For the design and stability analysis of hydroelectric projects, dams and other hydraulic structures, the parameters which are utmost needed are modulus of elasticity and Poissons ratio. In literature, the classical relationships for the estimation of modulus of elasticity (dynamic) and Poissons ratio (dynamic) employing compression wave velocity and shear wave velocity, have been in existence for long. The methods to determine the velocity of propagation of elastic waves in laboratory rock testing have been described in "ISRM Suggested Methods".
However, there is paucity of data of the non-destructive technique of testing for laboratory evaluation of properties of rocks, in the literature.
In this paper, the large body of data of compression wave velocity and shear wave velocity, based on the high frequency ultrasonic pulse technique are presented. The waves' velocity data, pertaining to different Indian rocks tested at Central Soil and Materials Research Station, New Delhi, along with the data of destructive testing conducted on the specimens, subsequently, help us arrive at the following conclusions:
- The assumptions underlying the relationships for the estimation of modulus of elasticity and Poissons ratio, are seldom valid. Hence, the same shall be employed with great caution and scepticism, and only if the validity of assumptions, within the acceptable deviations, is established.
- To determine the velocity of propagation of elastic waves through rock specimens, before destructive testing is eminently desirable for the following reasons:
- It helps in the selection of representative rock specimens for laboratory testing.
- Being indicative of the variations between rock cores, it helps us investigate the reasons, thereof.
- The data helps us in the interpretation of data obtained from destructive testing, and helps in arriving at the recommended parameters.
- The data is also employed for establishing relationships between velocity of propagation of elastic wave and modulus of elasticity.
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