Analysis, Design, and Performance of Anchored, Cast-in-Place Soldier-Pile Walls in Sand, Gravel, and Cobble Soils

As part of the PHX Sky Train project at Phoenix Sky Harbor International Airport in Phoenix, Arizona, the Taxiway S and T undercrossing consists of a depressed on-grade guideway section and service road which will be constructed using top-down construction methods to construct an additional end-span and new abutment at the two existing aircraft taxiway bridges. The soil conditions in this area generally consist of alluvial sand, gravel and cobbles (locally known as SGC) deposited by the nearby Salt River. Based on the anticipated loading conditions and the difficult ground conditions and after studying several alternatives, it was decided to design a drilled shaft soldier pile system which can be used for both foundation support of the Taxiway S and T undercrossing bridge abutment, and as the earth retention system for excavation support. The high loading conditions generated by aircraft loads are proposed to be carried by 4.5 foot diameter drilled shafts spaced 10 feet on center. To resist the lateral loads, the construction of the new bridge abutment included constructing anchor slabs behind the abutment and installing permanent ground anchors through sleeves in the abutment caps before excavating the soffit fill supporting the new cast-in-place bridge deck span. Numerical analyses were performed to predict the short- and long-term behavior of the new abutment wall. The results from the numerical modeling using PLAXIS software showed that the proposed solution is deemed adequate to provide the needed capacity with an acceptable factor of safety, along with acceptable deformation. Based on survey monitoring of the new abutment wall performed during construction, the recorded lateral movement of the wall is significantly below that calculated by numerical analyses