Seismic refraction in adit is conducted to determine the primary wave velocity and the shear wave velocity profiles along the adit walls. These parameters are used to calculate dynamic elastic modulus, shear modulus, Poisson ratio, … In addition, they also utilize to calculate the thickness of zone of affected explosives while digging.
To plant geophones on adit-walls and bed, we need to drill small holes with diameter of 42 mm and depth of 100 mm, above adit-bed about 1 m. Distance between holes is about 1m.
Seismic source utilizing in adit is hammer or explosives. Geophones and impact points place on the adit-wall and bed. One spread may be consist of 24 geophones or less depend on the length of adit. Geophone spacing is about 1 m, source spacing is about 11.5m.
Seismic data are displayed on Pickwin module of SeisImager 2D to pick the traveltime of primary wave and shear wave. These traveltimes are used to calculate primary and shear wave velocity, elastic modulus, Poisson ratio and thickness of layer affected by digging adit.
Fieldwork, processing and interpretation of seismic refraction in adit are carried out in accordance with ASTM 5777 – 00: Standard Guide for Using Seismic Refraction Method for Subsurface Investigation.