Soil properties can be measured in many ways and for a lot of different purposes, both in the field, or by taking samples from site and bringing them to laboratory for more rigorous testing. We have already talked about many soil properties before in this book.
Some tests are simple enough that can be performed in the field, or, it just makes more sense to do them in the field with sophisticated equipment. This is because many times it is important to keep the natural state of soil, since disturbing the soil would cause significant changes to one or more of these properties.
Or sometimes, samples can carefully be extracted from the soil, making sure to cause very little to no disturbance. After that they can be carefully stored, and transported to lab. These are called undisturbed samples. There are different methods available for obtaining undisturbed samples, but operator skill and equipment condition also plays an important role here. Samples should not be stored for extended periods of time and should be tested as soon as possible. If long duration storage is needed, care must be taken so as not to let the water content of the sample to change and keep it as close as possible to its natural temperature conditions.
Subsurface investigation and soil testing can seem to be expensive at first, but be sure that it is much, much cheaper in comparison to cost of the failure of a structure, after a project is completed or when it is underway. A considerable portion of construction claims stem from inadequate subsurface investigation or improper soil testing. Therefore, great care must be taken when obtaining subsurface information and testing soils, or, making sure that the soil properties at a project site is known with sufficient certainty from previously obtained data from prior work. The skills of engineer and other personell who perform these tests, and condition and maintenance of testing equipment are also important as it is very easy to obtain inaccurate or misleading results from soil tests. So, to put it in another way, the real challenge is that these tests aim to obtain sensitive data, which can be very easily affected from so many things, from a natural and highly variable material such as soil. As we mentioned before, while introducing categories of civil engineering, we said that although all civil engineers in any sub branch use their engineering judgment all the time, for a geotechnical engineer this is probably the highest of all. It is not uncommon for a geotechnical or civil engineering consulting firm to experience difficulty in finding a skilled, well educated and experienced geotechnical engineer, or field or lab technicians.
Now let’s discuss field and lab tests for both soils and rocks below:
In the next post of this series, we will discuss “Field (in-situ) Soil Tests”