Scalar fluxes from urban street canyons. Part I: Laboratory simulation

Flow over urban surfaces depends on surface morphology and interaction with the boundary layer above. However, the effect of the flow on scalar fluxes is hard to quantify. The naphthalene sublimation technique was used to quantify scalar vertical fluxes out of a street canyon under neutral conditions. For an array of eight canyons with aspect ratio H/W=0.75 (here, H is building height and W is the street width), increased flux was observed in the first two or three canyons for moderate and low roughness upstream. This is consistent with predictions of the length scale for initial adjustment of flow to an urban canopy. The flux was constant after the initial adjustment region and thus dependent only on local geometry. For a street canyon in the equilibrium part of the array, each facet of the street canyon was coated with naphthalene to simulate scalar release from street, walls and roof, to evaluate the effect of street canyon geometry on fluxes for H/W=0.25, 0.6, 1 and 2. Fluxes from the roof and downstream wall were considerably larger than fluxes from the street and upstream wall, and only the flux from the downstream wall exhibited a simple decrease with H/W. For each H/W there was a monotonic decrease between downstream wall, street and upstream wall transfer. This suggests that flow decelerates around the recirculation region in the lee of the upstream building, i.e. a recirculating jet rather than a symmetrical vortex. The addition of a second source within the street canyon resulted in reduced fluxes from each facet for H/W>0.25, due to increased concentration of naphthalene in the canyon air.     

作用在海洋移动式平台上的风倾载荷

本文在归纳国内外对作用在海洋移动式平台风倾载荷的研究文献的基础上，分析了目前船级社的规范中风载荷计算方法中的几个问题。本文介绍了作者编制的风倾力臂横截曲线计算程序，并给出了计算实例     

地下气库(LPG)洞室围岩稳定性数值分析

地下气库的围岩稳定性关系到地下气库的安全与使用。影响地下洞室稳定的因素很多,解析法虽然可以得到精确解,但是只能针对圆形洞室。而数值计算方法可以计算各种情况下围岩的应力、变形、塑性分布等情况。利用有限元分析软件分析了洞室形状对围岩稳定性的影响,确定了合理的洞形;讨论了围岩应力应变随深度的变化规律,以及不同的支护类型对围岩变形的影响,确定了经济合理的支护类型。最终为该地质条件下的洞室围岩稳定设计提供了依据。     

地铁盾构线路穿越运营隧道的沉降影响

针对地铁修建过程中穿越运营地铁线路时需动态监测隧道的安全状态问题,该文以深圳地铁某区间盾构隧道穿越过程为例,利用测量机器人,以0.5~2h/次的频率对监测点进行全程观测。断面数据分析表明:在下穿过程中,上下隧道间距在1.823和6.028m之间存在某个临界距离,当小于这个临界值时,穿越时要注意隆起对既有隧道,尤其是对道床轨面沉降差的影响;盾构机从进到出1号线左、右线隧道引起的沉降量各占相应穿越线路总沉降量的50%~86%,盾构穿越已有隧道的过程应增大观测频率,及时进行二次注浆;总的监测断面布设数量不受上下隧道间距的影响,距离上、下隧道正交断面10m外的相邻断面只需布设两个观察点。从而实现最优点位布设密度和监测频率,节约施工成本。     

全站仪参考弧在坑道测量中的应用

在坑道施工中,坑道中弯道的放线通常采用传统的偏角法,但偏角法放样的流程较烦琐,且误差累积较大,而全站仪的参考弧程序可以很好地解决上述问题。坑道施工中,采用参考线(弧)放样快速准确地进行开挖、支护及被复的定位,可以提高效率,保证工期及质量。本文以徕卡TPS800全站仪参考弧程序为例,从参考弧的定义方法、使用方法等方面,对参考弧程序进行了探讨、分析,以起到抛砖引玉的作用。     

Preliminary Analysis of Seismic Risk in Taiwan Strait and Study on Feasibility of Construction of Tunnel Across the Strait

The collision between Eurasian and Pacific plates along the eastern margin of the Asian continent resulted in formation of a series of island-arcs, one of which is the Taiwan Island-arc, and the Taiwan Straits is a foreland basin in the continent-arc collision zone. The Quaternary fine-grained sediments occur evenly in the upper part of the basin, and the Pliocene deposits in the lower part. The stepped faults run in the deposits, indicating that the tectonic movement tended to weaken after the Pliocene. Strong seismic zones of Taiwan Island released large amount of plate overthrust-collision compressive stress and have their screen and prevention roles for the straits. Only the intersections between offshore NW-trending transform-like faults and seashore NE-trending faults on the southern and northern terminations of the Island are prone to strong earthquakes. The possibility of occurrence of M ≥ 6 earthquake should be very low in the area for the planned future tunnel. Moreover, the seismic intensity is rapidly attenuated from the surface downward. Thus, the seismic intensity for the tunnel under the seabed will be much lower. In seismotectonic view, the construction of tunnel is feasible.     

Wind tunnel simulation of the effects of freeze–thaw cycles on soil erosion in the Qinghai–Tibet Plateau

Intense freezing and thawing actions occur in the Qinghai–Tibet Plateau because of its high elevation and cold temperature. The plateau's unique environment makes it easy to generate wind erosion under dry, windy weather conditions, resulting in the emergence of desertification. As a major form of freeze–thaw erosion, freeze–thaw and wind erosion is displayed prominently on the Qinghai–Tibet Plateau. Therefore, in this study, soil samples were collected from the surface of the plateau to undergo freeze–thaw and wind erosion simulation experiments. Results show that wind erosion strength increases with an increasing number of freeze–thaw cycles, water content in the freezing–thawing process, and the difference in freeze–thaw temperatures. Therefore, in the conditions of water participation, the main reason for the freeze–thaw and wind erosion in the Qinghai–Tibet Plateau is the damage to the soil structure by repeated, fierce freeze–thaw actions, and the sand-bearing wind is the main driving force for this process. The research results have theoretical significance for exploring the formation mechanism of freeze–thaw and wind erosion in the Qinghai–Tibet Plateau, and provide a scientific basis for freeze–thaw desertification control in the plateau.     

重庆南山隧道工程涌水隐患研究

运用地下水动力学法计算隧道涌水影响半径,采用地下水动力学法、古德曼经验公式,经验解析法公式计算涌水量,并比较中梁山铁路隧道修建对漏水的影响,得到以下结论:(1)从涌水半径来看,南山隧道涌水半径(642m)比轻轨隧道涌水半径(727m)小。轻轨隧道高程较南山隧道高程低,因此轻轨隧道拦截了一部分集雨面积,使得南山隧道涌水量降低。(2)科斯加科夫渗透入量法结果与调查结果更为接近。(3)涂山湖大湖漏水的影响远远小于小湖。这可从中梁山隧道引起的漏水得到启示。涂山湖在南山隧道的影响半径之内,其中大湖因为泥沙淤积时间长,因此受影响小,涂山湖的小湖因为成湖时间不长,因此受影响大。同时要注意南山隧道漏水,浮托力消失,在隧道漏水影响范围内注意岩溶塌陷的隐患。在积极面对南山隧道漏水可能存在的隐患之外,还应该调动群众的力量,将损失影响减少到最小。     

盾构地铁隧道区间在地震作用下的三维动力时程响应分析

地铁已成为城市地下空间结构和轨道交通网络的重要组成部分。为预估和降低地震灾害的影响,以西安盾构地铁区间隧道为例,建立了地铁隧道区间三维计算模型,进行三维抗震时程响应分析。采用粘弹性局部人工边界模拟地基结构的半无限性,利用不同超越概率水平下的地震动参数作为参考,考虑相位随机性影响,拟合地震动时程样本,建立了地基与结构相互作用的三维有限元模型。计算结果表明,地震发生时,顶部、底面、侧面、以及联络通道处虽产生变形影响,但均在规范规定范围内;位移时程曲线、位移分布云图、拉压应力云图清楚显示区间结构在地震持续时的抗震情况,数据表明结构最不利位置在联络通道处,而内力和变形均满足规范安全要求。