PROBLEMS IN THE PREDICTION OF THE TBM ADVANCE RATE WITH ROCK MASS CLASSIFICATION AND THEIR POSSIBLE SOLUTIONS

Taking the TBM performance in four tunnels as case examples, this paper analyzes the two reasons that there are problems in using the conventional rock mass quality classification systems to predict the TBM performance. The first reason is the factors which control the rock mass quality are not the factors that influence the rock mass boreability. The second is that most of the factors in rock mass classification systems are semi-quantitative. As a result of the two reasons, the value of the rock mass quality cannot reflect the rock mass boreabilty. According to the purpose of the rock mass classification for tunnels tunneling by TBM and the features of the TBM cutting process, this paper suggests two systems to classify the rock mass: (a) the rock mass boreability classification system for estimating how difficulty the rock mass are bored by TBM and (b) the rock mass quality classification system for estimating the stability of surrounding rock mass. The factors which are used to classify the rock mass boreability group in the system (a) are lithology, weathering degree and joint characters. The factors which are used to classify the rock mass quality in the system (b) are factors which will cause geological problems in the cutting process. The system (a) predicts the net penetration rate (PR) of the TBM, the system (b) evaluates the utilization (U) of the TBM, then the advance rate (AR) of the TBM is calculated by PR and U.