一种用于突发性场地污染模拟的解析模型

为了及时有效地应对各种突发性环境污染事故,有必要开发一种简单实用、适于各类型污染物的场地污染数学模型。通过污染事故发生后污染物在包气带、饱和带迁移转化的概化,建立了污染物运移的自由入渗模型以及降雨入渗模型并给出各自相应的解析解。无降雨时,考虑污染物在重力作用下随包气带向下渗透的作用,建立一维垂直入渗模型。有降雨时,考虑污染场地（包气带）中污染物迁移和转化的对流作用、扩散作用及挥发、生物降解、吸附、根系吸收等作用,建立包气带剖面二维溶质运移模型和饱和带平面二维溶质运移数学模型。建模过程中,假定降雨量的平均分布及土壤质地、水力参数以及有机物成分、种类均相同,同时假定污染物与多孔介质间的作用为线性吸附,植物根系对污染物的吸附遵循一级动力学。基于模型的解析解,实现案例的模拟计算。模拟结果表明：该模型具有适用范围广、模拟高效快捷等优点,能够较准确预测污染发生后污染物在土壤中的动向、到达饱和带的时间以及饱和带中污染物的迁移情况。     

汶川地震区文家沟泥石流成因模式分析

文家沟2008～2010年期间8次泥石流事件是在地震滑坡堆积体上因持续强降雨渗透变形溃决和后续侵蚀产生的,不同于一般的沟谷型和坡面型泥石流。文家沟滑坡堆积体上新生的泥石流沟共冲出松散固体物质总体积约180×104m3,2010年的"8.13"泥石流事件是其中规模最大的一次,冲出的松散固体物质体积约在115×104m3。文家沟泥石流的成因模式是,强降雨过程在滑坡堆积体上先期出现"渗流管涌、暂态壅水、溃决滑塌"的造沟作用模式,后期出现"溯源侵蚀、冲刷刨蚀、侧蚀坍塌、混合奔流(搅拌机)"的扩沟作用模式。2008年的"6.21"和2010年的"7.31"泥石流事件主要起因于前者,其他事件主要起因于后者。松散堆积体因排泄持续降雨入渗的能力不足而造成地下水滞留和水位升高是导致斜坡体稳定性降低的内在原因。当地下水壅高水位面达到水平时,堆积体内渗透动水压力达到最大,堆积斜坡的稳定性最低,成为堆积体表层发生滑塌溃决的临界条件。     

降雨型浅层滑坡危险性预测模型

通过分析SHALSTAB和TRIGRS等浅层滑坡物理确定性模型存在的问题,提出了基于降雨入渗动态守恒的瞬态降雨入渗模型,该模型考虑了初期降雨过程、降雨历程以及饱和非饱和入渗过程,证明了SHALSTAB模型是该模型的特殊形式,并克服了TRIGRS模型参数繁多及一维入渗路径的问题.将无限边坡模型、瞬态降雨入渗模型和GIS进行耦合,研发了可用于大范围降雨型浅层滑坡危险性预测的集成系统,根据边坡的地质条件、地形参数和降雨特征即可对降雨条件下浅层滑坡的危险性进行评估.     

饱和土体中空沟对移动荷载被动隔振的 2.5D边界元法分析

根据饱和土Biot理论及移动荷载特性,采用积分变换方法,推导了半无限饱和土体频域-波数内的边界积分方程,讨论了2.5D边界积分方程中Cauchy的奇异性,并分析了空沟对移动荷载引起饱和土体振动的被动隔振效果。通过与已知文献结果比较,验证了算法的正确性。数值结果表明,采用2.5D BEM不仅可以解决具有复杂表面的移动荷载作用下动力响应问题,而且可极大减小计算工作量。对于饱和土体受高速移动荷载作用,空沟更能有效减小土体孔压、竖向位移的振幅;当荷载速度较小时,空沟对土体表面的水平向位移几乎不起衰减作用,甚至有放大效应。另外,随空沟距振源的距离增大,空沟能够更好阻隔土体表面波传播。     

Changes of Precipitation Infiltration Recharge in the Circumstances of Coal Mining Subsidence in the Shen‐Dong Coal Field,China

Coal mining subsidence is a universal environmental-geological problem in mining areas. By selecting the Shen-Dong coal mining subsidence area as the research field, this paper studies the changes in precipitation infiltration recharge in the circumstances of coal mining subsidence by means of field geological investigation and laboratory simulation experiments, which is expected to provide a scientific basis for eco-environmental restoration in the mining area. The results indicate that at the unstable stage of subsidence, three types of subsidence in the Shen-Dong mining area have positive effects on the precipitation infiltration recharge, and the type of full-thickness bedrock subsidence has the greatest influence. In the stable stage of subsidence, the precipitation infiltration process after long-term drought and the moisture migration in the aeration zone undergo three different stages: evaporation-infiltration before precipitation, infiltration-upward infiltration-infiltration during precipitation and evaporation-infiltration after precipitation. During a heavy rainfall infiltration process, the wetting front movement in fine sand, coarse sand and dualistic structure of fine-coarse sand consists of two stages: the stage of wetting front movement during precipitation, in which the wetting front movement distance has linear relationship with the depth, and the stage of wetting front movement after precipitation, in which the wetting front movement distance has the power function relationship with the depth. The wetting front movement velocity is influenced by the rainfall amount and the lithology in the aeration zone. However, as the depth increases, the movement velocity will decay exponentially.     

同位素信息确定Philip入渗模型稳定入渗率

通过流域水循环中各要素同位素含量的测定,扩大建模信息利用量,增加确定模型参数所需信息,提高参数可识别性,可在一定程度上减少参数的不确定性.以仅有两个参数且物理意义明确的Philip入渗模型为例,利用同位素信息确定Philip入渗模型参数稳定入渗率,并通过室内降雨入渗实验来检验同位素信息确定模型参数结果.结果表明,利用同位素信息确定的Philip入渗模型稳定入渗率与实测值接近.氢氧稳定同位素的分析精度对利用同位素信息确定模型参数结果有一定影响.     

马里亚纳南部弧内坡橄榄岩中的角闪石成分对于弧下地幔交代流体的指示

马里亚纳弧前的橄榄岩被认为是SSZ型蛇绿岩的现代等同物,记录了弧下地幔与俯冲流体的交代反应,其中的角闪石被认为是俯冲流体交代的产物.电子探针的数据表明角闪石主要包括透闪石和镁闪石两种,其中前者具有低的钠含量,后者则具有明显高的钠、铝含量,但Mg#较低.角闪石的组成反映了俯冲流体具有高硅、钙、铝、钠等元素的特征.形成成分...     

An analytical solution for rainfall infiltration into an unsaturated infinite slope and its application to slope stability analysis

Surficial slope failures in residual soils are common in tropical and subtropical regions as a result of rainfall infiltration. This study develops an analytical solution for simulating rainfall infiltration into an infinite unsaturated soil slope. The analytical solution is based on the general partial differential equation for water flow through unsaturated soils. It can accept soil–water characteristic curve and unsaturated permeability function of the exponential form into account. Numerical simulations are conducted to verify the assumptions of the analytical solution and demonstrate that the proposed analytical solution is acceptable for the coarse soils with low air entry values. The pore‐water pressure (pwp) distributions obtained from the analytical solution can be incorporated into a limit equilibrium method to do infinite slope stability analysis for a rain‐induced shallow slip. The analysis method takes into account the influence of the water content change on unit weight and hence on factor of safety. A series of analytical parametric analyses have been performed using the developed model. The analyses indicate that when the residual soil slope, consisting of a completely decomposed granite layer underlain by a less permeable layer, is subjected to a continuous heavy rainfall, the loss of negative pwp and the reduction in factor of safety were found to be most significant for the shallow soil layer and during the first 12 h. The antecedent and subsequent rainfall intensity, depth of a less permeable layer and slope angle all have a significant influence on the pwp response and hence the slope stability. Copyright © 2012 John Wiley & Sons, Ltd.     

非均质土坡降雨入渗的耦合过程及稳定性分析

针对天然土质边坡通常呈现非均质特性这一问题,进行了降雨入渗作用下非均质土坡稳定性分析,考虑了渗流场和应力场之间的耦合作用。以一简化非均质土坡模型为例,对比了耦合和非耦合情况下渗流场的差异,验证耦合的客观性和其必要性;细-粗型和粗-细型土坡的降雨入渗过程可分别分为2个和3个阶段;运用有限元强度折减法,以特征部位位移突变并结合塑性区贯通作为失稳判据,进行了土坡稳定性分析,发现雨水到达土坡土层接触面的时刻即为边坡稳定性突变的时刻;并通过深入分析孔隙水压力分布,揭示了降雨诱发非均质土坡的变形破坏机制。同时,就降雨强度、历时和渗透系数对非均质土坡入渗过程和稳定性的影响进行了大量的计算和分析,发现只有当雨水进入到下层土体时,该层土体渗透系数才会对土坡稳定性产生较大影响。     

Salt water infiltration in two artificial sea inlets in the Belgian dune area

In the dune area of the Westhoek Nature Reserve, situated in the western Belgian coastal plain, two artificial tidal inlets were made aiming to enhance biodiversity. The infiltration of salt water in these tidal inlets was carefully monitored because a fresh water lens is present in the phreatic dune aquifer. This forms an important source of fresh water which is for instance exploited by a water company. The infiltration was monitored over a period of two years by means of electromagnetic borehole measurements (EM39) and by measurements of fresh water heads and temperature using a large number of observation wells. EM39 observations point to aquifer heterogeneity as a determining factor in the movement of the salt infiltration water. It is shown that part of the infiltration water moves further in the dunes instead of towards the sea. On the long term run, possibility exists that salt water enters the extraction’s capture zone. This issue needs further monitoring and study. Fresh water head and temperature data illustrate that the main period of infiltration is confined to spring tide when large amounts of salt water enter the tidal inlets.