Finite Element and Reliability Analyses for Slope Stability of Subansiri Lower Hydroelectric Project: A Case Study

The partly constructed and excavated power house slopes of Subansiri Lower Hydroelectric Project experienced extensive collapses through complex mode of failure. A detailed study is attempted in this paper to understand the reasons for the failure and assess the stability of the existing constructed slopes using limit equilibrium and FEM solutions and also to propose modified design for rebuilding the slopes. To take into account the uncertainty associated with the rockmass and soil properties, probability and reliability analyses have also been carried out. Based on the field observations and stability analyses of the natural and cut slopes, suitable support systems such as slope flattening with various angles, weldmesh, shotcrete, rockbolts and drainage holes have been considered to meet the stability requirements. In this study, it is demonstrated that the probabilistic approach when used in conjunction with deterministic approach helps in providing a rational solution for quantification of stability in the estimation of risk associated with the power house slope construction.     

Optimal Design of the Seepage Control for Xianglushan Diversion Tunnel Under High External Water Pressure

Geotechnical and Geological Engineering - The high external water pressure in the deep tunnel has an adverse impact on the lining, resulting in disasters such as water inrush, mud inrush and tunnel...     

东深供水改造工程凤岗隧洞段岩体参数位移反分析

通过东深供水改造工程凤岗隧洞段的岩体参数反分析,探讨了在计算中采用对屈服单元进行弱化来模拟开挖引起的松动与破坏范围的新方法,所得结果与实测值相吻合。     

Paleozoic and Lower Mesozoic magmas from the eastern Klamath Mountains (North California) and the geodynamic evolution of northwestern America

The Paleozoic to Early Mesozoic geology of the eastern Klamath Mountains (N California) is characterized by three major magmatic events of Ordovician, Late Ordovician to Early Devonian, and Permo-Triassic ages. The Ordovician event is represented by a calc-alkalic island-arc sequence (Lovers Leap Butte sequence) developed in the vicinity of a continental margin. The Late Ordovician to Early Devonian event consists of the 430–480 Ma old Trinity ophiolite formed during the early development of a marginal basin, and a series of low-K tholeiitic volcanic suites (Lovers Leap Basalt—Keratophyre unit, Copley and Balaklala Formations) belonging to intraoceanic island-arcs. Finally, the Permo-Triassic event gave rise to three successives phases of volcanic activity (Nosoni, Dekkas and Bully Hill) represented by the highly differentiated basalt-to-rhyolite low-K tholeiitic series of mature island-arcs. The Permo-Triassic sediments are indicative of shallow to moderate depth in an open, warm sea. The geodynamic evolution of the eastern Klamath Mountains during Paleozoic to Early Mesozoic times is therefore constrained by the geological, petrological and geochemical features of its island-arcs and related marginal basin.

A consistent plate-tectonic model is proposed for the area, consisting of six main stages:

1. (1) development during Ordovician times of a calc-alkalic island-arc in the vicinity of a continental margin;

2. (2) extrusion during Late Ordovician to Silurian times of a primitive basalt-andesite intraoceanic island-arc suite, which terminated with boninites, the latter suggest rifting in the fore-arc, followed by the breakup of the arc;

3. (3) opening and development of the Trinity back-arc basin around 430–480 Ma ago;

4. (4) eruption of the Balaklala Rhyolite either in the arc or in the fore-arc, ending in Early Devonian time with intrusion of the 400 Ma Mule Mountain stock;

5. (5) break in volcanic activity from the Early Devonian to the Early Permian; and

6. (6) development of a mature island-arc from the Early Permian to the Late Triassic.

The eastern Klamath Mountains island-arc formations and ophiolitic suite are part of the “Cordilleran suspect terranes”, considered to be Gondwana margin fragments, that have undergone large northward translations before final collision with the North American craton during Late Mesozoic or Cenozoic times. These eastern Klamath Mountains island-arcs could be associated with the paleo-Pacific oceanic plate that led to accretion of these allochthonous terranes to the American margin.     

Dinocyst biostratigraphy of the Lower Cretaceous in North Siberia

The described scheme of the Lower Cretaceous (Berriasian-Barremian) stratigraphic subdivisions is elaborated based on palynological study of sections in the Khatanga depression, Ust-Yenisei region, Pur-Taz interfluve, and around the Ob River latitudinal segment, the North Siberia. Stratigraphic distribution of microphytoplankton studied in detail is used to distinguish 10 biostratigraphic units in the rank of dinocysts zones. Stratigraphic position of the zones is determined with confidence using data on the Lower Cretaceous reference sections in the Khatanga depression, which were principal ones by constructing the Boreal standard zonation. In majority, boundaries of the dinocysts beds are of a high correlation potential and can be regarded as reliable stratigraphic markers, as they are recognizable not only in Siberia, but also in northern Europe and America.     

Sediment-water interactions in the metal-contaminated floodplain of the Clark Fork River,Montana, USA

The distribution and concentration of metals and metalloids in the floodplain of the Clark Fork River of western Montana, USA, are mainly controlled by post-depositional diagenetic mechanisms of metal fractionation. Due to the influx of wastes into the river's headwaters from mining processes around the turn of the century, extensive amounts of contaminated material were deposited onto the floodplain. Tailings were deposited as widespread overbank deposits and point bars adjacent to abandoned channels, and are characterized by orange and gray mottled sediment, which is devoid of vegetation and covered by a blue metal sulfate precipitate during dry periods. Examination of stratigraphic profiles of floodplain sediment indicates three periods of deposition: 1) pre-mining, represented by coarse sand and organic overbank deposits under reducing conditions; 2) syn-mining, characterized by transition sediments and tailings deposits under oxidizing conditions; and, 3) post-mining, distinguished by grass-bound topsoil.Sites were established where sediments and water throughout the stratigraphic section were collected and analyzed. Chemical analyses indicate enriched concentrations of cadmium, copper, manganese, and zinc in sediments and porewater, and arsenic in groundwater, in areas contaminated by tailings deposits. Vertical trends in concentrations of metals show that they are distributed based on apportionment of metal phases between reducing-oxidizing environments and pH fluctuations.     

中宁县黄河滩地傍河取水工程辐射井设计与施工

中宁县地处黄河中游,黄河滩地地下水受黄河补给,是具有巨大开采潜力的水源地。针对中宁黄河滩地第四系含粘粒土砂卵石地层的傍河水源地,选择辐射井作为取水建筑物,完成5眼辐射井。集水井成孔采用反循环方法,并配有专用钻头打捞含水层中粒径＞200 mm的漂石,用具有扭力、推力、拉力和振冲力的全液压水平钻机进行水平辐射管施工。采用“等效大口井法”计算辐射井抽水量。对抽水试验的数据及相关资料进行分析,比较辐射井、管井和大口井的稳定出水量和降深,结果表明采用辐射井开采类似水源地是有效的取水方式。     

某引水工程中长输水隧洞断面初选设计分析

断面比选设计是为了研究输水隧洞在复杂的地质条件中能够更好的施工,在运行期具有更好的过流能力,并且在建设中节省工程投资而进行的不同断面设计分析。以在建某长输水隧洞为例,选择城门洞型和马蹄形两种不同设计断面,从水力参数设计、施工方法、工程量及工程投资等各个方面进行对比分析计算,选择出易于施工,水利条件好并节省投资的设计断面,再进行输水隧洞正常水深、临界水深、临界底坡的水力计算,并分析了设计断面的水力特性。最后,提出了在输水隧洞断面设计上的几点建议,供水利设计和施工人员参考。     

高水压顶管隧道管节修复装置的设计与应用

富春江顶管工程为例,介绍了一种可快速拆卸的用于深埋顶管隧道对管节局部破损进行修复的装置。装置结构简单、紧凑,易于在圆形截面的隧道中进行快速拼装。该装置最高耐水压力0.8 MPa,可对地下水位以下30~80 m顶管隧道中出现沿轴线长＜0.4 m环状破损的管节进行注浆修复。这种设计能够有效解决深埋顶管隧道小面积局部破损、小范围漏水涌砂等问题,为深埋顶管等方法构筑的圆形隧道提供应急修复保障。     

黑河干流拟建水利工程对下游生态环境的影响分析

依据典型年份实际调查资料和以往研究成果, 采用地下水均衡方法, 定量对比分析了黑河拟建水利工程对下游地区地下水资源变化趋势, 并利用Visual Modflow三维地下水非稳定流软件系统模型对下游盆地未来20 a(2008—2028年)地下水位及其生态环境变化趋势进行了预测.结果表明: 在拟建工程实施20 a后黑河下游地下水位总体上处于下降趋势, 但下降幅度呈逐年减少状态直至趋于新的动态平衡.金塔-鼎新盆地地下水位下降幅度最大的地段是黑河沿岸为0.51~0.87 m, 但由于人工农业绿洲补充, 故生态环境不会有大的改变.额济纳盆地地下水位下降幅度最大的地段是古日乃及外围, 分别为1.0 m以上和0.5~1.0 m, 将引起植被的衰亡和种群的更替变化; 大部分地段地下水位下降幅度介于0.0~0.50 m之间, 对现有的生态与环境影响不显著; 桃来三达-额济纳旗以北地下水位呈现上升趋势, 上升幅度为0.10~0.87 m, 东居延海一带上升幅度大于0.87 m, 这一地区植被长势趋于良好, 植被覆盖率会有所增加, 将形成围绕海子的天然绿洲.     

珠江口盆地白云北坡珠江组下部陆架边缘沉积演化

根据层序地层学理论,运用地震相、地震沉积学等分析手段,结合钻井、测井等资料,对珠江口盆地白云北坡珠江组下部的沉积演化进行了研究,研究发现:珠江组下部发育陆架边缘三角洲-海相沉积体系,地震剖面中陆架边缘三角洲前缘分布在Y2井区及以南区域,平面上呈菱形,其两侧发育改造的滨海砂坝,南部发育斜坡浊积扇,这三者形成了海退体系中的主要岩性圈闭;X1、Y1井区及以北发育海进体系中的滨海砂坝圈闭。海平面升降、物源供给和构造古地貌对沉积演化和圈闭形成过程中起明显的控制作用。21.0~19.0Ma期间,海平面下降和河流回春作用是形成陆架边缘三角洲的主要原因,构造古地貌及其控制的古水深控制了相带展布与边界。     

新楼兰工程——塔里木河下游及罗布泊地区生态重建与跨越式发展设想

1 “新楼兰工程”的提出 我国最长的内陆河流塔里木河下游以及南疆东部向罗布洼地汇聚的数条水系(孔雀河、车尔臣河、瓦石峡河、若羌河、米兰河等)，面积约40.8×10.4 km2[5, 13]，人口约70万。受自然条件和历史因素的影响，这里的人居环境极为严酷，生产力十分低下，生态环境治理与重建任务因此也最为紧迫和繁重。     

Evaluation of Reinforced Concrete Design for an Underground Outlet Manifold in Shanxi Yellow River Diversion Project

Summary In order to verify the design feasibility of the reinforced concrete lining of the outlet manifold in Shanxi Yellow River Diversion Project (YRDP), field investigations on rock mass deformability, in situ stress and hydraulic jacking measurements have been carried out. Based on the results obtained, 3-D FEM numerical analyses have been performed to calculate the stress distribution in a reinforced concrete lining under internal and external water pressure. Furthermore, the initial designed shape and steel ratio of concrete have been modified to satisfy the requirements for the limit crack width design criteria in China and decrease the tensile stress level in concrete. The new steel ratio of reinforced concrete has been calculated on the basis of the numerical results considering the modified shape of the outlet manifold. Both the owner and designer of YRDP have adopted the steel ratio of concrete in the working design and construction of the outlet manifold.     

穿黄隧洞束窄河道对河段水沙特性的影响分析

利用建立的平面二维非恒定水流泥沙数学模型,在上游来流为10000年一遇的特大洪水过程情况下,就初步拟定的南水北调中线穿黄方案之一的孤柏嘴线路3 0km隧洞工程方案,穿黄隧洞束窄河道对河段水流流态、泥沙运动及河床变形的影响进行了计算和分析比较。计算结果表明,在该洪水过程情况下,穿黄隧洞束窄河道对河段水沙运动特性有一定影响,但影响不大。     

黄河下游悬河稳定性因素分析

黄河悬河的形成是自然营力与人为因素综合作用的产物。悬河的稳定性关系到黄河下游广大人民的生命财产安全。影响黄河悬河稳定性的因素有：地质构造控制机制，河流地貌的影响，河床质与土体结构，河流动力地质作用和治理工程对悬河稳定性的影响。在此基础上，制定出一系列治理黄河悬河的对策。     

Stratigraphic evidence for multiple drainings of glacial Lake Missoula along the Clark Fork River, Montana, USA

Glacial Lake Missoula, a source of Channeled Scabland flood waters, inundated valleys of northwest Montana to altitudes of ∼ 1265 m and to depths of  >600 m, as evidenced by shorelines and silty lacustrine deposits. This study describes previously unrecognized catastrophic lake-drainage deposits that lie stratigraphically beneath the glacial-lake silts. The unconsolidated gravelly flood alluvium contains imbricated boulder-sized clasts, cross-stratified gravel with slip-face heights of 2-> 35 m, and 70- to 100-m-high gravel bars which all indicate a high-energy, high-volume alluvial environment. Gravel bars and high scablands were formed by catastrophic draining of one or possibly more early, high lake stands (1200-1265 m). Most glacial-lake silt, such as the Ninemile section, was deposited stratigraphically above the earlier deposits, represents a lower lake stand(s) (1050-1150 m), and was not deposited in lake(s) responsible for the highest discharge events. The glaciolacustrine silt-covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake. Significant erosion associated with the last lake draining was confined to the inner Clark Fork River canyon.     

A case history of Tunnel Boring Machine jamming in an inter-layer shear zone at the Yellow River Diversion Project in China

This is a case study of a Tunnel Boring Machine (TBM) jamming in a section of the Connection Works No. 7 tunnel of the Yellow River Diversion Project (YRDP) in China. Analysis of tunnel lithology, rock convergence by shearing, rock strength and ground stress, indicates that a high rate of convergence within an inter-layer shear zone in the lower part of an anticline was a dominant factor in the jamming. In addition, the shield encountered unfavorable tunnelling conditions in the form of wet clay, groundwater inflow, and cavities, coincident with tensile stresses in the lower part of an adjacent syncline. Based on these diagnoses, economical and quick measures were adopted, including additional excavation outside of the shield leaving free space to release the TBM. After 9 days of being jammed, the TBM was totally released and resumed normal excavation. This example highlights lessons learned from folding and inter-layer shear zone in TBM tunnelling.     

南水北调中线一期工程下穿京九铁路隧道工程设计

文章详细介绍了下穿隧道的明挖段、暗挖段的工程措施,对京九铁路路基、轨道的加固措施以及监控量测的方法.为日后类似工程提供一定的设计、施工经验.     

长江中下游成矿带深部结构层析成像图像揭示华北板块的东南向俯冲

远震层析成像结果所揭示的华北板块东南向俯冲到扬子板块之下对于重新认识长江中下游地区成矿机制具有重要意义.利用来自中国地震台网中心,包括湖北、河南、安徽、江西、浙江、江苏等省级地震台网记录的波形数据对长江中下游地区深部结构进行了远震P波层析成像反演.综合研究结果显示,三叠纪华北与扬子板块俯冲碰撞,华北板块越过郯庐断裂带,向东南俯冲到扬子板块之下.推断板块碰撞的深部缝合线在郯庐断裂带以西位于大别造山带以南,在郯庐断裂带以东位于长江一线.经历后期的中生代构造转换过程,该带发生活化,成为中生代含矿岩浆和流体上升的通道,并形成著名的大型成矿带.      

2360aBP古洪水对小浪底设计洪水的作用

根据我国频率计算中广泛采用的Ｐ－Ⅲ型分布,应用统计试验方法,分别对仅由历史调查洪水和实测洪水组成的不完全系列,以及加入考虑流量误差情况下的古洪水资料后的系列进行了计算,得到后者比前者抽样误差大为减小的结论。