Soil Investigation

Soil And Foundation 

  A surface and subsurface investigation looks at a number of factors that include but is not limited to, water drainage, water tables, topography, soil types and characteristics, and other laboratory test  that are required to ascertain the fitness and suitability of the soil for support of the proposed structural.

 We made mention of some of these topics earlier, but we should dig a little deeper to uncover some of the hidden effects that take place under different loads and stresses with different soil types; for example; gravel to clay mixtures or silty soils with a high sand or clay mixtures, and how it reacts when these stresses and loads are applied.

Classification and Description

  Soils consist of grains; rock fragments and clay particles, with water and gas, either air or condensation, these particles are trapped in the void spaces between the grains. A soil classification scheme is used to separate soils into broad groups each with broad similiar type and behaviour.

  The different classification schemes fall under, agricultural: based on how soil supports crops. Geological: based on the age of the deposit or nature of grain. Civil Engineering: based on mechanical behaviour of the soil and many others. The subject of soil is vast in scope and for our purposes we don't need to go into all the technical aspects and breakdown sciences. but we will investigate some basic areas and facts about soil that is of interest and specific to what we, in our endeavors, will lead toward accomplishing our goal. 

  Soil description is essentially a catalogue of what soil is and describe the soils features. There are several of these schemes available; published in the National Standard, and to some extent reflect the characteristics of most common soils in the region. Consult the relevant standard for the region where you work.

For a concise and in-depth study of soil you can go to or consult:

• The United States Department of Agriculture, (USDA). Natural Resources Conservation Services, (NRCS) website.
• For Engineering; the Unified Soil Classification System (USCS)
• Soil Mechanics; By R.F. CRAIG
• Geo-technical Materials in Construction; By Marion P. Rollings, P.E. and Raymond S. Rollings, Jr., P.E.
• The Mechanics of Soils and Foundations; By John Atkinson

  External loads and water pressure interact with each other to produce a stress that is effective in controlling soil behaviour and as external loads are applied, compression of soil volume occurs and the grains rearrange themselves and the void spaces change from compaction.

  Soil shearing is basically frictional so that strength increases with normal stress, and with depth in the ground. Soil stiffness also increases with normal stress and depth. Combining these basic features of soil behaviour leads to the observation that soil strength and stiffness decrease with increasing water pressure and with increasing water content. 

  Soil compression and distortion are generally not fully recoverable on unloading, so soil is essentially inelastic. This is a consequence of the mechanics of compression by rearrangement of the grains; they do not un-rearrange on unloading.