Wind tunnel experiments of air flow patterns over nabkhas modeled after those from the Hotan River basin,Xinjiang,China(Ⅱ):vegetated

This paper examines the results of wind tunnel experiments on models of nabkha, based on those studied in the Hotan River basin. Semi-spherical and conical models of nabkhas were constructed at a ratio of 40:1 in light of the on-site observation. Artificial vegetation of simulated Tamarix spp. was put on top of each model. Parameters of the shape, including height, width, and diameter of vegetated semi-spherical and conical nabkha, were measured in the Hotan River basin. Wind tunnel experiments on the semi-spherical and conical nabkha used clean air devoid of additional sediments at five different wind speeds (6–14 m/s) to study the influence of vegetation on airflow patterns. Results of the experiments indicate that vegetation at the top of the nabkhas enhances the surface roughness of the sand mounds, retards airflow over the sand mounds, reduces airflow energy, eliminates erosional pits occurring on the top surface of non-vegetated sand mounds and enhances the range of influence of the vortex that forms on the leeward slope. Vegetation changes the airflow pattern upwind and downwind of the sand mound and reduces the transport of sand away from the nabkha. This entrapment of sediment by the vegetation plays an important role in sustaining the nabkha landscape of the study area. The existence of vegetation makes fine materials in wind-sand flow to possibly deposit, and promotes nabkha formation. The imitative flow patterns of different morphological nabkhas have also been verified by on-site observation in the river basin. __________ Translated from Journal of Desert Research, 2007, 27(1): 15–19 [译自: 中国沙漠]     

上海长江隧道工程岩土地质与施工沉降控制

上海长江隧道工程穿越长江河口,工程施工面临诸多技术难关。分析评价了所在区域的水文与岩土地质特征,阐述了工程施工特点及地面沉降控制技术。     

Measurement of sand creep on a flat sand bed using a high‐speed digital camera: Mesoscopic features of creeping grains

The characterization of aeolian sand creep motion remains incomplete. In this study, a top‐view imaging system was constructed in a wind tunnel experiment to record sand creep motion on a flat sand bed. In addition, a set of ‘mesoscopic’ parameters was defined based on the creep trajectory that was reconstructed by a particle tracking algorithm. Statistical results show that the parameters representing the lifespan of the creep motion follow a lognormal distribution, whereas those representing the sideways grain motion deviate from the lognormal distribution. As the wind velocity increases, the sideways motion is strengthened and the lifespan of the creep motion is shortened, indicating a stronger transition from creep to saltation. Furthermore, under a ‘pure rolling’ hypothesis, the creep trajectory can be transformed into two numbers of rolling cycles from the perspectives of space and time. The ratio of the two numbers is useful in identifying the specific mode of the creep motion.     

铁路隧道围岩监控量测信息化管理系统研究

铁路隧道围岩监控量测是保证隧道施工安全的重要手段之一,针对现有的隧道监控量测技术存在"干扰因素多、数据处理慢、反馈不通畅"的弊端,结合现代网络通信技术、自动化控制技术、现代数据库技术的高速发展,自主研发了"铁路隧道围岩监控量测信息化管理系统"。通过该系统,测量人员可使用智能移动终端设备(PDA手簿、手机)通过蓝牙来操控全站仪量测数据,同时利用移动网络实时把量测数据传送至主服务器,主服务器对数据自动处理后进行相应分析,当出现超警值时及时向相关人员发布预警信息,相关人员根据自身授权可利用手机访问主服务端,随时掌握隧道监控量测情况。该管理平台可自动实现对某条铁路乃至全国铁路隧道围岩监控量测,具有"数据可靠、传递高效、预警及时、管理简洁"的特点,实现了对隧道监控量测的信息化管理。     

TBM组装洞岩壁梁岩台缺陷处理技术研究

TBM组装间岩壁梁在施工过程中,由于受地质条件及人为因素影响,导致TBM组装间岩壁梁在施工过程中发生无法成型或岩壁梁岩台存在缺陷,对后序岩壁梁上部吊车轨道安装埋下严重的安全隐患。以吉林引松供水总干线三标TBM组装间岩壁梁为研究背景,对岩壁梁缺陷处理进行了详细分析和研究,提出了岩壁梁岩台缺陷的处理技术,并对研究结果进行了验证,对类似工程有一定的参考价值。     

预应力锚索孔内扩孔工艺的研究

预应力锚索技术是进行滑坡治理、边坡锚固等地质灾害治理中的常用技术,传统锚索内锚头自由地搁置在内锚固段孔内,在无预应力状态下进行内锚固段注浆;而自承载式预应力锚索在有预应力的状态下注浆,有利于充分发挥浆体材料及岩体的力学性能。对于中硬以下碎裂岩层,采取在锚固段进行扩孔,在扩孔段安装自承载式锚索承载体,承载体扩体后,利用孔壁的摩擦力和扩孔段端部的承载力进行初张拉锁定。因此,研究了一种适用于中硬以下岩层（抗压强度＜30 MPa）且适合使用空气潜孔锤钻进工艺的扩孔钻具和钻孔工艺,通过进行扩孔钻进室内试验,结果表明,该扩孔钻具和工艺能够实现在锚固段进行分段扩孔。     

地铁盾构穿越建筑物施工位移的数值分析

在总结地铁盾构施工的控制原则以及盾构通过临近群桩的动态预测方法的基础上,结合武汉地铁的设计,采用数值模拟方法对地铁盾构穿越汉口火车站区时地面及建筑物桩群进行模拟,分析了盾构穿越一般底层和穿越群桩基础两种不同的情况的位移情况,从而对盾构隧道对城市地面以及建筑物的影响做出评价,提供了盾构穿越建筑物施工安全控制的建议。     

大断面浅埋黄土隧道锚杆作用效果的试验研究

黄土隧道系统锚杆的作用效果问题一直是争论的焦点。结合正在修建的郑州-西安铁路客运专线大断面黄土隧道,采用现场对比试验方法对系统锚杆作用效果进行研究。为了使试验结果有可比性,选取试验条件基本相同的贺家庄隧道洞身段作为试验段,分别设置有系统锚杆段40 m和无系统锚杆段40 m。对比试验的内容包括：拱顶下沉、拱脚下沉、水平收敛、围岩压力、初支钢架应力、锚杆轴力等。试验结果表明,有系统锚杆段比无系统锚杆段的拱顶沉降大40 %左右、水平收敛大25 %左右,两者的土压力和钢架应力相差不大;锚杆轴力较小,且拱部受压。经综合分析认为,拱部锚杆的支护效果不明显,取消拱部锚杆可减少施工工序,加快隧道初期支护断面及早封闭,能更好地控制支护沉降与变形,并节约工程投资。     

深埋TBM施工输水隧洞结构的三维仿真分析

考虑围岩材料的弹塑性,引入有限元程序中的生死单元,建立了可模拟隧洞开挖过程的围岩三维仿真模型,求得了深埋隧洞围岩变形的分布模式;并在此基础上,采用接触模型和库仑摩擦模型模拟管片接头的非线性连接作用,建立了TBM隧洞管片结构的三维仿真模型,分析在不同工况（施工期、运行期、检修期）、不同围岩类型以及不同衬砌时机下管片的应力应变特征,为输水隧洞的适时衬砌和安全运行提供了依据。     

盾构法隧道施工阶段管片的力学分析

盾构隧道衬砌管片在施工阶段处于复杂的受力状态,易出现局部破损现象。阐明了盾构施工阶段管片的受力特点,对其常见的局部破损现象及产生原因进行了总结与分析,在此基础上构建了施工阶段的管片力学模型,即一端固定、一端简支的受力构件。以某盾构工程施工参数为例,运用有限元方法实现该力学模型,按不同工况对其进行了数值模拟,并与现场实测结果进行了对比分析。研究表明：盾构施工阶段,衬砌管片会在第5～7环之间产生局部破损,与现场出现的管片破损部位十分接近;千斤顶推力的大小、倾角及偏差是导致施工阶段管片局部破损的主要原因,并给出了盾构施工阶段减轻管片破损的一些建议。