Effect of different types of wetting fluids on the behaviour of expansive soil during wetting and drying

This paper presents the results of an experimental investigation into the mechanical behaviour of an expansive soil during wetting and drying cycles. The experimental tests were conducted in a modified oedometer under two different surcharge pressures (10 and 20 kPa). During the tests, the samples were inundated with different types of wetting fluids (distilled water, saline water and acidic water). The volumetric deformation, void ratio and water content of the samples were determined during cycles of wetting and drying. The results show that the swelling potential increases with an increasing number of wetting and drying cycles. The effect of the distilled water on the swelling potential is not the same as that of the saline water or the acidic water, particularly for different surcharge pressures. The variations in void ratio and water content show that, at the equilibrium condition, the wetting and drying paths converge to nearly an S-shaped curve. This curve consists of a linear portion and two curved portions, and the majority of the deformation is located between the saturation curves of 90% and 40%.     

Laboratory measurement of hydraulic conductivity functions of two unsaturated sandy soils during drying and wetting processes

The importance of applying unsaturated soil mechanics to geotechnical engineering design has been well understood. However, the consumption of time and the necessity for a specific laboratory testing apparatus when measuring unsaturated soil properties have limited the application of unsaturated soil mechanics theories in practice. Although methods for predicting unsaturated soil properties have been developed, the verification of these methods for a wide range of soil types is required in order to increase the confidence of practicing engineers in using these methods. In this study, a new permeameter was developed to measure the hydraulic conductivity of unsaturated soils using the steady-state method and directly measured suction (negative pore-water pressure) values. The apparatus is instrumented with two tensiometers for the direct measurement of suction during the tests. The apparatus can be used to obtain the hydraulic conductivity function of sandy soil over a low suction range (0–10 kPa). Firstly, the repeatability of the unsaturated hydraulic conductivity measurement, using the new permeameter, was verified by conducting tests on two identical sandy soil specimens and obtaining similar results. The hydraulic conductivity functions of the two sandy soils were then measured during the drying and wetting processes of the soils. A significant hysteresis was observed when the hydraulic conductivity was plotted against the suction. However, the hysteresis effects were not apparent when the conductivity was plotted against the volumetric water content. Furthermore, the measured unsaturated hydraulic conductivity functions were compared with predictions using three different predictive methods that are widely incorporated into numerical software. The results suggest that these predictive methods are capable of capturing the measured behavior with reasonable agreement.     

Suction variations and soil fabric of swelling compacted soils

This study addresses firstly the soil fabric variations of loose and dense compacted soil samples during a single wetting/drying cycle at suctions between 0 and 287.9 MPa using mainly the mercury intrusion porosimetry（MIP） tests.Two suction techniques were employed to apply this wide suction range：the osmotic technique for suctions less than 8.5 MPa,and the vapor equilibrium or salt solution technique for suctions higher than 8.5 MPa.Secondly,the soil water retention curves（SWRCs） were predicted by the MIP test results for both loose and dense soil samples.A reasonable correspondence between MIP results and SWRCs was found on the wetting path at lower suctions close to saturation and on drying path at higher suctions.     

Variability of Physical and Consolidation Test Results for Relatively Uniform Clay Samples Retrieved from Osaka Bay

Samples collected from both Holocene and Pleistocene layers in Osaka Bay were examined in this study. The objective of this study is to evaluate variations of soil parameters in a sample length of about one meter. The retrieved samples from EL. (elevation) -37.5 to -38.5 m and from EL.-125.5 to -126.5 m with a length of about one meter were divided into every 25 mm long to trim consolidation specimens. Variations of soil parameters obtained from laboratory tests were evaluated. Clay microfabric was also evaluated by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The clay layers are relatively homogeneous with variation coefficient CV in a range of 0.025 to 0.12 for the consolidation parameters (e, p′_c, C_c and c_v). CV of void ratio e is only 0.025 to 0.056. In contrast, CV values of the other consolidation parameters are significantly greater than this, but the average is less than 0.1. It can be concluded that CV of soil consolidation parameters for the homogeneous natural clay deposits dealt in this study is less than about 0.1. These variations are mainly influenced by sedimentary environment. Even the soil is said to be homogeneous, because the specimen size for the laboratory tests is sufficiently large in consideration of microscopic heterogeneity obtained from SEM and MIP.     

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).      

干湿循环过程中膨胀土的胀缩变形特征

为了了解干湿循环过程中膨胀土的胀缩变形特征,分别开展了两组干湿循环试验。在控制吸力干湿循环试验中,吸力控制范围为 0.4 ～ 262 MPa ,采用了两种吸力控制方法,分别为渗析法（吸力＜ 4 MPa ）和蒸汽平衡法（吸力＞ 4 MPa ）,当每一级吸力达到平衡时,测量试样对应的含水率和体积;在常规干湿循环试验中, 采取了两种干缩路径,分别为全干燥和部分干燥,并测量试样在每次干湿循环过程中的轴向变形及循环结束后的含水率。结果表明： 在脱湿和吸湿过程中,试样孔隙比随吸力变化可分 3 个典型阶段：大幅变化阶段（ 0.4 ～ 9 MPa ）、过渡阶段（ 9 ～ 82 MPa ）和平缓阶段（ 82 ～ 262 MPa ）; 当吸力大于 113 MPa 时,试样的胀缩变形基本可逆,而当吸力小于 113 MPa 时,试样的胀缩变形 表现出明显的不可逆性,且不可逆程度随吸力的减小而增加。试样在常规干湿循环过程中的胀缩变形随循环次数的增加逐渐趋于稳定;胀缩特征受干缩路径的影响非常明显,全干缩路径中测得的膨胀率高于部分干缩路径,膨胀速率随干湿循环次数的增加而增加;试样在干湿循环过程中的膨胀率大小在一定程度上取决于吸湿能力。     

考虑孔隙比和水力路径影响的非饱和土土水特性研究

以非膨胀性黏土为试验研究的对象,利用压力板法研究了初始孔隙比对不同水力路径下非饱和压实土土水特性的影响。试验结果表明,不同初始孔隙比土水特征曲线均存在明显的滞洄现象;当吸力大于某一值时,以含水率与吸力关系表示的话,不同初始孔隙比主脱湿土水曲线几乎重叠;以饱和度与吸力关系表示,初始孔隙比对土水特征曲线存在较大的影响。还提出归一化处理全吸力范围内不同初始孔隙比土水特征曲线的方法。最后,在归一化的处理方法基础上,提出了考虑初始孔隙比影响的非饱和土滞洄特性的模拟方法,并利用相关实测数据加以验证。     

Effect of temperature on the soil–water retention characteristics in unsaturated soils: Analytical and experimental approaches

In unsaturated soil mechanics, the soil–water retention curve (SWRC) continues to play an important role, since it provides the necessary links between the properties and behaviour of unsaturated soils with a variety of engineering challenges. The temperature has been identified as the main factor influencing SWRC as compared to a variety of other parameters. The goal of this research is to describe theoretical and experimental aspects of the temperature effect on unsaturated soil water retention phenomena. Theoretically, a brief review of the constitutive laws governing the thermal-hydro-mechanical (THM) behaviour of unsaturated soils is presented, along with links between variations in suction with water content, temperature, and void ratio. It also provides a broad framework that would to be well adapted to describing many specific circumstances. Through a closed-form predictive relationship that is developed in this framework, the effect of temperature is examined. By using this relationship, the soil–water retention curve at arbitrary temperature could be determined from one at a reference temperature, therefore significantly decreasing the number of tests necessary to describe the thermo-hydro-mechanical behaviour of a soil. Besides, the SWRC of kaolinite clay was also measured at three different temperatures in an experimental program. The test findings reveal that when the temperature rises, the SWRC decreases significantly. The experimental results were then integrated with sixteen other available data sets covering a wide range of soil types, densities, and suction to create a complete verification program for analytical models. The proposed model has a good performance and reliability in forecasting the fluctuation of non-isothermal SWRC than any existing model, according to statistical assessment results. The analytical model can be used to examine the thermo-hydro-mechanical characteristics of unsaturated soils in numerical simulations.     

膨胀土增湿过程中吸力–孔隙比–含水率关系

通过不同初始孔隙比条件下的土水特征试验及增湿试验,研究了膨胀土的土水特征曲线拟合参数及体积膨胀曲线拟合参数与初始孔隙比的关系,采用曲面拟合法建立了孔隙比与重量含水率及初始孔隙比的关系曲面、孔隙比与吸力及初始孔隙比的关系曲面、重量含水率与吸力及初始孔隙比的关系曲面、体积含水率与吸力及初始孔隙比的关系曲面。试验结果表明,在重量含水率(或吸力)–初始孔隙比–孔隙比坐标系中的体变曲面由饱和部分及非饱和部分组成;在增湿过程中,曲面由非饱和区进入饱和区的转折点对应的重量含水率随着初始孔隙比的增大而增大,转折点对应的吸力随着初始孔隙比的增大而减小;在吸力–初始孔隙比–重量含水率或体积含水率坐标系中,与特定初始孔隙比对应的土水特征曲线是纵坐标恒定的平面曲线;在吸力–孔隙比–重量含水率或体积含水率坐标系中,与特定初始孔隙比对应的土水特征曲线是纵坐标在变化空间曲线,它能同时表示初始孔隙比的影响及试验过程中孔隙比的变化。     

压实膨胀土非饱和渗水系数函数的密度与水力滞回效应

为探讨密度与水力滞回对膨胀土非饱和渗水系数函数(hydraulic conductivity function, HCF)及非饱和渗流的影响,以压实弱膨胀土为研究对象,开展变水头渗透试验获得饱和渗透系数-孔隙比e关系。基于van Genuchten-Mualem(VGM)模型,采用TRIM(transient release and imbibition method,瞬态脱湿与吸湿)试验方法获得6种密度下脱/吸湿过程的HCF模型参数α,n,并构建α,n与e的经验公式。基于所获HCF模型参数在Hydrus中开展降雨入渗数值分析。结果表明:①土体密度与水力滞回对α,n影响显著;无论脱/吸湿过程,α,n均随e增大而增大;相同密度下,脱湿过程α,n均小于吸湿过程对应值。②密度与水力滞回均对吸力表达的HCF影响显著;不同e下HCF存在"交叉"现象:相同吸力下,交叉点前,密度小的试样渗水系数k值大;交叉点后,密度大的试样k值大;同一密度相同吸力下脱湿过程k值明显大于吸湿过程k值。③密度对体积含水率θ表达的HCF影响显著,相同θ下,密度大的试样k值小,但不存在"交叉"现象;水力滞回对θ表达的HCF影响微弱,同一密度下脱/吸湿过程HCF接近。④数值分析表明,土体密度对非饱和渗流影响显著,但密度变化对湿润锋前进速度快慢影响不具单调性;水力滞回对渗流分析结果影响明显;采用形式简单的HCF模型如VGM模型,采用α,n与e的经验公式,对不同密度、不同脱/吸湿路径采用对应的模型参数值,是综合考虑密度与水力滞回对非饱和渗流影响的可行方法。     

非饱和黄土初始剪切模量与孔径分布试验研究

土的初始剪切模量G_0是地震、爆破响应中一个非常重要的土动力学参数,对预测地表沉降、土工建筑物周围土体变形等具有重要作用。黄土在中国及世界各地分布广泛,且现场常处于非饱和状态。对非饱和黄土的压实试样进行了吸力控制的共振柱试验以及压汞试验,研究非饱和黄土初始剪切模量G_0与孔径分布的关系。试验表明:干湿循环过程中,试样的G_0随吸力的增大而增大,再随吸力的减小而减小。主要原因是试样内孔隙密度最大的孔径大小随吸力的增大而减小,试样内大孔隙减少,小孔隙增多,导致毛细水所占比例增加,土颗粒接触更加紧密。同一吸力作用下,湿润段试样的小孔隙比例比干燥段大,故毛细水作用更显著,从而湿润段试样的G_0大于干燥段。     

Soil-water characteristics of Gaomiaozi bentonite by vapour equilibrium technique简

Soil-water characteristics of Gaomiaozi (GMZ) Ca-bentonite at high suctions (3–287 MPa) are measured by vapour equilibrium technique. The soil-water retention curve (SWRC) of samples with the same initial compaction states is obtained in drying and wetting process. At high suctions, the hysteresis behaviour is not obvious in relationship between water content and suction, while the opposite holds between degree of saturation and suction. The suction variation can change its water retention behaviour and void ratio. Moreover, changes of void ratio can bring about changes in degree of saturation. Therefore, the total change in degree of saturation includes changes caused by suction and that by void ratio. In the space of degree of saturation and suction, the SWRC at constant void ratio shifts to the direction of higher suctions with decreasing void ratio. However, the relationship between water content and suction is less affected by changes of void ratio. The degree of saturation decreases approximately linearly with increasing void ratio at a constant suction. Moreover, the slope of the line decreases with increasing suction and they show an approximately linear relationship in semi-logarithmical scale. From this linear relationship, the variation of degree of saturation caused by the change in void ratio can be obtained. Correspondingly, SWRC at a constant void ratio can be determined from SWRC at different void ratios.     

p-s平面上不同应力路径的非饱和土力学特性研究

 通过7个吸力和净平均应力同时变化的非饱和含黏砂土固结试验,研究7条不同应力路径的试验在p-s-v,p-s- ,p-s- 和p-s-w空间曲线形状随角度?(净平均应力和吸力夹角)的变化规律,分析引起变化的机制,指出净平均应力是决定体变的重要因素,吸力是决定水分变化的首要条件。并探讨p-s平面上7条应力路径屈服点连线轨迹的统一表达式,建立p-s平面上屈服点连线的统一抛物线表达式。最后运用该公式预测已有的试验数据,预测结果较为理想,说明该式预测p-s平面上不同应力路径各屈服点变化规律是较为可靠的。     

Joints in unsaturated rocks: Thermo-hydro-mechanical formulation and constitutive behaviour

A formulation for the coupled analysis of thermo-hydro-mechanical (THM) problems in joints is first presented. The work involves the establishment of equilibrium and mass and energy balance equations. Balance equations were formulated taking into account two phases: water and air. The joint element developed was implemented in a general purpose finite element computer code for THM analysis of porous media (Code_Bright). The program was then used to study a number of cases ranging from laboratory tests to large scale in situ tests. A numerical simulation of coupled hydraulic shear tests of rough granite joints is first presented. The tests as well as the model show the coupling between permeability and the deformation of the joints. The experimental investigation was focused on the effects of suction on the mechanical behaviour of rock joints. Laboratory tests were performed in a direct shear cell equipped with suction control. Suction was imposed using a vapour forced convection circuit connected to the cell and controlled by an air pump. Artificial joints of Lilla claystone were prepared. Joint roughness of varying intensity was created by carving the surfaces in contact in such a manner that rock ridges of different tip angles were formed. These angles ranged from 0° (smooth joint) to 45° (very rough joint profile). The geometric profiles of the two surfaces in contact were initially positioned in a “matching” situation. Several tests were performed for different values of suctions (200, 100, and 20 MPa) and for different values of vertical stresses (30, 60, and 150 kPa). A constitutive model including the effects of suction and joint roughness is proposed to simulate the unsaturated behaviour of rock joints. The new constitutive law was incorporated in the code and experimental results were numerically simulated.     

从变形、水量变化和强度三方面验证非饱和土的两个应力状态变量

为了验证非饱和土两个应力状态变量的合理性,对常规非饱和土三轴仪进行了改进,采用3个压力–体积控制器分别控制孔隙水压力、内室压力和外室压力,提高了量测体变和含水率的精度;用加荷器施加轴向荷载,可以方便地控制偏应力。在笔者前期用各向等压试验验证非饱和土的两个应力状态变量的基础上,使用改进的非饱和土三轴仪和重塑Q_3黄土做了两类验证试验:第一类是两组控制净围压、偏应力和吸力的固结不排水剪切试验,第二类是3组控制净围压和吸力的固结排水剪切试验。在第一类试验中,等值改变(增加或减少)总围压、孔隙水压力和孔隙气压力而保持净围压、吸力和偏应力本身不发生变化,发现试验过程中土样的体积变化和含水率变化均非常小,可以忽略不计。第二类试验的每一组包含两个控制净围压和吸力分别相同的固结排水剪切试验,其中一个试样在固结完成后直接进行排水剪切试验,另一个试样在固结完成后等值增加总围压、孔隙水压力和孔隙气压力而保持净围压和吸力本身不发生变化的条件下进行排水剪切试验,发现二者的抗剪强度、剪切过程中的体积变化、排水量和广义剪应变都分别十分接近,可以认为两两相等。研究结果从变形(包括体应变和剪应变)、水量变化和强度3个方面说明描述非饱和土的两个应力状态变量是合理的,进一步夯实了非饱和土力学的应力理论基础,为非饱和土的两个应力状态变量理论提供了牢靠的试验依据。     

Properties of very soft clays: A study of thixotropic hardening and behavior under low consolidation pressure

In a study on the properties of very soft clays, bender element testing was used to evaluate thixotropic hardening behavior; that is, to measure the stiffness with resting time under constant volume and water content. A laboratory vane test, which measures the undrained shear strength of the materials, was also carried out for comparison purposes. To investigate the mechanism of the thixotropic phenomenon, a consolidation test with very low pressure was also performed in a cell equipped with bender elements. The most important findings from this study are as follows: (1) regardless of soil types, the effect of thixotropy was significant around the liquid limit state and less remarkable at the lower and higher ranges; (2) the shear modulus at the liquid limit after 24 h resting is around 200 kPa; (3) the correlation between the shear modulus and the undrained shear strength of very soft clays is similar to that of cement-treated soil proposed by Seng and Tanaka (2011); (4) the increment of the shear modulus developed in the thixotropy process appears to be noticeably higher than that in the secondary consolidation process. It is believed that these findings are very useful to establish a new theory for the consolidation of ground filled by very soft clays or dredged soils with extremely high water content as well as to understand the effects of ageing on the consolidation properties of natural soils.     

土水特征曲线在滑坡预测中的应用性探讨

 通过模型试验与数值分析方法的结果对比,研究土水特征曲线中的主要增湿路径与主要减湿路径对降雨型滑坡预测的影响。研究结果表明,采用不同状态路径的土水特征曲线来进行降雨条件下边坡的有限元渗流分析,会得到不同的基质吸力和孔压变化趋势,进而影响强度折减有限元法的计算结果;而对于相同的基质吸力条件下,采用主要增湿路径所预测的非饱和渗透系数会低于主要减湿路径的预测值,使得主要减湿路径预测滑坡破坏时间较主要增湿路径快。此外,若边坡产生滑动型破坏,则实际滑坡发生时间在主要减湿路径与主要增湿路径的预测值之间。研究成果说明,采用作为界限的主要增湿和主要减湿路径作为土水特征曲线的滞后模型,对降雨型滑坡灾害的防灾预警具有一定的实用价值,可利用主要增湿与减湿路径预测滑坡发生的时间差,规划与建立合适的滑坡雨量预警基准。     

Degradation of Compacted Marls: A Microstructural Investigation

Embankments made with marl and other soft clayey rocks result in an agglomerated structure of finite size particles. These particles evolve however, resulting in major changes of the overall behaviour of the aggregate. The development of settlements and the loss of strength in time are the main concerns in practice. The mechanisms leading to the breakage and eventually the destructuration of one single rock particle are investigated using the concepts of unsaturated soil mechanics since wetting and drying cycles, controlled by atmospheric changes, result in strong suction changes and are one of the main reasons for rock degradation. Numerical simulations of the behaviour of individual rock fragments when wetted until full saturation were performed. Several contributing factors, namely suction change rate, initial suction and confinement were investigated. The knowledge learned with the simulation of the degradation of single rock fragments was extended to simulate the behaviour of particle arrangements under some representative stress and suction paths. Some results of suction controlled tests used for the calibration of the models are presented. The calculated behaviour of single particles and aggregates under wetting is discussed and qualitatively compared with experimental observations of the individual rock fragments and the compacted material. The results obtained provide a new insight into the nature of degradation induced by wetting and drying. They provide also a mechanical explanation, at the level of rock fragments, for the overall behaviour of aggregates.     

Mechanical characterisation of traditional adobes from the north of Spain

Mud is one of humankind’s oldest construction materials. The paper presents a technical study of straw-stabilized adobe, prepared in the traditional manner using wooden frames and compacting the mixture manually. The mud is selected from a specific area in the province of León (Spain) where adobes had been employed traditionally from long years ago using two different proportions of straw: 25% and 33% of total volume. The laboratory tests have followed the standard EN protocols. The different tests developed were of two types: for the natural soil granulometric analysis, relative density and Atterberg limits were made; for the adobes the following were done: shrinkage during drying, density, compressive and flexural strength.Results show an average compressive strength of 3.8 N/mm² and an average flexural strength of 0.68 N/mm², so it can be stated that traditional adobes can be used as an adequate construction material.     

非饱和土热–水–力全耦合本构模型及其验证

在地热资源开发与利用、核废料地质处理、垃圾填埋场等诸多岩土工程领域都需要考虑温度对非饱和土性质的影响。为了更为全面描述非饱和土在热–水–力耦合条件下的变形及持水特性,以平均土骨架应力、修正吸力和温度为应力变量,以比体积和饱和度为应变变量,建立了一个非饱和土热–水–力全耦合本构模型。模型通过屈服面方程及屈服面之间的耦合规律来反映热–水–力之间的相互影响,主要包含温度和饱和度对力学特性的影响,吸力和超固结比(应力历史)对热变形的影响,密度、温度和滞回效应对持水特性的影响,温度、应力和滞回效应对干化及湿化变形的影响。利用建立的模型,对不同应力路径下的试验进行预测。通过预测与试验结果的对比,验证了模型的适用性。