Subsurface transport behavior of micro-nano bubbles and potential applications for groundwater remediation.

Micro-nano bubbles (MNBs) are tiny bubbles with diameters on the order of micrometers and nanometers, showing great potential in environmental remediation. However, the application is only in the beginning stages and remains to be intensively studied. In order to explore the possible use of MNBs in groundwater contaminant removal, this study focuses on the transport of MNBs in porous media and dissolution processes. The bubble diameter distribution was obtained under different conditions by a laser particle analyzer. The permeability of MNB water through sand was compared with that of air-free water. Moreover, the mass transfer features of dissolved oxygen in water with MNBs were studied. The results show that the bubble diameter distribution is influenced by the surfactant concentration in the water. The existence of MNBs in pore water has no impact on the hydraulic conductivity of sand. Furthermore, the dissolved oxygen (DO) in water is greatly increased by the MNBs, which will predictably improve the aerobic bioremediation of groundwater. The results are meaningful and instructive in the further study of MNB research and applications in groundwater bioremediation.

Comparisons of operating envelopes for contaminated soil stabilised/solidified with different cementitious binders

This work initiated the development of operating envelopes for stabilised/solidified contaminated soils. The operating envelopes define the range of operating variables for acceptable performance of the treated soils. The study employed a soil spiked with 3,000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel. The binders used for treatment involved Portland cement (CEMI), pulverised fuel ash (PFA), ground granulated blast furnace slag (GGBS) and hydrated lime (hlime). The specific binder formulations were CEMI, CEMI/PFA = 1:4, CEMI/GGBS = 1:9 and hlime/GGBS = 1:4. The water contents employed ranged from 13 % to 21 % (dry weight), while binder dosages ranged from 5 % to 20 % (w/w). We monitored the stabilised/solidified soils for up to 84 days using different performance tests. The tests include unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. The water content range resulted in adequate workability of the mixes but had no significant effect on leachability of contaminants. We produced design charts, representing operating envelopes, from the results generated. The charts establish relationships between water content, binder dosage and UCS; and binder dosage, leachant pH and leachability of contaminants. The work also highlights the strengths and weaknesses of the different binder formulations. © 2013 Springer-Verlag Berlin Heidelberg.

PAA对不同土壤保水和蒸发性能的影响

采用土柱法研究了不同PAA施入量对3种黄土高原主要土壤类型(黄绵土、黑垆土和塿土)的持水性能、土壤饱和导水率和土壤蒸发量的影响,以进一步阐明PAA的保水和蒸发作用。结果表明,施入PAA提高了土壤的持水性能。在未加入PAA之前黑垆土的持水性能最低,塿土的最高,黄绵土的次之;加入PAA后,黑垆土的持水能力显著增加,几乎为对照的2倍,塿土和黄绵土也都比对照高。土壤的供水能力随PAA用量的增加而增强,不同土壤类型之间表现为:塿土>黑垆土>黄绵土。未加入PAA时,3种土壤饱和导水率大小为:塿土>黑垆土>黄绵土;加入PAA后,3种土壤的饱和导水率都降低,且基本随PAA用量的增加而降低。在一定水分条件下,PAA的施入提高了土壤的抗蒸发性能,随PAA用量的增加,塿土和黑垆土的土壤蒸发量增加,但都低于对照,而黄绵土的土壤蒸发量随PAA用量的增加而降低。其中施PAA54.5 mg/kg的塿土、黑垆土和施PAA225.8 mg/kg的黄绵土与对照相比,土壤蒸发量分别减少了44.0%,44.6%和30.6%。

子午岭植被恢复对土壤饱和导水率的影响

通过对子午岭林区不同植被的土壤性质进行实验室测定和野外调查,对饱和土壤水分运动的重要参数之一土壤饱和导水率(Ks)及其相关因子进行了多元分析和通径分析,揭示了植被恢复提高土壤水分传输性能的机理,主要结论如下:土壤有机质是子午岭林区九种植被下土壤饱和导水率提高的主要驱动因子。不同植被下的土壤饱和导水率均随深度的增加而迅速降低,尽管草地和先锋草地在5～10cm深度有一强透水层。土壤饱和导水率在剖面上的平均值,从辽东栎、早期森林、灌丛、先锋草地、弃耕地到草地依次降低。灌丛与草地、弃耕地的差异达到显著水平,辽东栎顶级群落的饱和导水率最高,植被的恢复明显提高了土壤饱和导水率。土壤容重、毛管孔隙度、>0.25mm团聚体含量及粘粒含量直接影响土壤饱和导水率。土壤有机质含量的提高能够改善容重、毛管孔隙度、团聚体含量等物理性质。

黄土高原坡地表层土壤饱和导水率和水分含量空间变异特征

表层土壤水分含量和饱和导水率对深层土壤水分的动态的变化具有重要的决定作用。在黄土高原坡地(50m×360 m)范围内进行网格(10 m×10 m)取样,用地统计学方法研究表层(0~30 cm)土壤饱和导水率和水分含量的空间变异特征。结果表明:1)坡地表层土壤密度变化规律为坡下位大于坡上位,土壤饱和导水率变异系数为0.37,属于中等变异强度;2)饱和导水率和自然对数化的饱和导水率在360 m尺度内均不具备空间结构特征,是纯随机变量,线性有基台模型适用于描述表层土壤水分的分布特征,水分分布存在明显的块金效应,并且随滞后距离的增加半方差变大;3)饱和导水率和水分含量从坡上位到坡下位均呈现波浪式变化,饱和导水率大的采样点土壤水分含量低,反之则高。

Effects of Fracture Seepage on the Stability of Landslide during Reservoir Water Level Fluctuation

The hydraulic conductivity function of fractures is a key scientific question to describe and reveal the process and the role of water seepage reasonably. In this paper, the generation technology of random fracture network and the latest numerical computation method for equivalent permeability tensor of fracture network are applied to analyze the landslide located at Wangjiayuanzi in Wanzhou District of Chongqing by simulating the changes of the seepage field caused by the running of the Three Gorges Reservoir. The influences of the fracture seepage on the seepage field and stability of the landslide were discussed with emphasis. The results show that the fractures existing in the soil increase the permeability coefficient of the landslide body and reduce the delay time of the underground water level in the landslide which fluctuates relative to the water level of reservoir，that causes the safe coefficient of the slope changes more gently than that of the same slope without fractures. It means, if only water level fluctuating condition is concerned, the fractures existing in the soil plays a positive role to the stability of slopes.

陕北水蚀风蚀交错区两种生物结皮对土壤饱和导水率的影响

该文以陕北水蚀风蚀交错区普遍发育的地表和地上两种生物结皮为研究对象,分别以3种非生物结皮(无结皮、物理结皮、去除生物结皮)为对照,使用盘式入渗仪测定其饱和导水率。结果表明:与无结皮土壤相比,两种类型生物结皮均可极显著降低土壤饱和导水率;与去除生物结皮土壤相比,两种类型生物结皮对土壤饱和导水率的降低均不显著;与有物理结皮发育的土壤相比,地表生物结皮对土壤饱和导水率的降低不显著,而地上生物结皮对土壤饱和导水率的降低显著。一方面,两种生物结皮对土壤饱和导水率均有明显降低作用,预示生物结皮在降雨活动中可能会增加径流、降低入渗,阻碍研究区水分亏缺条件下的植被恢复和生态与环境建设。另一方面,与不同的对照相比,生物结皮对土壤饱和导水率的影响截然不同,该结论可在一定程度上解释当前有关生物结皮影响土壤水分入渗方面所存在的分歧。

黄土塬区不同地形部位和土地利用方式对土壤物理性质的影响

在黄土塬区王东沟流域采集不同地形部位和不同土地利用方式下土壤样品,测定其颗粒组成、容重和饱和导水率,借助变异系数、非参数检验等方法研究了不同地形部位和不同利用方式对土壤物理性质的影响.结果表明:土壤物理性质在水平方向和沿垂直剖面都存在变异,但在同一地形部位或同一土地利用类型内,容重和颗粒组成基本相似.水平方向,饱和导水率属强变异,粘粒和砂粒含量属中等变异,粉粒含量和容重属弱变异;沿垂直剖面,土壤的粒级分布具有连续性,但0~25cm的土壤容重和饱和导水率与下层土壤差异显著.沿坡面从上向下,土壤趋向粘重,但饱和导水率增大;其中上坡位和中坡位的土壤性质相似,在相关研究中可以进行合并.草地与其他利用方式下的土壤性质差异显著,主要受地形部位的影响;耕地和果园的土壤性质相似且不同于其他利用类型,表明人为干扰对土壤物理性质有重要影响.

黑龙江省安达市草地碱化后土壤物理性状变化

调查了安达市盐碱地生物资源环境研究中心试验区羊草Leymus chinensis地土壤物理性状,包括土壤硬度、含水量、饱和导水率、粒径分布、剖面特征和土壤温度等。阐明土地碱化对土壤物理性质的影响,为安达市以及松嫩平原生态环境的修复和土地资源的永续利用提供科学依据。同时,讨论了地下水化学成分和土壤冻融变化对碱化的可能影响,认为在没有植被覆盖的条件下,冻融变化会加剧土壤的碱化程度。

推求土壤水分运动参数的简单入渗法──Ⅱ.实验验证

预报土壤中水分流动需要的土壤导水特性可通过观测水平土柱的入渗过程来确定，这一观测过程的分析是基于对Richards方程求积分解。土壤水分特征曲线中的参数由观测的水平立柱的特征湿润长度和吸力来确定，非饱和土壤导水率由已确定的特征曲线中的参数和测定的饱和导水率导出。供试土壤有三种，它们的质地从砂壤到粘壤。由这种方法所确定的这三种土壤的水分特征曲线与实测的特征曲线符合良好，所确定的砂壤的非他和导水率与实测值的比较令人满意。利用数值法和积分法分别计算了土壤含水量剖面，计算结果吻合良好，说明了这种方法的合理性。

推求土壤水分运动参数的简单入渗法 I.理论分析

预报非饱和土壤水分运动必须首先获得土壤水分运动参数。土壤水分运动参数包括土壤水分特征曲线和导水率。本文使用积分方法求解了一维水平非饱和土壤水分运动问题，根据其解建立了推求非饱和土壤水分运动参数的简单入渗法，用以推求ｖａｎ Ｇｅｎｕｃｈｔｅｎ特征曲线模型中的参数α和ｎ。α和ｎ是根据湿润区的特征长度、吸渗率和土壤的饱和导水率（ｋｓ）来确定的，而非饱和导水率可由α、ｎ和Ｋｓ确定。这一新的简单入渗法是基于Ｒｉｃｈａｒｄｓ方程和土壤导水特征的闭合型方程。简单入渗法提供了利用瞬态水流方法来确定土壤水分特征曲线而替代通常的平衡法。简单入渗法是一个全新的、简捷的确定土壤导水特性的方法。

根径向水流导度测定技术的改进

根系径向流的水力学性质主要是根的径向水流导度 ,它取决于根径向水流通道的状况。利用改进的现有原位测定根系径向水流导度的蒸腾计技术 ,设计了一个简便的 4室吸水测定装置 ,可一次性获得根木质部水势和根径向水流导度 ,缩短测定时间 10min ,确保测定精度。然后用改进的装置测定了生长在不同水分条件下冬小麦(TriticumaestivumL .)根系的径向水流导度 ,结果显示根系的平均径向水流导度为 4.6 3× 10 -7m·s-1·MPa-1,并随连体植株水分胁迫程度的增大而降低。

压力室测定根系导水率方法探讨

用压力室连续测定了玉米根系升压和降压过程的导水率。结果表明 ,降压过程测得的根系导水率显著大于用升压过程的 ,并且前者的相关系数大于后者。这种差异是由于这两个过程中质外体途径细胞壁空间充水量不同造成的。开始升压时 ,由于细胞壁空间含水量低 ,质外体途径阻力大 ,导致非结构阻力 ;随着压力的升高 ,细胞壁空间含水量增大 ,质外体途径导度增大 ,减小甚至可以消除非结构阻力。降压法可以使根系快速复水 ,消除传统方法因长时间复水所致根结构的改变。建议用降压法测定根系导水率

土石混合介质饱和导水率的研究

采用恒定水头法对土石混合介质的饱和导水率进行测定,分析不同碎石含量及碎石直径对饱和导水率的影响,同时利用实测值对Peck-W atson及Bouw er-R ice两个传统估算方程的估测精度进行比较。结果表明:(1)饱和导水率随碎石含量先增大后减小,且两者呈二项式关系;(2)饱和导水率随碎石直径增大而减小,两者呈幂函数关系;(3)碎石直径介于1.0~5.0 cm时,Bouw er-R ice和Peck-W atson方程对饱和导水率的估算结果均大于实测值。

填土边坡水文作用机理与破坏过程研究—以深圳羊宝地填土滑坡为例

A full understanding of failure mechanism, critical hydrological condition, and process of mobilization and deposition of a landslide is essential for optimal design of stabilization measure and forecasting of landslide hazard. This requires a quantitative study of hydrological response of a slope to rainfall through field monitoring, laboratory test and numerical modelling. At 13:40 on September 18, 2002, a fill slope failed following a period of prolonged rain in Shenzhen, resulting in 5 fatalities and 31 injuries. The failed mass with a volume about 2.5×104m3 traveled about 140m on level ground. Field monitoring, laboratory test, theoretical analysis and numerical modelling were carried out to undestand the hydrological response and failure mechanism of this fill slope. This thesis mainly focuses on the following aspects: (1) The hydrological responses and failure processes of slopes under rainfall infiltration were reviewed. Firstly, the factors influencing on the hydrological responses of slopes were analysed. Secondly, the change of stress state of slope soil and modelling methods of slope failure under rainfall infiltration were reviewed. (2) The characteristics of the Yangbaodi landslide and associated rainfall triggering the failure were presented. The failure was characterized by shallow flowslide, due to an increase of ground water table caused by rainfall infiltration. (3) A fully automated instrumentation was carried out to monitor rainfall, and saturated – unsaturated hydrological response of the fill slope, using a raingauge, piezometers, tensiometers and moisture probes. A conceptual hydrogeological model was presented based on field monitoring and borehole data. Analysis of monitoring data showed that the high pore water pressure in fill slope was caused by upward flow of semiconfined groundwater in the moderately decomposed granite. (4) Laboratory and in-situ testing was performed to study the physical and mechanical properties of fills. Isotropically consolidated undrained compression tests and anisotropically consolidated constant shear stress tests were carried out to understand the failure mechanism of the fill slope. It is indicated that loosely compacted soil is of strain-softening behaviour under undrained conditions, accompanied with a rapid increase in excess pore water pressure. In anisotropically consolidated constant shear stress tests, a very small axial strain was required to induce the failure and the excess pore water pressure increased quickly at failure. This indicated that static liquefaction caused by rise in groundwater table due to rainfall infiltration occurred. (5) The hydraulic conductivity of the highly and moderately decomposed granite was estimated using monitering data of pore water pressure. A saturated – unsaturated flow was modeled to study the hydrological response of the fill slope using rainfall records. It was observed that the lagged failure was due to the geological conditions and the discrepancy of hydraulic conductivity of slope soils. The hydraulic conductivity of moderately decomposed granite is relatively higher than the other materials, resulting in a semiconfied groundwater flow in the moderately decomposed granite, and subsequent upward flow into the upper fill layer. When the ground water table in the fill layer was increased to the critical state, the fill slope failed. (6) Numerical exercises were conducted to replay the failure process of the fill slope, based on field monitoring, laboratory and in-situ testing. It was found that the fill slope was mobilized by a rapid transfer of the concentrated shear stress. The movement of failure mass was characterized by viscosity fluid with a gradual increase in velocity. The failure process, including mobilization and subsequent movement and deposition, was studied using numerical methods.