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Recommended policies and procedures for soil sampling
Due to the varying complexity of projects and subsurface conditions, it is difficult to establish a rigid format to be followed in conducting geotechnical investigations. However, there are fundamental, required data that should be obtained and basic steps that should be followed for any project investigation. The collected field data and assessments are the basis for all subsequent engineering decisions, and, as such, are of paramount importance to the design and success of a project. By following these requirements and steps, it will be possible to standardize procedures, and considerably reduce time and expense that would be required to return to the project site and obtain important information not obtained during the initial investigation. The following are fundamental. required data that should be obtained during a geotechnical investigation:
* Identification and delineation of existing soil and rock strata.
* Condition and performance of existing transportation structures.
* Qualitative and quantitative information on the character and engineering properties of the soil and rock strata.
* Ground water levels and environmental concerns.
* Slope stability condition, faults and other geologic hazards or constraints.
When it comes to soil sampling, all samples should be properly preserved and carefully transported to the laboratory to maintain sample integrity.
Disturbed Sampling
Disturbed sampling refers to methods of retrieving samples that incidentally cause the material to be remolded or at least partially altered. It should be understood that disturbed samples generally are not suitable for specialized tests requiring undisturbed soil specimens. However, disturbed samples have value for many geotechnical tests and usually are easier to obtain.
Bulk samples can provide a large amount of representative soil for compaction and sub-grade testing. Bag samples usually are obtained from test pits. In some cases, bulk samples can be obtained during auger drilling, collecting materials as they come to the surface in the flight of the auger. The auger method is less desirable because the depths of the sample cannot be accurately defined and some mixing of the soil occurs. A preferred approach when using an auger is to drill a shallow hole, then to remove the auger and collect a sample from the sidewall of the hole (after first clearing the smear zone). The quantity...