Abstract:

The solution to the broken of deep old loess tunnel primary support caused by surrounding rock degradation is necessary. Hence, by taking the primary support broken section caused by surrounding rock degradation of deep old loess of Yangshan Tunnel on Menghua Railway for example, the stress characteristics of deep loess and surrounding rock under the condition of deterioration are compared and analyzed by means of supplementary survey, numerical analysis and stress monitoring. The conclusions are drawn as follows: (1) Under the condition of the original surrounding rock parameters, the shotcrete is under full ring compression, the shotcrete on the top heading is under greater stress, the maximum compressive stress is at the crown, and the arch foot on the top heading has greater shear stress. (2) Under the condition that the surrounding rock is deteriorated but no continuous slip surface is formed, the bending compressive stress of top heading increases significantly, the maximum compressive stress is still located in the crwon, and the arch foot of the top heading is prone to compression shear failure. (3) Under the condition of surrounding rock deterioration and continuous slip surface formation, the maximum shear stress and the maximum compressive stress are located in the same position, the upper boundary of the contact between the slip body and the lining, where compressive shear failure is easy to occur and the position varies with the variation of the rupture slip surface, and the distribution range is from the arch waist of the top heading to the arch foot.

Key words: deep old loess tunnel,  surrounding rock deterioration,  fracture slip surface,  mechanical characteristics of support