共查询到20条相似文献，搜索用时 15 毫秒
1.
基于某真空井点降水综合试验,建立了三维地下水流数值模拟模型,将模型模拟预测数据与试验观测数据进行对比,研究真空负压和井点间距对真空井点降水效果的影响,得出了真空井点周围渗流场的变化性状,提出了真空井点周围真空及重力场耦合区、耦合场与重力场过渡区和重力场区3个区的概念。得出了不同负压在不同井点深度条件下对地下水渗流场的影响变化。对比结果表明,建立的真空井点降水模拟分析方法,能够较好的模拟真空井点周围观测井水位与出水量的相关关系;分析方法可用于真空井点降水试验分析,且为真空井点降水设计提供了依据。 相似文献
2.
R.J. Wakeman 《International Journal of Mineral Processing》1979,5(4):395-405
The dynamic dewatering model is extended to systems where the total pressure loss across the cake is constant (that is dewatering is effected by a pump which is able to maintain the vacuum). Using the model, prediction of dewatering characteristics is facilitated when a representative value is assigned to the pore size distribution index. The effects of altering process variables on the decreasing cake saturation and increasing air flow rate are quantified and discussed. The methods presented may be a useful tool for assessing changes in process variables or in the initial sizing of filters. 相似文献
3.
针对真空预压作用下排水板淤堵与排水条件受限等问题,提出絮凝−真空−电渗联合加固法。首先通过沉降柱试验确定合适的有机絮凝剂,然后采用该絮凝剂,分别在 48 h（开始介入真空预压,固结度为0 ）、60 h（排水速率明显下降,固结度为60%）及 84 h（排水速率近乎 0,固结度为 80%）时介入电渗,开展不同电渗介入时间的絮凝−真空−电渗联合加固试验。试验从排水量、十字板剪切强度、含水率与孔压等对比分析联合加固的有效性,确定其最佳电渗介入时间。试验结果表明：当固结度为 80% 时介入电渗,絮凝−真空−电渗联合加固法能够有效地抑制排水速率减小的趋势,增长有效排水时间。同时,土体的抗剪强度和承载力亦得到大幅提升,孔压消散更加均匀。此外,在阳离子聚丙烯酰胺絮凝剂的作用下,初始排水速率快,在一定程度上使土体的渗透性得到提升,有效地解决了排水板淤堵问题,说明絮凝−真空−电渗联合加固法具有较强的优越性。 相似文献
4.
单井点和单排井点布置的真空降水现场试验及比较研究 总被引：2，自引：0，他引：2
研究单井点和单排井点真空降水条件下,地层中地下水水位和抽水流量,在重力场和真空压力场耦合作用下的变化过程,并进行比较分析。试验表明,对于单井点排水条件,随着真空负压力和抽水井深度的增大,水位的下降有一定增加,而离开抽水井点较远处的水位下降更为明显。单排井点布置条件下,随着抽水井深度和抽水井间距的增大,无论是抽水井点布置方向还是垂直于抽水井点布置方向的地下水位的下降深度将有明显增大,而沿抽水井布置方向的水位下降深度更为显著。此外,在多次反复降水条件下,后续降水过程中地下水位的下降速率将有增快的趋势。试验还表明,抽水井井口的负压力小于真空泵出水口处的负压力,损失量可达12.5%,因此,在进行真空降水设计时需要考虑出水管道的长度。 相似文献
5.
D. Tao B. K. Parekh J. T. Liu S. Chen 《International Journal of Mineral Processing》2003,70(1-4):235-249
Ultrafine coal dewatering is of great importance to the coal industry due to its impacts on the handling and utilization characteristics of coal products. Commercially available filtration techniques are either ineffective or costly for dewatering of ultrafine coal to the desired moisture level of about 20%. Considerable efforts have been devoted to understanding the dewatering process and developing new technologies for applications in the coal industry. Most of the previous work on ultrafine coal filtration was focused on the final filter cake moisture and few studies have been conducted to investigate the filtration kinetics. The present investigation was undertaken to better understand the kinetics of vacuum filtration of ultrafine coal under various conditions. The filtrate weight was continuously monitored using a precise load cell during the entire filtration process. Operating parameters such as vacuum pressure and reagent conditioning time were examined for their impacts on filtration kinetics. Use of cationic and anionic flocculants showed significant improvement in filtration kinetics. Kinetic data obtained from the study were used to determine the fundamental parameters of filtration such as cake permeability, specific cake resistance, and filter medium resistance using the integrated form of the Darcy's law. 相似文献
6.
采用自主改装的变压头黏土渗透仪,模拟疏浚淤泥脱水过程中水分在淤泥颗粒多孔介质中的迁移运动过程,通过测定疏浚淤泥脱水过程中渗透系数与过滤常数、渗水量与滤液量、泥饼含水率与孔隙率,探究了负载压力为100 kPa时,不同负载方式（负载时间及负载压力梯度变化）对疏浚淤泥脱水过程中过滤和渗流规律的影响。研究发现：负载下的过滤和渗流同时进行,负载1 h期间,前期0～40 min内过滤占主导地位,后期40～60 min内渗流起关键作用。负载压力梯度由原来1 h内间隔变化1次,变为以20 kPa为梯度递增变化5次,随着压力变化梯度减小,渗透系数、过滤常数增加,淤泥脱水性能得到较明显的改善,并且前期负载压力越小,脱水效果越好。 相似文献
7.
以济南市轨道交通R1线大杨庄站主体基坑降水工程为例,研究表明发育于济南区域孔隙黏性土地层黏性土内具有独特的空间网状孔隙、孔洞结构。通过4种渗透性试验成果对比分析,室内试验、声纳渗流试验测定的渗透系数均较小,与实际地层渗透能力相差很大;抽水试验与回灌试验测定的渗透系数相近,远远大于一般黏性土的渗透性,渗透系数随着回灌压力的增加而呈线性提高,回灌引起周边地下水位上升较小,影响范围有限,符合济南孔隙黏性土地层的富水性强和渗透性好特性,具有独特性和鲜明的区域特点。相关试验成果可以为相关区域基坑降水与回灌设计、施工和泉水环境保护提供参考。 相似文献
8.
基坑降水的成功与否,关系到整个基坑的安全。南通市南山湖综合楼基坑开挖过程中虽建立了止水帷幕,但仍需对基坑降水的方案进行安全评估。采用MIDAS/GTS数值分析软件建立三维渗流模型,通过对现场单井抽水试验进行模拟分析,综合地勘报告中室内试验渗透系数和抽水试验的渗透系数,反向推演出符合工程实际的渗流边界函数和渗透系数;然后利用反推得到的计算参数,建立三维渗流模型,模拟群井抽水状态下水位降深与时间的变化关系,对群井降水效果进行分析,验证降水井设计是否合理,指导基坑土方的开挖。 相似文献
9.
The problem of predicting dependence of constant pressure batch dewatering of particulate suspensions on feed solids concentration is considered. Scaling transformations which demonstrate that evolution in the cake consolidation stage of dewatering is governed by an underlying self-similar behavior are proposed. The self-similar master curve, which can be obtained using only one set of experimental dewatering data obtained with a feed suspension having solids concentration above the gel point, is employed for estimating dependence of key dewatering process parameters on feed solids concentration. Using the parameter estimates in a Darcy's law based dewatering model, it is shown that the complete evolution of dewatering for a desired feed solids concentration can be predicted with reasonable accuracy. The approach is simpler to implement in comparison to available pressure filtration models, which require several suspension characterization experiments. 相似文献
10.
A finite element model is developed for modelling coupled fluid expulsion/deformation behaviour of dewatering sediments subjected to external loadings under isothermal conditions. The non-linear deformation behaviour of the sediment (soil) skeleton is based on the force equilibrium equation in which the constitutive relationship of stress and strain is implemented by the modified Cam-Clay model in soil plasticity. The fluid flow behaviour in the model is described by the generalized porous media flow equation. The model allows temporal and spatial variations of porosity and permeability. The fluid viscosity and density are assumed to be temperature-dependent. The model also allows the development of single and multiple faults, depending upon the material (sediment and fluid) properties, loading and boundary conditions. Procedures are implemented for (1) updating the material properties such as porosity, permeability, fluid density and viscosity and (2) the development of faults which allow the formation of high-permeability conduits for fluid flow. The solution algorithm for displacements of the sediments and the excess pore (fluid) pressure is based on a residual load technique to handle the non-linear (elastic-plastic) deformation behaviour of the sediment skeleton. The model can be applied to one- and two-dimensional problems. Examples of a plane strain saturated sediment layer subjected to stepwise horizontal tractions versus time are given. 相似文献
11.
Axisymmetric consolidation of multi-layered soils induced by groundwater extraction from a dewatering well is studied with consideration of the anisotropic permeability and the well length. Laplace-Hankel transforms are utilized to solve the governing equations. The analytical layer-element method is used to build relationships between displacements, stresses, excess pore pressure and seepage velocity in the transformed domain. The real solutions can be obtained by the inversion of Laplace-Hankel transforms. A series of parametric studies, especially the length of a dewatering well and the combined effect of pumping and recharging, are conducted to analyze the consolidation behaviors of layered soils. 相似文献
12.
A design of a dewatering system is necessary for site improvement prior to the construction of some structures. The design
of an efficient dewatering system requires estimating the value of the in-situ coefficient of permeability. The available
relationships for estimating the permeability coefficient were developed based on limited field measurements and conditions,
and their predictions vary by several orders of magnitudes. Therefore, it was necessary to conduct field measurements of permeability
and determine the relationship that best fits these measurements prior to the design of a dewatering system for specific geological
and site conditions.
This paper presents field measurements of permeability in complex chaotic and diagenetic limestone strata. It also offers
comparative analysis of several relationships available in the literature for predicting the in-situ coefficient of permeability.
The analysis is conducted for both steady and nonsteady conditions. The results show that the coefficient of permeability
value is dependent on the water table level, which is affected by the tidal condition. The US Navy equation is shown to give
the best correlation with field measurements.
Electronic Publication 相似文献
13.
为分析利用真空井点进行沿海软土地基处理的可行性,在天津汉沽区南部沿渤海区域某电厂建筑场地,布置了利用真空轻型井点抽水的现场地基固结试验,为分析其固结试验效果,试验过程中进行了地下水位、孔隙水压力的现场监测,试验前后安排了现场检测试验。抽水固结试验结束后,经试验前后的静力触探试验、十字板剪切试验及室内土工试验对比分析,证明加固效果显著。抽水试验开始后较短的时间（75 d内）即可使加固的地基达到固结稳定,比贯入阻力提高200～300 kPa,十字板试验抗剪强度平均提高30～50 kPa,地基承载力可达120 kPa。试验说明,采用真空轻型井点处理沿海浅部软土地基是可行的。 相似文献
14.
钻孔灌注桩后压浆后,与坑外含水层相比,基坑范围内含水层的渗透系数减小,这对基坑降水渗流场具有比较明显的影响。某广场式建筑由五幢塔楼和地下车库组成,采用桩侧后压浆钻孔灌注桩,基坑开挖深度21m,承压含水层组厚10m,透水性较强,采用敞开式完整井降水,井位主要沿基坑周边布置。在对水文地质条件进行概化后,建立了地下水三维非稳定流数值模型,进行了非均质渗流场模拟,并与均质渗流场作比较。结果表明,坑内后压浆区域的渗透系数减小后,坑内水力坡度变陡,单井涌水量减小,井数应相应增加;若模型计算域全部按注浆后的渗透系数考虑,则会严重降低补给强度、低估基坑总涌水量;在相同的降深要求下,坑内后压浆后渗透系数减小、但坑外渗透系数不变,基坑总补给量基本没有变化。现场监测与模拟结果较为一致。研究成果对类似工程地下水控制有一定的借鉴意义。 相似文献
15.
基坑降水的成功与否,将对基坑开挖和周边环境产生重要影响,因此有必要对基坑降水方案进行评估。针对扬中金源时代购物中心基坑降水问题,采用MIDAS/GTS对基坑降水效果进行研究。首先,依据地勘报告中提供的土体渗透系数,结合单井、双井抽水试验结果,反演出MIDAS/GTS中需要的土层渗流系数和边界函数;然后利用反演得到的参数,建立了考虑回灌井补水效应的三维基坑降水效果分析模型,模拟基坑内水位降深与时间的变化关系,并对基坑降水效果进行分析和评估,以期指导土方开挖工程的施工。 相似文献
16.
深厚强透水含水层超大基坑降水群井效应研究 总被引：1，自引：0，他引：1
基坑减压降水的幅度与群井效应密切相关。某超大面积基坑,含水层组厚40m,中下部透水性强,采用非完整井降水。对水文地质条件概化,建立了地下水三维非稳定流数值模型,对均匀布置群井、不均匀布置群井、分块开挖降水、不同的井结构、布设回灌井等工况,进行了渗流场模拟。研究表明,强透水性含水层超大面积基坑降水的群井效应极为明显;井位角密中疏布置,可实现降深调平,避免降深不足和超降;基坑分块降水,可减少坑外降深;短滤管井结构可减少基坑总涌水量和坑外降深;强透水性含水层可灌性强,回灌对减少坑外水位下降有较明显的效果。模拟结果与现场监测较为一致。研究成果可为类似工程地下水控制设计提供参考。 相似文献
17.
工程渣土在水洗砂过程中产生的洗砂泥浆存在脱水效果差、不稳定的问题,这与泥浆的脱水性能密切相关。通过模拟现场洗砂工艺获得不同脱水性能的洗砂泥浆,开展了改进滤失试验及模拟压滤试验,研究了洗砂泥浆脱水性能受洗砂工艺的影响规律,获得了一种能够快速表征泥浆脱水性能的指标,用以指导优化渣土洗砂工艺。结果表明：洗砂泥浆脱水性能受洗砂粒径和加水量影响明显,滤失量及渗透系数与脱水性能有较好的相关关系;而30 min滤失量与最终滤失量、最终泥饼含水率呈现较好的相关性,能够较准确地反映泥浆脱水性能;经模拟压滤试验进一步验证,30 min滤失量可以作为洗砂泥浆脱水性能的快速表征指标。基于此提出了一套洗砂泥浆脱水性能的快速检测及工程渣土洗砂工艺优化方法,能够及时为洗砂工艺参数调整提供指导,以获得脱水性能较优的洗砂泥浆,最终使脱水效果得以改善和稳定。 相似文献
18.
Si-jie Liu Xue-yu Geng Hong-lei Sun Yuan-qiang Cai Xiao-dong Pan Li Shi 《国际地质力学数值与分析法杂志》2019,43(4):767-780
The system of vacuum pressure combined with vertical drains to accelerate soil consolidation is one of the most effective ground improvement methods. The consolidation theories of soft soil improved by vertical drains including void ratio–dependent compressibility and permeability have been widely applied in practice to predict the consolidation behavior. In this paper, analytical solutions of the consolidation of vertical drains are derived incorporating the loss and propagating stage of vacuum pressure. In addition, special solutions are obtained for the cases of instantaneous surcharge loading and staged surcharge loading, based on the general solution. The solution is verified by ignoring the propagating stage of vacuum pressure formation and comparing it with an existing solution. The effects of vacuum pressure loss and propagating stage combined with other parameters are investigated through the ratio between excess pore water pressure and surcharge loading. 相似文献
19.
疏浚淤泥含水率高、强度极低,真空梯度作用下排水板周围会快速形成致密“土柱”,导致排水固结能力迅速下降,即出现淤堵现象。由疏浚淤泥真空固结室内模型试验获得了出水量变化情况和土体含水率、渗透系数的时空分布情况,确定了排水体周围淤堵区的形成时间与范围,提出了考虑时间效应与淤堵效应的真空度传递模式,同时考虑疏浚淤泥土体压缩和渗透的非线性,建立了考虑淤堵效应的固结分析模型,获得了相应的解析解,通过与已有数据和现场试验结果对比验证了该解答的有效性。利用该解析解,分析了真空度传递模式、淤堵系数λ和淤堵比c对沉降的影响。结果表明,淤堵效应明显减缓了沉降速率,也严重降低了疏浚淤泥的最终沉降量。 相似文献