基于扩展有限元分析的页岩水力压裂裂缝扩展规律探究

水力压裂是开采地下页岩气资源的有效技术手段,探究页岩水力压裂裂缝的扩展规律,可为页岩气的高效开采提供科学的指导依据。通过运用大型有限元软件ABAQUS中的扩展有限元模块,针对不同地应力差工况条件下均质页岩中初始裂缝的位置、方位角、数量和含层理页岩中层理的构造方向、内部倾角、岩性对水力裂缝扩展的影响进行探究。结果表明：对于垂向扩展的水力裂缝,水平主应力增大使裂缝更不易扩展,裂缝扩展长度减小、起裂压力增大;在注液体积流量相同时,向初始裂缝两端同时起裂所形成的水力裂缝长度大于仅向一侧起裂;当初始裂缝处于页岩中部且呈45°方向时,裂缝会向最大水平主应力方向偏转,且偏转程度随最大水平主应力的增大而增大;分时多簇压裂时,裂缝间的扩展会相互干扰,且会较大地影响裂缝扩展的形态和起裂压力,但对裂缝注液点裂缝宽度的影响较小;对于含水平和竖直构造层理的页岩,改变层理内部倾角,水力裂缝会出现不同程度偏转,且其偏转程度随着层理内部倾角的增大而减小;对于含45°方向构造层理的页岩,水力裂缝在层理分别为砂岩、煤岩和泥岩中的偏转程度依次增大,且裂缝偏移比随着最大水平主应力的增大而增大。     

基于单三轴试验与直剪试验的层状软岩模拟

为探究模型试验中层状软岩模拟方法,依托九绵高速层状软岩隧道现场取样的室内试验结果,多次试验确定重晶石粉、石英砂、石膏粉、滑石粉和水的最优配比以模拟软岩基体,采用带孔薄膜模拟层理弱面的黏结作用,并通过直剪试验确定孔隙率,最后对不同层理角度与层理厚度的试样开展直剪与单、三轴试验以反映各向异性情况。结果表明：软岩基体模拟最优配比为0.55:0.15:0.07:0.06:0.17,重晶石粉对强度及破坏变形起决定作用,含量过低易压溃,含量过高产生上下贯通裂缝;采用30%孔洞率的薄膜模拟层理效果最佳;土样强度随层角呈U形变化,层厚减小（不小于2 cm）,强度减小。直剪试验中,45º层理剪切面朝层理方向倾斜,90º层理导致剪切面上下产生裂缝与碎裂,单三轴结果中,0º层理会产生小角度倾斜裂缝,45º层理产生垂直层理面的斜裂缝及二次破裂,90º层理产生顺层理的竖向劈裂;与现场结果对照后确定最优层厚为 3 cm,对层角与层厚的直剪与单三轴试验结果整体一致,揭示土样孔隙压密闭合−弹性−塑性胀裂破坏−徐变的过程。     

Comparison of Static,Kinematic and Dynamic Geodetic Deformation Models for Kutlugün Landslide in Northeastern Turkey

Being the cause of the loss of life and damaging property, landslide is an important natural hazard. Therefore, landslides have to be monitored and preventive measures taken accordingly. In Geodesy, landslides can be determined with static, kinematic and dynamic geodetic models. The aim of this study is to develop a dynamic geodetic model for landslides and compare it with static and kinematic geodetic models. A study area was selected in the Northeastern Black Sea Region of Turkey where landslides are the most effective natural hazard. Movements were determined with static, kinematic and dynamic geodetic models using geodetic, geologic and geophysical measurements made in the study area. Groundwater levels changes were regarded as causative forces in the formulation of the dynamic model. The dynamic model delivered more detailed information (direction, values, velocity, acceleration of movements) about landslide movements. It is possible to formulate more realistic strategies about prevention of landslides by using this information. As a result, it can be suggested that dynamic geodetic models are more useful in landslide studies.     

Potential of Satellite Remote Sensing and GIS for Landslide Hazard Assessment in Southern Kyrgyzstan (Central Asia)

Big landslides are one of the main natural hazards in Kyrgyzstan, which are concentrated in the foothills of the high mountain ranges along the Eastern rim of the Fergana Basin. Because of the high number of landslides and their occurrence over large areas there is a strong need for effective and objective landslide hazard assessment at a regional scale. In Kyrgyzstan satellite remote sensing data represent the only source of multitemporal information about surface conditions covering large areas. Against this background the goal is the development of a satellite remote sensing and GIS-based system for quantitatively oriented and spatially differentiated hazard assessment. During the presented pilot investigations in the area of the Upper Maili Suu river basin a methodological framework has been developed incorporating remote sensing and GIS techniques for various levels of information extraction. So far, methodological investigations have been focused on the potential of satellite remote sensing data from different optical (Landsat-(E)TM, ASTER, MOMS-2P) and radar (ERS-1/2) systems for the creation of an improved knowledge basis for hazard assessment. This includes landslide identification, generation of topographic information and characterization of the geological setting. The derived primary information have been analyzed in a GIS environment to gain an improved process understanding as a main prerequisite for successful hazard assessment. The results show that currently available satellite remote sensing data are suitable for landslide investigation in Kyrgyzstan. Full exploitation of their information potential requires combined analysis with other thematic information based on methods of interactive and automated information extraction.     

Undrained dynamic-loading ring-shear apparatus and its application to landslide dynamics

Landslides are gravitational mass movements of rock, debris or earth. Some move very slowly, thus conforming to the field of statics, but some move rapidly. Study of the initiation and motion of rapid landslides needs to develop Landslide Dynamics involving dynamic loading and dynamic generation/dissipation of excess pore-water pressure. New developments in science can be facilitated by new technological advances. This study aimed to develop a new apparatus that can geotechnically simulate the formation of the shear zone and the following long and rapid shear displacement that occurs in high-velocity landslides. Professor K. Sassa and his colleagues at DPRI (Disaster Prevention Research Institute), Kyoto University, have worked to develop an undrained dynamic-loading ring-shear apparatus for this purpose. A series of different types of apparatus (DPRI-3, 4, 5, 6, 7) have been developed from 1992 to the present. This paper describes the development of this apparatus and its application to the study of earthquake-induced landslides and the latest landslide-triggered debris flow in Japan. Also, tests of the latest version (DPRI-7) with a transparent shear box for direct observation of the shear zone during a rapid shearing are described.     

Characteristics of rapid giant landslides in China

Factual data for 70 rapid, giant landslides since 1900 show that the occurrence of these landslides was largely predisposed by tectonics, geological structures, lithology and topography, and often triggered by rainfall and earthquakes. In terms of mobile behavior, the giant landslides can be classified into three types: slides, slide-flows and flows. It is found that each type of landslide was constrained to certain geologic and topographic regimes. There are good correlations between kinematic parameters of landslides and slope geometries, which confirm the important role played by topographical condition in the mobile behavior of landslides. Moreover, it is also found that each type of landslide presents distinct geotechnical characteristics in terms of nature of the slip zone and properties of sliding mass. Brief analyses of five typical cases illustrate that landslide mechanisms can be conceptually depicted by failure mechanisms of their slip zones prior to onset of movement and following energy conversion during movement. Problems and questions related to experience in China suggest that comprehensive and systematic investigation and study on rapid giant landslides are urgently needed.     

甘肃岷县永光村滑坡特征及其成因研究

泥流型黄土滑坡发生的条件除一般滑坡具有的条件之外,还应包括特殊的状态因素、触发因素及相应的驱动剪应力条件。通过对甘肃岷县永光村滑坡的现场勘察和实地调查,分析其成因,结果表明：永光村滑坡平面形态虽与泥流类似,但其具有滑坡形成区以及滑坡发生所需要的特殊的地形地貌、岩土体性质以及水文地质条件。永光村滑坡发育于沟道上游的黄土塬地带,临空面较大,滑坡剪出口位置高,具有较高的势能,滑坡体的主要岩土体是马兰黄土,黄土具有大孔隙结构,垂直节理发育,有利于地表水的下渗。下部为新近系泥岩,渗透系数低,为一相对隔水层。长期灌溉导致地下水位较高,黄土层存在软弱夹层,地下水位上升,导致其软化饱和,强度迅速降低,形成潜在滑动面。永光村滑坡亦具有圆弧形的滑坡后壁,滑坡后缘顶部分布有多条拉张裂缝,在前期发生降雨的外部条件下,在岷县“7·22”地震诱发下,发生了低角度、快速和远程的泥流型黄土滑坡,滑体在冲出沟口后形成了扇形堆积区。永光村滑坡是一种特殊的地震引发的泥流型黄土滑坡。目前,泥流型黄土滑坡的研究还处在探索阶段,是作为黄土滑坡分类的一种补充,建议进一步加强对此类灾害发生机理及其稳定性计算方法的深入研究。     

海底斜坡土体失稳的研究进展

根据国内外最新的文献,综述了海底斜坡失稳研究核心问题的进展情况。这些进展主要包括海底斜坡土体失稳的定性和定量研究,以及海底斜坡土体失稳后演变趋势的定性和定量研究。     

Study of the interaction between dry granular flows and rigid barriers with an SPH model

This study uses an incompressible smoothed‐particle hydrodynamics model to investigate the interaction between dry granular material flows and rigid barriers. The primary aim is to summarise some practical guidelines for the design of debris‐resisting barriers. The granular materials are modelled as a rigid‐perfectly plastic material where the plastic flow corresponds to the critical state. The coupled continuity equation and momentum equation are solved by a semi‐implicit algorithm. Compared with flows in controlled flume experiments, the model adequately reproduces both the kinetic of the flows and the impact force under various conditions. Then the numerical simulations are used to study the detailed interaction process. It is illustrated quantitatively that the interaction force consists of two parts, ie, the earth pressure force caused by the weight of the soil and a dynamic force caused by the internal deformation (flowing mass on top of a dead zone). For the estimation of impact load, this study suggests that an increased earth pressure coefficient depending on the Froude number should be incorporated into the hydrostatic model.     

Solid–fluid transition modelling in geomaterials and application to a mudflow interacting with an obstacle

Given the contrasting behaviour observed for geomaterials, for example, during landslides of the flow type, this contribution proposes an original constitutive model, which associates both an elasto‐plastic relation and a Bingham viscous law linked by a mechanical transition criterion. This last is defined as the second‐order work sign for each material point, which is a general criterion for divergence instabilities. Finite element method with Lagrangian integration points is chosen as a framework for implementing the new model because of its well‐known ability to deal with both solid and fluid behaviours in large deformation processes. A first boundary model considering a sample of initially stable soil, a slope and an obstacle is performed. The results show the power of the constitutive model because the consistent evolution of initiation, propagation and arrest of the mudflow is described. A parametric study is led on various plastic and viscous parameters to determine their influence on the flow development and arrest. Finally, forces against the obstacle are compared with good agreement with those of other authors for the same geometry and a pure viscous behaviour. Copyright © 2014 John Wiley & Sons, Ltd.