How do you calculate over consolidation ratio?

It is obtained by dividing the preconsolidation pressure by the present effective stress value applied on the soil. The expression for computing the OCR is as given below. Here, the term OCR is over consolidation ratio, is preconsolidation stress and is effective overburden stress.

What is over consolidated 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 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.

What is the over consolidation ratio for normally consolidated clay?

The clayey soil can be termed as normally consolidated clay, when the over-consolidation ratio (OCR) equals to one.

How do you calculate OCR of sand?

The OCR can be computed by the following equation:(8) OCR = 2 1 1.95 M + 1 q t – u 2 σ v 0 ′ 1 / Λ where M is the slope of the critical state line in a p′–q plot (where p′ is the mean effective stress and q is the deviator stress) defined as, M = 6 sin ϕ ′ 3 – sin ϕ ′ . In Eq.

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, σ ′ p .

What is Geotech OCR?

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 normally and Overconsolidated soil?

If the current effective stress, s’, is equal (note that it cannot be greater than) to the preconsolidation stress, then the deposit is said to be normally consolidated (NC). If the current effective stress is less than the preconsolidation stress, then the soil is said to be over-consolidated (OC).

How do you determine if a soil is normally consolidated or Overconsolidated?

Overconsolidation. If the current state of soil is on the normal compression line it is said to be normally consolidated. If the soil is unloaded it becomes overconsolidated.

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.

Is the over consolidation ratio the same as the OCR?

Over consolidation ratio. It can be defined as. The ratio of pre consolidation stress to the initial vertical effective stress is known as over consolidation ratio. OCM remains same throughout the data but OCR varies as a function of depth. It cannot be used to compute pre consolidation stress at other depths in a stratum.

Which is the correct equation for consolidation settlement?

Consolidation equation Consolidation settlement ( S ) = C c / ( 1 + e 0 ) · H · log 10 · ( p 0 ‘ + δ p ) / p 0 ‘ Here, C c , compression index; e 0 , initial void ratio of the clay layer; H , thickness of the clay layer; p 0 ′, initial effective stress at midpoint of the clay layer; δ p increase of effective stress due to pile load.

How to calculate The overconsolidation ratio of soil?

The overconsolidation ratio (OCR) allows characterising the stress history of soils. This parameter can be computed from the preconsolidation stress, σ ′ p, and the overburden vertical effective stress for a given soil, σ ′ z, as (5.2) OCR = σ ′ p σ ′ z

What is the ratio of pre consolidation to effective stress?

The ratio of pre consolidation stress to the initial vertical effective stress is known as over consolidation ratio. OCM remains same throughout the data but OCR varies as a function of depth.