Assessment of tunnels stability in the Maya archaeological area of Copán, Honduras

Abstract

Copan is an important heritage site known by its preserved Maya ruins and recognized by UNESCO as a World Heritage Property since 1980. To investigate and understand the site development, extensive archaeological tunnels were excavated in the earthen fills of the temples in the twentieth century.Archaeologists found a series of superimposed temples, built one upon another, in a very complex chronological sequence and spatial disposition. Even though the tunnels were initially excavated in the earthen fill without putting in place any supporting structure, masonry lining was applied in parts of the unnels years after they were excavated, in areas that suffered local collapses. Thick walls were built, forming tunnels about 1.0 m wide and 2.0 to 3.0 m high. The excavated soil is unsaturated, and thus has a strength depending on its water content and suction. Since most of the observed collapses take place during raining events, the effect of the change of the saturation degree on tunnels stability was investigated with numerical analyses. As typical in numerical simulations, the positive effects of desaturation were considered in this work through a simplified approach, introducing an 'apparent cohesion'depending on the soil water content. The outcomes indicate that in order to ensure sufficient safety margins in the tunnels, water content within the soil mass close to the tunnels, in critical sections, should be carefully monitored, and drainage in the lined sections should be ensured to avoid direct water pressure on the lining.