Question

In your opinion, what is the importance of studying soil mechanics?       Justify your opinion by giving any two practical examples.

Answer 1

Soil mechanics is a branch of civil engineering that deals with engineering application of law of mechanics and hydraulics in soils. From the ancient times, soil has been most important raw material for construction purpose. Every structure, whether be it dam or embankment, buildings, roads or railways are founded on soils. All the loads structure carry, ultimately has to bear by soil or earth. Failure of soil in any case may lead to collapse of the structure, which is a dangerous scenario.

Soil, which is the base of any structure, should have that properties to bear the ultimate load in worst condition also. Soil has properties such as bearing capacity, permeability, cohesion ,etc .As the technology is taking pace, more and more efforts are being put to improve the engineering properties of soil. So, we study soil mechanics

Let us look at some examples in real life

• Consider a case of floating raft

In many cases , when earth has low bearing strata, raft foundation is used to distribute load to a greater area. ( In raft foundation, the total area covering the structure is excavated and footing is spread all over the area, on which column is raised. ) Now, consider this concept, the strata upto which soil is excavated has carried the load of excavated soil. If the structure carries the load same of magnitude of excavated soil, then net pressure on the strata will be zero.

qnet = qc - YDf

qnet = net pressure on soil

Y = density of soil

Df = depth of foundation

YDf = pressure of excavated soil

qc = pressure due to footing (load on structure)

Now, from the above concept if pressure due to footing will be equal to weight of excavated soil (pressure of excavated soil ) , OR ,

qc = YDf

Therefore , qnet = 0

That is net pressure on soil is zero.

Although , this is not completely true in real case due to some unanticipated load or unbalanced moments, but we get floating raft upto some extent.

• Now consider case of road construction

Road is also founded on soils, but we have to compact the soils so that there will be no settlements of road, as settlement of roads may induce cracks on roads. To achieve optimum compaction, we often take soil sample and test in lab. The test gives us the relation between water content and dry unit weight. Now from test in laboratory, we find maximum dry density for optimum moisture content. If the density will be lower than this value, then soil can be compressed under traffic load, so this test is necessary. Rollers are also different types for different of soils.For example, for clayey soils, Sheepfoot rollers are preferred, as they have kneading action and compress more than any other type of roller.

• Some other application are - (i) application in earth pressure for retaining walls. (ii) Application in stability of slopes in prediction or prevention of landslides or sloping earth. (iii) Application in seepage analysis of dams and embankments, uplift pressures. (iv) vibration due to heavy machinery or even earthquake.