Wall and Ground Movements Associated with Deep Excavations Supported by Cast In Situ Wall in Mixed Ground Conditions

Field monitoring data on lateral wall deflection and ground settlement from 14 deep excavation case histories in Hong Kong involving cast in situ concrete wall were collected and analyzed. Mixed ground conditions consisted of successive layers of fill, marine deposit and/or alluvium, and decomposed geomaterials. The measured data were differentiated into two groups based on the standard penetration test $N$ values of the ground $-N\le 30$ (Group A) and $N>30$ (Group B) at half of the excavation depth. The mean values of the maximum wall deflection $\left({\delta }_{\mathrm{hm}}\right)$ and ground settlement $\left({\delta }_{\mathrm{vm}}\right)$ in the excavations in Group A are 0.23 and 0.12% of the excavation depth $\left(H\right)$ , respectively. For the excavations in Group B, the mean value of ${\delta }_{\mathrm{hm}}$ is $0.13\%H$ which is similar to other excavations in predominantly other stiff soils $({\delta }_{\mathrm{hm}}∕H=0.10–0.16\%)$ , but ${\delta }_{\mathrm{vm}}$ is only $0.02\%H$ which is small when compared to other similar database $({\delta }_{\mathrm{hm}}∕H=0.1–0.2\%)$ . The settlement influence zone of the excavations in both groups reaches a distance of $2.5H$ , which lies between that observed in other soft clays and sands $(d=2H)$ and in other stiff clays $(d=3H)$ . The measured wall deflection and ground settlement are relatively insensitive to the system stiffness of the support system using cast-in-situ concrete wall.