Saguaro Ranch Tunnel
Geotechnical Exploration | Tunnel Project
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Project Description
Saguaro Ranch was a planned exclusive residential development in the Tortolita Mountains near Tucson, Arizona. Development owners envisioned a 690-foot long private roadway tunnel entrance to the community. The tunnel would be drilled through protomylonite granite and, once completed, would have a cross-section approximately 20 feet high by 33 feet wide.
Team Members
Saguaro Ranch Development Corp., Affholder Inc., Brierley Associates, Crux Subsurface Inc.
Crux's Role
Crux provided geotechnical drilling services, completing a single 698-ft horizontal boring through the ridge transected by the tunnel. Initial portal development was provided by the owner to access the proposed top heading area, and the boring was drilled from a 19.7-ft wide preliminary roadway at the portal cut.
Geologic conditions consisted of a protomylonite granite that was highly sheared and altered from faulting. A large, 82-ft-wide major fault zone was encountered within the tunnel alignment. Crux used an HQ3 triple tube coring system and a systematic drilling mud program to accomplish 100% core recovery in zero rock-quality-designation (RQD) rock conditions. Drill fluid circulation was lost approximately 141 ft into the boring and was never recovered.
The boring was drilled starting in the crown of the south portal and terminated at the north portal at the tunnel invert. This resulted in continuous rock mass data from portal to portal, and from crown to invert. Brierley Associates developed an RQD histogram from the core recovery, which was used by Affholder for planning each day's excavation and support cycles for the top heading. The borehole was also used as a pilot tunnel for the rest of the work and as a “burn” hole with the blast pattern.
The exploration program consisted of a single horizontal boring from portal to portal. By eliminating the need to complete a traditional exploration program, which would require multiple vertical borings along the tunnel alignment, Crux was able to reduce the exploration costs, eliminate reclamation costs and provide continuous data along the tunnel alignment.
To request additional information, please use our Contact Page or call 866-CRUXSUB (866-278-9782).
