Excavation of an Underground Theater below the St

This paper describes part of the construction of a second theater in the underground museum complex, below the Gateway Arch in St Louis. Given the needs for relatively quiet, non-intrusive rock removal, and yet precise cutting within the museum complex a method of using low pressure (35 MPa) abrasive laden waterjets was developed for cutting the vertical walls of the theater down to a depth of 4.5 m., within an accuracy of 5 cm. (2 cm. was sustained in most cases). In order to emplace 2.5 cm diameter resinbonded rock bolts an abrasive waterjet drill was also developed and field tested. The main volume of the rock within the room was concurrently excavated using a method known as CUSP, where the rock is drilled to a depth of 0.6 m., split using a DARDA rock splitter, and the resulting crack grown out to delineate 450 kg. blocks using an 7.5 kw impact breaker attached to 743 series Bobcat. This system proved effective in breaking out the blocks in rock from plain dolomite to layers which included beds of chert several centimeters thick. Production rates within the room were constrained by the limited space available but exceeded 3.2 cu m/hr. Considerable clay was encountered in the excavation , as were significant layers of chert. Methods of analyzing and dealing with these are included in this case history.