Abstract: China’s coal industry has for a long history. The power engineering, highway, railway, water conservancy projects and other structures are inevitably constructed above the coal mines with mine voids. The characteristics of mined voids in the small coal mines, such as, lack of historical mining data, small mining depth, complex distribution and high concealment, have potentially great influence on proposed engineering constructions. Since the current small coal mined void stability analysis method is not mature, the current engineering load critical influence depth method is commonly used to evaluate the stability of the small coal mine site, but the physical significance of the engineering parameters is inconsistent with the various technical specifications. In this paper, the mechanical balance analysis is adopted to derive the formula of load critical influence depth method from the mechanical principles. The physical and mechanical significance of each parameter is clarified.

Key words: Small Coal Mined Voids, Critical Depth of Influence, Stability Evaluation, Mechanical Meaning