If the foundations are left open for one rainy season it will enable the soil to settle down, and it will also be known whether the material movements of the soil below due to increment of moisture are likely to cause any damage. Foundation in bad soil can be improved by:
Increasing the depth of foundation except when the material grows wetter as the depth increases.
Compacting the soil by ramming.
Ramming in sand, gravel, murum, broken stone or brick bats in-situ between the foundation concrete and soil. This is useful for silt or black cotton, soils and also clayey soils.
Removing the poor soil and filling the gap with sand, rubble stone, gravel or other hard material. This will increase the bearing power to about twice its original value. In this method the foundation trenches are excavated to a depth of about 1.5 m and 45 cm wider, and filled with the hard material to a thickness of about 30 to 45 cm and heavily rammed with water so as to force the hard material into the soft soil. It the filled material is buried completely then another layer of the hard material may be filled in to a depth of about 15 to 23 cm and well rammed. This method is especially useful for black cotton soils.
Cement grouting the rammed materials will make the foundations much harder.
Draining out water from wet foundations.
Driving piles, either of wood or concrete or driving and with-drawing piles and filling the holes with sand or concrete. This will increase the density of the soil.
Artificial stabilization can be used to seal off permeable strata for deep excavations or to give soft soils additional strength if they are likely to flow.
Cement grout, water bearing gravel and coarse sand can be made very much less permeable by pumping cement grout into them. The process is successful only on coarse sands and gravels where the grout can fill up the voids; finer sands necessitate some form of chemical or bituminous emulation treatment. Grouting is of much use for deep excavations, such as tunnels.
