【作者】 王伟；

【导师】 王晓川；

【作者基本信息】 武汉大学 ， 水利水电工程， 2023， 硕士

【摘要】 随着我国水能资源的开发,国家对水利工程建设投入力度不断增大,水库建设不可避免要涉及页岩岸坡,消落带内页岩岸坡在库水位周期性升降过程中因干湿循环作用容易发生劣化问题,给水库的稳定运行带来不利影响,目前有关库水位升降引发页岩岸坡失稳的研究相对较少,亟需深入研究系统揭示。本文以四川长宁地区志留统五峰组-龙马溪组出露页岩为研究对象,开展了室内气体渗透试验和单轴抗压试验,对页岩在干湿循环作用下的渗透特性和力学性能进行了评价;通过SEM、EDS、XRD等微观分析技术,研究了页岩细观结构、组分等指标对干湿循环的响应特征,从细观角度揭示了干湿循环诱导页岩渗流劣化机理,研究成果为评估库水位升降作用下页岩岸坡劣化行为及库岸运行防护提供理论支撑。本文的主要研究内容及成果如下:(1)通过开展不同围压和渗透压差下层理页岩的气渗试验,分析了围压、渗透压及干湿循环次数对页岩渗透特性的影响。结果表明:渗透率随干湿循环次数增大而增大,但增大幅度受围压和渗透压影响。低围压高渗透压差下页岩气体渗透率随干湿循环次数增加变化幅度较大,当围压增大、渗透压差减小,页岩气体渗透率随干湿循环次数增加变化幅度减小。(2)基于干湿循环处理后页岩试样的力学性能测试,获取了干湿循环次数、层理倾角等因素对页岩抗压强度和弹性模量的影响。结果表明:干湿循环次数越多,页岩力学性质越弱,干湿循环次数与弹性模量和峰值强度的近似呈指数衰减相关;页岩受压力学性质与层理倾角有关,峰值强度分布近似符合JPW模型,薄弱节理面模型对页岩等层理结构岩体峰值强度估算具有较好的适用性。(3)利用SEM、EDS、XRD、光学轮廓仪扫描等测试手段,探究了干湿循环处理后页岩微观结构、元素组分、表面形貌等微观演化特征。结果表明:干湿循环对页岩微观结构影响主要体现在块体细化,块体水化,孔洞微小化,尖锐棱角平滑化等方面;亲水矿物占比对干湿循环作用响应大于非亲水矿物和有机质;随着干湿循环作用次数增加,页岩试样平整表面的粗糙度略微增大。(4)结合干湿循环作用页岩宏观和细微观特征,阐释了干湿循环作用下页岩渗流劣化机理。结合干湿循环作用下页岩宏观渗透和力学特性变化规律、基质和节理面宏观破坏模式、页岩微观结构和矿物成分变化情况,分析了干湿循环作用对页岩内部节理面贯通、渗流通道改变、微缺陷发育及矿物水化等微观过程的促进作用,系统阐释了干湿循环作用页岩劣化机理。更多还原

【Abstract】 With the development of pumped storage power station in China,the national investment in water conservancy project construction is constantly increasing,and the construction of reservoir inevitably involves shale bank slope,which is prone to deterioration due to the dry-wet cycle in the periodic rise and fall of reservoir water level in the water-leveling zone,which brings adverse effects on the stable operation of reservoir.At present,there are relatively few studies on the instability of shale bank slope caused by reservoir water level rise and fall.In this paper,gas permeability tests and uniaxial compressive tests were carried out to evaluate the permeability and mechanical properties of the Silurian Wufeng-Longmaxi shale in Changning area of Sichuan Province under the action of wetting and drying cycles.Microscopic analysis techniques such as SEM,EDS and XRD were used to study the response characteristics of shale meso-structure,composition and other indexes to the dry-wet cycle,and the mechanism of shale seepage degradation induced by the dry-wet cycle was revealed from the mesoscopic perspective.The research results provide theoretical support for the evaluation of the deterioration behavior of shale bank slope under the influence of reservoir water level rise and fall and the operation protection of reservoir bank.The main research contents and achievements of this paper are as follows:(1)The influences of confining pressure,osmotic pressure and the number of dry-wet cycles on the permeability characteristics of shale are analyzed by conducting gas permeability tests of underlayed shale with different confining pressure and osmal pressure differences.The results show that the permeability increases with the number of dry-wet cycles,but the increasing range is affected by confining pressure and osmotic pressure.With low confining pressure and high osmotic pressure difference,shale gas permeability changes greatly with the increase of dry and wet cycles.With the increase of confining pressure and the decrease of osmotic pressure difference,the change range of shale gas permeability decreases with the increase of dry and wet cycles.(2)Based on the mechanical properties test of shale samples treated with dry and wet cycles,the influences of the number of dry and wet cycles,bedding dip Angle and other factors on the compressive strength and elastic modulus of shale are obtained.The results show that the more dry-wet cycles there are,the weaker the mechanical properties of shale.The number of dry-wet cycles is approximately exponentially correlated with the elastic modulus and peak strength.The compressive mechanical properties of shale are related to bedding dip Angle,and the distribution of peak strength is approximately in accordance with JPW model.The weak joint plane model is suitable for estimating peak strength of rock mass with equal bedding structure of shale.(3)Using SEM,EDS,XRD,optical profilometer scanning and other testing methods,the micro-evolution characteristics of the shale after the dry-wet cycle treatment,such as microstructure,element composition,surface morphology,etc.The results show that the effects of dry and wet cycling on the microstructure of shale are mainly reflected in the aspects of block thinning,block hydration,pore minimization,sharp edges smoothing,etc.The proportion of hydrophilic minerals is higher than that of non-hydrophilic minerals and organic matter.The roughness of flat surface of shale sample increases slightly with the increase of dry-wet cycles.(4)Combined with the macro and micro characteristics of shale under the dry-wet cycle,the mechanism of shale seepage degradation under the dry-wet cycle is explained.Combined with the changes of macroscopic permeability and mechanical properties of shale under the action of dry-wet cycle,the macroscopic failure mode of matrix and joint surface,and the changes of shale microstructure and mineral composition,the promoting effects of dry-wet cycle on the internal joint surface penetration,the change of seepage channel,the development of microdefects and mineral hydration of shale are analyzed,and the deterioration mechanism of shale under the action of dry-wet cycle is systematically explained.更多还原