Abstract: An EPB shield used in the construction of No. 6 line of Chongqing Metro was jammed when boring in hard rocks. Technologies, including removing the rock mass above the shield by means of blasting, extending the cutting tools and enlarging the excavation diameter, and backfill grouting for the voids created by blasting, are adopted to release the jammed shield. Recommendations, such as TBMs with copy cutters should be used in hard rock conditions and regular inspection should be made on the cutter heads, are proposed to avoid shield jamming.

Key words: EPB shield, jamming, jamming releasing technology, blasting, grouting 