Stability of the loess tunnel foundation reinforced by jet grouting piles and the influence of reinforcement parameters

The special geological characteristics of loess, such as collapsibility and vertical joint development, usually bring great difficulties to the construction of tunnel inverts. Effectively resolving the subsidence of the tunnel bottom, shortage of the bearing capacity, and uneven subsidence caused by weak loess has been a key challenge during the construction and operation of loess tunnels. Jet grouting piles are widely used because they can effectively improve the geological characteristics of loess and enhance the stability of the foundation. To investigate the reinforcement effect of jet grouting piles in loess tunnel foundations and the effect of changes in the geometric parameters of jet grouting piles on the stability of tunnel foundations, centrifugal model tests and numerical simulations were used to analyse the mechanical properties and the deformation characteristics of the tunnel lining. The results show that the deformation of the loess tunnel bottom caused by the operation and construction can be reduced effectively by using jet grouting piles, but the surrounding rock pressure and settlement of the tunnel vault will be increased at the same time. The length of the jet grouting piles has a better impact than the diameter to improve the reinforcement effect on the stability of the foundation, and the deformation of the tunnel bottom and the stress of the surrounding rock at depth are reduced greatly. Based on the relationship between the length and the reinforcement efficiency of jet grouting piles, the length of jet grouting piles is recommended to be 5-12 m.