Roughness control on hydraulic conductivity in fractured rocks

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.

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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.

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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.

     

云南天文台三孔较差视宁度监视仪的建立

较详细地讲述了云南天文台三孔较差视宁度监视仪的情况,然而,与一般天文理论和天文技术的专题研究不一样,天文仪器的研制有如说是研究,还不如说是归纳;它不是分析一个具体的尚未解决的难题,而是把许多已知的理论和技术综合起来,构成一台具体的仪器。所以,本文把许多至少是表面上互不相关的理论和技术问题归纳到一篇论文中。仪器是有许多模块组成的,为了看起来逻辑性较强,我们将仪器分模块叙述,全文遵循如下顺序：１在第一篇中,回顾世界各天文台视宁度测量设备的发展史和云南天文台的宁静度测量发展史;２在第二篇中,介绍：１）云南天文台三孔较差视宁度研制任务的来源,仪器的整体状况;２）介绍云南天文台三孔较差视宁度仪的硬件系统;３）介绍云南天文台三孔较差视宁度仪的软件系统;若大模块中有多个小模块,在每一个大模块中,又遵循下述顺序：１）本模块的总体功能;２）构成该模块的基本技术;３）这些基本技术如何构成整体和完成预定功能。３在第三篇中,介绍我们所作的与视宁度测量有关的一些实验和实验结果。     

Laboratory modelling of shear behaviour of soft joints under constant normal stiffness conditions

Shear behaviour of regular sawtooth rock joints produced from casting plaster are investigated under constant normal stiffness (CNS) conditions. Test results obtained in this investigation are also compared with the constant normal load (CNL) tests. It is observed that the peak shear stress obtained under CNL conditions always underestimates the peak shear stress corresponding to the CNS condition. Plots of shear stress against normal stress show that a nonlinear (curved) strength envelope is acceptable for soft rock joints subjected to a CNS condition, in comparison with the linear or bilinear envelopes often proposed for a CNL condition. Models proposed by Patton (1966) and Barton (1973) have also been considered for the predictions of peak shear stress of soft joints under CNS conditions. Although Patton's model is appropriate for low asperity angles, it overestimates the shear strength in the low to medium normal stress range at higher asperity angles. In contrast, while Barton's model is realistic for the CNL condition, it seems to be inappropriate for modelling the shear behaviour of soft joints under CNS conditions. The effect of infill material on the shear behaviour of the model joints is also investigated, and it is found that a small thickness of bentonite infill reduces the peak stress significantly. The peak shear stress almost approached that of the shear strength of infill when the infill thickness to asperity height ratio (t/a) reached 1.40. This paper also introduces an original, empirical shear strength envelope to account for the change in normal stress and surface degradation during CNS shearing. © Rapid Science Ltd. 1998     

Strain fields and mechanical response of a highly to medium fissured bentonite clay

This article presents the developments of an ongoing research aimed at modelling the influence of fissuring on the behaviour of clays. In particular, it recalls the main results of an extensive laboratory investigation on a fissured bentonite clay from the south of Italy and presents the data of a new investigation on the evolution with shearing of the strain fields developing within the clay, resulting from Digital Image Correlation (DIC). Element test results are analysed in the framework of continuum mechanics and linked to the clay fissuring features, once characterised using the Fissuring IDentity (F‐ID) chart. This article compares the bentonite behaviour with that of other fissured clays of different F‐IDs, highlighting the common behavioural features. Thereafter, the soil response at the macro level is related to the DIC‐derived strain fields evolving within the clay with loading. For this purpose, DIC was successfully used to investigate the deformation processes active in the fissured clay and the sources of the localisation phenomena. DIC is shown to provide indications of the extent to which highly to medium fissured clays element test results can be of use to model the clay behaviour according to continuum mechanics. Copyright © 2012 John Wiley & Sons, Ltd.     

Internal testing of a numerical model of hillslope–channel coupling using laboratory flume experiments

The numerical model COUP 2D simulates the hydrological coupling between hillslopes and the river channel during a rainfall event. In order to test the numerical model, a 1:100 scaled laboratory flume which was modified to incorporate lateral hillslope elements, was used to run a series of experiments in which hillslope angle, channel angle, hillslope discharge and channel discharge were the varying parameters. Overall, there were 18 different experimental configurations with three replicates carried out for each condition, leading to a total of 54 experiments. These conditions were then used to parameterize and run COUP 2D. Internal model outputs of flow depth and flow velocity at four cross‐sections in the channel were compared to the measurements made in the physical model for the same parameter conditions. Statistical comparisons of the measured and modelled data were carried out for each experiment and across all experiments, using two goodness‐of‐fit measures—root mean square error and Nash–Sutcliffe coefficient of efficiency—in order to assess the performance of the model over an entire simulation as well as over all the simulations. The main effects on the goodness‐of‐fit measures for flow depth of each experimental variable, as well as the interactions between variables, were evaluated using statistical modelling. The results show that the model captures flow‐depth variations in response to changing channel and hillslope parameters. Statistical modelling suggests that the main effects on model error are cross‐section position, channel angle and channel discharge. Significant interactions also occur between all the channel variables and between the channel variables and hillslope discharge. The results of the testing procedure have significant implications for the consideration of different model components and for the interaction between data‐ and model evaluation. Copyright © 2007 John Wiley & Sons, Ltd.     

同幅双速跟踪成像CCD相机模拟电路系统设计

讨论了同幅双速跟踪成像技术对CCD相机系统的特殊要求,详细地介绍了该相机前端模拟系统的设计思想、系统结构和主要的电路模块。对系统中一些关键电路模块进行了仿真和测试,并对仿真和测试结果进行比较分析,以检验电路系统设计的合理性。     

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我国抗震防灾研究的发展及其作用

我国是一个地震灾害严重的国家之一。为抵御地震对人民生命财产和国家经济的破坏,使得抗震防灾研究显得尤为必要。本文主要从工程角度,简要介绍了我国抗震防灾研究的历史、现状、前沿问题及未来发展,并且阐述了抗震防灾研究在我国社会主义经济建设中的重要性。     

大唐国际东营一期49.5 MW风电场工程桩基施工及其原体试验

大唐国际东营风电一期工程拟建风电场场区位于东营市东部沿海区域,拟建场地上覆第四系地层,结构松散,厚度较大,工程性质较差,地基强度较低,不能满足重要建（构）筑物对其强度及变形的要求,且场地内的饱和粉土及砂土在地震影响烈度达Ⅶ度时将可能产生液化现象,因此需进行地基处理。根据现场岩土条件,拟采用预应力高强混凝土管桩（PHC）,需进行桩基原体试验。主要介绍了桩基原体试验施工过程、检测方法及试验成果等。