A lightweight composite panel for the repair of cave roofs at the Mogao grottoes,China

Abstract

Erosion of the soft conglomerate of the cliff face at the Mogao grottoes of Dunhuang, China by windblown sand has thinned the rock of the roofs of many upper-level grottoes. In some cases, holes have formed; in others, the danger of roof collapse is imminent. To strengthen weakened roofs and to seal existing holes in an aesthetically acceptable manner, a lightweight, composite reinforcing and capping element was developed. The element, or panel, is made of a metal grid on a wood frame covered by geosynthetic materials, covered with sand and gravel. Potassium silicate is used to bind the sand and pebbles, thus presenting a natural appearance. Where holes exist, the interior is mud plastered on the metal grid. Experiments were conducted in the laboratory and in simulations at the Mogao grottoes to evaluate the concept and design prior to implementation. One field experiment was conducted on the ground to test cohesion and adhesion between the elements of the composite panel. The second experiment was conducted on a simulated cave (a pit in the ground) to test the final design. The method was implemented in Cave 460 in the spring of 1993. Part of the roof of this cave had collapsed, and a composite panel 4.3 × 3.1m was installed. Advantages of the method are durability of materials, light weight and a natural appearance externally, with virtually no visual intrusion on the site. After five years the performance of the panel has been entirely satisfactory. The technique will be implemented above the threatened caves at the site.