1. Construction in reinforced round concrete culverts
1) Excavation is manually-operated or conducted through a combination of manual work and small machines. When the culvert is built in the original irrigation ditch, temporary channels should be excavated to ensure normal irrigation for the farmland. After being excavated to the designed elevation, the culvert will be added a gravel cushion and concrete is poured into the foundation. The reinforced concrete pipe joints are prefabricated on site according to design specifications by using a spreader approved by the supervision engineer into installation.
2) The pipe joint installation starts from the downstream, so that the joint faces upstream, and the pipe sections are smooth and straight along the slope of the water flow. Each section of the entire culvert pipe is closely attached to the laid foundation to ensure that the culvert is evenly stressed.
(3) The pipe joints are made of collar joints. Asphalt hemp, cement slurry or tar sand is used to tightly fill all joints to make them stable, durable and watertight. Before filling the tar sand, the asphalt coating will be applied to the outer and inner surface of the round pipe to enhance viscosity. Tying ropes will be also fixed according to the design drawing to avoid leakage of the tar sand.
(4) After installation of the round pipe, the backfilling operation shall be carried out after the approval of the supervision. The backfilling is carried out by layering the clay on both sides of the pipe joint and compacting with a small compacting machine.
2. Construction in slab culverts
(1) The excavation of the foundation is similar to that of the round culvert. The foundation is directly built on the soil when the soil foundation enjoys sufficient bearing capacity. Otherwise, a gravel cushion or a gravel cushion will be laid.
(2) As for the foundation, the culvert and the opening structure (except the cap stone) made of stone, the layered grouting method must be used in time in case of water leaking. The upper and lower layer will be processed separately with the joint being made at last.
3) The slab is prefabricated on site, and installed by autocrane.
(4) When the strength of the culvert reaches 70% of the designed strength, the slab will be installed. Before installing, the size of the end product and the side wall will be checked. After installation, mortar or other materials approved by the engineer will be utilized to fill the hoisting position on the slab. Cement mortar is used to fill the adjacent plates.
(5) The backfilling behind abutment must be conducted on the supporting beam (or culvert bottom) and the slab with the strength of mortar reaching 70%. The installation is symmetrically carried out on both sides of the culvert. When filling the soil above the slab, minimum paving and rolling thickness of the first layer shall not be less than 30cm and 20cm respectively to prevent severe impact.