Hammer blow technique

If the object is only to investigate the depth of overburden, geophysical methods can advantageously be applied. In a case where the overburden is of a loose or fairly soft character, seismic measurements, more particularly by means of the hammer blow technique, are very suitable, as they can be performed quickly and inexpensively. However, this technique does require a relatively level surface of the limestone. If the surface is very irregular, e.g., as a result of underground water percolation, this method of investigation cannot be used. The application of the hammer blow technique in conjunction with penetration tests is especially to be recommended. 

With greater overburden thicknesses it is alternatively possible to use a geo-electric method (based on contrasts in theelectrical resistivity of strata), which can be very effective more particularly when used in combination with the hammer blow technique. 

Hammer blow and geo-electric methods represent two simple geophysical techniques which can be used with relatively little effort and expense for determining the depth of overburden, the thickness of consolidated and unconsolidated strata, the detection of waterbearing strata, and ascertaining the ground water table. In addition, determination of the velocity of sound transmission in the ground provides indications as to whether the material can be broken out by ripping. 

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