雨量变化对珊瑚岛礁淡水透镜体的影响

为探索雨量变化对珊瑚岛礁淡水透镜体的影响，应用质量守恒、Darcy定律和Ghyben-Herzberg比率，推导了珊瑚岛礁淡水透镜体的数学模型。根据西沙地区1989年-1998年10年的月均降雨量及最高、最低年降雨量，用有限差分法计算了永兴岛淡水透镜体的外型和贮水量的变化。结果表明，永兴岛淡水贮量4月最小，10月最大，相差值为4月贮水量的10．5％，而10年间降雨量最大和最小年淡水透镜体贮量与平水年相比，分别多16．8％乖少7．2％，这一结果可用于制定淡水透镜体的开采战略，实现淡水资源的安全、科学、持续开发利用。     

降雨强度对边坡稳定性影响的数值模拟研究

影响边坡稳定性的因素很多,利用数值模拟分析方法研究了降雨历时、降雨强度对边坡稳定性的影响.模拟结果表明,在相同坡角、相同降雨时间时,降雨强度越大,安全系数下降越快,土中孔隙水压力变化越快,土体位移变化越大,边坡稳定性降低越快;降雨强度大的边坡滑动要先于降雨强度小的边坡,降雨强度越大土体越先达到稳定状态,降雨强度大的边坡的入渗深度总是大于降雨强度小的边坡的入渗深度,降雨强度大的边坡安全系数始终低于降雨强度小的边坡的安全系数.     

基于FDTD方法的垂直接地体冲击时-频特性分析

基于L-D(Liew and Darveniza)提出的土壤非线性击穿效应模型,根据电磁场理论开发了一套三维时域有限差分(3-D FDTD)算法,建立了垂直接地体仿真模型,利用该模型于时域内从电场强度,电导率分布,最大暂态地电位升和暂态冲击阻抗的角度来研究了不同接地体长度和不同电流幅值对垂直接地体冲击散流特性的影响,于频域内从电场强度和电导率分布的角度来研究了垂直接地体在不同正弦电流频率中的散流特性。研究表明:1)接地体长度越长,土壤横向击穿区域越小,纵向击穿区域越大,最大暂态地电位升越小,暂态冲击阻抗越小;2)电流幅值越大,土壤横向和纵向击穿区域越大,最大暂态地电位升越大,暂态冲击阻抗越小;3)正弦电流频率越高,土壤的"趋肤效应"越强,极大影响了接地体的散流过程。     

膨胀土边坡渗流数值模拟及稳定性分析

采用有限元软件(Seep/W和Slope/W)开展一系列瞬态渗流和极限平衡分析,研究不同降雨强度与历时对膨胀土边坡渗流场的影响,分析降雨强度及历时、不同坡比和坡高等因素对边坡稳定性的影响,分析其浅层破坏的原因。结果表明:必须考虑风化裂隙导致浅表层土体渗透系数增大对膨胀土边坡渗流场的影响;降雨强度及历时对边坡土体孔隙水压力分布影响显著,相同降雨强度条件下,历时越长,影响深度越深、范围越大,孔隙水压力变化越大;相同历时条件下,持续降雨强度越小,影响深度越浅、范围越小,孔隙水压力变化越小;安全系数随降雨强度的增大,其下降速率越快,达到破坏所需的时间越短;边坡浅层达到饱和时,坡高及设置平台对边坡安全系数影响不大,均发生浅层破坏;安全系数随坡率的增大而增大,但对某些膨胀土边坡而言,采用放缓坡率的做法并不可取。     

考虑潜蚀影响的降雨入渗边坡稳定性分析

在降雨入渗作用下土坡内细颗粒会随渗流发生运移产生潜蚀作用。通过联立颗粒运移方程与非饱和土渗流方程,结合非饱和土水力特性方程和土体潜蚀本构关系,建立了渗流潜蚀耦合的边坡稳定性分析模型。采用有限元方法模拟了降雨入渗作用下潜蚀和入渗的相互作用,分析了初始饱和渗透系数、进气值参数对入渗和边坡稳定性的影响。结果表明：潜蚀主要发生在湿润锋范围内浅层土体,潜蚀加速了湿润锋下行速度,进一步降低边坡稳定性;饱和渗透系数、进气值是影响渗流潜蚀作用的主要因素;当降雨入渗强度大于饱和渗透系数时,饱和渗透系数越大,潜蚀对入渗和边坡稳定性的影响越显著;进气值越小,潜蚀作用对入渗和边坡稳定性的影响越显著。     

珊瑚岛淡水透镜体的形成特征及影响因素

淡水透镜体是一种宝贵的淡水资源,正受到人们的高度关注。本文叙述了珊瑚岛淡水透镜体的形成特征及其影响因素,以便更好地开发利用。     

基于强度衰减模型的降雨对边坡渗流影响的研究

以某工程实例为对象的数值模拟得到以下结论:土体深度越浅,孔隙水压力越小,渗透力越大,受降雨渗流的影响越大,中间深度土体的渗流速度最大,地下水位以下土层的渗流参数基本不受降雨影响,渗流参数随降雨强度、降雨时长的增加而增大。     

降雨入渗条件下非饱和黏土边坡稳定性分析

大量研究表明,主要且直接诱发边坡失稳的主要因数是降雨,雨水入渗对非饱和土质边坡稳定性的影响最大。分析非饱和黏土边坡基质吸力和渗流场影响,采用有限元软件FLAC2D建立非饱和黏土边坡的数值模型,研究计算在降雨强度不同条件下,降雨时间相同和降雨总量相同这两种情况对边坡稳定性的影响。结果表明:非饱和黏土边坡内部的剪应变增量随降雨强度的变大而增大,边坡的位移也和降雨强度呈正相关关系,降雨强度越大越容易造成黏土边坡表层失稳。     

非饱和砂质黏性紫色土一维渗透特性试验研究

利用土体瞬时渗透特性测试仪,对重庆非饱和砂质黏性紫色土进行一维土柱垂直渗透试验。模拟不同降雨条件(5 mm/h、15 mm/h、30 mm/h)下,其入渗率、累积入渗量、浸润峰、体积含水率和吸力等随时间的变化规律;分析得到其渗透特性和持水特性。结果表明:(1)在初始含水率相同的情况下,降雨强度越大,初期入渗率越大;土体的入渗率与含水率有关,含水率越低的土体,其入渗率越大;(2)不同降雨强度下,水入渗到同一监测点的时间不同;且降雨强度越大时,含水率增大到某一稳定值的数值也越大;(3)降雨强度并不会影响土体的饱和渗透系数和持水性能。从试验规律可知非饱和砂质黏性紫色土的体积含水率θ与渗透系数的对数lgk之间存在线性关系,拟合的线性方程,可应用于相应紫色土地区土体的非饱和渗流分析。     

降雨条件下一维土柱垂直入渗模型试验研究及其渗透系数求解

 为研究降雨条件下一维土柱的入渗规律及求解非饱和土体的渗透系数,开发一套模拟降雨条件下一维土柱垂直入渗模型试验装置,对非饱和重塑黄土土柱做了4组不同降雨强度下的一维垂直入渗试验,得到不同降雨强度下垂直土柱的入渗率时程曲线、浸润峰深度时程曲线及监测点体积含水率的变化规律;提出计算非饱和土体渗透系数的新方法,并结合试验结果,得到试验土样非饱和渗透系数与基质吸力的关系曲线。结果表明：(1) 降雨强度对垂直土柱的入渗影响较大,当降雨强度小于土柱最小入渗能力时,入渗率等于降雨强度;当降雨强度大于土柱最小入渗能力时,入渗率时程曲线呈无压入渗、有压入渗和饱和入渗3阶段变化。(2) 不同降雨强度下,土柱出现积水点和饱和点的历时不同,降雨强度越大出现积水点和饱和点的时间越短,有压入渗阶段越长。(3) 在同一降雨强度下,监测点距土柱上表面越远,其体积含水率时程曲线越密集;而同一监测点,降雨强度越大,其体积含水率时程曲线越稀疏。(4) 非饱和重塑黄土渗透系数随基质吸力的增大而减小,且渗透系数的对数与基质吸力呈线性变化。     

非平稳随机场下饱和渗透系数空间变异性的无限长边坡稳定概率分析

土体饱和渗透系数表现为天然的空间强变异性,其均值通常沿土层深度方向呈递减趋势,但目前鲜有文献考虑这一特性。为此,以FLAC为平台,利用fish语言基于局部平均法建立了表征土体饱和渗透系数均值随深度递减的一维非平稳随机场模型,采用FLAC两相流模块模拟雨水的入渗过程,以蒙特卡罗法为框架,结合考虑正孔隙水压力的广义有效应力无限边坡稳定模型,探讨了饱和渗透系数空间变异性在不同降雨时刻下对边坡最危险滑裂面分布规律以及相应的边坡破坏概率的影响。结果表明：忽略饱和渗透系数的空间变异性的确定分析方法将不能真实反映边坡的安全性;随着降雨持时的增加,边坡最危险滑裂面发生在坡底基岩处的概率逐渐降低;随着饱和渗透系数竖向相关距离的增加,边坡最危险滑裂面发生在坡底的概率逐渐增加,而相应的边坡破坏概率却随竖向相关距离的增加而逐渐降低。     

Estimating the amenity value of rainfall

The amenity value of two measures of rainfall are investigated in this study: long term average annual rainfall and the variation in rainfall within the year. Estimates of the economic value of rainfall and variation in rainfall are found using the hedonic property value technique. The results indicate that rainfall is an attribute for which the distribution as well as the average annual level is important. Home buyers prefer less annual rainfall, but, holding annual rainfall constant, buyers will also pay more for greater seasonal variation in rainfall.The author thanks Gardner Brown, Robert Mendelsohn, and George Parsons for their comments and suggestions with this research. Any errors and omissions remain the author's responsibility. Research supported in part by the Nevada Experiment Station.     

Rainfall intensity and phosphorus source effects on phosphorus transport in surface runoff from soil trays

Phosphorus runoff from agricultural fields amended with mineral fertilizers and manures has been linked to freshwater eutrophication. A rainfall simulation study was conducted to evaluate the effects of different rainfall intensities and P sources differing in water soluble P (WSP) concentration on P transport in runoff from soil trays packed with a Berks loam and grassed with annual ryegrass (Lolium multiflorum Lam.). Triple superphosphate (TSP; 79% WSP), low-grade super single phosphate (LGSSP; 50% WSP), North Carolina rock phosphate (NCRP; 0.5% WSP) and swine manure (SM; 70% WSP), were broadcast (100 kg total P ha-1) and rainfall applied at 25, 50 and 75 mm h-1 1, 7, 21, and 56 days after P source application. The concentration of dissolved reactive (DRP), particulate (PP), and total P (TP) was significantly (P<0.01) greater in runoff with a rainfall intensity of 75 than 25 mm h-1 for all P sources. Further, runoff DRP increased as P source WSP increased, with runoff from a 50 mm h-1 rain 1 day after source application having a DRP concentration of 0.25 mg L-1 for NCRP and 28.21 mg L-1 for TSP. In contrast, the proportion of runoff TP as PP was greater with low (39% PP for NCRP) than high WSP sources (4% PP for TSP) averaged for all rainfall intensities. The increased PP transport is attributed to the detachment and transport of undissolved P source particles during runoff. These results show that P source water solubility and rainfall intensity can influence P transport in runoff, which is important in evaluating the long-term risks of P source application on P transport in surface runoff.     

黄土高原的石油类物质坡面径流污染研究

延河流域石油类污染物的暴雨径流污染是当地地表水体的一种重要污染形式。为了探明石油类物质的径流污染规律,进行了室内模拟试验。结果表明：降雨强度、土壤污染强度、受雨坡面的坡度等因素都能明显影响降雨径流污染过程;污染过程中的水相石油类物质是由径流含沙量和径流泥沙石油污染强度共同决定的,在试验条件下,水相污染强度可达１．５６～５．１９ｍｇ／Ｌ,足以对径流造成严重的污染。     

Estimating biozone hydraulic conductivity in wastewater soil-infiltration systems using inverse numerical modeling

During operation of an onsite wastewater treatment system, a low-permeability biozone develops at the infiltrative surface (IS) during application of wastewater to soil. Inverse numerical-model simulations were used to estimate the biozone saturated hydraulic conductivity (K(biozone)) under variably saturated conditions for 29 wastewater infiltration test cells installed in a sandy loam field soil. Test cells employed two loading rates (4 and 8cm/day) and 3 IS designs: open chamber, gravel, and synthetic bundles. The ratio of K(biozone) to the saturated hydraulic conductivity of the natural soil (K(s)) was used to quantify the reductions in the IS hydraulic conductivity. A smaller value of K(biozone)/K(s,) reflects a greater reduction in hydraulic conductivity. The IS hydraulic conductivity was reduced by 1-3 orders of magnitude. The reduction in IS hydraulic conductivity was primarily influenced by wastewater loading rate and IS type and not by the K(s) of the native soil. The higher loading rate yielded greater reductions in IS hydraulic conductivity than the lower loading rate for bundle and gravel cells, but the difference was not statistically significant for chamber cells. Bundle and gravel cells exhibited a greater reduction in IS hydraulic conductivity than chamber cells at the higher loading rates, while the difference between gravel and bundle systems was not statistically significant. At the lower rate, bundle cells exhibited generally lower K(biozone)/K(s) values, but not at a statistically significant level, while gravel and chamber cells were statistically similar. Gravel cells exhibited the greatest variability in measured values, which may complicate design efforts based on K(biozone) evaluations for these systems. These results suggest that chamber systems may provide for a more robust design, particularly for high or variable wastewater infiltration rates.     

冻结风立井白垩系砂岩导热特性的试验研究

为掌握我国西部白垩系富水基岩的热物理特性,采用基于瞬态平面热源技术的Hot-Disk 热常数分析仪对不同温度(-30 ℃、-20 ℃、-10 ℃、-5 ℃、0 ℃、10 ℃、27 ℃)、不同含水(干燥、微量含水、大量含水、饱水)、不同粒径(中粒、粗粒)白垩系砂岩的热导率λ进行了测试。结果表明:饱水砂岩热导率λ随温度降低而先增大后略有减小并趋于稳定,-10 ℃时达峰值3.375 W/m·K;砂岩热导率λ随含水率ω增加呈先增大后减小趋势,λ的范围在0.368-2.242 W/m·K之间,当ω=6.282%-7.539%时热导率λ较大,此时中砂岩最大热导率可达2.242 W/m·K;常温下,相同含水的非饱和白垩系粗砂岩热导率总大于中砂岩0.254~0.284 W/m·K,其中粗、中砂岩平均孔隙度分别为15.169%、21.863%,说明非饱和时砂岩孔隙度越小、颗粒粒径越大则热导率越大。可为西部白垩系地层深厚富水基岩煤矿立井冻结设计提供科学的理论依据。     

Environmental consequences of cattle feedlot manure on saline soils

In a long‐term experiment at the Directorate of Land Reclamation, the effects of cattle manure on soil characteristics were determined after five annual applications. The results indicate that during high rainfall NO₃‐N moves below 150 cm soil layer and causes pollution problems for shallow groundwaters. Long‐term annual application of cattle manure to saline soils at rates greater than recommended [20 Mg/ha and 40 Mg/ha (wet wt.) for nonirrigated and irrigated land, respectively] is not advisable.     

Stable expression and control parameters in the numerical simulation of unsaturated flow

The Richards’ equation describes the flow phenomenon in unsaturated porous media and is essential to hydrology and environmental science. This study evaluated the numerical stability of two different forms of the Richards’ equation. Sensitivity analyses were performed to investigate the control parameters of the equation. The results show that the h-form Richards’ equation has better applicability for calculating variable saturation flows than the θ-form Richards’ equation. For the h-form Richards’ equation, the hydraulic conductivity of the soil in the low-suction range and the specific moisture capacity in the high-suction range primarily influenced the solution. In addition, sensitivity analyses indicated that the saturated hydraulic conductivity, initial condition, and air-entry pressure have a higher sensitivity to the simulation results than the saturated water content, rainfall intensity, and decline rate of hydraulic conductivity. Moreover, their correctness needs to be guaranteed first in numerical simulations. The research findings can provide a helpful reference for improving the reliability of numerical simulations of unsaturated flows.