Evaluation of alternative methodologies to minimize movements of a diaphragm wall close to buildings

In the framework of the construction of the high-speed railway passing through Barcelona, a large excavation (21m depth) has made to about 2 m of a building. The excavation was done in the quaternary material typical of the Barcelona plain which consists mainly of low plasticity and slightly cemented compact clays. This material due to its high stiffness can be considered as a "hard soil". In order to minimize movements, several methodologies were considered: change in the thickness of the diaphragm walls, increasing the length of the diaphragm walls and location of struts. The predictions of movements were performed using PLAXIS code, considering model parameters estimated from pressuremeter tests and resonant column. The smallest displacements were obtained if struts were placed in advance just below the maximum excavation level. Those struts had only 3 m thickness below the maximum excavation depth, and were built every 5.5 m in horizontal direction. The measured movements were somewhat lower than expected and the building suffered no damage. The paper demonstrates that struts below the maximum excavation level constitute a safe design when movements induced to buildings are a major concern