松动岩体群洞围岩稳定性研究

【作者】 席先武；

【导师】 彭建兵；

【作者基本信息】 长安大学 ， 地质工程， 2004， 博士

【摘要】 黄河黑山峡大柳树坝址区广泛分布着松动岩体,该松动岩体是中寒武统香山群本身所具有的软硬相间特性以及其所处的特殊区域稳定动力学背景共同作用的产物。作为洞室围岩的松动岩体,岩体内断裂发育,局部有架空现象;波速低,透水性强、地下水位深;岩体不均一和完整性差;绝大部分围岩属Ⅲ类和Ⅳ类,且以为Ⅳ类为主。 本文在系统研究大量资料的基础上,以数值模拟为手段,视松动岩体为等效连续介质,以大柳树坝址Ⅲ线勘探剖面上分布的群洞为研究对象,首次系统地研究了重力场、地下水动力条件、地震动作用以及多场耦合作用下松动岩体群洞效应问题。得到了以下认识:(1)松动岩体群洞之间存在明显的相互影响和相互作用,特别是间距较小的5条引水发电洞两两洞室之间的围岩内,竖向应力的极值均在5～8MPa,为洞室开挖前原始应力的两倍左右,塑性区相互沟通,软弱带ji22与洞室交汇的部位位移超出1m,有塑性挤出的现象,其两侧洞室围岩中的应力分布明显受到ji22存在的影响;(2)因松动岩体具强透水性,地下水的渗流使群洞效应更加明显。地下水主要通过降低岩体中的有效应力而降低围岩强度,由此,群洞区域的剪切应变增量的量值和波及范围均较无地下水渗流时大为增加;洞壁围岩也由剪切屈服向拉张屈服转变;(3)通过对比单洞与群洞的地震响应,发现群洞区域观测点的加速度时程(特别是竖向加速度时程),其幅值明显较单洞时有所放大,群洞区域迫振后的自振幅值往往较高;(4)在重力场、地下水渗流场以及地震波动场的多场耦合作用下,地震使岩体进一步松动、扩容,因此岩体中不会出现超静水压力,有效应力有所上升。 本文还首次基于非连续介质模型,研究了松动岩体单洞以及群洞的成洞条件,锚喷支护对松动岩体Ⅲ类特别是Ⅳ类围岩的适应性,锚喷支护后地震作用下的松动群洞围岩稳定性。结果表明:(1)松动岩体单洞稳定性较差,围岩将出现大范围破坏和塌方现象,因群洞效应,松动岩体群洞围岩稳定性比单洞围岩更差,且其最严重的破坏并不出现在洞顶,而是偏向邻近洞室一侧;(2)对松动岩体围岩需采用锚杆+钢筋网+喷砼联合方式进行支护,但对于其中的Ⅳ类围岩,这种支护方式的支护效果并不理想,需对松动岩体进行超前灌浆处理;(3)基于弹粘性模型理论,采用锚喷支护的松动岩体Ⅲ类围岩,预测其最终流变变形量为16.8mm,Ⅳ类围岩最终流变变形量为22.7mm;(4)在地震作用下,采用锚喷支护的群洞围岩,其位移和切向应力并不随振动持时而单调增加或减小,在振动2s后,即保持在一定值附近往返波动;静力条件下稳定性好的锚喷支护围岩,在地震作用下其稳定性依然较好,相反,静力条件下稳定性差的锚喷支护围岩(如更多还原

【Abstract】 There is plenty of Relaxed Rock Mass in Huanghe Heisanxia Daliushu dam site, which results from itself soft-rigid nature acting with the special area stability dynamics condition. In Relaxed Rock Mass, plenty of faults and holes can be found, the wave is slow, the permeability is high, and the groundwater level is deep. As cavities’ surrounding rock, Relaxed Rock Mass is cracked, much of which belong to Ⅲ and Ⅳ rank surrounding rock, and the Ⅳ rank rock is majority. In this thesis, large numbers of data have been studied. Daliushu dam site cavities distributed along the 3th exploration line are the research objective, the Relaxed Rock Mass Multi-cavity effect, under gravity、 groundwater seepage、 dynamic and multi field coupling acting condition, has been systematically researched firstly, by using numerical method, based on equivalent continuum theory. The result shows: (1)The Multi-cavity effect is sharp, especially In the surrounding rock between the five close diversion cavities, the stress is twice larger then before, and the local area in which the rock is in plastic intercommunicates each other. The distributing character of the stress in surrounding rock is affected by the existence of weak zone ji22; (2) The seepage of groundwater results in the effect sharper then before, owe to the high permeability of Relaxed Rock Mass. The groundwater reduces the strength of surrounding rock by reducing the effective stress of the rock, as the result, the shear strain increment in the area of cavities is larger then before, and the surrounding rock on cavity wall changes its plastic form from shear to tensile; (3) By comparing the earthquake response of single cavity with which of cavities, it is be observed that the acceleration of cavities is higher then which of single cavity; (4) Under multi-filed coupling acting condition, the earthquake makes the rock more relaxed and more expansion then before, so the effective stress become higher and the exceed hydraulic pressure can not be found.In this thesis, the status of cavitation of single cavity and cavities in Relaxed Rock Mass, the adaptability of bolt-reinforcement to the Ⅲ and Ⅳ rank surrounding rock and the stability of bolt-reinforcement surrounding rock under earthquake condition has been researched based on non-equivalent continuum theory. The result says: (1) The stability of single cavity surrounding rock in Relaxed Rock Mass is poor, large scope of wreck and collapse rock can be found. As for Multi-cavity effect, the stability of multi-cavity surrounding rock is more bad then the single’s, and theworst is not on the tip of the cavity wall, but on the side of surrounding rock lean to the other cavity; (2) The adaptability of bolt-reinforcement to IV rank surrounding rock is bad, and the IV rank surrounding rock need to be grouted; (3) Based on elastic-creep model theory, the long-time strain of bolt-reinforcement surrounding rock has been forecasted, and the long-time displacement of Illrank rock is 16.8mm and which of IV rank rock is 22.7mm; (4) Under earthquake condition, the bolt-reinforcement surrounding rock with good stability is also stable, but the one with bad stability becomes worse then before; (5) The bolt-reinforcement strengths the surrounding rock to withstand earthquake by enhancing the shear strength and tensile strength of which.更多还原