# Bright Hub Engineering

## Soil Mechanics

written by: drcole89 • edited by: Lamar Stonecypher • updated: 1/16/2010

Soil mechanics is the study of soil and the factors such as bearing capacity, pore water pressure, and effective stress, to name a few, that make soil able to hold up a structure.

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### Soil Mechanics

Soil mechanics is basically the study of the behavior of ground when mechanical loads are applied or water flows through it. This can be used to solve real life problems, and doing so is what is known as geotechnical engineering. Problems that soil knowledge could help to solve are things such as designing a building, a road, a bridge, or maybe a landfill. Basically it involves anything that would need to be built on the ground. Soil, unlike what you might think, is more than just old fashioned brown dirt. It is made up of three phases: solid, liquid, and gas. The solid phase of soil is usually crystalline clay, and non-clay minerals, non-crystalline clay material, organic matter, and salts. That is a lot more than just dirt, and it’s only one part of what soil consists of. The second phase is liquid, which usually just consists of water that contains different types and amounts of dissolved electrolytes. The last phase is gas, and it is usually just good old air.

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### Factors Involved in Soil Mechanics

In soil mechanics, just like all other forms of engineering, there are several factors or variables that you must take into consideration when planning to, say, build a house. The factors that must be taken into consideration are: effective stress, total stress, pore water pressure, sheer strength, consolidation, lateral earth pressure, bearing capacity, slope stability, and lastly permeability and seepage.

Effective stress is the measure of stress on the soil, and it determines where the soil is strong enough to hold your house. Total stress is basically that the total stress that you find when putting together the weight of the soil directly on top of the ground and the weight of your house. Next up is pore water pressure. This is the pressure of the water in the soil. Sheer strength, which is a little more difficult to understand and that only because it is so important when building, is the maximum strength of the soil at the point where it will plastically deform or yield. Consolidation is when the soil loses volume. This happens because something was put on it that makes it sink down, causing the loss of volume. Lateral earth pressure is the amount of pressure that the soil itself will exert perpendicular to gravity or in the horizontal plane. The next one is another that I feel is pretty self explanatory- bearing capacity is the capacity of soil to hold up your house without giving in. Slope stability is the stability of a slope in and on the ground. Finally there is permeability and seepage, permeability is a measure of the ability for liquid to flow through something porous, and seepage is that flow.

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### Soil Mechanics in a Nutshell

This in a nutshell is soil mechanics. I know at first glance or first mention, soil might seem to be a tiny factor in creating the world we live in. Well, let me be the first to tell you it’s not. It is one of the most basic factors, yes, but one of the most important nonetheless. I like to think of it as the foundation of the foundation. Soil mechanics is making creating our world better and easier everyday.