A large number of river valley projects are being developed in the Himalayan region of Indian subcontinent. Most of the rocks show the strain softening in their behaviour. The paper presents the characterization of three types of sandstones viz., Kota sandstone, Dholpur sandstone and Pancheswar sandstone using closed-loop servo-controlled testing machine in the laboratory and their constitutive modeling. The testing on the sandstones is performed using strain controlled loading under unconfined state and confining pressures varying from 5 MPa to 57 MPa. The brittle to ductile transitions is observed for Dholpur and Pancheswar sandstones. The effect of softening is more on fine grained sandstones than that on coarse grained sandstone. The behaviour of sandstones is predicted using Mohr-Coulomb strain softening model available in FLAC. The material parameters for the model are determined from the experimental results. The stress-strain-volume change response of the sandstones is then predicted using the material parameters and is compared with the experimentally observed results. The predicted results and observed responses are generally in good agreement. The effect of confining pressures on modulus of elasticity and Poisson's ratio of sandstones is also studied. The equations between modulus of elasticity and confining pressures and Poisson's ratio and confining pressures are also proposed. The proposed equations are very promising and can be used for field problems.
Many hydroelectric, transportation, metro rail, nuclear waste repository projects are under construction in the country. The structures for these projects like dams, tunnels, power house caverns are mostly constructed on/in rocks. The rock characterization is the basic input to design these structures. Many rocks generally show strain softening behaviour under loading. Therefore it is very important to incorporate the strain softening behaviour for the analysis and design of these structures. Strain softening is defined as the progressive loss of strength when material is compressed beyond peak [1]. The strain softening has significant impact on tunnel behaviour. Very few researchers have considered the effect of strain softening of rocks on tunnels [2,3,4]. The paper presents the characterization of three types of sandstones viz., Kota sandstone, Dholpur sandstone and Pancheswar sandstone using closed-loop servo-controlled testing machine in the laboratory and their constitutive modelling.
The paper presents the characterization of three types of sandstones viz., Kota sandstone, Dholpur sandstone and Pancheswar sandstone using closed-loop servo-controlled testing machine in the laboratory and their constitutive modeling. Kota sandstone is from Rajasthan belonging to Bhander series of upper Vindhyan and is medium to fine grained with reddish colour with small grey spots. Dholpur sandstone is Pinkish in colour and fine grained and is from Rajasthan. The machine used for testing has a loading capacity of 1000 kN and has loading rate capability in the range of 0.001mm/s to 10 mm/s. The stiffness of the machine is 1700 kN/mm. High pressure triaxial cell which has the capability of applying 0–140 MPa confining pressure and has sufficient space to accommodate extensometers inside, is used for the testing.
