Prediction of expansive soil swelling based on four micro-scale properties

A comprehensive study of expansive soil behavior includes understanding the surface phenomena of clay particles within the soil matrix. This research studies four micro-scale properties of four remolded expansive soils––matric suction, pH, surface conductance and percentage of montmorillonite––in order to predict soil swelling. An approach to approximate surface conductance is presented. Linear regression analyses were undertaken in an attempt to predict percent swell and swell pressure based on each of these micro-scale properties. Matric suction was found to be the most accurate predictor of the swelling behavior of the studied soils, which were initially compacted at optimum moisture content. Surface conductance, which is a combination of specific surface area, cation exchange capacity and cation mobility, also gave good predictions, except for one soil with high acidity.     

Determining osmotic suction through electrical conductivity for unsaturated low-plasticity soils

Determining osmotic suction from the electrical conductivity (EC) of soil pore water was widely reported in the literature. However, while dealing with unsaturated soils, they do not have enough soil pore water to be extracted for a reliable measurement of EC. In this paper, the chilled-mirror dew-point hygrometer and contact filter paper method were used to determine the total and matric suctions for low-plasticity soils with different salinities (0.05‰, 2.1‰, and 6.76‰). A new piecewise function was proposed to calculate the osmotic suction, with the piecewise point corresponding to the first occurrence of precipitated salt in mixed salt solutions (synthetic seawater). EC, ion and salt concentrations used for osmotic suction calculation were transformed from the established relationships of mixed salt solution instead of experimental measurement. The calculated osmotic suction by the proposed equation and the equations in the literature was compared with the indirectly measured one (the difference between the measured total and matric suctions). Results showed that the calculated osmotic suction, especially the one calculated using the proposed function, was in fair agreement with the indirectly measured data (especially for specimens with higher salinity of 6.76‰), suggesting that the transformation of EC and concentrations from the established relationship is a good alternative to direct measurement for low-plasticity soil. In particular, the proposed method could be applied to unsaturated low-plasticity soils which do not have enough soil pore water for a proper EC measurement.     

非饱和重塑土的干燥收缩试验研究

基质吸力和净平均应力的增大均可引起土体的压缩变形。针对砂土、粉土、黏土和软土4种不同类型土体,结合试样收缩曲线和土水特征曲线分析了土体干燥过程中基质吸力和孔隙比的关系。试验结果表明:土体干燥收缩过程中随着基质吸力的增大试样不断发生收缩,当基质吸力增大到某特定值时,基质吸力的增大对试样收缩变形无明显影响,称此基质吸力为缩限吸力。屈服吸力s0和缩限吸力ss将试样收缩过程分为弹性阶段、弹塑性阶段和缩限阶段3个阶段。并且不同类型土体的缩限吸力不相同,缩限吸力值与土体的塑性指数密切相关。在干燥收缩过程中,当试样的饱和度减小到90%时试样完成了绝大部分收缩,当试验饱和度达到70%时土样的孔隙比基本保持不变。     

伊犁黄土总吸力和基质吸力土水特征曲线拟合模型

新疆伊犁黄土具有湿陷性强烈、易溶盐含量高的特点,描述其非饱和土应力状态中的吸力参量时,须同时考虑总吸力和基质吸力两个参量。为此,通过滤纸法开展了不同含盐量下伊犁黄土的土水特征曲线试验,测量了不同含盐下伊犁黄土的总吸力与基质吸力,计算了不同含盐量下土样中溶液浓度,分析了含盐量对湿陷的影响,基于Gardner模型,提出了可以考虑易溶盐含量影响的伊犁黄土总吸力和基质吸力土水特征曲线的拟合模型。研究结果表明:含盐量对新疆伊犁黄土的基质吸力有一定影响,对总吸力与渗透吸力影响较大;土样溶液浓度随着含盐量的增大而增大,总吸力与溶液浓度之间呈线性关系;随着土样内易溶盐含量的增加,土样湿陷系数明显增大;提出的土水特征曲线模型可以考虑易溶盐含量的影响,可以统一描述伊犁黄土总吸力和基质吸力随含水率、易溶盐含量变化的规律。     

Behavior and characteristics of compacted expansive unsaturated bentonite-sand mixture

Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore,there is much more room for improvement.In this study,expansive(bentonite-sand(B-S) mixture) and non-expansive(kaolin) soils were tested in different water contents and dry unit weights chosen from the compaction curve to examine the effect of water content change on soil properties(swelling pressure,expansion indices,shear strength(soil cohesion) and soil suction)for the small soil samples.Large-scale model was also used to show the effect of water content change on different relations(swelling and suction with elapsed time).The study reveals that the initial soil conditions(water content and dry unit weight) affect the soil cohesion,suction and swelling,where all these parameters slightly decrease with the increase in soil water content especially on the wet side of optimum water content.The settlement of each soil at failure increases with the increase in soil degrees of saturation since the matric suction reduces the soil ability to deform.The settlement observed in B-S mixture is higher than that in kaolin due to the effect of higher swelling observed in B-S mixture and the huge amount of water absorbed which transformed the soil to highly compressible soil.The matric suction seems to decrease with elapsed time from top to bottom of tensiometers due to the effect of water flowing from top of the specimen.The tensiometer reading at first of the saturation process is lower than that at later period of saturation(for soil sample B-S3,the tensiometer #1 took 3 d to drop from 93 kPa to 80 kPa at early stage,while the same tensiometer took 2 d to drop from 60 kPa to 20 kPa).     

滤纸法测定南阳中膨胀土土水特征曲线试验研究

介绍了滤纸法量测非饱和土吸力的工作原理,以及滤纸接触法量测土体基质吸力和非接触法量测土体总吸力的试验方法和注意事项。利用NaCl盐溶液法建立了国产“双圈”No.203型滤纸的总吸力率定曲线,得到了总吸力率定曲线的双线性表达式。分析了“双圈”No.203型滤纸的总吸力率定曲线和王钊等率定得到的基质吸力率定曲线的关系特性。应用滤纸法分别测试了不同含水率下南阳中膨胀压实土的总吸力和基质吸力值,分别给出了含水率介于16~30%之间的南阳中膨胀压实土的总吸力和基质吸力土水特征曲线。     

An Active Control System for Matric Suction Measurement

Matric suction is an important stress state parameter in unsaturated soil mechanics. Many studies have been carried out in the past to determine the matric suction through direct and indirect methods. Direct measurement of matric suction has been proven possible with high-suction tensiometer; however high-suction tensiometers are still susceptible to cavitation. The axis translation technique developed by Hilf (1956) has been employed in many laboratory tests for unsaturated soils to avoid problem of cavitation in the water pressure measurement system. However in laboratory testing of unsaturated soils, air and water pressures are usually independently controlled and there is no need for a feedback control. The matric suction of soil can be measured using a modified pressure plate apparatus by actively changing the air pressure to maintain the water pressure to be close to zero thus imposing negligible water content change in the soil. A major setback of the existing practice is the need to manually adjust the air pressure of the modified pressure plate in response to the changes in the water pressure. This paper presents an active control system for the modified pressure plate apparatus for matric suction measurement. The experimental results obtained from modified pressure plate apparatus with active control system show good performance as compared to the high suction tensiometer.     

Triaxial apparatus equipped with elastic waves and matric suction measurement techniques

A recently developed technique for elastic wave measurement, a disk transducer method, and a pressure membrane technique for suction measurement were merged into a modified triaxial testing apparatus enabling the procurement of both the elastic waves and the matric suction of a cylindrical specimen. The apparatus was employed to evaluate the variation in suction in sandy soil possessing a low range of suction (less than 100?kPa). Fine sand with two types of fines, namely, non-plastic silt and kaolin clay, was mixed with Toyoura sand in order to prepare sandy soil specimens. Both compressional and shear wave velocities were evaluated in conjunction with the associated matric suction. The matric suction was varied by injecting water into the specimens, and the relevant elastic wave velocities were obtained by a disk transducer. This research has corroborated the applicability of the disk transducer method to unsaturated soil specimens as well as the effects of matric suction on the mechanical behaviour of sandy soils possessing a low range of suction.     

考虑中间主应力的非饱和土上埋式涵洞竖向土压力公式

基于非饱和土的平面应变抗剪强度公式,考虑中间主应力和基质吸力的共同影响,分别建立了均匀与线性2种吸力分布下非饱和土上埋式涵洞的竖向土压力公式,并对其进行可比性分析,对比文献数值模拟和模型试验进行正确性验证,最后探讨了各参数的影响特性。研究结果表明:所建立的上埋式涵洞竖向土压力公式为系列化的有序解析解,可退化为文献已有解答并包含众多新解答,并能计算涵顶上方不同高度处的竖向土压力,工程应用前景广泛; 基质吸力对涵顶竖向土压力具有重要影响,且线性吸力影响不如均布吸力明显,应考虑回填土的非饱和特性并实测吸力分布; 中间主应力效应随基质吸力和填土高度的增大而更加显著,同时均布吸力下中间主应力效应较明显,应合理选取强度准则以反映回填土强度的中间主应力作用; 等沉面高度与回填土物理力学性质、中间主应力效应、基质吸力及分布形式等有关; 基质吸力及其分布影响、中间主应力效应均与填土高度密切相关,体现了多因素对涵顶竖向土压力的综合影响。     

含盐遗址重塑土的吸力测定及土水特征曲线拟合

在水、盐等多种因素的长期共同影响下,珍贵的交河故城本体普遍形成了表层结皮剥蚀病害,引发遗址不可逆转的破坏。非饱和土的特性与其吸力大小密切相关,因此准确确定土水特征曲线是深入研究土遗址劣化机理的基本前提。针对交河遗址土配制NaCl含量不同的泥浆,采用5种吸力测定方法(盐溶液蒸气平衡法、露点水势仪、滤纸法、压力膜仪和高容量张力计)获取被测土体干燥过程中的总吸力和基质吸力,开展不同方法所得吸力值之间的差异分析,借助van Genuchten(vG)和FredlundXing(FX)两种模型拟合基质吸力的土水特征曲线。结果表明,NaCl对遗址土基质吸力几乎没有影响,但由于引发渗透吸力而使总吸力在高含水率段显著增大。不同吸力测定方法反映的遗址土持水特性大体相似;综合多组试验数据可降低曲线拟合误差,在全吸力范围内获得可靠的土水特征脱湿曲线。vG模型和FX模型的拟合效果都比较好,结果为进一步定量化分析土遗址表层结皮开裂病害的形成演变过程提供了科学依据。     

Feasibility of using electrokinetics and nanomaterials to stabilize and improve collapsible soils

Loess as a subcategory of collapsible soils is a well-known aeolian deposit generally characterized as a highly-porous medium with relatively low natural density and water content and a high percentage of fine-grained particles.Such collapsible soil sustains large stresses under a dry condition with natural water content.However,it can experience high and relatively sudden decreases in its volume once it reaches a certain water content under a certain load and therefore,the natural condition of the soil might not be suitable for construction if the possibility of the exposure of the soil to excessive water exists during the lifetime of the project.This research presents the utilization of an innovative method for stabilization and improvement of Gorgan loessial soil.This method uses electrokinetics and nanomaterials to instigate additives to move through soil pores,as an in situ remedial measure.To assess the acceptability of this measure,the deformability and strength characteristics of the improved collapsible soil are measured and compared with those of the unimproved soil,implementing several unsaturated oedometer tests under constant vertical stress and varying matric suction.The result emphasizes the importance of the matric suction on the behavior of both improved and unimproved soils.The test results indicate that the resistance of the soil was highly dependent on the water content and matric suction of the soil.The oedometer tests on samples improved by 3% lime and 5% nanomaterials show considerable improvement of the collapse potential.Results also reveal that stabilized samples experience notably lower volume decrease under the same applied stresses.     

非饱和膨胀土抗剪强度的试验研究

膨胀土是一种特殊的非饱和土，经典的土力学理论在膨胀土问题中己显得无能为力。因此，用非饱和土力学理论来研究膨胀土问题在理论和实际两方面都具有重大意义。在非饱和土抗剪强度理论中，吸力的量测在工程实际中仍没有一种简单易行的方法。基于这种实际情况，试图通过其他间接的途径来代替吸力的量测，以确定非饱和土的吸附强度。对于膨胀土这种典型的非饱和土，膨胀力是其很重要的性质之一，它的大小受含水量的影响很大；另一方面，膨胀土的抗剪强度也随含水量的变化而不断地变化。进行了大量的膨胀力试验和抗剪强度试验，以确定膨胀土的膨胀力与吸附强度是否有一定的关系。通过对黑山土和梅山土的重塑试样试验得到的试验数据分析发现：膨胀力和含水量之间存在良好指数关系；粘聚力的对数和内摩擦角均随含水量的增大线性减小；非饱和膨胀土的吸附强度与膨胀力之间存在较好的线性关系，并在此基础上优化了非饱和膨胀土抗剪强度公式。     

干密度和基质吸力对重塑非饱和黄土变形与强度特性的影响

 为解决填方工程沉降和边坡稳定性问题,采用非饱和土三轴仪,对延安新区填方的重塑Q3黄土,进行3种初始干密度下一系列控制基质吸力的三轴剪切试验,研究重塑黄土的变形和强度变化规律。研究结果表明：初始干密度和吸力对重塑黄土的破坏形态、变形特性和强度特性影响较大;随初始干密度的增大,试样的偏应力–轴向应变曲线逐渐由应变硬化型向理想弹塑性再向应变软化型转变;初始干密度和吸力越大,试样的剪胀性越显著,强度越高;有效黏聚力、内摩擦角和吸力摩擦角均随初始干密度的增加而增大;内摩擦角随吸力几乎不变,而黏聚力随吸力呈线性增加;初始切线杨氏模量和切线体积变形模量均随初始干密度与吸力的增加而提高。根据研究结果提出考虑初始干密度和吸力影响的重塑黄土的抗剪强度参数与非线性模型参数的表达式,可用于预估不同初始干密度、不同吸力下重塑黄土的强度和变形参数,为工程应用和数值模拟提供了依据。     

非饱和土的基质吸力和张力吸力

首先在既往关于非饱和土分类方法的基础上,根据孔隙水弯液面与土颗粒表面的搭接状态,将双开敞非饱和土进一步细分为搭接双开敞非饱和土和不搭接双开敞非饱和土。然后基于热力学原理,提出了另外一个与基质吸力紧密相关而又不同的吸力概念-张力吸力。通过基于水封闭非饱和土的理论计算,得出了张力吸力与基质吸力之间的定量关系,同时利用作者们所提出的等效吸力概念,对比了由基质吸力、张力吸力所产生的等效吸力,从而一方面揭示了张力吸力在非饱和土力学中的重要性,另一方面论证了等效吸力概念的科学性与实用性。     

Hydromechanical behavior of unsaturated expansive clay under repetitive loading

Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses and wetting conditions during field serviceability.Coupling between hydraulic and mechanical repeated loading provides insight understanding to the induced progressive deformation of expansive clay.This study was conducted to investigate the hydromechanical behavior of unsaturated compacted expansive clay under repeated loadingeunloading (RLU) conditions.Two series of onedimensional (1D) oedometer tests were conducted under controlled matric suction up to 1500 k Pa using the axis translation technique (Fredlund soil-water characteristic curve device,SWC-150).The first test series was carried out at different levels of controlled matric suction for non-repeated loading eunloading (NRLU) cycles.RLU cycles were applied in the second test series at different repetitivestress levels and under different levels of matric suction.The results indicated increasing axial wetting strain ε_a(s),axial swell pressure s_s(s),compression index C_c(s),and swell index C_s(s) with suction reduction.The estimated loadecollapse (LC) curves obtained from NRLU series (LCN) and RLU series (LCR)indicated increasing yield stress s_y(s) with increasing suction.This is attributed to the developed apparent cohesion between soil particles,which in turn rigidifies the material response.Applying repetitive loading induced a notable reduction of compression index C_c(s) at the same level of suction,whereas swell index C_s(s) seems to be independent of repetitive loading.Finally,repetitive loading exceeding initial yield stresses results in plastic hardening and,hence,enlargement of yield stress locus(i.e.LC_R curve).     

Analyse du comportement d’un sol argileux sous sollicitations hydriques cycliques

Expansive soils swell and shrink regularly when subjected to moisture changes. Clayey soils are available worldwide and are a continual source of concern causing substantial damage to civil engineering structures. Cyclic expansion and shrinkage of clays and associated movements of foundations may result in cracking and fatigue to structures. In France, the damage caused by this phenomenon was estimated to be more than 3.3 billion euros in 2002 (Vincent in 3^ème conférence SIRNAT-Forum des journées pour la Prévention des Risques Naturels, Orléans, janv. 2003) and the Paris region is one of the most affected. The objective of this study is to investigate the swell–shrink behaviour of a natural clayey soil considered to be responsible for a lot of damage observed on buildings in the Paris region, and thus contributing to the characterisation and understanding of expansive clayey soils. The studied soil, Argile verte de Romainville, is a lagoonal-marine deposit and is part of the Paris Basin Tertiary (Oligocene) formations (Fig. 1). It is a clayey soil sampled in the eastern region of Paris. The mineralogical and geotechnical properties of the soil are presented in Table 1. The soil contains quartz (15–20%), carbonates (12–20%) and traces of mica and feldspars. X-ray diffraction showed that carbonates are essentially dolomite and the clay minerals are dominantly illite, kaolinite and a small amount of smectite (Fig. 2). A grain size analysis shows that the clay content (<2 μm) varies between 78 and 80%. The study of its microstructure by means of the scanning electron microscope indicates that the clayey soil has structural elements oriented in the direction of bedding. The structure of the sample generally consisted of dense and continuous clay matrices with very limited visible pore spaces (Fig. 3). At its natural water content (w = 25%), the soil shows mainly a unimodal pore size distribution with an average pore radius of 0.07 μm and a very limited porosity with radii larger than 10 μm (Fig. 4). To assess the effect of suction on the simultaneous changes in void ratio and degree of saturation under zero external stresses, drying–wetting tests are performed on the natural samples. The osmotic technique (Polyethylene glycol solutions) and various salt solutions are used to control the suction values ranging from 1 to 300 MPa. Once equilibrium is reached at the given suction, the samples are weighed and their volume is measured. A synthesis of the drying–wetting paths is given on Fig. 5. The swelling potential of the soil is evaluated using both indirect (or empirical methods Tables 2 and 3) and direct methods. Swell percentage and swell pressure of the soil are measured in a conventional oedometer apparatus according to ASTM (D 4546-85). The test specimens are 70 mm in diameter and the height varies between 12 and 24 mm. The swell percentage is measured under a nominal pressure of 0.7, 2.0 and 6.3 kPa. Swelling pressure of the soil is measured by the conventional consolidation test method (free swell and load, ASTM D 4546-85 method A) and by a constant volume method (ASTM D 4546-85 method C). The test parameters and results for each specimen are given in Tables 4 and 5, and on Fig. 7. Cyclic swell–shrink tests are carried out on similar samples taken from the same monolith. A scheme that permits the study of the clayey soil behaviour at the extreme states of wetting and drying is chosen. The test begins by wetting the samples at their natural moisture content and density. When swelling is stabilized, the water is removed from around the samples and they are dried in an oven maintained at 45°C until the vertical deformation (shrinkage) is stabilised and are then rewetted and so on. Some experiments are stopped at different swelling phases for microstructural study of the soil. The test parameters of the specimens are given in Table 9 and the results are shown in Figs. 9 and 10. The evolution of the microstructure during wetting and drying cycles is investigated using scanning electron microscope and mercury intrusion porosimetry. Observations are made only on soil specimens taken at the end of the swelling phase of the selected cycles. In order to preserve the microstructure, the specimens are cut in small pieces, frozen by liquid nitrogen and finally sublimated. The results of the drying–wetting path including the water retention curve are shown on Fig. 5. The results show that on the drying path (in the void ratio versus water content plane) the soil first follows nearly the saturation line and then, as the water content decreases, the void ratio tends towards a constant value. A shrinkage limit of w = 14.5 % and a corresponding suction value of 15 MPa is deduced from this path. An air entry value of 10 MPa is obtained from degree of saturation versus suction curve. The wetting path shows that the wetting–drying path is reversible for suction values higher than 60 MPa. The different indirect methods used to assess the swelling potential of the Argile verte de Romainville show a general agreement with respect to its swelling potential ranging from high to very high (Table 3). Examination of the free swell test results shows that the Argile verte de Romainville exhibits swell percentage in the range of 15–26% and that its degree of swelling depends on the initial conditions (water content, dry density) and the applied load (Table 4). The higher the water content and the applied load, the lower the swell percentage. A specimen taken parallel to the bedding plane shows similar values of swell percentage with a steep volume change versus time curve indicating an anisotropy of permeability. The two direct methods used to assess the swelling pressure of the Argile verte de Romainville give different values (Table 5). The values obtained by the constant volume method are relatively close and are about 700 kPa. Lower values varying between 360 and 540 kPa are obtained by the conventional consolidation test (free swell-consolidation). This indicates that besides the initial conditions, the swelling pressure is strongly dependent on the stress path followed. The results obtained from the wetting–drying cycle tests show that the magnitude of the first swell cycle is controlled by the initial water content, the maximum deformation occurring on the second cycle and the stabilization of swelling deformation from the third cycle (Figs. 9, 10). Furthermore, the experimental data indicate that upon repeated wetting and drying, the swelling rate of the soil becomes faster, which is explained by an increase in permeability of the soil due to the development of preferential flow paths (micro cracks) on drying. With an increasing number of cycles, a permanent increase in the volume of the samples is observed. This suggests that the swelling–shrinkage behaviour of expansive soils is not completely reversible. Mercury intrusion porosimetry analysis and SEM observations before and after different numbers of cyclic swelling indicate that the swelling–shrinkage cycles are accompanied by a continual reconstruction of the soil structure (Figs. 11, 12). The mercury intrusion porosimetry results show that with an increasing number of wetting–drying cycles the pore volume and the average diameter of the pores increase progressively (Fig. 11). Larger modifications are observed in the pores with radius in the range of 0.1–5 μm. SEM observations also show further destruction of large aggregates and disorientation of structural elements as the number of cycles increases (Fig. 12). After the fifth cycle, the soil original structure is totally lost and a disoriented homogeneous and loose structure with more homogeneous pore spaces is observed (Fig. 12d).      

垃圾填埋场覆盖层现场试验及特性评价(英文)

填埋场覆盖系统由不同的土层组成,它们具有不同的性质和功能。覆盖层直接与大气和植被接触,因此土的含水率随季节和天气条件不断变化。冬天,土的饱和度增加。夏天,土的含水率减少,同时土中吸力增加。如果土中吸力达到某个极限值,将出现干缩裂缝。这时,粘土阻隔层的密封功能将受到损害。为了研究粘土覆盖系统的长期性状,我们进行了两个大规模现场试验。本文介绍第一批现场试验结果,包括水流量、土中吸力和温度的变化规律。重点介绍保护层(营养层)厚度对覆盖系统水平衡的影响。     

Unsaturated creep tests and empirical models for sliding zone soils of Qianjiangping landslide in the Three Gorges

Creep of sliding zone soils may cause significant displacement in large-scale landslides in the Three Gorges reservoir area.To investigate the effects of water on the soil creep behavior of the Qianjiangping landslide,a series of unsaturated triaxial creep tests on the sliding zone soils were performed.Based on the analyses of testing results,a new stress intensity incorporating matric suction was defined and an unsaturated Singh-Mitchell creep model was developed.Predicted results are in good agreement with the experimental results,which indicates that the established unsaturated model can reasonably simulate the effects of water on the soil creep behavior of the landslide.Finally,relationships between matric suction and the parameters of the model were analyzed.This study provides a calculation model and parameters for the evaluation of long-term stability of landslides under the influence of water.     

Upper bound seismic limit analysis of geosynthetic-reinforced unsaturated soil walls

The assessment of the internal stability of geosynthetic-reinforced earth retaining walls has historically been investigated in previous studies assuming dry backfills. However, the majority of the failures of these structures are caused by the water presence. The studies including the water presence in the backfill are scarce and often consider saturated backfills. In reality, most soils are unsaturated in nature and the matric suction plays an important role in the wall's stability. This paper investigates the internal seismic stability of geosynthetic-reinforced unsaturated earth retaining walls. The groundwater level can be located at any reinforced backfill depth. Several nonlinear equations relating the unsaturated soil shear strength to the matric suction and different backfill type of soils are considered in this study. The log-spiral failure mechanism generated by the point-to-point method is considered. The upper-bound theorem of the limit analysis is used to evaluate the strength required to maintain the reinforced soil walls stability and the seismic loading are represented by the pseudo-dynamic approach. A parametric study showed that the required reinforcement strength is influenced by several parameters such as the soil friction angle, the horizontal seismic coefficient, the water table level, the matric suction distribution as well as the soil types and the unsaturated soils shear strength.     

盐渍土土水特征曲线的研究

通过对以洛阳黄土加NaCl配成的盐渍土物理性质分析,利用压力板仪对不同含盐量、不同干密度、不同含水量的盐渍土在不同压力条件下的基质吸力和含水率关系进行试验研究,并根据试验结果,绘制盐渍土的土水特征曲线,进行比较,分析其变化规律,得出结论：（1）基质吸力随着含水率减小而增大;（2）土水特征曲线有交叉现象出现,即不同条件的试样基质吸力相同;（3）干密度对盐渍土基质吸力影响不大;（4）含盐量对盐渍土的基质吸力有一定的影响。