A large volume trim blast for slope stabilization, US 97A near Wenatchee, Washington

摘要

The recent removal of a roughly 4,000 cubic yard mass by trim blasting was successfully completed for a 170 foot high rock slope located on US 97 A just north of Wenatchee, Washington. The mass was bound by a very persistent discontinuity that dipped toward the highway at about 55 degrees. The large bolting forces required to stabilize the mass coupled with the apparent instability were determining factors to remove the mass. Overhead high voltage transmission and fiber optic lines, a railroad, and the Columbia River were immediately adjacent to the slope and highway. The blast design entailed drilling 130 blast holes, during which time the mass was remotely and continuously monitored with tensiometers. Blast holes were carefully located and logged, and decked explosives and stemming were tailored to each hole. Each hole was individually delayed in a pattern to optimize the movement and fragmentation of the debris. The mass was draped with geotextile and chainlink fabric to control flyrock, and a temporary earthen berm between the highway and railroad helped contain the debris. The design efforts resulted in near complete containment of debris behind the berm, no damage to the railroad or utility lines, very little flyrock, and excellent fragmentation. The slope was scaled, and the highway was reopened to two-way traffic within 8 hours of the blast.