the trenching must be carried out in strict accordance with design drawings or excavation route guided by project supervisor. it shall not change without obtaining the consent of relevant department.
the trench depth should meet the following provisions:
a、when buried under road way, the burial depth of the pipe top should not be less than 0.9 meters.
b、when buried under sidewalk, the supporting pipes of the pipeline should not be less than 0.75 meters.
c、under green belt or residential area, the supporting pipes of the pipeline should not be less than 0.6 meters.
d、when buried in permanent frozen earth or seasonal frozen earth, the burial depth of the pipe top should be below the frost line.
the trench width is the minimum spacing for pipe connection/foundation construction and operation of backfill. under general condition, the trench width is 0.8 meters narrower than cement laying trench. this may reduce the excavation workload.
the trench bottom should be flat generally so that the pipe pillows placed on it are flat and not inclined. at places where the earth is loose, pave sand or a layer of plain concrete with thickness of 100mm. if the soil texture is bad, it suggests paving a layer of reinforced concrete bottom plate at the bottom plate of sleeve pipes. the concrete grade is c20.