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1.
This paper provides the theoretical basis for a forward numerical model of rock block systems. This method was developed to compute stress, strain, sliding and opening of rock blocks; rigid body movement and deformation occur simultaneously. Input data consist of block geometry, loading forces, the deformability constants E and v, and the restraint or boundary conditions of the block system. Output data give the movements, deformations, stresses and strains of each block, and the sliding and detachment or rejoining of blocks. The forces acting on each block, from external loading or contact with other blocks, satisfy the equilibrium equations. Equilibrium is also achieved between external forces and the block stresses. Furthermore, this analysis fulfills constraints of no tension between blocks and no penetration of one block into another. To acheive equilibrium and satisfy these constraints, simultaneous equations are solved repeatdly with partial changes of the coefficients each time the contact constraints are chosen. 相似文献
2.
利用几何大地测量监测数据考察某一岩石圈板块或块体的运动 ,目前的主要方法是选择某一相对稳定点或直接选择地固参考系作为运动参考系 ,计算被考察的板块或块体相对于该相对稳定点的运动或在地固参考系中的运动。显然 ,这种计算结果无法全面直观地表达被考察板块或块体的内部相对运动 ,以及周围板块或块体相对于被考察板块或块体的运动。文中首次尝试了直接选择被考察板块或块体即欧亚板块东南部块体作为参考块体 ,利用一种高精度的几何大地测量监测数据 ,即国际地球参考框架 (ITRF)速度场计算了欧亚板块东南部块体在ITRF参考系中的线性运动模型 ,从而建立了欧亚板块东南部块体的块体参考系 ,并在该块体参考系中计算欧亚板块东南部块体内部及周围板块现今三维相对运动 ,进而分析中国大陆及周围板块的现今相对运动规律 ,以及板块边界处板块的现今相对运动规律。 相似文献
3.
大兴安岭南段赛罕乌拉石海剖面分析及其与蒙山拦马墙石河结构对比 总被引：1，自引：0，他引：1
石海（石河/冰石河）作为冰缘地貌的重要标志之一,在国内地学界尚未引起足够的重视,以至于缺少介绍石海结构特征的中文文献,更未建立判别标准,在地貌认知阶段就发生很多误判。为了揭示石海的剖面结构特征,笔者等对位于大兴安岭南段的赛罕乌拉国家级自然保护区乌兰坝石海首次进行了开挖解剖,从而归纳了原生石海的基本结构特征：岩块棱角鲜明,呈镂空状堆积,岩块直径总体上上大下小。根据野外调查确认,赛罕乌拉海拔1800 m以上的区域至少还存在着局部现代石海,也就是说,还残存着不连续冻土带,而且保持年平均气温0℃左右的气候环境。根据赛罕乌拉现今气候记录和石海分布,笔者等估算了全新世初期赛罕乌拉石海开始发育时的地表温度在0~-4℃,而今天年平均气温已经升高到2℃,升温幅度2~6℃。根据赛罕乌拉石海剖面结构特征,笔者等对山东蒙山石河进行了结构对比,认为二者剖面结构基本一致,排除了前人近年来争议明显的冰川侧碛堤和泥石流成因说。结构对比揭示山东蒙山境内全新世早期至少局部存在过冰缘气候环境,而这也为山东境内更新世冰川地貌研究提供了重要的信息。此外,本研究也为中国冰缘地貌解剖和资源调查提供了一个可以参考的研究实例。 相似文献
4.
华北陆块是由陆核→地块(体)→联合地块逐渐生长、增大、拼合形成的。根据大量的地质构造、地层岩石、同位素年代学、含矿特征、地球化学、地球物理等多方面的信息,华北陆块可划分为辽吉、燕辽、阴山、晋冀、豫皖、阿拉善前寒武纪地块和鲁西、胶北前寒武纪地体,鄂尔多斯、华北中新生代盆地,共10个构造单元。华北陆块是多地块拼(缝)合形成。据现有的岩石记录,始太古代-中太古代主要是陆核生成阶段,不排除在早期有绿岩带形成;新太古代主要是花岗岩-绿岩带的生成阶段,花岗岩-绿岩带环绕地核周边形成地块,是华北陆块结晶基底的主要生长时期;古元古代是联合地块的形成阶段,多个地块(体)拼合形成联合地块;中元古代是稳定环境下的拉伸阶段,沿陆块南北两缘形成三大裂谷系(燕辽、狼山—渣尔泰、熊耳山—西阳河);新元古代-古生代陆块形成稳定环境的沉积盖层,除南北两缘外,内部很少有岩浆活动;中-新生代陆块大部分地区为活动大陆边缘的环境,出现大规模的构造-岩浆活动。 相似文献
5.
由于地下工程处于一定水平的地应力环境中,块体边界法向应力概化的正确与否直接关系到块体的稳定性分析结果,现通过实测途径确定块体边界法向应力的研究还较少。基于大型地下厂房块体稳定性分析,通过在块体范围及邻区不同方向布置多个钻孔,首次将原生裂隙重张试验引入到块体边界法向应力的测定,对开挖后与块体主要边界产状相近的所有原生裂隙的法向应力进行了测试,成功取得了块体边界上的法向应力状态及其空间变化规律。研究结果表明：洞室开挖完成后,块体边界应力分布不均匀,但具一定规律,垂直向表现为从浅部到深部结构面的法向应力依次增大,在水平向上,随与洞室开挖面距离的增大而增大;结构面的法向应力实测值稍小于基于围岩应力的估算值,但总体一致。该成果可为确定围岩块体的边界力学状态和应力模型简化提供参考和依据。 相似文献
6.
This paper proposes an extension to the key‐block method, called ‘key‐group method’, that considers not only individual key blocks but also groups of collapsable blocks into an iterative and progressive analysis of the stability of discontinuous rock slopes. The basics of the key‐block method are recalled herein and then used to prove how key groups can be identified. We reveal that a key group must contain at least one basic key block, yet this condition is not entirely sufficient. The second block candidate for grouping must be another key block or a block whose movement‐preventing faces are common to one or more single key blocks. We also show that the proposed method yields more realistic results than the basic key‐block method and a comparison with results obtained using a distinct element analysis demonstrates the ability of this new method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
This paper presents a general method of key block analysis for cylindrical surfaces with numerous real or statistically produced joint traces. General tunnel curves, analytically represented, are unrolled to yield a ‘developed view’ on which the joint traces are continuous curves. Then, using extended block theory, the maximum key block regions are delimited from the curved polygons of the unrolled joint trace map. The methods discussed here apply to a cylindrical tunnel of any shape in section and in any orientation, including inclined tunnels and shafts. The trace maps for which the method applies can be generated statistically, as described herein, or surveyed from real traces on exposed tunnel walls. A brief introduction to the basic theory about tunnel key blocks is provided here so that this paper can be understood without reference to other papers on block theory. 相似文献
8.
An extensive examination of the discontinuous deformation analysis (DDA) in block dynamic sliding modeling is carried out in this paper. Theoretical solutions for a single block sliding on an arbitrarily inclined plane by applying the horizontal/vertical seismic loadings to the sliding block as acceleration time histories or to the base as constraint displacement time histories are derived. As compared with the theoretical solutions, for a single block sliding, the DDA predicts the sliding displacements and block interaction forces accurately under various base incline angles and friction angles under both the harmonic loadings and a real seismic loading. The vertical seismic component may influence the block sliding displacements to different extent, and the DDA can capture these phenomena successfully and give accurate results. For the calculation of the single block relative sliding, both the theoretical and the DDA solutions indicate that applying the seismic accelerations as constraint displacement time histories (derived by integrating the seismic accelerations twice) to the base is equivalent to applying the seismic accelerations as volume forces to the sliding block in the opposite directions. The DDA modeling also demonstrates that this conclusion still stands for the case of multi‐block sliding. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
9.
张文佑院士是我国最杰出的构造地质学家和大地构造学家,他提出和倡导的地质构造力学分析和历史分析相结合及断块构造理论符合当代构造地质和构造运动研究的新方向。断块构造是地球构造运动最基本的型式,板块构造是全球范围内的岩石圈构造,是最高一级的岩石圈断块构造。活动断块是现今构造运动最基本的型式,它既控制主要活动构造带和地震活动带的分布,也控制不同地区地震活动特征的差异。断块边界构造带是在构造变形和运动场中的不连续变形带,应力在此释放,应变在此局部化,位移在此发生,其差异活动最为强烈,因此,断块边界构造带是强震发生带,其活动性质会控制震源断层的特性。大地震孕育和发生在边界活动构造带的某些特殊部位,对其成核的构造和物理过程尚需深入进行研究。要特别注意断块整体性活动对地震活动的控制作用,断块的这种整体性活动与一定时期内地震活动主体地区分布有密切关系,所以,在活动构造研究中,要把断块的整体性活动与活动构造带的个体活动结合起来。 相似文献
10.
松潘-甘孜地块的基底构造性质对于探讨青藏高原的形成至关重要,备受国内外学者的关注。然而,由于松潘-甘孜地块被广泛分布的三叠纪复理石沉积所覆盖,关于松潘-甘孜地块基底属性的研究并不多见,它属于洋壳还是陆壳,至今仍在争论之中。本文利用跨越松潘-甘孜地块的深地震反射剖面、深地震测深剖面、区域航磁异常和花岗岩同位素地球化学等资料,通过综合分析研究其地球物理与地球化学特征,发现松潘-甘孜地块的下地壳存在元古代变质基底,该基底具有亲扬子地块的性质。 相似文献
11.
Flexible rockfall barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible rockfall barriers is conventionally performed using full-scale field tests by dropping a block onto the barriers in accordance with the European test standard ETAG 027. The block typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. Little attention has been paid to the effects of the block shape on the impact force and structural response. This paper aims to quantitatively reveal the influence of the block shape on the dynamic response of flexible rockfall barriers. First, an ellipsoidal model is established to approximately simulate the block, and the sphericity is employed as the representative index of the block’s shape. A full-scale test on a typical flexible barrier system is carried out and then used to calibrate an advanced three-dimensional finite element model. Finally, the dynamic responses of flexible rockfall barriers are analyzed and discussed, focusing on the effects of the block’s shape. The numerical results show that the sphericity will obviously influence the maximum elongation of flexible barriers, the peak impact force, the peak force of the upslope anchor cable, the peak force of the lower main support cable, the axial peak force of the post, and the peak shear force at the post foundation. The assumption of spherical or polyhedral blocks in the test standard could lead to the defensive failure of flexible rockfall barriers in some impact scenarios.
相似文献12.
David Toe Franck Bourrier Ignacio Olmedo Jean-Matthieu Monnet Frédéric Berger 《Landslides》2017,14(5):1603-1614
The objective of this research was to use numerical models based on mechanical approaches to improve the integration of the protective role of forests against rockfall into block propagation models. A model based on the discrete element method (DEM) was developed to take into account the complex mechanical processes involved during the impact of a block on a tree. This modelling approach requires the definition of many input parameters and cannot be directly integrated into block propagation models. A global sensitivity analysis identified the leading parameters of the block kinematics after impact (i.e. block energy reduction, trajectory changes, and rotational velocity): the impact velocity, the tree diameter, and the impact point horizontal location (i.e. eccentricity). Comparisons with the previous experimental and numerical studies of block impacts on trees demonstrated the applicability of the DEM model and showed some of the limitations of earlier approaches. Our sensitivity analysis highlights the significant influence of the impact velocity on the reduction of the block’s kinetic energy. Previous approaches usually also focus on parameters such as impact height, impact vertical incidence, and tree species, whose importance is only minor according to the present results. This suggests that the integration of forest effects into block propagation models could be both improved and simplified. The DEM model can also be used as an alternative to classical approaches for the integration of forest effects by directly coupling it with block propagation models. This direct coupling only requires the additional definition of the location and the diameter of each tree. Indeed, the input parameters related to the mechanical properties of the stem and the block/stem interaction in the DEM model can be set to average values because they are not leading parameters. The other input parameters are already defined or calculated in the block propagation model. 相似文献
13.
14.
在阿拉善地块东缘发现新生代中新世挤压构造,形成近SN或NE-SW走向的逆冲断层及卷入新生代地层的褶皱.其形成背景关系到阿拉善地块新生代的变形特征以及与青藏高原扩展的关系.为了进一步探讨阿拉善地块东缘的挤压构造是否受青藏高原扩展控制,为青藏高原北缘新生代扩展过程的研究提供资料,通过详细地质填图、区域地质调查与对比方法,确定了这些挤压构造的几何样式以及运动学特征,结合断层滑动矢量,恢复出变形时的古应力场.室内外的分析表明,形成这些挤压构造的最大主应力方位为NW-SE或近EW向,结合盆地地震反射资料、卷入构造的地层,推测变形的时代是中新世中晚期.这期变形的动力可能是阿拉善地块受到青藏高原北缘的挤压向东运动所致.同时在阿拉善地块向东运动的过程中,其内部发育的早期东西向构造带发生右行走滑,和阿拉善东缘的挤压构造一同调节地块的变形.晚中新世之后,高原东北缘最大主应力方位发生顺时针旋转,阿拉善东缘挤压构造被后期构造叠加. 相似文献
15.
可靠地划分地震区可奠定地震预测与地震危险性评价的地质基础,具有十分重要的意义。笔者等通过研究分析指出板内孕震构造块体侧向边界可由区域性大断层或由区域性大断层与板块边界界定,底边界为康拉德面或低速高导层;板间孕震构造块体为俯冲板块,可由区域性大断层和(或)板块边界约束;在同一个孕震构造块体和同一轮地震周期的地震具有内在联系。因此,地震区可定义为代表相应孕震构造块体地震活动的区域,其可表征该块体内源自锁固段破裂的地震活动。基于笔者等提出的孕震构造块体和相应地震区边界确定原则,把全球两大地震带(环太平洋地震带和欧亚地震带)划分为62个地震区;每个地震区的分区方案均通过了多锁固段脆性破裂理论的检验,这说明方案可靠。进而,笔者等归纳总结了地震区划分方法。 相似文献
16.
Through the application of remote sensing techniques followed by field checks, the exact extension and nature of Suruli shear
zone in Madurai block of southern granulite terrain (SGT) in south India is brought out for the first time in this work. The
dominant rock type exposed in this area is charnockite intruded by granites. The Suruli ductile shear zone extends from just
west of Kadaiyanallur in the south to Ganguvarpatti in the north over a length of 150 km. Between Kadaiyanallur and Kambam,
the shear zone extends roughly in N-S direction. From Kambam, it swerves towards NE and then towards ENE near Ganguvarpatti.
The strongly developed transposed foliation and mylonite foliation within the shear zone dip towards east only and so the
eastern block (Varushanad hills) is the hanging wall and the western block (Cardamom hills) is the footwall of the shear zone.
In the eastern block, three distinct phases of regional scale folding (F1, F2 and F3) are recognized. In complete contrast,
the western block recorded only the last phase (F3) regional scale folding. As the more deformed eastern block (older terrain)
moved over the relatively less deformed western block (younger terrain) along the Suruli shear zone, it is proposed that this
shear zone is a thrust or reverse fault, probably of Proterozoic age. As there are evidences for decreasing displacement from
north to south (i.e., from Ganguvarpatti to Kadaiyanallur), the Suruli shear zone could be a rotational thrust or reverse
fault with the pivot located close to Kadaiyanallur. As the pivot is located near Achankovil shear zone which trends WNW-ESE
(dip towards SSW), the Suruli shear zone could be splaying (branching) out from Achankovil shear zone. In a nutshell, the
Suruli shear zone could be a splay, rotational thrust or reverse fault. 相似文献
17.
Based on a block structure model of the inner belt of central Japan, an examination was conducted of the space-time distribution patterns of destructiv magnitudes M 6.4 or greater (M =Japan Meteorological Agency Scale). The distribution patterns revealed a periodicity in earthquake activit seismic gaps. Major NW—SE trending left-lateral active faults divide the inner belt of central Japan into four blocks, 20–80 km wide. The occurrenc A.D. with M ≥ 6.4, which have caused significant damage, were documented in the inner belt of central Japan. The epicenters of these earthquakes close to the block boundaries.
Using the relationship between the magnitude of earthquakes which occurred in the Japanese Islands and the active length of faults that generated them, movement is calculated for each historical earthquake. Space—time distributions of earthquakes were obtained from the calculated lengths, the latitud of generation. When an active period begins, a portion or segment of the block boundary creates an earthquake, which in turn appears on the ground surf active period ends when the block boundary generates earthquakes over the entire length of the block boundary without overlapping.
Five seismic gaps with fault lengths of 20 km or longer can be found in the inner belt of central Japan. It is predicted that the gaps will generate ea magnitudes of 7.0. These data are of significance for estimating a regional earthquake risk over central Japan in the design of large earthquake resist
The time sequences of earthquakes on the block boundaries reveal a similar tendency, with alternating active periods with seismic activity and quiet pe activity. The inner belt of central Japan is now in the last stage of an active period. The next active period is predicted to occur around 2500 A.D. 相似文献
18.
以二元结构河岸崩塌模式为研究背景,在弯道水槽中展开系列试验,研究凹岸坡脚处成型崩塌体在水力作用下输移过程及其对岸坡稳定性与河床冲淤的交互影响。试验成果表明,崩塌体经水力分解破碎呈块状、片状或颗粒状起动,部分随水流带至凸岸或下游,堆积在坡脚附近的崩塌体残留量随水力作用大小及土体特性不同而变化。崩塌体临水面周围尤其上下游端水流紊动强烈易形成较大剪切力区,临坡面上下游端附近剪切力较无崩塌体时减小;崩塌体体积越大,对剪切力区特征的改变也越明显。崩塌体的存在虽不能制止附近岸坡的再次崩塌,但可能抑制崩岸发展及附近河床淤积的程度,崩塌体的粘性或体积越大,这种抑制作用越显著;相同崩塌体抑制附近河床淤积的程度较抑制岸坡崩塌的程度大。 相似文献
19.
Block theory has been widely applied to stability analysis of rock engineering due to its clear concept and elegant geometrical theory. For a general block with multiple discontinuity planes, it is assumed that contact is only maintained on a single plane (single-plane sliding) or two intersecting planes (double-plane sliding) in block theory analysis. Since the normal forces and shear resistances acting on the other discontinuity planes are omitted, it can cause unreasonable estimations of block failure modes and incorrect calculation of factors of safety. In this study, a new method is presented that permits to consider the contribution of the normal forces and shear resistances acting on each discontinuity plane to the block stability. The proposed method meets all of the force-equilibrium and moment-equilibrium conditions and provides a rigorous solution for stability of general blocks with any number of faces and any shape. Some typical polyhedral blocks in rock slopes are analyzed using block theory and the proposed method. The results indicate that the traditional block theory may give a misleading conclusion for the predictions of stability and sliding direction of rock blocks when contact occurs on more than two discontinuity planes. 相似文献
20.
Summary Discontinuities in a rock mass can intersect an excavation surface to form discrete blocks (keyblocks) which can be unstable. Once a potentially unstable block is identified, initial normal and shear stresses on each block face are calculated using elastic theory, and are then modified by discontinuity deformations as the keyblock displaces. The modified stresses are summed into resultant forces to evaluate block stability. Since the resultant forces change with displacement, successive increments of block movement are examined to see whether the block ultimately becomes stable or fails. Calculated keyblock stability increases with larger in situ stress magnitudes, larger lateral stress ratios, and larger shear strengths. Discontinuity stiffness controls block displacement more strongly than it does stability itself. Large keyblocks are less stable than small ones, and stability increases as blocks become more slender. 相似文献