Research purposes:There are three methods for comparing and evaluating the increase of the shear strength of soft soil foundation : the effective stress method, effective consolidation pressure method and specification method. When describing the increase of the shear strength of the unit soil on one spot,It is necessary to indicate the stress state of the unit soil and research the increase of the shear strength of the soil surface.
Research conclusions:(1) For the unit soil of the dam foundation s middle axle or the toe, when the effective stress method is used,the increase of the shear strength of the large main stress acting face is bigger than that of the shearing damaged face,and the increase of the shear strength obtained by using the specification method is between the above values. (2) For soil - stone dam built on the soft soil foundation, the increase of the unit soil of the dam foundations middle axle becomes less with the increase of the depth after its consolidating for a period of time while in the unit soil of the toe,this kind of becoming less trend is not obvious. ( 3 ) This research result is available for researching the increasing regulation of the shear strength in the drainage consolidation.