Abstract:

There are many engineering geological problems in the dam foundation; and one new problem is how to evaluate and determine the mechanical properties of the columnar jointed basalt at the dam abutment. Using the true triaxial apparatus is an available measure to study the engineering geological property of the basalt in so compound field environment with high stress conditions and special rock structures. Based on the investigation and analysis of engineering geological condition in situ, a series of physical model tests by brittle material with the true triaxial apparatus were carried out to find out mechanical properties of columnar jointed basalt. The fracture and deformation mechanism of the sample, that is the compound columnar jointed basalt, was studied. Eight different stress ratios( ) are used in the strength test with the true triaxial apparatus; and the results show that the strength and deformation properties of the compound columnar jointed basalt is influenced by the columnar jointed characteristics and the stress ratios. The stress ratios can influence the value of ultimate breaking load of the rock. The test results show that when the stress ratio is less than 3, the stress ratio and the joints control the value of ultimate breaking load and the failure mode. When the stress ratio is higher than 3, the effect of stress ratio is more obvious than that of the joints. With the increase of stress ratio, the effect of intermediate principal stress varies from confinement to load and the ultimate breaking load and the failure mode varies with the change. Six different load models are used during the test; and the results show that the anisotropy of strength and deformation of the basalt is obvious. But if the microfissure distributing widely in the columna is considered, the columnar jointed basalt can be simplified as lateral isotropy.

Key words: columnar joint, true triaxial apparatus, anisotropy, stress ratio