This paper investigates the performance of Earth Pressure Balance Tunnel Boring Machines (EPM TBMs) in rock-soil interface mixed-face ground based on the Deep Tunnel Sewerage System project in Singapore. Several methods are available to estimate TBM tunnelling performance in homogenous rock or soil. However, the existing models cannot be reliably used to estimate TBM performance rate in mixed ground. The tunnels in this study were excavated in adverse mixed-face ground conditions. The geological profiles and the TBM operational parameters are compiled in a database and analysed statistically. The influence of different geological face compositions on the performance of the TBMs is studied. The statistical analysis shows that there is a possible correlation between the mixed-face ground characteristics and the TBM penetration rate. A method is proposed to predict the TBM performance in mixed-face ground for project planning and optimization.