Performance of a deep excavation and the influence on adjacent piles:A case history in karst region covered by clay and sand

This paper presents a case study of deep excavation adjacent to an existing bridge in karst region of Guangzhou city,China.The movements of retaining structures,settlements of surrounding ground and pipelines,and the responses of bridge piles were measured and evaluated.A sudden surge of groundwater was recorded at the north pit when excavated halfway.Soil-cement columns using the Metro Jet System(MJS)method was employed along the outer perimeters of the diaphragm wall where water inflow occurred,for the sake of blocking the flow channels.The measured maximum wall deflection dhm in this case ranged from 0.13%H to 0.3%H,with a mean value of 0.2%H(H is the excavation depth),which agreed well with the empirical prediction in mixed ground.During the MJS treatment,the wall and surrounding soils experienced notable lateral deflection and settlement.The bridge piles experienced significant settlement since the excavation commenced,which might be attributed to the inherent deficiency in geological condition and pile length.The soil disturbance induced by the adjacent deep excavation accelerated bridge settlement.The finite element analysis revealed that the excessive settlement of the bridge piles and ground surface resulted from confined-water withdrawal in sand layers.