共查询到19条相似文献，搜索用时 31 毫秒
1.
《岩土力学》2018,(Z2)
基坑工程中坑内承压水降水引发的坑外土体沉降与含水层土体性质及应力状态密切相关,但在天津地区承压含水层的土体应力状态及其沉降变形规律均缺乏系统地研究。首先通过天津市第一、二含水层组的历史水位变化,分析各含水层组土体的应力状态。再结合2组现场抽水试验,分析了各承压层降水-恢复过程土体沉降变形规律。根据对历史数据的分析表明,受补给关系和自然条件影响,天津市第一含水层组中上部水位变化较小,处于正常固结和轻度超固结状态。而20世纪60～80年代天津市深层地下水由于大规模开采形成了以市区为中心的降深漏斗,造成了严重的地表沉降。80年代后限制开采,天津市区的地下水位得以部分恢复,导致第一含水层组底部和第二含水层组处于严重的超固结状态。抽水试验结果表明,基本处于正常固结状态的第一承压层在抽水-恢复过程中变形以塑性变形为主,处于超固结状态的第二承压层变形以弹性变形为主,在反复降水-恢复中仍然会产生一定量的塑性变形,即当水位恢复时承压层压缩变形并不能完全恢复;受"土拱"作用影响,承压含水层降水引发的土体沉降最大值并不位于地表,而是位于抽水含水层上覆弱透水层附近。 相似文献
2.
过去对地下水位持续下降条件的地面沉降研究较多,但对水位大幅持续抬升过程中的地面沉降研究较少。本文根据
上海大量地面沉降、水位观测和钻孔资料,系统分析上海市90年代末以来地下水位大幅抬升条件下各土层的变形特征。自
1998年以来,上海市通过大幅压缩开采量、回灌地下水等措施使第二、三、四和五承压含水层水位分别平均抬升2.1 m,
3.6 m, 12.4 m, 12.7 m。水位的抬升使上海市地面沉降平均速率由1998年的12.2 mm/a减小到2011年的1.83 mm/a,减少85%。
通过对27组分层标数据分析发现：现阶段主要压缩层位在第一、二软土层,年沉降速率为2~4 mm/a;而第二含水层以下土
层已经有少量回弹。在水位持续大幅抬升过程中,本文总结了两种变形特征：1） 变形和水位变化基本同步,残余变形量非
常小,变形可概化为线弹性变形,这种变形主要发生在第一、二、三和五承压含水层、第五和六弱透水层;2） 压缩速率逐
渐减小,无明显持续回弹趋势,有较大残余压缩量且存在变形滞后现象,变形可概化为弹塑性变形,这种变形主要发生在
地第二、三和四弱透水层。第四承压含水层变形较复杂,两种变形特征都有。其中较大残余变形量主要由塑性贮水率比弹
性贮水率大2个数量级引起;变形滞后主要由弱透水层中超孔隙水压力消散较慢引起。本文研究成果对于掌握水位抬升过
程中土层变形方式、发生发展机理、预测未来地面沉降及地下水科学管理和资源评价具有重要意义。 相似文献
3.
《岩土力学》2017,(1):61-66
弱透水层是含水层系统的重要组成部分。弱透水层的渗透系数K_v和弹性贮水率值S_(ske)对研究地面沉降及地下水资源评价具有重要的意义。在相邻含水层降深随时间周期性波动的条件下,推得了超固结弱透水层中无量纲形式的降深解析解,并基于该解析解进一步得到了超固结弱透水层累计变形量随时间变化的理论曲线。由于弱透水层的低渗透性,其变形总是滞后于相邻含水层的降深变化。根据弱透水层变形的滞后时间与含水层降深波动半周期的关系,提出了一种用以确定超固结弱透水层垂向渗透系数和弹性贮水率的方法,该方法对于弹性变形的超固结土具有很好的适用性。使用该方法之前,首先要根据分层标和水位资料确定含水层降深的变化周期以及弱透水层变形的滞后时间。应用该方法确定了上海地区f_(10-7)分层标处第2弱透水层的水力参数为K_v=4.12×10~(-10)m/s,S_(ske)=1.07×10~(-4) m~(-1)。经实例计算结果具有一定的可靠性。 相似文献
4.
当基坑需进行非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,考虑了既有隧道相对于承压含水层不同位置时,既有隧道周围土体应力场、既有隧道横断面内力和变形。研究结果表明,隧道全部或者大部分位于承压含水层中时,抽水除可引起隧道发生整体隆起或沉降外,还将导致隧道自身产生较大的竖向压缩变形;当隧道全部位于上、下部隔水层时,含水层抽水对其隧道的变形影响不大,但当隧道位于上部隔水层情况下,抽水将会引起隧道产生整体下沉。 相似文献
5.
在天津滨海新区中新生态城服务中心开展了承压含水层抽水引起地面沉降的现场试验,采用振弦式孔隙水压力传感器和一孔多标数据采集器实时监测孔隙水压力和分层标的变化,分析了土体的变形性质和分层沉降的规律。试验结果表明,黏土层变形明显滞后于承压含水层水位的变化,以塑性变形为主且存在蠕变现象,而砂层既存在弹性变形,也存在一定的塑性变形和蠕变性。短期抽取地下水会使抽水井附近承压含水层上覆土体出现上小下大的沉降规律,且最大沉降出现在有明显孔隙水压力变化的土层顶板位置。 相似文献
6.
常州地区地面沉降及地层压缩性研究 总被引：4，自引：0，他引：4
系统分析了常州地区地下水开采动态和地面沉降发生发展历史,概述了研究区地面沉降的框架,在此基础上,系统研究了常州市分层标从1984年至2002年的分层沉降资料。根据常州地区地下水含水层系统及土层特性,将研究区松散土层垂向划分为四个不同层次,分别研究了它们的压缩变形历时特性及其与累计地下水开采量的关系,研究了各自的应变特性。由于土层结构及物理力学性质的不同、地下水开采层次及强度的差异、土层不同应力历史的影响等诸多因素的综合效应,导致了地面沉降及分层压缩特性的显著差别。常州地区的主要压缩层为第II承压含水层的顶板弱透水层,与含水层距离近的土层变形量及应变量均较大,其次是第II承压含水层本身及其与第III承压含水层之间的弱透水层。地面沉降及地层压缩与地下水开采之间的滞后效应在常州地区表现得并不明显,这一点至少在月或年的时间尺度上是正确的。 相似文献
7.
由于地下水突涌风险,地下空间在施工作业中有必要通过抽水试验确定承压含水层的水文地质参数。依据勘察报告的初步评价,基坑开挖15.5m时,场地内第⑦1层承压含水层有可能产生突涌,为确保工程安全施工,需开挖前进行承压含水层抽水试验,取得场地承压含水层水文地质参数及降水引起的沉降特征,为地下空间设计和施工提供可靠依据。本次布设抽水井、观测井、分层沉降标组、孔隙水压力观测孔及地面沉降观测点,依据抽水试验技术要求获取渗透系数、抽水影响半径等相关水文地质参数。最后,针对工程场地内承压水情况及特点进行分析,提出基坑开挖时的承压水降压建议方案。 相似文献
8.
某深大基坑位于长江下游岸边,场地地层为典型的二元结构,基坑开挖涉及的两层承压含水层间的弱透水层局部缺失,之间水力联系密切,基坑场地地质条件极为复杂,基坑施工降水直接关系到基坑工程的安全。这里将基坑分3个区,分别进行降水设计。具体降水方案:Ⅰ区两层承压含水层和Ⅱ区第一承压含水层被围护结构隔断内外水力联系,采用疏干井降水;Ⅱ区第二承压含水层未被围护结构隔断,Ⅲ区两层承压含水层水力联系密切,针对这两个区域设计了两套降水方案,方案一在Ⅱ区和Ⅲ区均布置有降水井,在Ⅱ区对第二承压含水层降水,在Ⅲ区对第一承压含水层降水;方案二仅在Ⅲ区布置降水井对第一承压含水层降水。为了更好地对降水方案进行对比分析,验证方案的可行性,对此进行了数值模拟分析,计算结果显示,两种方案均能满足降水要求,不过方案二布井数量少,基坑外水位降深较小,对周边环境影响更小,优于方案一。 相似文献
9.
常州地区含水层系统土层压缩变形特征研究 总被引：6，自引：1，他引：6
根据近十几年来分层标和含水层水位观测资料分析了常州地区土层压缩变形特征,表明承压含水砂层中的压缩变形不容忽视,且含水砂层的压缩变形与弱透水层的粘土、粉质粘土相似,均表现出明显的变形滞后现象.为此从水位与时间关系、土层变形与时间关系和水位与变形关系出发,结合室内试验方法,通过选取常州地区含水层系统中第一、二、三承压含水层以及二、三承压含水层间弱透水层和第三承压含水层下覆弱透水层的原状土样,采用单轴侧限压缩试验,分析了常州地区砂土和粉质粘土的次固结（蠕变）特性.试验结果表明常州地区不论是粉质粘土还是砂土,均存在一定的次固结变形,从而启示我们该地区地面沉降模拟中应同时考虑含水砂层的蠕变特性. 相似文献
10.
地下水位变化模式下含水砂层变形特征及上海地面沉降特征分析 总被引：5，自引：0，他引：5
土体变形特征与其经历的应力状态有关。由于抽灌水位置和水量的变化,同一土层中不同时期的地下水位可以呈现不同的变化模式,土层表现出不同的变形特征。论文根据上海1400多个水位孔近40a的水位观测资料和各土层的变形资料,从土层变形角度将地下水位的变化方式划分为5种模式。分析了每种地下水位变化模式下土层的变形特征,并进一步分析了上海地面沉降在时间和空间上的特征。分析结果表明:地下水位的变化模式对上海土层的变形有显著影响。同一土层在不同的水位变化模式下可表现为弹性、弹塑性或粘弹塑性的变形特征;地面沉降与地下水开采量、地下水开采层次与主要沉降层具有密切的关系,开采地下水是上海地面沉降的主要原因;与现阶段含水层的水位变化模式相联系,第四承压含水层是上海最近几年来地面沉降的主要沉降层。 相似文献
11.
Study on Deep Well Dewatering Optimization Design in Deep Foundation Pit and Engineering Application 总被引：2，自引：0，他引：2
HuChunlin Yanghuijun 《中国地质大学学报(英文版)》2002,13(1):78-82
Based on analyses of the theories of groundwater unsteady flow in deep well dewatering in the deep foundation pit,Theis equations are chosen to calculate and analyze the relationship between wa-ter level drawdown of confined aquifer and dewatering duration.In order to reduce engineering cost and diminish detrimental effect on ambient surrounding,optimization design target function based on the control of confined water drawdown and four restriction requisitions based on the control of safe water level,resistance to throwing up from the bottom of foundation pit,avoiding excessively great subsidence and unequal surface subsidence are proposed.Adeep well dewatering project in the deep foundation pit is optimally designed.The calculated results including confined water level drawdown and surface subsid-ence are in close agreement with the measured results,and the optimization design can effectively control both surface subsidence outside foundation pit and unequal subsidence as a result of dewatering. 相似文献
12.
Jianxiu Wang Tianrong Huang Jian Hu Lingao Wu Guo Li Ping Yang 《Environmental Earth Sciences》2014,71(7):3245-3257
A whirlpool foundation pit is a small-diameter, deep circular pit. Because of its depth and small diameter, a large drawdown is required, and a limited number of wells can be installed inside the pit. During excavation, partially penetrating wells inside and outside the foundation pit have to be installed to lower the water level when the aquifer is too thick. However, partially penetrating wells near partially penetrating curtains cannot be treated by analytical methods. Therefore, it is necessary to use numerical methods to predict dewatering during excavation. Field experiments were performed on whirlpool foundation pit 1880 of Baosteel Group, Shanghai, China, to obtain pumping rates and drawdown, pumping with a single well and two wells in the confined aquifer. The results indicate that the drawdown inside the pit induced by pumping wells outside the foundation pit was small, whereas it was large for pumping wells inside the pit. The pumping wells inside and outside the pit had to be combined to lower the water level. A three-dimensional numerical model was developed to simulate the dewatering process. The hydraulic conductivities of the confined aquifers were inversed by using the pumping tests. Operation schedules were simulated with the corrected model for different combinations of wells inside and outside the pit. The results suggest that different schedules and operation conditions affect drawdown. The monitored results during dewatering indicate that the simulation and field measurements were in agreement. The results can be applied to similar situations. 相似文献
13.
Ye-Shuang Xu Huai-Na Wu Bruce Zhi-Feng Wang Tian-Liang Yang 《Environmental Earth Sciences》2017,76(9):351
Foundation dewatering has become a major cause of land subsidence in Shanghai. The burial depth of foundations in relation to geotechnical construction works is less than 75 m, and the corresponding groundwater includes phreatic, low-pressure artesian, and the first confined aquifers. Based on the geological and hydrogeological conditions beneath Shanghai, methods of dewatering may be divided into three modes and further five patterns according to the insertion depth of the dewatering-retaining system. The most common dewatering mode aims to reduce the water pressure in the confined aquifer by setting the dewatering wells inside the pit, whilst the retaining walls are buried in the confined aquifer and partially cut off the confined aquifer layer. To predict the settlement due to foundation dewatering, numerical models are generally adopted, which are similar to those used to predict land subsidence induced by regional groundwater withdrawal; however, since foundation dewatering is conducted along with the setting of retaining walls and foundation pit excavation, which differs from regional groundwater withdrawal, interactions between the retaining wall-dewatering well, the dewatering-excavation, and dewatering-recharge are important factors affecting the analytical model. Since the grading of the shallow soil layers is different, stratified settlement characteristics of the shallow soil strata and seepage erosion, which results in additional deformation, need to be given particular consideration. 相似文献
14.
Hydraulic barrier function of the underground continuous concrete wall in the pit of subway station and its optimization 总被引：4，自引：0，他引：4
Jianxiu Wang Lisheng Hu Lingao Wu Yiqun Tang Yanfei Zhu Ping Yang 《Environmental Geology》2009,57(2):447-453
Subway traffic is now being developed in China on a large scale and the planning subway stations are often located in dense
district with tall building. The dewatering of confined aquifer may cause ground settlement, the cracking, deformation and
tilting of the building, and even collapse. Combing with the dewatering project of environment protection of the pit of Yishan
Road station of Shanghai subway No. 9, through the inversion of seepage parameters based on the field pumping test, the hydraulic
barrier function of the underground continuous wall is simulated. The result indicates that with the reduction of the exposed
length of the filter tube and the increase of that enclosed, the drawdown of the confined aquifer decreases. Especially with
the increase of the enclosed length of the filter tube, the drawdown outside the pit can be controlled effectively. According
to the result of the numerical simulation, the design of the continuous concrete wall of the pit for Shanghai Subway No. 9
is altered and the depth of the continuous concrete wall of the standing part and that in the end well are increased to 61
and 62 m, respectively. The monitored result of the equal drawdown pumping test indicates that the drawdown outside the pit
with a distance of 1–6 m to the wall is less than 2 m; It means that there is nearly no influence on the environment around
the pit during dewatering. 相似文献
15.
Wang Jianxiu Liu Xiaotian Liu Shaoli Zhu Yanfei Pan Weiqiang Zhou Jie 《Acta Geotechnica》2019,14(1):141-162
Water level is decreased during foundation pit excavation to avoid water inrush under confined water pressure. Cut-off wall is often used as waterproof curtain to partially cut off the dewatered aquifer. When a foundation pit is located in a built-up area and the underlying confined aquifer is not cut off, the drawdown must be minimized outside the pit to avoid land subsidence in buildings and pipelines. The coupling effect of the cut-off wall and pumping well is used to control the drawdown outside the foundation pit. However, the coupling mechanism is not intuitively well understood because of the limitations of existing experimental methods. In this study, transparent soil was introduced to model the coupling mechanism in the physical model test. High-purity fused silica and mixed paraffin oil were used as skeleton and fluid to simulate the confined aquifer and groundwater. Industrial solid dye and paraffin oil were used as tracers. A camera was used to collect flow information. Tests were performed for the combinations of cut-off wall and partially penetrating pumping wells. The insertion depth ratio of the cut-off wall most effectively influenced the drawdown. The layout of the pumping wells in horizontal direction influenced water level distribution and flow rate. The optimal depth of the pumping wells was 1–5 m above the bottom of the cut-off wall, and the optimal horizontal distance between the cut-off wall and the pumping wells was 25% of the pit width. Non-Darcy flow was observed within the range of 0–10 m around the bottom of the cut-off wall. These results were significant in understanding the cut-off wall and pumping well coupling effect on foundation pit dewatering.
相似文献16.
弱透水层储存的地下水是地下水资源的重要组成部分,弱透水层水文地质参数对地下水资源管理与评价以及地面沉降等具有重要意义。通过室内试验对定降深条件下弱透水层水流运移规律进行了研究,并探讨了弱透水层释水过程中的变形规律和释水规律。试验结果表明,在相邻含水层定降深条件下,弱透水层固结变形滞后于相邻含水层的降深变化,且变形速度逐渐变小并趋于零。基于室内试验,利用配线法求得弱透水层不同应力状态下的水文地质参数,对比分析,大变形和小变形试验中土层的渗透系数变化不大,但贮水率明显变小,土层的固结系数变大。因此,土层的应力历史对土层的渗透系数影响不大,而对贮水率有较大的影响。 相似文献
17.
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。 相似文献
18.
现有基坑相关研究主要关注土方开挖过程引起的变形,认为围护结构变形起点是土方第1次开挖。然而,一些工程实测表明,基坑开挖前降水阶段即可引起围护结构及周边地层发生厘米级的变形。显然,未考虑开挖前变形的基坑监测数据将低估基坑施工的环境效应。为了研究基坑开挖前降水引发基坑变形的机制,开展了室内模型试验,对基坑开挖前降水过程进行了缩尺精细化模拟。通过微型降水井的设置与调控,模型试验真实再现了实际基坑降水过程中井流效应对围护结构受力变形的影响。试验过程中发现,随着降水的进行,坑外降水漏斗不断扩展,围护结构悬臂式侧移及坑外拱肩式地面沉降也随之产生。另外,降水导致墙前水压力明显减小,并诱发墙前侧向总压力重分布（以减小为主）,围护结构为此发生指向坑内的悬臂式运动以寻求新的受力平衡,并通过墙后土体损失诱发坑外地层变形。 相似文献
19.
针对黄土地区深基坑降水导致地层不均匀沉降,危及坑周建筑物的问题,论文基于基坑降水诱发地面沉降机理分析,以分层总和法和剪切位移法为基础,推导出降水引起地面沉降的简化计算公式。在忽略群井效应和土层侧向变形的前提下,依据Dupuit公式得出基坑降水曲线方程,将坑周土体以降水曲线为界分为疏干区和饱和区。引入修正系数,对黄土地区不同性质土层因孔隙水压力减小产生的有效应力增量修正,同时考虑桩-土界面侧摩阻力对土体的约束作用,分别计算距井轴不同距离处的沉降量,叠加后得出最终的沉降值。对比数值模拟计算结果及工程实例监测值,分析表明:在桩-土交界处,侧摩阻力对土体竖向沉降的约束作用最明显;在1.5倍降水深度范围内的沉降计算值精度远高于规范算法,能够较好的预测降水期间黄土地区坑周不同距离处的地面沉降量。 相似文献