Engineering and soil

A material is said to be permeable if it contains continuous voids. Since such voids are contained in all soils including the stiffest clays, and in practically all nonmetallic construction materials including sound granite and neat cement , all these materials are permeable. Furthermore, the flow of water through all of them obeys approximately the same laws. Hence the difference between the flow of the water through clean sand and through sound granite is merely one of degree. The permeability of soils has a decisive on the cost and the difficulty of many construction operations, such as the excavation of open cuts in water-bearing sand, or on the rate at which a soft clay stratum consolidates under the influence of the weight of a superimposed fill. Even the permeability of dense concrete or rock may have important practical implications, because water exerts a pressure on the porous material through which it percolates. This pressure, which is known as seepage pressure,

Darcy’s law The flow of free water through soil is governed by Darcy’s law. In 1856, Darcy demonstrated experimentally that for laminar flow in a homogeneous soil, the velocity of flow ( ) is given by, The velocity of flow is also known as the discharge velocity or the superficial velocity . Eq. 8.2 is known as Darcy’s law, which is one of the corner stones of soil engineering. The discharge is obtained by multiplying the velocity of flow ( ) by the total cross-sectional area of soil (A) normal to the direction of flow. The area A includes both the solids and the voids. The coefficient of permeability can be defined using Eq. 8.2 . If the hydraulic gradient is unity, the coefficient of permeability is equal to the velocity of flow. In other words, the coefficient of permeability is defined as the velocity of flow which would occur under unit hydraulic gradient. The coefficient of permeability has the dimensions of velocity [L/T]. it is measured i

Atterberg limit tests: they are designed to give an idea or index, how the soil will act under certain conditions. Bentonite clay has been added to increase the plasticity of the soil. LL test Liquid Limit is defined by the moisture content, in which a soil begins to act less as a viscous fluid and act more like a plastic putty. By convention: this is defined as the water content at which a groove cut into a soil pat the casagrande device requires 25 blows to close distance of 13mm PL test plastic limit is defined as the moisture content at which a material begins to act less like a plastic putty and more like a brutal solid. LL test procedure If the No. of blows falls between 15&20 : Scoop out some of the soil in place and one of the pre weight air cans and record the new weight for moisture content determination, place the can in the oven and reweight in 24 hours. If the No. of blows falls below 15 : Mix the soil to dry it out, clean &