Analysis of Monitoring Data over the Construction Period of the North Anchorage Foundation Pit of Fuma Yangtze River Bridge at Wanzhou District,Chongqing City

The surface soil layer at the north bridge area of Fuma Yangtze River Bridge is characterized of great thickness and low strength,the underlying pelitic rock mass is highly sensitive to water,and thus the stability of the natural slope is relatively poor.In order to ensure the construction safety and perform feedback analysis of the north anchorage foundation pit,systematic safety monitoring had been carried out during the construction period of the foundation pit.Monitoring results showed that,shallow deformation and failure was easily triggered by rainfall in top soil layer at the periphery of the foundation pit,resulting in the displacements of several monitoring points exceeded the alarm value.Fortunately,deformation of peripheral slope had been effectively controlled after the completion of shotcrete-rockbolt protection.Displacement of the retaining pile increased rapidly when the fully and strongly weathered strata were excavated,while the displacement increased slowly when the moderately weathered stratum was excavated.The surficial and deep horizontal displacement of support structure did not exceed the alarm values at last.The prestress of cable changed smoothly during the construction period,and the accumulative variation of the prestress was far less than the alarm value.Monitoring results comprehensively reflect that the side-wall and the support structure of the north anchorage foundation pit were in a state of safe and stable.Meanwhile,the reasonability of the conditions and parameters adopted in the stage of engineering design had been verified.Furtherly,research results in this paper can help accumulate experience for similar excavation engineering in respect of design,construction and monitoring.