INTRODUCTION
Purpose of Wall System There were 2379.88 m (meters) of tied back wall along Interstate 77 in the Capitol Complex area in Charleston, West Virginia. The main purposes of this wall system was for aesthetics, reduction of excavation, saving the forested slopes, and control of sloughage of the back slopes onto the Interstate. Failure At 1 PM on Thanksgiving Day, 1982, 3 wall panels fell from the insitu position onto the interstate in a matter of seconds. See Fig. 1. The total length of wall that fell was 29.25m. The height of the three panels varied from 10.06m to 10.36m and each individual panel had a length along the highway of 9.75m. These were abutting panels that were approximately in the middle of a section of wall 165.81m long. The panels separated from the remainder of the wall at 2 expansion joints that occur at the ends of every 3rd panel. The reinforced portland cement concrete panels were designed on a 76.2mm (millimeter) batter. See Fig. 2 for Wall Dimensions. The footer for these panels was 1m wide, was keyed into sandstone bedrock 0.30m and was approximately 1.52m below the portland cement concrete pavement and shoulder. Thirteen of the 17 panels in this section of wall were tied to the sandstone bedrock behind the wall by either 25.4mm or 34.93mm hollow rock bolts. Two panels on each end of the wall were cantilever type walls. The panels that failed had 25.4mm hollow rock bolts. A portion of each panel adjacent to both sides of the failure was pulled out from the rock face and appeared to be in imminent danger of also failing. All of the 21 rock bolts in the panels that fell were separated either at the backface of the wall, in the extension from the wall to the rock face or at the rock face. None of the rock bolts had been pulled out of the bond length in the sandstone bedrock. After considering the condition of the wall and rock bolts, it was decided that the remainder of this section of wall (14 remaining panels) should be taken down. Attempts to take the remaining wall down, even the 2 panels adjacent to the 3 that failed, were unsuccessful until almost all of the existing rock bolts that were still intact were cut and large construction equipment used to push these panels over. The 3 north bound lanes of 1-77 were closed during the 3 days of around the clock removal of the wall. No personal injuries occurred as a result of the failure, although one automobile was narrowly missed by the failing wall. Method of Investigation The technical investigation was assigned to the Soil and Rock Mechanics Section of the Materials Control, Soil and Testing Division of the Department of Highways assisted by D. R. Piteau and Associates. Dr. Carl D. Lundin of Materials Application Inc was employed to evaluate the corrosion of the bolts. The investigation was to determine the cause of the failure and if it was attributable to external causes. It was also to be determined immediately if the failure was the result of bedrock or overburden movement.
