The performance of a TBM in a squeezing ground at Uluabat, Turkey

Abstract Squeezing characteristics of the ground in the Uluabat Tunnel, Turkey, are discussed and the analysis of TBM performance data around zones where the TBM jamming problems occurred is presented. Detailed analysis shows that a squeezing index of the ground can be defined which is related to the change in thrust force, time and length of tunnel where the increase of thrust starts and terminates with squeezing of TBM. This index is found to increase linearly with overburden and although the relationship is not strong, particularly with decreasing RMR values. It is also shown that the delays in tunnel excavation or TBM stoppages also play an important role in the squeezing of TBM shield. It was possible to mitigate the squeezing problem by means of bentonite injection through the shield. As a result, a methodology of predicting critical zones for shield blockage and problems caused by squeezing characteristics of difficult ground is discussed in detail.