23-08-2013, 04:01 PM
DEFORMATION AND SETTLEMENT OF SOIL
DEFORMATION.ppt (Size: 2.94 MB / Downloads: 31)
SETTLEMENT
Definition
The total vertical deformation at the surface resulting from :
External Load
Dewatering
Settlement Components
Immediate Settlement ; Se
Primary Consolidation Settlement ; Sc
Secondary Settlement (Creep) ; Ss
IMMEDIATE SETTLEMENT
Defined as settlement which occurred directly after the application of a load, without a change in the moisture content.
Caused by soil elasticity behavior
The magnitude of the contact settlement will depend on the flexibility of the foundation and the type of material on which it is resting.
For clay, the immediate settlement generally very small comparing to the consolidation settlement, therefore this immediate settlement mostly ignored.
Usually considered at sand or sandy soil.
CONSOLIDATION
When the stress on a saturated clay layer in the field is increased, the pore water pressure in the clay will increase.
Because the coefficients of permeability of clays are very low, it will take some time for the excess pore water pressure to dissipate and the stress increase to be transferred to the soil skeleton gradually.
Consolidation is the process of dissipation of excess pore water pressure in a row of time.
Note:
Dissipation of pore water pressure occurs simultaneously with the squeezing out of the pore water. Therefore the consolidation time depend on:
The distance of pore water to be squeezed out
The coefficient of permeability of soft soil
EXAMPLE
The specimen thickness was 25.4 mm and drained on both sides. The time required for the specimen to reach 50% consolidation was 4.5 min.
A similar clay layer in the field, 2.8 m thick and drained on both sides, is subjected to similar average pressure increase that is po = 140 kN/m2 and po+p = 212 kN/m2. Determine the following :
1. The expected maximum consolidation settlement in the field
2. The length of time it will take for the total settlement in the field to reach 40 mm
3. Repeated no.2 problem in case of drained on one side