西藏白朗南部地区三叠纪地层沉积环境及物源

综合露头剖面、砂岩碎屑组分、地球化学、阴极发光等资料的研究,对西藏白朗地区南部三叠系沉积环境及物源开展了研究。该区三叠纪地层以灰黑色泥岩、浅灰白色石英砂岩、长石石英砂岩、灰色灰岩为主,沉积背景为拉轨岗日被动陆缘盆地的浅海-半深海环境。碎屑岩及其地球化学分析结果反映,物源总体来自克拉通内部。阴极发光结果表明,物源区石英主要为变质成因,次为火成岩成因。综合判定,研究区该套地层为下—中三叠统吕村组和上三叠统涅如组,物源区来自南部高喜马拉雅基底杂岩带。     

库车坳陷新生代构造应力场恢复

库车坳陷的构造变形及演化与南天山造山带的发育密切相关。库车坳陷新近纪以来的喜马拉雅晚期构造运动最为强烈,形成了天山山前大型冲断带,并造就了现今的构造格局。通过对库车坳陷北部构造样式的识别及各种应力场指示标志的测量、统计和构造解析,对野外获得的应力场指示标志划分了期次,认为喜马拉雅晚期应力场标志为近南北向挤压。结合库车坳陷区域构造要素,如地质体几何形态、边界条件、岩石力学参数等,运用弹性力学有限元数值模拟的方法获得了喜马拉雅晚期库车坳陷的区域应力场。模拟结果表明,库车坳陷喜马拉雅晚期最大主压应力方向为近南北向,与古应力场标志拟合较高,可以为库车坳陷裂缝预测和评价提供依据,对勘探开发有应用价值。     

阿尔金北缘岩石变形机制——来自X光组构分析的证据

对阿尔金北缘地区变形蚀变花岗岩、花岗质糜棱岩、变形酸性火山岩和变形英安质凝灰岩中石英和绢云母2种矿物进行X光岩石组构分析,认为本区岩石变形比较明显,宏观面理近于东西向展布,绢云母变形较强,平行于面理定向排列;而石英以底面或近底面滑移为主,部分样品兼有柱面Ⅰ型滑移和柱面Ⅱ型滑移,反映本区岩石变形机制为中浅层次的脆-韧性变形(10~15km、250~350℃、0.25~0.40GPa)。通过岩石组构特征与宏观面理产状,推断本区韧性变形以右行运动为主,与板块碰撞在阿尔金北缘大平沟地区产生的韧性变形带特征一致。     

Distribution of calcareous nannoplankton in surface sediments along the northern KwaZulu-Natal Bight,South Africa

The coccolith assemblages from seafloor sediments over the inner shelf in the northern region of the KwaZulu- Natal Bight on the east coast of South Africa were identified and their distribution determined. In all, 29 Recent species and taxonomic groups, as well as 29 reworked species were recorded. The distribution of the Recent species appears to be governed by environmental features that have been documented in other studies: temperature, salinity, nutrient concentration and water circulation pattern, which reveals the long-term existence of a circulation cell in the sector between Durban Bay and the Thukela River. The outer edge of the cell consists of nutrient-enriched mixed layers and is characterised by an enhanced abundance of Gephyrocapsa oceanica, whereas the central region consists of a stratified nutrient-depleted water mass with elevated abundance of Umbilicosphaera sibogae, Florisphaera profunda, and a group of umbelliform species. The elevated levels of G. oceanica, coupled with the rarity of U. sibogae, F. profunda and the umbelliform species, confirm the presence of a permanent upwelling cell off Richards Bay. The maximum abundance of F. profunda found between Richards Bay and Lake Nhlabane indicates a region of nutrient-depleted (except for nitrite) conditions.     

Rotation Center and Horizontal Bearing Capacity of the Bucket Foundation in Soft Ground

In the last 20 years, the bucket foundation has been developed as a new type of offshore platform structure. Because of its short period of application to engineering practices, the theoretical decision on the rotation center and horizontal bearing capacity of the bucket foundation has yet to be agreed. A limit analysis method is used to determine the updated rotation center position and horizontal bearing capacity to evaluate the failure mechanisms of the bucket foundations. The results are compared with numerical simulation and experiments, and also with other theoretical methods. The proposed method can satisfactorily consider the engineering conditions and the result is accurate in determining the rotation center and horizontal bearing capacity.     

Numerical Studies on Piled Gravity Base Foundation for Offshore Wind Turbine

This study aims to investigate a hybrid gravity base foundation to support offshore wind tower. A new hybrid gravity base foundation considered in this study has five component piles, referred to as ‘piled gravity base foundation’. The three-dimensional finite element analyses were carried out for the piled gravity base foundation subjected to a combined load with a lateral load and overturning moment. The parametric analyses were undertaken varying the loading height and direction, the rigidity of the piled gravity base foundation, the field soil layers, and the clay strength. Overall, the response of the piled gravity base foundation was significantly influenced by the interaction between the cone base piles and the surrounding soil. The increased strength of the soil led to a significant reduction of the pile and gravity base foundation responses, in terms of the bending moments, axial forces, lateral displacements, and rotations.     

The Sediment Source and Transport Trends around the Abandoned Yellow River Delta,China

Sediment source and transport trends are influenced by various hydrodynamic factors, and thus play important roles in sedimentary evolution and coastal stability. To examine sediment transport trends around the abandoned Yellow River delta promontory and its erosion mechanism, we employ empirical orthogonal function (EOF) analysis to study sedimentary characteristics and transport trends of the abandoned Yellow River delta in northern Jiangsu Province, China. The results showed that: (1) the main sediment source in the abandoned Yellow River delta is the submarine coastal slope and both sides of the abandoned Yellow River Delta; (2) the main hydrodynamics controlling sediment transport is the current that runs along the shore, coupled with waves, especially southward currents; (3) the sediment of the study area was redistributed under hydrodynamics; coarse sediments were eroded and broadly transported to the south. Therefore, it is concluded that the sediment sources and transport have important influence on coastal evolution: the sediment source area shows mass loss of deposits and erosion; deposits in the submarine coastal slope provide the source and were continuously eroded to provide materials to other places as a sediment source.     

The Effect of Concrete Deformation on Displacement of an Axially Loaded Drilled Shaft

This article presents the settlement of drilled shafts resulting from their structural deformations. Although drilled shafts are widely used as foundations for settlement-sensitive structures such as bridges and high-rise buildings, the structural deformations of drilled shafts are not typically taken into account in the design process. However, if unexpected structural deformations of drilled shafts cause additional settlement to the foundation, the serviceability of the superstructure can be jeopardized. Unfortunately, very few research efforts have been made to quantify the structural deformation of drilled shafts; this needs to be addressed to accurately predict the settlement of drilled shafts. In this study, we investigate the effect of structural deformation on displacement of axially loaded drilled shafts. Finite element analyses were performed to quantify the structural deformation of drilled shafts. The analysis results indicated that the structural deformation of drilled shafts could be quite significant for long drilled shafts. The main factors that affected the structural deformation of drilled shafts were found to be pile length, the material properties of drilled shafts, and the relative humidity of surrounding soil. An approximate equation is proposed to estimate the long-term deformation of drilled shafts.     

Development of Prebored Screw Pile Method and Evaluation of Its Bearing Characteristics

The pile-driving method produces considerable noise and vibrations. Hence, an auger-drilled pile method was developed as a low-noise and -vibration substitute. However, this method does not guarantee the bearing capacity of the pile unless some amount of pile-driving is performed. Therefore, the noise and vibration problems cannot be completely solved. In this study, a prebored screw pile method is proposed to solve these problems. In this method, piles are constructed by the rotary penetration of a screw pile into a prebored hole filled with some cement milk and whose diameter is smaller than that of the screw pile. To determine the shape of the screw pile, laboratory tests with model screw piles were conducted. Also, field load tests were conducted on an actual screw pile fabricated based on the laboratory test result and on a smooth-surfaced pile. In addition, the behavior of the screw pile was estimated by using three-dimensional finite element analysis. The results of the field load test and the numerical simulation showed that the ultimate bearing capacity and the unit skin friction of the screw pile are very superior to those of the smooth-surfaced pile and the cement milk is an important factor in the prebored screw pile method.     

Distribution and feeding modes of macrobenthos within three oceanographic feature areas of the KwaZulu-Natal Bight,South Africa

The composition and distribution of macrobenthic communities was investigated in three areas in the KwaZulu- Natal Bight, a section of shelf off the east coast of South Africa. Areas were pre-selected on the basis of three known oceanographic features, posited to deliver land- or Agulhas Current-derived nutrients onto the shelf and to drive ecosystem functioning in this region. Replicate sediment samples were collected with a 0.2 m² van Veen grab, during two surveys (A, B) corresponding with normal periods of high and low rainfall, respectively. A subset of the full station array was selected across the shelf in an arrangement of increasing depths (inner-, mid- and outer shelf) through each feature area to investigate the spatial distribution and feeding modes of macrobenthic taxa. The two periods showed some differences in abundance and numbers of macrobenthic taxa, but were not statistically different. Total macrobenthic abundance from Survey A was 20 215 individuals from 642 taxa, decreasing to 18 000 individuals from 503 taxa during Survey B. Polychaeta and Crustacea were the dominant taxa sampled; abundance of the latter was attributed largely to a proliferation of Paguristes sp.1 at inner-shelf samples in the midbight (Thukela) region during Survey B. Similarity classification distinguished seven sample groups reflecting differences in feature areas and shelf positions under investigation. The Thukela River midshelf community supported the highest macrobenthic abundance, while the midshelf off the southern bight (Durban region) was most species rich. Findings were attributed to the habitat complexity of the midshelf which includes a palaeo-dune cordon at the 60 m isobath. Functionally, the community was dominated by interface- and deposit-feeding fauna, emphasising the importance of trophic plasticity in an environmentally variable and heterogeneous shelf environment.