Question

Describe laboratory and geophysical methods to measure intact rock strength. Explain why measurements of rock strength alone are insufficient to assess the difficulty of excavation and the likely stability of the rock mass during and after construction.

Answer 1

● Laboratory methods:-

In the destructive methods,point load index tests, splitting tensile strength tests, block punch index tests are conducted.

In the non-destructive methods, Schmidt hammer and ultrasonic pulse velocity tests are performed.

● Geophysical methods:-

IMPACT METHODS (standard geological hammer of about 1 kg used) which fall from a height and by some calibration we can measure the strength of intact rock. Generally geological Strength Index is used in this method.

● There are some other important properties of intact rocks which govern more in excavation and stability of rock mass before and after like texture, minor lithological characteristis, density, porosity, hardness, and deformability.​​​​​

Like in excavation hardness is most important property which governs method and cost of the excavation.

Like in stability of intact rocks the defomability, density, etc are also important along with strength.

So that only rock strength alone is insufficient to assess the difficulty of excavation and stability after and before the construction.

Thank you.