For deeper targets (up to ~350m depending on local conditions), a special truck mounted accelerated weight hammer is used. Downhole seismic sources can also be implemented such as explosives. For shallow targets (5m - 20m) a sledgehammer is used as the energy source. The actual depth penetrated depends on the surface length of the profile As a rule of thumb, 1/3 length of profile equals the depth penetration. During one day, two to four profiles of approximately 235 meters length can be recorded (shorter and longer profiles can be recorded as well). The refraction method is executed in a quick and simple operation. Finding specific variations in the subsurface.This method is used in construction and infrastructure projects where large area coverage is needed. The product of such a survey is a 2D profile of the velocity variation in depth. These seismic wave velocities are correlated to changes in rock/soil properties, such as hardness and density. The method focuses on both pressure "P" and Shear "S" waves. Seismic refraction and MASW/ReMi methods are used to map contrasts in seismic velocities in the subsurface, usually in the first tens of meters.
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