为研究软岩隧道超前导洞的适用性，基于经典弹塑性理论，建立深埋软岩隧道超前导洞法开挖应力释放的力学模型，采用2阶段的方法推导考虑超前导洞应力释放的隧道开挖弹塑性解。定义围岩应力释放比来反映应力释放的效果，并研究不同地应力、围岩弹性模量、强度等条件下超前导洞开挖半径对应力释放效果的影响。结果表明：
通过施作超前导洞可以降低作用在支护结构上的围岩压力，尤其是在高地应力环境或围岩较软弱的条件下，采用超前导洞法进行应力释放效果更加明显。但导洞半径并非越大越好，现场试验表明：
对于3车道大断面软岩隧道，导洞断面太大对隧道围岩的稳定不利。隧道施工中，应在保障围岩稳定的前提下进行应力释放，做到初期支护尽早封闭成环，实现隧道安全快速施工。
To investigate the applicability of stress release for
pilot heading in soft rock tunnel, the mechanical model of stress release for
soft rock tunnel excavation by pilot heading method is established based on the
classical elasticplastic theory. The elasticplastic solution of tunnel excavation considering the stress release
of pilot tunnel is derived by a twostage method. The
stress release ratio of surrounding rock is defined to reflect the effect of
stress release, and the influences of pilot tunnel radius on stress release
effect under different insitu stresses, elastic
modulus and strengths of surrounding rock are studied. Results show that the
ground pressure applied on the support can be reduced by the excavation of a
pilot tunnel, especially in high geostress environment or weak rock, the stress
release effect is much more obvious by pilot heading method. However, the pilot
tunnel radius is not as larger as possible. The field tests show that for a
threelane large crosssection
soft rock tunnel, the large section of the pilot tunnel is unfavorable to the
stability of the surrounding rock. Stress release measure should be carried out
under the premise of ensuring the stability of surrounding rock in tunnel
construction. Thus, the primary support should be installed as soon as possible
to realize the safe and rapid construction.
