【作者】 李识博；

【导师】 王常明；

【作者基本信息】 吉林大学 ， 地质资源与地质工程， 2014， 博士

【摘要】 西藏高原高山宽谷河流区是当地重要的农业区，由于其分布有深厚粗大的强渗透性冲洪积层，因此在这类地区兴建水库工程时，坝基渗漏问题常常存在规模大、投入高、设计施工技术复杂、防渗效果差等问题。在对以往的资料进行查阅时，发现不同地区很多水库，在没有增加任何附加防渗处理的情况下，经过几年的运行，坝基土体出现渗透性降低、渗漏问题明显减弱等现象，且后期的水库蓄水位可以达到设计要求。对此现象，作者所在课题组做了初步的探索、研究，发现坝基渗漏减弱过程中有淤堵现象的发生，且此现象对坝基土体的渗透性有重要影响。为此结合国家自然科学基金面上项目“淤堵作用对高原水库坝基松散介质渗透性的影响及机理”（No.41072197），针对松散坝基土体的特殊性质，结合土质学、土力学、泥沙动力学、水动力学等多学科，利用自行研制的渗透-淤堵试验装置开展一系列室内渗透-淤堵模拟试验和现场渗透试验，并结合图像分析、分形分维计算及数值模拟等方法对渗透-淤堵现象进行细观分析，系统地研究高原水库坝基松散介质渗透-淤堵的整个过程。论文共分七章，第一章介绍了选题依据和研究意义，总结了工程中常见的淤堵现象、淤堵试验、研究方法、机理分析等方面的国内外研究现状及目前的研究不足，给出了论文的研究内容与技术路线，并提出了创新之处。第二章以卓玉水库上坝址线为研究对象，进行了野外实地调查取样，并开展了现场试坑双环注水试验。第三章以粗粒土为研究对象，开展渗透-淤堵试验。第四章以松散坝基土体为骨架颗粒开展了天然试样和击实试样的渗透-淤堵模拟试验。第五章以室内试验得出的结论，开展渗透-淤堵现象的细观分析与计算。第六章结合渗透-淤堵试验的宏观分析计算和细观分析计算，对渗透-淤堵机理进行分析，并利用数值模拟方法，建立了三维颗粒流渗透-淤堵数值模型，模拟了渗透-淤堵的全过程。第七章对论文进行总结，并提出今后的研究和改进建议。论文探讨了淤堵作用对坝基松散介质的减渗效应，明确了淤堵作用使土体渗透性降低的机理，提出坝基防渗设计的新理念与新思路。这将为解决高山宽谷河流坝基渗漏问题，实现人工淤堵减渗新方法奠定理论依据。限于作者理论水平和实践经验有限，难免会有错误和疏漏，不当之处敬请各位专家批评指正。更多还原

【Abstract】 Alluvial-proluvial substances were distributed in the wide valley of Tibet plateau, whichwere thick and loose packed gravel layer as reservoir dam foundation. The permeability of layerwas critical for storage capacity and leakage of the reservoir, and also could affect the damnormal operation. In recent years, some small reservoirs in Shannan region of Tibet wereinvestigated. It found that the leakage was a more serious problem in early reservoir operation,but the amount of leakage was gradually reduced and the storage capacity was progressivelyrestored with the operation of reservoir storage. Therefore, mechanism of infiltration-cloggingand test for plateau loose dam foundation were carried out. It would be provide a theoreticalbasis for solving leakage problems of alpine gully river dam and artificial clogging infiltrationreduction. The research has important theoretical and practical value.In this paper, we focused on the thick and loose gravel layer of dam foundation in Zhuo Yureservoir. According to field investigation and field pit bicyclical water injection test,infiltration-clogging tests in the condition of different size range of coarse grained soil, naturalsoil and compacted soil were carried out. The infiltration-clogging process was researched frommacroscopic to microcosmic and also simulated by three-dimensional particle flow software.The primary results and conclusions as following:(1) Taking the alluvial fan edge along the upstream rivers of Zhuo Yu ditch as the researchobject, six locations were selected for sampling. And the dry density and soil particle sizedistribution curve are obtained. The local soil situ permeability was1.98×10-2cm/s through fieldpit bicyclical water injection test.(2) A series of indoor clogging tests was conducted on seven kinds of samples. The grainsize range of samples was from32mm to64mm,16mm to32mm,8mm to16mm,4mm to8mm,2mm to4mm,1mm to2mm and0.5mm to1mm separately. According to the monitoredfluid velocity and hydraulic gradient, and the result of sieving analysis at the end of test, theclogging can be divided into three types: surface clogging, internal blockage and unclogging.Then the internal blockage also can be divided into two types: internal partial pore blockage andsurface-internal clogging. The discrimination criterion of clogging types for gravel group soilwas obtained by “equivalent grain size criterion”. The effective porosity model of skeleton grainswas established. The clogging criterion based on “effective aperture of grain criterion” was that:when De/det(ratio of equivalent grain size of skeleton grains and equivalent grain size of addinggrains) less than1, clogging type was surface clogging; when De/detless than2and greater than1, clogging type was surface-internal clogging; when De/detless than4and greater than2, clogging type was internal partial pore blockage; when De/detgreater than4, clogging type wasunclogging. Characteristics aperture of six groups samples(16mm to32mm,8mm to16mm,4mm to8mm,2mm to4mm,1mm to2mm and0.5mm to1mm) were obtained by effectiveaperture of grain criterion, which is3.987mm、1.986mm、1.013mm、0.528mm、0.247mm、0.128mm separately. At the same time, the optimal range of clogging grain size are got, that is2.819-5.638mm,0.993-1.986mm,0.506-1.013mm,0.264-0.528mm,0.124-0.247mm,0.064-0.128mm separately. Compared with the range of clogging grain size corresponding to thephenomenon of obvious clogging in indoor test, the optimal range of clogging grain size wascalculated by effective aperture of grain criterion in the condition of the surface-internal cloggingtype was more consistent. It shows that using effective aperture of grain criterion can determinethe clogging types.(3) Three different gradations of natural soils and four same gradations but differentcompaction degree soils were tested. The optimal range of clogging grain size was calculated byeffective aperture of grain criterion. The tests of different compacted soil exhibited less seepageflow and lower permeability than tests of nature soil. And to reduce the seepage flow anddecrease permeability need by add clogging material.(4) Phenomenon of surface clogging, surface-internal clogging and internal partial poreblockage was analyzed on infiltration-clogging tests in the condition of different size range ofcoarse grained soil, natural soil and compacted soil. After the test, the natural soil and compactedsoil were sieved. Particle size range of three clogging phenomenon was statistics. The statisticalresults were consistent with the conclusions by effective aperture of grain criterion. Thegranularity fractal dimension value of skeleton grains and soil samples after tests were calculatedby the method of granularity fractal dimension. The value of soil samples after tests was muchmore than Skeleton grains’. It mean particle volume was increased and the effective pore volumewas decreased, namely, the clogging phenomenon. The value of first layer in natural soil washighest in four layers. It mean the mainly clogging type was surface-internal clogging. Forcompacted soil, the granularity fractal dimension values of first layer soil and entire soil wereincreasing with compaction times. The more times, the better clogging phenomenon appears.The most obvious clogging phenomenon appeared in the soil sample of105compaction times.(5) According to the field investigation and indoor physical simulation test, theinfiltration-clogging process of the loose dam foundation was split into three stages: particlesadjustment stage, seepage stabilization stage and seepage variation stage. And the seepagedeformation was divided into three types: seepage compaction, seepage failure and infiltrationclogging. Based on the mechanical characteristics of seepage deformation, the mechanism of thethree types of seepage deformation was analyzed. Particles movement in the pores was analyzed. When the particles along the throat were subject to a downward force, moving characteristic ofgrains appeared migrating, piping or suffosion erosion. When the particles along the throat weresubject to upward force, moving characteristic of grains appeared suspending. When the particlesalong the throat were subject to balance force，moving characteristic of grains appeared clogging.(6) Using three-dimensional particle flow code software, the whole process ofinfiltration-clogging was simulated. In numerical simulation, the velocity, position of singleparticle, porosity of specimens and permeability coefficient was monitored in the infiltrationclogging process. The results revealed that: clogging particle motion had randomness anduncertainty in infiltration clogging process; clogging particles changed the partial structures ofthe samples, and the porosity and permeability coefficients were also changed. When addingclogging materials, the porosity and permeability coefficient of specimens were graduallydecreases with time step for both natural soil and compacted soil. The numerical simulationresulted more consistent with the results of laboratory tests.更多还原