复杂应力路径下大理岩三轴渗透试验研究

在隧道施工过程中,围岩的应力条件非常复杂,研究复杂应力路径下围岩渗透性能的变化规律对在高水压地区修建隧道具有重要意义。以锦屏水电枢纽二级电站交通辅助洞大理岩为研究对象,进行了常规三轴渗透试验与控制轴向应变（简称应变 ）、围压先升后降的三轴渗透试验,探讨了轴压与围压之差的绝对值 （简称应力差）与渗透率的关系。试验结果表明: (1)常规渗透试验大理岩渗透率的变化过程有3个重要的特征点：渗透率最低点、渗透率峰值点以及渗透率稳定点;(2)大理岩的渗透率随着应力差的增大而减小,两者呈负指数关系;(3)对某一固定的应力差,升围压阶段测得的渗透率大于降围压阶段测得的渗透率;(4)对任何试验岩样总存在一阈值,当应力差小于该值时,应力差的改变对渗透率有显著影响;(5)应力差减小过程中岩样渗透率的“恢复能力”随着岩样轴向应变的增大而逐渐减弱。     

GDS空心圆柱仪动力试验能力探讨

为更好地模拟多向应力和主应力轴旋转等复杂应力路径,与英国GDS公司合作研发了能施加轴向和扭矩动载的空心圆柱仪。文中介绍了该仪器的工作原理和性能,分析对比了其与传统单向动三轴仪试验结果,并探讨该空心圆柱仪所完成的5组典型动力荷载及一组不规则随机波动力试验能力。动力加荷时,通过调整设定刚度参数,实测波形与设定波形误差较小。该仪器能很好地模拟地震、波浪和交通荷载引起的应力,为研究复杂应力状态下土体动力本构关系提供了很好的工具。     

Influence of shallowness,bank inclination and bank roughness on the variability of flow patterns and boundary shear stress due to secondary currents in straight open-channels

Boundary shear stress and flow variability due to its interaction with main flow and secondary currents were investigated under conditions that extend previous research on trapezoidal channels. Secondary currents that scale with the flow depth were found over the entire width in all experiments. These findings contradict the widespread perception that secondary currents die out at a distance of 2.5 times the flow depth from the bank, a perception which is largely based on experiments with smooth boundaries. The reported results indicate that a stable pattern of secondary currents over the entire channel width can only be sustained over a fixed horizontal bed if the bed's roughness is sufficient to provide the required transverse oscillations in the turbulent shear stresses. Contrary to laboratory flumes, alluvial river bed always provide sufficient roughness. The required external forcing of this hydrodynamic instability mechanism is provided by the turbulence-generated near-bank secondary currents. The pattern of near-bank secondary currents depends on the inclination and the roughness of the bank. In all configurations, secondary currents result in a reduction of the bed shear stress in the vicinity of the bank and a heterogeneous bank shear stress that reaches a maximum close to the toe of the bank. Moreover, these currents cause transverse variability of 10–15% for the streamwise velocities and 0.2u_*²–0.3u_*?² for the bed shear stress. These variations are insufficient to provide the flow variability required in river restoration projects, but nevertheless must be accounted for in the design of stable channels.     

Velocity profiles and incipient motion of frazil particles under ice cover

A series of experiments for the incipient motion of frazil particles under ice cover have been carried out in laboratory under different flow and boundary conditions.Measurements on flow velocities across the measuring cross-section at different water depths have been conducted.Based on these experiments under both ice-covered and open flow conditions,the impacts of solid boundary(such as ice cover and flume sidewall) on the distribution of flow velocity profiles have been discussed.The criteria for the inc...     

Hydraulic parameters in channels with wall vegetation and gravel bed

In this experimental study,field observations and laboratory experiments have been carried out to assess the impacts of the vegetated channel walls and aspect ratio on flow velocity profiles,shear stress distribution and roughness coefficient of channel.Results show that the presence of vegetation cover on channel wall causes deviation of the Reynolds stress distribution from the linear one under uniform flow condition.It is also noticed that the Reynolds stress distribution is influenced by the aspect rati...     

The influence of El Niño-Southern Oscillation (ENSO) cycles on wave-driven sea-floor sediment mobility along the central California continental margin

Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures.     

大型数据平台搭建技术在地震行业中的应用与研究

依据地震行业业务系统的数据处理和存储需求,提出了数据模型和数据平台建设思路。结合地震行业网中数据平台的建设,在国家中心、区域中心和台站节点分别采用了相应的数据库平台和数据存储平台技术,设计了各类节点的数据备份策略,实现了满足海量数据流高效运行的大型数据平台。     

恭城—栗木断裂带的应变特征与变形环境探讨

通过系统的有限应变测量与差异应力估算,探讨了恭城—栗木断裂带的应变特征与变形环境,以其推动该断裂带的研究向更深层次发展。结果表明：①付林指数K的变化范围为0.32～1.67;应变主轴平均方位为276°∠21°,与断裂带的整体逆冲方向基本一致;断裂带的平均应变程度为2.26～3.00,属中等应变程度;断裂带的应变类型属压扁型应变与单剪型平面应变的一种复合叠加类型。②断裂带的差异应力值为40～80 MPa,变形深度小于10 km,属半脆性—半韧性的变形域。③断裂带的应变特征与变形环境及宏观构造样式基本吻合。     

Effect of Initial Stress Conditions on the Threshold Shear Strain of Nanjing’s Saturated Fine Sand

By using GDS dynamic hollow cylinder torsional apparatus, a series of cyclic torsional triaxial tests under complex initial consolidation condition are performed on Nanjing saturated fine sand. The effects of the initial principal stress direction α0, the initial ratio of deviatoric stress η0, the initial average effective principal stress p0 and the initial intermediate principal stress parameter b0 on the threshold shear strain y, of Nanjing saturated fine sand are then systematically investigated. The results show that y, increases as η0, P0 and b0 increase respectively, while the other three parameters remain constant. α0 has a great influence on y,, which is reduced when α0 increases from 0° to 45° and increased when α0 increases from 45° to 90°. The effect of α0 on γt plays a leading role and the effect of η0 will weaken when α0 is approximately 45°.