Probabilistic Assessment of Stability of Sloped Pavement Shoulders Subjected to Super Heavy Load (SHL) Vehicles

Super Heavy Load (SHL) vehicles typically carry heavy loads that exceed the permissible truck weight/size limits set forth by state highway agencies. Operation of wide SHL trailers with heavy wheel loads and non-conventional axle arrangements can potentially jeopardize the stability of pavement shoulders. This study presents a methodology for assessment of the stability of sloped pavement shoulders under SHL vehicle operations. The proposed approach extends the conventional Limit Equilibrium Method (LEM) to a probabilistic methodology that accounts for the uncertainties associated with shear strength properties of pavement unbound layers. Another major point of departure of the proposed methodology from the traditional LEM pertains to its capability for handling the demanding loading conditions imposed by SHL vehicles. To accomplish the research objective, initially, the authors devised a plan of field testing to collect relevant information on traffic loading conditions, pavement layer properties, and shoulder characteristics in ten representative sites in overload corridors in Texas. Subsequently, this information was incorporated into a 3D finite-element system to calculate the horizontal driving forces applied to the pavement shoulder due to SHL vehicle movement. A Monte Carlo Simulation (MCS) was then used to randomly generate the shear strength parameters of the base and subgrade layers. Ultimately, the resisting shear forces were compared with the sliding forces along the trial slip surfaces to determine the probability of failure for the sloped shoulders, with consideration of the SHL-induced surcharge loads, weight of the sliding block, and lateral earth pressure from the adjacent soil. The results underscored the significance of the wheel load and shoulder slope in stability analysis procedure, as operation of SHL vehicles with higher load magnitude on tires resulted in a substantial increase in the probability of failure for pavement shoulders with steep side slopes. The proposed approach can provide means to assess the potential risk against failure of sloped shoulders subjected to SHL vehicles, considering the non-conventional axle assembly of SHLs, and unique characteristics of pavement shoulders in the network.