Design and construction method for staged cofferdam plastic diaphragm wall

Abstract

The invention discloses a staged cofferdam plastic diaphragm wall design and construction method, a staged cofferdam comprises a first-stage cofferdam and a second-stage cofferdam, and the first-stage cofferdam is constructed one dry period ahead of time; the cofferdam in each stage is provided with a plastic diaphragm wall, the plastic diaphragm wall of the first-stage cofferdam needs to be subjected to flood control once, and the method comprises the steps of overall design of the plastic diaphragm wall of the cofferdam, design and construction of the plastic diaphragm wall of the first-stage cofferdam, overflow protection and closure of the plastic diaphragm wall of the first-stage cofferdam, and construction of the plastic diaphragm wall of the second-stage cofferdam. According to the staged design and construction method for the plastic diaphragm wall of the cofferdam, construction of the plastic diaphragm wall of the cofferdam is involved in advance before river closure, implementation of the plastic diaphragm wall of the cofferdam is completed in two dry periods, the construction time of the plastic diaphragm wall is prolonged, and the overall construction period of the cofferdam is better guaranteed. Construction of the cofferdam diaphragm wall is involved in advance, the construction period of the cofferdam diaphragm wall is prolonged, and equipment needed for construction of the cofferdam diaphragm wall is greatly reduced. And through effective protection measures, the flood fighting safety of the first-stage plastic diaphragm wall of the cofferdam is guaranteed.

Description

Technical Field

[0001] The invention relates to the fields of water conservancy and hydropower engineering and port and navigation engineering, and relates to a design and implementation technology of an anti-seepage wall in a cofferdam project, in particular to a design and construction method of a plastic anti-seepage wall of a staged cofferdam. Background Art

[0002] Water conservancy, hydropower, and port and shipping engineering projects often require the construction of temporary cofferdams to retain water while facilitating the construction of permanent structures. The design and construction of the cofferdam's anti-seepage structure are crucial. The safety and stability of the cofferdam's anti-seepage structure directly impacts the amount of seepage in the foundation pit and the safety of the slope. Any safety incidents involving the cofferdam or foundation pit slope can significantly impact project timelines and costs.

[0003] Most existing plans require that all cofferdam construction be completed within one dry season. The anti-seepage wall is constructed in two sequences within one dry season, requiring a large amount of equipment to be invested in at one time. The cofferdam implementation is highly cyclical; if one dry season is missed, it will be necessary to wait until the next dry season, which has a significant impact on the project schedule.

[0004] There is also a method of using a dry season cofferdam, that is, construction activities in the foundation pit are carried out after the flow in the flood season and drainage in the dry season. This plan greatly shortens the construction time of the foundation pit, which is not conducive to the construction period of the buildings in the foundation pit. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention discloses a phased design and construction method for a plastic anti-seepage wall for a cofferdam. This method employs a phased construction scheme for the plastic anti-seepage wall of the cofferdam. This method, taking into account the characteristics of cofferdam construction, enables the plastic anti-seepage wall to be constructed one dry season earlier, extending the construction period, further ensuring the safety of the cofferdam construction, and reducing equipment investment.

[0006] The present invention is achieved through the following technical solutions:

[0007] A design and construction method for a phased cofferdam and a plastic anti-seepage wall is characterized in that: the phased cofferdam includes a first-phase cofferdam and a second-phase cofferdam, the first-phase cofferdam is constructed one dry season in advance; each phase cofferdam is provided with a plastic anti-seepage wall, and the plastic anti-seepage wall of the first-phase cofferdam needs to be constructed once during the flood season, including:

[0008] Overall design of plastic anti-seepage wall of cofferdam:

[0009] (1) The plastic anti-seepage wall of the cofferdam is an integral part of the cofferdam. The design includes the overall design of the cofferdam and the design of the additional first-stage cofferdam. Based on the overall design of the plastic anti-seepage wall of the cofferdam, the design of the first-stage cofferdam plastic anti-seepage wall is added, and a flood season plan is designed for the plastic anti-seepage wall.

[0010] Design and construction of plastic anti-seepage wall of the first phase cofferdam:

[0011] (2) The plastic anti-seepage wall of the first-phase cofferdam is combined with the overall anti-seepage design of the cofferdam, and the construction elevation of the first-phase anti-seepage wall and the second-phase anti-seepage wall is the same;

[0012] (3) The plastic anti-seepage wall of the first-stage cofferdam is designed to control its scope, and the first-stage cofferdam does not occupy the main river channel area to reduce the river flow capacity;

[0013] (4) Control the first-phase cofferdam filling elevation to the plastic anti-seepage wall construction elevation. After the first-phase cofferdam filling is completed, build temporary facilities for the anti-seepage wall construction and complete the first-phase anti-seepage wall construction; use a total station to record the endpoints of the first-phase plastic anti-seepage wall construction;

[0014] Overcurrent protection of the plastic anti-seepage wall of the first phase cofferdam:

[0015] (5) Use stone blocks to protect the plastic anti-seepage wall of the first phase cofferdam. The stone block size for overflow protection is set according to the scouring conditions of each area;

[0016] (6) The protective blocks on the overflow protection plane are leveled by bulldozers, and the slope protection is filled by dumping. The slope protection dumping on the water flow axis meets the water flow state;

[0017] (7) During the flood season, the water level and flow of the river and the scouring of the protective blocks shall be monitored at any time. During the low water level of the flood season, compensation filling shall be carried out immediately;

[0018] Interception:

[0019] (8) The closure is carried out in a single-walled manner, with the first-stage cofferdam advancing towards the other side of the river bank to avoid excessive flow velocity at the dragon mouth, which may cause a large amount of erosion of the first-stage cofferdam and further erosion of the first-stage plastic anti-seepage wall that has been constructed;

[0020] Construction of plastic anti-seepage wall of the second phase cofferdam:

[0021] (9) After the cofferdam is closed, the cofferdam filling below the anti-seepage wall construction platform shall be completed according to the overall design plan of the cofferdam, and the filling shape shall be the same as the overall design of the cofferdam;

[0022] (10) Construct temporary facilities required for the construction of the second phase plastic anti-seepage wall and complete the construction of the second phase plastic anti-seepage wall;

[0023] (11) After the construction of the plastic anti-seepage wall is completed, the cofferdam continues to be filled upward to the design elevation. After the upper geomembrane anti-seepage body and the plastic anti-seepage wall are reliably connected, it is filled to the design elevation.

[0024] Furthermore, in the method (1), the axis lengths of the first-phase cofferdam and the plastic anti-seepage wall match the hydrological conditions of the river channel to meet the flow of the river channel during the flood season; the implementation area of ​​the first-phase plastic anti-seepage wall is a relatively shallow position of the riverbed, which does not occupy the main river channel.

[0025] Furthermore, the plastic anti-seepage wall is formed by impact drilling, the wall is protected by bentonite slurry, concrete is poured by vertical rising pipe method under mud, and joint pipes are used to connect the groove sections.

[0026] Furthermore, the ends of the first-phase plastic anti-seepage wall and the second-phase plastic anti-seepage wall are grooved with joint pipes to reserve joint positions; after the second-phase plastic anti-seepage wall is grooved, a steel brush is used to roughen the plastic anti-seepage wall at the joint position to ensure that the joint is tight.

[0027] Furthermore, the top elevation of the first-phase plastic anti-seepage wall is the same as that of the second-phase plastic anti-seepage wall. The connection between the plastic anti-seepage wall and the geomembrane is achieved by manually chiseling a cup-shaped opening on the top of the plastic anti-seepage wall, fixing the geomembrane at the bottom of the cup-shaped opening, and then pouring plastic concrete to fill it tightly.

[0028] The present invention adopts the phased implementation of the plastic anti-seepage wall of the cofferdam, which solves the current situation that all the construction of the plastic anti-seepage wall of the cofferdam must be completed in one dry season, thereby solving the problem of a large amount of equipment being invested in the construction of the plastic anti-seepage wall of the cofferdam at one time and difficulty in organizing resources, thereby achieving the purpose of significantly reducing costs; under the condition of limited resources, the phased implementation of the plastic anti-seepage wall of the cofferdam in advance can better guarantee the construction period.

[0029] Compared with existing technologies, this invention offers the following advantages: It allows for the construction of plastic anti-seepage walls on the cofferdam to be carried out before river diversion, allowing for completion of the cofferdam plastic anti-seepage wall over two dry seasons. This prolongs the construction period and ensures the overall cofferdam construction schedule. This early intervention in the cofferdam plastic anti-seepage wall construction significantly reduces the equipment required for construction. Effective protective measures ensure the safety of the first-phase cofferdam plastic anti-seepage wall during flood seasons. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Overall design plan of the cofferdam according to the embodiment of the present invention;

[0031] Figure 2 A longitudinal section view of the overall design of the cofferdam according to an embodiment of the present invention;

[0032] Figure 3 Cross-sectional view AA of the overall design of the cofferdam according to the embodiment of the present invention;

[0033] Figure 4 Schematic diagram of the connection between the geomembrane and the bank slope according to an embodiment of the present invention;

[0034] Figure 5 Schematic diagram of the connection between the geomembrane anti-seepage body and the plastic concrete anti-seepage wall according to an embodiment of the present invention;

[0035] Figure 6 Plan view of the first phase cofferdam according to the embodiment of the present invention;

[0036] Figure 7A longitudinal section of the plastic anti-seepage wall of the first phase cofferdam according to an embodiment of the present invention;

[0037] Figure 8 Cross-sectional view A'-A' of the plastic anti-seepage wall of the first phase cofferdam according to the embodiment of the present invention;

[0038] Figure 9 Schematic diagram of the sequential construction of the plastic anti-seepage wall of the first phase of the cofferdam according to the embodiment of the present invention;

[0039] Figure 10 Schematic diagram of the plan view of the overcurrent protection of the first phase cofferdam according to the embodiment of the present invention;

[0040] Figure 11 Cross-sectional view of the overcurrent protection of the first phase cofferdam according to the embodiment of the present invention;

[0041] Figure 12 A longitudinal cross-sectional view of the first phase of the cofferdam overcurrent protection according to an embodiment of the present invention;

[0042] Figure 13 Schematic diagram of the sequential construction of the plastic anti-seepage wall of the second phase cofferdam according to the embodiment of the present invention;

[0043] Figure 14 Schematic diagram of the layout of temporary facilities for the construction of the first phase of the anti-seepage wall according to an embodiment of the present invention.

[0044] Description of the marks in the figure:

[0045] 1: cofferdam axis; 2: river bank slope; 3: riverbed rock line; 4: riverbed line; 5: curtain grouting anti-seepage body; 6-1 and 6-2: plastic concrete anti-seepage body 1&2 phases; 7: geomembrane anti-seepage body; 8: capping concrete; 9: intercepting dike fill body; 10: fill body zone I; 11: fill body zone II; 12: block stone slope protection fill body; 13: guide trough; 14: plastic concrete connector; 15: bank slope concrete and rock connection anchor bar; 16: bank slope phase 1 concrete; 17: bank slope phase 2 concrete; 18: sand protection layer; 19: graded material buffer layer; 20: transition material layer.

[0046] I-1: First-phase plastic cut-off wall; I-1-1: First-phase plastic cut-off wall 1st sequence groove; I-1-2: First-phase plastic cut-off wall 2nd sequence groove; I-2: Riverbed line; I-3: Plastic cut-off wall guide groove; I-4: Riverbed rock line; I-5: Plastic cut-off wall rock entry line; I-6: Filling area downstream of cofferdam; I-7: Filling area upstream of cofferdam; I-8: Filling area in the middle of cofferdam.

[0047] I'-1: Plastic concrete anti-seepage wall; I'-2: Riverbed line; I'-3: Riverbed rock line; I'-4: Cofferdam filling body; I'-5-1~5: Phase I cofferdam overflow protection blocks.

[0048] II-1-1: Second-phase plastic cut-off wall 1st sequence groove; II-1-1: Second-phase plastic cut-off wall 2nd sequence groove.

[0049] I-9: sedimentation tank; I-10: bentonite slurry tank. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with specific embodiments. The specific embodiments are further explanations of the principles of the present invention and do not limit the present invention in any way. Technologies that are the same or similar to the present invention do not exceed the scope of protection of the present invention.

[0051] Combined with the attached drawings.

[0052] The design and construction method of the plastic anti-seepage wall of the phased cofferdam in this embodiment includes: firstly, during the first dry season, the plastic anti-seepage wall of the first phase cofferdam is implemented and the flood protection of the first phase cofferdam is completed; and during the second dry season, the plastic anti-seepage wall of the second phase cofferdam is implemented and filled to the top, including:

[0053] Implementation of plastic anti-seepage wall and safety protection of the first phase cofferdam:

[0054] (1) According to the design of the cofferdam as a whole and the plastic anti-seepage wall of the first-phase cofferdam, the construction content of the first-phase cofferdam was completed first. After the filling of the first-phase cofferdam was completed, the temporary construction required for the implementation of the plastic anti-seepage wall was completed first, including the mud pool, bentonite slurry pool, and guide trough; the first-phase cofferdam anti-seepage wall was implemented in two sequences according to the design axis length, with the first sequence trough length of 6.8m and the second sequence trough length of 4.8m. The trench was formed by an impact drill rig, and two impact drills controlled one first sequence trough section and one second sequence trough section in the main trough section (the trench depth was deeper).

[0055] (2) Use the parallel excavation method to first drill the main hole to a certain depth (generally 6 to 8 meters ahead of the auxiliary hole), and then construct the auxiliary hole. After the auxiliary hole is constructed to a depth of 6 to 8 meters, the small wall is constructed in parallel (the depth of the auxiliary hole is 3 to 5 meters ahead of the small wall). After the construction of the small wall is completed, the conditions for trenching are met.

[0056] (3) Based on the flow pattern of the river channel and the filling conditions of the first-stage cofferdam itself, the rock protection is divided into the top flat area of ​​the first-stage cofferdam and the upstream bank slope area as non-key protection areas; the main river scouring area and the upstream anti-scouring area are key protection areas. The top flat area I'-5-4 of the first-stage cofferdam and the upstream bank slope area I'-5-5 are non-key protection areas. The rock protection material particle size is 0-80cm, the content of rock particles smaller than 10cm is less than 10%, and the protection thickness is 2.5m.

[0057] The I'-5-2 area is the axis area of ​​the anti-seepage wall. This area is the core area of ​​the block stone protection. During the second phase of construction, it is necessary to impact drill a groove to connect the anti-seepage wall. If the particle size of the protection block is too large, it will affect the groove formation of the anti-seepage wall. Therefore, this area adopts the method of reducing the particle size of the protection block and increasing the thickness for protection. The particle size of the block stone protection material is 0-30cm, of which the content of block stones with a particle size of less than 10cm is not more than 10%, and the protection thickness is 5m.

[0058] The primary scour areas at the upstream pier I'-5-3 of the Phase I cofferdam and at I'-5-1 on the main channel side are designated as key protection areas. Because the protective fill thickness in the area around the cutoff wall axis I'-5-2 is 5 meters, to ensure smooth water flow and minimize scouring, the protective fill blocks at both the upstream pier I'-5-3 and the main channel side of the Phase I cofferdam are 5 meters thick. The particle size of the protective rock material ranges from 0 to 150 cm, with no more than 30% of the rock being less than 20 cm in diameter.

[0059] During the flood season, monitor the scouring of the first phase cofferdam and replenish stone protective materials in a timely manner.

[0060] Implementation of plastic anti-seepage wall of the second phase cofferdam:

[0061] (4) After the river is cut off, the cofferdam is filled as a whole to the construction elevation of the anti-seepage wall according to the design, and the lower anti-seepage wall is constructed according to the descriptions in (1) and (2). After the anti-seepage wall construction is completed, the cofferdam is continued to be filled upward to the design elevation, and the upper geomembrane anti-seepage body is implemented according to the filling progress.

[0062] The present invention primarily addresses the problems of tight construction schedules for plastic anti-seepage walls of cofferdams, requiring completion in a single dry season, requiring a large amount of one-time resource investment and high costs. The innovative phased implementation of the plastic anti-seepage wall increases the construction period of the wall; phased investment of resources for the plastic anti-seepage wall reduces the difficulty of organizing resources. The plastic anti-seepage wall is constructed in two dry seasons, adjusting the construction process from one phase and two sequences to two phases and two sequences. Construction equipment for the two dry seasons can be reused, significantly reducing the investment in impact drills and lowering equipment procurement costs.

[0063] The design of the plastic cutoff wall for the first-phase cofferdam was based on the overall cofferdam design and was determined by calculating the peak flood flow during the flood season. The flood season protection solution for the plastic cutoff wall was riprap protection, covering the upstream and downstream surfaces, the riverside surface, and the top plane of the first-phase cofferdam. The axis of the plastic cutoff wall on the riverside surface was the core protection area.

[0064] The construction elevation of the Phase I cofferdam's anti-seepage wall was the same as that of the Phase II cofferdam. The elevations of both phases were required to meet peak flood levels during the dry season. The temporary design for the Phase I cofferdam's anti-seepage wall included a sedimentation tank, a bentonite slurry tank, and a guide channel. The anti-seepage wall was constructed using impact drilling. The Phase I plastic anti-seepage wall was constructed in two stages. The endpoints of the Phase I plastic anti-seepage wall were recorded using a total station.

[0065] The core of the first-phase cofferdam protection is to prevent the flood season water flow from scouring the plastic anti-seepage wall. The top flat area and upstream slope area of ​​the first-phase cofferdam are non-key protection areas; the main river channel scouring area and upstream anti-scouring area are key protection areas, and block stones are used for protection.

[0066] The top flat area of ​​the first-phase cofferdam must be protected with good flatness to ensure it does not affect the flow pattern. The sloped fill area adjacent to the main river channel is designed to control fill thickness and smoothness. A total station is used to monitor fill height and thickness.

[0067] During the flood season, sufficient protective materials should be prepared for the first phase cofferdam anti-seepage wall. After the flood peak, the scouring of the protective blocks of the first phase cofferdam should be monitored with the help of a total station, and compensatory filling of blocks of stones should be carried out depending on the scouring situation.

[0068] Temporary facilities required for the construction of the second-phase cofferdam anti-seepage wall, such as the sedimentation tank and bentonite slurry tank, can be rebuilt in conjunction with the facilities built during the construction of the first-phase cofferdam plastic anti-seepage wall.

[0069] The connection between geomembrane and plastic anti-seepage wall is handled by artificially opening a cup-shaped groove on the top of the plastic anti-seepage wall, pressing the geomembrane into it, and then backfilling with plastic concrete to connect the two different anti-seepage bodies.

[0070] The following describes the implementation plan of the plastic anti-seepage wall of the cofferdam in stages using a sand dam cofferdam as an example:

[0071] The plastic anti-seepage walls of the temporary cofferdams upstream and downstream of a certain sand dam were implemented in phases. The axis length of the upstream cofferdam is 204m, and the axis length of the downstream cofferdam is 385m.

[0072] If the dam cofferdam construction were completed within a single dry season, the river would have to be shut off and the cutoff wall construction platform completed by late November. All cofferdam construction would have to be completed by the end of April of the following year (before the flood season), resulting in a construction period of approximately five months. The main channel section of the plastic cutoff wall of the cofferdam could only be constructed in two phases: Phase I channel construction would take two months, and Phase II channel construction would take one month. This would require approximately 48 percussion drills. After the cutoff wall construction was completed, only two months remained for the upper cofferdam fill and geomembrane construction, creating a tight schedule and tying up significant earthwork equipment and resources.

[0073] By adopting a phased implementation plan for the plastic cutoff walls of the cofferdams, approximately 50% of the plastic cutoff walls on the right bank of the upstream and downstream cofferdams were completed ahead of schedule during the first dry season. The remaining plastic cutoff walls and the second-phase cofferdam were completed during the second dry season. The first-phase cofferdams safely survived the flood season, and 24 impact drills were ultimately deployed, reused over two dry seasons. No accidents occurred during the construction process.

Claims

1. A design and construction method for a staged cofferdam plastic cut-off wall, characterized by: The phased cofferdam includes the first phase cofferdam and the second phase cofferdam. The first phase cofferdam is constructed one dry season in advance. Each phase cofferdam is equipped with a plastic anti-seepage wall. The plastic anti-seepage wall of the first phase cofferdam needs to be constructed once during the flood season, including: Overall design of plastic anti-seepage wall of cofferdam: (1) The plastic anti-seepage wall of the cofferdam is an integral part of the cofferdam. The design includes the overall design of the cofferdam and the design of the additional first-stage cofferdam. Based on the overall design of the plastic anti-seepage wall of the cofferdam, the design of the first-stage cofferdam plastic anti-seepage wall is added, and a flood season plan is designed for the plastic anti-seepage wall. Design and construction of plastic anti-seepage wall of the first phase cofferdam: (2) The plastic anti-seepage wall of the first-phase cofferdam is combined with the overall anti-seepage design of the cofferdam, and the construction elevation of the first-phase anti-seepage wall and the second-phase anti-seepage wall is the same; (3) The plastic anti-seepage wall of the first-stage cofferdam is designed to control its scope, and the first-stage cofferdam does not occupy the main river channel area to reduce the river flow capacity; (4) Control the first-phase cofferdam filling elevation to the plastic anti-seepage wall construction elevation. After the first-phase cofferdam filling is completed, build temporary facilities for the anti-seepage wall construction and complete the first-phase anti-seepage wall construction; use a total station to record the endpoints of the first-phase plastic anti-seepage wall construction; Overcurrent protection of the plastic anti-seepage wall of the first phase cofferdam: (5) Use stone blocks to protect the plastic anti-seepage wall of the first phase cofferdam. The stone block size for overflow protection is set according to the scouring conditions of each area; (6) The protective blocks on the overflow protection plane are leveled by bulldozers, and the slope protection is filled by dumping. The slope protection dumping on the water flow axis meets the water flow state; (7) During the flood season, the water level and flow of the river and the scouring of the protective blocks shall be monitored at any time. During the low water level of the flood season, compensation filling shall be carried out immediately; Interception: (8) The closure is carried out in a single-walled manner, with the first-stage cofferdam advancing towards the other side of the river bank to avoid excessive flow velocity at the dragon mouth, which may cause a large amount of erosion of the first-stage cofferdam and further erosion of the first-stage plastic anti-seepage wall that has been constructed; Construction of plastic anti-seepage wall of the second phase cofferdam: (9) After the cofferdam is closed, the cofferdam filling below the anti-seepage wall construction platform shall be completed according to the overall design plan of the cofferdam, and the filling shape shall be the same as the overall design of the cofferdam; (10) Construct temporary facilities required for the construction of the second phase plastic anti-seepage wall and complete the construction of the second phase plastic anti-seepage wall; (11) After the construction of the plastic anti-seepage wall is completed, the cofferdam continues to be filled upward to the design elevation. After the upper geomembrane anti-seepage body and the plastic anti-seepage wall are reliably connected, it is filled to the design elevation.

2. The design and construction method of the staged cofferdam plastic cut-off wall according to claim 1 is characterized in that: In the method (1), the axis lengths of the first-stage cofferdam and the plastic anti-seepage wall match the hydrological conditions of the river channel to meet the flow of the river channel during the flood season; the implementation area of ​​the first-stage plastic anti-seepage wall is a relatively shallow position in the riverbed, and does not occupy the main river channel.

3. The design and construction method of the staged cofferdam plastic anti-seepage wall according to claim 1 is characterized in that: The plastic anti-seepage wall is formed by impact drilling, the wall is protected by bentonite slurry, concrete is poured by vertical rising pipe method under mud, and joint pipes are used to connect the groove sections.

4. The design and construction method of the staged cofferdam plastic anti-seepage wall according to claim 1 is characterized in that: The ends of the first-phase plastic anti-seepage wall and the second-phase plastic anti-seepage wall are grooved with joint pipes to reserve joint positions; after the second-phase plastic anti-seepage wall is grooved, a steel brush is used to roughen the plastic anti-seepage wall at the joint position to ensure that the joint is tight.

5. The design and construction method of the staged cofferdam plastic anti-seepage wall according to claim 1 is characterized in that: The top elevation of the first-phase plastic anti-seepage wall is the same as that of the second-phase plastic anti-seepage wall. The connection between the plastic anti-seepage wall and the geomembrane is achieved by manually chiseling a cup-shaped opening on the top of the plastic anti-seepage wall, fixing the geomembrane at the bottom of the cup-shaped opening, and then pouring plastic concrete to fill it tightly.

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