Three-Dimensional Responses of a Tied-Back Excavation through Clay

The three-dimensional ground deformations measured during construction of a 12.8 m deep tiedback excavation in Chicago are presented. The excavation was supported by a PZ-27 sheet pile wall and three levels of regroutable ground anchors. The excavation was made through granular soils into soft to medium stiff clays. Extensive field performance data were collected including lateral and vertical optical survey data and lateral inclinometer data. Construction procedures are summarized and correlated with monitoring data. The three dimensional pattern of ground surface deformations around the excavation is summarized. A performance-based relation to estimate the maximum horizontal ground movements for flexible wall systems as a function of factor of safety against basal heave and excavation depth is proposed. An empirical approach to estimate the distribution of ground movements parallel to a supported wall is presented.