Question

Outline the operational principles, relative advantages and disadvantages of the range of drilling methods for sampling unconsolidated material, solid rock and marine sediments.

Answer 1

Soil-Sampling Equipment

Drilling methods, as well as the equipment used, continue to evolve. Traditional methods include auguring, bentonite mud drilling, and rock core drilling. Equipment has evolved to obtain the right type of sample. These include augers, split-spoon samplers, and Shelby tubes. Much depends on whether an undisturbed sample is required, or whether a disturbed sample is sufficient. Procedures for using soil-sampling equipment are provided by the American Association of State Highway and Transportation Officials (AASHTO) and the American Society for Testing and Materials (ASTM). These assure that the samples are obtained with appropriate accuracy and consistency from one project to another, across the country. In this age of the internet, images of all the various types of drilling equipment and soil-sampling devices abound.there are a wide range of reasons that soil needs to be tested. For some applications, it is important to get data about soil that is sub-surface, and in many cases getting data from deep under a site can be useful or essential. When most people imagine how you would gather data from soil that is deep underground, they imagine using a drilling rig of some kind. Sure enough, there are special kinds of boring tools that will let you drill deep into the ground and extract a sample of the soil at depth for analysis.

Advantages & Disadvantages of Geotechnical Boring

Using Geotechnical Boring, whether it be small-diameter or large-diameter equipment allows users to see the solid that is extracted. This can be useful for gaining an understanding of the sub-surface topology if a goal is to create a multi-dimensional map of the subsurface Geological conditions. There are significant disadvantages however to using Geotechnical Boring to obtain soil samples for testing. One disadvantage is that the operation of boring is for obtaining samples only, you can't gather data from the boring activity itself and therefore all of this investment in equipment, labor and time provides value only in that it presents a sample for testing. Another disadvantage is that the soil being sampled then needs to be tested using some type of laboratory equipment. This often means removing a large number of samples from the site, getting them safely in an organized way to a lab facility somewhere, hopefully nearby, and waiting for the lab results to come back. If there are apparent conflicts in data, or a particular part of the site needs more evaluation, the entire process needs to be started up from scratch again. Perhaps the biggest disadvantage with Geotechnical Boring is that the act of boring for the sample and extracting it can substantially change the physical characteristics of the sample itself. The sample can be 'disturbed' in that at a boundary layer between two soil types, soils can become intermixed and a clear boundary condition made harder to identify. The sample is likely loosened and soil that is really quite solid can test as less dense or cohesive than it actually is. The act of boring can affect the grain size of the sample being extracted.

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