As manual excavation: the trench bottom is required to be flat, dense and free of hard objects. If over-excavation is required, it must be compacted.
B, mechanical excavation, must have a margin of manual excavation, can not use mechanical excavation in place, need to have a margin of 200mm.
c. For construction in areas with high groundwater level or in rainy season, dewatering or drainage is required. For sections with poor geology, trench support or foundation treatment shall be provided.
d. When excavating the pipe trench, the soil shall be thrown to one side as far as possible, and the distance from the edge of the trench shall not be less than 0.5m.
E, when the bottom of the groove is hard earth and stone, the hard stone shall be dug not less than 150mm, the ditching part shall be backfilled with fine sand or fine soil, and when the original soil is salt, fine sand and fine soil shall be paved.
F, when the soil quality at the bottom of the trench is extremely poor, the trench can be dug deeper, then filled with gravel at the bottom of the trench, then rammed with cement mortar, and paved with a layer of fine sand, thickness = 150mm.