WorldWide Drilling Resource

68 DECEMBER 2021 WorldWide Drilling Resource® RENEW - SUBSCRIBE NOW! What is Underfoot Determines What is Constructed on Top Compiled by the Editorial Staff of WorldWide Drilling Resource® There are several ground investigation techniques that can be used either individually or in combination, and project managers should consider the specific information needed to reduce potential project risks rather than just the costs. Investigations will also allow them to mitigate any issues arising during construction work, eliminating larger financial costs and lost time. Principal reasons for investigations are to determine the makeup of the soil strata, measure the level of bedrock, obtain samples of soil and rock for analysis, and identify the groundwater conditions. The major question is what type of ground investigation to conduct. Is gathering a variety of different samples on a budget the goal? Or does the investigation need to be clean, quick, and powerful enough to drill through overburdened deposits? Perhaps the easiest method for investigating is trial pits, a cost-effective way of obtaining samples. A relatively rapid investigation of shallow soil strata, typically to depths of around 10 to 13 feet, is performed. This can be particularly useful where buried structures or contamination is suspected or needs further investigation. Minimal equipment is needed, saving on fuel and transport costs. Pits can be excavated by backhoe excavators or by hand, which is usually reserved for special situations where subsurface services or structures are expected. However, these pits do not yield the same depth of information as other investigatory drilling methods. Window sampling can also be a quick, economical, minimally-invasive way to get soil samples for small-scale projects. Inserting tubes of varying lengths into the ground delivers high-quality sample results. This method tends to be used for fairly shallow substrates and formations due to its depth limit of around 16 feet. Window sampling can be achieved using either handheld pneumatic samplers or tracked percussive samplers. Cable percussion drilling, also known as shell and auger boring, is a versatile method of ground investigation. This technique offers flexible performance across both consolidated and unconsolidated superficial formations. Suitable for sites with poor access or low headroom, it uses a trailer-mounted tripod rig to drill boreholes of up to 17 inches in diameter and depths of up to 230 feet. A range of in situ tests can be performed in these boreholes, and disturbed or undisturbed soil samples can be recovered. Instrumentation such as gas/groundwater observation wells, piezometers, inclinometers, and settlement gauges can also be installed. When necessary to investigate the properties of underlying rock or other solid geological formations such as dense gravel, rotary drilling can be used. Multiple types of rotary drilling, including but not limited to mud and air flush, are used in typical geotechnical settings. By lowering a core barrel into the borehole and circulating a flush or air/mist or water, this method brings rock cores to the surface for examination and logging. Depths of up to 328 feet can be achieved with this fast, flexible, and reliable form of drilling. Sonic drilling is another type of ground investigation. Using high-frequency energy generated inside a sonic head, which rapidly vibrates to advance a core barrel downward through a substrate, this technique is particularly suited to overburdened and superficial deposits. The vibrations fluidize soil particles at the drill face, allowing easy penetration through most geological formations. Some benefits of this method include an elevated level of safety, fast process, clean work, return of high-quality samples, minimal borehole deviation, and less environmental impact. Whichever method of ground investigation is selected for the present geological conditions and construction project, the results should be able to provide adequate information for successful project completion. The level of detail and information quality about ground conditions will inform the project team, giving them the ability to develop an appropriate, efficient, and easy-to-implement design. Photo courtesy of the Arkansas Department of Transportation. C&G Visit us at Booth 1538

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