PREDICTING THE GROUND MOVEMENT ABOVE A TUNNEL IN CHITTAGONG COASTAL AREA OF BANGLADESH UNDER SEISMIC LOADING

Abstract

Settlement is the vital issue for analysis of a tunnel in any conditions of soils such as sand, clay etc. Many researches have been carried out to predict surface settlement above a tunnel but some technique needs further research to be established. In this paper, analysis of EPB-TBM (Earth Pressure Balanced Tunnel Boring Machine) tunnel has been considered along a straight line through homogeneous sand layer which has been observed in the Chittagong Coastal area, Bangladesh. Circular type tunnel is considered for analysis. Direct effect of seismic fault has been neglected. Phased construction method has been incorporated to analyze this event. Important parameters for surface settlement of tunnel are tunnel depth, tunnel diameter, tunnel construction technique, different relative densities of sand etc. In this paper, the variation of tunnel depth and tunnel diameter has been considered and analyzed. Analysis has been performed through finite element based software PLAXIS 3D. Surface settlement along transverse and longitudinal to the tunnel axis has been predicted. Variation of depth (distance between free surfaces to top surface of the tunnel), tunnel diameter and length (phased excavation) have been considered to evaluate surface settlement for static and dynamic cases in sands.