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Uniaxial compressive strength of rock and its determination
It refers to the ultimate breaking strength obtained when the specimen is pressed in only one direction, that is, the pressure strength measured when the rock test is placed between the upper and lower pressure plates of the press until the sample is crushed.
The uniaxial compressive strength test is as follows:
The sample is a cylindrical core or cube with a smooth surface. The length to diameter ratio of the cylinder is 2.5 to 3.0, the cube is 50 mm × 50 mm × 50 mm, and the pressing speed is 1000 to 5000 kg/min. The schematic diagram of the pressure principle is shown in Figure 1.
Figure 1 Schematic diagram of the principle of single-axis compression test
When a sample with a radius of r 0 (cm) and a length of ι 0 (cm) is subjected to p (kg) pressure, the compressive stress is:
σ=40p/πr 0 2 ,MPa
When the longitudinal axis direction is compressed and deformed by Δι, the axial strain is:
ε α =△ι/ι 0
At the same time as the axial compression deformation occurs, the radial direction will expand. If the radial direction has an increment of Δr than the original diameter, the radial strain is:
ε b =△r/r 0
When the rock sample is broken, the ultimate pressure is p pole, then
σ pole = 40p pole / πr 0 2 , MPa
The σ pole is the uniaxial compressive strength of the rock.
In the uniaxial test, the rock stress-strain curve recorded by an electronic instrument such as an x-y function meter is shown in Fig. 2.
Figure 2 Stress-strain curve of uniaxial compression test
If the rock sample while the axial load is applied to the p, is applied on rock samples in certain confining pressure q, the resulting triaxial compressive strength, triaxial compressive strength σ '[sigma] electrode and the uniaxial compressive strength of extremely The relationship can be expressed as:
σ' pole = σ pole + Kq
Where: K - the coefficient related to the nature of the rock, K ≥ 1.