total settlement I in mm, which is the response to the stress applied to the soil, can be calculated as the sum of the three components
,I ,C ,s
= total settlement, mm
II = instant or deformation settlement, mm
IC = primary consolidation settlement, mm
Is = secondary compression settlement, mm
Primary consolidation and secondary compression settlements are usually small if the effective stress in the foundation soil applied by the structure is less than the maximum effective back pressure of the soil.
1. immediate settlement
immediate settlement II Is a change in the shape or deformation of the soil due to applied stress.
- The calculation of immediate settlement in unconsolidated soils is complicated by a non-linear hardness that depends on the stress condition. Empirical and semi-empirical methods are used to calculate immediate settlement in contemporary soils.
- Immediate settlement in cohesive soils can be estimated using the elastic principle, especially for saturated soils, clay shale and most rocks.
2. primary consolidation settlement
primary consolidation settlement IC Additional porosity occurs in adhesive or compressive soils during fluid pressure dissipation, and is controlled by the gradual removal of fluid from voids in the soil, leading to an associated compression of the soil skeleton.
Excess pore pressure is the pressure that exceeds the hydrostatic fluid pressure. The pressure of a hydrostatic fluid is the product of the unit weight of water and the difference in height between a given point and the height of the free water (the phreatic surface). The pore fluid is usually water with some dissolved salts. The opposite of consolidation settlement (earthen agglomeration) can occur if the excess pore water pressure is initially negative and reaches zero after absorption and adsorption of the available fluid.
- Primary consolidation settlement is generally insignificant in non-cohesive soils and occurs rapidly because these soils have relatively high permeability.
- Soils connecting the primary aggregates take considerable time because they have relatively low permeability. The time of consolidation increases with the thickness of the soil layer and is inversely related to the coefficient of permeability of the soil. Consolidation settlements determined from the results of one-dimensional consolidation tests also include some immediate settlements. II,
3. Secondary Compression Settlement
Secondary Compression Settlement Is A form of soil creep that is largely controlled by the rate at which skeletons of compressed soils, especially clays, silts and peat, can yield and compress. Secondary compression is often easily recognized to follow primary consolidation when additional orifice fluid pressure can no longer be measured; However, both processes can occur simultaneously.