Experimental Investigation on Flow Characteristics at Leeside of Suspended Flexible Curtain for Sedimentation Enhancement

A new patent registered device- suspended flexible curtain （SFC） for sedimentation enhancement is proposed in this paper, which consists of two parts： a light-weight curtain with sediment-passing windows and a heavy pillar for the device stability. The mechanism of trapping nearbed sediment by the SFC is such that a primary and a secondary circulations with horizontal hubs would be formed at the leeside when it is placed on beds in running flow; the velocities within the sediment-passing windows are locally accelerated, the nearbed sediments would be brought by the flow through the windows, and then settled down within the primary circulation zone. Experimental tests on hydraulic characteristics are conducted in a laboratory flume with rigid bed. It is found that the dimensions of the curtain and the sediment-passing windows determine the characteristics of the primary and the secondary circulations. The intensity of the primary and the secondary circulations is dominated by the size of the sediment-passing window. Whether the secondary circulation would contact the bed or not depends on the level of the sediment-passing window. The length and the height of the primary circulation zone demonstrate quasi linear relationships with the effective height of the SFC. And the tests on sandy bed flume show that the sediment deposition happens just in the primary circulation zone.

Retention of clay-solidified grouting curtain to Cd^(2+), Pb^(2+) and Hg^(2+) in landfill of municipal solid waste

The effects of components and their ratio of grouts on anti-seepage capability of clay-solidified grouting curtain and its permeability of heavy metal cations were investigated by permeating experiments, using reactive solute transport model to study the permeation of heavy metals (Cd2+, Pb2+ and Hg2+). The study of permeating for different mixture ratios of cement and clay indicates that hydraulic conductivity of clay-solidified grouting curtain with different ratios of solid to liquid or with the same ratio of solid to liquid but with different ratios of cement to clay is changed. The laboratory simulation test results also show that precipitates produced in heavy metal cation migration process in curtain block up water flowing passage which makes the hydraulic conductivity of the solution-permeated curtain decrease with the leakage time. The permeation velocities for different heavy metal cations vary with ionic concentration, exchange capacity and ion radius etc. The test results indicate that the permeation rapidity order of heavy metals cations in clay-solidified grouting curtain is Hg2+>Pb2+ in the same experimental circumstance. In addition, permeability for different mixture ratios and antisepsis capabilities of clay-solidified grouting curtain were studied in tests.

深厚含水层悬挂式截水帷幕设计实践

在长江中下游地区,部分深基坑位于深厚含水层区域,截水帷幕无法隔断坑内外的水力联系,需要采用悬挂式截水帷幕。截水帷幕选择合适的嵌入深度有助于在保证工程安全的情况下节约工期、降低成本。本文结合上海某项目降水设计与施工,阐述在深厚含水层中如何利用其渗透系数各向异性的特征,确定经济合理的截水帷幕嵌入深度,首次引入截水帷幕等效绕流距离的概念,将截水帷幕嵌入深度、截水帷幕底端与降水井滤管底端的高差、水平渗透系数与垂向渗透系数比这三个影响水位降深因素统一用截水帷幕等效绕流距离表示,提出了截水帷幕嵌入深度设计快速判断方法,为类似项目提供了经验和参考。

敏感城市环境悬挂止水帷幕基坑降水施工案例分析

为研究敏感城市土工环境约束下,悬挂止水帷幕基坑降水施工对周边保护建(构)筑物的影响,以实际工程为例,介绍降水历程、采取的针对性措施及周边环境监测结果。数据对比证明深坑分段施工有效缩短了降水高峰持续时间,缓解了对周边土工环境的影响。阐述了紧邻坑边回灌的局限性,分析了不同回灌方案的优势与不足,揭示了水位下降引起建(构)筑物沉降与地质条件、建(构)筑物自身结构特性等均有关系,差异性明显。案例可为类似城市土工环境中深基坑施工提供参考。

考虑止水帷幕插入比的降水井滤管参数设计优化研究

以武汉市某基坑工程实例为背景,基于承压层坑内外水位降深及坑外地表沉降两大观测指标,采用有限元软件ABAQUS建立群井降水三维数值计算模型进行了数值模拟分析,通过设置多组计算工况,对在悬挂式止水帷幕不同插入比λ条件下,降水井不同滤管长度L及滤管埋深H对承压层坑内外水位降深及坑外地表沉降的影响规律进行了研究。研究结果表明:插入比λ对承压层坑内外水降深及坑外地表沉降的影响要远大于降水井滤管长度L及滤管埋深H的影响。在止水帷幕插入比λ=0.4~0.6时,通过改变滤管长度L及滤管埋深H来提高承压层坑内水位降深或降低承压层坑外水位降深具有较大的空间。止水帷幕插入比λ>0.6后起到较好的隔水效果,滤管埋深H宜位于承压含水层顶部,滤管长度L不宜超过0.4倍的承压含水层厚度M。

上拉杆式悬挑脚手架在异形幕墙施工中的应用研究

对型钢悬挑脚手架及上拉杆式悬挑脚手架等2种类型悬挑脚手架钢梁受力模式进行了对比,说明了上拉杆式悬挑脚手架的受力优势。重点分析了上拉杆式悬挑脚手架体系的上拉杆上端偏离悬挑梁所在竖平面对该体系受力的影响。以上海某城市核心区综合体项目幕墙装饰施工为例,针对裙房影院部分调控区外墙为非结构混凝土墙,外部为异形幕墙装饰,导致施工存在的难题,为保证现场施工进度及施工安全,成功应用了上拉杆式悬挑脚手架,确保了施工过程安全并降低工程费用,总结的经验可供类似工程参考。

某富水砂层深基坑悬挂式止水帷幕评估与研究

针对某富水砂层基坑体量大、边界长、紧邻天然基础大断面管廊(结构变形控制要求高)的特点,采用多种方式获取了准确的富水砂层参数,并进行了悬挂式止水帷幕情况下管廊的沉降研究及评估。采用超深静力触探判定砂层密实程度,获得准确的力学参数并据此快速评估降水对周边地表沉降的影响;通过现场抽水试验进一步获得富水砂层的水文参数并验证沉降数据;然后采用获得的力学参数及水文参数,通过有限元计算精确分析不同止水帷幕深度情况下基坑降水对综合管廊变形的影响;最后,针对三轴搅拌桩在密实砂层钻进速度慢、工效低的问题,通过优化桩长及适当的设备改造,确保了顺利施工。本项目为富水砂层基坑止水帷幕的优化设计、施工提供了一套可行的评估思路,可为类似深基坑工程提供借鉴经验。

Hydraulic head difference at two sides of suspended waterproof curtain during multi-grade dewatering of excavation

This paper proposes an approach to calculate the head difference at two sides of suspended waterproof curtains during multi-grade dewatering.The seepage during the dewatering process can be subdivided into three regions:(i)seepage in pit,(ii)seepage between cur-tains,and(iii)seepage outside the pit.The flow rate of the first region is equal to the pumping rate,and the flow rate of the second and third regions can be obtained by numerical analysis.A numerical model is established to simulate the seepage in the second and third regions and its performance is validated by using the measured data of a series of field tests.The flow rate of each region is then used to derive formulae for the head difference in conventional dewatering,which can be used to determine the head difference at two sides of each waterproof curtain during multi-grade dewatering.The proposed formula expresses the head difference as a function of the relative depth of the curtain inserted into the confined aquifer,the thickness of the aquifer,the distance between two curtains,and the anisotropy of the hydraulic conductivity of the aquifer.The proposed numerical approach is further validated by using data derived from numerical analysis.The validation results demonstrated that the predictions of the proposed approach are acceptable and convenient.

悬挂式止水帷幕基坑降水对临近地铁变形影响分析

采用悬挂式止水帷幕的深基坑承压水降水对周边环境的影响问题不容忽视。以上海某临近地铁换成节点的深基坑项目为依托,分析了基坑开挖前试降水对临近地铁车站和隧道结构变形的影响规律。结果表明,采用悬挂式止水帷幕情况下坑内降水对坑外地铁结构变形影响量和影响范围均比较大,地铁结构变形量与结构刚度、与降水基坑的距离、降水基坑的面积、水位降深有比较大的相关性。

深厚强透水地层下基坑水平封底方案研究

本文以长沙地铁某项目为依托,针对深厚强透水卵石地层下的地铁深基坑工程,通过对悬挂式止水帷幕与水平封底方案不同止水方案的分析,确定悬挂式止水帷幕与基坑水平封底隔渗帷幕的设计参数。最后,通过三维有限元模型对车站深基坑水平封底方案进行分析,进一步分析基坑深层水平封底隔渗帷幕的性能。研究结果表明:基坑水平封底帷幕整体隔渗性能较好,基坑内部水位降深能够满足施工要求,且基坑外水位降深基本无变化。

Vibration Characteristic Analysis and Experiment of Non-Rigid Airship with Suspended Curtain

In order to evaluate the vibration characteristics of non-rigid airship with suspended curtain,we introduce vibration characteristic analysis method of the inflatable membrane structure.Modal numerical method of the inflatable membrane structure under the pressure difference is validated by the model testing of the inflatable cantilever tube.The finite element model of 75 m airships is established to simulate the vibration characteristics subjected to only pressure difference and the resultant force of weight and buoyancy.The nonlinear static deformation and stress analysis are investigated for two kinds of equilibrated configurations with various pressure differences,as well as the vibration characteristics.The structural efficiency of the suspended curtain is investigated through the force transfer ratio at the assumed equilibrated point.The effects of manufacture error of the suspended cable length on the structural behavior are analyzed.The results indicate that the local area of airship envelope connected to the suspended cable is a weak part.Various pressures and pressure gradients have significant effects on the global airship structure and the suspended curtain.The suspended curtain is effective to transfer the equilibrated force from the bottom to the top of airship envelope.Manufacture error of the suspended cable length could result in obvious deformation of local airship envelope.The presented work is valuable to the structural engineering design of stratospheric airship.

悬挂式帷幕地铁深基坑变形特性研究

基于江漫滩地铁深基坑的变形实测资料,采用理论分析、经验公式和有限元数值模拟方法,总结了悬挂式帷幕基坑变形规律,给类似工程设计和监测提供依据。结果表明:悬挂式帷幕基坑地表沉降曲线呈凹槽形,地表沉降考虑流固耦合作用大于不考虑流固耦合作用;地下连续墙的最终形态为内凸胀肚型,墙顶水平位移不完全是朝坑内移动,地下连续墙最大水平位移与基坑挖深的比值和全止水帷幕基坑差异不大,最大水平位移点深度位于坑底附近;由降水引起的地表沉降占总沉降量的比值约为0.54;地表沉降范围可以划分为主要影响区、次要影响区和微弱影响区;地表沉降曲线可根据影响分区选用不同的函数表达式;最大地表沉降点位置大于同等条件下全止水帷幕基坑约1.0~3.0m。

复杂地层中基坑降水引发的水位及沉降分析与控制对策

在深大基坑工程中,若止水帷幕设置不合理,基坑内外水力联系将不能被完全截断,这样基坑内降水不但会引起坑外土体沉降,还会引发围护结构变形。在天津地铁5号线某车站基坑工程中,由于场地地层较为复杂,含水层不连续且存在大量透镜体,因此在开挖前进行了预降水试验,判断基坑内外水力联系。文章通过对预降水试验进行数据分析得出,该基坑内外承压含水层连通,且各含水层存在水力联系,原设计的落底式止水帷幕未能彻底截断承压含水层,造成了较大的围护结构变形与显著的建筑物沉降。因此,当场地承压含水层构造较为复杂时,应当在勘察阶段进行场地抽水试验,或者在基坑开挖前进行预降水试验,以全面掌握场地水文地质情况及基坑内外含水层水力联系。同时预降水前应在坑外合理设置回灌井,避免降水引发坑外沉降,并提前施工基坑第一道水平支撑,增加围护结构抗侧移刚度,减小降水引发的围护结构变形。

悬挂式帷幕入土深度对涌水量影响及优化设计

为实现悬挂式帷幕条件下涌水量定量计算以及基于此的优化设计,根据地下水动力学原理,分析了悬挂式帷幕影响下形成的绕流和非绕流两个区的渗流特征;利用Dupuit假设和阻隔理论,在一定理论推导基础上,系统地提出了悬挂式帷幕条件下潜水和承压水涌水量计算的修正大井法,并根据实际应用需要提出了相应的近似表达式;然后,以潜水含水层为例,采用系统的数值试验分析了修正大井法中水位加权系数随悬挂式帷幕深度变化规律,同时也验证了修正大井法近似公式精度;最后对悬挂式帷幕优化设计进行了探讨,提出了优化模型和求解方法,并进行了相关数值案例的应用.

江漫滩悬挂式止水帷幕基坑地表沉降变形研究

为研究江漫滩特殊地质条件下悬挂式止水帷幕地铁深基坑施工引起的周边地表沉降规律,以7个江漫滩基坑工程的实测地表沉降数据为基础,采用理论分析、经验公式和有限元数值模拟的方法,总结了基坑开挖和坑内降水二者耦合作用引起的周边地表沉降变形规律。结果表明:1)地表沉降范围可以划分为主要影响区、次要影响区和弱影响区3个区,主要影响区地表沉降主要由开挖和降水共同引起,次要影响区主要由降水引起。2)地表沉降曲线可根据划分的影响分区选用不同的函数表达式。3)基坑地表最大沉降点位置与坑边的距离xm为12.0~15.0 m,xm与基坑开挖深度h的比值约为0.7。4)在最大沉降点处,由开挖引起的地表沉降量占比为0.21~0.49,由降水引起的地表沉降量占比为0.51~0.79。

高承压水基坑降水对周边环境的影响分析

高承压水基坑施工常因隔水层厚度不足诱发坑底突涌,而盲目的坑内降水又会造成基坑周边地表不均匀沉降、基坑内外水位突变、周边环境变形等,导致基坑事故频发。笔者基于工程实例数据与群井抽水试验,通过数值模拟研究在基坑内降水的同时增加止水帷幕长度并超出降压井过滤器底部一定深度但不打穿整个承压含水层,形成"悬挂隔水帷幕"时对地表沉降及周边环境的影响。结果表明:随悬挂隔水帷幕长度的增加,坑内总涌水量显著降低,地表沉降量减小,且当隔水帷幕底超出最深的降压井底约6m时,工程实用价值最高,研究结果对实际工程具有较好地参考借鉴作用。

柔性飞艇及其悬挂屏体系结构力学性能分析

为研究大型柔性飞艇及其悬挂屏结构体系力学性能,以25 m验证飞艇(ZY-1)放大3倍的模型为对象,分析了仅考虑内外压差自平衡体系和考虑浮力、重力的平衡体系结构性能。基于柔性飞艇主气囊初始形状,通过充气压力静力非线性分析得到充气平衡形态位形和应力。利用兰索斯法分析了含悬挂屏飞艇结构在2种平衡体系中不同气压下的自振特性;探讨了悬挂屏悬索制作误差对自振特性影响。分析表明:悬挂屏悬索与囊体连接部位是飞艇的薄弱部位,囊体的内外压差和压力梯度的大小对悬挂屏力学性能影响显著;悬挂屏悬索制作误差导致囊体局部形变,从而改变悬挂屏力学性能。

坝基防渗墙及墙下灌浆帷幕渗流及渗透稳定性分析

采用三维有限元计算软件SEEPAGE1.0对扎雪水电站坝基进行了稳定渗流计算,分析了悬挂式防渗墙下灌浆帷幕深度对渗流场的影响,探讨了覆盖层中的渗透稳定性问题,确定了经济合理的防渗方案,并分析了防渗墙开裂对渗流场的影响。结果表明,覆盖层中帷幕底部的渗透坡降最大,并以此处为中心,向四周迅速减小。整体渗透稳定性较好,防渗墙底部出现交错裂缝对渗控效果影响不大。

悬挂式止水帷幕基坑控水优化方法

基于地下水渗流连续性原理并结合达西定律,推导出了止水帷幕在不同插入深度下的圆形基坑涌水量计算公式.在此基础上,借鉴我国船舶工程中广泛采用的阻力系数法,提出了考虑悬挂式止水帷幕的地表沉降量计算方法.最后综合涌水量和地面沉降计算方法,以控水成本为目标,以基坑涌水量和坑外地面沉降量为约束条件,建立了一套完整的兼顾基坑设计安全性和经济性的悬挂式止水帷幕基坑控水设计优化方法,并以北京市通州区某工程场地为例,对所建立的控水优化方法进行了具体应用.

悬挂式止水帷幕基坑降水引起坑外地面沉降计算方法

悬挂式止水帷幕的挡水效应能够减轻基坑降水对周边环境的影响,但帷幕插入深度与坑外地面沉降之间的定量关系尚不明确.本文基于有效应力原理,并根据渗流场和应力场的部分耦合关系,考虑地下水位下降引起的土体孔隙比和压缩指数变化,通过止水帷幕插入深度与水位降深的关系提出了不同止水帷幕插入深度下潜水含水层中基坑降水引起坑外地面沉降的计算方法.结合室内渗流模型箱试验对所提方法进行验证,结果表明地面沉降的试验监测结果与计算结果基本一致,从而为准确预测地面沉降和设计合理的止水帷幕插入深度提供了重要参考.