Design-Built Semi-Rigid Rockfall Barrier on U.S. Routes 11/15 in Perry County, Pennsylvania

摘要

A series of rock cut slopes along U.S. Routes 11 and 15 (combined) near Marysville, Pennsylvania has presented a chronic rockfall hazard, and the stabilization of these slopes became a high priority for the Pennsylvania Department of Transportation (PennDOT) Engineering District 8-0. The cuts expose steeply inclined clastic sedimentary rocks of Ordovician, Silurian and Devonian age, having variable resistance to weathering. The primary challenge to developing rockfall mitigation measures was the very limited lateral space between the high rock slope to the west of the road and railroad tracks to the east, which are situated along the western shore of the Susquehanna River at a lower elevation than the roadway. With slope heights of up to about 240 feet, very large impact loads (2,000 kJ) had to be resisted without deflecting beyond the roadway edge. Standard tested flexible rockfall fence as per the European Norm ETAGE 027 couldn't be used because the elongation would have far exceeded the allowable value for the specified impact energies, which were developed by CRSP simulations performed by the District's preliminary design team. As such, the fences for this project had to be custom designed to perform as semi-rigid structures at impact. The design approach for modelling the behavior of the semi-rigid barrier was developed by Cantarelli and Al in "Modeling Rockfall Protection Fences". The design theory refers to the elastic deformation of the net under impact in relation with the area of contact surface for a tested barrier.