Pile driving by numerical cavity expansion

A cavity expansion procedure for the simulation of pile driving is presented and assessed in this paper. The analysis uses a non-linear finite-element model and the penetration of the pile into the soil is simulated by a radial opening of the soil around the pile. The case of a pile advanced by expansion will be compared to a similar pile subjected to computational driving (referred to, respectively, as ‘expanded’ and ‘driven’ piles for convenience). The state of stress and deformation, and the evolution of pore-water pressure in the soil will be monitored for the expanded and driven piles. Further computational driving will be applied to both cases and the pile response and soil resistance will be compared. The computational cost of advancing the pile by expansion will finally be investigated. Copyright © John Wiley & Sons, Ltd.     

抗液化排水刚性桩沉桩过程的土压力响应

抗液化排水刚性桩是一种将刚性桩与竖向排水体相结合的新桩型。基于某建筑桩基工程,开展了抗液化排水刚性桩和不含排水体的普通刚性桩的沉桩对比现场试验,采用了动态土压力传感器实时监测沉桩过程中桩周土体内产生的土压力响应,对比了排水桩与普通桩沉桩对桩周土体水平方向应力及有效应力影响的差异。试验结果表明：抗液化排水刚性桩能够有效减小沉桩过程对桩周深部可液化土体的扰动,在桩身近侧（距桩心0.6 m）深部埋深（-15 m）位置,排水桩的水平土压力响应峰值仅为普通桩的1/4;排水桩能够有效降低沉桩对可液化土层有效应力的影响,使桩周土体更加稳定;在单次沉桩过程中,对于浅部埋深（-5 m）,排水桩对桩周土压力峰值的影响作用较小,对于存在可液化土层的深部埋深（-10、-15 m）,排水桩对土压力峰值的有效影响半径可达4倍桩径。现场试验数据为抗液化排水刚性桩的桩间距选择提供了有力的设计参考依据。     

黄河沙漠宽谷段水沙变化特征及驱动因素

根据定位观测、第一次全国水利普查、遥感影像解译的数据,利用MWP、双累计曲线、水土保持分析法、数学模拟等方法,分析了黄河上游水沙变化特征,评估了多元驱动因素对2000-2012年黄河下河沿-头道拐沙漠宽谷段水沙变化的贡献率。结果表明:与20世纪70年代以前的基准期相比,2000年以来径流量、输沙量同步减少,水沙关系也发生变化,单位径流量的输沙量明显减少;沙漠宽谷段径流量减幅沿程不断增加而输沙量减幅沿程变化不大,水沙年内分配较基准期发生倒置,来沙系数不断减小;灌区引水引沙、水土保持措施、水库拦沙、支流来水来沙、水库调蓄及河道冲淤是沙漠宽谷段水沙变化的主要影响因子;经济社会发展用水对沙漠宽谷段径流量减少的作用最大,贡献率为81%,其次是水库蓄泄量,占15%以上;水库拦沙对头道拐输沙量减少的贡献率最大,占41%,其次是支流水土保持措施,贡献率约占13%,入黄风沙减少的贡献率并不大,约为6%,而河道淤积量、灌区引沙量较基准期都是减少的,贡献率分别约为-41%和-8%;近10多年来降雨等自然因素对水沙变化的作用相对不大,起主要作用的是水库运用、水土保持、经济社会发展等人类活动因素。     

Sediment yield of the lower Tana River,Kenya, is insensitive to dam construction: sediment mobilization processes in a semi‐arid tropical river system

Dam construction in the 1960s to 1980s significantly modified sediment supply from the Kenyan uplands to the lower Tana River. To assess the effect on suspended sediment fluxes of the Tana River, we monitored the sediment load at high temporal resolution for 1 year and complemented our data with historical information. The relationship between sediment concentration and water discharge was complex: at the onset of the wet season, discharge peaks resulted in high sediment concentrations and counterclockwise hysteresis, while towards the end of the wet season, a sediment exhaustion effect led to low concentrations despite the high discharge. The total sediment flux at Garissa (c. 250 km downstream of the lowermost dam) between June 2012 and June 2013 was 8.8 Mt yr^‐1. Comparison of current with historical fluxes indicated that dam construction had not greatly affected the annual sediment flux. We suggest that autogenic processes, namely river bed dynamics and bank erosion, mobilized large quantities of sediments stored in the alluvial plain downstream of the dams. Observations supporting the importance of autogenic processes included the absence of measurable activities of the fall‐out radionuclides ⁷Be and ¹³⁷Cs in the suspended sediment, the rapid lateral migration of the river course, and the seasonal changes in river cross‐section. Given the large stock of sediment in the alluvial valley of the Tana River, it may take centuries before the effect of damming shows up as a quantitative reduction in the sediment flux at Garissa. Many models relate the sediment load of rivers to catchment characteristics, thereby implicitly assuming that alterations in the catchment induce changes in the sediment load. Our research confirms that the response of an alluvial river to external disturbances such as land use or climate change is often indirect or non‐existent as autogenic processes overwhelm the changes in the input signal. Copyright © 2015 John Wiley & Sons, Ltd.     

兰新第二双线铁路防风明洞实验段风荷载数值模拟研究

介绍了高速铁路防风明洞的基本作用及设计方法;利用计算流体动力学原理中的数学模型及控制方程,对兰新第二双线铁路防风明洞大风作用下的风荷载进行了分析;通过计算工况的假定以及边界条件的合理设定,采用有限体积法建立防风明洞数值分析模型,并模拟计算了平地路段、浅路堑地段和路堤地段三大类工况和70、60、50、40m/s4种风速情况。研究结果表明：①开孔情况下,明洞各部位所受风荷载随着风速增大而增大;②明洞迎风侧均为正压,平地地段与路堤地段所受正压较接近,最大值出现在风速为70m/s时,迎风边墙正压为3202Pa;③明洞拱顶及背风侧均为负压,浅路堑地段所受负压最大值出现在风速为70m/s时,拱顶负压为-3550Pa;④各地段背风侧所受负压均小于-1500Pa,背风墙脚与背风边墙受力基本相同;⑤各地段各风速情况下,拱顶处负压均为最大;⑥开孔情况下的明洞各部位风荷载,普遍小于不开孔情况;⑦明洞开孔附近有回流风速,并随着外界风速增大而增大。     

中国石油资源空间流动的驱动机制分析

采用重心分析方法、指示克里金内插方法和空间相关系数,探讨了中国石油资源空间流动的驱动机制,结果表明：① 多数年份内,汇地系统重心演变受经济发展的影响更大;而2003 年以后经济重心对源地系统重心的影响也在逐渐加强。② 从源地系统空间相关分析来看,石油生产-进口量的区域差异,决定了源地系统与国内油田和国内油田-石油进口港（口岸） 的空间相关程度;而石油流动要素的空间分布及演变,对空间相关系数的数值变化产生一定影响,这使得源地系统在1985 和1995 年主要由单一国内油田驱动机制所决定,在1999、2003 和2009 年则由国内油田-进口石油港（口岸）的双重驱动机制所决定。③ 对汇地系统来说,国内炼厂的资源需求是汇地系统空间格局演变的重要驱动力。     

城市旅游驱动力的转化及其实践意义

本文旨在探索城市旅游驱动力的转化问题,以从一个侧面阐释改革开放以来中国城市旅游目的地相对变化的原因。在一般分析的基础上,着重以大连、深圳和珠海三个较具代表性的城市为例,对城市旅游驱动力的转化过程做个案剖析,并得出了三点结论:第一,每个城市旅游目的地的发展都存在相应的主导驱动机制;第二,城市旅游的主导驱动机制因时因地而不同;第三,城市旅游要实现可持续发展就必须跟随外部环境的变化(主要是需求结构的变化),适时转变自己的主要驱动力。     

黄土高原发展过程中的五大转折

1 Introduction W hatim portanttransform ations have taken place during the form ation ofthe Loess Plateau in China? Research on this problem has especially im portantscientific significance forus to learn ofthe evolution oftheLoessPlateau and predictthe f…     

A new look at the phenomenon of offshore pile plugging

Abstract

Open‐pipe piles are widely used for offshore structures. During the initial stage of installation, soil enters the pile at a rate equal to the pile penetration. As penetration continues, the inner soil cylinder may develop sufficient frictional resistance to prevent further soil intrusion, causing the pile to become plugged. The open‐ended pile then assumes the penetration characteristics of a closed‐ended pile. The mode of pile penetration significantly alters the soil‐pile interaction during and after installation. This affects the ultimate static bearing capacity (mainly in granular materials), the time‐dependent pile capacity (in clays), and the dynamic behavior and analysis of the piles.

Following a summary demonstrating the effects of pile plugging, a review of the common view of offshore pile plugging is undertaken. The interpretation of plugging by referring to the average plug length has led to the erroneous conclusion that in most piles significant plugging action does not occur.

Establishment of an analogy between soil samplers and open‐ended piles enabled correct identification of plugging by referring to the incremental changes in plug length. Examination of case histories of plugging of offshore piles revealed that beyond a certain penetration depth‐to‐diameter ratio, most piles are plugged.     

Analyzing land-use change in farming-pastoral transitional region using autologistic model and household survey approach

Land change science （LCS） strives to understand and model land-use change, which will further advance the understanding of multiple issues in the socio-ecological systems. Based on GIS/RS techniques, autologistic model, and household survey method, this study investigated major land use changes and their causes from 1978 to 2008 in Uxin Banner （county-level）, Inner Mongolia in China and then developed an understanding of the relationships between household livelihood and land-use pattern. Results showed that cultivated land increased from 1988 to 2000, and leveled offafter 2000. Built-up land increased stably for the period 1978 2008. The change of grassland and bare land differed among the three periods. From 1978 to 1988, grassland increased by 23.3%, and bare land decreased by 20.48%. From 1988 to 2000, bare land expanded by 1.7%, but grassland declined by 1.3%. From 2000 to 2008, an increase in grassland area by 1.8% was observed, but a decrease in bare land area by 9.0% was witnessed. The autologistic models performed better than logistic models as indicated by lower Akaike Information Criterion （AIC） values. Factors associated with human activities significantly correlated with the change of cultivated land, forest land, grassland, and built-up land. The produce prices and extensive cultivated land use are major issues in the farming area. This study suggests that completing land circulation systems and maintaining the stability of price are effective solutions. By contrast, reclamation and overgrazing are major concerns in the pastoral areas. Implementing environmental policies effectively, transferring population out of rural pastoral areas, and developing modem animal husbandry are effective ways to address these issues.