降雨条件下坡积土边坡暂态饱和区形成机理及分布规律

降雨是引起坡积土边坡失稳的最常见外部因素之一。雨水的入渗在引起土体抗剪强度参数降低的同时,还将导致土体重度的增加、基质吸力的降低,最终造成边坡的失稳。开展雨水在边坡内部的渗流过程研究已成为分析边坡在降雨条件下稳定性的前提。基于有限元数值模拟方法,进行了雨水在土体中渗流过程的模拟,着眼于降雨条件下边坡暂态饱和区的形成、分布及消散特征,描述了该过程中边坡内部含水率、基质吸力、水力梯度的变化规律。结果表明：暂态饱和区形成的主要原因是土体中向湿润锋下方渗出的雨水量小于降雨入渗补给量,从而使得土体中的含水率累积升高;暂态饱和区的形成与降雨强度、降雨时间具有十分密切的关系,暂态饱和区形成时间、雨水入渗深度、土体表面体积含水率大小分别与降雨强度存在函数关系;清晰描述了暂态饱和区形成发展消散地下水位升高的全过程,从该过程看,边坡排水措施的设计值得思考。     

Rainfall''s Effect on the Stability of Unsaturated Slopes

Aimed to analyze the influence of rainfall on slope stability. The finite element method (FEM) is used for the calculation of 2-D transient seepage in the unsaturated slope, while the method of limit equilibrium is used for computing its safety factor. The change of pore water pressure, slip surface and safety factor are investigated through numerical calculations with consideration of various intensity and duration of rainfall. Special attention has been paid to slope stability after rainfall. It is found that sometimes the minimum safety factor may occur several hours or several days after the rainfall, instead of the time during the rainfall or when the rain just stops.     

饱和渗透系数空间变异性对边坡稳定性的影响

研究了降雨雨型、雨强和持时对边坡孔隙水压力分布的影响以及降雨入渗条件下饱和渗透系数的空间变异性对孔隙水压力、含水率、抗剪强度参数、局部安全系数等参数空间分布的影响。研究结果表明,降雨特性对边坡孔隙水压力的影响较大;受渗流主方向影响,降雨条件下饱和渗透系数的水平波动尺度对孔隙水压力及含水率的变异性影响小于竖向波动尺度,降雨致滑坡的临界滑面基本与坡面平行且深度较浅;随着饱和渗透系数水平波动尺度的增加,滑坡深度随之增大,从总体上坡体上部局部安全系数随饱和渗透系数竖向波动尺度的增加而减小。     

降雨入渗对宁南山区黄土梯田边坡稳定性的影响

为了研究降雨入渗对宁南山区黄土梯田边坡稳定性的影响。采用ABAQUS软件建立降雨入渗下的宁南山区黄土梯田边坡稳定性有限元模型,研究了水平梯田、隔坡梯田、原始边坡（对照）3种边坡类型,在降雨入渗强度(28~38 mm/h)和边坡坡度(15°—30°)下的破坏时间和安全系数的变化规律。结果表明:降雨入渗下,黄土梯田边坡的破坏时间随降雨入渗强度的增大而减小,且呈幂函数关系,水平梯田的破坏时间显著高于隔坡梯田和原始边坡;安全系数也随降雨入渗强度的增大而减小,但呈线性关系,水平梯田的安全系数与隔坡梯田和原始边坡并无显著差异。降雨条件下,修筑梯田能增加浅层梯田边坡的稳定性,而对于深层梯田边坡的稳定性影响不大。     

Cropping system effects of maize on infiltration,runoff and erosion on loess soils in South-Limbourg (The Netherlands): A comparison of two rainfall events

Two natural rainfall events are compared to evaluate the effects of three cropping systems of silage maize on soil moisture content, infiltration, runoff and erosion. Both rainfall events took place in early summer. One was a low intensity event with 27.6 mm of rain in 9 hours, and the other a high intensity event with 33.4 mm in 42 minutes. Cropping systems were:

• 1.(I) a spring tilled system (conventional),
• 2.(II) an autumn and spring tilled system with summer barley as spring cover crop, and
• 3.(III) an autumn tilled system with winter rye as winter cover crop and direct drilling of silage maize.

During the low intensity event, soil moisture content of the top 5 cm rose to field capacity on all three cropping systems. No runoff was generated. During the high intensity event, soil moisture content rose to field capacity on the two spring tilled cropping systems but was only slightly raised in the direct drill system, in spite of 17.7 mm of infiltrated rain. Runoff coefficients of the high intensity event were 41.7% (conventional system), 14.9% (autumn and spring tilled system) and 47.0% (direct drill system). The direct drill system showed a severely slaked soil surface in early summer, caused by winter rain.The response to rainfall of soil moisture content is ascribed to:

• 1.(I) a predominance of matrix infiltration on all cropping systems during the low intensity event and on the spring tilled systems during the high intensity event, and
• 2.(II) a predominance of infiltration via continuous macropores, open to the surface (of biologic origin), by-passing the soil matrix, on the direct drill system during the high intensity event.

The presence of continuous, vertical macropores on the direct drill system explains its surprisingly high infiltration capacity, considering its strongly slaked appearance. The smooth soil surface of the direct drill cropping system may have delayed infiltration during the flooded stage of the high intensity event by not providing vent points for the escape of soil air. Soil loss from the direct drill system during the high intensity event was only 15.6% of that from the conventional system. This is ascribed to low detachment rates of soil material by drop impact and/or overland flow, due to the presence of winter rye remains and, especially, the relatively high soil surface shear strength of the direct drill cropping system in early summer.     

辽西北沙地流动沙丘土壤水分时空变化特征研究

以辽西北沙地流动沙丘为对象,研究了土壤水分运动的时空变化特征。结果表明：流动沙丘土壤含水率的时间变化与降雨有密切关系,春季土壤含水率较低,为0.1%~3.1%;夏季土壤含水率较高,为2.5%~5.1%;秋季土壤含水率略高于春季,为2.2%~3.6%。土壤含水率垂直变化位为：0~10cm土壤含水率变异程度较大,受降雨和蒸发影响强烈;10cm~80cm变异程度相对小些;80cm~120cm土壤含水率比较稳定。流动沙丘不同部位的土壤含水率受干沙层厚度频繁变化和降雨量影响显著,阴坡底含水率＞阳坡底＞阳坡中＞丘顶＞阴中。     

简单屋顶绿化的滞蓄特性

设计了模拟降雨与数据采集系统,研究了短时强降雨下简单屋顶绿化基质(配比：陶粒57.0%、草炭41.5%、保水剂1.5%)的降雨产流过程,基于37次模拟降雨实验,归纳了降雨产流的一般过程、规律和特性,分析了降雨强度、基质厚度和基质初始含水率对简单屋顶绿化滞流蓄水特性的影响。结果表明：基质厚度和基质初始含水率对简单屋顶绿化的蓄水特性有显著影响,基质初始含水率越低、基质厚度越厚时蓄水特性越佳。建立了产流时间数学模型,简单屋顶绿化降雨产流时间与降雨强度呈负相关,同时也受初始含水量和基质厚度影响。随着干湿循环次数增加,基质的厚度总体呈现下降趋势,储水性能逐渐下降,延迟产流时间逐渐缩短。     

异位发酵床垫料的直剪切及压缩试验研究

为研究不同含水率的条件下异位发酵床垫料:抗剪强度、黏聚力、内摩擦系数、压缩载荷的变化规律.本研究采用土壤力学试验方法,测定垫料五种不同含水率的相关参数.结果表明:当垫料含水率为29.22％～36.13％时,抗剪强度、内摩擦角系数会随着含水率的增大而增大;当含水率为45.55％～61.11％时,抗剪强度、内摩擦角系数会随...     

渤海西岸一次副热带高压边缘暴雨特征分析

为探究夏季西太平洋副热带高压边缘暴雨特征,改进暴雨天气预报模型和可预报因子,提高暴雨预报准确率。利用micaps、高低空风场、T639L60 物理量资料,对2010 年8 月4—5 日发生在渤海西岸的暴雨天气过程的环流形势、高低空急流、垂直速度、相对湿度特征进行分析。结果表明：副热带高压、西风槽和中低层切变线以及地面气旋是造成此次暴雨天气过程的影响系统,高空冷空气和低空暖湿空气在渤海西岸地区交汇触发了此次天气过程;高层辐散、低层辐合为空气上升运动提供了有力的动力条件,中低层的西南风急流和近地面层持续的偏东风为降水区提供了充沛的水汽;此次暴雨出现在副高588 dagpm 等值线与584 dagpm 等值线之间中低层存在切变线的位置和200 hPa 高空急流入口处的右侧、850 hPa 低空急流的左侧所对应区域;高低空急流增强、上干下湿的对流不稳定层结发展、空气上升运动增强、高层有干冷空气侵入、低层有较强暖湿空气输送预示将出现强降水天气;高低空急流减弱消失、低层暖湿空气输送减弱消失及干冷空气侵入低层预示强降水将减弱停止。     

不同耗水强度下节水灌溉稻田土壤含水率与非饱和土层厚度关系研究

为了探索基于土壤非饱和层厚度指导水稻节水灌溉的可能性,研究节水灌溉稻田土壤含水率与非饱和土层厚度的关系非常必要。本文通过设计盆栽试验,针对不同耗水强度开展连续观测,根据实时观测的土壤含水率与非饱和土层厚度,建立起两者之间的定量关系。结果表明：稻田日耗水强度越大,其非饱和土层厚度随时间增加的速率越大,达到最大值所需的时间越短。非饱和土层随时间增加时对应的土壤含水率则随时间下降,两者之间成负相关关系。通过建立土壤含水率与非饱和土层厚度的二次抛物线关系,结果显示将非饱和土层厚度作为水分控制指标指导灌溉精度高、切实可行。最后,将土壤含水率与非饱和土层厚度关系曲线运用到水稻控制灌溉的实践中,推算出土壤含水量下限对应的非饱和土层厚度值,确定以非饱和土层厚度为指标的控制灌溉方法,为黑龙江地区水稻节水灌溉管理技术提供参考,为下一步的水分运动模型率定及模拟更多土质和更多耗水情形下的土壤水分提供依据。     

宁南黄土丘陵区不同生态恢复与重建中的土壤水分变化研究

针对宁南黄土丘陵区存在的生态脆弱、环境恶化的突出问题,对黄土丘陵区不同生态恢复过程中的土壤水分变化进行了研究。研究结果表明：在退化山地的植被恢复过程中, 0~60cm土层,土壤水分含量随恢复年限的增长而增加,在60cm土层以下,土壤含水量随着退耕年限的不断增长不断减小;对于不同恢复方式的土壤水分含量,88542水平沟>人工草地>鱼鳞坑>天然草地;对于不同植被类型的土壤水分含量,草地>灌木地>林地;对于不同地形的土壤水分含量,阴坡>半阴坡>阳坡,坡下部>坡中部>坡上部,并且随着坡度的不断增加,土壤水分含量不断减小。     

Effect of Rainfall Collecting with Ridge and Furrow on Soil Moisture and Root Growth of Corn in Semiarid Northwest China

A plastic‐covered ridge and furrow farming of rainfall collecting (RC) system were designed to increase water availability to corn for improving and stabilizing agricultural production in the semiarid Loess region of northwest China. This system comprised two elements: the ridge mulched by plastic film that acts as a rainfall harvesting zone and the furrow as a planting zone. To adopt this system for large‐scale use in the semiarid region and bring it into full play, it is necessary to test the appropriate rainfall range for RC farming. A field study (using corn as an indicator crop) combined with rainfall simulation was conducted to determine the effect of RC on soil moisture, root characteristic parameters and the yield of corn under three different rainfall levels (230, 340 and 440 mm) during the growing seasons of 2006 and 2007. The results indicated that with the rainfalls ranging within 230–440 mm, the soil moisture at 0–100 cm depth for RC system in furrows was significantly higher (P < 0.05) than that of conventional flat (CF for control) practice. At 100–200 cm soil depth, there was no significant difference (P > 0.05) between soil moisture in the RC₂₃₀ plots and in the CF₂₃₀ plots during the corn growing seasons, while the soil moisture both in the RC₃₄₀ and RC₄₄₀ plots were significantly higher (P < 0.05) than those in the CF₃₄₀ and CF₄₄₀ plots. The root length, root surface area, root volume and root dry weight for RC₂₃₀ and RC₃₄₀ plots all significantly increased (P < 0.05) compared with CF₂₃₀ and CF₃₄₀ plots, but these root characteristic parameters at 440 mm rainfall slightly decreased compared with those of CF practice. Compared with the CF_230–440 pattern, the increasing amplitude of grain yield under the RC_230–440 pattern diminished with the rainfall increase and there was no obvious yield‐incrementing effect (P > 0.05) between two patterns at 440 mm rainfall in 2006. In comparison with these two farming practices, the RC system not only improved soil moisture of dry farmland, but also promoted the development of corn root systems when the rainfall ranged between 230 and 440 mm. Thus, it could be concluded that the optimal upper rainfall limit for the RC system is below 440 mm in the experiment. For corn, the adoption of the RC practice in the 230–440 mm rainfall area will make the system more effective during the whole growth period and offer a sound opportunity for sustainable farming in semiarid areas.     

固结煤矸石抗剪强度特征试验

依据现场大型剪切试验和室内直剪试验,研究了固结煤矸石的抗剪强度特性。试验剪应力-剪位移过程曲线表明,一定含水率条件下的固结煤矸石呈现明显的粘塑性体力学特性。以现场大型剪切试验煤矸石作为试样配料进行了室内直剪试验,分析了含水率和密实度对良好固结煤矸石试样剪应力-剪位移试验曲线以及抗剪强度参数的影响,在此基础上探讨了试样内煤及其它细颗粒的状态变化对固结煤矸石抗剪强度的弱化作用机理,最后对比分析了现场大型剪切试验抗剪强度参数值和室内直剪试验抗剪强度参数值的差异及其产生的主要原因。     

Soil surface densification under simulated high intensity rainfall

The formation of surface crusts in agricultural soils has adverse effects on seedling emergence and infiltration and causes excessive water loss by runoff. Changes in soil surface characteristics of Zamora soil were examined under high intensity (76.2 mm/hr) simulated rainstorms A hard, dense, several-cm-thick, consolidated layer developed on the soil surface upon drying. The thickness and bulk density of this layer were strongly related to rainfall duration. A strong exponential function was found between the thickness of the consolidated layer and the soil wetted depth. Soil surface strength was strongly correlated with rainfall duration and with the initial bulk density of the soil despite the marked change in the density of the consolidated layer. The largest changes in both strength and bulk density occurred within the first 10 min of the rainstorm. Mechanisms known to be responsible for crusting appear to partly hold for the densification process, but they do not adequately explain the deeper consolidation. Particle reorganization and close-packing associated with settling under saturated or near-saturated conditions appear to provide more logical mechanisms. The relative change in bulk density was inversely correlated with the initial soil bulk density. Measurements of soil strength with a small penetrometer probe indicated an agreement between surface strength and the cohesion of the consolidated layer as determined by a triaxial shear test. Temperature of drying had slight, but mostly inconsistent effects on the strength and density of the consolidated layer. Soil densification was also found to markedly decrease the infiltration rate. The physical properties of both the consolidated layer and the subsoil, however, appeared to control the infiltration process.     

The effect of grass roots on shear strength variations with moisture content

This study investigated the relationship between vane shear strength and moisture content for root-free and root-permeated sandy clay loam and clay soils, with a view to determining the effect of root density on the relationship. The results indicate that for both root-free and root-permeated soils, shear strength increases exponentially with decreasing moisture content. As expected, increases in root density considerably increase the magnitude of shear strength at all moisture contents investigated. In all cases, roots increased the magnitude of the shear strength of the clay soils much more than the sandy clay loam soils. Relative to the root-free soils, the roots increased shear strength in both soils by at least 500%. In the clay soils a higher relative increase of up to 850% is achieved in samples with a root density of 1.80 g cm⁻³. Also, relative to root-free soils, root permeated soils were found to exhibit a higher rate of shear strength increase with soil drying. This, it is suggested, is because of the higher shading effect of the shoots of the root-permeated samples leading to a slower rate of soil drying than in the root-free samples.     

砾石覆盖层截留降雨的模拟实验研究

砾石覆盖技术可减少土壤水分蒸发,在世界的一些干旱半干旱地区得到了不同程度的应用。但在降雨时,雨水通过覆盖层进入土壤的过程中,覆盖层也会截留一定的降雨量。此文通过模拟降雨实验,表明：在降雨强度、降雨历时和铺设方式等相同的条件下,烘干砾石的吸水量随着降雨历时的延长而增大,并逐渐达到饱和吸水量;烘干砾石达到吸水饱和所需的降雨历时随着砾石平均等效粒径的减小而缩短;随着砾石平均等效粒径的增加,覆盖层砾石颗粒间的滞留水量逐渐减少;饱和砾石覆盖层的截留水量也逐渐减小,用指数衰减拟合模型进行拟合,具有高度的显著性。     

亚热带花生旱坡地的水分动态特征分析

为研究红壤旱坡地的水分动态特征,进行了2001—2003年田间实测。花生旱坡地水分状况随年降水周期和坡位不同变化。0~150cm土壤贮水量大致分为盈余期、消耗期和补充期三个阶段。土壤水势变化与贮水量三阶段相对应,总体由大变小再回升,只是土壤剖面空间从上而下,水势值增大,变幅减小,100cm土层以下近乎常年稳定。在四个水势段出现频率中,水势较高的水势段出现频率越大,顺序为饱和>湿润>亏缺>干旱。饱和－湿润段出现频率比例总体上底土>心土>表土,坡下>坡上;低水势干旱段主要出现在坡上、土壤上层和伏秋干旱季节。旱坡地在雨季有壤中流产生,坡下降雨后深层出现较长时间的饱和区,而坡上深层水势出现较短时间的饱和区或未出现变化;旱季降雨对坡地水分影响较小。     

一次短时强降水过程的中尺度分析

为了提高短时强降水预报准确率,及时为政府提供准确的预报服务,笔者利用常规观测资料和Micaps系统提供的资料,使用天气学诊断和中尺度分析方法,对2015年8月1日夜间发生在山西省中部的短时强降水天气过程进行实况分析、中尺度分析和卫星云图分析。结果表明：强降水出现时间与 850 hPa切变线和地面辐合线移动,以及TBB负值中心的移向相联系;强降水出现在地面幅合线的附近,850 hPa暖切的南侧,200 hPa高空急流分流幅散区的下方;强降水出现的区域与TBB<-52℃区域,以及地面辐合线有很好的对应关系;强降水中心落在TBB值低于-52℃的负中心内。     

马尾松对喀斯特石漠化地区土壤有机质的影响

以桂西北喀斯特地区为例,研究了石漠化生态恢复过程中,马尾松对土壤有机质含量的影响,并对坡向、海拔高度、恢复年限、植被类型等生态因子与马尾松样地土壤有机质含量的相关性进行了分析,结果表明：土壤水分含量﹑电导率、凋落量、纤维素分解强度等与马尾松林土壤有机质含量呈正相关,凋落物有机质含量与马尾松林土壤有机质含量呈负相关。坡向对土壤有机质含量有较明显的影响,东南坡土壤有机质含量比西北坡高;在一定范围内,植被恢复时间越长,土壤有机质含量就越高;马尾松林土壤有机质含量通常随海拔的升高而有下降的趋势。但是,喀斯特地区生态环境十分脆弱,极易受到人为因素的影响。人为干扰的频度和强度不同,土壤有机质的变化规律也不同,干扰越大,有机质含量越低,土壤就越贫瘠。     

砂田降雨入渗过程的模拟实验研究

砂田是一种具有综合效能的旱作技术,在干旱半干旱地区得到了不同程度的应用。为了研究砂石覆盖下降雨入渗的规律,笔者进行了室内模拟实验,对土壤水分的动态变化过程进行了研究。结果表明：在模拟降雨过程中,砂石覆盖下土壤的累计产流量一直低于裸土,说明砂石覆盖有利于减少土表降雨产流。砂石覆盖的土壤的各个深度土壤含水率均比裸土对照组要高,表明砂石覆盖有降雨入渗到土壤中。在经过一定时间的降雨后,砂石覆盖土柱中不同深度的土壤含水率变化会趋于稳定,且数值接近,表明砂石覆盖的土壤比裸土更快地进入稳渗阶段。