Layout optimization for non-equidistant thrust system of tunneling machine based on geometric progression under mixed ground

For the difference of rock and soil strength on the tunneling face, curved tunneling, and the top-heavy structure of the main machine forming the complex geological structure, the adoption of uniform thrust system arising from large unbalanced load easily causes cracks and dislocations in the rear segments. Therefore, non-equidistant driving system would be adopted in this composite foundation. This article presents a geometric progression method for layout design of non-uniform thrust system. Based on the force transmission laws of the thrust system, the geometric progression increasing difference model of arranging non-uniform driving system has been proposed. Then, the characteristics of the design method have been discussed in detail. Finally, the model has been applied to a diameter of 9.49 m of tunneling machine with a thrust system of 14 pairs of jacks which has been successfully used in curved tunnel construction in Germany. By adopting the coefficient of variation representing the force transmission performance derived from all thrusts for jacks, it indicates that the performance of the optimized thrust system is better than the original one. The results would provide a theoretical basis for the design of a non-equidistant thrust system with better force transmission performance under working geological conditions.