Can Overconsolidation ratio be less than 1?
The overconsolidation ratio, OCR, is the ratio of σp to σ o, and nu- merically represents the state of consolidation: an OCR equal to 1 is a normally consolidated sediment, an OCR greater than 1 shows over- consolidation, and an OCR less than 1 shows underconsolidation.
What is an Overconsolidated soil?
The soil which had its load removed is considered to be “overconsolidated”. This is the case for soils that have previously had glaciers on them. The highest stress that it has been subjected to is termed the “preconsolidation stress”.
How can I reduce my consolidation settlement?
Note: the consolidation settlement can be reduced by conducting any of the following: 1. Increase the length of piles (when the length of piles are increased, “H” value in the preceding equation would reduce. “H” is the thickness of the compressible portion of the clay layer).
What is OCR in geotechnical engineering?
In geotechnical engineering, generally a parameter called the overconsolidation ratio (OCR) is used to indicate the stress history of a soil deposit. Value of OCR can be determined by conducting an odometer test using an undisturbed soil sample.
What is the OCR equal to?
The OCR is defined as the ratio of the maximum past effective consolidation stress and the present effective overburden stress. OCR is a function for undrain shear strength ratio (Su/p′), which is equal to 0.22 in the case of normally consolidated clay with a shear stress angle equal to 26 degrees.
What is settlement of soil?
Settlements refer to the soil’s movement in the vertical direction typically induced by stress changes. Immediate settlement occurs in the soil upon load application and involves reduction in void space and rearrangements of the soil particles in response to that load.
What are the three types of settlement?
There are generally three types of settlements: compact, semi-compact, and dispersed. Each is based on its population density. Compact settlements have the highest density of population.
How do you limit soil settlement?
In such circumstances, it becomes essential to improve the foundation soil to address permissible settlements by means of the following:
- Compacting the soil.
- Draining the soil, in case of cohesive types.
- Compacting the soil, in case of cohesion less soils.
- Confining the soil, increasing stiffness.
- Grouting.
What is a high void ratio?
If void ratio of a soil is high i.e. the soil is loose, then under loading voids have a tendency to minimize themselves. So, for soils with high void ratio, civil. engineer may take a decision either to reduce the loading or pre-compact the soil.
What does it mean when soil is overconsolidated?
On the other hand, it is said to be overconsolidated if the present overburden pressure is less than the effective overburden pressure it has experienced in the past. The ratio of the maximum overburden pressure it has experienced in the past and the current overburden pressure is known as the ‘overconsolidation ratio’ (OCR).
Why are normally consolidated soils compressed without recovery?
Since a normally consolidated clay is experiencing the maximum pressure of its history, it is more likely to get compressed without recovery (plastic recovery) when subjected to additional external pressure in their natural state.
What does the pre consolidation pressure in soil mean?
Pre-consolidation pressure is the yield point that indicates the beginning of the plastic deformation during the compressive loading in a soil. The ratio of the preconsolidation pressure and the applied effective pressure is the overconsolidation ratio.
What’s the difference between normally consolidated and overconsolidated clay?
For instance, the natural moisture content of a normally consolidated clay is usually close to the liquid limit, while the natural moisture content of an overconsolidated clay is usually close to the plastic limit. Clay soils in their natural state have memory of the magnitude of the highest pressure they have experienced in the past.