Performance Assessment of Geofoam-Soil Cushion of a Rock-Shed Tunnel Designed for a Rockfall-Prone Slope Along Jammu-Kashmir National Highway, India
摘要
This study presents a site-specific design for a cushioning system in a rock-shed tunnel proposed for the Udhampur-Ramban section of National Highway 44 in Jammu and Kashmir, India. Located in the lesser Himalayas, the region is highly vulnerable to rockfall events. Slope and rock properties were characterized through site investigations and laboratory testing, and these data were used to estimate rockfall impact energies using statistical trajectory analyses. Two cushion systems were evaluated: a local soil-based cushion and a combined expanded polystyrene (EPS) geofoam-local soil cushion, using dynamic finite element analyses. Laboratory tests determined the properties of local soil and EPS at densities of 16, 20, and 30 kg/m3. These parameters were then input into numerical simulations to assess the performance of the cushioning systems and determine the optimal configuration that would limit roof-slab deformation within serviceable limits. The results show that a soil-only cushion is insufficient to prevent slab deformation under rockfall impacts. Increasing soil thickness reduces deformation but adds excessive dead load. The most effective solution was a 2 m layer of EPS (30 kg/m3) combined with a 0.3 m soil layer. These findings offer valuable insights into cushioning system performance, aiding the design of rock-shed tunnels in rockfall-prone areas.