Taking excavation of a high stress roadway as an object and based on unloading rock mechanics theory and Hooker theorem, an equivalent 3D model of -850 m level main cross drift in a mine was built, the unloading zones of drift excavation was ascertained, and the functional expression between rock mechanical parameters in different unloading part and unloading quantity was established, thus parameter deteriorating Jaw of unloading rock mass was acquired. The results show that tunnel face and surrounding rock could be divided into three unloading parts as I, II, III along drift excavation, which was corresponding to broken zone, plastic zone and elastic zone. In the process of unloading, the internal friction angle, cohesion and elastic modulus in different unloading parts declined gradually, whereas Poisson's ratio increased. The function between rock mechanical parameters and unloading amount provides a theoretical basis for analysis of unloading response of drift excavation.
The construction of roadway in high ground stress has always been technical difficult problem, which shows evidence in horizontal ground stress. Roadway experiences an unloading process along with the release of ground stress (Chen et al. 2013, Kang et al. 2007). Structural weaknesses that exist in rock mass still remain good mechanical properties under the state of loading. However, these weaknesses would reduce the quality of rock mass fast under unloading location, especially under the condition that unloading amount is large and tensile stress occurs, resulting in the dramatically decline of the rock mechanical properties and the non-coincidence of rock mass mechanical properties with study conclusions under loading conditions (Zhang et al. 2013, Chen et al. 2004).
The depth of main shekmum is 874 m at -850 m level of a mine and its surrounding rock is politic siltstone. In situ stress at typical points was measured with stress relief method, the results showed that surrounding rock was mainly affected by tectonic stress and gravity stress that the tectonic stress was higher than gravity stress. In other words, the stress in horizontal direction was higher than that in vertical direction.
