Relationships of the Physical and Mechanical Properties Obtained in Ignimbrites from a Tunnel in Morelia, Mexico

Tunnel construction is important to reduce the length of the geometric road design as well as the environmental impact. However, its construction is one of the most complex challenges due to the variability of the geotechnical properties. Stability of the tunnels in rock can be compromised for the rock mass deterioration which can cause faults during and after construction. Deterioration rate depends on the rock properties together with the environmental factors. Rock deterioration predictions can be achieved by in situ explorations and by performing laboratory tests. One important test is the slake durability, since it considers wetting and drying cycles subjected to the material wastage. This paper is focused on determining and obtaining relationships of the durability of ignimbrites from Morelia, Mexico. The ignimbrite was obtained from one geotechnical borehole of 100 m of length on the axis of a road tunnel and the physical and mechanical properties of the ignimbrites were determined, hence the deterioration of the rocks. This last, was measured using five cycles instead of the two cycles considered in the Normative. Results obtained show that from the third cycle, a constant deterioration of the rock is observed impacting in the slake durability index (I_d) and furthermore, it depends in the rock hardness. The I_d after the fifth cycle (I_d5) was associated to estimate the physical and mechanical properties of the ignimbrites. It was found that the increase in I_d5 correlates with the increase in density, compressive strength, tensile strength, P-wave velocity and decrease in porosity and absorption.