A method for designing and constructing a phased cofferdam plastic seepage barrier

Abstract

This invention discloses a phased cofferdam plastic cutoff wall design and construction method. The phased cofferdam includes a first-phase cofferdam and a second-phase cofferdam, with the first-phase cofferdam constructed one dry season in advance. Each phase of the cofferdam is equipped with a plastic cutoff wall. The first-phase cofferdam plastic cutoff wall needs to withstand one flood season. The method includes: overall design of the plastic cutoff wall, design and construction of the first-phase cofferdam plastic cutoff wall, flow protection of the first-phase cofferdam plastic cutoff wall, river closure, and construction of the second-phase cofferdam plastic cutoff wall. This phased cofferdam plastic cutoff wall design and construction method intervenes in the construction of the plastic cutoff wall before river closure, completing the plastic cutoff wall implementation in two dry seasons, extending the construction time of the plastic cutoff wall, and ensuring a more guaranteed overall construction period for the cofferdam. Early intervention in the construction of the plastic cutoff wall extends the construction period and significantly reduces the equipment required for cofferdam plastic cutoff wall construction. Through effective protective measures, the safety of the first-phase cofferdam plastic cutoff wall during the flood season is guaranteed.

Description

Technical Field

[0001] This invention relates to the fields of water conservancy and hydropower engineering and port and waterway engineering, and to the design and implementation technology of anti-seepage walls in cofferdam engineering, specifically a design and construction method for a phased cofferdam plastic anti-seepage wall. Background Technology

[0002] In the construction of water conservancy and hydropower projects and port and waterway engineering, it is often necessary to build temporary cofferdams to block water for the construction of permanent structures. The design and construction of the cofferdam's seepage prevention body is crucial. The safety and stability of the cofferdam's seepage prevention body directly affects the seepage volume of the foundation pit and the safety of the slope. Any safety accidents involving the cofferdam or the foundation pit slope will cause significant losses to the project schedule and costs.

[0003] Existing solutions typically involve completing all cofferdam construction for the entire year within a single dry season, with the anti-seepage wall constructed in two phases within the same dry season, requiring a large initial investment of equipment. Furthermore, the cofferdam implementation is highly cyclical; missing one dry season necessitates waiting until the next, significantly impacting the project's schedule.

[0004] Another approach is to use a dry season cofferdam, where the water flows through during the flood season and is drained during the dry season before construction activities take place inside the foundation pit. This approach significantly shortens the construction time of the foundation pit but is detrimental to the construction period of the structures inside the foundation pit. Summary of the Invention

[0005] This invention discloses a phased design and construction method for a plastic cutoff wall for cofferdams, addressing the shortcomings of existing technologies. The invention designs a phased construction scheme using a plastic cutoff wall for cofferdams. Targeting the characteristics of cofferdam construction, this invention allows for the construction of the plastic cutoff wall to be advanced by one dry season, extending the construction cycle and further ensuring the safety of the cofferdam construction while reducing equipment investment.

[0006] This invention is achieved through the following technical solution:

[0007] A method for designing and constructing a phased cofferdam with a plastic cutoff wall, characterized in that: the phased cofferdam includes a first-phase cofferdam and a second-phase cofferdam, with the first-phase cofferdam constructed one dry season in advance; each phase of the cofferdam is equipped with a plastic cutoff wall, and the first-phase cofferdam's plastic cutoff wall needs to withstand one flood season, including:

[0008] Overall design of cofferdam plastic seepage barrier:

[0009] (1) The plastic seepage barrier wall of the cofferdam is a component of the cofferdam. The design includes the overall design of the cofferdam and the design of the additional first-phase cofferdam. The plastic seepage barrier wall of the cofferdam is designed on the basis of its overall design, and the design of its flood season flood control plan is also designed.

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

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

[0012] (3) The design of the plastic anti-seepage wall of the first phase cofferdam controls its range, and the first phase cofferdam does not occupy the main river channel area to reduce the river channel flow capacity.

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

[0014] Flow protection of the first-phase cofferdam plastic seepage barrier:

[0015] (5) Use riprap to protect the plastic seepage barrier wall of the first phase cofferdam. The riprap particle size is set according to the scouring situation of each area for the flow protection.

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

[0017] (7) During the flood season, monitor the river level and flow rate and monitor the scouring of the protective blocks at any time. During the low water level period of the flood season, carry out compensation filling immediately.

[0018] Interception:

[0019] (8) The diversion is carried out by a single-pronged approach, with the first-phase cofferdam advancing towards the other side of the riverbank to avoid excessive flow velocity at the sluice gate, which would cause a large amount of scouring of the first-phase cofferdam and then scouring of the already constructed first-phase plastic anti-seepage wall.

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

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

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

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

[0024] Furthermore, in the method (1), the axial length of the first-phase cofferdam and the plastic anti-seepage wall is matched with the river hydrological conditions to meet the river flow during the flood season; the first-phase plastic anti-seepage wall is implemented in a shallow riverbed area and does not encroach on the main river channel.

[0025] Furthermore, the plastic seepage barrier wall is constructed by using an impact drill to form trenches, bentonite slurry for wall protection, and concrete pouring via a vertical tremie pipe method under the slurry. Connecting pipes are used to link the trench sections.

[0026] Furthermore, the ends of the first-phase plastic cutoff wall and the second-phase plastic cutoff wall are grooved using joint pipes, with reserved joint positions; after the second-phase plastic cutoff wall is grooved, the joint position of the plastic cutoff wall is roughened with a steel brush to ensure a tight joint.

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

[0028] This invention adopts a phased implementation of the plastic seepage barrier wall, which solves the problem that the construction of the plastic seepage barrier wall must be completed in one dry season. This solves the problem of large equipment investment and difficulty in resource organization during the construction of the plastic seepage barrier wall, thus achieving the goal of significantly reducing costs. Under the condition of limited resources, the phased implementation of the plastic seepage barrier wall provides a better guarantee for the project schedule.

[0029] Compared with existing technologies, this invention has the following advantages: By intervening in the construction of the cofferdam's plastic seepage barrier before river closure, and completing the construction in two dry seasons, the construction time of the plastic seepage barrier is extended, thus ensuring a more secure overall construction period for the cofferdam. Early intervention in the cofferdam's seepage barrier construction extends the construction period and significantly reduces the equipment required for construction. Effective protective measures ensure the safety of the first-phase cofferdam's plastic seepage barrier during the flood season. Attached Figure Description

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

[0031] Figure 2 Longitudinal section view of the overall design of the cofferdam in this embodiment of the invention;

[0032] Figure 3 Cross-sectional view AA of the overall design of the cofferdam in this invention embodiment;

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

[0034] Figure 5 A schematic diagram illustrating the connection between the geomembrane seepage barrier and the plastic concrete seepage barrier wall in an embodiment of the present invention;

[0035] Figure 6 Plan view of the cofferdam in the first phase of this invention;

[0036] Figure 7Longitudinal section view of the plastic seepage-proof wall of the cofferdam in the first phase of this invention;

[0037] Figure 8 Cross-sectional view A'-A' of the plastic seepage barrier wall of the first phase of the present invention;

[0038] Figure 9 A schematic diagram of the sequential construction of the plastic seepage-proof wall of the cofferdam in the first phase of this invention;

[0039] Figure 10 Schematic diagram of the flow protection plan of the cofferdam in the first phase of this invention;

[0040] Figure 11 Cross-sectional view of the cofferdam for overflow protection in the first phase of this invention;

[0041] Figure 12 Longitudinal cross-section of the cofferdam for flow protection in the first phase of this invention;

[0042] Figure 13 Schematic diagram of the phased construction of the plastic seepage prevention wall of the cofferdam in embodiment two of the present invention;

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

[0044] Explanation of markings in the diagram:

[0045] 1: Cofferdam axis; 2: Riverbank slope; 3: Riverbed rock line; 4: Riverbed line; 5: Curtain grouting seepage barrier; 6-1 and 6-2: Plastic concrete seepage barrier phases 1 & 2; 7: Geomembrane seepage barrier; 8: Cap concrete; 9: Interception dike fill; 10: Fill area I; 11: Fill area II; 12: Rubble slope protection fill; 13: Guide channel; 14: Plastic concrete connector; 15: Anchor bar connecting the bank slope concrete and rock; 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: Phase I plastic cutoff wall; I-1-1: Phase I plastic cutoff wall, first sequence trench; I-1-2: Phase I plastic cutoff wall, second sequence trench; I-2: Riverbed line; I-3: Plastic cutoff wall guide trench; I-4: Riverbed rock line; I-5: Plastic cutoff wall rock ingress line; I-6: Downstream filling area of ​​the cofferdam; I-7: Upstream filling area of ​​the cofferdam; I-8: Middle filling area of ​​the cofferdam.

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

[0048] II-1-1: Phase II plastic cutoff wall, first trench; II-1-1: Phase II plastic cutoff wall, second trench.

[0049] I-9: Sedimentation tank; I-10: Bentonite slurry tank. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments. These specific embodiments are further explanations of the principles of the present invention and are not intended to limit the present invention in any way. Any technology that is the same as or similar to the present invention does not exceed the scope of protection of the present invention.

[0051] Refer to the attached diagram.

[0052] This embodiment describes a phased cofferdam plastic cutoff wall design and construction method. During the first dry season, the first-phase cofferdam plastic cutoff wall is constructed and flood protection is completed. During the second dry season, the second-phase cofferdam plastic cutoff wall is constructed and filled to its top, including:

[0053] Implementation of Phase I Cofferdam Plastic Cutoff Wall and Safety Protection:

[0054] (1) Based on the overall design of the cofferdam and the plastic cutoff wall of the first phase cofferdam, the construction of the first phase cofferdam was completed first. After the first phase cofferdam was filled, the temporary buildings required for the implementation of the plastic cutoff wall were arranged first, including mud pits, bentonite slurry pits, and guide trenches. The first phase cofferdam cutoff wall was implemented in two sequences according to the design axis length, with the first sequence trench being 6.8m long and the second sequence trench being 4.8m long. Impact drilling rigs were used for trenching, with two impact drills controlling one first sequence trench section and one second sequence trench section in the main trench section (which is deeper).

[0055] (2) The parallel tunneling method is adopted to first drill the main hole to a certain depth (generally leading the secondary hole by 6 to 8 m), and then construct the secondary hole. After the secondary hole is constructed to a depth of 6 to 8 m, the small wall is constructed in parallel (the depth of the secondary hole leads the small wall by 3 to 5 m). After the small wall is constructed, the conditions for trenching are met.

[0056] (3) Based on the river flow pattern and the filling conditions of the first-phase cofferdam itself, the riprap protection is divided into non-key protection areas: the top plane area of ​​the first-phase cofferdam and the upstream bank slope area; and key protection areas: the scouring area of ​​the main river channel and the upstream erosion-resistant area. The top plane I'-5-4 and the upstream bank slope I'-5-5 of the first-phase cofferdam are non-key protection areas. The particle size of the riprap protection material is 0-80cm, the content of riprap with a particle size of less than 10cm is less than 10%, and the protection thickness is 2.5m.

[0057] Zone I'-5-2 is the axis area of ​​the cutoff wall, which is the core area of ​​the riprap protection. During the second phase of construction, it is necessary to use impact drilling to create trenches to connect the cutoff wall. If the particle size of the protective blocks is too large, it will affect the trenching of the cutoff wall. Therefore, this area adopts the method of reducing the particle size of the protective blocks and increasing the thickness for protection. The particle size of the protective block material is 0-30cm, of which the content of blocks with a particle size of less than 10cm is no more than 10%, and the protection thickness is 5m.

[0058] The upstream pier I'-5-3 and the side adjacent to the main river channel I'-5-1 of the first-phase cofferdam are the main scour zones and require key protection. Since the protective thickness in the area where the anti-seepage wall axis I'-5-2 is located is 5m, to ensure smooth water flow and reduce scouring in this area, the thickness of the protective blocks at the upstream pier I'-5-3 and the side adjacent to the main river channel I'-5-1 of the first-phase cofferdam is also 5m. The particle size of the riprap protective material is 0–150cm, with the content of riprap smaller than 20cm not exceeding 30%.

[0059] During the flood season, monitor the scouring of the first-phase cofferdam and replenish the protective material with riprap in a timely manner.

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

[0061] (4) After the river is dammed, the cofferdam is filled up to the construction elevation of the anti-seepage wall according to the design. The lower anti-seepage wall is constructed as described in (1) and (2). After the anti-seepage wall is completed, the cofferdam is filled up to the design elevation. The upper geomembrane anti-seepage body is implemented according to the filling progress.

[0062] This invention primarily addresses the problem of tight construction schedules for cofferdam plastic cutoff walls, requiring large-scale resource and cost investments to complete within a single dry season. It creatively employs a phased approach to the plastic cutoff wall construction, extending the construction period and reducing resource organization difficulties. By constructing the plastic cutoff wall over two dry seasons, the process is adjusted from a one-phase, two-sequence method to a two-phase, two-sequence method. Construction equipment can be reused between the two dry seasons, significantly reducing the need for impact drills and lowering equipment procurement costs.

[0063] The design of the first-phase cofferdam plastic cutoff wall is based on the overall cofferdam design, with its implementation scope broken down. The implementation scope of the first-phase cofferdam plastic cutoff wall is determined by calculation based on the peak flood flow during the flood season. The flood season protection scheme for the first-phase cofferdam plastic cutoff wall is riprap protection, and its protected surfaces include the upstream and downstream faces of the first-phase cofferdam, the river-facing face, and the top plane. Among them, the axial area of ​​the plastic cutoff wall on the river-facing face is the core of the protection.

[0064] The construction elevation of the first-phase cofferdam cutoff wall is the same as that of the second-phase cofferdam cutoff wall. The construction elevations of both phases must meet the requirements of the dry season flood peak during their construction. The temporary design for the first-phase cofferdam cutoff wall construction includes a sedimentation tank, a bentonite slurry tank, and a guide trench. The cutoff wall construction uses impact drilling for trenching. The first-phase plastic cutoff wall construction is carried out in two sequences. The endpoint positions of the first-phase plastic cutoff wall are recorded using a total station.

[0065] The core of the first-phase cofferdam protection is to prevent the plastic anti-seepage wall from being eroded by the floodwaters during the flood season. The top plane area and the upstream bank slope area of ​​the first-phase cofferdam are non-key protection areas; the scouring area of ​​the main river channel and the upstream erosion-resistant area are key protection areas, and their protection is carried out by riprap.

[0066] The top planar area of ​​the first-phase cofferdam requires good flatness and should not affect the flow pattern. For the sloping fill area, the thickness and smoothness of the fill in the area adjacent to the main river channel are controlled using a total station. The total station records the fill elevation and thickness.

[0067] During the flood season, sufficient protective material sources should be prepared for the first-phase cofferdam seepage prevention wall. After the flood peak, the erosion of the protective riprap of the first-phase cofferdam should be monitored with a total station, and riprap should be filled in to compensate for the erosion.

[0068] Temporary facilities required for the second-phase cofferdam seepage prevention wall construction, such as sedimentation tanks and bentonite slurry tanks, can be modified based on the facilities built during the first-phase cofferdam plastic seepage prevention wall construction.

[0069] The connection between the geomembrane and the plastic cutoff wall is achieved by manually cutting a cup-shaped groove on the top of the plastic cutoff wall, pressing in the geomembrane, and then backfilling with plastic concrete to connect the two different cutoff materials.

[0070] The following uses a cofferdam of a sand dam as an example to illustrate the phased implementation scheme of the plastic seepage prevention wall of the present invention:

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

[0072] If the dam cofferdam is to be constructed within one dry season, the river needs to be closed by late November, and the anti-seepage wall construction platform needs to be filled in. All cofferdam construction must be completed by the end of April of the following year (before the flood season), with a construction period of approximately 5 months. The main trench section of the plastic anti-seepage wall can only be planned for two-stage construction, with the first stage trench construction period of 2 months and the second stage trench construction period of 1 month, requiring approximately 48 impact drilling rigs. After the anti-seepage wall construction is completed, there are only 2 months left for the construction of the upper cofferdam filling and geomembrane, resulting in a tight schedule and significant consumption of earthwork and equipment resources.

[0073] After adopting the phased implementation plan for the plastic cutoff wall of the cofferdam, approximately 50% of the plastic cutoff wall construction on the right bank of the upstream and downstream cofferdams was completed ahead of schedule during the first dry season. The remaining plastic cutoff wall and the second-phase cofferdam construction were completed during the second dry season. The first-phase cofferdam safely weathered one flood season, ultimately requiring 24 impact drills, which were reused during both dry seasons. No safety accidents occurred during construction.

Claims

1. A method for designing and constructing a phased cofferdam plastic seepage barrier, characterized in that: The phased cofferdam system includes a first-phase cofferdam and a second-phase cofferdam. The first-phase cofferdam is constructed one dry season in advance. Each phase of the cofferdam is equipped with a plastic cutoff wall. The plastic cutoff wall of the first-phase cofferdam needs to withstand one flood season, including: Overall design of cofferdam plastic seepage barrier: (1) The plastic seepage barrier wall of the cofferdam is a component of the cofferdam. The design includes the overall design of the cofferdam and the design of the additional first-phase cofferdam. The plastic seepage barrier wall of the cofferdam is based on its overall design, and the design of the first-phase plastic seepage barrier wall of the cofferdam is added, and its flood season flood control plan is designed. Design and construction of the first-phase cofferdam plastic seepage barrier: (2) The first phase of the cofferdam plastic anti-seepage wall is combined with the overall design scheme of the cofferdam anti-seepage, and the construction elevation of the first phase anti-seepage wall and the second phase anti-seepage wall is the same. (3) The design of the plastic anti-seepage wall of the first phase cofferdam controls its range. The first phase cofferdam does not occupy the main river channel area and does not reduce the river channel flow capacity. (4) Control the filling elevation of the first phase cofferdam to be the construction elevation of the plastic anti-seepage wall. After the first phase cofferdam is filled, construct temporary facilities for the construction of the anti-seepage wall and complete the construction of the first phase anti-seepage wall. Use a total station to record the endpoints of the construction of the first phase plastic anti-seepage wall. Flow protection of the first-phase cofferdam plastic seepage barrier: (5) Use riprap to protect the plastic seepage barrier wall of the first phase cofferdam. The riprap particle size is set according to the scouring situation of each area for the flow protection. (6) The protective blocks on the flow 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 pattern. (7) During the flood season, monitor the river level and flow rate and monitor the scouring of the protective blocks at any time. During the low water level period of the flood season, carry out compensation filling immediately. Interception: (8) The diversion is carried out by a single-pronged approach, with the first-phase cofferdam advancing towards the other side of the riverbank to avoid excessive flow velocity at the sluice gate causing a large amount of scouring of the first-phase cofferdam, which in turn scours the already constructed first-phase plastic anti-seepage wall. Construction of the second-phase cofferdam plastic seepage prevention wall: (9) After the cofferdam is closed, the cofferdam filling below the anti-seepage wall construction platform shall be completed in accordance with the overall design plan of the cofferdam, and the filling body shape shall be the same as the overall design of the cofferdam. (10) Construct temporary facilities required for the second phase of plastic seepage barrier construction and complete the second phase of plastic seepage barrier construction; (11) After the construction of the plastic seepage barrier is completed, the cofferdam continues to be filled upward to the design elevation. After the upper geomembrane seepage barrier is reliably connected to the plastic seepage barrier, it is filled to the design elevation.

2. The design and construction method of the phased cofferdam plastic seepage barrier according to claim 1, characterized in that: In the method (1), the length of the first-phase cofferdam and the plastic anti-seepage wall axis matches the river hydrological conditions to meet the river flow during the flood season; the first-phase plastic anti-seepage wall is implemented in a shallow riverbed area and does not occupy the main river channel.

3. The design and construction method of the phased cofferdam plastic seepage barrier according to claim 1, characterized in that: The plastic seepage barrier wall is constructed by using an impact drill to form trenches, bentonite slurry for wall protection, and concrete pouring using a vertical tremie pipe method with mud slurry. Connecting pipes are used to link the trench sections.

4. The design and construction method of the phased cofferdam plastic seepage barrier according to claim 1, characterized in that: The ends of the first-phase plastic cutoff wall and the second-phase plastic cutoff wall are grooved using joint pipes, with reserved joint positions. After the second-phase plastic cutoff wall is grooved, the plastic cutoff wall at the joint position is roughened with a steel brush to ensure a tight joint.

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

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