Abstract:

To address the untimely and inadequate support strengths in shallowlyburied mined tunnels in soft surrounding rocks in urban settings, numerical simulation and indoor model tests are introduced to investigate the principle of a spatial reticulated grid boltshotcrete support and the mechanical characteristics of bearing capacity. Simultaneously, the concept of timely highstrength support is proposed to form a strong support in a timely manner that bears the load of surrounding rocks in real time. Moreover, the prefabricated spatial reticulated grid support structure and joint type are designed innovatively, and a highstrength spatial reticulated grid boltshotcrete support system  is established. The results reveal the following: (1) The use of a highstrength spatial reticulated grid as the primary support of the tunnel is convenient for improving the stress state and the overall bearing capacity of the structure. (2) When subjected to compression and bending loads, the upper main leg steel tube first experiences yield failure, and the bolted endplate joint component demonstrates higher bearing capacity and bending stiffness than the jointless component. (3) In terms of failure modes, the concrete component with the bolted endplate joints shows a vertical crack development in the midspan region, whereas the concrete component without joints shows a larger range of crack development. (4) The concrete component without joints has good deformability, and its ultimate bearing capacity is 1.2 times that of the concrete component with the bolted endplate joints. However, the bending stiffness of the concrete components with the bolted endplate joints is higher, and the deformation control effect is better.

Key words:  mined tunnel; prefabricated spatial reticulated grid, timely highstrength support, numerical simulation, indoor fullscale test