Abstract:

To control severe squeezing deformation of thin extremely soft rock under high geostress in the Muzhailing tunnel under construction, a design scheme based on active support with combination of prestressed long and short anchor cables, Wshaped steel belt, and flexible fiber mesh is proposed based on engineering geological analysis, design changes, and monitoring and measurement work carried out onsite. The scheme adopts the construction order of anchor first and then support. The design scheme is verified by numerical analysis and test section construction. The results show that the active support can fully reinforce the surrounding rock, improve the shear resistance of surrounding rock, control the release state of deformation energy of surrounding rock, effectively control the deformation of surrounding rock, and control the deformation of supporting within 20 cm(that is 50% reduction). In the engineering practice, anticorrosion, support parameters, and construction equipment selection of anchor cable are optimized and adjusted to ensure the smooth progress of tunnel construction.

Key words: extremely high geostress, soft rock tunnel, large deformation, prestressed anchor cable, support design