10 factor affecting in selection of foundation | Determination of foundation depth.
The foundation or footing must be placed at the required depth from the ground surface for proper purpose. The vertical distance between the ground surface and the footing base is called the depth of footing (D). Depth of footing depends on ultimate bearing capacity and settlement. Apart from that, the following points have to be considered to determine the footing depth. For example-
1. Depth of Top Soil: If the soil below the top soil is composed of organic matter, footings should be placed at that level. The topsoil should be removed slightly more than the footing.
2. Frost Depth: Footings should be placed below the penetration depth. Providing insufficient depth of footing may result in damage to frost action.
3. Soil volume change area: Mud has high plasticity qualities. Block cotton soils, on the other hand, vary greatly in size. Such soil settles when dry and swells when wet. Volume change is greater near the surface and decreases with increasing depth.
4. Lateral Footings and Boundary Lines: Footings should be provided at a distance such that the existing structure is not damaged. Vibration, undermining or lowering of the water table when constructing new footings. etc. due to the surrounding structure may be damaged.
5. Sloping footing: For footings on sloping ground, the distance from the sloping surface to the bottom side of the base should be at least 90 cm.
6. Water Table: Footings should be placed as far above the water table as possible. Because the presence of water in the soil around the footing reduces the bearing capacity of the soil and makes construction difficult. Apart from that, humidity
Resistive problems arise.
7. Scudier Depth: Footings on the sides of flowing water should be placed below the depth of the flowing water.
8. Underground Corrosions: Footings can be damaged in the presence of underground corrosions, caving and mining etc. Apart from that, the footing can also be damaged due to man-made sewer lines, water lines, cable lines etc. So a safe distance footing should be provided from all these.
9. Root hole: If there is a hole in the root of the plant or any other hole in the soil, then the animals living in the hole or earthworms can move through the tunnel. Therefore the depth of footing should be below the affected area
10. Minimum Depth: Minimum depth of footing should be provided as per Rankin’s formula.
