Numerical studies on the effect of temperature on the unsaturated hydraulic response of geotextiles

A series of coupled thermo-hydraulic simulations were performed on a soil–geotextile column to understand the effect of temperature on suction distribution throughout the soil column and on the hydraulic performance of the geotextile as a drainage/capillary barrier layer. Two different constant temperatures of 0 °C and 38 °C and a temperature gradient of 4 °C along the column were modeled. Changing the temperature from 0 °C to 38 °C did not have a significant effect on the suction head distribution in the soil–geotextile column. The temperature gradient resulted in appreciable thermal vapor flow and changes in suction head and hydraulic conductivity of the geotextile. During drainage, the temperature gradient and lower temperature at the top of the column increased suction in the geotextile and its ability to function as a capillary barrier. During capillary rise, the temperature gradient and lower temperature at the top of the column decreased the suction in the geotextile and its ability to function as a capillary barrier. Changing the direction of the thermal gradient reversed the water vapor flow direction and its effect on the suction in the geotextile. A temperature gradient did not have a noticeable effect on the suction head of the geotextile when positive pore pressure was developed in the geotextile and adjacent soil during drainage.     

Design of drainage blankets for leachate recirculation in bioreactor landfills using two-phase flow modeling

Drainage blankets (DB) are used for leachate recirculation in bioreactor landfills and consist of highly permeable material placed over a large area of the landfill with the leachate injection pipe embedded in the material at specified locations. DBs are generally installed at different depth levels during the waste filling operations. Very limited information is reported on performance of DBs, and that which exists is based on a small number of field monitoring and modeling studies. A rational method for the design of landfills using DBs has not been developed. This study performs a parametric analysis based on a validated two-phase flow model and presents design charts to guide the design of DBs for given hydraulic properties of MSW, the leachate injection rate and the dimensions and locations of the DB as measured from the leachate collection and recirculation system (LCRS) located at the bottom of the landfill cell. Numerical simulations were performed for the two established MSW conditions: homogeneous–isotropic and heterogeneous–anisotropic waste. The optimal levels of leachate saturation, wetted width, wetted area and developed pore water and pore gas pressures were determined, and design charts using the normalized parameters were developed. An example is presented on the use of design charts for typical field application.     

西江枯季径流退水系数与流域特征关系研究

文章采用基于遗传算法的经典退水曲线对西江上游主要站点枯季日平均流量进行研究,所率定的退水系数经验证精度较好,能够反映所在流域的径流特性。通过退水系数与流域面积、下垫面性质、植被覆盖度、多年平均径流深等流域特征关系的分析,发现退水系数值(1)对降雨和蒸散发的变化不敏感,整体上随流域面积和植被覆盖度的增加而减小;(2)随地形高差和下垫面透水性的下降而减小;(3)对喀斯特岩溶地貌尤其敏感,表现为退水系数值较非岩溶地区偏大;(4)随多年平均径流深的增大而增大,二者具有指数函数关系。退水系数与流域特征因子的这些规律,可为无资料流域水文预报提供思考和借鉴。     

深水油气浅层钻井的“三浅”地质灾害

深水浅层钻井过程中可能遇到浅水流、浅层气以及天然气水合物层分解等3种浅层地质灾害（简称＂三浅＂）。要规避这些风险,必须需要开展浅水流、浅层气和天然气水合物成因机理、识别特征及工程危害等方面的研究。国外利用地球物理识别技术和数值模拟方法,结合深水油气钻井测井开展了这方面的研究,在＂三浅＂地质灾害的形成机理和控制因素方面取得了较为重要的研究进展。目前国内学者利用地球物理方法在南海北部深水区LW3-1大气田的周围发现了超压系统、浅层气和天然气水合物。深水水道砂体的发现也推断南海北部深水区具有＂三浅＂地质灾害发育的地质条件。随着深水油气勘探开发的不断深入,评估和预测南海北部深水钻井的＂三浅＂地质灾害十分迫切。     

基坑工程管井回灌优化设计探讨

目前基坑管井回灌设计及优化尚无专门成熟的方法,通过不同基坑回灌类型的分析,提出了基坑管井回灌设计原则及设计流程,并对回灌参数进行了探讨,对回灌可施加的最大压力进行了分析,通过285组基坑水文地质数值模型的计算,对比分析了不同渗透各向异性系数、回灌井结构、回灌井位置和保护建（构）筑物位置下的渗流特征,提出了回灌设计综合指数,从经济、技术及施工难度角度综合评估回灌对保护建（构）筑物以及对坑内降水的双重作用,指导抽灌一体化设计。     

自钻式原位剪切旁压模型不同固结荷载颗粒流数值试验

自钻式原位剪切旁压仪具有扰动小,能同时测出不同深度土的变形和强度参数,在精确测定土体参数方面具有广阔的应用前景。然而,目前受分析手段与研究水平的限制,对SBISP多级加载过程中周围土体的变形响应研究较少,而土体变形参数的确定与其变形机制是密切相关的。基于此,应用PFC3D颗粒流程序对不同固结荷载SBISP模型进行了仿真数值试验,试验结果表明:随着剪应力的逐级施加,中间区域颗粒的位移量不断增大,且位移矢量方向性更加显著,在第5级剪应力作用下,影响区域位移矢量形状呈现为倒锥形;而随着上覆固结压力的增大,探头周围试样的受影响范围逐渐变小;在探头作用下球颗粒的运动轨迹呈台阶状,台阶形态随距探杆中心距离增大而趋于平缓,球颗粒的Z向位移量亦随之呈负指数形式衰减;此外,剪应力与探头摩擦系数呈正相关关系,但当摩擦系数达到某一阈值时,剪应力-位移曲线不再变化。其研究成果对于深入开展SBISP试验多级加载过程中影响域内土体变形过程与变形模量之间关系研究具有重要启迪意义。     

分层岸滩侧蚀坍塌过程及其水动力响应模拟

非均质岸滩广泛分布于冲积河流中,其侧蚀过程沿垂向具有分层特点。基于全三维水沙模型及河岸侧蚀坍塌力学模式,提出动态网格跟踪技术,构建了非均质岸滩侧蚀沿垂向差异的三维动力学模拟方法。以连续弯道概化水槽为例,模拟分析了非均质河岸侧蚀过程中三维水流结构的响应特征。研究结果表明:坡脚冲刷后,底部主流向凹岸偏移,在已有弯道环流的基础上,于坡脚处出现一反向次生流;上部粘性土层坍塌后,崩塌土体堆积于坡脚处,上部主流明显左偏,下部次生流消失;随着坡脚堆积体的冲刷搬运,下部主流进一步向凹岸偏移;如此循环,主流不断向凹岸偏移,致使岸坡持续崩退、河道摆动。     

离心实验在污染物迁移研究中的应用

离心实验模拟以其可以获得与原型一致的应力水平并且能够大大缩短原型历时而被应用于污染物迁移实验研究。在离心相似理论及离心实验模拟的相似基础上,重点回顾了离心机在饱和带水分、非饱和带水分、保守性溶质、NAPLs、重金属、核素迁移以及污染场地修复方面的实验应用。最后讨论了离心模拟中土壤预制和加速度选择的问题,并简单介绍了离心监测方法。可以得出结论:离心机能够成功用于各类物质迁移的实验研究中,离心实验模拟能够为理论和数值等分析方法快速提供真实可靠的参数依据,但离心实验的理论基础和监测方法需要进一步完善,此外也应积极开展更接近实际情况下的离心实验模拟研究。     

Analysis of the Grain Size Properties and Flow Body Classes of the Mud Sand Flow: An Example of Liantanggang Collapsing Hill and Gully in Wuhua County of Guangdong

Mud sand flow is a kind of solid-liquid two-phase flow formed in collapsing hill and gully basin during rainfall. It is the main way to export erosion product. The discrimination of its fluid type is one of the collapsing hill and gully control theoretical basis. This paper analyzed the basic characteristics of mud sand flow like grain size and so on through fieldwork and sampling. The results show that the density of mud sand flow is between 1.16~1.60 t/m³ and the solids content is between 257.03~960.55 kg/m³, both of which decrease from the upper to the lower channel. The slurry of mud sand flow is composed mainly of silt and clay. As the density increases, the particle size distribution curve transforms from a single peak to the bimodal distribution similar to the weathering crust with no sorting, and the grain size of mud sand flow becomes coarser which shows a well positive linear correlation between the sediment median particle diameter and density of mud sand flow. The comparison during mud sand flow, hyperconcentrated flow and debris flow shows that collapsing hill and gully mud sand flow, which belongs to an intermediate class between hyperconcentrated flow and debris flow, has a closer link with debris flow. Therefore, mud sand flow can be considered as a sub-class of generalized debris flow that may be called as collapsing hill and gully type debris flow.     

新流动范式下非流动性的研究进展与展望北大核心CSCDCSSCI

新冠疫情下的中断与非流动性改变新流动性范式的叙事逻辑,作为现代社会基本原则的流动性受到挑战与质疑,而正确认识非流动性事关新流动范式的未来转向与变革。为此,本研究对新流动范式下的非流动性研究进行综述,思考流动性与非流动性的辩证关系,为新流动范式的转型提供新的路径。本研究发现,新流动范式下非流动性的研究领域具有四个重要转向:从批判解构到辩证关系的认识;从本体不可能到有可能的思考;从宏观视野到微观解释的叙述;从方法二元到方法平衡的转变。同时,非流动性研究中存在四大重要议题:地方性非流动人口;支撑性的停泊空间;非表征的静默身体;跨时空的节点主体。最后,本研究为非流动性的未来研究提出相关展望:关注非流动性的人口异质性;关注多样化的非流动性空间;认识后人类技术与非流动性身体;探讨可持续发展的流动性。