【作者】 李平；

【导师】 骆亚生；

【作者基本信息】 西北农林科技大学 ， 岩土工程， 2007， 硕士

【摘要】 常规的室内渗透试验由于没有考虑取样过程中土体应力释放的实际,且一般仅考虑孔隙比这一渗透性影响因素是不合理的。为了获得理想的渗透试验成果,试验条件原则上应与现场环境相一致,要求被测土的扰动程度最小。而室内渗透试验总要取样,将不可避免地引起应力释放和土的结构扰动,常规渗透试验过程中试样的应力状态与实际差异很大,因而常会得到不能令人满意的结果。采用三轴渗透试验则能够更好的模拟原状土的实际受力状态,得到比较合理的渗透试验结果,从而可以在很大程度上克服室内常规渗透试验的先天不足。本文在分析和总结前人对黄土渗透性研究的基础上,以我国山西和陕西关中地区多个土坝和土石坝用黄土土料为研究对象,对所选黄土土样进行大量的各种物理力学指标测试、常规南55渗透试验和三轴渗透试验研究,对比分析各种影响因素特别是周围压力、结构性、试验条件等因素对其渗透特性的定量、定性影响规律,并应用有关三轴渗透试验资料对具体黄土坝体进行具有探索性的渗透稳定分析,从而为保证黄土坝体的合理设计、施工和安全运行提供理论支持。本文对饱和原状黄土和重塑黄土分别从水平和垂直两个方向上进行三轴渗透试验研究,结果表明:饱和原状黄土与重塑黄土的渗透系数均随着固结围压力、控制干密度和固结度的增大而减小,且具有一定的规律性,并在此基础上提出了渗透系数与固结度间的拟合关系式;对于饱和重塑黄土在逐级施加的围压下固结完成后进行渗透试验,随初始干密度的增大其渗透系数也增大,当初始干密度增大到某一值后,渗透系数才随着初始干密度的增大而减小。本文在比较分析常规南55渗透试验和三轴渗透试验的资料中得到,由常规南55渗透试验所测得的渗透系数要大于在不同围压状态下由三轴渗透试验所测得的渗透系数;塑性指数越大两种试验得到的渗透性差别也越大,即粘性土有荷条件下的渗透系数,在固结压力增大时,随孔隙比的减小而减小的程度不同,其中粉质粘土略有减小,而粘土则显著减小,且在同一条件下塑性指数越大其渗透系数越小。实例分析初步表明,三轴渗透试验结果比常规渗透试验更为合理和接近实际情况。本文对试验过程中条件因素的分析表明,在同一初始干密度下,一次加载到某一围压下和逐级加载到同一控制围压下固结后进行三轴渗透,一次加载的渗透系数要明显小于逐级加载的渗透系数;击实条件、应变速率、橡皮膜的弹性、制样含水率、土样扰动程度等对土体的渗透性均有一定的影响,需要在试验结果中适当的加以考虑,而渗透压力、试验历时、渗流流程等对渗透系数的影响均很有限,可忽略不计。本文通过对饱和黄土的三轴渗透试验研究,得到了黄土在接近实际工程状态下的一些初步定量化的规律及有益的成果,对沉寂良久的三轴渗透试验研究重新引起人们的重视提供了一个良好的契机,对黄土的三轴渗透性规律的进一步研究和应用具有很好的推动作用。更多还原

【Abstract】 Normal seepage test does not consider the stress releasing of soil body during borrowing those loess samples and generally take void ratio as the only one influence factor on the permeability ,that’s not reasonable . The test requires the test condition should be the same with the field condition in principle and the disturbance should be the lest, and the laboratory seepage test must take samples, it will inevitably cause up stress releasing and the disturbance, so can not obtain satisfied results. In order to simulate the actual stress condition of undisturbed loess, the triaxial seepage test is applied which can overcome the defect of laboratory test.Based on analyzing and summarizing the previous study results of loess seepage, this paper focuses on taking loess of many earth dams and the earth- rock dams of Shanxi and Shaanxi Guanzhong areas as the research object, and carries various physical test,the convention 55 seepage tests and the triaxial seepage tests on them,then contrasts and analyzes each influence factors especially the periphery pressure ,constitution and the test conditions in order to find out how those factors affect the seepage on quantity and quality .In order to provide the theory supportion of reasonable design,construction and use safely,it should also be related with the triaxial seepage data of the loess dam for further analysis of the seepage stability.This paper through the triaxial seepage tests of saturated reconstituted loess and undisturbed loess which are carried on from horizontal and the vertical directions discovery that,the seepage coefficient is reducing with the increasing of periphery pressure ,density and degree of consolidation,it also has the certain regularity, and the corresponding expression between the seepage coefficient and the degree of consolidation is brought up; Along with the smaller initial dry density‘s increasing the seepage coefficient increase, but after achieve some value, the seepage coefficient then reduce along with the initial dry density’s increasing.This paper contrasts Nan55 seepage test with the triaxial seepage test find out the seepage coefficient obtained by the Nan55 convention test is bigger;The bigger the plasticity index the more different of the seepage coefficient,in other words,with the increasing of periphery pressure the reduction of seepage coefficient is different with the void ratio reducing,for example,the reduction of silty soil is smaller than the clay and at the same condition the bigger the plasticity index the smaller the seepage coefficient. Real example analysis indicates that, the triaxial seepage test result is more reasonable than the normal seepage test and approaches the actual situation.This paper also performs the consideration to the test conditions, the seepage coefficient of increasing pressure at one time is bigger than increasing pressure step by step to the same pressure through the initial dry density is the same;In addition the compaction condition,the strain rate,the rubber extension modulus,the water content ratio,the disturbance degree and so on all have certain influence on the permeability and should be taken into consideration, but influence factors include the seepage pressure,the test lasted,the seepage path and so on is very limited and can be ignored.In this paper some new outcomes and quantificative regularities are obtained through the research on triaxial seepage test of saturated loess, it will rebrought people’s attention to the research on triaxial seepage test which has been quiet for long time and can stimulate the research on triaxial seepage test and it’s application.更多还原