Relationships among mechanical, physical and petrographic properties of Siwalik sandstones, Central Nepal Sub-Himalayas

Mechanical and physical characteristics of rocks generally depend on their composition and texture, because they are reflective of their environments during sedimentation, diagenesis and weathering in each location. To understand this, relationships between mechanical and physical indices and composition and texture have been analyzed using several rock samples obtained from Mio-Pleistocene sandstone sequence of the Siwalik Group, widely distributed in foothills of the Nepal Himalayas.Sandstones are quartzo-feldspathic to quartzo-lithic and quartzo-feldspathilithic. Cement, matrix and void vary from 6 to 41%, 0 to 18% and 1 to 12%, respectively. Ferroan calcitic and siliceous cements are the dominant cements, and their ratio to total cement varies from 0.2 to 1.0. Packing density of sandstones ranges from 59 to 95%. Clasts are loosely to closely packed and are weakly to strongly bonded by cement.Results of correlation analyses show that sandstones strongly depend on several indices, that is percent void, strong cement over total cement, strong over weak contacts, concavo–convex contacts and packing density, most of which are measured on thin sections. Contrarily, they depend little on grain size, shape, mineralogical maturity index and the other petrographic indices. Increased interlocking and strong cementing with reduced void tends to possess high densities, low porosity and offer good resistance against deformation. Therefore, proportion of strong cement over total cement, void content, strong over weak contacts, grain-to-void contact, concavo–convex contact and packing density are meaningful indices considering the sandstones of the Siwalik Group.Based on the multiple regression, correlation analyses and then stepwise multiple regression analysis, some regression equations with significant explanatory indices are indicated for estimating mechanical and physical properties. In other words, such relationships may be useful in estimating mechanical and physical properties using the significant petrographic indices.