A Method Combining Numerical Analysis and Limit Equilibrium Theory to Determine Potential Slip Surfaces in Soil Slopes

This paper describes a precise method combining numerical analysis and limit equilibrium theory to determine potential slip surfaces in soil slopes. In this method, the direction of the critical slip surface at any point in a slope is determined using the Coulomb’s strength principle and the extremum principle based on the ratio of the shear strength to the shear stress at that point. The ratio, which is considered as an analysis index, can be computed once the stress field of the soil slope is obtained. Th...     

A method combining numerical analysis and limit equilibrium theory to determine potential slip surfaces in soil slopes

This paper describes a precise method combining numerical analysis and limit equilibrium theory to determine potential slip surfaces in soil slopes. In this method, the direction of the critical slip surface at any point in a slope is determined using the Coulomb’s strength principle and the extremum principle based on the ratio of the shear strength to the shear stress at that point. The ratio, which is considered as an analysis index, can be computed once the stress field of the soil slope is obtained. The critical slip direction at any point in the slope must be the tangential direction of a potential slip surface passing through the point. Therefore, starting from a point on the top of the slope surface or on the horizontal segment outside the slope toe, the increment with a small distance into the slope is used to choose another point and the corresponding slip direction at the point is computed. Connecting all the points used in the computation forms a potential slip surface exiting at the starting point. Then the factor of safety for any potential slip surface can be computed using limit equilibrium method like Spencer method. After factors of safety for all the potential slip surfaces are obtained, the minimum one is the factor of safety for the slope and the corresponding potential slip surface is the critical slip surface of the slope. The proposed method does not need to pre-assume the shape of potential slip surfaces. Thus it is suitable for any shape of slip surfaces. Moreover the method is very simple to be applied. Examples are presented in this paper to illustrate the feasibility of the proposed method programmed in ANSYS software by macro commands.     

Tectonic Evolution of the Wanan Basin,Southwestern South China Sea

Quantitative studies on the extension and subsidence of the Wanan Basin were carried out based on available seismic and borehole data together with regional geological data.Using balanced cross-section and backstripping techniques,we reconstructed the stratigraphic deposition and tectonic evolution histories of the basin.The basin formed from the Eocene and was generally in an extensional/transtensional state except for the Late Miocene local compressoin.The major basin extension ocurred in the Oligocene and Early Miocene(before ~16.3 Ma) and thereafter uniform stretch in a smaller rate.The northern and middle basin extended intensely earlier during 38.6–23.3 Ma,while the southern basin was mainly stretched during 23.3–16.3 Ma.The basin formation and development are related to alternating sinistral to dextral strike-slip motions along the Wanan Fault Zone.The dominant dynamics may be caused by the seafloor spreading of the South China Sea and the its peripheral plate interaction.The basin tectonic evolution is divided into five phases:initial rifting,main rifting,rift-drift transition,structural inversion,and thermal subsidence.     

Late Cenozoic Tectonic Deformation in the Dongsha Islands and Adjacent Sea Area

Dongsha Island and the adjacent sea area locate at the northern continental margin of the South China Sea (SCS), and is connected to the east by the Manila Trench. Analyses of seismic stratigraphy and gravity, magnetic and drilling wells data led to the discovery of three post-fault sequences (Ⅴ, Ⅵ, Ⅶ). Extensive tectonic uplift, magma activity and erosion occurred in Dongsha Island and the adjacent area, where most of the faults in the northeastern SCS were still active during Pliocene and Quaternary. Two groups of faults trending NEE and NW were developed during Late Cenozoic. We conclude that three important tectonic movements, especially Dongsha movement(4.4 - 5.2 Ma) and Liuhua movement (1.4 - 1.89 Ma), controlled the structural framework in the Dongsha rise; whose deformation in the east is stronger than that in the west and whose stress field variation suggests that the tectonic uplift in the study area contributed to magmato-tectonic events correlated to the main collision phases between the East China and Taiwan 5 - 3 and 3 - 0 Ma ago.     

鄂尔多斯盆地马家沟组四段岩相古地理新认识及勘探区带优选

准确的岩相古地理恢复对鄂尔多斯盆地奥陶系马家沟组四段有利储集层预测及勘探选区选带具有重要意义。依据野外露头剖面勘查、大量新钻井岩心和岩石薄片观察、单因素图分析、测井岩石结构组分解释和地震资料解译,建立了马家沟组四段台地—台缘—盆地的沉积模式,认为台地边缘带主要沿中央古隆起展布,同时受继承性发育的寒武纪乌审旗古隆起控制,台地内发育近北东向展布的榆林—志丹次级低隆带,低隆带两侧发育台内洼地,进而形成台地内部隆洼相间的沉积格局。重磁及地震资料解释表明,鄂尔多斯盆地中晚元古代发育沿北东向展布的裂陷槽,结合怀远运动构造背景,认为该裂陷槽对马家沟期沉积格局具有重要影响。受古地貌和古裂陷槽的共同作用,马家沟组四段颗粒滩主要发育在中央古隆起和榆林—志丹低隆带,总体呈北东向近似雁列式分布,藻丘发育在盆地东部神木—米脂盐隆地区。综合构造、沉积、储集层特征及勘探实践,优选出榆林—志丹次级低隆带和神木—米脂藻丘发育带是马家沟组四段天然气大规模成藏的有利勘探区。研究结果可为鄂尔多斯盆地马家沟组四段有利储集层的预测及勘探区带优选提供重要依据。     

哈达湾老工业区监测浅析

采用国情监测理论与方法,结合统计学原理,利用吉林省吉林市哈达湾老工业区改造前2010年和改造中2017年两期的地上建筑物变化、用地性质变化、绿地变化、空气污染变化等情况的监测结果,开展综合统计分析,客观评价哈达湾老工业区搬迁改造实施的成效.对哈达湾老工业区现状进行全面具体评估,为未来的城市建设与政府决策提供很好的支撑,成为国情监测在实际应用上的典例,为哈达湾老工业区搬迁改造持续进行提供了有力的支持.     

Sedimentary processes in Zenisu deep-sea channel revealed by side-scan imagery

1 INTRODUCTIONThe eastern Nankai Trough is a submarinetrench reflecting subduction zone where the earth'soceanic crust plunges beneath Japan Islands andcharacterized by extreme topographic relief (Fig.1).The convergent margin off Japan is characterizedmorphologically by numerous deep sea channels(such as the Nankai channel and Zenisu channel),which are closely related to the subduction proc-esses. Channel systems are considered to represent adistinct deep water sedimentation environmen…     

森林火灾对典型小流域径流影响模拟

以澳大利亚东南部Mcmahons Creek 流域1983年发生的森林火灾为例,运用AWRA-L和新安江模型模拟火灾后流域的基准径流过程,进而估算火灾对径流的影响。AWRA-L和新安江模型模拟结果表明,火灾发生后14年(1983—1997年)内流域产水量分别增加140 mm和123 mm,占火灾前(1974—1982年)年均径流量的33%和29%;火灾发生14年后的1998—2004年,增加量分别为43 mm和33 mm,占火灾前年均径流量的10%和8%。说明森林火灾引起短期内流域径流量的明显增加,随着植被的恢复流域产流增加量减少,森林砍伐是后期径流增加的重要原因。该研究对森林流域的水资源管理具有重要的参考价值。     

美国天然气水合物研究计划介绍

以美国近年来提出的天然气水合物研究计划和项目申请书为基础,介绍美国科学家在天然气水合物研究领域中所关心的关键科学与技术问题和研究焦点,供我国天然气水合物研究者在项目设计和开展研究工作时参考。美国天然气水合物研究关注的重点科学问题主要集中在 4个方面：天然气水合物的物理与化学特性研究;天然气水合物开采技术研究;天然气水合物灾害-安全性与海底稳定性研究;天然气水合物在全球碳循环中的作用研究。在研究方法上主要采取天然气水合物区的现场地质地球化学观测、实验室合成和测定及计算模拟,特别关注与水合物和油气冷泉相关的生命过程及与水合物的相互作用研究。     

Balanced Cross Section for Restoration of Tectonic Evolution in the Southwest Okinawa Trough

On the basis of the multi-channel seismic data and the other data, using 2DMove software, the tectonic evolution in three seismic profiles was restored since Pliocene. The tectonic restoration results show that: (1) the initial active center lay in the west slope and then was transferred to east and south via trough center during the evolution process; (2) several main normal faults controlled the evolution of the southern Okinawa Trough; (3) since Late Pliocene, the southern Okinawa Trough has experienced two spreading stages. The early is depression in Early-Middle Pleistocene and the late is back-arc spreading in Late Pleistocene and Holocene, which is in primary oceanic crust spreading stage.