Geodetic Accuracy in Observational Construction of an Excavation Stabilized by Top-Down Method: A Case Study

Traffic disorder and excavation hazards due to substructure construction are of the foremost challenges in great cities. Deep excavation causes stress changes in adjacent soil mass near the excavated site which induces ground deformations. Magnitude of this deformation depends on many factors including excavation geometry, ground conditions, supporting system, construction quality, time interval of execution, and construction delays. Field monitoring utilizing appropriate instruments allows conductor to predict the ground deformation trends and is useful in risk management and improvement of construction stages. It is important to measure the accuracy of the selected monitoring tool in the field precisely. In this study, accuracy of monitoring tool and observational construction of a deep excavation in an overcrowded street are discussed. In observational construction method, construction sequences are monitored and the obtained data are analyzed frequently, so construction stages or designed elements of the structure can be modified to increase safety or to enhance the economy of the project. In this article, ground deformation trends in an excavation supported by Top-Down method in the city of Qom, in Iran is surveyed by means of Total Station TS02 and the precision of the gathered information is evaluated using statistical analysis and numerical model. On this basis modifications are applied and construction stages of southern side of the excavated area are reconsidered to cease the increasing failure in this side.