On many sites in the Kingdom, drilling reaches rock such as limestone, mudstone or sandstone. A rock layer may be a good founding stratum, or it may be fractured, weak or sensitive to water, and only testing can tell.
Recovering and logging the cores
Cylindrical rock cores are recovered with diamond-bit double-tube core barrels. On site the recovery is measured, along with the rock quality designation (RQD), the share of intact pieces longer than 10 cm in each run, and the rock type, weathering and fracturing are described.
Laboratory tests
- Unconfined compression with modulus of elasticity and Poisson’s ratio: gives the strength of the rock and how it deforms under load.
- Point load test: a quick test that indicates strength and suits irregular samples.
- Indirect tensile (Brazilian) test: measures the tensile strength of the rock.
- Slake durability: shows how much mudrocks and weak rocks break down under repeated wetting and drying.
- Bulk density, specific gravity, absorption and porosity.
How are the results used?
They feed into bearing capacity and founding depth on rock, the design of rock-socketed piles, and the stability of deep excavation faces.