Abstract: To examine the influence of various support parameters of pipe-roof grouting steel pipes on the bearing capacity of tunnel pipe-roof supports, the Pasternak two-parameter model is adopted to develop an accurate mechanical model of tunnel pipe-roof supports. Indoor experiments are conducted to assess the bearing capacities of pipe-roof grouting steel pipes with varying pipe diameters, wall thicknesses, and grouting fullness, as well as with and without reinforced steel cages. The experimental results reveal the following: (1) The influence of various support parameters of pipe-roof grouting steel pipes on the bearing capacity of the pipe roof follows the order of pipe diameter > grouting fullness > wall thickness > steel cage. (2) Increasing the pipe diameter significantly improves the bearing capacity of the pipe roof. For instance, compared to a pipe diameter of 108 mm, pipe diameters of 159, 219, and 299 mm increase the bearing capacity of the support by 183.58%, 398.62%, and 874.86%, respectively. (3) The grouting fullness substantially impacts the bearing capacity of the support. Specifically, as the grouting fullness of the pipe roof decreases from 100% to 75% and then to 50%, the bearing capacity drops by 29.8% and 34.5%, respectively. However, at the grouting fullness of 50%, the bearing capacity of the pipe roof is similar to that of a nongrouted pipe roof. (4) The reinforced steel cage and the wall thickness of the pipe roof slightly impact the bearing capacity of the pipe roof. Hence, in practical applications, increasing the pipe diameter is the most efficient approach for enhancing the bearing capacity of the pipe roof. Furthermore, reducing the wall thickness of the steel pipe can lower steel consumption without requiring a reinforced steel cage.

Key words: tunnel, pipe roof, support parameters, bearing capacity, pipe diameter, wall thickness, grouting fullness, steel cage