Remediation of uncontrolled inflows caused by technical failures in deep excavations

• Dewatering represents a technical challenge in the presence of confining layers. • The geotechnical and dewatering design should be complementary. • Even with adequate dewatering plans, unexpected seepage and flooding can arise. • Solutions require an agreement between theoretical knowledge and practical experience. Dewatering for water table control may cause undesirable effects on adjacent properties, the site or the environment. Risks include inflows and seepage that could result from the existence of confined aquifers that were deemed unimportant at the project stage. We describe three cases of excavations with problems associated with inflows caused by such aquifers and pre-existing unsealed boreholes. In addition, in two of the cases, problems were worsened by the compartmentalization effect caused by internal foundation elements that limit horizontal flow to the extraction wells. For each case, we discuss solution methodologies. These range from pumping the deep aquifer, laying high permeability layers at the excavation bottom, and sealing the abandoned borehole, which we describe in detail. We conclude that, when there is consensus between theoretical knowledge and practical experience, creative solutions can be applied to overcome the situation in a reasonable way, even in unforeseen situations.