A.0.0~0.1m B.0.1~0.2m C.0.2~0.3m D.0.3~0.4m
A.≤25m B.25~100m C.50~200m D.≥200m
A.溝端開挖法 B.溝側(cè)開挖法 C.多層接力開挖法 D.溝角開挖法