Salinity effect on the compaction behaviour,matric suction,stiffness and microstructure of a silty soil

To better understand the salinity effect on the compaction behaviour of soil,standard Proctor compaction test was conducted on soil samples with different salinities.Matric suction and small-strain shear modulus,G_(max),were determined and pore size distribution was also investigated on samples statically compacted at different water contents.Results showed that with the decrease of soil salinity from initial value of 2.1‰(g of salt/kg of dry soil) to zero,the maximum dry density increased and the optimum water content decreased,whereas there was no significant change with the increase of soil salinity from2.1 ‰ to 6.76‰.Interestingly,it was observed that G_(max) also decreased when the soil salinity decreased from initial value of 2.1‰ to zero and kept almost constant when the soil salinity increased from 2.1‰ to6.76‰, for dry samples with similar matric suction and also for samples compacted at optimum state and on wet side whose matric suctions were slightly different due to the difference in remoulded water content.Furthermore,the effect of salinity on compaction behaviour and G_(max) decreased for samples compacted from dry side to wet side.The pore size distribution exhibited bi-modal characteristics with two populations of micro-and macro-pores not only for samples compacted on dry side and at optimum state,but also for those compacted on wet side.Further examination showed that the modal size of micro-pores shifted to lower values and that of macro-pores shifted to higher values for saline soil compared to the soil without salt.     

压实黄土强度及渗透各向异性研究

为揭示各向异性对黄土强度和水分场的影响,通过抗剪强度试验和渗透试验对压实黄土强度和渗透各向异性进行研究。结果表明:压实黄土存在强度各向异性,其垂直方向强度参数大于水平方向;压实黄土粘聚力各向异性随含水率增大而减小,干密度对压实黄土粘聚力各向异性无显著影响;含水率和干密度对压实黄土内摩擦角各向异性均无显著影响;压实黄土存在渗透各向异性,水平方向渗透系数大于垂直方向;压实黄土渗透系数随着干密度、围压的增大而减小,且增大到一定程度后变化趋于平缓;干密度、围压对压实黄土渗透各向异性都有较大影响,随着干密度和围压的增大,压实黄土的渗透各向异性会逐渐削弱。     

珞珈山粘土压缩性的试验研究

对武汉大学珞珈山粘土完成了15组不同含水量和压实度的室内压缩试验,分析了压实度、压实含水量及压实土体的饱和状态三因素对粘性填土压缩性能的影响,并通过压实土体结构方面的理论对其影响机理进行了阐释：这三方面因素主要是通过对土体结构及土中的基质吸力产生影响从而影响到土体的压缩变形性。试验表明,压实度和压实含水量均是在一定的应力范围内对粘性填土的压缩变形性能产生影响,在最优含水量附近粘性填土的压缩变形随着压实度的减小、压实含水量的增大而增大;压实土体浸水饱和后的压缩变形远大于饱和前的变形,压实含水量大的土体在其它条件相同的条件下因饱和引起的压缩变形小于压实含水量小的土体。     

混合型缓冲回填材料抗剪强度特性研究

高放废物深地质处置中,缓冲回填材料的抗剪性能对处置库的安全设计、施工及运营有重要的影响。本文从工程应用的角度出发,测试不同掺砂率时膨润土-砂混合物标准击实样在最优含水率条件下的抗剪强度指标。研究结果表明:随着掺砂率的增大,膨润土-砂混合物的抗剪强度指标略有下降;纯膨润土的抗剪强度指标随着干密度的增大而增大,随着含水率的增大而减小。通过测试和分析不同干密度和含水率时纯膨润土的抗剪强度指标,引入有效粘土密度和有效含水率的概念,对最优含水率条件下不同标准击实样的抗剪强度指标进行分析。     

路基压实黄土动力特性的试验研究

 在大量动三轴试验的基础上,对压实黄土的动力特性进行研究。试验结果表明：压实黄土的动应力–应变曲线在一定条件下近似为双曲线模型,并得到部分试样的模型参数取值。压实黄土动弹性模量随着动应变的增加而减小,逐渐趋于稳定,并且在不同干密度、不同含水率及不同围压状态下变化趋势基本相同。阻尼比受含水率、固结应力比、干密度及围压等因素的影响,综合反映为随动应变的增加而增加,取值为0.2～0.3,但离散性较强。振陷变形与干密度、含水率及荷载作用次数有着密切关系,干密度愈大,含水量越小,振动次数愈大;在同等的应力条件下,振陷变形愈小,并且存在一临界动应力。当动应力小于该值时,振陷变形较小,与动应力近似线性关系;当动应力大于该值时,振陷变形增加较快,呈现明显的非线性。     

含水率变化下压实路基土动态回弹模量试验研究与预估模型

路基土动态回弹模量MR是路面设计和使用性能评价采用的关键参数,运营期间受含水率变化影响显著。以压实红黏土为研究对象,制备了6个不同含水率和3种不同压实度的试样,采用滤纸法测试了不同状态下的基质吸力,并通过动三轴试验研究了含水率、压实度、动偏应力和围压对动态回弹模量的影响。试验结果表明:MR随压实度、围压的增大而增大,随动偏应力增大呈非线性减小;MR随含水率增大急剧降低,从最佳含水率增加4.5%时,不同压实度下MR均降低约50%,动偏应力和压实度对MR的影响随含水率增大逐渐减弱;MR随含水率和饱和度的变化规律与土性显著相关,而不同土样的MR随基质吸力变化趋势基本一致。进而引入基质吸力,建立了综合考虑含水率和应力水平影响的压实路基土MR预估模型,通过本文和文献试验数据证实了该模型的适用性,并基于13种土样的试验结果建立了模型参数与物性指标之间的经验关系。     

A linear graphical method to predict the effect of compaction on the hydraulic conductivity of clay liners and covers

It is proposed to present compaction relationships by plotting the inverse of the dry density versus the molding water content. In the proposed graph, the curves for equal degree of saturation become straight lines. The proposed new graph is shown to be very convenient to assess the saturated hydraulic conductivity, k _sat, of non-swelling compacted clay, using a dual porosity model. The value of k _sat depends on the secondary porosity between clay clods. The equation developed for equal k _sat value appears also as a straight line in the proposed graph. It facilitates the prediction of k _sat from field compaction data and thus the prediction of field performance of clay liners and covers.     

粘性土剪切带破坏研究

压实粘性土是静水压力和应变率相关性材料,在低围压下表现出软化现象,在高围压下表现出硬化现象.在同一含水率,不同围压下粘性土随周围压力的增大,同一轴向应变所对应的偏应力也越大;压实度一定时,含水率越高,粘聚力越大,而摩擦角越小,粘性土的抗剪强度越弱;含水率一定时,压实度越高,粘聚力越大,而摩擦角越小,抗剪强度也越大.利用TSZ10-1.0型应变控制式三轴仪,对四川绵阳地区粘性土进行了常规三轴压缩试验,研究了不同围压和含水率下粘性土的应力-应变关系、抗剪强度指标,并对粘性土的剪切带破坏进行了拟合分析.     

Experimental investigations on suffusion characteristics and its mechanical consequences on saturated cohesionless soil

The characteristics of suffusion and its mechanical consequences on saturated cohesionless soil with different initial fines contents at various stress states are presented in this paper. A series of seepage tests is performed by constant-flow-rate control mode with the measurement of the induced pore water pressure difference between the top and bottom of the tested specimen under the isotropic confining pressure. Back pressure is maintained constant in the tested soil specimen to ensure fully saturated soil condition. Cumulative eroded soil mass is continuously recorded by a consecutive monitoring system. Suffusion induced axial strain and radial strain of the 70mm-in-diameter and 150mm-in-height specimen is recorded during the seepage tests. The gap-graded cohesionless soil, which are assessed as internally unstable by existing evaluation methods, are tested. The mechanism of suffusion is demonstrated by the variation of hydraulic gradient, hydraulic conductivity, percentage of cumulative fines loss and volumetric strain during suffusion. The parametric study on the influence of two variables, effective stress level and initial fines content, on the mechanism of suffusion is elaborated. The mechanical consequences of suffusion are evaluated by conducting monotonic drained compression tests on the eroded specimens. Companion specimens without suffusion are tested for comparison purpose. The test results reveal that with the progress of suffusion, hydraulic gradient would drop and hydraulic conductivity would increase. Large amounts of fines are eroded away and correspondingly, contractive volumetric strain occurs. The larger effective confining pressure would lead to the less extent of suffusion. With larger initial fines content, more fines would be eroded away. The monotonic compression tests indicate that suffusion would cause the reduction of the soil strength at the major stage of drained shearing.     

路基土的压实度分析

就路基土的压实度问题，探讨了理想的最大干密度与最佳含水量，介绍了土的湿密度和土的含水量的测定方法，对压实度进行了计算，并分析了其误差，提出了处理措施，以更好地检测路基土的压实度，从而保证公路的质量和使用年限。     

荆门膨胀土的水稳定性及其力学效应

本文针对湖北襄荆高速公路膨胀土,在室内开展了原状土在脱湿吸湿过程的无侧限抗压强度演化特征与击实土的胀缩性状及力学效应试验研究,发现原状膨胀土的工程性状同时受含水率与裂隙性的耦合影响,耦合程度随裂隙发育程度和膨胀潜势等级而各异;膨胀土的CBR值随其含水率的变化规律类似于击实曲线,但CBR峰值含水率大于最佳含水率,并非压实度最大时CBR值也最大,CBR值取决于击实膨胀土浸水膨胀后的含水率与干密度以及结构所处状态;膨胀土路堤填筑除考虑压实度与CBR值要求外,尚需考虑胀缩总率的影响,为深入认识膨胀土的工程特性提供了帮助。     

从压实土体的强度特征看黄土的现场压实控制

本文就一种典型的黄土讨论了其强度及强度参数随压实程度和含水量变化的规律，指出黄土现场压实作业时高效而经济的含水量为塑限含水量ｗｐ     

高填方土石混合料强度与变形特性及沉降预测研究

 为解决高填方土石混合料强度与变形计算难题,对不同初始含水量不同初始干密度的土石混合试样进行剪切试验和压缩试验,深入分析不同土石比试样的强度与变形特性随初始参数的变化规律。结果包括：(1) 初始压实度越小的试样侧限压缩应变越大,初始含水量越大的试样侧限压缩应变越大;压缩系数随竖向压力的增大整体先增大后减小,压缩模量随竖向压力的增大整体呈增大趋势;(2) 类似高填方工程中填筑体初始压实度宜控制在0.93以上,初始含水量控制在最优含水量±(2%～3%),土石比控制为2∶8～4∶6;(3) 粉质黏土和砂质泥岩混合料压实土的干密度与竖向压力之间呈幂函数关系,建立由填土层的初始状态和所受荷载预测填筑土层强度和沉降量的算法;(4) 考虑初始状态的填方沉降预测方法是合理的,采用其略微偏大的变形计算结果进行高填方设计或施工,可使得高填方地基质量控制偏于安全;(5) 最优含水量范围内不同压实系数引起的沉降差异较小;随着压实系数的增大,地基沉降变形明显减小;土石比为2∶8时压实度增大对地基沉降的影响程度大于土石比为4∶6的高填方地基。研究成果可用于土石混合料高填方地基变形分析与计算。     

高铁路基粗颗粒土非饱和水力学及微观特性研究

高铁路基粗颗粒土的水力学特性对路基内部水分运移及路基的长期累积变形有重要影响。采用了一种新型TDR与大直径渗透柱装置研究了不同压实度下高铁路基粗颗粒土的水力学特性,推导了考虑双层孔隙结构的不同干密度下的土水特征曲线模型。同时,由于土体的水力学特性与其微观结构密切相关,将水力学测试结果与扫描电镜实验以及压汞试验结果进行了对比分析。实验结果表明,随着压实度的增加,低吸力下,细粒含量为15%的路基填料的体积含水率降低,在高吸力下,体积含水率趋于一致。土体的微观特性结果显示,细粒含量为15%的路基填料中表现出双层孔隙结构,随着压实度的增加,大孔隙结构逐渐被压缩,而小孔隙结构则难以被压缩。微观测试结果与水力学测试结果一致,解释了不同压实度下路基填料的水分运移规律。     

Experimental research on compaction characteristics of aeolian sand

Unlike other road materials, aeolian sand has some compaction characteristics that are key factors in construction qualities of highway in the desert. In order to study the characteristics, a series of laboratory and field tests were performed, including sieve analysis, standard modified compaction, vibrating compaction and field test. By analyzing the sieve analysis test data, it was found that the gradation of aeolian sand was bad, with fine grains whose diameters mostly ranged from 0.25 mm to 0.074 mm. Then, from the laboratory compaction test results, a compaction curve similar to the horizontally-written letter S was obtained. That was quite different from the other kinds of road materials. There were two peak values in the curve with the increase of water content, which was the special characteristic of aeolian sand: to be well compacted whether it was dry or wet. Also, according to laboratory vibrating test results, the best vibrating frequency range was proposed. It was from 45 Hz to 50 Hz. Moreover, some field compaction tests were carried out. On the construction site of the highway, the aeolian sand subgrade was compacted in the condition of natural water content with optimizing construction machines. Its compaction degree reached 96%, meeting the current specifications. At last, comparative studies were carried through with electron microscope. It was shown that the microstructure of compacted dry aeolian sand is much denser than that of the natural one in the field test.     

浸水对击实黄土的压缩变形影响的试验研究

回填地基或路基在施工运营后产生沉降变形往往与浸水有关。通过对轻型和重型击实黄土的试验研究,分析比较了浸水和不浸水条件下击实黄土的压缩变形随压力变化的规律,定义了浸水压缩变形影响系数,通过该系数反映击实黄土的水稳定性,结果表明,重型击实土的水稳定性优于轻型击实土,当击实土的含水量为相应击实能对应的最优含水量时,无论是轻型击实土或是重型击实土均表现良好的水稳定性;含水量低于最优含水量时,压实黄土遇水膨胀软化,水稳定性差;含水量高于最优含水量时,压实黄土遇水不膨胀,但浸水压缩变形影响系数仍较最优含水量试样的值要大些。     

One-Dimensional Flow Infiltration Through a Compacted Fine Grained Soil

Compacted soils are widely used in engineering work and engineers often specify that cohesive soils be compacted either around or on the wet side of optimum water content. In general, at the corresponding degree of saturation values, water component in soil voids is continuous but the air phase is not. The modelling of the infiltration process through compacted soils requires that unsaturated hydraulic functions be defined. A theoretical soil water retention function for soils with a discontinuous air phase is derived using the theory proposed by Schuurman (1966). Data from the test results provide encouraging evidence of the validity of the proposed theory. An empirical hydraulic conductivity function where the air is present in the form of occluded bubbles is also determined by curve fitting to the experimental measurements. A numerical solution of Richards' equation for one-dimensional flow, which incorporates the experimental findings, was used to simulate the measured transient water flow. The results show that the proposed constitutive relationships are capable of producing simulations of the measurements of the unsaturated flow that are both qualitatively and quantitatively realistic.     

高放废物处置库缓冲材料导热性能研究

 缓冲材料是高放废物深地质处置库中的重要工程屏障,其导热性能参数是高放废物处置系统设计的关键参数之一。利用ISOMET导热仪,研究内蒙古高庙子天然钠基膨润土GMZ01与石英砂和石墨混合材料GMZM不同压实密度和不同含水量样品的导热性能。结果表明,GMZM的导热系数、热容量和热扩散系数随压实密度的增大而显著增大,随着含水量的增大而增大;与GMZ01的导热性能相比,随着压实密度的增大,石英砂和石墨作为添加剂可以明显提高缓冲材料的导热性能和热扩散性能,但对比热没有显著影响。压实干密度大于1.8 g/cm3后,GMZM的导热系数和热扩散系数比GMZ01的导热系数和热扩散系数均提高20%以上。缓冲材料的导热性能与其含水量、干密度、矿物组成和微结构等有关,导热系数随着含水量和干密度的增大而增大,但是导热系数与含水量和压实干密度不具有一致的线性关系。当GMZ01的饱和度大于20%时,不同压实干密度样品的导热系数、比热、热容量、热扩散系数均与饱和度具有线性关系。     

Characteristics of Strength for Hydraulic Fracturing of Buffer Material

The fundamental characteristics of strength for the hydraulic fracturing of highly compacted bentonite were studied. Firstly, the constant pressurize rate tests were carried out for the material having various specifications. Secondly, the cyclic pressurize test was carried out to examine the self-sealing function as a buffer material. Thirdly, the constant pressure test was carried out to observe the change in strength during seepage. The observed phenomena were analytically examined. As a result, it was found that the strength for hydraulic fracturing of the buffer material increased with the increase of initial dry density, decrease of sand-mixture ratio and decrease of water content. The swelling pressure of the buffer material worked as a constraint stress for the strength for hydraulic fracturing. The fracture made by hydraulic fracturing was fixed through the supply of water. However a long period of low-pressure supply was needed to recover the strength at the failed parts. While the tensile failure was dominant, the specimen having a low dry density might be failed initially by the shear failure. When the water content became large during seepage, the strength for hydraulic fracturing reduced.     

砂土路用动态特性试验研究

为研究砂土在重复荷载作用下的路用动态特性,开展系列动三轴试验。根据累积塑性应变随加载次数的变化规律,获得不同含水量、压实度下砂土的临界动应力。研究结果表明,砂土动态回弹模量随围压、压实度的提高而增大,随循环偏应力和含水量的增大而减小。采用偏应力和体应力为变量的动态回弹模量本构模型对试验数据进行回归分析,结果表明所选模型具有较高的决定系数,证明所选模型具有较高的合理性与可靠性,可为基于动力学的路面结构设计提供参数。为运用上述动态特性评价公路路基填料,提出基于动力特性的公路路基设计思路。