The observed ground movements of excavations in layered ground are examined with emphasis on the relationship to the construction process and the ground condition. A finite element analysis is performed based on field measurements to predict and examine overall ground movements. For excavations in layered ground conditions, it is necessary to consider a drastic variation in the pattern and magnitude of lateral displacements due to the large stiffness difference between geolayers.
The basic purposes of excavation support systems are to provide stability and minimize movements of the adjacent ground. Stability generally means preventing failure, i.e., designing the excavation support system to remain open without threat to construction personnel or causing very large movements that endanger surrounding structures. Design measures for stability include the selection of earth pressures, determining the potential for base soil failure, and a layout of the dewatering system to prevent piping and blowout along the walls and bottom of the excavation. The control of ground movements generally is based on the types of buildings and public facilities near the excavation. The key factor among the measures necessary for control is the prediction of displacements at various distances from the excavation. In addition, control measures include the protection of adjacent structures and the use of control methods to restrict ground movements in order to be consistent with the acceptable performance of surrounding facilities (O'Rourke, 1981). While methods for predicting system stability are reasonably well established, this is not the case for movements. To assist the decision-making process regarding both the potential for damage and protection of nearby structures due to ground movements associated with excavations, many researchers suggest the patterns of settlement and lateral displacements by excavations in general terms on a case history basis (O'Rourke, 1981).
