Discussion of “Use of Surface Waves in Statistical Correlations of Shear Wave Velocity and Penetration Resistance of Chennai Soils” by R. Uma Maheswari, A. Boominathan, G. R. Dodagoudar     

Ümit Gülerce 《Geotechnical and Geological Engineering》2010,28(6):925-927

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The effect of the geomagnetic activity to the hourly variations of ionospheric foF2 values at low latitudes     

Erdinç Timoçin  Ali Yeşil  İbrahim Ünal 《Arabian Journal of Geosciences》2014,7(10):4437-4442

In this study, the relationship between the hourly changes of the ionospheric critic frequency values of F2 layers in low latitudes and geomagnetic activity is examined by using statistical methods. The ionospheric critical frequency data has been taken from the Manila (121.1° E, 14.7° N) ionosonde station. In order to investigate the effect of sun activity on ionospheric critical frequency, the data of 1981 when the sun was active and of 1985 when the sun was less active has been used. According to the Granger causality test results, on 5 % significance level, a causality relationship from disturbance storm time (Dst) index values to ionospheric critical frequency values direction has been observed. However, a causality relationship from ionospheric critical frequency values to Dst values has not been observed. From the results of cause-and-effect analysis, it is evaluated that the effect of a shockwave occurring in geomagnetic activity on ionospheric critical frequency continues along 72 h, that is, geomagnetic activity has a long-term effect on ionospheric critical frequency. The response of ionospheric critical frequency to geomagnetic activity substantially depends on seasons. This response is more observed especially in equinox period when the sun is active and in winter months. The increase in geomagnetic activity causes ionospheric critical frequency to decrease in night hours and increase in day hours. The same relationship has not been observed exactly, though observed very little in winter months, for 1985 when the sun was less active.  相似文献   

Investigation of surface and subsurface displacements due to multiple tunnels excavation in urban area     

Alireza Talebinejad  Hamid Chakeri  Mahdi Moosavi  Yılmaz Özçelik  Bahtiyar Ünver  Mehmet Ali Hindistan 《Arabian Journal of Geosciences》2014,7(9):3913-3923

Underground structures are currently widely used and are built as urbanism develops. The interactions between perpendicularly crossing and parallel tunnels in the Tehran region are investigated by using a full three-dimensional (3D) finite difference analysis with elastic-plastic material models. Special attention is paid to the effect of subsequent tunneling on the support system, i.e., the shotcrete lining and rock bolts of the existing tunnel. Eventually, as the tunnels are excavated at certain levels, the interaction between the tunnels will certainly have a significant influence on both stress distribution and consequently deformations. Since multilayer tunneling is a three-dimensional phenomenon in nature, 3D numerical solutions must be utilized for analyzing effect of perpendicularly crossing tunnels at various levels. As Tohid twin tunnels and Line 7 pass beneath the Line 4 metro tunnel, changes in stress distribution, deformations, and surface settlements are studied for various conditions and the results are presented in this paper. Consequently, it is shown that there is a significant interaction between tunnels that necessitate certain preventive measures to maintain a stable tunneling operation.  相似文献   

Crack Initiation and Crack Propagation in Heterogeneous Sulfate-Rich Clay Rocks   总被引：2，自引：1，他引：1  

Florian Amann  Ömer Ündül  Peter K. Kaiser 《Rock Mechanics and Rock Engineering》2014,47(5):1849-1865

Brittle fracture processes were hypothesized by several researches to cause a damage zone around an underground excavation in sulfate-rich clay rock when the stress exceeds the crack initiation threshold, and may promote swelling by crystal growth in newly formed fractures. In this study, laboratory experiments such as unconfined and confined compression tests with acoustic emission monitoring, and microstructural and mineralogical analyses are used to explain brittle fracture processes in sulfate-rich clay rock from the Gipskeuper formation in Switzerland. This rock type typically shows a heterogeneous rock fabric consisting of distinct clayey layers and stiff heterogeneities such as anhydrite layers, veins or nodules. The study showed that at low deviatoric stress, the failure behavior is dominated by the strength of the clayey matrix where microcracks are initiated. With increasing deviatoric stress or strain, growing microcracks eventually are arrested at anhydrite veins, and cracks develop either aligned with the interface between clayey layers and anhydrite veins, or penetrate anhydrite veins. These cracks often link micro-fractured regions in the specimen. This study also suggest that fracture localization in sulfate-rich clay rocks, which typically show a heterogeneous rock fabric, does not take place in the pre-peak range and renders unstable crack propagation less likely. Sulfate-rich clay rocks typically contain anhydrite veins at various scales. At the scale of a tunnel, anhydrite layers or veins may arrest growing fractures and prevent the disintegration of the rock mass. The rock mass may be damaged when the threshold stress for microcrack initiation is exceeded, thus promoting swelling by crystal growth in extension fractures, but the self-supporting capacity of the rock mass may be maintained rendering the possibility for rapidly propagating instability less likely.  相似文献   

A New Lizard (Lepidosauria: Squamata) from the Upper Cretaceous of Henan, China     

XU Li  WU Xiaochun  Lü Junchang  JIA Songhai  ZHANG Jiming  PU Hanyong  ZHANG Xingliao 《《地质学报》英文版》2014,88(4):1041-1050

Funiusaurus luanchuanensis gen. et sp. nov. was described on the basis of an incomplete skull from the Upper Cretaceous Qiupa Formation of the Tantou Basin in Luanehuan County, Henan Province. It is the second representative of lizards known from Luanchuan and adds a new member to the Luanchuan Fauna. F. luanchuanensis is a small-sized lizard and systematically assigned to the Polyglyphanodontidae of the Teiioidea because of the presence of a caniniform tooth and an elongate posterior process of the postorbital. It is distinctive in that the heterodont dentition bears 19 teeth in both the upper and lower jaws, the 3^rd maxillary tooth is large and caniniform, the post-caniniform teeth in maxilla and those posterior to the 3^rd dentary tooth are chisel-like in lateral view, the prefrontal possesses a fossa on its lateral surface, the postorbital with an extremely elongate posterior process and the well-developed retroarticular process has a deep fossa on its dorsal surface. In phylogeny, our analysis suggests a close relationship of Funiusaurus to the large-sized Tianyusaurus from the same basin within the Tuberocephalosaurinae. The discovery of Funiusaurus is significant in confirming the status of the Tuberocephalosaurinae, which includes a group of the Asian members of the Polyglyphanodontidae only.  相似文献   

‘PALEOVAN’, International Continental Scientific Drilling Program (ICDP): site survey results and perspectives     

Thomas Litt  Sebastian Krastel  Michael Sturm  Rolf Kipfer  Sefer Örcen  Georg Heumann  Sven Oliver Franz  Umut B. Ülgen  Frank Niessen 《Quaternary Science Reviews》2009,28(15-16):1555-1567

Lake Van is the fourth largest terminal lake in the world (volume 607 km³, area 3570 km², maximum depth 460 m), extending for 130 km WSW–ENE on the Eastern Anatolian High Plateau, Turkey. The sedimentary record of Lake Van, partly laminated, has the potential to obtain a long and continuous continental sequence that covers several glacial–interglacial cycles (ca 500 kyr). Therefore, Lake Van is a key site within the International Continental Scientific Drilling Program (ICDP) for the investigation of the Quaternary climate evolution in the Near East (‘PALEOVAN’). As preparation for an ICDP drilling campaign, a site survey was carried out during the past years. We collected 50 seismic profiles with a total length of ～850 km to identify continuous undisturbed sedimentary sequences for potential ICDP locations. Based on the seismic results, we cored 10 different locations to water depths of up to 420 m. Multidisciplinary scientific work at positions of a proposed ICDP drill site included measurements of magnetic susceptibility, physical properties, stable isotopes, XRF scans, and pollen and spores. This core extends back to the Last Glacial Maximum (LGM), a more extended record than all the other Lake Van cores obtained to date. Both coring and seismic data do not show any indication that the deepest part of the lake (Tatvan Basin, Ahlat Ridge) was dry or almost dry during past times. These results show potential for obtaining a continuous undisturbed, long continental palaeoclimate record. In addition, this paper discusses the potential of ‘PALEOVAN’ to establish new results on the dynamics of lake level fluctuations, noble gas concentration in pore water of the lake sediment, history of volcanism and volcanic activities based on tephrostratigraphy, and paleoseismic and earthquake activities.  相似文献   

含水率对岩石电荷感应信号影响规律研究     

郑文红  施天威  潘一山  罗浩  吕祥锋 《岩土力学》2022,43(3):659-668

水是诱发矿井灾害的主要因素之一,研究水?岩相互作用下的岩石破坏电荷信号,可丰富矿井水引起灾害的监测方法。为研究含水率对岩石破坏电荷感应信号的影响规律,基于损伤理论推导了岩石损伤破坏力?电耦合模型,得到了感应电荷量与岩石力损伤和水损伤的理论关系。利用自主研制的电荷感应信号数据采集系统,对不同含水率条件下的岩石试样进行了单轴压缩电荷感应信号监测试验,分析了水对岩石力学性质和岩石破坏过程中各阶段电荷感应信号的影响规律,并对含水率影响感应电荷产生的机制进行了讨论。结果表明：岩石变形破坏过程中的电荷感应信号与岩石的损伤程度有关,累积感应电荷量与感应电荷总量的比值可以表示岩石在水和力作用下的损伤量,且含水率越高,试样越易在较低的应力下产生大量的电荷感应信号。不同含水率岩石的宏观破坏特征明显不同,随着含水率升高,岩石的抗压强度降低,裂隙发育,岩石破坏形式由单剪式破坏向张拉和剪切混合破坏转变。电荷感应信号分布形态上,含水率的升高使得高幅值电荷簇数增加,并向弹性阶段发展,且高幅值电荷感应信号主要分布在弹性阶段后期和塑性阶段。感应电荷量上,随着含水率的升高,弹性阶段的感应电荷释放量占比逐渐增大,塑性阶段占比逐渐减小,两阶段的感应电荷量之和占试样变形破坏过程中产生感应电荷总量的90%以上。水通过弱化岩石颗粒和渗透压作用,使岩石在较低应力下产生或扩展裂隙,感应电荷信号更丰富。  相似文献   

絮凝−真空−电渗联合加固滩涂软土的模型试验研究     

张雷  吕延栋  王炳辉  金丹丹  竺明星  方晨 《岩土力学》2022,43(9):2383-2390

针对真空预压作用下排水板淤堵与排水条件受限等问题,提出絮凝−真空−电渗联合加固法。首先通过沉降柱试验确定合适的有机絮凝剂,然后采用该絮凝剂,分别在 48 h（开始介入真空预压,固结度为0 ）、60 h（排水速率明显下降,固结度为60%）及 84 h（排水速率近乎 0,固结度为 80%）时介入电渗,开展不同电渗介入时间的絮凝−真空−电渗联合加固试验。试验从排水量、十字板剪切强度、含水率与孔压等对比分析联合加固的有效性,确定其最佳电渗介入时间。试验结果表明：当固结度为 80% 时介入电渗,絮凝−真空−电渗联合加固法能够有效地抑制排水速率减小的趋势,增长有效排水时间。同时,土体的抗剪强度和承载力亦得到大幅提升,孔压消散更加均匀。此外,在阳离子聚丙烯酰胺絮凝剂的作用下,初始排水速率快,在一定程度上使土体的渗透性得到提升,有效地解决了排水板淤堵问题,说明絮凝−真空−电渗联合加固法具有较强的优越性。  相似文献   

黄豆脲酶诱导碳酸钙沉淀多变量试验研究     

崔猛  符晓  郑俊杰  吕苏颖  熊辉辉  曾晨  韩尚宇 《岩土力学》2022,43(11):3027-3035

植物源脲酶诱导碳酸钙沉淀（enzyme induced carbonate precipitation,简称EICP）可以显著改善砂土的工程力学特性,但在具体操作时,参数取值无对应规范,固化效果有待提升。基于黄豆脲酶,研究了温度、脲酶浓度、尿素浓度、钙浓度、pH值、钙源种类等变量对脲酶活性与碳酸钙沉淀的影响,并进行了沉淀物（碳酸钙晶体）的扫描式电子显微镜（scanning electron microscope,简称SEM）与X射线衍射（X-ray diffraction,简称XRD）测试,在此基础上开展了黄豆脲酶固化砂的无侧限抗压强度与固化效果试验研究。结果表明：脲酶活性随脲酶浓度的增加而线性增长,但存在温度阈值,温度超过阈值后,脲酶将完全失活,且阈值随脲酶浓度的增大而降低;尿素浓度与pH值共同影响脲酶活性,二者存在一个最优组合,当尿素浓度在0.1～1.0 mol/L时最优pH值为7,当尿素浓度在1.0～1.5 mol/L时最优pH值为8。脲酶是沉淀反应的催化剂,脲酶浓度越高,反应越完全,碳酸钙沉淀率越高;尿素与钙溶液则主要通过掺入量影响碳酸钙沉淀量,掺量比例宜为1:1,且二者浓度与pH值可通过影响脲酶活性来影响碳酸钙的沉淀情况;不同钙源对碳酸钙沉淀量的影响幅度不大。不同钙源沉淀碳酸钙晶体的成分与密度基本相同,但晶体结构差异较大,氯化钙沉淀碳酸钙晶体以块状为主,表面分布球状、类球状晶体,胶结面大,可作为EICP技术中较为理想的钙源。基于黄豆脲酶和氯化钙钙源固化砂的无侧限抗压强度约为掺粉煤灰砂样的6倍,通过SEM图像可发现,沉淀碳酸钙晶体包裹并黏结砂粒成为整体,固化效果非常理想。  相似文献   

1980-2019年青藏高原积雪深度时空差异性分析北大核心CSCD     

王芝兰  张飞民  王澄海  孙旭映  吕春艳 《冰川冻土》2022,44(3):810-821

积雪是地表特征的重要参数,其对辐射收支、能量平衡及天气和气候变化有重要影响。利用1980-2019年被动微波遥感积雪深度资料对青藏高原积雪时空特征进行分析,在此基础上将高原划分为东部、南部、西部及中部4个区域,并分区域讨论了多时间尺度积雪的变化特征及其与气温、降水的相关关系。结果表明:不同区域积雪深度在不同时间尺度的变化特征存在差异,高原东部积雪深度累积和消融的速率比西部快,南部积雪深度累积和消融速率比中部快。季节尺度上,冬季积雪高原东部最大,中部最小;春季积雪高原东部消融速率最大,西部积雪消融较慢但积雪深度最大;夏季高原西部仍有积雪存在。年际尺度上,各区域积雪深度在1980-2019年均呈现缓慢下降趋势,但东部积雪减少不显著;高原东部积雪深度在1980-2019年呈现出增加-减少-增加-减少的变化,其余3区均呈现出减少-增加-减少-增加-减少的变化。不同区域积雪深度对气温、降水的响应不同,高原东部和中部积雪深度与气温相关性较好;各区域积雪深度与降水呈不显著的正相关关系。  相似文献