复合土工膜自然老化特性及抗拉强度变化规律研究

复合土工膜作为一种新型的防渗材料，在当今水利工程已得到相当广泛的应用。针对当前人们极为关注的老化问题，采用模拟覆盖法对其自然老化特性进行研究。通过不同时期的试验，取得了极其宝贵的数据，对这些数据进行数学上的拟合处理，得到复合土工膜强度随时间变化的数学表达式，从而求出复合土工膜在工作应变范围内强度随时间变化的规律，为老化特性的研究和工程设计提供可靠的依据。     

复合土工膜老化特性及抗拉强度变化

土工膜主要用于各种防渗工程。薄膜受荷时易被相邻的尖角材料或不平整的凸面顶破而丧失其防渗性能；在自然条件下复合土工膜也会随时间延长发生老化，材料老化导致其强度和延伸率(变形)变化。产生老化的外界因素可分为物理因素、化学因素和生物因素，如：太阳光、氧、热、水分、工业污水以及微生物、破坏等。目前常用的老化试验方法主要有：人工快速老化、大气暴露老化、实际应用老化等。     

PVC复合土工膜老化性能初探

复合土工膜以其优良的防渗性能在工程中已广泛应用．目前关注的焦点是它的抗老化性．通过对PVC复合土工膜在不同试验条件下的老化性能研究及和现场运行膜的取样测试对比，分析了环境对老化性能的影响，并初步提出了PVC复合土工膜老化性能的判定方法和进一步改善老化性能的途径：即以伸长率下降为零失去适应变形能力的时间为标准较为合适，而增塑剂品种的优选将是进一步改善其老化性能，延长使用时间的有效途径．     

复合土工膜的老化试验研究

对复合土工膜的老化性能进行长期试验研究,分析其应力应变随时间的变化规律,拟合出相应的曲线,预测其发展趋势,为设计应用提供了可靠的依据.     

土工膜和复合土工膜的品种和特性

本文介绍土工膜、复合土工膜、加筋土工膜的常用品种,它们的产品规格和力学性质。介绍这些土工膜与接触介质的摩擦系数供抗滑稳定计算之用。综述了多年来对聚合物使用寿命的研究成果。     

复合土工膜砂砾料界面摩擦特性研究

复合土工膜与粗粒砂砾料垫层的界面摩擦特性对工程结构稳定性十分重要。现有的试验研究多集中在粒径较小的土料与土工织物接触, 对于由粒径较大的砂砾料与土工膜界面特性的研究较少。利用大型土工合成材料直剪仪开展了砂砾料与土工膜界面直剪摩擦试验研究, 讨论了砂砾料级配以及相对密度对界面摩擦特性的影响。试验结果表明:相对密度一定时, 粗颗粒含量越大, 摩擦因子越大;相同级配条件下, 相对密度越高, 摩擦因子越大。最后探讨了土工膜与剪切下盒基座间的固定方式对界面摩擦参数的影响, 求得不同的固定方式导致界面摩擦角相差可达1倍以上。     

高土石坝粘土心墙和复合土工膜防渗性能研究

高土石坝在静力情况下的应力、变形特性和防渗性能一直是高土石坝设计和施工的关键问题。以一座高为127.5 m的高土石坝为例,通过室内试验和三轴试验测得坝体材料的物理性质指标和邓肯张E-B模型参数,采用有限元计算方法,计算竣工期和渗流稳定期复合土工膜高土石坝坝体应力、应变和变形以及大坝渗流量,并和粘土心墙防渗计算结构进行对比,并对复合土工膜心墙是否发生水力劈裂进行判断。结果表明:由于堆石体材料的流变性,引起了坝体的竖向位移和水平位移。复合土工膜心墙与粘土心墙相比,复合土工膜对降低坝体浸润线、减小坝体孔隙水压力均有显著作用,减小幅度在50%左右,且复合土工膜不会发生水力劈裂等不利问题。     

阿克兰干水库复合土工膜厚度计算理论研究

本文用邓肯-张（Duncan-Chang）双曲线模型，分析了阿克兰干水库挡水坝设计断面在施工和蓄水过程中的应力和变形状态，从而采用应力应变曲线法，为阿克兰干水库碾压式均质土坝斜墙防渗，选择复合土工膜厚度提供了依据。     

饱和湿态混凝土有效模量及有效抗拉强度研究

孔隙水的存在对混凝土的有效弹模及强度等力学性能产生很大的影响。采用三相球模型分析得到了饱和湿态混凝土的有效体积模量与孔隙率之间的定量关系；不考虑孔隙水的抗剪能力，得到了湿态混凝土的有效弹性模量和泊松比。基于最大拉应力破坏准则，推导得到了饱和湿态混凝土的有效抗拉强度及其峰值应变与孔隙率之间的定量关系。理论分析结果与Yaman的试验结果吻合较好，表明了本文方法能够用来预测饱和湿态混凝土的弹性模量；与干燥混凝土相比，孔隙水的存在使得湿态混凝土弹性模量和有效抗拉强度均有所提高。     

THE TENSILE STRENGTH OF WATER IN DEPRESSION TANK

This paper presents the data of tensile strength of water in depression tank whichwere measured by small venturi during cavitation investigation of a series of real project models.These measurements show that in depression tank water has slight tensile strength in case of highvacuum.But it influences the incipient cavitation number.In tests we also studied the influenceof tensile strength on scale effect of cavitation models.     

复合土工膜防渗堆石坝渗流观测资料分析

运用统计相关、对比等分析方法，对钟吕水库大坝１９９９年和２０００年渗流观测资料进行分析，得出钟吕大坝渗流的主要特征．以进一步了解复合土工膜防渗坝的渗流状态。     

加筋碎石土的抗剪强度特性研究

通过对比分析碎石土加筋前后高压大三轴饱和固结排水试验结果 ,研究碎石土加筋的抗剪强度特性。结果表明 :加筋碎石土复合体的应力 -应变 -体变关系仍然表现出不加筋碎石土的基本特性 ,加筋后的应力 -应变 -体变曲线比不加筋前显著提高 ,其本构关系可用邓肯 -张双曲线模型来描述。不论加筋与否 ,碎石土的加卸荷循环曲线基本都呈相互平行的直线。加筋增强了碎石土抵抗变形和破坏的能力 ,碎石土加筋的效果可以显著提高凝聚力 ,但对其内摩擦角影响很小。颗粒越粗硬 ,对提高强度、减小变形越有利。     

复合土工膜在赣东大堤丰城A标段堤身防渗中的应用

介绍江西省赣东大堤丰城A标段堤身防渗采用复合土工膜的施工情况和应用效果，说明复合土工膜在堤防建设中用作堤身防渗，施工质量易于控制，效果好．     

Netlon土工网格CE131拉伸特性的试验研究

详细介绍不同宽度的土工网格ＣＥ１３１拉伸试验，包括试样的制备、试验现象的分析以及成果的整理与评价。指出采用无侧限的宽条拉伸试验是可行的，如何确定设计容许强度是仍待进一步探讨的问题。     

多参数强度准则与非线性本构关系在砼坝有限元应力分析中的应用

简述砼强度理论和本构关系的研究和应用现状，提出了多参数强度准则和增量型非线性本构关系在砼坝有限元应力分析中的应用方法。     

COMPOSITE MODELING APPROACH AND EXPERIMENTAL STUDY FOR SUBSURFACE TRANSPORT OF CONTAMINANTS FROM LAND-DISPOSAL SITES

1 .　INTRODUCTIONThecontaminationofsoiland groundwatersystemsandtheadverseeffectsofthecontamina tionoftheseresourceshavebecomeamatterofconsiderableconcern .Thetransportofcontami nantsinsoilandgroundwaterisacompositionofcomplexchemicalandhydraulicphenomena .Dur ingthepastdecadesmuchattentionhasbeengiventothetheoryandmodelingofcontaminanttrans portinsaturatedsoil (Davidetal.1996 ;Bouchard1988;Brusseauetal .1989) .Thisdevelopmenthasbeenacceleratedandincreasedduetothedifficultyandhighcostsof…     

THE FLUCTUATION CHARACTERISTICS OF NATURAL AND VENTILATED CAVITIES ON AN AXISYMMETRIC BODY

Natural and ventilated cavitations generated on a smooth-nosed axisymmetric body were studied experimentally. The characteristics of small scale and localized fluctuations of “steady cavities” were measured by pressure transducers. Comparisons between natural and ventilated cavities at different measured points for several cavitation numbers were done. It was observed that the dominant fluctuations were concen trated in the frequency range of 0Hz 50Hz for all the cavitation cases, Similar shapes and magnitudes of the frequency spectra were detected for both natural and ventilated cavities.Much larger spectral amplitude in the cavity closure region suggested as fluctuations source. From partial cavitating flow to supercavitating flow, the dominant frequency and the corre sponding amplitude decreased with decreasing cavitation number, which meant that cavity became more steady while developing.     

DETACHED EDDY SIMULATION OF HYDRAULIC CHARACTERISTICS ALONG THE SIDE-WALL AFTER A NEW ARRANGEMENT-SCHEME OF THE SUDDEN LATERAL ENLARGEMENT AND THE VERTICAL DROP

In order to study the cavitation damage in a side-wall when a sudden lateral enlargement and a vertical drop are imposed at the radial gate,a new arrangement-scheme is proposed,where the sudden lateral enlargement and the vertical drop can be imposed at the outlet of the gate chamber.The hydraulic characteristics along the side-wall are simulated by the detached eddy simulation and the Volume Of Fluid (VOF) method.The numerical results agree well with those of experiment.The experimental and numerical results show that the flow condition is smooth with only a weak water-wing appearing behind the lateral cavity,and the length of the lateral cavity becomes longer and is mainly affected by the size of the lateral enlargement and the zone of negative pressure after the water impacts the side-wall would disappear.The hydraulic characteristics of the new arrangement-scheme are beneficial to the prevention of the cavitation damage in the side-wall and the Detached Eddy Simulation (DES) with the VOF method can well predict the hydraulic characteristics after the new arrangement-scheme of the sudden lateral enlargement and the vertical drop.