Excavation of a tunnel provides an opening into which the soil can deform and gives rise to "ground loss". The ground loss is generally defined as the volume of soil that has been excavated in excess of the theoretical design volume of tunnel excavation. In practice, the ground loss values are estimated from empirical correlations based on past experiences. Rowe et al (1992) presented a theoretically-based method for the estimation of ground loss from first principles. This method considers the parameters related to tunnel boring method and soil conditions. In this paper, design charts are presented to estimate ground loss by performing a detailed parametric study via the theoretical method presented by Rowe et al (1993). These design charts include;
a stability parameter which considers tunnel depth from the ground surface, tunnel diameter, earth pressure coefficient, vertical effective stress at the tunnel springline, tunnel face supporting pressure and pore pressure at the tunnel springline,
average soil strength above the tunnel, and
physical gap parameters involved with the tunnel boring machine, including the effects of thickness of tail piece, clearance for the erection of lining, length of shield, maximum allowable excess pitch and thickness of the cutter bead.
The design charts have then used to estimate the ground loss values in the soft ground tunnelling operations for the new Sydney airport link tunnel. These ground loss values have then been used to estimate the surface settlement troughs, and to compare the estimated settlements with those measured. In total, six sections in soft soil have been analysed, and the agreement between theoretical estimates and the measurements has been found to be encouraging.
Rapid growth in urban development has resulted in increased demand for the construction of transportation systems, water supply, and sewage disposal systems.
