Slip zones of the large landslides in the Three Gorges area are commonly composed of fine-grained soils with substantial amount of coarse-grained particles, particularly gravel-sized particles. In this study, residual strength of the soils from slip zones of these landslides were examined in relation to their index properties based on a survey of 170 landslides. It was found that laboratory-determined residual friction angle using gravel-free fraction of the disturbed soils from the slip zones was closely related to clay content, liquid limit and plasticity index. On the other hand, in-situ residual friction angle of these soils (i.e. including gravel fraction) showed very weak correlations with clay content and Atterberg limits, but was largely dependent on gravel and fines (clays + silts) contents, increasing with gravels and decreasing with fines, and displayed strong linear correlation with the ratio of gravel to fines contents. These observations indicate that among the index properties, clay content and Atterberg limits can be used to estimate residual strength of the soils finer than 2 mm, but they are not appropriate evaluate the residual strength of the soils containing considerable amount of gravel-sized particles. For the latter, particle size distribution (particularly the ratio of gravel to fines contents) appears to be a useful index. Additionally, it was found that there was no identifiable correlation between relative abundance of individual major clay minerals and residual friction angles of both gravel-free fraction of disturbed and in-situ soils, suggesting that influence of clay minerals on residual strength of these soils can not be simply evaluated based on their abundance. 相似文献
The influence of rock fabric on physical weathering due to the salt crystallization of selected brecciated dolostones is discussed. These dual-porosity dolostones are representative of heterogeneous and anisotropic building rocks, and present highly complex and heterogeneous rock fabric features. The pore structure of the matrix and clasts is described in terms of porosity and pore size distribution, whereas the relative strength for each textural component is assessed using the Knoop hardness test. The whole characterisation process was carried out using the same samples as those used in the standard salt durability test (EN-12370), including connected porosity, the water saturation coefficient, fissure density, compressional wave velocity and waveform energy.
Results show the most important rock fabric elements to be considered are the matrix and clast properties and the nature of fissures. Firstly, a relatively weak matrix was the focus of major granular disintegration as it presents high porosity, low pore radius and reduced strength. Secondly, narrow micro-fissures appear to be important in the decay process due to the effectiveness of crystallization pressure generated by salt growth. On the contrary, macro-fissures do not contribute greatly to rock decay since they act as sinks to consume the high supersaturations caused by growth of large crystals. Additionally, an analysis of stress generated by crystallization was carried out based on the general situation of a lenticular crystal geometry. Finally, the relationships between whole petrophysical properties and durability were established using a principal component analysis. This analysis has clearly established that the durability of rocks affected by salt crystallization mechanisms diminishes in weaker and anisotropic rocks with high porosity and fissure density. 相似文献
The influence of joint roughness on the typologies of fluid flow inside fractures is well known and, thanks to experiences
in the field of hydraulics, it has been studied from both a physical and mathematical point of view. Nevertheless, the formulations
adopted by traditional hydraulic models are hardly applicable in the geological field, because of the difficulty encountered
in the roughness parameter estimation. Normally this parameter can be estimated using the joint roughness coefficient (JRC),
which considers both the asperity height and its regularity and directional trend. The main advantage in using the JRC arises
from the fact that it can easily be obtained from geological-technical surveys and from comparison with the standard Barton
profiles. Some relationships have been built up that allow for the estimation of the hydraulic conductivity tensor (an essential
parameter for understanding water flow in fractured rock masses), not only as a function of traditional parameters like aperture,
spacing, dip and dip direction, etc., but also of joint roughness, precisely expressed in terms of the roughness coefficient.
These relationships have been studied initially from a theoretical point of view and then practically, through laboratory
investigations.
Resumen Se conoce muy bien la influencia de la rugosidad de las grietas en las tipologías del flujo de fluidos a lo interior de las
fracturas y gracias a las experiencias en el campo de hidráulica ha sido posible estudiarla desde puntos de vista matemáticos
y físicos. Sin embargo, las formulaciones adoptadas por los modelos hidráulicos tradicionales tienen poca aplicabilidad en
el campo geológico debido a la dificultad relacionada con la estimación del parámetro de rugosidad. Normalmente este parámetro
puede estimarse usando el coeficiente de rugosidad de grieta (JRC) el cual considera tanto la altura de la aspereza como su
regularidad y tendencia direccional. La principal ventaja de utilizar el JRC se deriva del hecho que puede obtenerse fácilmente
de levantamientos técnico-geológicos y de la comparación con los perfiles Standard Barton. Se han construido algunas relaciones
que permiten la estimación del tensor de conductividad hidráulica (un parámetro esencial para el entendimiento del flujo de
agua en masas de roca fracturadas), no solo en función de parámetros tradicionales como apertura, espaciado, buzamiento y
dirección de buzamiento, etc., sino también en función de la rugosidad de la grieta estimada con precisión en términos del
coeficiente de rugosidad. Estas relaciones se han estudiado inicialmente desde un punto de vista teórico y luego de modo práctico
a través de investigaciones de laboratorio.
Résumé L’influence de la rugosité des joints sur les types d’écoulement de fluide dans les fractures est bien connue et a été étudiée
aussi bien du point de vue physique que mathématique grace à des expériences menées dans le domaine de l’hydraulique. Cependant
les formulations adoptées dans les modèles hydrauliques traditionnels sont difficilement applicables dans le domaine de la
géologie à cause de la difficulté rencontrée pour estimer la rugosité. Ce paramètre peut normalement être apprécié grace au
coefficient de rugosité du joint (JRC), lequel prend en compte à la fois la hauteur de l’aspérité ainsi que sa régularité
et sa direction. Le principal avantage dans l’utilisation du JRC réside dans le fait qu’il peut facilement être obtenu à partir
d’études techniques-géologiques et par comparaison avec la classification de Barton. Des relations qui permettent une estimation
du tenseur de conductivité hydraulique (un paramètre essentiel pour comprendre l’écoulement de l’eau dans les masses rocheuses
fracturées) ont été élaborées, pas seulement en fonction de paramètres traditionnels tels que l’ouverture, l’espacement, l’inclinaison
et la direction d’inclinaison, etc , mais aussi en prenant en compte la rugosité des joints à travers le coefficient de rugosité.
Ces relations ont initialement été étudiées d’un point de vue théorique puis expérimentalement à travers des recherches en
laboratoire.
ABSTRACTThis paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil. 相似文献