应力主轴往返旋转条件下砂土变形规律试验研究

在已有空心圆柱扭剪仪上开发新的控制模块,实现应力主轴以任意初始方向角开始并以任意角度幅值进行往返旋转。在此基础上,对丰浦砂开展系列应力主轴往返旋转试验。试验结果表明:1应力主轴往返旋转角度幅值和初始主应力方向角均对砂土变形有不可忽视的影响;2不同于应力主轴连续循环旋转的情形,应力主轴往返旋转时砂土由于"楔入效应"可能出现体胀。     

Significance of boulder shape,shoreline configuration and pre-transport setting for the transport of boulders by tsunamis

Research on tsunami-induced coarse-clast transport is a field of rising interest since such deposits have been identified as useful proxies for extreme-wave events (tsunamis, storm waves) that provide crucial information for coastal hazard assessment. Physical experiments are, beside in-situ observations, the foundation of our understanding of how boulders are transported by tsunamis and provide clues to the development of empirical equations and numerical models describing the processes and fundamental mechanics. Nevertheless, investigating tsunami-induced boulder transport is a comparatively young discipline and only a few experimental studies focusing on this topic have been published so far. To improve the knowledge on nearshore tsunami hydrodynamics, physical experiments utilizing real-world boulder shapes have been carried out simulating three different shore types in a wave flume. Crucial insights were gained into boulder transport hydrodynamics and data resulting from the experiments were analysed in an empirical, statistical, quantitative and qualitative manner. The regular cuboid boulder – one of the specific shapes used in the experiments – showed the longest transport distances compared to a complex, natural boulder and a flat cuboid boulder, but also significant fluctuations regarding the total transport distance. The experiments indicate a strong influence of the shore shape on boulder transport behaviour. Experimental setups of increased mean transport distances also led to a higher spreading of results. This spreading was further amplified between the idealized-shaped cuboid and the complex-shaped boulder, which is associated with a lower drag coefficient. Due to the highly sensitive boulder reaction to divergent experimental setups, the need to recognize boundary conditions overcoming commonly considered parameters (e.g. roughness or Flatness Index) in field studies and numerical models is underlined. Beside the strong influence of initial boulder submergence and alignment, both the boulder shape and shore type influence the boulder transport pattern, increasing the total transport distance by more than 350% in some cases. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Erosion characteristics of loess tunnels on the Loess Plateau: A field investigation and experimental study

Loess tunnels are a common geo-hazard in the Loess Plateau and not only cause considerable soil and water loss, but also aggravate and even induce the occurrence and development of other disasters such as ground fissures, mudflows, collapses, and landslides. To date, research on the hydrological characteristics and erosion behaviour of loess tunnel systems has focused on field investigation data and limited river basin observation data, whereas field test information and data are very scarce. In this study, field surveys, observations, field scouring experiments, and laboratory-based sediment percentage tests were conducted to analyse the erosion characteristics, spatial distribution, and hydrological characteristics of a large-scale loess tunnel system in the hilly Loess Plateau southeast region of northern China. The results showed that the loess tunnel erosion exhibited periodicity. Tunnel erosion in each period shows a similar erosion process, that is, thin-layer water flow erosion and lateral expansion, tunnel wall collapse and deposit due to the loss of support from the lateral erosion, and erosion and transport of deposits by water flow. Waterfall erosion, lateral erosion, headward erosion, and the resulting collapses were the main forms of tunnel erosion. Besides this, the base level of erosion significantly affects the erosion characteristics of the loess tunnel. The hydrological characteristics during field scouring experiments exhibited three different stages: a lag effect, attributed to the temporary loss of water velocity in the first stage; small water flow fluctuations in the second stage; and an increase in total seepage loss with increased water injection flow in the third stage. The erosion rate was positively correlated with the flow quantity. The results of this study not only provide valuable reference data for research on the mechanism and velocity of erosion events in loess, but also provide a theoretical basis for the prevention of loess tunnel disasters in engineering construction. © 2020 John Wiley & Sons, Ltd.     

小高宽比隔震结构双向输入振动台试验研究及数值分析

本文对高宽比为2.5的普通钢框架隔震结构模型,采用多种不同的地震动进行了水平向和竖向双向地震输入的振动台试验研究,并利用时程分析法完成了模型结构地震反应的数值分析。试验结果表明,高宽比隔震结构在水平向和竖向双向输入情况下隔震层基本上不会进入拉伸应力状态,即使在9度大震E l Centro和Hach inohe波输入时,隔震层支座仍以受压为主。因此小高宽比隔震结构在场地好的情况下,结构不会出现倾覆,仅需考虑软弱土场地的受拉情况。试验发现竖向地震输入对小高宽比隔震结构水平反应的影响相当小;对小高宽比隔震结构进行水平向地震反应分析时,可以忽略竖向地震对结构的影响。     

四川盆地长宁地区海相页岩吸附气含量演化特征 ——以N201井五峰组—龙马溪组一段为例

吸附气是页岩气的重要赋存形式和组成部分.为了明确四川盆地长宁地区五峰组—龙马溪组一段页岩在埋藏过程中吸附气含量的演化规律,利用页岩等温吸附实验、钻井现场解吸和测井综合解释资料,建立了页岩吸附气含量与地层温度、地层压力、页岩TOC等主要影响参数的多元回归数学公式,结合典型评价井(N201井)的埋藏史、热史,对不同地质时期...     

树木年轮密度实验方法及其在内蒙古准格尔旗树轮研究中的应用

在介绍树木年轮密度实验方法基本原理、国内外研究现状以及详细的实验方法和流程的基础上,建立了内蒙古准格尔旗油松树轮宽度年表,以及早材、晚材、最大、最小四个密度年表。年表之间相关分析表明树轮密度比宽度包含更多更复杂的气候环境变化因子。通过树轮密度年表与气象资料相关分析发现,准格尔旗树轮密度年表与该地区全年降水量之间有很好的相关性,早材密度和最小密度与降水量之间呈负相关关系,晚材密度和最大密度与降水量之间呈显著的正相关关系。无论正、负相关关系,均能够从树木生理角度予以合理解释。     

卫星资料的非线性反演同化与一次强降水预报试验

利用地球同步气象卫星红外资料,通过优选BP人工神经网络和最优拟合回归这两种非线性方法,建立了反演宁夏大气相对湿度场的数学模型。反演湿度场经过变分同化与质量控制后,代入中尺度数值预报模式MM5,对一次突发性强降水过程进行了预报试验。结果表明,使用该资料后,数值预报模式对这次突发强降水过程的预报能力明显提高,模式输出产品具有预报指示意义,spin-up问题得到了一定程度的改进。     

不同参数化方案对长江中游汛期降水模式预报试验

利用中尺度模式多个物理过程组合成不同预报方案,对长江中游汛期降水预报进行了对比试验.试验结果表明,使用不同物理过程参数化方案对长江中游汛期降水的预报效果存在差异,这种差异随降水预报量级的提高而愈加明显;而就试验而言,Grell积云对流参数化方案与Blackadar边界层参数化方案的组合预报效果相对较好;就单个降水个例而言,预报效果相对好的参数化方案存在不确定性,集合平均预报相对稳定且优于大多数方案,其对降水评分的改进尤其体现在暴雨以下量级的预报中.     

水体对气温观测影响的试验分析

2011年项目组设计了浙江省大型水体观测试验方案,选择较大水体,在其上、下风方向特定距离处布设自动气象站,同步观测各站气温,研究气温受水体影响的量化规律。结果表明,水体对周边陆地有白天降温、夜间增温效应,且离水体越近,这种效应越明显;夜间升温效应比白天降温效应显著,3—5月白天降温效应比1—2月明显;在一天中正午的降温影响最大;2km2的水域对下风向100m范围内温度观测有明显影响,100m以远影响不明显。该研究对量化水体影响的范围和量值进行了有益的探索,为气象站科学选址提供了依据。     

川藏铁路复杂地层水平孔钻探护壁堵漏研究与应用

川藏铁路地处青藏高原东南部,由于构造活动发育,岩体松散破碎,裂隙及承压水发育,勘察这些地层过程中时常发生塌孔、掉块卡钻、冲洗液漏失等复杂情况。本文针对隧道出口段地层设计的定向水平孔,在钻进过程中出现孔壁失稳和冲洗液漏失等问题,通过分析孔内地层特征、漏失情况,提出了适宜的冲洗液体系。随后,进行正交实验快速得到护壁堵漏材料掺量的最优组合,并通过后续的工程实践结果验证并改进,使得冲洗液工艺效果明显。优化配方后的冲洗液,能够大幅度减少孔内事故,有效地促进勘探进度,取得了显著的经济效益和社会效益。