Houquan Liu

Collapsible loess tunnel foundation reinforcement is a new challenge in the construction process of tunnel engineering. According to the field displacement and stress monitoring of the Fujiayao loess tunnel, this paper investigates the reinforcing effect of a high‐pressure jet grouting pile on a collapsible loess tunnel foundation in the deep large‐span tunnel. The field monitoring method was employed to address the performance of tunnel foundation settlement, additional stress, earth pressure, rock pressure, etc. The results indicate that the stress on the pile tops and the earth pressure between piles increase gradually over time in two stages: stress increases rapidly in the first 45 days and, after this period, stress tends to gradually stabilize. Further, stress increases uniformly with the distance from the centerline of the tunnel, and the rock pressure of the tunnel sidewalls tends to be stable within two months of being constructed. Additional stress on the tunnel foundation increases linearly with time, and it is uniformly distributed in the vertical and horizontal directions of the tunnel section. Settlement of the tunnel foundation also gradually increases with time, and it tends to be stable at 50 days from the time of construction. Additionally, the settlements of different monitoring points are similar at the same depth. The research results will further improve the theoretical knowledge of tunnel bottom reinforcement in the loess tunnel, which not only can effectively guide the design and construction of the loess tunnel and reduce disease treatment cost but also can provide the necessary basic research data and scientific theoretical basis for revision of the corresponding specifications of highway tunnels and railway tunnels.

Cement fly-ash gravel (CFG) pile is a widely used ground reinforcement technique. This paper aims to address the mechanical characteristics of CFG composite foundation in consolidating saturated mine tailings (MTs) dam. The field static load tests were employed to explore the bearing capacity of the CFG composite foundation, and finite element (FE) models in three dimensions validated through comparison with experimental results were used to discuss the pile-soil stress distribution and pile-soil stress ratio of the CFG composite foundation. The results indicate that the distribution of earth pressure and pile stress is relatively homogeneous and stable over depth and load, while the development of CFG composite foundation bearing capacity is insufficient, in which the developed bearing capacity of CFG piles is less than 50% of its characteristic value. Additionally, compared with the laboratory model test results, the pile-soil stress ratio decreases with the increasing of the load in FEM results proved to better conform to the actual engineering conditions. Furthermore, the deformation modulus and thickness of cushion exert significant influence on pile-soil stress ratio and integral bearing capacity of CFG composite foundation.