【作者】 张钊；

【导师】 刘东海；

【作者基本信息】 天津大学 ， 水利工程， 2019， 硕士

【摘要】 如何有效改善心墙拱效应是高粘土心墙堆石坝建设中亟需解决的重要问题。通常采用粘土中掺砾,以提高心墙的变形模量,但对于300m级高坝,砾质土心墙应力拱效应仍较为明显,而更多掺砾,会导致心墙防渗性能下降,增大水力击穿破坏的风险。本文基于国内外现有研究基础,在砾质土基础上,以水泥及国内外常见的两种固化剂(Evo Crete~?和HAS~?)为外掺剂,制备胶结砾质土料,开展其力学与耐久性能试验研究和有限元数值分析,研究胶结砾质土对心墙堆石坝应力与变形,以及心墙拱效应和水力劈裂的影响,进而分析胶结砾质土作为高堆石坝心墙的可行性。本文主要研究内容和成果如下:(1)通过界限含水率试验、颗粒分析试验和击实试验,得到了试验所用土料的基本工程性质,包括:细粒粘土的液塑限和塑性指数,砾质粘土的颗粒级配,不同固化剂掺量下土料的最大干密度和最优含水率,以及压实特性规律,并为后续力学性能和耐久性能试验的试样制备提供了控制标准。(2)分析了胶结砾质土的无侧限抗压强度和劈裂抗拉强度随固化剂类型、掺量和龄期的变化规律;通过渗透试验和冻融循环试验,研究了不同固化剂类型和掺量下胶结砾质土的耐久性能,发现HAS胶结砾质土表现出了更高的抗压和抗拉强度优势,更大的变形模量优势和更好的韧性优势,有利于改善心墙的应力拱效应和抗水力劈裂能力,而且,HAS具有更好的抗渗和抗冻性能,能在一定程度上减轻或避免冻融循环的不利影响;利用SEM扫描电镜,分析了不同种类胶结砾质土的微观结构,从水化物发育角度解释了不同胶结砾质土性能差异的原因。(3)对砾质粘土、固化剂掺量为2%和6%的HAS胶结砾质土进行了三轴固结排水剪切试验,分析了不同土样的应力应变关系和抗剪强度特性,并得到了心墙胶结土料的邓肯-张模型参数。研究表明:HAS土壤固化剂可显著提高土样的粘聚力和内摩擦角,表现出一定程度的剪胀和软化现象。(4)以某心墙堆石坝为例,开展了有限元模拟,分析了HAS胶结砾质土对心墙堆石坝应力与变形的影响,以及对心墙应力拱效应的改善效果,并从力学角度,判断了不同土样心墙发生水力劈裂的可能性。研究结果表明:随着固化剂掺量的增加,坝体最大沉降值显著降低,心墙内的大小主应力均增加,心墙拱效应减弱,6%固化剂掺量下的心墙内已不存在水力劈裂的力学条件。该研究成果可为超高心墙堆石坝心墙坝料选择提供一种新的可能,为解决300米级超高心墙堆石坝的拱效应问题提供新途径。更多还原

【Abstract】 How to improve the arch effect of core wall effectively has become an important problem for high soil core wall rock-fill dams.A common solution for the issue is to mix a certain amount of gravel into the clay soil to increase the deformation modulus of the core wall.However,the arch effect is still obvious for these dams.If more gravel is mixed,the modulus of the core wall can undoubtedly be improved,but it maybe lack in its impermeability,and the risk of hydraulic fracturing will increase.Based on previous researches,this research comprehensively investigates the effect of cemented gravel-mixed soil on deformation,stress,arch effect and hydraulic fracturing of core rock-fill dams by the means of mechanical experiments,durability experiments and finite element analysis.The cemented gravel-mixed soil in this research takes cement and two common soil solidifiers(Evo Crete? and HAS?)as additives.The feasibility of cemented gravel-mixed soil as core wall of high earth-rock dams was evaluated.The main research achievements of this thesis are as follows:(1)Through the limit moisture content test,particle analysis test and proctor test,the engineering properties of the soil used in the experiments were obtained,which includes the plasticity index and the particle size distribution of the soil,,the maximum dry density and optimal moisture content of the cemented gravel-mixed soil with different solidifier content,and the compaction characteristics.These properties provide a control standard for specimen preparation of subsequent experiments.(2)Various factors including ages,solidifier types and solidifier contents that have effects on the unconfined compressive strength and splitting tensile strength of cemented gravel-mixed soil were analyzed and discussed.The durability of cemented gravel-mixed soil with different solidifier types and contents was studied by penetration test and freeze-thaw resistance test.It is found that the HAS cemented gravel-mixed soil has the advantages of higher compressive and tensile strength,larger deformation modulus and better toughness,which is beneficial to improving the arch effect of the core wall and avoiding the occurrence of hydraulic fracturing.In addition,HAS cemented gravel-mixed soil has better impermeability and frost resistance,which can reduce or avoid the adverse effect of freeze-thaw cycle.Then,the microstructure of cemented gravel-mixed soil was analyzed by scanning electron microscope test,and the reasons for the performance differences of cemented gravel-mixed soil were explained.(3)A triaxial test was performed on gravel-mixed soil and HAS cemented gravelmixed soil with 2% and 6% solidifier content.The stress-strain relationships and strength behaviors of the soil were analyzed,and the Duncan-Chang model parameters of cemented gravel-mixed soil were obtained.The research results indicate that the HAS cemented gravel-mixed soil can significantly increase the cohesion and internal friction angle of specimens,and the stress-strain curve shows a certain degree of shearswelling and softening.(4)Taking a core rock-fill dam as an example,finite element analysis was carried out.The influence of HAS cemented gravel-mixed soil on the stress and deformation of the core rock-fill dam and the improvement effect of the arch effect were analyzed.The possibility of hydraulic fracturing for different soil core walls was evaluated from the mechanical perspective.The research results indicate that with the increase of the proportion of HAS solidifier,the maximum settlement of dam is significantly reduced,the stress in the core wall is increased,and the arch effect is weakened.There is no mechanical condition of hydraulic fracturing in the core wall when the proportion of HAS solidifier reaches 6%.The research results can provide a new alternative for the selection of core wall materials of high core rock-fill dams,and a new way to solve the arch effect issue of high core rock-fill dams.更多还原