New engineering geological weathering classifications for granitoid rocks

•A triangular weathering classification with 19 parts was proposed.•Among physico-mechanical parameters, σc, Is, Vp and QAI are selected for the determination of weathering degrees.•Microfracture index and decomposition index were used to define weathering types.•The proposed classifications were supported by other researcher's works.

In this research, several physico-mechanical properties are measured on three types of Alvand granitoid rocks across five weathering grades ranging from fresh to completely weathered rocks. Also, weathering processes of the rocks are evaluated by petrographic studies. It is evident that a realistic weathering classification is necessary, mostly for establishing the geotechnical models in engineering geological studies. For this reason, development of a quantitative weathering classification is the main purpose of our study. In the proposed triangular-weathering classification diagrams, four index tests, including uniaxial compressive strength, point load strength, P-wave velocity and quick water absorption, are selected to predict weathering grades. Also, types of weathering have been determined using two petrographic indices. The new triangular-engineering, geological-weathering classifications are supported by other researchers' reported data. The obtained results indicate that the classifications can be used for a wide range of granitoid rocks.