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非饱和粘土强度测试中采用传统的击实法制备重塑土样,其试验结果通常会由于土样分层性明显、水分分布不均而与天然粘土的强度特性出入较大,甚至会得出粘聚力随土体饱和度增加而增大的错误结论。为此,基于非饱和固结原理,通过模拟自然土体的一次脱湿固结循环过程,提出了一种适用于非饱和粘土强度测试的重塑土制样方法——脱湿固结制样法,并以三峡地区粉质粘土为例,对比分析了击实重塑样、原状土样及脱湿固结样不同饱和度下的强度测试结果。结果表明,与原状土强度相差较大的击实重塑样相比,脱湿固结样不仅在强度大小上较为接近原状土,其粘聚力随饱和度变化规律也基本相似。 相似文献
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鉴于目前超固结土本构模型不能较好地反映土体的实际变形,基于广义塑性理论并引入伏斯列夫面及超固结参数的概念,建立了一个可以反映超固结土变形特性的广义塑性本构模型,该模型采用能较好反映试验资料的Lagioia剪胀方程,在此基础上推导出超固结参数、塑性流动和加载方向张量,并构造了一个可以较好反映土体变形特性的塑性模量,且基于SMP变换应力法将模型三维化,使其能适用于一般应力状态。根据试验资料获得饱和Fujinomori粘土的本构模型参数,利用新的模型编制程序预测超固结土的变形特性,发现预测结果与试验数据吻合较好,表明新的模型可以合理地反映超固结土的变形特性。 相似文献
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为研究崩岗区重塑非饱和花岗岩残积土变形特性,利用双压力室非饱和土三轴仪做了重塑土的控制吸力固结排水剪切试验,研究了干密度、净围压和基质吸力对剪切破坏阶段的体积变形的影响,分析了重塑非饱和花岗岩残积土在控制吸力条件下剪切过程中的体变性状。试验结果表明,重塑非饱和花岗岩残积土的体变特性不仅取决于干密度和净围压,还与基质吸力密切相关,但净围压比基质吸力对土体体积应变的影响大。研究成果可为崩岗侵蚀区灾害防治及其体积变形、沉降量预测提供参考。 相似文献
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鉴于降雨入渗过程中土体饱和度变化对库区边坡稳定性的影响,基于Bishop非饱和土抗剪强度理论和van Genuchten土水特征曲线模型,建立了直接考虑饱和度影响的多参数土体抗剪强度理论模型,并采用三峡库区红壤土设计了土水特征曲线试验和三轴剪切试验,获得了基质吸力和抗剪强度随饱和度变化的试验结果,进而验证了模型的合理性。结果表明,模型预测值与试验实测值的吻合度较好,建立的模型能较好地预测三峡库区红壤土的抗剪强度。进一步分析可知,红壤土抗剪强度指标——粘聚力和内摩擦角均随饱和度的增加呈非线性递减;在净总应力一定的情况下,红壤土抗剪强度随饱和度的增加呈对数关系递减。 相似文献
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在大量三轴试验资料基础上,分析了胶结粗粒土在围压、养护时间、水泥含量等因素下的应力应变关系,并与无胶结试样的应力应变关系进行对比.结果表明,各影响因素对胶结粗粒土的变形和强度影响显著,与无胶结的粗粒土相比,胶结粗粒土的应力应变曲线呈明显的应变软化现象,且试样的剪胀现象明显,为确定胶结粗粒土的应力应变关系奠定了基础. 相似文献
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应用自主研发的试验仪对土与结构物相互作用进行试验,试验时使竖向应力和围压达到要求应力值,研究结构物以恒定速率运动时结构物位移对接触面力学特性的影响,进而利用PFC2D对土与结构物在不同位移下相互作用的试验进行数值模拟,分析了土与结构物相互作用时的剪应力变化和土体变形情况。结果表明,接触面剪应力随结构物位移的增加先快速增加,再逐渐趋缓,最后趋于稳定;结构物的剪切作用对接触面土体的影响尤为明显,对远离接触面的土体影响较小,使接触面处土体颗粒从右侧向左侧运动,导致量测圈1内土体堆积发生剪胀,剪应力值增大至140 kPa,量测圈3内土体疏松发生剪缩,剪应力值减小至35 kPa。 相似文献
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为了研究荆江河段岸坡土体的渗流特性及失稳机理,对荆江中州子护岸工程段河岸土样做了渗透系数和土水特征曲线室内试验,并基于Van Genuchten模型对土水曲线的试验结果进行拟合。在获得土体水力参数的基础上,根据该河段岸坡二元结构土体的特点,基于饱和—非饱和渗流理论,探讨了水位下降及降雨条件下岸坡不同粘性土层厚度对岸坡渗流场的影响规律。结果表明,地下水的下降速率随粘性土层厚度的增加而减少;粉质粘土层厚度越大,降雨对岸坡孔压场的影响范围也越大,且在一定程度上增大了土体的暂态饱和区,不利于岸坡的稳定性。 相似文献
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含水率对工程常用土导热系数影响的试验研究 总被引:1,自引:0,他引:1
岩土的导热系数对工程施工和工程运行有较大影响,研究不同含水率条件下的导热系数变化规律对岩土的导热理论和工程实践具有重要意义。根据《土工试验规程》制备出粗砂、中砂、细砂、粉砂和粘土等5种工程常用土,试验分析了不同含水率时的导热系数变化规律,并根据试验结果得到5种土导热系数随含水率变化的拟合公式。结果表明,5种土的导热系数均随含水率的增加呈非线性增加。含水率在0~15%时,导热系数由大到小顺序依次为粗砂、中砂、细砂、粉砂和粘土;含水率超出20%时,中砂、细砂、粉砂的导热系数变化趋于平缓并呈轻微下降趋势;含水率大于25%时,粘土导热系数呈下降趋势。 相似文献
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可变涡轮增压器在运行过程中其涡轮喷嘴环会受到尾气颗粒的冲蚀磨损,造成喷嘴环叶片失效和涡轮运行效果下降。借助CFD软件对可变混流涡轮内部的气固两相流进行数值模拟计算,分析喷嘴环开度的变化和颗粒粒径对喷嘴环磨损规律的影响。结果表明:喷嘴环处于不同开度下时,磨损率和磨损区域均有所不同,磨损区域主要集中在喷嘴环压力面的中后段区域,随着开度的增大,磨损率和磨损区域均减小,压力面的磨损程度明显大于吸力面;尾气中的小颗粒因惯性较小对气流的跟随性较好,主要撞击喷嘴环前缘,且开度对喷嘴环前缘的磨损影响较小;尾气中大颗粒的运动轨迹趋于直线,主要撞击喷嘴环压力面的中后段区域;由于涡轮进气涡壳结构的周向不对称性,使得涡轮内部流场沿周向分布不均匀,导致不同周向位置的喷嘴环磨损率和磨损区域有所不同,且随着开度的增大,各喷嘴环之间的磨损差异也增大。 相似文献
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WANG Jinhua HUANG Zuohua LIU Bing ZENG Ke YU Jinrong JIANG Deming 《Frontiers in Energy》2008,2(2):194
An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO2 concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO2 do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction is over 10%. 相似文献
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Jinhua Wang Zuohua Huang Bing Liu Ke Zeng Jinrong Yu Deming Jiang 《Frontiers of Energy and Power Engineering in China》2008,2(2):194-201
An experimental study on the combustion and emission characteristics of a direct-injection spark-ignited engine fueled with
natural gas/hydrogen blends under various ignition timings was conducted. The results show that ignition timing has a significant
influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing
is a very important parameter for direct-injection natural gas engines. The turbulent flow in the combustion chamber generated
by the fuel jet remains high and relative strong mixture stratification is introduced when decreasing the angle interval between
the end of fuel injection and ignition timing giving fast burning rates and high thermal efficiencies. The maximum cylinder
gas pressure, maximum mean gas temperature, maximum rate of pressure rise and maximum heat release rate increase with the
advancing of ignition timing. However, these parameters do not vary much with hydrogen addition under specific ignition timing
indicating that a small hydrogen fraction addition of less than 20% in the present experiment has little influence on combustion
parameters under specific ignition timing. The exhaust HC emission decreases while the exhaust CO2 concentration increases with the advancing of ignition timing. In the lean combustion condition, the exhaust CO does not
vary much with ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust
CO and CO2 do not vary much with hydrogen addition. The exhaust NOx increases with the advancing of ignition timing and the behavior
tends to be more obvious at large ignition advance angle. The brake mean effective pressure and the effective thermal efficiency
of natural gas/hydrogen mixture combustion increase compared with those of natural gas combustion when the hydrogen fraction
is over 10%.
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Translated from Transactions of CSICE, 2006, 24(5): 394–401 [译自:内燃机学报] 相似文献
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真空相变锅炉低排烟温度设计与低温腐蚀 总被引:2,自引:1,他引:1
真空相变锅炉是否会明显发生烟气低温腐蚀,一直众说不一。文章从锅炉发生低温腐蚀的机理人手,通过理论分析计算并通过实践检验,提出了真空相变锅炉虽然不能完全避免低温腐蚀问题,但不论排烟温度是否高于烟气露点,低温腐蚀的程度都很弱的观点;给出了真空相变锅炉沿烟气流程金属壁面的腐蚀速度与壁面温度的关系曲线,和烟气温度低于酸露点时金属壁面的腐蚀速度与壁面温度的关系曲线;同时,文章推荐真空相变锅炉的设计排烟温度取130℃左右的低排烟温度。根据上述观点设计的数百台产品已经过多年实际运行,未发现明显 相似文献