Abstract:

The precast lining segments, pea-gravel backfilling and grouting are adopted in the double-shield TBM (tunnel boring machine) construction. which makes the segments, backfill layer and surrounding rock form an integral supporting structure. The compactness of pea-gravel backfill grouting is an important index affecting the working performance of TBM tunnel. However, the backfill grouting compactness is often low in practical projects. In order to study the influence of different backfill compactness on surrounding rock deformation, yield state and the stress of lining segment, a stochastic element model is proposed to simulate the different backfill grouting compactness based on the numerical simulation of Duoxiongla Tunnel. The relationship between the backfill grouting compactness and the mechanical state of support structure is analyzed. According to the influence of compactness on the surrounding rock deformation, the backfill grouting compactness is divided into five grades from A to E. Meanwhile, the suggestions on the backfill grouting compactness are given. In addition, the influence of local non-compactness at top and side of tunnel on supporting effect is simulated and analyzed. The analytical results show that: (1) The low compactness of backfill layer will lead to uneven stress distribution and large tensile stress of lining segment, as well as cause large deformation and yield area distribution of surrounding rock. (2) For Grade Ⅲ surrounding rock, the recommended compactness is over 70%, and for the surrounding rock with poor quality than Grade Ⅲ, the recommended compactness is over 80%. Additionally, the risk of the uncompacted backfill at the top of tunnel is greater than that at the side, and the stress distribution is the most uneven when the proportion of uncompacted backfill is 1/6. The results can provide reference for the backfill grouting compactness evaluation and the supplementary grouting treatment of similar projects in the future.

Key words: double-shield TBM, tunnel construction, pea-gravel backfill grouting, compactness, support effect