Modelling the effect of rainfall on instabilities of slopes along highways

Abstract

 During and after the very wet 1991/1992 winter experienced in Jordan, significant instabilities occurred in several sections of the new Irbid–Amman Highway in Jordan. A potential impact of surface and subsurface flow on the failed areas was noted. This paper is concerned with a hydrological study of the Irbid–Amman Highway, including watershed characteristics, hydrological data analysis, and hydraulic analysis of remedial works to failed areas and other parts of the highway drainage to minimize the impact of surface runoff and the effects of subsurface water with respect to the stability of the upslope and to limit the porewater pressure within the road formation. The study shows that the culvert capacity and the discharge velocity of the cross-highway drainage are deficient. Recommendations (e.g. gabion cascades) are therefore suggested to reduce drainage to the cross highway drainage structures. Grouting is suggested to stabilize the embankments above the inlets to culverts. Remedial drainage works are suggested for each major failed area. These include: culverts, table drain, drainage blanket beneath road formation, cut-off drains above cuttings, subsurface drains into the cut in the vicinity of springs, curtain drain beneath the lined table drain, and others.