Assessment of rock mass quality is of current interest in planning, design and construction of tunnels, underground powerhouse etc. as well as for foundation purposes. Site characterisation and rock mass classification are two important basis of planning and construction of underground structures for civil, mining and other applications. Assessment of loss of strength in concrete due to aging, fire or any other cause is also of great interest and importance.

Non-destructive testing using principles of engineering geophysics, radar tomography, ground penetrating radar system, electrical resistivity and seismic methods have helped the planners, engineers and scientists in various ways in characterising the rock mass on a macro scale.

The studies can be made both in the field and in the laboratory for quicker estimation of the rock and rock mass quality. These tests have their own advantages, disadvantages and limitations.

In this paper, it is attempted to highlight the importance and limitations of the various techniques of non-destructive testing for rock mechanics investigations used in the lab and the field. These techniques include laboratory determination of P & S wave velocity, laboratory electrical resistivity method, seismic and resistivity method used in the field, radar tomography, GPR system, pile integrity testing and ultrasonic testing of concrete by PUNDIT in the field. The basic principles of the above methods will also be discussed.