Techniques Used for Improving Bearing Capacity of Soil
The following techniques can be used for improving bearing capacity of soil as per the site condition.
- Increasing depth of foundation
- Draining the soil
- Compacting the soil
- Confining the soil
- Replacing the poor soil
- Using grouting material
- Stabilizing the soil with chemicals
1. Increasing Depth of Foundation
At deeper depths, the over burden pressure on soil is higher; hence the soil is more compacted at deeper depth. As a result it shows higher bearing capacity. This is applicable only for cohesionless soils such as sandy and gravelly soils. This method of improving bearing capacity of soil is not applicable if the subsoil material grows wetter as depth increase. This method has a limited use because with increase in depth, the weight and cost of foundation also increases.
2. Draining the Soil
With increase in percentage of water content in soil, the bearing capacity decreases. In case of sandy soil, the bearing capacity may reduce as much as 50% due to presence of water content. Cohesionless soils (i.e. sandy & gravelly soils) can be drained by laying the porous pipes to a gentle slope, over a bed of sand and filling the trenches above the pipes with loose boulders. These trenches subsequently should lead to the nearest well or any water body.
3. Compacting the Soil
If we compact soil using appropriate method, then there will be increase in its density and shear strength. As a result the bearing capacity of soil also increases. There are many methods of compacting soils on site. Few of them are mentioned below.
- By spreading broken stones, gravel or sand and thereafter ramming well in the bed of trenches.
- Using an appropriate roller as per the soil type to move at a specified speed.
- Br driving concrete piles or wood piles and withdrawing piles and subsequently filling the holes with sand or concrete.
4. Confining the Soil
In this method, the soils are enclosed with the help of sheet piles. This confined soil is further compacted to get more strength. This method is applicable for shallow foundations.
5. Replacing the Poor Soil
In this method the poor soil is first removed and then the gap is filled up by superior material such as sand, stone, gravel or any other hard material. In order to do this, first excavate a foundation trench of about 1.5 m deep, and then fill the hard material is stages of 30 cm. Then compact the hard material at every stage. This method is useful for foundations in black cotton soils.
6. Using Grouting Material
This method is applicable for soils where there is presence of pores, fissures or cracks etc underneath the foundation. In this method, poor soil bearing strata is hardened by injecting the cement grout under pressure, because it scales off any cracks or pores or fissures etc. For proper distribution of the cement grout, the ground is bored and perforated pipes are introduced to force the grout.
7. Stabilizing the Soil with Chemicals
This method of improving bearing capacity of soil is costly and applied in exceptional cases. In this method, chemical solutions, like silicates of soda and calcium chloride is injected with pressure into the soil. These chemical along with the soil particles form a gel like structure and develop a compact mass.This is called chemical stabilization of soil and used to give additional strength to soft soils at deeper depths.