A new support system is applied to excavation of double foundation pits.In this system

double large-diameter annular arched girders structural system is used.By construction monitoring in Tianjin Cause Bay Plaza

data about internal force of supporting system and horizontal displacement of soil are obtained.This article analyzes these data and also discusses the characteristic of internal force changing in annular arched girders and influence on environment in the course of excavation.By these analyses

the law of horizontal displacement in ambient soil is drawn;and the measures considering the construction factors can be adopted for the annular arched-girder structure design.