Assessment of Deformability Characteristics of Sandstone by Direct and Indirect Methods—A Case Study

Abstract

Knowledge of the stress–strain properties of rock and rock mass is important for any rock engineering project involving rock. Deformability behaviour of rock or rock mass is denoted by modulus of deformation (E_d). Deformation modulus of intact rock can be evaluated in the laboratory, whereas field testing is required for in-situ modulus of discontinuous rock mass. Uniaxial jacking test is one of the direct methods used for the assessment of in-situ deformation modulus. Indirect methods based on correlations between rock mass classifications and deformation modulus developed by many researchers are also available. Results of 28 in-situ tests conducted on fresh, hard, compact, medium-grained sandstone have been compared with values derived from empirical equations developed by Bieniawski (Int J Rock Mech Min Sci Geomech Abst 15(5):237–247, [9]), Barton et al. (Application of the Q-system in design decisions concerning dimensions and appropriate support for underground installations, pp. 553–561, [13]), Serafim and Pereira (Consideration of the geomechanics classification of Bieniawski, pp. II33–II42, [10]), Barton (The influence of joint properties in modelling jointed rock masses. Balkema, Rotterdam [11], Barton in Estimating Rock Mass Deformation Modulus for Excavation Disturbed Zone Studies, [14]) and Singh and Bhasin (Q-system and deformability of rock mass, pp. 57–67, [15]). Q values of rock mass range from 3.4 to 10. The study reveals that the modulus from indirect estimates gives very high modulus of rock mass. Indirect estimate suggested by Barton (Barton in Estimating Rock Mass Deformation Modulus for Excavation Disturbed Zone Studies, [14]) for excavation disturbed zone, provides value near to direct estimate, i.e. in-situ data set. Study further reveals the empirical equations based on Q-system of rock classifications are valid for Q > 1.