隔水层对深埋隧洞衬砌外水压力的影响研究

Influences of aquiclude on external water pressures on linings of deep-buried tunnels

目前计算外水压力的理论公式大多针对均质围岩,当地层中存在强隔水层时,计算结果较实际压力偏大较多,导致出现衬砌结构厚度大、工程超预算等问题。为使衬砌结构设计与参数选取更为经济合理,结合滇中引水工程大理Ⅱ段深埋长引水隧洞,采用数值模拟的方法,选取衬砌外表面3个特征点,通过对上覆岩层中隔水层的位置高度、厚度以及与围岩的相对渗透性开展敏感性分析,对衬砌外水压力变化规律进行了研究。结果表明:衬砌外水压力随着隔水层位置高度的增加而减小,但是变化不显著;隔水层厚度是影响衬砌外水压力的关键因素,衬砌外水压力随着隔水层厚度的增加而显著减小;衬砌外水压力随着围岩与隔水层渗透系数比值的增大而减小,衬砌外水压力对相对渗透性非常敏感,当相对渗透性增大到200以上时,隔水层承担了绝大部分水头压力,衬砌外水压力降低到一定程度并逐渐稳定下来。研究结果可为地层中含有隔水层的深埋长隧洞的衬砌设计提供借鉴和参考。

At present,the theoretical formulas for calculating the external water pressures are mostly for homogeneous surrounding rocks.When there is a strong aquiclude in stratum,the calculated results are larger than the actual pressures,which will lead to the problems of large thickness of lining structures and overestimation of project budget.In order to make the design of lining structures and selection of parameters more reasonable and economical,combined with the deep-buried long diversion tunnel of Dali Section II of Middle Yunnan Water Diversion Project,by using the numerical simulation method and selecting three characteristic points on the outer surface of the linings,the sensitivity analysis of the position height and thickness of the aquiclude in overlying strata and the relative permeability of surrounding rocks are performed,and the variation laws of the external water pressures on linings are investigated.The results show that the external water pressures on the linings decrease with the increase of the height of the aquiclude,but the change is not significant.The thickness of the aquiclude is the key factor affecting the external water pressures on the linings,and the external water pressures on the linings decrease significantly with the increase of the thickness of the aquiclude.The external water pressures on the linings increase with the ratio of the surrounding rocks to the permeability coefficient of the aquiclude.When the relative permeability increases to a certain value,the aquiclude bears most of the head pressures,and the external water pressures on the linings decrease to a certain extent and gradually stabilize.The research results may provide reference for lining design of deep-buried long tunnels with aquicludes in strata.