Construction preparation → whole slope cleaning → membrane bag laying → tensioning and positioning → anchoring and coping → soil returning and reinforcement → anti-seepage blanket construction → weir separation construction.

3.2 Construction Difficulties and Measures

(1) Positioning and laying of membrane bags: Before construction, the riverbed should be properly cleaned to ensure that the weir foundation is flat and free of sharp objects, so as to avoid damaging the membrane bags. Bag laying is started at the deepest part of the river bed, and construction is started at low tide and advection, which is convenient for operation. The film bag is positioned by bamboo piles. According to the size of the weir, bamboo is inserted in the four corners of the paving place, and the corner pull ring of the membrane bag is sleeved on the bamboo. When filling sand, the membrane bag sinks into the river bottom along the positioning pile.

(2) Cofferdam closure: Different from other types of cofferdams, other types of cofferdams are generally caused by closure, and the closure method is closure. Especially, when the cofferdam construction height reaches the water level change zone, no individual gap can be left in each flood tide and ebb tide, and the same membrane bag can be completed in each flood tide and ebb tide to avoid the scouring of the weir body by concentrated water flow.

(3) Seepage prevention of cofferdam: The leakage of cofferdam mainly includes three parts: the contact surface between the cofferdam body and the original riverbed; Contact surface between weir body and bank slope; Between the film bags. Especially the first two parts, are the most destructive and dangerous places. The main anti-seepage measures are:

① Make use of the characteristics of high mud content, good compactness and poor water permeability of cowhide sand to prevent seepage by itself.

② Leakage channels are easily formed between membrane bags. On the one hand, don't fill the cowhide sand too full, and let the film bag adjust its density by itself; On the other hand, it is also possible to fill cohesive soil between membrane bags and then cover them with woven soil bags.

(3) Two layers of geotextile are laid on the water-facing side of the weir body from the weir top to the weir foot, and the geotextile is 3 meters deep into the riverbed, and the woven cloth is fixed with a sand-wrapped plum-blossom pressing surface; In the lap joint of plastic woven cloth, sandbags should be used to fill it tightly.

(4) Local problem handling:

(1) At the junction of weir body and bank slope, clay should be tamped and embedded into bank slope to form embedded seepage-proof cut-off.

(2) The outer weir foot should be filled with soil and compacted as impervious body.

(3) During the construction, the weir shall be raised by layers and stages. Choose a reasonable time, fill the height of about 30cm every day, strictly control the filling speed and strengthen observation.

(4) During foundation pit pumping, the water level drop should be strictly controlled, about 50cm per day, and attention should be paid to the dewatering and seepage channels of the weir body to avoid centralized seepage and piping.