Research purposes: At present,the more and more foundation pits are built in soft soil areas,and its security and economical efficiency become the matter of the common concern. Setting up the reasonable monitoring and warning values is the effective way to reduce the risk of the foundation pit construction. The current warning values stipulated in the relative code are established on the base of the non - soft soil condition,and it is unsuitable for the soft soil condition. So it is necessary to draw up the warning value for soft soil areas.
Research conclusions: From the statistic analysis of the measured data of the foundation in soft soil area,it sis concluded: ( 1) The maximum deep horizontal displacement value of Grade A foundation pit is concentrated in the 60 -100 mm deep areas and it decreases with the increase of the excavation depth. ( 2) On the premise of no change of the support structure,the deformation volume of the support pile increases obviously,but the deformation law does not change. ( 3) The maximum horizontal displacement of the support pile is basically in nonlinear decrease state with the increase of the elastic modulus.