Engineering properties of quartz mica schist

Quartz mica schist, which is a highly anisotropic metamorphic rock, usually presents a geotechnical challenge in construction projects. To ensure a safe and economical design, a comprehensive in situ and laboratory investigation scheme is necessary for projects to be built in quartz mica schist. In this study, such a comprehensive laboratory study of the engineering behavior of quartz mica schist has been carried out. The P-wave velocity tests, tensile and uniaxial compressive strength tests, and creep deformation tests conducted on specimens with differently oriented schistose planes all reveal the strong anisotropic characters of the rock. The relevant crack-initiation stress and crack-damage stress analysis in uniaxial compression test, which has not been previously applied to studying schistose rock, has been performed in the present study. When loading is parallel to schistose planes, crack initiation stress and crack damage stress are lower than those in other loading directions. As the compressive loading is applied parallel to schistose planes, local tensile stresses are preferentially induced normal to the relatively weak schistose planes. Cracks are thus easier to develop than in any other loading directions. Since schistose plane orientation is one of the key factors to control the formation of macro-cracks and hence failures of unloading test specimens, these engineering geological characters should be taken into consideration in engineering design.

Research highlights
► P-wave velocity tests, tensile, compression and creep tests all reveal the strong anisotropic characters of schistose rock.
► The crack-initiation and crack-damage stress analysis performed in the present study is the first of such in schistose rock.
► Schistose plane orientation is one of the key factors to control the macro failures of unloading test specimens.