In civil engineering applications, the crosshole test is the most utilized method to determine the propagation velocities of in situ P and S waves of the different strata and, consequently, to calculate the dynamic elastic parameters of rock or soil samples. Otherwise, its use has been limited just to very important studies since the associated cost is very high for smaller constructions such as residential and ordinary buildings. This is mainly due to the fact that the equipment normally used to perform these tests needs special boreholes, with diameter uncommon in the investigation phase. In order to decrease the crosshole overall cost, a simple and inexpensive seismic source was developed. This source can be used in the same boreholes made during the standard penetration test (SPT). Its maximum external diameter is 40 mm, fitting in a PVC casing of 50 mm external diameter (46 mm internal). At the same time, the casing can be easily installed in a 75 mm (3") maximum diameter, leaving place to fill the annular space with mortar. The seismic source clamps on the borehole wall by a pneumatic system and, by means of a sliding piston, generates mainly S type waves. It has proven to be easy to use besides being lightweight and of small size.
Seismic source; Crosshole; Geotechnical study
