不同地连墙插入深度下承压含水层减压降水对既有隧道的影响

当基坑需进行未截断条件下的承压含水层降水时,承压水抽降产生的影响范围远大于基坑开挖的影响范围,其对基坑外既有隧道的影响值得重视。进行了承压层减压降水对既有盾构隧道影响的有限元仿真模拟,并分析了采用地下连续墙插入承压含水层时,不同插入深度对隧道变形的影响,结果表明：随着地下连续墙插入承压含水层深度的增加,直至完全截断承压含水层,既有隧道沉降逐渐减小,但受地下连续墙变形的影响,隧道在水平方向仍存在较大位移。因此,当既有隧道与减压井净距较小时,即使承压含水层被完全截断,也应重视减压降水对隧道水平方向变形造成的影响。此外,长期减压降水将会引起隧道产生可观的沉降。因此,应尽量避免承压含水层未被完全截断条件下进行长期减压降水。     

辐射井技术在北京地铁五号线降水中的应用

本文介绍了辐射井降水技术的新突破，特别是双壁反循环水平井施工及沉井和锚喷倒挂壁竖井施工工艺的引进与改进，成功解决了砂层水平井施工易产生“流砂”和施工场地狭小的难题。最后介绍了该技术在北京地铁降水中的应用，以及施工中出现的问题与处理的经验总结。     

邻近多条地铁的基坑降水技术

对地基沉降、位移极为敏感的邻近地铁隧道地区施工基坑降水工程时,为控制承压水采取回灌措施,既要克服基坑底板由于承压水造成基坑突涌等危害,又要减少基坑降水施工时对周边建（构）筑物造成的危害。通过邻近地铁2、4和9号线的上海盛大深基坑降水回灌工程成功实例,探讨邻近多条地铁区间隧道的超深基坑降水技术。     

南京长江隧道到达井基坑降水设计与施工

南京长江过江隧道梅子洲明挖段基坑主要包括引道段和盾构到达井,基坑规模大,地下水丰富,地质条件复杂,使得该基坑降水成为整个过江隧道众多关键技术之一。本次在抽水试验基础上设计了基坑降水方案,考虑到周边环境简单,采取了＂坑外降水为主,坑内降水为辅＂的降水方式,实际结果表明：降水方案合理可行,未对周边环境造成过大的影响。     

黑河流域过去40a来降水时空分布特征

对４０ａ来黑河流域降水的时空变化特征进行了分析,在空间上,降水由西北向东南呈现出明显的增加趋势,但平原区和山区,东部和西部之间存在着差异,在纬向上约以９９．５°Ｅ经线为界,降水在水汽补给上存在一定差异,导致流域东,西部降水年内分配具有不同特点,在经向上降水由北向南递增,在东,西部地区,降水随高度的变化有所不同,西部呈线性增加,而东部多为非线性增加,且在海拔２４００～３０００ｍ之间出现最大降水高度带     

Portland市东口混合污水隧道工程项目群创造微型隧道技术记录

Portland市东口混合污水隧道工程项目包括在6英里的内衬直径为22ft的隧道以及7个竖井,60001f的长微型隧道和30001f的开挖铺管工程。KBB公司采用了减少中间竖井的长距离顶进微型隧道施工技术,创造了北关顶管长度的历史记录。     

隧道降水施工对既有市政管线隧道影响研究

针对成都某新建铁路隧道近接下穿既有市政管线隧道的降水施工方案,运用有限差分法和流固耦合理论,分析研究了降水施工过程中,既有市政管线隧道的受力特性及位移变化规律,研究结果表明:距离降水井约50m范围内,地表沉降量变化显著,易发生差异沉降;既有管线隧道初期与二衬结构应力和位移变化及分布规律几乎一致,交叉处界面位移最大,沿隧道纵向向两端逐渐减小且呈对称分布;交叉处30m范围内,初期支护和二次衬砌拱顶纵向应力主要为负值即压应力,仰拱纵向应力主要为正值即拉应力且最大拉应力超过了混凝土的极限抗拉强度。由此可知,降水施工对上部市政管线隧道的影响较大,降水施工前应采取一定的特殊辅助措施,以保证隧道结构安全性。     

盾构辅助常压开仓技术在南宁地铁隧道中的应用

盾构开仓是盾构隧道施工中难以避免的一道工序，结合南宁地铁四号线总部基地站-飞龙路站区间隧道的盾构开仓实践经验，介绍了素桩加降水这一辅助常压开仓技术在南宁地铁隧道中成功应用的实例。在介绍工程应用背景的基础上，详细叙述了辅助开仓方法中素桩及降水施工的技术要点，可为南宁地区盾构开仓方案选择提供指导，也可为类似条件下盾构开仓方案的选择提供借鉴。     

天山乌鲁木齐河流域山区气候特征分析

乌鲁木齐河流域山区的地理特点使其气候特征与平原区不同；气温年变幅小，降水年内分配极不均匀。每年１１月至来年３月在海拔１０００－２４００ｍ处形逆温层。根据不同台站同期年平均降水量分析，天致在海拔１９００ｍ和３５００ｍ左右有两个较大降水带。气温与湿度随海拔的变化在不同高度带内并一不致。６０年代以来，其气温变化较平原地区要不得多，而降水量在减少的同时其变率增加。     

真空管井复合降水技术的试验分析

在基坑开挖工过程中,经常会遇到弱透水性的饱和含水层,普通管井降水技术无法对其进行有效疏干,出现的残留水会对基坑安全造成重大影响,特别是地铁暗挖施工的站体及区间隧道。真空管井复合降水技术的新思路能够彻底改变这一局面,它能有效解决粘性土、饱和粉土和界面残留水的疏干难题,大大降低暗挖结构施工的危险性。     

潘庄区块煤层气U型水平井下套管技术探讨

下入生产套管的煤层气U型井具有产气量高、成本低的优点,逐渐成为潘庄区块煤层气开发的主要井型。潘庄区块煤层埋深一般在500 m以浅,同时要求U型井的水平段在1000 m左右,生产套管的下入成为该区块垂深浅、水平段长的煤层气U型井的技术难题,经过多口井试验,优化钻井轨迹的平滑度,采用原钻具、短螺旋扶正器和生产套管内置钻铤3次划眼,以及严格控制下套管程序,可提高套管一次性下入的成功率,并提高生产效率。     

论龙永煤田坑柄矿区钻孔结构设计

针对龙永煤田坑柄矿区钻进过程中普遍存在的＂硬、漏、塌、涌、斜＂等复杂现象,在多年的实践基础上,摸索出一套适合本区的钻孔设计结构和钻进方法：开孔用φ130mm合金钻头钻至完整岩层,下φ127mm孔口套管,然后用S95mm金刚石钻具将上部硬岩钻穿,至稳定岩层后下φ89mm套管,最后用φ76.5-77.5mm合金金刚石钻头钻至终孔。另外,把S75mm钻具的钻头外径由φ75mm增加到φ77＋0.50mm,一方面可保证经过改扣的φ89mm套管能够继续作为技术套管使用;另一方面也有利于排除岩屑、防止糊钻、缩径卡钻、冲蚀孔壁、降低泵压、减轻抽吸和压裂孔壁造成的钻孔漏水坍塌等故障,更好的起到护壁防塌效果。经统计,该钻孔结构设计将钻孔的平均时效提高到1.68m/h,提高了50%;平均钻效达到626.34m/钻月,提高了21%;单孔最高钻效达到782.27m/钻月。     

Factors affecting site response to multi-directional earthquake loading

This paper presents an investigation into various factors that may affect the ground response to multi-directional earthquake loading, focusing mainly on the behavior of vertical ground motion and its relation with the horizontal counterpart. The factors investigated herein include the intensity of input motion and the associated soil nonlinearity, the location of input motion (rock outcrop versus bedrock), the variation of water table, and the damping property of soil. Influence of these factors is studied on the characteristics of site amplification in both vertical and horizontal directions, the response spectra of vertical and horizontal ground surface motions, the spectral ratio between the two components (V/H) at the ground surface, and the distributions of stresses and strains in the ground. One of the main results is that varying water table can bring about a significant impact on vertical motion and the relationship between vertical and horizontal motions. The surface response spectral ratio (V/H) can largely exceed the rule-of-thumb value of 2/3 at low periods with lowering the water table, but does not appear to be substantially affected at long periods.     

Hydrologic scenarios applied to the agricultural management of the northwest of the Buenos Aires Province,Argentina

The study area is located in the Pampean region of Argentina, in the northwest of Buenos Aires Province, covering about 50,000 km², within an area of great plain with particular hydrologic characteristics, where vertical water movements predominate over horizontal. The objective of this work is the analysis of the relations between different hydrologic scenarios (characterized by the soil water balance and the water table levels) and the yields of soybeans that have been increasing in recent years. It is concluded that water table fluctuations are strongly related to the elements of the local hydrologic balance. On the other hand, the geographic distribution of soybean yields corresponds directly with the values of the soil water reserve during the critical stages of the growth. After dry periods, the lowering of the water table makes access to water from the root zone difficult, and the crop is susceptible to the effects of drought. However, after wetter periods the extra contribution from the water table situated near the surface is favorable for growth, often preventing its deterioration in conditions of drought. Nevertheless, an excessive rise of the water table can produce disadvantages at seedtime and during harvest. The importance of an evaluation of the different scenarios that may have significant implications for agricultural activity is discussed.     

The role of hydrogeological base level in the formation of sub-horizontal caves horizons, example from the Dead Sea Basin, Israel

This paper deals with the hydrogeological relationship between base levels of saline lakes and the formation of sub-horizontal caves. The mechanism presented here suggests that many horizontal cave levels in carbonate sequences are created adjacent to the saline lakes shorelines because of the converging of the groundwater flow above the fresh–saline water interface. The main factors that control enhanced carbonate dissolution and cave formation are high groundwater flow velocities in the shallow phreatic zone during a relative long steady state of the water table. High groundwater flow velocities are evident close to the Dead Sea due to the convergent fast flows above the shallow interface adjacent to the shoreline. The same could prevail in the case of previous paleo-lakes that existed in the basin. The synergetic combination of the above preconditions for enhanced cave formation seems to be responsible for the formation of elevation-controlled alignment of paleo-near shore cave levels in the central and southern (Dead Sea) portion of the study area. These are found on the western fault escarpment and basin margin in different stratigraphic horizons of carbonate lithology. Many of the cave levels can be linked to late Quaternary–Holocene lake levels obtained from dated lake sediments within the basin. The most common cave’s elevation was found to be around 200 m below sea level which was the elevation of the Lisan Lake during part of its history. On the other hand, the Hula Basin in the northern part of the Dead Sea Basin was not occupied by saline water bodies since its formation as a base level, and thus the above preconditions for enhanced cave formation did not prevail. Indeed, this is evident by the lack of horizontal cave levels on its western carbonate margins unlike the situation in the south.     

Effectiveness of horizontal drains for slope stability

Horizontal drains have been commonly used in stabilising unsaturated residual soil slopes. This study examines the effectiveness of horizontal drains in stabilising residual soil slopes against rainfall-induced slope failures under a tropical climate. The study includes field instrumentation at two residual soil slopes complemented with a parametric study relating to drain position. Field monitoring results indicate that rainfall infiltration is limited to a certain depth below which infiltration becomes insignificant. This zone tends to be unsuitable for horizontal drains. Horizontal drains were found to be most effective when located at the base of a slope. The parametric study indicated conditions under which horizontal drains are effective or ineffective in improving the stability of a slope. It was also found that horizontal drains have little role in minimising infiltration in an unsaturated residual soil slope. Benefits of using horizontal drains can be obtained through the lowering of the water table.     

淮南刘庄煤矿定向水平井施工技术研究

刘庄煤矿的定向水平井,为首采工作面的沿煤层定向水平瓦斯抽排井,成井总进尺为1116.60m,终孔直径215.9mm。根据淮南矿区13-1煤层开采显现的三带岩移规律和瓦斯抽放效果的具体分析,该抽排井水平段的设计位置在内错风巷30m和13-1煤层顶板之上25m左右,基本上按照13-1煤层的走向延伸。施工后的实际结果为:水平方向,水平段内错上风巷最小19.88m,最大34.98m;垂直方向,水平段距13-1煤顶板最小距离20.79m,最大距离26.8m;与设计目标基本一致,后期瓦斯抽放效果良好。从介绍该井的井身结构和剖面设计入手,着重对该井在施工过程中的钻具组合、钻探施工、下管固井技术和定向技术进行了详细的说明,最后分析了该定向水平井施工技术取得的主要成效。     

Holocene climate inferred from glacier extent,lake sediment and tree rings at Goat Lake,Kenai Mountains,Alaska, USA

Lake sediment, glacier extent and tree rings were used to reconstruct Holocene climate changes from Goat Lake at 550 m asl in the Kenai Mountains, south‐central Alaska. Radiocarbon‐dated sediment cores taken at 55 m water depth show glacial‐lacustrine conditions until about 9500 cal. yr BP, followed by organic‐rich sedimentation with an overall increasing trend in organic matter and biogenic silica content leading up to the Little Ice Age (LIA). Through most of the Holocene, the northern outlet of the Harding Icefield remained below the drainage divide that currently separates it from Goat Lake. A sharp transition from gyttja to inorganic mud about AD 1660 signifies the reappearance of glacier meltwater into Goat Lake during the LIA, marking the maximum Holocene (postglacial) extent. Meltwater continued to discharge into the lake until about AD 1900. A 207 yr tree‐ring series from 25 mountain hemlocks growing in the Goat Lake watershed correlates with other regional tree‐ring series that indicate an average summer temperature reduction of about 1°C during the 19th century compared with the early–mid 20th century. Cirque glaciers around Goat Lake reached their maximum LIA extent in the late 19th century. Assuming that glacier equilibrium‐line altitudes (ELA) are controlled solely by summer temperature, then the cooling of 1°C combined with the local environmental lapse rate would indicate an ELA lowering of 170 m. In contrast, reconstructed ELAs of 12 cirque glaciers near Goat Lake average only 34 ± 18 m lower during the LIA. The restricted ELA lowering can be explained by a reduction in accumulation‐season precipitation caused by a weakening of the Aleutian low‐pressure system during the late LIA. Copyright © 2008 John Wiley & Sons, Ltd.     

龙26-平25长水平段水平井钻井技术

为了高效开发低渗透油藏,在大庆油田龙26区块部署了龙26-平25长水平段水平井。介绍了井身结构与井眼轨迹剖面设计特点,分析了钻井施工中的难点,从井眼轨迹控制、旋转地质导向钻井技术、摩阻与扭矩监测、井眼清洁等几个方面对该井采用的技术措施进行了详细阐述。龙26-平25井完钻井深4045.00 m,水平段长2033.00 m,各项指标均符合设计要求,创出了大庆油田应用水基钻井液施工水平井水平段最长的记录,为今后施工同类型长水平段水平井积累了宝贵的施工经验。     

深层振动密实对湿陷性黄土层水平应力变化的影响

深层垂直振动不仅会增加土体刚度,还会增加其水平有效应力。结合深层振动密实技术在我国西北地区处理湿陷性黄土地基的首次实践,探讨了深层振动密实对湿陷性黄土地基土层水平应力变化的影响,同时揭示了湿陷性黄土振动密实的机制。现场试验结果表明,处理深度范围内（–8 m）土层的锥尖阻力和侧壁阻力平均提高了2倍以上,摩阻比增加了20%～50%。–3 m以上范围内土层的侧壁阻力比值较大,且对应较高的水平应力变化值（ ）,土层水平应力增加显著。深度–3～–7 m范围内土层的侧壁阻力比保持在4左右,对应 值在3～4之间。–7 m以下土层的 值逐渐减小并趋于1。水平应力变化受土层侧壁阻力比的影响较大,受有效内摩擦角的影响小。分析认为,水平应力的增加,导致土层产生“预固结”效应,在微观上表现为黄土由疏松多孔的粒状结构趋向于镶嵌结构,以架空孔隙为主导的大孔隙或消失或演变为镶嵌孔隙等小孔隙,土体逐渐变得密实。