Questions and answers

What is Overconsolidation ratio?

What is Overconsolidation ratio?

The overconsolidation ratio (OCR) is a qualitative indicator of this densification or stiffening of the soil, and it is defined as the ratio of the maximum overburden stress ever experienced by the soil (i.e., with the ice sheet on top) to the present overburden stress (i.e., without the ice sheet).

Is London Clay hard or soft?

The London Clay is a stiff bluish clay which becomes brown when weathered and oxidized. Nodular lumps of pyrite are frequently found in the clay layers.

Is London Clay permeable?

The coefficient of permeability of the London Clay at Bradwell, Essex, has been measured using various methods, including a self-boring permeameter. Laboratory samples show that the ratio of horizontal to vertical permeability of the London Clay at the site is approximately 2.

Is London built on clay?

The main bedrocks are Chalk and London Clay, with much of the surface geology made up of sands and gravels from the Eocene, till and gravel from glacial activity, and recent non-glacial deposits caused by wind or water action.

How do you know if clay 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.

Is London Clay a rock?

Although the Cretaceous Chalk and the London Clay are the thick rock layers immediately under London, these aren’t the only rock layers. For instance, older rocks underlie the chalk, and other rock layers are found between the chalk and the London Clay, and also between the London Clay and the surface.

How deep is the London Clay?

433 feet
London Clay, lies up to 433 feet (132 metres) thick under the City of London and supports most of its tunnels and deeper foundations.

Where does clay come from in UK?

In the UK, china clay occurs as an alteration product of the Cornubian granites, from which it has been extracted for some 250 years. It is an ideal material as it withstands high temperatures while retaining its colour.

How deep should foundations be in clay?

Seasonal changes affect clay soils – causing them to swell in winter and shrink in summer. That’s why there are minimum foundation depths for each type of clay. Strip, trench fill or pad foundations must be cast at a minimum of 750mm in low plasticity clays, 900mm in medium, and 1000mm in the highest risk areas.

What is a high void ratio?

If void ratio is high (loose soils) voids in a soil skeleton tend to minimize under loading – adjacent particles contract. The opposite situation, i.e. when void ratio is relatively small (dense soils), indicates that the volume of the soil is vulnerable to increase under loading – particles dilate.

What is the range of void ratio?

The void ratio of a dense sandy gravel soil is about 0.3, that of a loose sand is about 0.6, while the void ratio of clays (in natural conditions) varies between 0.5 and 1.0 and decreases with depth of the soil layers.

What is The overconsolidation ratio of undrain clay?

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 normally consolidated clay with shear stress angle equal to 26°.

What is The overconsolidation ratio of organic soil?

If these values are ignored, the mean OCR for organic soil is 2.1. The OCR for clay was generally between 0.5 and 10. The OCRs > 10 were from samples at shallow depths of < 0.6 m. If these values are removed, the mean OCR for the soft clays is 3.5.

How is The overconsolidation ratio ( OCR ) calculated?

The overconsolidation ratio (OCR) is estimated using the equation: Su = actual undrained shear strength of clay having a given PI; and Sunc = undrained shear strength of the same clay, if normally consolidated at that depth.

What are the characteristics of the London Clay?

STRESS HISTORY FABRIC OF THE LONDON CLAY TECTONIC SHEARS INDEX PROPERTIES STRUCTURE IN SITU STRESSES SEISMIC WAVE MEASUREMENTS STRESS PROBES MODULUS DECAY CURVES BULK STIFFNESS EFFECTIVE STRESS STRENGTH… UNDRAINED STRENGTH BRITTLENESS DESTRUCTURING BY SWELLING PERMEABILITY DISCUSSION CONCLUSIONS