The interconnection of vesicles in basaltic flows greatly affects the engineering properties such as uniaxial compressive strength, modulus of elasticity, Poisson’s ratio, tensile strength and sonic velocities. Sometimes these vesicles are filled with secondary minerals such as quartz/olivine/calcite form as amygdules (which are impermeable). In the present study, to understand effect of porosity, vesicular and amygdular basaltic flows collected from central and west-central India were investigated for these engineering properties and correlated with apparent porosity of core samples. It is observed that a good level of correlation is obtained for uniaxial compressive strength (UCS), elastic modulus (E) and Poisson’s ratio in vesicular basalts when porosity >8-10%. In case of Brazilian strengths a linearly downward trend is observed with the increase in porosity values. And, no significant correlation is observed for waves’ velocities in both variants of basalts.

To measure the tensile strength, the load applied can be either tensile or compressive. The application of compressive load in order to induce tensile stresses can be either through point load (diametral loading) or line load. In this paper, for twelve variants of basalt and twelve variants of gneiss, an attempt has been made to correlate the two loads, i.e., point load and line load, to induce tensile failure. For each of the variants, the correlation between the point load and the line load data is discussed on the basis of recommended parameters only; in other words, the inherent variability of a given variant is not in focus here. The reported work also draws from previous researches and codes of practice. In case of Basalts, the ratios are ranging from 0.65 to 0.78. While, due to anisotropy in Gneisses, the ratio is ranging from 0.79 to 2.28, but, it is also observed that the ratio is decreasing to 0.80 as the value of anisotropy index is approaching unity. However, it can easily be inferred from the study that the ratio is rock type specific.

Sandstones from seven different hydroelectric projects have been assessed to compare their water-related properties and engineering parameters and the comprehensive analysis has been presented. The study has been done by categorizing the sandstones in to three categories i.e. weak, moderate & strong sandstones. The study leads to four broad inferences: (1), there could be very large variation between two sandstones; e.g., here, sandstone S2, S4 & S5, vis-à-vis other two strong sandstones, is superior in all respects. (2), the four weak sandstones differ in respect of some – not all – properties and parameters. (3), none of the four weak sandstones is better than the other two in respect of all properties and parameters. (4), moderate sandstone shows higher values of shear strength parameters in comparison to all the sandstones (including stronger sandstones also) except S3 strong sandstone. In respect of individual properties, the grain density of all sandstones is similar, though their bulk densities, apparent porosity and water content show great variation. The weak, moderate and strong sandstones show qualitative difference in their uniaxial compressive strength and wave velocity (compression and shear, both); and the two are directly proportional. The study clearly demonstrates that there is no one-to-one correspondence between any two properties and parameters, but there is a diffused and/ or qualitative relationship between different sandstones, or certain properties and parameters of a particular variant.