Effects of Jet-Grouting Piles on Loess Tunnel Foundation with Centrifugal Model Tests

Loess is a common soil layer of geological movement. It has macropores, vertical joints, and tubular pores and also low strength and strong water sensitivity. When building a tunnel in a weak loess stratum (Q(3) loess or Q(4) loess), the poor geological characteristics of loess usually bring great difficulties to the construction of tunnel invert, and it is very easy to cause subsidence at the tunnel base, uneven subsidence at the tunnel bottom, and cracks in the road and lining. The use of jet-grouting piles to strengthen the weak loess foundation is an effective method to improve the geological characteristics of loess. To investigate the effect of jet-grouting piles on the reinforcement of the tunnel foundation in weak loess areas, centrifugal model tests were used to analyze the subsidence and structural mechanics response characteristics of the tunnel base under the influence of jet-grouting pile length and pile diameter. Research shows that subsidence at the tunnel bottom can be reduced effectively and the adjustment time of the surrounding rock stress can be shorten significantly when using jet-grouting piles to reinforce the tunnel foundation. The length of the jet-grouting pile is better than the diameter in improving the strength of the foundation. However, with the improvement in the strength of jet-grouting piles, the efficiency of foundation reinforcement is reduced, the surrounding rock pressure and lining stress gradually increase, and the construction economy and structural safety are gradually reduced. When selecting parameters of jet-grouting pile, consideration should be given to safety, economy, and ease of construction.