Utilization of Impression Creep Tests as Index Testing Technique in Rock Mechanics and Rock Engineering

Abstract

ABSTRACT: Impression creep devices capable of applying a tip pressure up to 134 MPa for an indenter of 3 mm in diameter as an index creep testing technique was developed by the authors. In this study, a new monitoring system utilized in the impression creep devices is described and its utilization for evaluating creep responses of rock salt samples from Çankin and Tuzköy in Nevçehir Provinces of Turkey and Oya tuff from Tochigi Prefecture in Japan are presented and discussed. The experimental results obtained from impression creep tests are compared with those from conventional creep tests and the suitability of impression creep tests as an index test is explored. The most critical issue in creep tests is the determination of stress level. This issue is investigated theoretically and experimentally. It is suggested the short-term impression test can be utilized for determination of the stress level in impression creep tests. The experimental results clearly demonstrated that both conventional and index tests could be quite comparable and similar type responses are observed and it is concluded that there is a high possibility for the utilization of the impression creep as an index creep test. INTRODUCTION Creep experiments are of paramount importance for assessing the long-term stability of rock engineering structures. ISRM (2007) recognized this issue and a Suggested Method for Creep Test was developed (Aydan et al 2014a). The creep tests have been used in the field of rock mechanics and rock engineering for decades (e.g., Jaeger and Cook 1979; Aydan et al. 2011, 2014a, 2016; Aydan 2016). Apparatuses for creep tests can be of cantilever-type or load/displacement-controlled type. The major issue in creep tests is keeping sustained loading on samples and monitoring of displacement and other parameters throughout experiments without any interruptions. The authors involved with the methods for creep tests under indirect tensile stress regime of Brazilian test, uniaxial and triaxial compression tests and direct shear tests, to determine the creep characteristics of rocks. Ito et al. (2021) have recently developed a new monitoring system for continuous measurement of displacement, acoustic emissions in addition to environmental parameters and utilized in uniaxial compression, Brazilian tensile and bending tests. It is shown that the new monitoring system can measure long-term responses without requiring any conventional power system.