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The shrink–swell capacity of soils refers to the extent certain clay minerals will expand when wet and retract when dry. Soil with a high shrink–swell capacity is problematic and is known as shrink–swell soil, or expansive soil . [ 1 ]
The London Clay Formation is a marine geological formation of Ypresian (early Eocene Epoch, c. 54-50 million years ago) [1] age which crops out in the southeast of England. The London Clay is well known for its fossil content. The fossils from the lower Eocene rocks indicate a moderately warm climate, the tropical or subtropical flora.
Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; such soils are called vertisols. Soils with smectite clay minerals, including montmorillonite and bentonite, have the most dramatic shrink–swell capacity. The mineral make-up of this type of soil is responsible for the moisture retaining capabilities.
Soil map of Eastern Hertfordshire - by G. A Dean, 1864. The geology of Hertfordshire describes the rocks of the English county of Hertfordshire which are a northern part of the great shallow syncline known as the London Basin. The beds dip in a south-easterly direction towards the syncline's lowest point roughly under the River Thames.
The Lambeth Group is a stratigraphic group, a set of geological rock strata in the London and Hampshire basins of southern England.It comprises a complex of vertically and laterally varying gravels, sands, silts and clays deposited between 56-55 million years before present during the Ypresian age (lower Eocene).
The PI is the difference between the liquid and plastic limits (PI = LL-PL). Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay. Soil descriptions based on PI: [8] (0) – Non-plastic (<7) – Slightly plastic (7-17) – Medium plastic
For example, if a soil is 70 percent sand and 10 percent clay then the soil is classified as a sandy loam. The same method can be used starting on any side of the soil triangle. If the texture by feel method was used to determine the soil type, the triangle can also provide a rough estimate on the percentages of sand, silt, and clay in the soil.
In places, there are deposits of brickearth, which is a mixture of clay and sand that has supported London's long-standing brick-making industry. On top of these natural layers are the deposits of hundreds of years of human occupation. In the oldest parts the City of London and the City of Westminster this layer can be up to 6 metres deep. [5]