Just like all the subjects we covered for soil mechanics deal with soil properties, rock mechanics deal with the properties of rocks, in order to utilize them as foundations for our structures, and the same principles apply for determination of those properties, with some minor modifications as required. As in soils, the strength of rock increases with increasing depth, although there are exceptions.
The most significant difference between soil and rock is that rocks are much more rigid than soils and therefore they are far too great foundation materials than soils, in terms of the loads they can support. Because of this, if a rock strata is within reach, utilizing this strength by end bearing piles is always a great option, especially if we plan to build heavy structures.
As in soils, rocks are also analyzed for their bearing strength, settlement and sliding resistance in shear. In addition to most of the similar properties that we have covered in soil mechanics, rocks have different variables such as composition of their faults, fractures and shears, depth of weathering (decomposition of rock into soil), joint orientation and continuity.
Tests to measure rock properties, include below, but for these we will not go into further details:
- Slake Durability Test: Measures resistance of rock to disintegration during wetting drying cycles
- Schmidt Test: Measures hardness of rock
- Sound Velocity Test: Measures p-s waves (earthquake waves) traveling speed in rock
- Anchor / Rockbolt Loading: is used to determine rock anchor capacity
- Flat – Jack Test: is used for in – situ stress measurement of rock
- Pressure Injection: is used to determine rock mass permeability
- Hydrofracturing Test: is used for in – situ stress measurement of rock
In the next post of this series, we will discuss “Earthwork”