LIQUEFACTION POTENTIAL AND DEWATERING INJECTION STRUCTURES AT HERKENBOSCH - FIELD INVESTIGATIONS OF THE EFFECTS OF THE 1992 ROERMOND EARTHQUAKE, THE NETHERLANDS

Near-surface soils in the southern Netherlands include fine sands with , in some areas, a watertable at shallow depth. A reconnaissance study undertaken in 1987 to ascertain the potential for a liquefaction haza rd in areas south of Eindhoven revealed a high liquefaction potential in the area around and to the south of Roermond. The earthquake of 13 April 1992 caused sand eruptions to occur in numerous locations in the vicinity of Roermond. This study focuses on sand fissures and mounds located to the south of Herkenbosch, between the town and the River Ro er. Excavations revealed extensive disturbance of clay and silt deposi ts down to confined saturated sand deposits at depths of several metre s below the surface. Extensive ground cracking, with or without sand e xtrusion, occurred over an area of circa 0.5 km(2). Pit and trench exc avations permitted detailed mapping and sampling of over 30 m of sand- injected fissures. The evidence indicates that ground cracks were inje cted, almost passively, by sand entrained within water, driven upwards following liquefaction of the previously confined sand. Groundwater c onditions are such that sand volcanoes and spring pits developed at th e bottom of the deeper excavations.