Saturated clay response during braced cut construction

Strain fields that arose at various times during construction of a braced excavation through soft to medium-stiff saturated clays in Chicago are presented. Pile driving induced largely horizontal compressive strains and positive excess pore-water pressures within the adjacent clay. These effects tend to reduce the passive resistance provided by the soil between the sheet-pile walls and promote movements below the excavated grade at any early stage of excavation. The strains computed from data taken during excavation indicated that strains localized in distinct zones twice during construction. This phenomenon was associated with movements below the base of the excavation and with large increases in measured strut loads. The in situ response at the test section implies that strain-softening phenomena occurred within the lightly overconsolidated, saturated clay during excavation and bracing.