel pipe pile cofferdam with high overall strength, high flexural resistance, and large driving depth is selected as the structural form of the large-scale waterborne cofferdam, so that the conditions for dry excavation construction of the large-scale waterborne cofferdam are met. Then, through the method of layered pumping and dry excavation + hanging system to gradually lower the internal support layer by layer + block-by-block and interval pouring of cushion concrete, the rapid installation of the large-scale waterborne cofferdam is safely realized.

[0005] The present invention is implemented as follows: A rapid construction method for large-scale waterborne cofferdams applied to geological conditions with an impervious layer at the bottom, characterized in that the specific steps are as follows: A. During the pile foundation construction stage, a pile foundation steel casing needs to be installed. After the pile foundation construction is completed, it is necessary to install a large-scale waterborne cofferdam and excavate the soil inside the large-scale waterborne cofferdam for further construction of the pile cap. The lock-pile steel pipe pile cofferdam is a structural form of the large-scale waterborne cofferdam, which consists of lock-pile steel pipe piles, internal supports, and cushion concrete, and there are three layers of internal supports in total; First, a crawler crane is used in cooperation with a vibrating hammer to drive the lock-pile steel pipe piles to form a closed rectangular structure. A hanging system and steel corbels are installed on the steel casing of the pile foundation. The hanging system consists of a hanging beam, a balance beam, a jack, high-strength precision rolled threaded steel bars and supporting nuts. Three layers of internal supports are pre-assembled integrally on the steel corbels in advance. The high-strength precision rolled threaded steel bars of the hanging system are passed through the internal supports and connected and fixed. B. Pumps are used to drain the water inside the large waterborne cofferdam. Several long-arm excavators are used to dry-excavate the soil layer by layer from both sides of the long side direction of the large waterborne cofferdam in the order of first the middle and then the periphery. The thickness of each layer is about 1 m. At the same time, a dredging platform is installed on the top of the steel casing of the pile foundation in the middle area of the large waterborne cofferdam. Another long-arm excavator stands on the dredging platform to excavate the soil from the middle to improve the excavation efficiency. C. When the internal part of the large waterborne cofferdam is dry-excavated layer by layer to the design position of each layer of internal support, the steel corbels are cut off, and the jacks of the hanging system are used in cooperation with the high-strength precision rolled threaded steel bars and supporting nuts to alternately lift and lower, and gradually lower each layer of internal support to the design position as a whole. Steel corbels are installed on the lock-pile steel pipe piles to fix the internal support that has been lowered in place. D. After all three layers of internal supports are lowered to the design position, the hanging system is removed and the steel casing of the pile foundation is cut off. The remaining soil is continuously dry-excavated layer by layer until it is dry-excavated to 1 m away from the design base elevation of the large waterborne cofferdam. Then the bottom area of the entire large waterborne cofferdam is divided into 5 blocks. First, the middle block is dry-excavated to the design bottom elevation and the cushion concrete is poured. Then the two side blocks are dry-excavated to the design bottom elevation at intervals symmetrically. After each block is dry-excavated in place, the corresponding cushion concrete is poured to complete the installation of the large waterborne cofferdam. The innovation points of the present invention are as follows: 1. The present invention adopts the combination of "dry-excavation method + lock-pile steel pipe pile cofferdam" for the dry-excavation construction of the large waterborne cofferdam. Compared with the traditional underwater excavation method, since the excavation is carried out in a waterless environment in the present invention, the excavation efficiency is higher, there is no mud pollution, the cost and construction period can be greatly saved, and it is green and environmentally friendly. 2. The present invention adopts the method of "layered pumping and dry-excavation + gradually lowering the internal support as a whole layer by layer by the hanging system" to realize the rapid installation of the internal support of the large waterborne cofferdam. Compared with the traditional scheme of assembling the internal support separately inside the large waterborne cofferdam, there is sufficient construction space, higher construction efficiency, better construction quality and better safety. 3. The present invention adopts the method of dry-excavating each block in place at intervals and pouring the cushion concrete for the base construction of the large waterborne cofferdam. Compared with the traditional method of excavating the large waterborne cofferdam in one go and pouring the cushion concrete underwater, it can effectively avoid the bottom heave and gushing, the construction is safer, and the rapid installation of the large waterborne cofferdam is realized. The present invention has the following advantages: 1. Higher construction efficiency, saving construction period and cost. By creating a waterless environment for the excavation of the soil inside the large water-based cofferdam, the present invention has no excavation blind spots and can be excavated by the cooperation of excavators inside and outside, with higher excavation efficiency. At the same time, by pre-assembling the internal support in advance and using a hanging system to lower the internal support as a whole to the designed position, the construction speed is faster compared with the traditional method of assembling the internal support piece by piece inside the large water-based cofferdam, which can greatly save the construction period, thus saving the construction cost and being safer during construction. 2. Better construction quality. In the traditional method of assembling and installing the internal support piece by piece inside the large water-based cofferdam, due to the narrow installation space inside, it is difficult to control the installation quality of the internal support. In the present invention, the internal support is pre-assembled as a whole on the top of the large water-based cofferdam and then lowered as a whole through a hanging system, with sufficient construction space and easy quality control. At the same time, in the present invention, the cushion concrete is poured in a waterless environment, and compared with the traditional method of pouring the cushion concrete underwater, the construction quality of the cushion concrete is better. 3. Green and environmental protection. The present invention creates a waterless environment for the excavation of the soil inside the large water-based cofferdam. Compared with the traditional underwater excavation method, there is no pollution of mud and waste water during excavation, which is green and environmental protection.

[0006] In view of the characteristics of the geological layer containing an impermeable layer at the bottom, the present invention adopts a lock-pile steel pipe pile cofferdam suitable for implementing the dry excavation method as the structural form of the large water-based cofferdam, which can realize the rapid installation of the large water-based cofferdam, provides a new idea for the construction of the cofferdam of the large water-based bridge cap, and promotes the progress and development of bridge construction technology. Brief Description of the Drawings

[0007] Figure 1 It is a schematic diagram of construction step A of an embodiment of the present invention; Figure 2 It is a schematic diagram of construction step C of an embodiment of the present invention; Figure 3 It is a schematic diagram of construction step D of an embodiment of the present invention; Figure 4 It is a front elevation schematic diagram of the hanging system of an embodiment of the present invention; Figure 5 It is a schematic plan view of the hanging system and the cofferdam as a whole of an embodiment of the present invention; In the figure: 1, lock-pile steel pipe pile; 2, internal support; 3, cushion concrete; 4, pile foundation steel casing; 5, steel corbel; 6, hanging beam; 7, balance beam; 8, jack; 9, rolled thread steel; 10, matching nut. Detailed Description of the Invention

[0008] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0009] A rapid construction method for a large waterborne cofferdam applied to geological conditions with an impermeable layer at the bottom is as follows: A. During the pile foundation construction stage, a pile foundation steel casing needs to be installed. After the pile foundation construction is completed, a large waterborne cofferdam needs to be installed and the soil inside the large waterborne cofferdam needs to be excavated for further construction of the pile cap. The lock-pile steel pipe pile cofferdam is a structural form of the large waterborne cofferdam, which is composed of lock-pile steel pipe piles 1, internal supports 2, and cushion concrete 3. There are three layers of internal supports 2 in total. First, a crawler crane is used in cooperation with a vibratory hammer to drive the lock-pile steel pipe piles 1 to form a closed rectangular structure. Multiple sets of hanging systems and steel corbels 5 are installed on the pile foundation steel casing 4. The hanging system is composed of a hanging beam 6, a balance beam 7, a jack 8, a high-strength rolled thread steel bar 9, and a supporting nut 10. The supporting nut 10 is installed on the high-strength rolled thread steel bar 9. Both the hanging beam 6 and the balance beam 7 are made of section steel. The internal support 2 is pre-assembled integrally on the steel corbel 5, and the high-strength rolled thread steel bar 9 is passed through the internal support 2 and connected and fixed. B. The water inside the large waterborne cofferdam is pumped dry by a water pump. Several long-arm excavators are used to dry-excavate the soil in layers from both sides of the long side direction of the large waterborne cofferdam in the order of first the middle and then the periphery, with each layer about 1 m thick. At the same time, a dredging platform is installed on the top of the pile foundation steel casing 4 in the middle area of the large waterborne cofferdam, and another long-arm excavator stands on the dredging platform to excavate the soil from the middle to improve the excavation efficiency. C. When the internal part of the large waterborne cofferdam is dry-excavated in layers to the design position of each layer of internal support 2, the steel corbel 5 is cut off, and the jacks 8 on multiple sets of hanging systems are used to synchronously lift and lower, and at the same time, the supporting nuts 10 on the high-strength rolled thread steel bar 9 cooperate to alternately move and limit, so that the high-strength rolled thread steel bar 9 and the internal support 2 are gradually lowered with each fall of the jack 8 until each layer of internal support 2 is lowered to the design position, and the steel corbel support is welded and installed at the corresponding position on the lock-pile steel pipe pile to fix the lowered internal support 2.

[0010] D. After all three layers of internal supports 2 are lowered to the design position, the hanging system is removed and the pile foundation steel casing 4 is cut off. The remaining soil is continuously dry-excavated in layers to a height of 1 m from the design base elevation of the large waterborne cofferdam. The bottom area of the entire large waterborne cofferdam is divided into 5 sub-blocks. First, the middle sub-block is dry-excavated to the design bottom elevation and the cushion concrete is poured, and then the two side sub-blocks are dry-excavated symmetrically at intervals to the design bottom elevation. After each sub-block is dry-excavated in place, the corresponding cushion concrete is poured to complete the installation of the large waterborne cofferdam.

[0011] The present invention is not limited to the above best implementation mode. Anyone should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, fall within the protection scope of the present invention.

Claims

1. A rapid construction method for a large water cofferdam with an impermeable geological layer at the bottom, characterized in that: The specific steps are as follows: A. Pile foundation steel casing needs to be installed during the pile foundation construction phase. After the pile foundation construction is completed, a large water cofferdam needs to be installed and the soil inside the large water cofferdam needs to be excavated for further construction of the cap. The lock-mouth steel pipe pile cofferdam is a structural form of a large water cofferdam, which consists of lock-mouth steel pipe piles, internal supports, and cushion concrete, of which the internal supports have three layers; First, a crawler crane cooperates with a vibrating hammer to drive the locking steel pipe piles to form a closed rectangular structure; the hanging system and steel bracket are installed on the pile foundation steel casing, where the hanging system consists of a hanging beam, a shoulder beam, a jack, fine-rolled threaded steel bars and matching nuts; three layers of internal support are pre-assembled on the steel bracket, and the fine-rolled threaded steel bars of the hanging system are inserted into the internal support and connected and fixed; B. Use a water pump to drain the water inside the large water cofferdam, and use several long-arm excavators to dry-dig soil in layers from both sides of the long side of the large water cofferdam in the order of the middle first and then the surrounding areas, with each layer thickness of about 1m; at the same time, install a dredging platform on the top of the pile foundation steel casing in the middle area of ​​the large water cofferdam, and use another long-arm excavator standing on the dredging platform to dig soil from the middle to improve excavation efficiency; C. After the internal layered dry excavation of the large water cofferdam reaches the designed position of each layer of internal support, the steel brackets are cut off and the jacks of the hanging system are used to alternately lift and lower the fine-rolled threaded steel bars and matching nuts, and each layer of internal support is gradually lowered to the designed position as a whole, and the steel brackets are installed on the locking steel pipe piles to fix the lowered internal support; D. When all three layers of internal supports are lowered to the designed position, remove the hanging system and cut off the pile foundation steel casing, and continue to dry-dig the remaining soil in layers until it is 1m away from the designed base elevation of the large water cofferdam. Then divide the bottom area of ​​the entire large water cofferdam into 5 blocks. First, dry-dig the middle block to the designed bottom elevation and pour the cushion concrete. Then, dry-dig the blocks on both sides symmetrically at intervals to the designed bottom elevation. After each block is dry-digged in place, pour the corresponding cushion concrete to complete the installation of the large water cofferdam.

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