Environmentally friendly earth-rock cofferdam structure and construction technology in a first-level drinking water source protection area

Abstract

The present invention discloses an environmentally friendly earth-rock cofferdam structure for a first-level drinking water source protection zone, which is characterized in that: the environmentally friendly earth-rock cofferdam structure comprises a bottom clay layer (1), a sand and gravel layer (3) and a crushed stone layer (2) are laid in sequence from bottom to top, a river bank weir is arranged at the junction with the water source, the river bank weir comprises a reinforced gabion (6) at the base, and a clay layer (1), a crushed stone layer (2), a sand and gravel layer (3), a sand layer (4) and a filter geotextile layer (5) are arranged in sequence from inside to outside along the river bank.

Description

Technical Field

[0001] The invention relates to an environmentally friendly earth-rock cofferdam structure and a construction process for a first-level drinking water source protection zone. Background Art

[0002] Green and environmentally friendly construction is receiving increasing attention, especially within drinking water source protection areas, where water pollution is a serious health threat to nearby residents. Preventing water pollution from construction activities in drinking water source protection areas is a research topic of far-reaching significance. China Railway No. 5 Engineering Group Co., Ltd. pioneered and implemented an environmentally friendly earth-rock cofferdam construction method during the Qiujiayan Road Reconstruction Project in the Heilongtan Ecological Tourism Resort in Sichuan Province, achieving a breakthrough and achieving the project's goal of zero pollution to drinking water source protection areas.

[0003] The Qiujiayan Bridge, part of the Qiujiayan Road Reconstruction Project, spans the Qiujiayan Weir Pond. All seven piers are located within the pond area, while the abutments and roadbed are within the catchment area. The Qiujiayan Weir Pond is part of the Heilongtan Reservoir, a national first-class water source protection zone. Preventing water pollution from bridge foundation construction was a top priority for the project. Through meticulous research and repeated testing before construction, the cofferdam was ultimately constructed using a multi-layered structure of crushed stone + gravel + sand + anti-filtration geotextile. This effectively filtered and purified water seeping from the construction area. During construction, multiple tests of the water outside the cofferdam confirmed that it met the first-class drinking water source quality standards, effectively resolving the water pollution issues associated with construction activities within the drinking water source protection zone. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an environmentally friendly earth-rock cofferdam structure and construction technology for a first-level drinking water source protection area, thereby solving the water pollution problem caused by construction activities in the drinking water source protection area.

[0005] The technical solution of the present invention is: an environmentally friendly earth-rock cofferdam structure in a first-level drinking water source protection area, wherein the environmentally friendly earth-rock cofferdam structure comprises a bottom clay layer, on which a sand and gravel layer and a crushed stone layer are laid in sequence from bottom to top, and a river bank weir is set at the connection with the water source, wherein the river bank weir comprises a reinforced gabion at the base layer, and a clay layer, a crushed stone layer, a sand and gravel layer, a sand layer and a filter geotextile layer are arranged in sequence from the inside to the outside along the river bank.

[0006] The sand, crushed stone and gravel are packed in geotextile bags and stacked.

[0007] The clay is packed in woven bags and stacked. A drainage ditch is also provided, which is arranged on one side close to the weir, and both ends are connected to the six-stage sedimentation tank.

[0008] The construction process of the environmentally friendly earth-rock cofferdam structure in the first-level drinking water source protection area includes the following steps: (1) cofferdam and water source isolation measures: when constructing the cofferdam on the river bank, first construct isolation measures to isolate the construction range from the water source, then carry out cofferdam filling construction, remove river mud, and then manually excavate the weir foundation pit. After the foundation pit excavation is completed, the weir reinforcement stone cage foundation is first constructed, and anti-filtration geotextile is laid on the bottom. Then, geotextile bags filled with permeable materials are stacked on the geotextile. After the foundation pit is stacked, the stacking width is calculated according to the measured elevation and the slope of 1:0.75. Then, woven bags filled with clay are stacked on the side close to the construction range, and then crushed stone layer, gravel layer, sand layer and anti-filtration layer are stacked. After the geotextile layer and the weir bank are stacked to the design elevation, the cofferdam filling construction is carried out; (2) After the cofferdam isolation measures are completed, the silt in the cofferdam is cleaned and clay filling is carried out. The filling materials in the construction range are selected from bottom to top, including clay, sand and gravel and graded crushed stone. The clay filling adopts layered filling and layered compaction technology. During the filling process, the compaction degree is controlled to ensure the filling quality while also playing the role of a waterproof layer; at the same time, a 2% cross slope is set during the filling process and a temporary drainage ditch is set to drain rainwater to the sixth-level sedimentation tank; the clay surface layer is filled with sand and gravel and graded crushed stone; a drainage ditch is set on the side close to the weir bank. The drainage ditch is built with 24 bricks and a cover plate is set on the top of the drainage ditch. The cover plate is a rainwater grate.

[0009] The beneficial effects of the present invention are as follows: (1) The materials are simple to obtain, and crushed stone, gravel, sand, and filter geotextile are all commonly used materials in daily construction and production;

[0010] (2) Low material cost, easy construction, simple layered paving is sufficient, saving construction time and cost;

[0011] (3) The environmental protection effect is obvious. During the construction period, the water quality around the cofferdam was tested and found to meet the first-class drinking water source water quality standards;

[0012] (4) All materials are environmentally friendly and will not cause secondary pollution to the drinking water source protection area when the cofferdam is dismantled. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a cross-section diagram of the river bank weir;

[0014] Figure 2 It is the plan of the rainwater collection system;

[0015] Figure 3 This is the cross-section of the cofferdam;

[0016] Figure 4 This is the process flow chart of cofferdam construction. DETAILED DESCRIPTION

[0017] This environmentally friendly earth-rock cofferdam structure for a primary drinking water source protection area consists of a bottom clay layer 1, followed by a sand and gravel layer 3 and a crushed stone layer 2, laid in ascending order. A riverbank weir is located at the water source. The weir comprises a base layer of reinforced gabions 6, followed by a clay layer 1, a crushed stone layer 2, a sand and gravel layer 3, a sand layer 4, and a filter geotextile layer 5, laid out along the riverbank. The sand, crushed stone, and sand and gravel are bagged in geotextile bags; the clay is bagged in woven bags. A drainage ditch 7 is also included, located near the weir, with both ends connected to the sixth-stage sedimentation tank.

[0018] The construction process of the environmentally friendly earth-rock cofferdam structure in the first-level drinking water source protection area includes the following steps: (1) cofferdam and water source isolation measures: when constructing the cofferdam on the river bank, first construct isolation measures to isolate the construction range from the water source, then carry out cofferdam filling construction, remove river mud, and then manually excavate the weir foundation pit. After the foundation pit excavation is completed, first construct the weir reinforcement stone cage foundation, lay the anti-filtration geotextile on the bottom, and then stack geotextiles filled with permeable materials on the geotextile. After the foundation pit is stacked, the stacking width is calculated according to the measured elevation and the slope of 1:0.75, and then stack woven bags filled with clay on the side close to the construction range, and then stack the crushed stone layer 2, the gravel layer 3, the sand layer 4 and the anti-filtration geotextile. After the filter fabric layer is 5 and the weir bank is stacked to the design elevation, the cofferdam filling construction is carried out; (2) After the cofferdam isolation measures are completed, the silt in the cofferdam is cleaned and clay filling is carried out. The filling materials in the construction range are selected from bottom to top, including clay, sand and gravel and graded crushed stone. The clay filling adopts layered filling and layered compaction technology. During the filling process, the compaction degree is controlled to ensure the filling quality while also playing the role of a waterproof layer; at the same time, a 2% cross slope is set during the filling process and a temporary drainage ditch is set to drain rainwater to the sixth-level sedimentation tank; the clay surface layer is filled with sand and gravel and graded crushed stone; a drainage ditch is set on the side close to the weir bank. The drainage ditch is built with 24 bricks and a cover plate is set on the top of the drainage ditch. The cover plate is a rainwater grate.

[0019] The specific construction process is as follows:

[0020] (1) Cofferdam and water source isolation measures

[0021] When constructing a cofferdam on the river bank, isolation measures are first taken to isolate the construction area from the water source, and then the cofferdam filling construction is carried out to ensure that clay will not enter the natural water system and pollute the water source during the cofferdam filling process.

[0022] During underwater cofferdam construction, after the water level drops to 477.00 (Wusong elevation system), small machinery and transport vehicles are used to remove river mud. The weir foundation pit is then manually excavated to a depth of 100 cm. After the foundation pit excavation is completed, the reinforced gabion foundation of the weir is constructed first. A filter geotextile is laid on the base, and geobags filled with permeable material are stacked on top of the geotextile, ensuring that the geotextile completely envelops the permeable material. After the foundation pit is stacked, the stacking width is calculated based on the measured elevation and a slope of 1:0.75. Woven bags filled with clay are then stacked near the construction area, followed by geotextile bags filled with permeable material (crushed stone, gravel, sand). Note that the geotextile bags must be stacked within the filter geotextile. If the geotextile height is insufficient, they are connected by overlapping, with an overlap width of at least 20 cm. After the weir is stacked to the designed elevation, cofferdam filling construction is carried out.

[0023] To prevent surface water from seeping down from the cofferdam and directly entering the reservoir, a three-stage filtration and isolation system is employed. This allows a small amount of seeping water to be filtered and purified through the isolation system. The entire isolation system is wrapped in a geotextile fabric and extends 100cm into the clay layer to ensure its stability while also preventing muddy water from seeping through it. The foundation pit is excavated manually using small machinery to avoid contamination of the water source during excavation. The seeping muddy water is first filtered through the geotextile fabric and crushed stone layer to remove larger suspended matter. It is then filtered through the sand and gravel layer to remove both larger and smaller suspended matter. Finally, it is filtered through the fine sand layer and geotextile fabric to remove any remaining smaller suspended matter, ensuring that the seeping muddy water does not pollute the water source. To prevent damage to the sandbags caused by rainwater erosion, fine sand, crushed stone, and gravel are bagged and stacked in geotextile bags, while clay is bagged and stacked in woven bags.

[0024] (2) Rainwater collection and purification measures

[0025] After the construction of the cofferdam isolation measures is completed, the silt in the cofferdam is cleaned and clay filling is carried out. The filling materials in the construction range are clay, gravel and graded crushed stone from bottom to top. The clay filling adopts layered filling and layered compaction technology. During the filling process, the compaction degree is controlled to ensure the filling quality while also playing the role of a waterproof layer to prevent rainwater or construction sewage from soaking the clay layer and causing slurry overflow. At the same time, a 2% cross slope is set during the filling process and a temporary drainage ditch is set to divert rainwater to the sixth-level sedimentation tank to avoid Rainfall causes large-scale water accumulation; 60cm gravel and 20cm graded crushed stone are used to fill the area within 0.8m of the clay surface to ensure the solidity of the cofferdam site and prevent dust from being generated when construction vehicles leave the site; a 3.5m wide and 20cm thick C30 concrete construction access road is built between piers 0# and 1#; a 50*60cm drainage ditch is set up on the side close to the weir, the drainage ditch is built with 24 bricks, and a cover plate is set on the top of the drainage ditch, the cover plate is made of 400*600*30mm 3 The rainwater grates allow a large amount of rainwater and construction wastewater to be collected into the sedimentation tank through the drainage ditch for sedimentation and recycling; a small amount of infiltrating rainwater and construction wastewater is filtered and purified through sand, gravel and isolation measures.

[0026] The calculation formula for the total amount of rainwater runoff is:

[0027] Where: W——total design runoff of rainwater (m3);

[0028] ——Rainfall runoff coefficient, which is taken as 0.9 for runoff;

[0029] h y ——Design rainfall thickness (mm), usually the 24-hour rainfall thickness is used;

[0030] F——catchment area (hm2) (10,000 square meters).

[0031] According to the data, the average annual rainfall in Heilongtan Town is 1033mm, the average in July is 249mm, and the average in January is 9.3mm; rainfall exceeding 100mm per day is considered a heavy rainstorm, and rainfall exceeding 250mm is considered an extremely heavy rainstorm. y Assume that the rainfall on a heavy rain day is 250 mm; the catchment area F includes the existing road area of 1353.1 m2, the slope area of 773.2 m2, and the cofferdam area of 3189.5 m2, so F = 5320 square meters; the total design runoff of rainwater is

[0032] Calculation of drainage ditch water flow capacity:

[0033] Maximum water flow: Q = AC (Ri) 1 / 2 ;

[0034] Hydraulic radius: R = A / L;

[0035] Flow rate coefficient: C = R 1 / 6 / n.

[0036] Where: A——water flow area (m2);

[0037] L——wetted perimeter (m);

[0038] n——roughness coefficient, take 0.012;

[0039] i——slope, take 2%.

[0040]

[0041] From the table, the water flow capacity of the drainage ditch is Q = AC (Ri) 1 / 2 =1.11(m 3 / s), so the drainage ditch peak hour discharge volume Q 天 =60×60×Q=60×60×1.11=3996m 3 >1197 (total design rainwater runoff W), therefore, the drainage ditch size meets the requirements.

[0042] A six-stage sedimentation tank is set up at the starting and ending points of the bridge. After rainwater is collected in the sedimentation tank, it can be recycled after sedimentation, such as vehicle washing, spray dust removal and concrete maintenance. The excess water is promptly pumped into the water truck by a water pump and used for road cleaning, dust reduction and greening maintenance of other projects in the project area. The sedimentation tank is cleaned regularly and the sediment is transported to the waste dump for disposal to ensure the sedimentation effect of the sedimentation tank.

[0043] Cofferdam facility layout

[0044] (1) Rainwater from the cofferdam, temporary facilities and bridgehead roadbed is collected in drainage ditches and flows into the six-stage sedimentation tank. The sewage is filtered and recycled. After sedimentation, the excess purified water is discharged into the permanent simple sedimentation tank of the bridge for further purification before being discharged into the reservoir area.

[0045] (2) Before the cofferdam is constructed, the isolation and purification barriers between the cofferdam and the reservoir area and the rainwater collection and purification facilities should be constructed first. After it is determined that there will be no pollution to the water body, the earth cofferdam can be filled.

[0046] (3) During the cofferdam construction, the impact on the reservoir water must be strictly controlled. If turbid water is found, construction should be stopped immediately and construction can only be continued after taking corresponding measures.

[0047] (4) When constructing pile foundations on cofferdams, the operating range of mechanical equipment must be strictly controlled, and drilling slag must be promptly transported to the nearest dumping site designated by the owner for disposal. It is strictly prohibited to use mud wall protection that may cause pollution in bored pile construction.

[0048] (5) After the cofferdam is used, it is excavated during the low water level period. The excavation order is earthwork inside the cofferdam → cofferdam railings → rainwater collection facilities.

Claims

1. The construction technology of environmentally friendly earth-rock cofferdam structure in the first-level drinking water source protection area is characterized by: The following steps are included: (1) Cofferdam and water source isolation measures: When constructing a cofferdam on the river bank, first construct isolation measures to isolate the construction area from the water source, then carry out cofferdam filling construction, remove river mud, and then manually excavate the weir foundation pit. After the foundation pit excavation is completed, first construct the weir reinforced gabion foundation, lay anti-filtration geotextile on the base, and then stack geobags filled with permeable materials on the geotextile. After the foundation pit is stacked, the stacking width is calculated according to the measured elevation and the slope of 1:0.75, and then stack woven bags filled with clay on the side close to the construction area, and then stack the crushed stone layer (2), gravel layer (3), sand layer (4) and anti-filtration geotextile layer (5 ), after the weir bank is stacked to the design elevation, the cofferdam filling construction is carried out; (2) After the cofferdam isolation measures are completed, the silt in the cofferdam is cleaned and clay filling is carried out. The filling materials in the construction range are selected from bottom to top, including clay, sand and gravel and graded crushed stone. The clay filling adopts layered filling and layered compaction technology. During the filling process, the compaction degree is controlled to ensure the filling quality while also playing the role of a waterproof layer; at the same time, a 2% cross slope is set during the filling process and a temporary drainage ditch is set to drain rainwater to the sixth-level sedimentation tank; the clay surface is filled with sand and gravel and graded crushed stone; a drainage ditch is set on the side close to the weir bank. The drainage ditch is built with 24 bricks and a cover plate is set on the top of the drainage ditch; The environmentally friendly earth-rock cofferdam structure comprises a bottom clay layer (1), a gravel layer (3) and a crushed stone layer (2) laid in sequence from bottom to top, a river bank weir is set at the connection with the water source, the river bank weir comprises a reinforced gabion (6) at the base, a clay layer (1), a crushed stone layer (2), a gravel layer (3), a sand layer (4) and a filter geotextile layer (5) are laid in sequence along the river bank from inside to outside; and further comprises a drainage ditch (7), the drainage ditch (7) is set on one side close to the weir, and both ends are connected to the six-stage sedimentation tank.

2. The construction process of the environmentally friendly earth-rock cofferdam structure in the first-level drinking water source protection area according to claim 1 is characterized by: The sand, crushed stone and gravel are packed in geotextile bags and stacked.

3. The construction process of the environmentally friendly earth-rock cofferdam structure in the first-level drinking water source protection area according to claim 1 is characterized by: The clay is packed in woven bags and stacked.

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