Post-Failure Behavior of Rocks under Uniaxial Com­ pression, Obtained through an Artificially Increased Stiffness Testing Machine

Abstract

Common observation shows that underground excavations are surrounded, sornetirnes inevitably, by fractured rock yet those opennings do not collapse. Safe and econornic design of rnuch underground structures depends on the fractured rock behavior and consideration of a strength of failed rock is of great praticai irnportance, as increasing safety is allways desired.

A better understanding of rock behavior in failure and in post-failure siluations is recommended, but thisstudy is only feasible through very high stiffness loading system in order to record the complets   stress-strain characteristics. To obtain the same information out of conventional testing machines, artificial systems are available to increase their stiffness so that applied strains be independent on rock behavior.

In this paper three mechanical systems allowing the possibility of rising the stiffness of a common testing machine are utilized in uniaxial compression tests performed with two common rock types. Recording the complete stress-strain curves is achieved through both direct and indirect methods. A specific stiffness cell was constructed at the University of Luanda to standardize such measurements in the future, and experimental results are analyzed in terms of theoretical concepts of brittle failure criteria.