Empirical Relationship between Rock Structure Rating and Modulus of Deformation

During the early stages of construction of a railway line in southeast India, the tunneling works encountered numerous problems, such as rock falls, major water inflow, etc. In order to progress the works, it was necessary to undertake thorough classification of the rock masses and to obtain values of the in situ modulus of deformation for inputting into numerical analyses. It was not feasible to conduct a large number of in situ determinations of the modulus of deformation. Hence, an attempt was made to establish an empirical relationship between rock structure rating and modulus of deformation (Em) for the rock masses through which the railway passed. This was done using data from tests conducted on rock samples taken from 45 boreholes at various locations along the railway line, particularly in tunnel sections where distress was observed.