Effects of ground conditions on utilization factor of slurry TBMs in soft ground tunneling

Purpose In mechanized tunneling, TBM productivity has an influence on schedule and costs of the project, this indicates that inaccurate estimation of utilization factor may cause major project delays. Consequently, the claims in tunneling construction contracts are increased. Analysis and evaluation of slurry tunnel boring machine (STBM) performance includes the prediction of penetration rate ( PR ), advance rate ( AR ) and machine utilization ( U) . However, a guideline for predicting the utilization factor of TBM bored tunnels in soft ground is not available. Design/methodology/approach Evaluation of such effects is approached in the current paper through the use of field records obtained from tunnels constructed in Egypt. In this study, the relationship between the ground conditions, basically described by standard penetration test (SPT N-value), and Fines Content F c(av) , and the relation between boring performance represents of SPT N-value ( N ) and F c(av) and U are investigated using field data collected from the actual construction of Greater Cairo metro line 3. On the basis of the records presented and discussions made in the paper, good correlations between ground conditions and the utilization factor of slurry TBMs are established. Findings On the basis of the records presented and discussions made in the paper, good correlations between ground conditions and the utilization factor of slurry TBMs are established. The established correlations reveal that the U of slurry TBMs decreases with the increase of the SPT N-value ( N ) for the excavated ground and it increases with increase of F c(av) of the excavated ground. Research limitations/implications Some implications of the established correlations for the actual implementation for tunneling construction in soft ground are provided. In order to develop or validate these correlations, it would be warranted to further investigate about the various conditions (shield diameters, ranges of excavation depths, etc.) for tunneling in soft ground using STBM. Practical implications An important implication of established correlations in this paper is that they are contributing to cost estimation, cost controlling and development of more realistic time plans and supports decision-making on the selection of the appropriate type of TBMs and tunnel alignments for given ground conditions and projects. Originality/value The claims in tunneling construction contracts are increased. Analysis and evaluation of STBM performance includes the prediction of penetration rate ( PR ), advance rate ( AR ) and machine utilization ( U ). However, a guideline for predicting the utilization factor of TBM bored tunnels in soft ground is not available.