In shallow foundation, trenches are excavated as per the sanctioned or approved plan. Until the trenches are filled up after concreting of footing of columns, care is required to be taken while and after excavation of trenches. These have been listed below for your knowledge.
- All foundation trenches should be excavated to exact depth and dimensions as shown in the sanctioned plan. In hard and firm soils, the sides of trenches can be kept vertical for a depth of 1.5m from the top. For greater depths, trenches should be widened by providing 0.45m wide steps on either side of the trenches at every vertical interval of 1.5m depth. In case of soft and poor soils, the trench sides shall be sloped in 1:1 (1 horizontal : 1 vertical) slope. If sloping of sides is not possible, then ballies or bamboos should be driven in soil at a horizontal interval of 0.2m along the sides to avoid falling in of the sides.
- After excavation, the bed of all trenches should be shaped and dressed in level. After levelling, the bed of the trenches should be watered and rammed properly. If any soft patch is noticed, then it should be removed by excavating the portion in square shape and filled with either sand or concrete of proportion 1:3:6 or 1:4:8.
- If any trench has been excavated for more depth than the depth prescribed in the sanctioned plan, then the excess depth should not be filled with loose excavated soil. Instead, it should be filled either with sand or concrete of proportion 1:3:6 or 1:4:8.
- All the excavated soil and other materials should be placed atleast 1m to 1.5 m away from the edges of the trenches. Otherwise there will be a good chance of falling of loose excavated soil or material inside the trenches.
- For safety of the people working in the area of construction, the trenches should be fenced or guarded properly.