The Research On Peripheral Subsidence Caused By Deep Excavation In Soil-rock Mixture Strata

As the continuous development of science and technology,the focus of urban construction and development has gradually shifted from high altitude to the underground,and the construction of subway foundation can be universally found in bustling metropolises.The Anshan Road Station of Qingdao metro has an excavation depth of foundation exceeding 40 meters,marking it as the deepest metro foundation in Qingdao thus far.The general geology of Qingdao makes the foundation have to be constructed in upper-soft and lower-hard soil-rock mixture strata.In addition,the main approach of the excavation is now through blasting.Naturally,above mentioned facts in combination have brought considerably raising concern on peripheral buildings,structures and underground utilities as well as the regulation of surface subsidence as a consequence.Therefore,study on the impact of Qingdao subway foundation excavation on its periphery is of crucial research significance.In this article,we initially sorted out and summarized the existing theories on the support deformation and peripheral subsidence caused by foundation excavation.Based on a rich supply of data collected during long-term continuous monitoring on site,we further analyzed the unloading response of excavation.Using the method of numerical modelling,we revealed the impact that stratigraphic properties have on peripheral subsidence upon excavation process.As a final point,we established a set of risk assessment tools to evaluate safety risks at the periphery of excavating foundations,through which we assessed the peripheral safety risks considering excavation of Anshan Road Station.The main contents of our study presented in this article are concluded as follows:(1)We reviewed and summarized current existing related theories and mechanisms,including classical theories of earth pressure,deformation mechanisms of foundation excavation as well as the theories of subsidence during excavation,which provided theoretical reference for the further research on self-stability of the foundation and laws and patterns of the peripheral subsidence.(2)We performed an analysis on the general situation of construction site to determine a monitoring plan.By running an analysis based on measured data collected from3 typical supporting units,presenting surface subsidence,structure subsidence as well as pier subsidence and vertical displacement on the top of supporting piles respectively,we illustrated a general pattern of subsidence considering foundation excavation.(3)Making use of MIDAS-GTS,a numerical modelling software,we established a3 D finite element model to support research concerning influence that various stratigraphic properties have on peripheral subsidence and support deformation during excavation.(4)Based on rich experience of on-the-spot services,we established a set of assessment tools to evaluate peripheral safety risks of an excavating foundation.Following the guidance of national standards,safety condition of excavation can be classified into four safety degrees marked from I to IV,representing safety,follow up,early warning,alarm respectively.Additionally,we used measured data to evaluate our assessment tools by the analytic hierarchy process(AHP,a fuzzy comprehensive evaluation method).