engineering properties of soil
The following properties of clay are taken into consideration while dealing with clay as a building material.
- internal friction angle
It is the intrinsic molecular attraction that resists breaking or shearing of a material. Fine-grained soils achieve cohesion from films of water that bind together the individual particles in the soil mass. Cohesion is the property of fine-grained soils with a particle size of less than 0.002 mm. Soil cohesion decreases as moisture content increases. Well compacted soils have higher cohesion and are independent of the external load applied.
2. Internal friction angle
The resistance in sliding of particles of clay mass depends on the angle of internal friction. It is generally believed that the value of the angle of internal friction is almost independent of the normal pressure, but varies with the degree of packing of the particles, that is, the density. Soils subject to high normal stresses will have low moisture content and high bulk densities upon failure subject to low normal stresses and the angle of internal friction may thus change. The actual angle of internal friction of the soil is rarely zero and 26. as much as possible0, The angle of internal friction in granular soil is 28. may vary between0 from 500,
It is the ability of soil to transmit moisture in all directions regardless of any gravitational force. Water rises up through the pores of the soil due to capillary attraction. The maximum theoretical height of capillary rise depends on the pressure that forces water into the soil, and this force increases as the soil particles decrease in size. Capillary growth in a soil when wet can be as high as 4 to 5 times the height of capillary growth in the same soil when it is dry.
There is no capillary growth in coarse gravel; Contains up to 30 cm in coarse sand; In fine sand and clay capillary growth is up to 1.2 m but in dry sand there is very little capillary.
The capillary growth in clay can range from 0.9 to 1.2 m but the value of pure clay is very low.
The permeability of a soil is the rate at which water flows through it under the action of a hydraulic gradient. The passage of moisture through the inter-spaces or pores of the soil is calledpercolation, Soil that is porous enough to permeate is calledpenetrant‘ or ‘eligible for admission‘, while those which do not allow the passage of water are called ‘.Predominant‘ or ‘impenetrable, The flow rate is directly proportional to the top of the water.
Permeability is a property of soil mass and not of individual particles. The permeability of cohesive soils is normally very low. Knowledge of permeability is essential not only for seepage, drainage and groundwater problems but also for the rate of settlement of structures on saturated soils.
A soil is said to be elastic when it loses volume (or changes shape and bulk) when a load is applied, but quickly regains its initial volume when the load is removed. The most important characteristic of the elastic behavior of soil is that no matter how many times loads are applied to it, provided that the established stress in the soil does not exceed the yield stress, the soil is not deformed permanently. This elastic behavior is characteristic of peat.
Gravel, sand and silt are incompressible, i.e. if a moist mass of those materials is subjected to compression; They do not undergo any significant volume change. Clays are compressible, i.e. if a moist mass of clay is subjected to compression, moisture and air can be expelled, resulting in a volume loss that does not recover immediately when the compressive load is withdrawn. The amount of reduction per unit increase of pressure is defined as the compressibility of the soil, and a measure of the rate at which consolidation proceeds ‘given by’coefficient of consolidation‘Of clay. The compressibility of sand and silt varies with density and the compressibility of soil varies directly with water content and inversely with cohesive strength.