Case study of the impacts of pea-gravel grouting defects on loading responses of TBM tunnel segment lining with different surrounding rocks

• 3D finite element numerical models of segment lining, pea-gravel grouting and surrounding rock were constructed. • Four typical defects of pea-gravel grouting in TBM tunnel lining were introduced in the numerical analysis. • Impacts of the defects on loading response of segment lining are analyzed to identify possible risks of tunnel operation. • The local cavity defect at the top of the tunnel has the greatest impact on the load bearing of segment lining. Pea-gravel grouting, as a component of TBM tunnel lining, plays a role of transferring forces between segment lining and surrounding rock, and forms an integral seepage prevention with the segment to ensure the operation safety of the tunnel. During the TBM construction, how to properly treat the defects of pea-gravel grouting is a problem that always bothers the engineers. This needs a deep understanding of the impacts of different pea-gravel grouting defects on the loading response of segment lining. For this purpose, the 3D finite element numerical models of segment lining, pea-gravel grouting and surrounding rock were constructed in this paper, which considered the possible defects including local cavity, rich rock powder, rich grouting slurry and less dense grouting. The geological grade of surrounding rock was different at III, IV and V classes from strong and entirety to weak and broken. The most unfavorable positions of segment with maximum stress and displacement were found out based on the analysis of their variations. Results show that the stress state of tunnel segments is dominated by the surrounding rock class, the stress of the segments without pea-gravel grouting defects tends to be uniform and balanced with the surrounding rock changed from V-class to III-class. Among all kinds of pea-gravel grouting defects, the local cavity defect or the less dense grouting defect at the top of the tunnel creates a marked effect on the load bearing of segment lining. Under the condition of V-class surrounding rock, the coupling effect of three or more defects raises a risk of concrete cracking of segment lining with a high tensile stress over the limit of controlling. The results of this study provide a guidance for the engineers who can recognize the risk degree of different defects of pea-gravel grouting under different surrounding rocks and take targeted measures to ensure the pea-gravel grouting quality during the TBM construction.