2.3 Basal Heave Stability

The analyses of the basal heave failure are only applicable to clayey soils（On the other hand，the bearing capacity of sandy soils is quite large to avoid bearing failure；thus it is not necessary to examine the possibility of occurrence of basal heave failure for excavations in sandy soils.）.Sinceφ＝0 for clay，the failure surfaces of bearing capacity failures in clay（e.g.the slope stability problems，the ultimate bearing capacity problems of foundations，etc.）are circular arc surfaces.The basal heave failure due to excavation is also a kind of bearing capacity failure and might also have a main circular arc failure surface.The analysis method for basal heave varies with the assumed shapes of failure surfaces near the ground or excavation surface，though the main failure surface is still a circular arc.The analysis method for basal heave assumes many possible failure surfaces and finds their corresponding factors of safety according to mechanics.The one with the smallest factor of safety is the most likely potential failure surface.Many analysis methods have been proposed for basal heave，of which the most commonly applied are（1）Terzaghi’s method，（2）Bjerrum and Eide’s method，and（3）the slip circle method.This section will categorize these methods into the bearing capacity method，the negative bearing capacity method，and the slip circle method according to their characteristics.