Behavior of Full-Scale U-Shaped Walls Constructed by Deep Cement Mixing in Consolidating Ground

Abstract

Deep excavations in soft clays often demand heavy shoring supports. Closely spaced struts are known to impede construction within an excavation, resulting in longer construction time. This paper presents a novel strut-free retaining wall constructed by deep cement mixing (DCM). A new U-shaped DCM system (UDCM) was developed to support a 6.5-m-deep, 16-m-wide excavation in newly reclaimed land. Field measurements involving inclinometers and surface movement markers were interpreted using a fully coupled three-dimensional finite-element model. Results indicated a rotational deformation mechanism in the DCM wall. The mechanism was triggered by stress relief and basal heave. Due to the rigidity of the UDCM, the occurrence of basal heave caused the DCM walls to deflect outward toward the retained side. Such a mechanism is not typical in conventional retaining wall systems in which lateral props are installed after certain depths of excavation. The present UDCM possesses a distinctive characteristic, which is the capability to implement and activate props prior to excavation. It also is unique in that basal heave is used to regulate the rotation of the wall, thereby limiting lateral displacements during an excavation. This study includes a design chart developed for the prediction of lateral displacements with varying treatment geometries.