Geology/P.L and L.L
Q: sir Why Plastic and liquid limit Determination Test Is necessary ? How this Help full in House construction
Dear Waqar Ahmed, Goodafternoon and fraternal greetings!
My answer is given below for your question
Plastic limit, and liquid limit of the soils are the two parameters required for design of any engineering constructions. clayey soils take on increasing amounts of water, it undergoes dramatic and distinct changes in behavior and consistency. Depending on the water content of the soil, it may appear in four states: solid, semi-solid, plastic and liquid. In each state, the consistency and behavior of a soil is different and consequently so are its engineering properties.
The liquid limit of a soil is the moisture content, expressed as a percentage of the weight of the oven-dried soil, at the boundary between the liquid and plastic states of consistency. The moisture content at this boundary is arbitrarily defined as the water content at which two halves of a soil cake will flow together, for a distance of ½ in. (12.7 mm) along the bottom of a groove of standard dimensions separating the two halves, when the cup of a standard liquid limit apparatus is dropped 25 times
from a height of 0.3937 in. (10 mm) at the rate of two drops/second.
The plastic limit of a soil is the moisture content, expressed as a percentage of the weight of the oven-dry soil, at the boundary between the plastic and semisolid states of consistency. It is the moisture content at which a soil will just begin to crumble when rolled into a thread ⅛ in. (3 mm) in diameter using a ground glass plate or other acceptable surface.
It is preferable that soils used for liquid limit determination be in their natural or moist state, because drying may alter the natural characteristics of some soils.Organic soils in particular undergo changes as a result of oven-drying or even extended air-drying. Other soils containing clay may agglomerate, lose absorbed water which is not completely regained on rewetting, or be subject to some chemical change.
These distinctions in soil are used in assessing the soils that are to have structures built on. Soils when wet retain water and some expand in volume. The amount of expansion is related to the ability of the soil to take in water and its structural make-up (the type of atoms present). These tests are mainly used on clayey or silty soils since these are the soils that expand and shrink due to moisture content. Clays and silts react with the water and thus change sizes and have varying shear strengths. Thus these tests are used widely in the preliminary stages of designing any structure to ensure that the soil will have the correct amount of shear strength and not too much change in volume as it expands and shrinks with different moisture contents. Hence for any house construction, these parameters are very much essential to know the strength of the material.