【作者】 马国哲；

【导师】 言志信；

【作者基本信息】 兰州大学 ， 地质工程， 2013， 博士

【摘要】 人类对特大地质灾害的认识滞后于地质灾害的防治要求。在人口稠密和集中地区发生罕遇特大地质灾害所造成的人民生命和财产损失是惊人的,开展其形成机理研究是有效进行地质灾害防治工作的基础。笔者在应用岩体力学理论研究2008.5.12“汶川”Ms8.0级特大地震的成因时,提出了“龙门山活动推覆体”的概念：是一个由滑脱层和边界断裂围限而成的宏观岩体,长度接近500km,宽度接近50km,深度接近20km,推覆体岩体具有整体活动性,并处于以挤压构造应力为主的三维应力场中。与龙门山断裂带这一传统地质构造术语相比,活动推覆体不仅包含了地质构造、构造地貌因素,而且隐含了地壳岩体结构及岩体的受力、运动与破坏因素,因此该概念可以满足研究特大地质灾害所涉及地质体在深度及广度范围方面的要求。龙门山推覆体具备特大地质灾害孕育和发生必需的独特地质环境条件,是内动力地质灾害(地震、断裂)和外动力地质灾害(滑坡、泥石流)的孕育、发生和发展的统一体和承载体。内、外动力地质灾害之间形成地质灾害链,防治难度大。本文以龙门山活动推覆体地壳岩体作为研究对象,采用系统论的研究方法,在全面研究区域地质构造背景基础上,综合区域地质构造学、地球物理学、地震地质学、岩体力学、岩石物理学、工程地质学、灾害地质学、大地测量学等多学科的最新研究成果,尤其是运用岩体力学关于地壳岩体变形和破坏的相关最新理论成果,对龙门山推覆体以地震为主的内动力地质灾害形成机理,地震滑坡(崩塌)、震后泥石流等次生地质灾害的发生机理,内、外动力地质灾害之间的连锁激发关系,地质灾害链的构成特点及危害特点等诸多环节进行了全面研究,对诸如推覆体地壳深部流体对抗剪强度的影响、地震同震地表破裂形成的岩体力学机理、工程防治特大地质灾害的有效性等前沿问题进行了探讨。最后针对性地提出了三层次防治对策。主要结论有：1、以龙门山推覆体地壳岩体作为研究对象,能满足特大地质灾害研究所涉及地质体对深度与广度的要求。龙门山推覆体是一个由滑脱层和边界断裂围限而成的宏观岩体,长度接近500km,宽度接近50km,深度接近20km。内部包含了4条主干断裂和滑脱层几个主要构造结构面。位于中地壳顶界的滑脱层是推覆体发生逆冲推覆运动的底部动力边界,也是中、上地壳岩体之间最主要的构造结构面。埋深12-26kmm,沿南西向北东方向变深。其物理力学属性是因板块水平运动挤压而产生的地壳岩体局部剪切熔融层,表现出各向异性、低速高导等物理力学属性。2、在亚欧板块碰撞产生的挤压大地构造应力背景下,在青藏地块(巴颜喀拉)与华南地块(四川盆地)之间形成了龙门山推覆体型地块边界带,自晚更新带以来其新构造活动特征是活动推覆体,整体逆冲活动速率1～3mm/yr,方向南东。推覆体地壳岩体长期处于北西-南东向的挤压构造应力状态,主要沿已有区域性地质构造面发生剪切破坏。3、推覆体地壳岩体的变形和破坏规律符合岩体结构控制论。主要表现为沿已有构造结构面发生剪切滑移破坏,抗剪切滑移强度符合拜尔利定律(Byerlee’s law)。滑脱层具有发生剪切滑移(粘滑)的强度条件和几何条件,因而是龙门山活动推覆体发生7级以上特大地震的主要构造结构面(控震层)。沿滑脱层发生的剪切滑移(粘滑)是形成2008年5.12“汶川”特大地震及未来复发地震的岩体力学成因机制。4、龙门山地区地震强度与推覆体整体活动速率无关,而与控震结构面一滑的抗剪切滑移强度密切相关。与其埋深呈显著线性相关性：8级地震的震源深度接近20km；7级地震的震源深度接近14kmm；6级地震的震源深度接近lOkm。据此可以圈定出7级以上地震可能发生区域的范围。5、在7级地震、Ⅸ度以上地震烈度区发生的大型高速远程地震滑坡主要受斜坡的弹-塑性二元结构控制。地震波(P波)及强烈的地震水平加速度在斜坡弹一塑性介面突然产生强大的拉应力,导致斜坡风化覆盖层产生自上而下贯通的拉裂破坏,进而引起滑床区岩体发生快速剪切破坏,是形成数量众多的大型、深层、高速、远程地震滑坡的主要力学机制。6、从地质灾害防治的角度对龙门山推覆体特大地质灾害链提出了新的认识。地质灾害链主要表现为两大类。一类是强烈地震激发不稳定斜坡—滑坡(崩塌)同震型短时地质灾害链；另一类是区域暴雨激发滑坡(崩塌)—泥石流震后长周期地质灾害链。7、针对地震滑坡和震后泥石流提出了不同的防治思路。地震滑坡应在间震期将潜在不稳定斜坡作为防治对象。采取留置安全距离,辅助采取必要的锚固工程措施进行综合防治。震后泥石流应在调查、评估的基础上,采取规划避让为主、应急排险为辅,以防为主的防治思路。审慎采取工程防治措施。8、龙门山地区特大地质灾害具有自然性、长期性、区域性、群发性、成灾后果严重的诸多特点,宜采取预防为主、避让为主、重视宏观规划的防治原则。将避免城镇损毁作为该区特大地质灾害防治的首要目标。基于地质环境容量考虑基础之上,提出了三层次防治对策：区域战略性宏观控制对策、流域局部避让对策及单点工程治理相结合的综合防治对策。更多还原

【Abstract】 Human understanding of super-large geological disasters lags behind that of geological disasters prevention and control requirements.It is staggering for severe people’s life and property loss caused by the rare catastrophic geological disasters happened in densely populated areas.The research on its formation mechanism is the base for prevention and controlling effectively of geological disasters.The concept of "Active Longmenshan Nappe"was put forward for the study of mechanism in terms of rock mass of "Wenchuan "Ms8.0earthquake, in west Sichuan, on May12,2008. It consists of the detachment layer at the top of mid-crust as its bottom dynamic boundary, and lateral large regional faults as geometry boundary. Compared with the traditional concept of Longmenshan faults zone, it contains both factors of the geological structure and the rockmass with stress and movement,which could satisfy the requirements in depth and breadth for the study on extra-large geological disasters. Longmenshan nappe possess the unique geological environment conditions required for large geological disaster breeded and to happen. It is the supporting body for occurrence and development of dynamic geological disasterss (earthquake, fault) and induced ones (landslides and debris flows) disasters. There is formed geological disaster chains between the dynamic and indeced geological disasters, so it is more difficult to prevent and cure.In this paper the rock mass of the active Longmenshan nappe as the research object, on the basis of comprehensive study of regional geological structure background, synthesizing multidisciplinary research results of regional geological tectonics, geophysics, seismic geology, rock mechanics, rock physics, engineering geology, disaster geology and geodesy, in view of active blocks, the comprehensive study was carried on the dynamic formation mechanism of geological disasters, earthquake induced landslides (collapses), the mechanism of post-earthquake geological disasters such as mud-rock flow, geological disaster chains, the super-large geological disasters motivators, infestation characteristics, and finally the three levels of prevention and control countermeasures was put forward. The main conclusions are as follows:The Longmenshan nappe formed as a block boundary belt between the Qinghai-Tibet block (BayankaLa) and south China block (Sichuan basin),as the affected result by the plate extruding tectonic force from the collision between plates of Asian and Europe. It moves as a whole to south-east at a rate of1～3mm/yr since Late Leistocene. The detachment layer as dynamic boundary for thrust at its bottom, which buried12～21km, deeper from north west to south east. It is in the long period of extruding tectonic stress state from north west to south east.It is a macro rock body close to500km in length, width nearly50km, confined by the detachment and boundary faults. Four main fault belts cross into the detachment layer at bottom. The detachment layer is shear melting layer by extruding of crustal rock mass with anisotropy and high physical conductivity, low speed.The deformation and destruction of the Longmenshan nappe rock body conforms to the rockmass structure cybernetics. It is a process of re-breaking and mainly shearing-slip of the nappe rock body along the pre-existing structural planes. Which is suitable for Byerlee’s law. The detachment layer is the main tectonic structural planes for magnitude8earthquakes, and the Wenchuan earthquake on May12,2008was formed by shear sliding (stick-slip) along it.It is suggested that the possible earthquake intensity in the Longmenshan nappe has nothing to do with its overall rate of activity, but is relate to the buried depth of the earthquake-controlling structural plane. The earthquake magnitudes is closely related to the shear-sliding strength of the detachment layer with a linear relation with its buried depth. There is significant correlation among the earthquake magnitude and buried depth of the detachment layer, shear strength:8earthquake focal depth close to20km,7earthquake focal depth close to14km,6earthquake focal depth near10km. Based on depth of ancient earthquakes ratified,6above earthquakes possible scope and corresponding seismic fortification intensity of Longmen Shan nappe-Minshan block with adjacent area delineatedThe large high-speed-remote landslides triggered by an earthquake is mainly controlled by the elastic-plastic binary structure of slopes. The strong tensile stress suddenly caused by seismic waves (P wave) and horizontal acceleration in the slope elastic-plastic interface leads to crack top-down in weathered layer to form a large number of large high-speed-remote landslides.The different ways to prevention and control for landslides triggered by earthquakes and debris flows is suggested. The potentially unstable slope is suggested as control object for landslides triggered by earthquakes in seismic interval, the lien security distance+anchorage engineering as measures for prevention and control. It is given priority to prevention and control for post-earthquake debris flows, mainly taking planning and collision avoidance first, emergency as complementary based careful investigation and evaluation, and prudent to choice engineering as prevention and cure measures.The super-large geological disasters occurred in Longmenshan area have characteristics of natural, long-term, regional, clustering, and with serious consequences. It is advised to adopt the principle of prevention and control as the first, giving priority to avoidance, paying great attention to macroscopic planning. Take the avoidance of cities and towns damaged as the first goal. On the basis of consideration of geological environment capacity, comprehensive prevention and control countermeasures of three levels is put forward:regional strategic of macrocontrol countermeasure, local avoidance countermeasures and project control.更多还原