超大断面隧道开挖围岩荷载释放过程的模型试验研究

MODEL TEST STUDY OF SURROUNDING ROCK LOAD RELEASING DURING SUPER-LARGE SECTION TUNNEL EXCAVATION

以兰渝铁路两水隧道为工程背景,进行超大断面铁路隧道开挖支护的大比尺三维地质力学模型试验,对开挖过程中的围岩荷载释放过程进行研究。根据工程现场地质情况研制满足相似要求的新型模型试验相似材料,经室内试验验证,该相似材料与原岩材料的力学性质有很好的相似性,满足试验要求。结合现场实际工况在模型试验不同区段采用不同的开挖支护工法,首先研究全断面及台阶法开挖情况下的围岩荷载释放过程,通过试验数据的分析,揭示不同开挖工法隧道围岩荷载释放全过程的特点和差异。相同开挖工法下,同一断面上不同位置的荷载释放过程存在很大差异;同样,不同开挖工法条件下同一位置的围岩荷载释放过程也不尽相同。其次,掌子面前方围岩受开挖影响会在局部发生先行荷载集中,先行荷载集中程度与开挖工法和断面形式有很大关系,开挖面前方荷载集中程度过高会加剧掌子面围岩的挤出效应,不利于围岩的稳定。最后,通过有无支护开挖情况下围岩荷载释放过程的对比,说明施作支护能够有效缓解开挖过程中的掌子面先行荷载集中现象,减少荷载释放总量,优化隧道围岩荷载释放过程。

Against the background of the Liangshui tunnel of Lanzhou—Chongqing line and based on 3D large-scale geomechanical model test of excavation and support on large cross-section tunnel,the process of surrounding rock load releasing during tunnel excavation is studied.New similar material is developed according to the field geological condition,which is proved by the laboratory tests to be similar to original rock materials on mechanical properties and meets the test requirement.Construction methods of excavation and support on different sections are various and the load releasing processes of surrounding rock on full-face excavation and bench-cut excavation are compared firstly.Through analyzing the test data,the features and differences of load releasing processes with different excavation methods are revealed.There are great differences in load releasing processes at different locations of the same section using the same excavation method.Meanwhile,the load releasing process at the same locations of the same section are various when different excavation methods are used.Secondly,the phenomenon of first load concentration occurs in front of tunnel face affecting by the excavation.The degree of first load concentration is related with the excavation method and section form.High degree of load concentration in front of tunnel face would aggravate the crowding-out effect,which is unfavorable to surrounding rock stability.Lastly,by comparing the load releasing processes of support excavation and non-support excavation,it is known that support can response the first load concentration effectively,reduce the load releasing amount,and optimize the load releasing process of surrounding rock in construction.