During collection of soil samples from either shallow or deep location, there may have disturbance from small to large degree. When boring is of wash boring, a suspension of soil is collected; obviously this is a very disturbed sample. This method represents a soil that has almost lost all ambient properties (completely disturbed structure, altered natural moisture content etc); only provides information about changes in the layers.
With this complete disturbance, some methods provides less disturbed sample and there have some special method that provides least disturbed sample. There have some special method that provides nearly undisturbed sample. We have discussed about block sampling in our preceding post.
A soil sample may be disturbed in three consecutive stages either in any one stage or may be in combination of stages. These are:
a. Disturbance before sampling
b. Disturbance during sampling
c. Disturbance after sampling
Disturbance before sampling
During sampling generally we remove or cut out soils over the sample at desired depth. This method reduces vertical stress over the sample within a short duration reducing overburden pressure quickly. In some cases, soil layer beneath the sample may be deflected up for the same consequence of stress relief. In some sampling operation continuous collection of samples is applied depending on extent and requirement of soil investigation. In continuous sampling process, additional disturbance is observed due to shearing of previous sample by applying torsion to separate it from parent soil.
Next two disturbance phenomena will be discussed in our next part of this topic. In our upcoming post we will discuss about sample disturbance parameters that is used conveniently for determination of degree disturbance of a soil sample.