利用弹性理论建立了轴对称圆形地下洞室临时支护失效临界时间的七参数模型，该模型可指导合理地确定流变岩体中洞室临时支护加固范围和强度、适时地施作永久被覆。模型表明：支护范围与围岩应力正相关，与支护体的强度负相关；在特定的应力状态和支护强度组合下，无论加固范围多大，临时支护都不能有效工作。最后讨论了模型参数的测算公式，给出了模型运用的算例。

On the basis of elastic theory, a seven parameters model is built. This model is used for judging the ultimate loss of? efficiency in a symmetrical underground tunnel. Through this model, the range and strength of temporary supports in rheological rock can be determined reasonablly. The model result shows that: the supporting range has a positive correlation to the stress of surrounding rock, and presents a negative correlation to the strength of the supported object; with the specified composition of stress state and supporting strength, no matter where the reinforced range is widespread, the temporary support can not work effectively. Finally, the calculating method of parameters in this model is discussed, and the example of how this model is applied is given.