Q. Preloading - Control of settlements?
This method consists of loading the soil strata by a load intensity which will be equal to or higher than the expected load intensity. The soil strata will settle due to preloading. Later, remove the preload and construct the structure. The period of preloading depends on the time rate of settlement. Hence, if the rate of settlement is slow, then, period of preloading will be too long. The compression under preloading will be very rapid in porous soils with low relative density. Rebound after removal of preload is also less in such soil deposits. Addition of water during preloading may be advantageous, since it breaks the weak bonds in strata having silts and loosely packed sands. Organic silts, peats, sanitary fills can be precompressed effectively by preloading. Lowering of ground water table also contributes for preloading.
Reloading in the site is time consuming in soils where consolidation settlement is important unless drainage facility like sand drainslband drains, well points, electro-osmosis methods are used along with preload. Reloading is generally adopted in poor soils with relatively high water contents. With preloading, unless drainag; is rapid, pore pressure build up will take place, reducing the shear strength.