Mining subsidence in Twente, East Netherlands

Abstract

A method for forecasting the vertical and horizontal movements of points at the surface caused by saltmining subsidence has been developed for the special case of the Hengelo field. All possible data of a first case of caving-in of cavities created by the solution mining of salt were collected and studied. A theory was set up to explain two striking differences from other subsiding areas, i.e. the duration in time of the subsidence and the small area influenced at the surface in relation to the depth of the cavity mined out. Special attention is paid to the behaviour of the Triassic claystone formation ('Red Beds') above the salt layer. In 1973 this theory was used to predict the rate of subsidence of a second case over a 10 year period. This second area of subsidence was situated just under a new brine purification and vacuum plant. For each part of the installation within this area the movement with time was calculated. With these figures it was possible to arrange a long-term planning for preventive maintenance and by doing so to keep the complete plant operating.