Ground Deformation Distribution And Control During Installation Of Concrete Diaphragm Walls In Suzhou

The subway construction in China is concentrated in the densely populated eastern coastal areas where the subsurface strata mainly consist of saturated soft soils.With such ground conditions,the subway tunnels are mainly excavated using shield driving and the stations are mainly constructed using open-cut.The open-cut involves in deep excavation which is typically supported by concrete diaphragm wall(CDW)due to its small vibration,high bending stiffness,excellent water tightness,and wide adaptability.During the construction of CDWs,the surrounding soil undergoes a complicated stress release and compensation process,generating ground deformation.If not well controlled,the ground deformation may lead to trench collapse,damaging the adjacent structures and utilities.The ground deformation during the CDW installation process is typically neglected during the design and construction while the main attention is paid to the process of deep excavation.Using the project of Zhuhui Road station in Suzhou metro line No.5 as a case project,this thesis investigates the characteristics of ground deformation and control measures during the installation of the CDWs using case studies,field instrumentations and numerical simulations.The results can be beneficial to the construction of Zhuhui Road station of Suzhou metro line No.5 and provide reference to the construction of CDWs in Suzhou and surrounding cities.The major contents conclusions of this study include:(1)Through literature review and case analyses,the distribution of the settlement and lateral movement of the ground during the installation of the CDWs is summarized.According to the hydrological,geological and construction environment of the Zhuhui Road station,ground deformation control measures are proposed.The measures include increasing the stiffness of guide wall,selecting suitable trench excavation machine,controlling trench length,controlling slurry parameters and height,controlling the time of trenching and concreting,limiting adjacent ground surface surcharging,reinforcing the foundation of adjacent buildings,etc..(2)The distribution of ground deformation is summarized through filed monitoring the installation process of the CDW and data analyses.Field monitoring results show that the ground deformation mainly occurs in three stages:trench excavation,concreting and concrete hardening.Trench excavation generates stress release and leads to rapid ground deformation.The wet concrete applies lateral pressure on the trench wall during the concreting process.The lateral pressure compensates for the stress loss and squeezes the trench wall.During concrete hardening,the lateral pressure from concrete gradually decreases,and the ground deformation tends to be stabilized.(3)The settlement of ground surface decreases with the increase of depth and distance to the trench and can be neglected 15m way from the trench.The maximum value is about 2.5cm.The lateral ground deformation at the trech wall decreases with the increase of the depth and can be neglected below 10 m depth.The maximum value is about 2.5 cm.The building settlement is less than 1cm,which is smaller than the adjacent ground settlement benefical from the stiffness of the strucutre.In general,the ground deformation is controlled well during the installation of the Zhuhui Road station CDWs.(4)The influence factors of ground deformation during CDW installation is analyzed using numerical simulation.The results show that the UBCSAND model can well simulate the stress-strain relationship of soil for small deformation problem.The factors such as soil strength,trench size,guide wall,surcharge,slurry properties and height and reinforcement measures have a significant impact on the ground deformation.It is found that the numerical simulation results are consistent with the measured results.