How to Prevent Foundation Failure on Soft Soil
How to prevent Foundation Failure on Soft Soil? As we know that soft soil has tendency to shrink and swell excessively. When these type of soil come in contact with water, they swell and when becomes dry, it shrinks. This alternate process of swelling and shrinking results in the differential settlement of foundation which in turn causes cracks in building. The cracks thus formed are sometimes 15 to 20 cm wide and 2.5 to 4.5 m deep. Those facts are dangerous. As engineer, we should do anything to prevent foundation failure on soft soil. There are several precaution that we should consider to prevent foundation failure on soft soil, they are :
- The maximum load on soft soil should be limited to 5 tonnes/m2. If there is a chance for water to come in contact with foundation, then the load should be limited to 4.9 tonnes/m2.
- Foundation should be placed at a depth where the cracks cease to extend. The minimum depth of foundation should be at least 1.5 m.
- The main wall of the building must be provided with all round reinforced concrete ties or bands.
- Reinforced concrete ties or bands having 10 to 15 cm deep should be placed at plinth level, lintel level and eaves level.
- In case the depth of soft soil is only 1 m to 1.5 m, then completely remove the entire soft soil and place the foundation below that depth.
- Try to avoid direct contact of soft soil with foundation material. This can be achieved by making wider trenches for foundation and filling spaces on either side of the foundation masonry with sand.
- Compact the bed of the foundation trench to make it farm and hard. On this compacted bed, spread a thick layer of sand (i.e. 30 cm) in two layers, each layer being 15 cm. each layer should be water and compacted properly to get highest possible density. On this compacted layer of sand, place either stone upto desired height where concrete foundation bed has to be made.
- In case of important structures, raft foundation should be provided.
- For less important structures (such as boundary wall construction), the foundation should preferably taken at least 15 cm below the depth at which cracks in soil cease to occur.
- Construction should be done in dry season.
- For main walls or for load bearing walls, the width of the trench should be dug 40 cm wider than width of foundation. Then fill the space on either side of the trench (i.e. 20 cm in each side) with coarse sand. This is done to separate the foundation masonry from direct contact with soft soil. In case of compound wall this width of sand filling can be reduced to 15 cm on each side.
I hope those precautions can help you to prevent foundation failure on soft soils. If you need more update about Civil Engineering, please subscribe. Put your comments if you find any question or other things. Have a nice browsing. Keep sharing, keep caring.