南水北调工程复合土工膜老化特性及拉伸强度衰减规律研究

发布时间：2018-09-11 09:52

【摘要】：南水北调工程穿越黄河、长江、海河、淮河四大流域,涉及十多个省市、直辖市及自治区,工程规模庞大,输水线路横跨度广,经济效益巨大。该工程涵盖暗涵、pccp管道、水库、隧洞、运河、倒虹吸、河道、渠道、大坝、湖泊、泵站、渡槽等水利项目,投资成本巨大,对我国各方面的发展都有着极为深远的影响。南水北调工程的实施,在党中央、国务院的重视和指导下,相关机构和部门进行了全方位的调研和论证,在经过仔细勘察后,制定详细计划,进行严谨的设计,经过五十年的不懈努力,对上百种方案进行比选和研究,最终确定了由长江上游、中游、下游分别引水的南水北调西、中、东三条线路。其中,流经河南省境内的中线干线项目是整个南水北调工程的重要组成部分,该项目能够有效缓解黄淮海平原地区水资源不足的问题,同时还能够优化水资源配置,对受水区北京、天津、河北、河南等省市的发展有着重要的影响。在南水北调工程中,渠道是输配水的主要载体,其运行的安全可靠性和节能经济性,直接影响到工程的可靠性、安全性、可维护性。复合土工膜材料是土工合成材料的一种,系由高分子聚合物制成,它是以塑料薄膜作为防渗基材,与无纺布复合构成的高分子化学柔性材料,该材料具有延伸性较强、适应变形能力强、比重低等特点。采用复合土工膜进行渠道防渗日益成为渠道防渗的重要措施,并在南水北调工程渠道防渗中得到广泛应用。复合土工膜材料作为渠道防渗的主要材料,在自然环境中易受到紫外辐射、氧气、温度、湿度等环境因素的影响而产生老化,它的老化是指材料在温度及水溶液相互作用的过程中材料物理化学性能随着渠道运行年龄而变化的一种缓慢的过程,体现在材料力学强度方面就是指材料的抗拉强度随着外界环境的影响而逐渐降低,而材料的渗透系数会随着外界环境的影响而逐渐增大,从而导致渠道中复合土工膜材料所受应力及应变产生相应的变化,也最终会影响到渠道输水功能的正常发挥,缩短渠道的服役寿命,甚至会直接威胁到整个输水工程的安全。因此,以实际工程应用环境为依据,探究渠道用复合土工膜材料拉伸强度随时间的变化规律对整个南水北调工程安全有效的运行有着极为重要的意义。南水北调中线工程渠道结构中,渠道表面采用混凝土衬砌作为保护层,紫外线照射对于复合土工膜材料的老化并没有起到决定性的作用,引起复合土工膜材料老化的关键因素则是温度及湿度的综合作用。因此本论文依据南水北调工程实际应用环境,以复合土工膜材料拉伸强度衰减规律为研究主线,利用室内热老化试验仪,高低温综合试验箱及室内综合试验拉力机等试验设备,开展不同环境状况(室内热老化、室内湿热老化、自然气候老化)条件下的复合土工膜材料的老化试验研究,分析复合土工膜材料在室内热老化、室内湿热老化及自然气候老化条件下材料的老化特性,并建立起不同环境状况条件下材料的拉伸强度衰减规律模型;依据工程用复合土工膜材料的失效判据,利用建立的材料的拉伸强度衰减规律模型,对典型工程渠段中复合土工膜材料的使用寿命进行预测;同时运用数值分析方法就复合土工膜材料老化对调水工程安全的影响程度进行定量分析,为确保调水工程安全有效地运行与供水效益的实现提供技术支撑。本论文的主要研究内容及成果如下:1、通过对南水北调中线工程典型工程渠段复合土工膜材料应用情况的调研,结合当地环境条件因素、气候因素等,综合考虑引起复合土工膜材料老化的多种影响因素,根据实际工程应用环境,确定选择温度及湿度作为引起南水北调中线工程中复合土工膜材料老化的主要因素,设计出符合南水北调中线工程的复合土工膜材料的老化试验方案。2、选用南水北调中线工程典型工程渠段(鹤壁段)所用复合土工膜材料,以温度及湿度这两种因素作为材料的加速老化因子,开展复合土工膜材料室内热老化加速试验、室内湿热老化加速实验以及自然气候老化试验三种老化对比试验,分析得出复合土工膜材料在不同环境状况条件下所表现出的老化性能及材料的力学强度随时间的变化规律。3、复合土工膜材料在室内热老化、室内湿热老化及自然气候老化试验条件下,材料的主要力学性能指标:纵横向拉伸强度、纵横向伸长率及纵横向撕裂强力均随着老化时间的增加总体呈下降趋势;弹性模量随老化时间的变化不大;材料渗透系数随老化时间增加无明显变化,且均保持在同一数量级,能满足工程防渗的要求。4、室内热老化加速试验条件下,复合土工膜材料的纵横向拉伸强度、纵横向伸长率与纵横向撕裂强力下降速率随试验温度的变化较为显著。在三种不同的试验温度条件下,温度越高,测试指标下降速率越大,力学性能衰减越快;温度越低,测试指标下降速率越小,力学性能衰减较慢。并且在同一温度条件下,复合土工膜材料力学强度的变化规律表现为以材料的纵向拉伸强度下降速率最为明显。5、室内湿热老化加速试验条件下,复合土工膜材料的纵横向拉伸强度、纵横向伸长率与纵横向撕裂强力下降速率随试验温度、湿度变化也较为显著,在三种不同的试验温度、湿度条件下,温度越高,湿度越大,测试指标下降速率越大,力学性能衰减越快;温度越低,湿度越小,测试指标下降速率越小,力学性能衰减越慢。6、在试验湿度相同的情况下,试验温度越高,复合土工膜材料拉伸强度、伸长率、撕裂强力下降速度越快,复合土工膜材料的老化性能表现为随温度的升高呈现出老化速率加快的趋势。且在相同试验温度及湿度条件下,材料的纵向拉伸强度下降速率要大于材料的横向拉伸强度下降速率。而在温度相同的情况下,试验湿度越高,复合土工膜材料的拉伸强度、伸长率、撕裂强力下降速率越快,复合土工膜材料的老化性能表现为随湿度的升高呈现出老化速率加快的趋势。7、依据室内加速试验成果,运用数学分析方法,建立了复合土工膜材料在室内热老化与室内湿热老化加速试验条件下材料的拉伸强度衰减规律模型,并以材料的拉伸强度下降至初始强度的50%作为材料的失效判据,对复合土工膜材料在南水北调实际工程应用环境中的使用寿命进行预测。8、对湿热老化试验条件下复合土工膜材料的拉伸强度衰减规律模型进行了实际工程验证,将南水北调工程模型试验箱中复合土工膜材料自然气候老化条件下材料的取样检测值及西霞院工程5年试验区中的复合土工膜材料的拉伸强度的取样检测值分别同该湿热老化拉伸强度衰减规律模型的预测值进行对比,可以得出:模型预测的可靠度满足工程要求,说明即使对于不同规格的复合土工膜材料,在环境条件相似的情况下,该湿热老化拉伸强度衰减规律模型也仍然具有一定的工程应用和参考价值。9、运用数值分析软件FLAC3D就复合土工膜材料老化引起材料参数的变化对渠道边坡安全性的影响程度进行定量分析,分析认为复合土工膜材料参数的变化(纵、横向弹性模量不同;复合土工膜老化)对渠道边坡的位移分布及应力分布影响不大;渠道中复合土工膜材料受到的拉应力最大值远小于复合土工膜材料的失效破坏抗拉强度。渠道正常运行过程中边坡未产生较大滑移,渠道边坡整体稳定。
[Abstract]:The South-to-North Water Transfer Project crosses the Yellow River, the Yangtze River, the Haihe River and the Huaihe River, involving more than ten provinces, municipalities and autonomous regions. The project has a large scale, wide span of water transmission lines and huge economic benefits. The implementation of the South-to-North Water Transfer Project, under the attention and guidance of the Party Central Committee and the State Council, has been investigated and demonstrated in an all-round way by relevant institutions and departments. After careful investigation, detailed plans have been worked out and rigorous designs have been made. After 50 years of unremitting efforts, Through the comparison and study of hundreds of schemes, three routes of South-to-North Water Transfer from the upper reaches, middle reaches and lower reaches of the Yangtze River to the west, middle and East are finally determined. In the South-to-North Water Transfer Project, the canal is the main carrier of water transmission and distribution, and its operation reliability and energy-saving economy directly affect the reliability, safety and maintainability of the project. Membrane material is a kind of geosynthetical material, which is made of polymer. It is a kind of polymer chemical flexible material composed of plastic film and non-woven fabric. The material has the characteristics of strong elongation, strong adaptability to deformation and low specific gravity. Composite geomembrane material, as the main material of canal seepage control, is vulnerable to ultraviolet radiation, oxygen, temperature, humidity and other environmental factors in the natural environment, resulting in aging. Its aging refers to the interaction process of materials in temperature and water-soluble phase. The physical and chemical properties of medium materials change slowly with the age of canal operation, which is reflected in the mechanical strength of materials, that is, the tensile strength of materials decreases gradually with the influence of external environment, and the permeability coefficient of materials increases gradually with the influence of external environment, resulting in composite geomembrane in canal. The stress and strain of the material will change correspondingly, which will affect the normal function of the canal, shorten the service life of the canal, and even directly threaten the safety of the whole water conveyance project. The law is of great importance to the safe and effective operation of the South-to-North Water Transfer Project. In the canal structure of the middle route of the South-to-North Water Transfer Project, concrete lining is used as the protective layer on the surface of the canal. Ultraviolet radiation does not play a decisive role in the aging of composite geomembrane materials, and the key cause of the aging of composite geomembrane materials is caused. Therefore, according to the actual application environment of the South-to-North Water Transfer Project, this paper takes the attenuation law of tensile strength of composite geomembrane materials as the main line, and uses indoor thermal aging tester, high-low temperature comprehensive test box and indoor comprehensive test tensile machine to carry out different environmental conditions (indoor heat). The aging test of composite geomembrane materials under aging, indoor humid-thermal aging and natural climate aging conditions was carried out. The aging characteristics of composite geomembrane materials under indoor thermal aging, indoor humid-thermal aging and natural climate aging were analyzed, and the attenuation law model of tensile strength under different environmental conditions was established. According to the failure criterion of composite geomembrane materials used in engineering, the service life of composite geomembrane materials in canal section of typical engineering is predicted by using the tensile strength attenuation law model of composite geomembrane materials, and the influence degree of composite geomembrane materials aging on the safety of water diversion project is quantitatively analyzed by using numerical analysis method. The main research contents and achievements of this paper are as follows: 1. By investigating the application of composite geomembrane materials in the canal section of the middle route of South-to-North Water Transfer Project, considering the local environmental conditions and climate factors, the composite geomembrane materials are synthetically considered. According to the actual engineering application environment, the temperature and humidity are selected as the main factors causing the aging of composite geomembrane materials in the middle route of South-to-North Water Transfer Project. The aging test scheme of composite geomembrane materials in accordance with the middle route of South-to-North Water Transfer Project is designed. 2. The middle route code of South-to-North Water Transfer Project is selected. Composite geomembrane materials used in the canal section of the H-shaped project (Hebi section) were used to carry out indoor thermal aging accelerated test, indoor humid-thermal aging accelerated test and natural climate aging comparative test with temperature and humidity as accelerating aging factors. The aging properties and mechanical strength of composite geomembrane materials under different environmental conditions change with time. 3. The main mechanical properties of composite geomembrane materials are longitudinal and transverse tensile strength, longitudinal and transverse elongation and longitudinal and transverse tearing strength under indoor thermal aging, indoor humid and thermal aging and natural climate aging conditions. The modulus of elasticity has little change with aging time, and the permeability coefficient has no obvious change with aging time, and all keep the same order of magnitude, which can meet the requirements of seepage prevention. 4. The longitudinal and transverse tensile strength of composite geomembrane materials under indoor accelerated thermal aging test conditions. The longitudinal and transverse elongation and the longitudinal and transverse tear strength decrease rate change with the test temperature significantly. Under three different test temperature conditions, the higher the temperature, the greater the test index decline rate, the faster the mechanical properties decay; the lower the temperature, the smaller the test index decline rate, the slower the mechanical properties decay. The longitudinal and transverse tensile strength, longitudinal and transverse elongation and longitudinal and transverse tearing strength decrease rate of composite geomembrane materials with the test temperature and humidity changing significantly under indoor humid and thermal aging accelerated test conditions. At three different test temperatures and humidities, the higher the temperature, the greater the humidity, the greater the decline rate of test index, the faster the mechanical properties decay; the lower the temperature, the lower the humidity, the smaller the decline rate of test index, the slower the mechanical properties decay. 6. Under the same test humidity, the higher the test temperature, the higher the tensile strength of composite geomembrane materials. The faster the decrease of elongation and tearing strength is, the faster the aging performance of composite geomembrane materials tends to be accelerated with the increase of temperature. The higher the humidity is, the faster the decrease rate of tensile strength, elongation and tear strength of the composite geomembrane material is. The aging performance of the composite geomembrane material shows an accelerated trend with the increase of humidity. Tensile strength attenuation model of composite geomembrane materials under accelerated test conditions of internal heat aging and indoor humid heat aging was established. The failure criterion of composite geomembrane materials was that the tensile strength of composite geomembrane materials decreased to 50% of initial strength. The service life of composite geomembrane materials in practical engineering environment of South-to-North Water Transfer Project was predicted. 8. The test conditions of humid heat aging were studied. The attenuation law model of the tensile strength of the composite geomembrane material under the condition of natural climate aging in the model test box of the South-to-North Water Transfer Project is verified by the actual project. The testing values of the tensile strength of the composite geomembrane material in the five-year test area of Xixia Academy Project are the same as those of the composite geomembrane material under the natural climate aging condition. By comparing the predicted values of the model, it can be concluded that the predicted reliability of the model meets the engineering requirements, which indicates that the model still has certain engineering applications and parameters even for different specifications of composite geomembrane materials under similar environmental conditions. Value. 9. The influence of composite geomembrane material aging on the safety of canal slope is quantitatively analyzed by FLAC3D software. It is concluded that the variation of composite geomembrane material parameters (longitudinal and transverse elastic modulus is different; composite geomembrane aging) affects the displacement distribution and stress distribution of canal slope. The maximum tensile stress of the composite geomembrane material in the canal is far less than the failure failure tensile strength of the composite geomembrane material.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TV68;TV49

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