Rockslope engineering challenges for power transmission lines, Las Vegas, Clark county, Nevada

Design and construction of roads and foundations on steeply dipping slopes and weak bedrock creates challenging rockslope engineering problems because of the kinematic potential for failure into the rock excavations. Nevada Power Company (NPC) is constructing the 83 km (50 mile) Harry Allen Mead (HAMD) 500 kV power transmission line, their largest. Because ideal terrain was occupied by towers owned by another utility, tower pad HAMD 24/1 and access road had to be constructed on the dip slopes of the adjoining ridge. The slopes created design problems because they dip unfavorably into the excavation creating potentially large planar failures and rockfall. During construction NPC encountered engineering and geological challenges, which necessitated design modifications: adversely dipping rock structure, very weak and fractured unstable rock, rockfall, backbreak from preshear blasting, and poor bonding of resin grout. To stabilize the backwall of the tower pad and road, over 1311 m (4300 ft) of rockbolts and dowels were installed.