INITIAL GROUND SUPPORT FOR TUNNELING IN CENTRAL TEXAS, FROM DESIGNER'S AND OWNER'S PERSPECTIVES

摘要

Geologically, central Texas inherits one of the best tunneling media, "Austin Chalk" alongside some troublesome, weak sedimentary rock or pyroclastic materials, namely Grayson Marl and calcareous claystone or shale. The weak inhomogeneous rock mass usually exhibits relatively short stand-up time, which would require quick installation of closely spaced initial ground support, while Austin Chalk can have stand-up times exceeding several months and no more than spot bolting for stabilization. From a recently completed tunneling project in the Austin Metropolitan area and our literature review of past tunneling projects furnished in central Texas, structural and economical comparisons are made between each routinely used tunnel support system in terms of capacity, deformability, design and construction considerations, cost, and risks associated with unexpected fault zones, slaking, groundwater inflow, and block/rock fall, based on our design experiences. Finally, differences between the designer's and contractor's value engineered ground support systems are discussed from the owner's perspectives.