Abstract: The Characterization of Rock Masses Excavated by Tunnel Boring Machine (TBM)

Chris Laughton

In recent years Tunnel Boring Machines (TBMs) have become the "instrument of choice" for the mining of longer tunnels in all types of rock material. However, the rate of progress achieved by TBMs is strongly influenced by rock mass characteristics, such as the intact strength and discontinuity parameters. Many of these characteristics are difficult as predict based on site investigation data alone and renders the accurate prediction of TBM performance highly problematic. At present no single system has been developed to facilitate the proper selection and application of such equipment on the basis of predicted performance.

Work is being performed at the University of Texas at Austin to back-analyze case histories and identify the impact of rock mass characteristics on TBM performance under a variety of rock mass conditions. A TBM tunneling data base has been compiled which reports common rock mass and TRM parameters and the corresponding tunneling performance achieved.

At its most detailed the back-analysis consists of tracking the performance of the machine through short lengths of tunnel (10 meters) referred to as "unit cells." On the basis of this unit cell analysis, relationships are developed between rock mass and TBM performance. The performance and rock mass data are stored in a form which allows for the quantitative summary of rock mass conditions and TBM performance and allows for the simulation of variability under similar rock mass conditions.

The poster will present the methodology developed to systematically register the rock mass parameters within a rock formation, using tunnel mapping as the primary source of "real-scale" rock mass definition.

AAPG Search and Discovery Article #90960©1995 AAPG Southwest Section Meeting, Dallas, Texas