“四维动态”模拟应是今后采空区模拟研究的主要方法和手段，也是搞清采空区各场规律的必经之路，其中采空区内各处孔隙率的准确确定是此技术的关键性问题之一。因此，对采空区的孔隙率进行了空间立体分析。首先将采空区内的孔隙率视为二阶张量进行了研究，并得出各方向孔隙率的计算方法。随后对采空区垂直方向的孔隙率进行了分析，通过模拟试验得出了孔隙率与岩石粒径之间的关系，并绘制出了全程关系曲线。同时，利用现场观测与理论分析证明了此关系的正确性。最后利用数值模拟方法对采空区垂直方向的风流场进行了数值模拟，此模拟也充分说明了采空区三维立体模拟研究的必要性。

Four-dimensional dynamic simulation should be the principal method of goaf simulation and also the essential approach to understand laws of fields in the goaf. The exact determination of goaf porosity is a key problem for this method. In this research, the porosity of goaf is studied in three-dimensional space. At first, the porosity is regarded as a second-order tensor, and the computational method for the porosity in all directions is obtained. Secondly, porosity in the vertical direction is analyzed and the relationship between porosity and rock diameter is obtained through simulation test. The process curve is drawn and is proved to be correct by means of field observation and theoretical analysis. Finally, the air flow field of goaf in vertical direction is analyzed through numerical simulation, which in turn demonstrates the necessity to research on the goaf in three dimensions.