Liquefaction potential and dewatering injection structures at Herkenbosch: field investigations of the effects of the 1992 Roermond earthquake, the Netherlands

Abstract

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 hazard 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 Roer. Excavations revealed extensive disturbance of clay and silt deposits down to confined saturated sand deposits at depths of several metres below the surface. Extensive ground cracking, with or without sand extrusion, occurred over an area of circa 0.5 km2. Pit and trench excavations permitted detailed mapping and sampling of over 30 m of sand-injected fissures. The evidence indicates that ground cracks were injected, almost passively, by sand entrained within water, driven upwards following liquefaction of the previously confined sand. Groundwater conditions are such that sand volcanoes and spring pits developed at the bottom of the deeper excavations.