SOIL - WATER DISEQUILIBRIUM AS A CAUSE OF SUBSIDENCE IN NATURAL SOILS AND EARTH EMBANKMENTS

THE WIDESPREAD OCCURRENCE OF LOCALIZED SOIL SUBSIDENCES FOLLOWING SUB-SURFACE TUNNELLING, BOTH IN NATURAL SOILS AND IN EARTH EMBANKMENTS IS EXPLAINED IN TERMS OF A METASTABLE STATE INVOLVING CHEMICAL, HYDROLOGICAL AND MECHANICAL FACTORS. THE SOURCES OF EXCESSIVE VOIDS WHICH PRECONDITION THE SOIL FOR SUCH FAILURES ARE DESCRIBED, ALSO THE CONDITIONS UNDER WHICH WATER FLOW INTO THESE VOIDS ADVERSELY AFFECTS THE SAFETY OF THE SOIL STRUCTURE. THE HAZARDS ARE SHOWN TO BE MOST ACUTE WHEN THE SOIL ITSELF IS CAPABLE OF SPONTANEOUS DISPERSION AND/OR LOSS OF COHESION IN CONTACT WITH WATER OF A HIGH PURITY OR WHOSE CHEMICAL COMPOSITION IS NOT IN EQUILIBRIUM WITH THE SOIL. APPROPRIATE PROCEDURES FOR EVALUATION OF THE RISK OF SUCH TUNNELLING SUBSIDENCES ARE DESCRIBED, AND AVAILABLE REMEDIAL MEASURES NOTED. /AUTHOR/