What is an Overconsolidated clay?

over-consolidated clay Clay that has been more compacted than would be expected from the existing overburden, e.g. it has been subjected to pressure from overburden that has subsequently been removed by erosion. Compare NORMALLY CONSOLIDATED CLAY.

What is the difference between normally consolidated and Overconsolidated clay?

The overconsolidation ratio of a normally consolidated clay is unity, while the overconsolidation ratio of an overconsolidated soil is greater than unity. Overconsolidation can occur in clays due to reasons such as; Self-weight of the soil which has eroded. Weight of continental ice sheet which has melted.

What does OCR 1 mean?

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.

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 causes a clay to become Overconsolidated?

Overconsolidated soil “If the initial vertical effective stress of the soil sample is less than the preconsolidation stress, then the vertical effective stress in the field was once higher than its current magnitude, and the soil is called overconsolidated.”

Where can I find normal consolidated clay?

Steps to determine the normally consolidated soil: Draw the tangent at the point existing at the bottom of the curve and extend the line from the lower right in the upward direction to the left. Indicate it using the dashed line. The line will touch the line represented by the condition e = e 0 . Label the point as b.

What are the causes of over consolidation?

Why soil becomes overconsolidated ?

• Extensive erosion or excavation which results in the decrease of ground surface elevation.
• Extra loading from a glacier, which has since melted.
• Extra loading from a structure, such as storage tank, which has since been removed.

What is effective stress in soil mechanics?

Effective stress can be defined as the stress that keeps particles together. In soil, it is the combined effect of pore water pressure and total stress that keeps it together. It can also be defined in equation form as the total stress minus the pore pressure.

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 know if soil is Overconsolidated?

“If the initial vertical effective stress of the soil sample is less than the preconsolidation stress, then the vertical effective stress in the field was once higher than its current magnitude, and the soil is called overconsolidated.”

Does normally consolidated clay have cohesion?

Normally consolidated clays (NCC) usually don’t present significant cohesion, as usually is the case with soft sands; NCC behavior is often similar to soft sands behavior. Over consolidated clays (OCC) have cohesion, showing similar behavior to dense sands (apparent cohesion due to overlocking of sand particles).

When is clay soil said to be overconsolidated?

A clay soil is said to be normally consolidated if the effective overburden pressure that it is currently experiencing is the maximum it has ever experienced in its history. 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.

How is shear strength of overconsolidated clay measured?

Tests were conducted on samples of clays taken from depth 100-300 meters below ground level. All confined tests were performed in triaxial apparatus following TXCIU procedure. Selected samples were tested in overconsolidation state. The OCR ratio values ranged from 3 to 28.

How to calculate The overconsolidation ratio in soil?

5.3.4 Overconsolidation ratio 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

Which is stronger O / C Clay or N-C Clay?

The o/c clay will have greater undrained shear strength in contrast with its overburden stress than the n/c clay.