Strutting systems for deep excavations – technical challenges

Abstract

Constant development carried out in town centres causes that many problems related to earthworks and tunnelling must be resolved. Investors are required to ensure respective number of parking bays, which in turn demands 2-3 storeys of underground car parks. This paper presents interesting case studies of deep excavations in Wrocław, Poland. As the geotechnical works in the old city centres may bring some risks to the surrounding area, proper strutting or anchoring systems must be provided. Apart from solving engineering problems, one needs to meet very stringent requirements of heritage conservator supervision. In order to ensure the stability of the excavation walls, it is necessary to examine the foundations of neighbouring structures, and if necessary, to strengthen them for the process of installing the excavation protection walls, progressing the excavations and constructing basement storeys. Another problem refers to constructing underground storeys below the level of groundwater. This requires efficient cutting-off or long-term lowering of water table inside the excavation with a possibly limited intervention in hydrological regime beyond the project in progress. In the typical case of old cities in river valleys such “hoarding off’ the excavation and cutting off groundwater leads to temporary or permanent disturbances of groundwater flow and possible local swellings. Contemporary technologies make it possible to protect vertical fault and simultaneously cut-off groundwater inflow by means of steel sheet pilings, diaphragm walls or secant pile walls.