Method for estimating wall deflection of narrow excavations in clay

Abstract

The support system stiffness is crucial to designing the excavation support system by displacement control, but the current methods of estimating the system stiffness are inapplicable to narrow excavations. The field data from narrow excavations in the same site in Shanghai soft clay were analyzed and it was found that the deformations of these excavations were significantly affected by the width-depth ratio (B/H). 111 numerical simulations were carried out to study the contributions of wall bending stiffness (EI), average vertical support spacing (Sv) and width-depth ratio (B/H) to the support system stiffness. A parameter was proposed to quantify the support system stiffness for narrow excavations. It can consider the coupled effects of EI, Sv and B/H. An equation for the maximum wall deflection was presented based on the parameter and it was applicable to the cases with B/H less than 1.5. The proposed method was verified against the measured data from several narrow excavations in clay and the overall agreement was satisfactory.