Artificial ground freezing application in shield tunneling

Abstract

One of the methods to create a stable working environment around tunnel and seal the tunnel periphery against underground water is artificial ground freezing. The method is economically beneficial at large scale construction sites, and long-term containment. It is also superior method when temporary high strength soil or temporary impermeable barrier is needed. In this study, application of freezing in shield tunneling is investigate. A case study of a comprehensive underground tunneling project in Tokyo suburb is considered. The construction includes a junction of main tunnel with a ramp way that connect underground tunnel route to the ground surface. In this construction site, connection segment of main route and ramp way need to be widen. Because of this enlargement and sequence of works below water table, temporary stable work front and hydraulically water proof zone is demanded. As an effective way of ground improvement, freezing method is used in this case. In this way, a parametric study is conducted and amount of horizontal and vertical freeze-thaw induced displacement and effect of soil stiffness around tunnel is estimated numerically. In addition, the effect of design parameters of intermittent freezing on the thickness of freezing zone is investigated. Results of analyses indicates that based on reliable design scheme, an energy-efficient plan for application of freezing in shield tunneling is possible.