Paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna during the last 225 ka inferred from the volcanic succession of the ‘Timpe’, Acireale, Sicily

The tectonic escarpments locally known as ‘Timpe’ cut a large sector of the eastern flank of Etna, and allow an ancient volcanic succession dating back to 225 ka to be exposed. Geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures, as well as important changes in the nature, composition and magmatic affinity of the exposed volcanics. In particular, the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward-dipping to the progressive tectonic tilting of strata. These elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka BP and their relationship with tectonic structures active in the eastern flank of Etna. We propose a complex paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna, in which the Timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span.     

3-D P-wave velocity structure of the crust beneath the Loess Plateau and surrounding regions of China

The crustal P-wave velocity structure beneath the Loess Plateau and surrounding regions, which is a transition zone between the Tibetan Plateau and the Huabei and Huanan Blocks of China, was tomographically imaged for the first time down to the depth of 80 km. The seismic sources comprised both local and regional earthquakes and the reconstruction was accomplished using a newly developed simultaneous inversion procedure, which solves for both the earthquake hypocentres and the 3-D velocity field. Special features of the procedure include a modified shortest path algorithm for the bent ray tracing, an analytic Jacobian matrix for solution updating, and a damped, minimum norm, constrained non-linear solver based on a CG approach. The velocity structure obtained is more complex than previously thought. The lateral velocity variations are consistent with the U-shaped seismic ring structure but the vertical variations along the Fenwei seismic belt are consistent with the mechanism of the Mountain-Basin generalized system formation. The velocity images of Loess Plateau, the transition zone may help to build a geodynamic mechanism for inland China, to explain the formation of ground fissures so prevalent in the Loess Plateau.     

PSJ系列数字测井仪在工程勘察中的应用

在水利工程勘察中,利用PSJ系列数字测井仪测量自然伽马、长短源距人工伽马、视电阻率、井径、纵波速度等参数,并根据其相关曲线特征判定工程钻探中难以发现的软弱薄夹层、裂隙等地质隐患。其中裂隙在视电祖率和声波速度测井曲线上表现为低尖峰异常;而岩层破碎的表现则为小波速值、小密度值、小电阻率及大孔径值;另外在视电阻率和密度值均小的风氧化带区,根据纵波速度还可区分强、弱风氧化带。     

嵌岩灌注桩桩端持力层检验的新方法——谈地质雷达的原理及应用

人工挖孔嵌岩灌注桩以其成本低、工期短、承载力高等特点而受到普遍欢迎,但与此同时,相对滞后的桩端持力层检验方法却在制约着它的发展,地质雷达的出现为解决这个矛盾开辟了新的思路。详细阐述了地质雷达的工作原理及应用,并结合"济南市广播电视技术中心"工程实测雷达图像对几种典型地质情况下的图像作出逐一释读。     

水位特殊动态映象的裂纹蠕动要素及其前兆意义

对鲁０３井、２８井水位特殊动态图形有关指标统计的基础是，根据相关资料方法反演、估算了观测层构造裂纹蠕动要素，进而对本区间应力场主应力与唐山大地震生成的新应力场在一定时间内的合作方式，主、次关系进行相应分析，认为水位特殊动态图形是新应力与断裂构造格架组合模式控制的裂纹活动要素映象，一些具有前兆意义，另一些则不属于前兆类型。     

膨胀土裂隙的工程特性研究

裂隙是膨胀土的重要特征之一,长期以来,人们常常把分布于膨胀土大气影响深度范围内受干湿循环影响而产生的干缩裂隙与膨胀土地层中特有的原生裂隙混为一谈。在对膨胀土边坡失稳机制的研究中,也忽视了原生裂隙对边坡稳定的重要影响。为研究南水北调中线工程膨胀土地段渠道破坏机制,在河南省南阳市郊建设了一条长为2.05 km试验渠道,通过渠道开挖期间的地质勘察、现场观测和取样试验,以及对现场滑坡体的取样分析,研究了膨胀土裂隙及周边土体的物质成分、密度、含水率和强度特性,结合现场观测资料分析了裂隙与渠道滑坡的关系。研究表明,膨胀土地层中的原生裂隙有两种类型：光滑蜡状裂隙和有一定厚度充填黏土的裂隙。裂隙面上的物质成分与两侧土略有不同,且天然密度低、含水率高,强度远低于相邻土体的强度,一旦地层与边坡倾向一致,将产生沿裂隙面的滑动。     

江西瑞昌市横岗砖厂断裂探测及其活动特征研究

经化探、物探和槽探工程,对出露于江西瑞昌横岗砖厂取土开挖场地内的地裂缝的成因、特征及意义进行了分析。该区地裂缝总体走向均为北东向,呈“簇”状密集分布,总体延伸长度超过300 m,且地裂缝内均有灰白色、浅灰色矿物充填。解析认为该区分布一条北东走向陡倾正断裂,断裂倾向南东,倾角60°-75°。局部探槽开挖揭露该断裂其中一断裂面错动第四纪坡洪积物,断裂产状为155°∠71°,走向65°,上盘下降,错距达到3 m（未揭露到底）。断层壁平直,断裂面擦痕清晰,可见5条长1~2 m的铲刮沟槽,槽深5~20 mm,显示该断层呈左旋倾滑性质。取上断点地层沉积物ESR测年,测年范围为距今0.27~0.42 Ma,研究表明该断裂在中更新世中期显著活动过,为一条中更新世活动断裂。综合分析认为该区地裂缝发育受横岗砖厂断裂控制,地裂缝的形成是横岗砖厂断裂活动在第四系地表的响应。      

考虑裂隙水压力的岩体压剪裂纹扩展规律研究

在库水位大幅度升、降变化时,容易导致岩体内增量裂隙压力的集中,使断裂面上有效应力降低,裂纹面尖端的应力强度因子增加。当达到临界强度因子时,可能使岩体内裂纹、裂隙贯通、扩展,形成连续的复式破坏面,从而使边坡稳定性降低,造成边坡的失稳。基于此,从断裂力学角度分析了裂隙水压力对裂纹强度因子的影响,对考虑裂隙水压力作用的Ⅰ、Ⅱ型复合裂纹扩展规律进行了研究,结果表明：Ⅰ、Ⅱ型复合裂纹的裂纹扩展角的变化,不仅与裂纹的闭合程度、斜裂纹倾角、双向应力大小有关,还与裂隙水压力的大小、裂纹面的摩擦系数有关;并且在相同情况下,未闭合裂纹的扩展角要大于闭合裂纹的扩展角;对于闭合裂纹,裂纹面摩擦系数越小,扩展角越大;最后,推导了基于摩尔-库仑准则考虑裂隙水压力的岩体断裂韧度KIc、KIIc和压剪状态下Ⅰ、Ⅱ型复合断裂判据。研究成果为分析水岩作用下裂隙岩体的失稳破坏提供了重要的参考。     

基于颗粒元模拟的含软弱夹层类土质边坡变形破坏过程分析

采用基于离散单元法的颗粒元程序,引用平行连接模型,通过数值试验,确定土体细观参数与宏观力学性质的关系,并据此建立含软弱夹层的类土质边坡模型。通过路堑开挖卸荷过程模拟,再现了大变形条件下坡体渐进性破坏的完整过程,并对裂隙的发展演化过程进行实时监测。模拟结果显示,含软弱夹层类土质边坡的破坏过程历经裂隙的形成、扩大、发展直至贯通,最终发生大规模滑移破坏;裂隙从滑坡体前缘和软弱层面开始,范围逐步扩大,呈现典型的类土质边坡的渐进性破坏形式;滑坡发生后,土体结构破坏严重,承载能力大幅下降。边坡滑移过程模拟和最终滑移结果与现场滑坡状况完全吻合,表明该方法适用于类土质边坡变形破坏过程分析及其机理研究。     

瞬变电磁法在不稳定斜坡勘察中的应用

不稳定斜坡是一种常见的地质灾害,近年来,我国的不稳定斜坡地质灾害日渐频繁,对人民的生命财产造成了很大威胁。采用瞬变电磁法对某不稳定斜坡进行探测,结合钻孔资料推断了覆盖层厚度、岩石风化和完整程度,查明地面裂缝的分布特征,取得了较好的勘探效果,不仅效率高、成本低,而且结果直观、地质效果明显,为后期治理提供了可靠的地球物理依据。