How do you calculate Preconsolidation pressure?

Draw the bisector line between the previous horizontal and tangent lines, and draw the NCL; The vertical stress corresponding to the point of intersection between the bisector line and the NCL represents the preconsolidation pressure, .

What is meant by pre consolidation pressure?

It may be defined as. ” The maximum vertical effective stress the soil has ever experienced.” Or. ” The maximum effective past pressure is called the preconsolidation pressure.”

What is Preconsolidation pressure and Overconsolidation ratio?

The overconsolidation ratio (OCR) allows characterising the stress history of soils. This parameter can be computed from the preconsolidation stress, , and the overburden vertical effective stress for a given soil, , as. (5.2) In principle, values of 1 are associated with a underconsolidated state for the soil.

What is the Overconsolidation ratio?

The “over-consolidation ratio” (OCR) is defined as the highest stress experienced divided by the current stress. A soil that is currently experiencing its highest stress is said to be “normally consolidated” and has an OCR of one.

How is preconsolidation stress calculated?

The preconsolidation stress represents the maximum vertical effective overburden stress that the soil has experienced, and is used to define the stress history of the soil by means of the overconsolidation ratio OCR ( = σ’p/σ’v, where σ’v is the present vertical effective stress).

What is recompression index?

The recompression index is used to find the consolidation settlement for over consolidated clay. If the sum of existing stress and overburden and incremental stress in the soil is smaller than or equal to the preconsolidation stress, then the expression for computing the settlement is as below.

How do you calculate OCR?

OCR is evaluated by the formula: OCR = σ’p / σ’yy. If OCR≤1, the soil is considered to be normally consolidated, when OCR> 1 – it is overconsolidated. POP is evaluated by the formula: POP =|σ’p-σ’yy| and is not used in the classification of soils (Fig. 1).

Can the Overconsolidation ratio be smaller than 1?

A soil is over consolidated if the existing effective stress is less than the pre consolidation stress. Thus the ratio is less than 1.

How do you calculate soil OCR?

OCR is evaluated by the formula: OCR = σ’p / σ’yy. If OCR≤1, the soil is considered to be normally consolidated, when OCR> 1 – it is overconsolidated.

How do you calculate the recompression index of soil?

The recompression index is calculated by taking the slope in the recompression curve. Compute I it using the below expression. Here, the term C r is recompression index, Δe is the change in void ratio and is change in effective stress in log scale. It is otherwise called as swelling index.

How do you calculate compression index?

The Compression Index (Cc) is equal to the slope of the graph of pressure versus void ratio (log scale) [7]. Compression Index (Cc) for clay is in the range 0.258 to 0.968, while for laterite soil was in the range 0.101 to 0.940. Value of Compression Index (Cc) is different between each type of soil.

How is Preconsolidation stress calculated?

What is preconsolidation pressure?

Preconsolidation pressure is the maximum effective vertical overburden stress that a particular soil sample has sustained in the past. [1] This quantity is important in geotechnical engineering, particularly for finding the expected settlement of foundations and embankments.

What is the formula for hydrostatic pressure?

Hydrostatic Pressure Formula 1 p is the pressure exerted by the liquid in N.m -2, Pa 2 ρ is the density of the liquid in kg.m -3, slugs.ft -3 3 g is the acceleration due to gravity taken as 9.81m.s -2 4 h is the height of the fluid column in m

How do you determine the preconsolidation stress?

Preconsolidation stress may be determined from the laboratory data by using Casagrande procedure. Initial vertical stress is determined with the original field conditions without the new load and the original hydrostatic pore water pressure.

What can cause preconsolidation pressure in a soil?

Change in total stress due to removal of overburden can cause preconsolidation pressure in a soil. For example, removal of structures or glaciation would cause a change in total stress that would have this effect.