A gravity cofferdam and construction method

Abstract

A gravity cofferdam includes a reinforced concrete pipe-filled stone retaining wall arranged in front of a foundation pit, wherein the reinforced concrete pipe-filled stone retaining wall includes a plurality of reinforced concrete pipes arranged side by side, the reinforced concrete pipes are placed vertically, and a plurality of steel pipes are placed close to the inner wall of the reinforced concrete pipes. Underwater concrete is poured at the bottom of the reinforced concrete pipes, and a sand and gravel mixture is backfilled inside to form the overall structure of the retaining wall. Bags of soil are stacked behind the reinforced concrete pipe-filled stone retaining wall to form a bagged soil weir body. The gravity cofferdam structure of the present invention has clear stress conditions and a safe and reliable structure. The front row of reinforced concrete pipe gravity structures bear the lateral pressure of the bagged soil at the rear, and the bagged soil weir body at the rear bears the head pressure and anti-seepage function. The construction method has low cost, strong practicability, and convenient construction. It overcomes the limitations of conventional cofferdam forms in the application of steep slope rivers with rock foundations, and solves the problem of creating dry embankment construction conditions for bridge pier foundation pits on the slopes of mountainous rivers.

Description

Technical Field

[0001] The invention relates to the technical field of river engineering construction, and discloses a gravity cofferdam and a construction method. Background Art

[0002] When building a new bridge over a mountain river, the abutments are often set on the rock slope with good geological conditions. On the one hand, they have better stress conditions, and on the other hand, compared with the abutments set on the rear land, the bridge span can be reduced, reducing the project investment. The abutment construction excavates the foundation pit on the river slope. The top elevation of the foundation pit is often lower than the normal water level of the river. Facing the problem of river water backflow, it is necessary to build a cofferdam on the outside to block water and create dry land construction conditions for the abutment construction.

[0003] Conventional cofferdams mainly include bagged earth cofferdams, wood pile cofferdams and steel sheet pile cofferdams. Bagged earth cofferdams built on steep slopes have poor stability and large volume, which affects the river's flood discharge and navigation functions; and the rock foundation conditions cause difficulties in the construction of pile-based cofferdams. Conventional cofferdams are difficult to apply to river channels with steep rock foundations. Therefore, it is urgent to explore a new type of cofferdam and construction method suitable for steep rock foundations. Summary of the invention

[0004] The purpose of the present invention is to propose a gravity cofferdam to overcome the limitations of conventional cofferdam forms in application on rock-based steep slope rivers and to solve the problem of creating dry embankment construction conditions for bridge foundation pits on the slopes of mountainous rivers.

[0005] In order to solve the above technical problems, the present invention is solved by the following technical solutions:

[0006] A gravity cofferdam, characterized in that: a foundation pit is provided on a river channel slope, the gravity cofferdam comprises a reinforced concrete pipe-filled stone retaining wall arranged in front of the foundation pit, the reinforced concrete pipe-filled stone retaining wall comprises a plurality of reinforced concrete pipes arranged side by side, the reinforced concrete pipes are placed vertically, a plurality of steel pipes are placed close to the inner wall of the reinforced concrete pipes, underwater concrete is poured at the bottom of the reinforced concrete pipes, and a sand and gravel mixture is backfilled inside to form the overall structure of the retaining wall, and bagged soil is stacked behind the reinforced concrete pipe-filled stone retaining wall to form a bagged soil weir body.

[0007] Furthermore, the reinforced concrete pipe is formed by vertically splicing at least two reinforced concrete pipe sections.

[0008] Furthermore, bamboo mesh is laid vertically behind the reinforced concrete pipe to provide a flat interface for stacking bagged soil at the rear.

[0009] Furthermore, a PE anti-seepage membrane is laid as a whole in the foundation pit behind the bamboo mesh, and the end of the PE anti-seepage membrane is inserted into the groove on the upper side of the slope behind the foundation pit. The groove is backfilled with plain concrete, and bagged soil is stacked on the PE anti-seepage membrane, thereby forming a long anti-seepage body at the interface between the bagged soil and the original soil, lengthening the seepage path, and reasonably reducing the size of the bagged soil dam.

[0010] A construction method for a gravity cofferdam, characterized in that the method comprises the following steps:

[0011] (1) Partially excavate the river bank slope, dig out the cofferdam bed and level it;

[0012] (2) Installation of reinforced concrete pipe retaining wall: Arrange reinforced concrete pipe segments vertically on the leveled underwater base bed in an orderly manner, pour underwater concrete at the bottom of the reinforced concrete pipe segments, insert multiple steel pipes into the inner wall of the pipe before initial setting and fix them, backfill sand and gravel mixture to the top of the pipe segment after the concrete has finally set, backfill block stone and crushed stone mixture, insert the second reinforced concrete pipe segment to connect the height, and continue to backfill sand and gravel to the top of the pipe to form a reinforced concrete pipe retaining wall;

[0013] (3) Laying bamboo mesh and anti-seepage membrane: Lay bamboo mesh behind the reinforced concrete pipe retaining wall, lay PE anti-seepage membrane in the pit formed along the back of the retaining wall and the slope excavation surface, insert the end of the anti-seepage membrane into the groove on the upper side of the slope behind the foundation pit, and backfill with plain concrete;

[0014] (4) Stacking of bagged soil: Stack the bagged soil from the bottom of the pit upwards to the designed elevation.

[0015] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0016] 1. The cofferdam adopts a gravity structure, which can adapt to the construction conditions of rock foundation steep slope river channel through the combination of reinforced concrete pipe retaining wall and bagged soil.

[0017] 2. The stress conditions of the cofferdam structure are clear and the structure is safe and reliable. Under the condition of positive water retaining at normal water level, the rear bagged earth weir body bears the head pressure and anti-seepage function; under the condition of low water level, the front row reinforced concrete pipe gravity structure bears the lateral pressure of the bagged earth at the rear.

[0018] 3. Compared with the bagged soil pile cofferdam, the cofferdam has the characteristic of smaller volume, avoiding the construction difficulty of dumping large volume of bagged soil underwater, reducing the impact on river flood discharge, navigation and other functions, and saving construction costs.

[0019] 4. The cofferdam is not only applicable to rock foundations, but also more widely applicable to soil foundations with higher bearing capacity. Compared with the steel sheet pile cofferdam, the cofferdam only needs to excavate the bank slope locally, and does not need to pull out the piles after use, which has less impact on the bank slope. Compared with the steel sheet pile cofferdam, the cost is cheaper.

[0020] 5. The reinforced concrete pipes of the cofferdam adopt standard pipes for drainage engineering, and the steel pipes inside the sleeve adopt standard steel pipes for scaffolding. Pipes of different sizes are spliced ​​and bagged soil is piled up to meet different water retaining head requirements.

[0021] 6. The reinforced concrete pipes, scaffolding steel pipes and bagged soil used in the cofferdam can be recycled and reused after the construction is completed, thereby reducing the use cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings:

[0023] Figure 1 It is a schematic plan view of a novel gravity cofferdam and a cofferdam in a construction method suitable for a rock foundation steep slope according to the present invention;

[0024] Figure 2 It is a structural schematic diagram of the cofferdam in the present invention;

[0025] Figure 3 It is a schematic diagram of the structure of the reinforced concrete pipe in the present invention.

[0026] In the figure: 1- reinforced concrete pipe retaining wall; 2- bagged earth weir; 3- bridge pedestal construction pit; 4- reinforced concrete tongue and groove pipe; 5- steel pipe; 6- crushed stone and block stone mixture; 7- underwater concrete; 8- bamboo mesh; 9- PE anti-seepage membrane; 10- bagged earth; 11- groove; 12- center line of retaining wall; 13- cofferdam top; 14- slope line; 15- foundation pit excavation edge line; 16- river slope; 17- cofferdam bed. DETAILED DESCRIPTION

[0027] The present invention will be described more clearly and completely below according to the preferred embodiments of the present invention and in conjunction with the accompanying drawings. These embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0028] like Figure 1As shown in the figure, the bridge pier is arranged on a river bank with a steep rock foundation. The top elevation of the foundation pit on the river side is lower than the normal water level of the river. It is necessary to build a cofferdam on the bank slope to create dry land excavation construction conditions. A gravity cofferdam is adopted. The outer reinforced concrete pipe retaining wall 1 bears the lateral pressure of the bagged soil behind, and the bagged soil weir body 2 bears the head pressure and anti-seepage function. The retaining wall constrains the bagged soil behind the wall, so that the bagged soil pile of a certain height can stand stably on the steep slope, reducing the volume of the bagged soil pile and improving the stability of the underwater bagged soil. The pouring of underwater concrete is conducive to enhancing the bonding effect between the bottom of the pipe and the base surface, improving the anti-slip stability of the reinforced concrete pipe retaining wall, and at the same time, together with the backfill sand and gravel, it fixes the eight steel pipes on the inner wall of the pipeline, which is beneficial to the overall bending strength of the reinforced concrete pipe.

[0029] like Figure 2As shown, firstly, the survey and setting out are carried out. According to the design requirements and plane position of the drawings, the layout position of the cofferdam is determined on the river slope, and based on this, the scope and elevation of the slope excavation are determined, and the marking line is made; then, the upper part of the river slope (the foundation pit position of the bridge cap) is first partially excavated to create a construction interface. Then, the land excavation construction method is used to excavate the earth and stone on the foundation surface that has been set out, and the base bed is leveled, preferably with a 1:20 reverse slope; then the river slope 16 is partially excavated to excavate the cofferdam base bed 17 and level it. The position of the cofferdam base bed 17 should be as close to the shore as possible on the premise of meeting the requirements of the bridge cap foundation pit excavation surface 15 and the size requirements of the bagged earth weir body 2. The reinforced concrete tongue and groove pipe 4 is placed vertically (in order to avoid special prefabrication and other links, a universal standard drainage pipe is used) to form a reinforced concrete pipe retaining wall 1. A reasonable size is selected according to the design standard, and the plane position of the retaining wall center line 12 is at a distance from the bridge cap that meets the foundation pit construction requirements. When the length of the reinforced concrete tongue and groove pipe 4 is insufficient, multiple reinforced concrete tongue and groove pipes 4 are connected in series from top to bottom, and 8 steel pipes 5 with a diameter of 48 mm are evenly placed close to the inner wall of the reinforced concrete tongue and groove pipe 4. The length of the steel pipe 5 should meet the design requirements. Multiple sections of reinforced concrete tongue and groove pipes 4 are connected in series. 500 mm thick C30 underwater concrete 7 is poured into the bottom of the reinforced concrete tongue and groove pipe 4, and the crushed stone and block stone mixture 6 is backfilled to the top elevation. The pouring of underwater concrete 7 is conducive to enhancing the bonding effect between the bottom of the pipe and the base surface, improving the anti-sliding stability of the reinforced concrete pipe retaining wall 1, and at the same time, the eight steel pipes 5 on the inner wall of the pipe are fixed together with the backfilled sand and gravel 6, which is conducive to the overall bending strength of the reinforced concrete tongue and groove pipe 4. The reinforced concrete pipe retaining wall 1 constrains the bagged soil 2 behind the wall, so that the bagged soil pile 2 of a certain height can stand stably on the river slope 16, reducing the bagged soil pile volume and improving the stability of the underwater bagged soil body. A 30mm*30mm bamboo mesh 8 is placed vertically close to the inner side of the reinforced concrete pipe, and a 1.5mm PE anti-seepage membrane 9 is laid behind it and extended to the top of the foundation pit. A 300mm*400mm groove 11 is excavated, and the top of the 1.5mm PE anti-seepage membrane 9 is buried in the groove 11, and the groove 11 is backfilled with C20 plain concrete. Bags of soil 10 are stacked from the bottom of the pit to the design elevation 13 of the top of the weir behind the reinforced concrete groove pipe 4 as the main water-retaining anti-seepage weir body. The top width of the weir body is greater than 1m, and it is placed on the river slope 16 according to the 1:1 slope line 14. The bagged soil 10 is not allowed to be filled with garbage and corrosive materials.

[0030] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0031] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A gravity cofferdam, characterized in that: A foundation pit is provided on the river channel slope. The gravity cofferdam includes a reinforced concrete pipe-filled stone retaining wall arranged in front of the foundation pit. The reinforced concrete pipe-filled stone retaining wall includes a plurality of reinforced concrete pipes arranged side by side. The reinforced concrete pipes are placed vertically. A plurality of steel pipes are placed close to the inner wall of the reinforced concrete pipes. Underwater concrete is poured at the bottom of the reinforced concrete pipes, and sand and gravel mixture is backfilled inside to form the overall structure of the retaining wall. Bags of soil are stacked behind the reinforced concrete pipe-filled stone retaining wall to form a bagged soil weir body. The reinforced concrete pipe is formed by vertically splicing at least two reinforced concrete pipe sections. A bamboo mesh is vertically laid behind the reinforced concrete pipe to provide a flat interface for stacking bagged soil at the rear.

2. The gravity cofferdam according to claim 1, characterized in that: A PE anti-seepage membrane is laid in the foundation pit behind the bamboo mesh, and the end of the PE anti-seepage membrane is inserted into the groove on the upper side of the slope behind the foundation pit. The groove is backfilled with plain concrete, and bagged soil is stacked on the PE anti-seepage membrane, thereby forming a long anti-seepage body at the interface between the bagged soil and the original soil, lengthening the seepage path.

3. A construction method for a gravity cofferdam, characterized in that The method comprises the following steps: (1) Partially excavate the river bank slope, dig out the cofferdam bed and level it; (2) Installation of reinforced concrete pipe retaining wall: Arrange reinforced concrete pipe segments vertically on the leveled underwater base bed in an orderly manner, pour underwater concrete at the bottom of the reinforced concrete pipe segments, insert multiple steel pipes into the inner wall of the pipe before initial setting and fix them, backfill sand and gravel mixture to the top of the pipe segment after the concrete has finally set, backfill block stone and crushed stone mixture, insert the second reinforced concrete pipe segment to connect the height, and continue to backfill sand and gravel to the top of the pipe to form a reinforced concrete pipe retaining wall; (3) Laying bamboo mesh and anti-seepage membrane: Lay bamboo mesh behind the reinforced concrete pipe retaining wall, lay PE anti-seepage membrane in the pit formed along the back of the retaining wall and the slope excavation surface, insert the end of the anti-seepage membrane into the groove on the upper side of the slope behind the foundation pit, and backfill with plain concrete; (4) Stacking of bagged soil: Stack the bagged soil from the bottom of the pit upwards to the designed elevation.

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