蒋吉方(1989-), 男, 主要从事环境岩土研究, E-mail:
Jiang Jifang(1989-), main research interest:environment geotechnical, E-mail:
Yu Chuang(corresponding author), professor, PhD, E-mail:
温州制革、电镀等轻工业发达,废水中Cu2+含量较高,多处地下水和土壤受到污染。选取典型温州软黏土,将土样重塑,加入不同浓度的Cu2+和适量水泥进行固化,通过测试不同土样电阻率来研究Cu2+对土体性能的影响。电阻率测试在改装的一维压缩固结试验中进行,压缩中部分土样电阻率变化不显著,但可量测到压缩过程中电阻率的变化规律。试验结果表明:电阻率可以很好地评估加入水泥之后土体性质的改变,在实际工程中可以用来反映土体的污染程度; 土体在Cu2+含量和含水量很高时,不宜采用电阻率法评估土体污染压缩的过程。
The previously developed industry has contaminated part of groundwater and soils in Wenzhou with high concentration of Cu2+ in waste water, such as tannery, electroplating and etc. To study the characteristics of typical Wenzhou soft clay with Cu2+, the soil samples are remodeled to test the electrical resistivity with different concentrations of Cu2+ and reasonable amount of cement for consolidation. Electrical resistivity tests were carried out via the self-designed one-dimensional consolidation compression apparatus. The resistivity variation can be directly observed during the compression process. The testing results indicate that:while the concentration of Cu2+ and water in soil is high, electrical resistivity measurement should not be applied to assess the compression process of the soil. However, this measurement is a good indication for characteristics changes in soil after adding cement. Therefore the electrical resistivity might be taken as an effective means to estimate the degree of contamination of soil in practical engineering.
温州位于浙江省东南沿海地区, 东濒东海, 南接福建, 是中国著名的软粘土地区。温州软粘土成因类型为泻湖相, 沉积厚度达到35 m, 呈现流塑状态, 深厚均匀, 有不规则的粉砂层或透镜体, 属于高压缩性、低强度的软弱土[
土的电阻率作为土体的固有参数, 也可以表征土体的导电性, 具有连续、快捷、无损等优点[
本文在分析前人研究成果的基础上, 采用电阻率法研究不同铜离子浓度和水泥掺入量对温州软粘土的影响特性, 揭示电阻率与其他参数之间的关系。
土体的导电性有3个不同路径:孔隙水导电、颗粒表面(阳离子)导电或二者的综合作用, 如
粘性土中电流的3种流通路径示意图(据Rhoadels等[
Three conductance pathways unsaturated soil model (From Rhoades et al)
同时, 土体的导电性能主要由两个参数控制孔隙水中的盐含量及其饱和度:土的比表面积与粘土矿物含量。电流通过单位立方土体产生的电阻值被称为电阻率(Ω·m), 用
1) Wenner方法。直接通电流的Wenner法(DC法)是室内和现场测定的主流方法, 其示意图见
Wenner法示意图
Wenner method for determining soil resistance
2) 二相电极法。二相电极法示意图如
二相电极法示意图
Two electrodes method for determining soil resistance
试验在改装过的一维固结仪(WG-2A型双联固结仪)下进行, 环刀采用自制高强度树脂绝缘环刀; 打了小孔的透水石; 分析天平; 电阻测试采用Precision LCR Meter(LCR-800)电阻测试仪, 用两相电极法测得土样电阻
试验所用土为温州地区软黏土, Cu2+采用分析纯的CuCl2·2H2O晶体, 高纯水和普通水泥。
1) 试验准备。首先改装固结仪, 将原有的不锈钢护环进行绝缘处理, 用绝缘环刀代替不锈钢环刀, 绝缘上盖代替原不锈钢上盖。再制作数片圆形薄铜片, 使其直径与环刀内径一致; 最后, 在透水石上钻孔, 方便测试电阻的导线与试样上的金属片接触。
2) 试验开始。最先进行的是常规试验, 根据土工试验规范对土样进行基本测试, 测出其基本物理指标。然后进行试样的制备。配置不同含量Cu2+的土样, 称量CuCl2·2H2O晶体, 置于烧杯中, 缓缓倒入高纯水, 并持续搅拌, 配置样本污染液, 以每千克土样中所含不同Cu2+的量作为梯度浓度, 分别为3、6、9、12 g/kg。对土样进行烘干磨细, 称量后缓慢倒入托盘内, 缓慢倒入溶液进行充分搅拌后, 击实制成环刀样(先用不锈钢环刀制样, 制样前内壁涂上凡士林, 然后, 再平稳地转移到绝缘环刀内)。环刀两侧附上铜片, 放置改装的固结仪上进行电阻测试。
固结仪上土电阻率测试示意图
Electrical resistivity measurement with modified oedometer consolidation cell
采用上述制样方法, 制定相应的实验方案控制变量, 如
实验方案
Experiment of different conditions
含水量/ % | 离子浓度/ (g·kg-1) | 水泥掺入量/ % | 养护时间/d |
30 | 3 | 0 | 0 |
30 | 6 | 0 | 0 |
30 | 9 | 0 | 0 |
30 | 12 | 0 | 0 |
30 | 3 | 0 | 0 |
35 | 3 | 0 | 0 |
40 | 3 | 0 | 0 |
50 | 3 | 0 | 0 |
40 | 12 | 5 | 0 |
40 | 12 | 10 | 0 |
40 | 12 | 20 | 0 |
40 | 12 | 30 | 0 |
40 | 12 | 35 | 0 |
40 | 12 | 10 | 0 |
40 | 12 | 10 | 7 |
40 | 12 | 10 | 14 |
土体基本物理力学性质指标:天然含水量为70.34%, 密度为1.870 g/cm3, 比重为2.71, 液限为58%, 塑限为26%。
含水量30%时, 不同的离子浓度下电阻率试验结果见
不同浓度Cu2+污染土电阻率试验结果
Electrical resistivity test results of contaminated soils with different Cu2+ concentration
不同孔隙率污染土电阻率试验结果
Electrical resistivity test results of contaminated soils with different porosity
Cu2+浓度为3 g/kg时, 不同含水量下的电阻率试验结果见如
污染土不同含水量电阻率试验结果
Electrical resistivity test results of contaminated soils with different water content
含水量40%, Cu2+浓度12 g/kg时, 不同的水泥掺入量下土样电阻率试验结果见
污染土不同水泥含量电阻率试验结果
Electrical resistivity test results of contaminated soils with different cement content
同一含水量40%, 离子浓度12 g/kg, 水泥掺入量为10%, 不同养护时间下电阻率试验结果见
水泥污染土不同龄期电阻率试验结果
Electrical resistivity test results of contaminated soil-cement with different curing time
如
1) 孔隙率较小时, 电阻率特性不明显, 不能很好地评估土体特性的改变。
2) 含水量和Cu2+浓度较高时, 土体电阻率的变化区间减小, 不宜采用电阻率法来表征土体的性质的改变。
3) 加入水泥和养护之后, 电阻率值突变综合分析表明:温州软黏土中Cu2+的流动性在水泥固化土中被抑制, 水化反应越完全, 土体中孔隙越小, 导电性能降低, 电阻率升高。
4) 电阻率值可用于评估工程中土体重金属的污染程度, 反应水泥固化土体中重金属的效果。
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