Variation of specific yield with depth in an alluvial aquifer of the Platte River valley, USA

Estimation of specific yield (Sy) of an aquifer is of great importance in water resource management. In this study, an experimental drainage method was developed to determine specific yield of an alluvial aquifer of the Platte River valley, Nebraska, USA. Sets of sediment cores with continuous interval depth were collected to plastic tubes using the direct push technique and then taken to the laboratory. During the Sy experiment, those sediment cores were re-saturated by placing them vertically in a large water tank. Sy was determined by the water drained from the sediments by force of gravity in a bracket. Our results show that the values of Sy varied largely with depth at each site and the variability for Sy with interval depth between the test sites is also observed. This spatial heterogeneity in Sy might result from the variation of grain size, grain shape, sorting and compaction of sediments in different cores with interval depth. The Sy for all sediment cores ranged from 0.01 to 0.18 and the mean value was 0.08±0.04. Our drainage method can functionally preserve the sedimentary structures in their original state and it is easier to experiment at a lower expense.     

覆岩中断层活化突水的力学分析及其应用

据资料统计,国内煤矿的突水淹井事故80%以上是由断层引起的,大多数是原始地质条件下的非导水断层在采动影响下活化发生突水。出于安全生产和保水采煤的需要,对采场覆岩中断层因工作面的推进而活化突水进行力学分析,研究防止断层活化突水和保水采煤的开采方法。由摩尔-库仑破坏准则得出断层的活化准则,推导出断层活化的临界倾角、断层活化时的临界开采深度和间隔式开采断层活化时工作面临界推进距离。结果表明,断层的破坏形式与断层倾角有很大关系,随着断层倾角的增大,断层的破坏形式依次表现为,随着工作面的推进断层和覆岩一同破坏、剪切破坏和拉破坏。断层倾角越大,越容易活化。以大柳塔煤矿保水采煤为例,应用研究成果计算了间隔式开采工作面的临界推进距离,并且以相似模拟试验验证了计算结果。     

多孔介质固液耦合相似材料的研制

为研究地下结构与富水多孔岩体的相互作用问题,根据模型试验相似理论,研制出了一种多孔介质固-液耦合相似材料,该材料由中粗砂、水泥、透水混凝土增强剂合水按一定配比均匀拌和压制而成。运用正交试验设计原理进行配比试验,制作模型小试件,进行了单轴抗压强度、渗透系数、重度、弹性模量、泊松比等参数测试,找出了相似材料各成分对配比试件的影响特征,可根据需要在物理模拟试验中选取不同配比。该配方力学指标稳定,满足一次性浇筑大尺寸模型试件的要求,适用于进行结构与围岩体耦合失效破坏模式的大型物理模拟试验,为富水条件下地下结构风险评估提供了相似试验材料     

A three-scale model for ionic solute transport in swelling clays incorporating ion–ion correlation effects

A new three-scale model is proposed to describe the movement of ionic species of different valences in swelling clays characterized by three separate length scales (nano, micro, and macro) and two levels of porosity (nano- and micropores). At the finest (nano) scale the medium is treated as charged clay particles saturated by aqueous electrolyte solution containing monovalent and divalent ions forming the electrical double layer. A new constitutive law is constructed for the disjoining pressure based on the numerical resolution of non-local problem at the nanoscale which, in contrast to the Poisson–Boltzmann theory for point charge ions, is capable of capturing the short-range interactions between the ions due to their finite size. At the intermediate scale (microscale), the two-phase homogenized particle/electrolyte solution system is represented by swollen clay clusters (or aggregates) with the nanoscale disjoining pressure incorporated in a modified form of Terzaghi’s effective principle. At the macroscale, the electro-chemical–mechanical couplings within clay clusters is homogenized with the ion transport in the bulk fluid lying in the micro pores. The resultant macroscopic picture is governed by a three-scale model wherein ion transport takes place in the bulk solution strongly coupled with the mechanics of the clay clusters which play the role of sources/sinks of mass to the bulk fluid associated with ion adsorption/desorption in the electrical double layer at the nanoscale. Within the context of the quasi-steady version of the multiscale model, wherein the electrolyte solution in the nanopores is assumed at instantaneous thermodynamic equilibrium with the bulk fluid in the micropores, we build-up numerically the ion-adsorption isotherms along with the constitutive law of the retardation coefficients of monovalent and divalent ions. In addition, the constitutive law for the macroscopic swelling pressure is reconstructed numerically showing patterns of attractive forces between particles for bivalent ions for particular ranges of bulk concentrations. The three-scale model is applied to numerically simulate ion diffusion in a compacted clay liner underneath a sanitary landfill. Owing to the distinct constitutive behavior of the swelling pressure and partition coefficient for each ionic species, different compaction regimes and diffusion/adsorption patterns, with totally different characteristic time scales, are observed for sodium and calcium migration in the clay liner.     

The role of crust thickness in runoff generation from microbiotic crusts

Contrary to humid areas where runoff takes place following the saturation of the soil column, runoff in arid and semiarid zones takes place when rain intensities exceed the infiltration capability of the upper soil crust, whether physical crust or microbiotic crust (MC). This type of overland flow, known as Hortonian overland flow (HOF), is not fully understood, especially in the case of MC. In particular, little is known regarding the effect of crust thickness and its fine (silt and clay) content on runoff generation, with some scholars claiming that runoff generation is positively correlated with crust thickness and fine content. In an attempt to determine the effect of crust thickness and to assess the role played by the silt and clay on runoff generation, a set of field and lab experiments were undertaken on MCs inhabiting sand dunes in the Negev Desert (Israel). These included sprinkling experiments coupled with measurements of the physical (thickness, silt and clay) and biological (chlorophyll, protein, total carbohydrates) properties of 0.5–10‐mm‐thick crusts. The data showed that runoff generation took place on surfaces as thin as ~0.5–0.7 mm only, and was not correlated with the fine (silt and clay) content. The implications for HOF and for arid ecosystems are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Bed morphological changes around a finite patch of vegetation

For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid‐channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non‐dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd.     

盾构刀盘偏置中心刀对刀盘推力和扭矩的影响

盾构机是地下工程中的典型掘进装备,具有结构复杂、体积庞大、重型巨载等特点。刀盘载荷是装备的核心力学参量,实现刀盘载荷的合理计算是装备正向设计的理论基础,也是不同地质情况隧道施工中载荷控制的重要科学依据。盾构刀盘中心刀结构在掘进过程中承受很大比重的轴向载荷,为了进一步分析中心刀结构的改变对刀盘载荷的影响,采用数值仿真方法与模型试验方法对盾构刀盘与土体的相互作用进行了研究,得到了刀盘法向和切向切削载荷空间分布规律以及掘进过程中刀盘总推力和扭矩随掘进时间的变化规律,重点分析了偏置中心刀结构对刀盘推力和扭矩的影响。对比几种不同的中心刀结构,研究表明,偏置中心刀结构刀盘的总推力与总扭矩小于鱼尾中心刀结构刀盘的总推力与总扭矩。刀盘模型试验结果与数值仿真结果趋势一致。从载荷角度考虑,偏置中心刀刀盘优于鱼尾中心刀刀盘。该研究结果可为新型刀盘结构设计提供参考。     

卤水浸泡环境下盐岩剪切特性影响因素分析

为了解水溶造腔过程中盐岩在卤水浸泡环境中的剪切特性,设计了盐岩剪切特性影响因素的正交试验,研究了卤水浸泡时间、温度和加载速率对盐岩剪切特性的影响规律。试验结果表明,卤水浸泡会弱化盐岩的抗剪强度,卤水浸泡时间越长盐岩抗剪强度越低,但最终趋于稳定;卤水温度升高,加剧盐岩内部损伤,盐岩抗剪强度随之降低;经一定温度卤水浸泡后盐岩的抗剪强度随加载速率的增大而降低,且其延性特征也随浸泡时间、温度和加载速率的增大逐渐减弱。通过对任意两个影响因素分别进行二元线性回归,根据其标准回归系数对盐岩抗剪强度的相对重要性比值构建判断矩阵,运用层次分析法计算出温度、加载速率和浸泡时间等影响因素的权值分别为0.397,0.340,0.263。极差分析和权值计算表明,盐岩剪切强度的影响因素主次关系依次为温度、加载速率和浸泡时间。     

基于有限元法的层状岩体破裂规律探讨

层状岩体的非均质性及各向异性导致其破裂方式及规律与均质岩体有显著不同。对层状岩体分别进行不同方式的单轴、双轴、三轴试验, 分析应力-应变曲线特征; 再利用ANSYS有限元软件进行数值模拟, 观察应力、应变在岩体上的分布, 通过曲线和图件的对比分析, 并结合岩石破裂理论, 总结不同应力状态下层状岩体的破裂方式、顺序及规律; 最后以富台地区为例, 对分析结果进行验证。研究结果表明, 不同受力方式对层状岩体破裂的影响体现在施加的载荷及约束与层面的方位。当应力方向与岩层面平行时, 强度大的石灰岩岩体发生集中应力, 首先破裂; 而应力与岩层面垂直时, 强度小的泥岩岩体首先破裂。岩石试验、数值模拟结果以及实例均成功验证了这个规律。      

中国区域协调发展改革实验研究综述

改革试验区的设立是中国改革开放探索新模式的标志。在概述改革实验的内涵、理论依据的基础上,对中国改革实验的研究内容进行梳理,包括基本条件、空间效应、类型和模式等,深入分析对区域协调性差的典型区域——江苏省的改革实验研究。发现中国区域协调发展改革实验研究存在内涵认识不统一,困难研究不足;实证研究较多,理论研究不足;研究方法和工具有待进一步改进等。基于此提出今后中国区域协调发展改革实验研究的重点。