Abstract：In order to study the structural deformation characteristics of shallow-buried large-cross-section loess tunnels strengthened by jet grouting piles and the choice of time for foundation reinforcement，indoor model tests and numerical simulations were performed，and the influence of piles and application time on the mechanical deformation characteristics of the tunnel structure was analyzed. The results show that the reinforcement effect of jet grouting piles to the foundation is remarkable and the deformation of surrounding rock at the bottom of the tunnel can be effectively reduced. In the case of full cross-section reinforcement by piles，the stress release of the surrounding rock is relatively sufficient with a large deformation. The displacement of the initial support easily exceeds the limit range in actual construction，and all the piles at the bottom of the tunnel are under pressure，which is beneficial to mobilize the effective bearing capacity of the piles in the later period. It is recommended that the full cross-section reinforcement scheme is adopted while the surrounding rock of the tunnel is stable. In the case of pile reinforcement in stages，however，the earlier closure of the support system is beneficial to the stability of the tunnel structure，but the piles in the middle of the bottom of the tunnel are in tension state and hence，are easy to break during the construction period. It is suggested that the second scheme can be used when the surrounding rock of the tunnel is unstable and at the same time，the piles should be reinforced. The research can provide a reference for the choice of time reinforcement of rotary jet grouting piles for loess tunnel base.
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2019, Vol. 38 
