Permanent Deformation Behaviour of Jointed Dolomite Rock Mass

Rock mass is a discontinuous medium with fissures, fractures, joints, bedding planes, and faults. These discontinuities may exist with or without gouge material. Reliable characterisation of the deformation behaviour of jointed rocks is very important for safe design of civil structures on rocks. This behaviour depends on the orientation of joints with respect to loading direction, in-situ stress condition, spacing of joints, and loading area. In-situ testing by means of uniaxial jacking is practised to determine the modulus of rock mass. It is combination of recoverable and permanent deformations. Two cases, viz., Anji Khad Bridge site (case-1) and Kuri-Gongri site (case-2) where jointed dolomites belong to fair and poor rock mass respectively exist are considered for study. Five uniaxial jacking tests were conducted at both the sites, and their results, with focus on the permanent deformation, are discussed in the paper. The average permanent deformation in case-1 is 0.6 mm which is 33% of total deformation in 5th loading cycle. In case-2, average permanent deformation is 0.4 mm, which is 78% of total deformation in 5th loading cycle. The study reveals that though the large portion of deformation is of permanent nature in case-2, the absolute value of deformation is less as compared to case-1. In addition, poor rock mass shows high deformation modulus than fair rock mass, and the details are presented in the paper.