Use of TBM Muck as Construction Material

Tunnel boring machines (TBM�s) are widely used in tunnel construction. The muck they produce is rarely used for construction applications, however, mainly because the suitability of the muck for construction purposes is poorly understood. Yet the muck appears to be of approximately the correct average size for some applications, so if it can be determined to be suitable in other important respects, cost savings can be realized in tunnel construction, because aggregate is a common requirement. A review of standard construction aggregate specifications indicates that minimally processed hardrock TBM muck would be suitable for several construction applications with a minimum of processing: shotcrete, pavement (both asphalt and concrete), structural concrete, and railroad ballast. A brief review of processing options also is discussed, for cases where the TBM muck is nearly, but not quite, suitable. A 0.65 metric ton (1 420 lb) sample of TBM muck generated by a laboratory tunnel boring machine operating in a welded tuff is analyzed and graded for suitability for different construction applications. Also, numerous tunneling projects that use or have studied TBM muck for construction purposes are described.