User's Guide: Computer Program for Simulation of Construction Sequence for Stiff Wall Systems With Multiple Levels of Anchors (CMULTIANC)

Abstract

Abstract : This report describes the PC-based computer program CMULTIANC, used to evaluate the effects of staged construction activities (i.e., excavation and tieback post-tensioning) on wall and soil behavior. The CMULTIANC simplified, construction sequencing analysis is applicable to stiff walls with a single row or multiple rows of post-tensioned tieback anchors. Top-down construction is assumed in this analysis procedure. The retaining wall system is modeled using beam on inelastic foundation methods with elastoplastic soil- pressure deformation curves (R-y curves) used to represent the soil behavior. The R-y curves are developed within the CMULTIANC program in accordance with the reference deflection method. The retaining wall is analyzed on a per-unit length run of wall basis. One-dimensional finite elements are used to model the retaining wall with closely spaced inelastic concentrated springs to represent soil-to-structure interactions on both sides of the wall. Discrete concentrated, elastoplastic springs are used to represent the anchors. For each level of excavation (associated with a particular tieback installation) CMULTIANC performs three sequential analyses: (a) staged excavation analysis (to the excavation level needed for anchor installation) to capture soil loading effects, (b) R-y curve shifting to capture plastic soil movement effects, and (c) tieback installation analysis to capture tieback anchor prestressing effects. R-y curves are shifted to capture the plastic movement that takes place in the soils as the wall displaces toward the excavation for those conditions where actual wall computed displacements exceed active computed displacements. R-y curve shifting is necessary to properly capture soil reloading effects as tieback anchors are post- tensioned and the wall is pulled back into the retained soil.