Finite element design procedures for hybrid MSE/Soil-nail retaining wall systems
In recent years, many departments of transportation are working to keep pace with population growth by considering major infrastructure improvements to their highways. The successive expansion of the highway system to meet increasing demand has made extension of the right-of-way economically prohibitive. The use of earth retaining walls has allowed highway upgrades to be constructed within existing right-of-ways, consequently lowering the additional cost of acquiring separate lands. Texas Department of Transportation and other DOTs construct Hybrid MSE/Soil-nail retaining wall systems to replace existing highway embankments that separate two sections of a roadway. These systems are typically used to allow for widening both sides of the road by constructing a new lane to each roadway while excluding the need to acquire additional right-of-way. The design of such systems, in particular for the soil nail wall, is done using computer programs such Goldnail and Snail. These computer codes are based on limit-equilibrium methods and are typically used as design tools for conventional wall systems in which some degree of wall deflection is tolerated. They do not however, address large deflection due to significant surcharge caused by the use of excessive height of MSE wall. Moreover, these methods do not account for the additional outward thrust expected to occur at the soil nail/MSE wall interface. As a result, the requirements for designing hybrid walls systems should not only be based on stability but should also be based on wall deformation. The focus of this research study is to examine the adequacy of the current method recommended by TxDOT and to develop a design procedure for the hybrid wall systems which will address the shortcomings in the currently used methods in practice. The new performance method is based on extensive finite element analysis that will address not only the stability of the structure but also the wall deformations as well as the force transfer in the reinforcements.