Sunita Mishra

In the present study, a comparative assessment on the performance of conventional and advanced tunnel lining materials subjected to blast loading is done using a three-dimensional non-linear finite element analysis procedure. The conventional tunnel lining materials analyzed herein are plain concrete, steel, reinforced cement concrete, and steel fiber–reinforced concrete. The advanced tunnel lining materials analyzed herein are dytherm, polyurethane, and aluminum syntactic foam sandwich panels with steel–foam–steel composites. The pressure generated by 10 kg Trinitrotoluene (TNT) is applied to each element on the inner wall of the tunnel which has an effect equal to the scaled distance Z = 1.16 m/kg^1/3. Analyses are conducted by varying the thickness of lining materials for a tunnel built in rock domain. The response of the tunnel lining materials, for example, deformation, stresses, and strains generated at different interfaces, is compared with each other to assess the best suitable material for the present blast scenario discussed herein. It is observed from the simulations that the reinforced cement concrete and steel–aluminum syntactic foam (90 µm)–steel are found to be the suitable tunnel lining materials for the present blasting scenario described herein. Moreover, a set of probabilistic analysis is also performed for the suitable tunnel lining materials decided through deterministic analyses using Monte Carlo simulations. The results obtained are normal random distribution curves depicting the extent of deformation in lining materials. A probability failure curve is also proposed for the suitable lining materials.

In the present work, dynamic stress-strain response of compact basalt is tested under high loading rates using 38 mm split Hopkinson pressure bar (SHPB) device. The physical and static mechanical properties of compact basalt, e.g., density, specific gravity, static compressive strength and elastic modulus values are also determined. Petrological studies of compact basalt are carried out through X-ray diffraction (XRD) test and scanning electron microscope (SEM) test. In the SHPB tests, it is observed from the stress-strain response that the dynamic peak stress increases with increasing strain rate however the elastic modulus is nearly constant with increase in strain rate. Dynamic force equilibrium at the incident and transmission bar ends of the rock samples is attained in all tests till the failure of the rock samples. Dynamic increase factor (DIF) for the rock is determined at a particular strain rate by comparing the dynamic to static peak compressive stress. Correlation equation for dynamic strength increase factor with respect to strain rate has been proposed herein.

In the present work, the dynamic stress-strain responses of three types of rock, compact basalt, metadolerite, and granite, are tested under high loading rates using the 38-mm-diameter split Hopkinson pressure bar (SHPB) device for the first time in the literature. The static characterization of the rocks, i.e., the physical and static mechanical properties of the three types of rock, was also determined. Petrological studies of the rocks were carried out through scanning electron microscope and X-ray diffraction tests. In the dynamic tests using the SHPB device, the stress-strain response, dynamic peak stress, and dynamic elastic modulus were studied. The effect of the mineralogy of the rock on peak stress and the dynamic elastic modulus was also studied under varying strain rates. Two correlation equations for the dynamic strength increase factor of compact basalt and granite are proposed herein.