Inverse analysis of excavations in urban environments

The observational approach is a long established method in geotechnical engineering practice, whereby observed performance in the field is used to alter the design of a project. With the advent of advances in computational power, instrumentation and remote data acquisition, it is possible to automate this process. Inverse analysis techniques can rationally minimize differences between observed an predicted response and effectively quantify the parameters that affect the performance. This approach is applied herein to excavations in urban environments and focuses on earth retention systems designed to limit movements of the soil around the excavation. Sites are embedded in an urban environment and, as such, nearby buildings, tunnels, utilities and other structures may be affected if movements become excessive.; The excavations examined in this work are located in Chicago and were excavated through compressible Chicago glacial clays. The objective of the inverse analysis is to find the values of selected soil parameters that produce the best fit between observed and calculated displacements and other performance data. The inverse analysis technique used in this work is based on a gradient method.; The elements of the inverse analysis problem are carefully developed for each case. The excavations are represented in 2D, assuming the center portion of the wall is in plane strain conditions throughout the excavation process, and are checked against the available theory, observed performance, and results of 3D simulations. The field observations are selected from locations that comply with these conditions and are larger than measurement errors so that a meaningful estimation is possible. Various ways to represent structural elements, soil profiles and excavation sequences are evaluated. The results of the inverse analyses are supported by comparing the optimized soil parameters to laboratory data from stress probe tests conducted on high quality block samples obtained from the sites.; Results of the two cases are compared to each other and to a similar precedent case study. It is shown that the optimized parameters can serve as a guide in the design of future excavations made through these soils.