A continuum framework for three-phase soils including microstructural effects

Nature as described by classical mechanics is governed by a set of physical laws in the balanced form of various physical entities, including mass, linear and angular momenta, energy, and entropy (entropy inequality). These laws must be obeyed in the development of any theory of applied mechanics. In soil mechanics, one deals with porous material composed of solids and fluids strongly interacting with each other. Within the framework of continuum mechanics, materials are assumed to be infinitesimally continuous, which renders an unavoidable hypothesis for soil. That is, each of the solid, liquid, and gaseous phases can be treated as a ‘smeared’ medium superimposed by and interacting with other constituents at the same infinitesimal point. Such treatment, however, requires the fundamental balance laws be recast into more elaborative forms involving microstructural effects (inter-phase actions).

This paper introduces such a continuum framework based on existing theories of immiscible mixtures. To accommodate the pre-flow response, in the present work, the energy terms attributable to shear deformation and spin, allied with a coupling effect, are included. In the framework, a set of extended effective stresses is defined; indicating that the soil skeleton has an effective stiffness, which may still be positive-definite after failure. The framework is general and may pave a way for solving practical geotechnical problems covering both pre- and post-failure stages.     

混合型缓冲回填材料非饱和水分扩散试验研究

设计了专门的浸水试验装置,测定了膨润土-石英砂混合物在非膨胀条件下吸水引起的水分分布及膨胀应力变化,研究了混合型缓冲回填材料非饱和水力学性质。试验结果表明,干密度约1.70 g/cmP3、掺砂率为30%的GMZ001膨润土-砂混合物的水分扩散系数与含水率的关系呈U型变化,即随着含水率增加,汽态水分扩散系数减小,液态水分扩散系数增大。根据理论推导建立非饱和导水率估算方程。计算发现,混合物的非饱和导水率随含水率的增大而增大。其中,汽态水分非饱和导水率先增大后略有减小,液态水非饱和导水率始终增大。试验发现,试样吸水后干密度趋于均匀化,试样内部不同位置的应力发展与水分迁移过程密切相关：渗入端的应力在入渗初期增长很快,随后减慢;渗出端的应力持续稳定增长;入渗96 h后,两端应力趋于一致。估算出的水分扩散系数及非饱和导水率,可用于评价混合型缓冲回填材料阻隔核素迁移安全性。     

膨润土-砂混合型缓冲/回填材料土-水特征曲线研究

高放废物（HLW）深地质处置中,在膨润土中添加一定比例的石英砂能优化缓冲/回填材料的性能。利用水汽平衡法,对高庙子压实膨润土-砂混合物在不同温度、掺砂率和干密度条件下的土-水特征曲线（SWCCs）进行试验研究,分析温度、掺砂率与干密度对混合物土-水特征曲线的影响。试验结果表明,随着温度升高,混合物的持水能力明显下降;在试验控制吸力范围内,低吸力段掺砂率对土-水特征曲线影响明显,高吸力段掺砂率对混合物土-水特征曲线的影响逐渐降低;干密度对混合物的土-水特征曲线基本没有影响。根据试验数据建立了不同温度和掺砂率条件下膨润土-砂缓冲/回填材料土-水特征曲线的经验公式,可用来预测不同温度和掺砂率条件下的膨润土-砂混合型缓冲/回填材料土-水特征曲线     

Interrogating the time and processes of development of the Las Liebres rock glacier,central Chilean Andes,using a numerical flow model

The Las Liebres rock glacier is a large (~2.2 km long) Andean rock glacier whose internal composition and kinematics are known from previous studies. We investigate its development by posing and testing the following null hypothesis: the rock glacier has developed from a constant supply of debris and ground ice in periglacial conditions and resulting creep of the ice‐rock mixture. A rheological model was formulated based on recent advances in the study of ice‐rock mixture rheology, and calibrated on the known surface velocities and internal composition of the rock glacier. We show that the rock glacier viscosity is inversely related to both water and debris fractions, in agreement with recent field and theoretical studies of ice‐rock mixture rheology. Taking into account the possible variations in water fraction, the model was used to estimate the time spans of development (0.91–7.11 ka), rates of rock wall retreat (0.44–4.18 mm/a), and rates of ground ice formation (0.004–0.026 m/a) for the rock glacier. These results support the null hypothesis of a periglacial origin of the Las Liebres rock glacier. Copyright © 2016 John Wiley & Sons, Ltd.     

掺砂率对高放废物处置库中缓冲/回填材料收缩特性的影响

缓冲/回填材料的收缩特性对高放废物处置库的长期安全性和稳定性具有重要影响。以高庙子（GMZ） 膨润土-砂混 合物缓冲/回填材料为研究对象,探究了0~50%掺砂率下,试样蒸发失水过程中的收缩特性。试验结果表明：（1） 试样的水 分蒸发过程可分为常速率阶段、减速率阶段和残余阶段,且掺砂率对各阶段水分蒸发过程均有显著影响;（2） 掺砂率对试 样缩限值基本没有影响,但收缩应变却随着掺砂率的增大而减小;试样收缩系数在掺砂率为30%时达到最大,之后随掺砂 率的增大而减小;（3） 在不同掺砂率下,试样收缩均呈现出明显的各向异性;（4） 掺砂率越高,试样进气点对应的含水率 越大,最终孔隙比也越大。     

粗粒筑坝材料的增量流变模型研究

针对全量型流变模型与加载应力路径无关,不能考虑施工或蓄水期在变应力作用下土石坝流变遗传特性的问题,基于继效理论,结合某工程堆石料的三轴流变试验资料,提出了适合于土石坝筑坝材料流变特性分析的7参数增量流变模型;利用试验各级增量荷载作用下的最终体积流变量与对应体积应力之间为近似线性关系,最终剪切流变量与对应的试验广义剪应力之间接近双曲线关系,整理得到其流变体积模量和剪切模量等模型参数;验证分析表明,建议的增量流变模型计算值与试验结果吻合较好,其可应用于实际土石坝的流变研究     

生态护坡基材土-岩接触面原位剪切试验研究

基材土-岩接触面剪切力学性能是生态护坡体系长久稳定的关键,相关研究可为解决基材脱落难题、完善生态防护技术体系提供必要依据和指导。采用自制的原位剪切仪对4种不同粗糙起伏的基材土-岩接触面进行了原位剪切试验,结果表明,基材土-岩接触面剪切应力-位移表现出典型的软化特性,具有明显的初始线弹性变形、弹塑性变形、峰后软化以及残余剪切变形4个阶段。分析发现,文中试验条件下凸起高度算数平均偏差Ra在4 mm以下时,峰值剪切强度增加速度较快,随后呈逐渐减弱趋势;残余剪切强度、峰值剪切位移以及进入残余阶段的剪切位移与粗糙凸起高度算数平均偏差呈近线性正相关关系。可见实施生态护坡时合理地控制坡面粗糙起伏,有助于提高土-岩接触面峰值剪切强度和残余剪切强度,改善其变形性能,对防护体系的长期整体稳定具有促进作用。     

Sequential indicator conditional simulation and indicator kriging applied to discrimination of dolomitization in GER 63-channel imaging spectrometer data

Laboratory reflectance spectra of synthetic mixtures of the carbonate minerals calcite and dolomite were measured in the visible and near-infrared wavelength region (0.4–2.5 m) using a high-spectral resolution laboratory spectrometer. The instrument measured reflectivity with an accuracy of 0.001 m, allowing detailed resolution of the carbonate spectrum. The spectra of calcite and dolomite could be characterized by the presence of a strong absorption band centered at 2.3465 m for pure calcite and at 2.3039 m for pure dolomite. Nine mixtures of intermediate composition were analyzed demonstrating that the position of the carbonate absorption band is semilinearly related to the calcite content of the sample. Theoretically, this model allows mapping of dolomitization from high-spectral resolution remotely sensed imagery, GER 63-channel imaging spectrometer data from southern Spain were used to attempt such a mapping. First, pixels of vegetation were removed. For the remaining pixels, the wavelength center of the carbonate absorption band was detected and converted to a category of calcite fraction. The percentage of calcite for the remaining pixels was estimated using direct indicator kriging (IK) and sequential conditional indicator simulation, assuming that the calcite content could be represented as a category variable (SCIS category variable) and as a continuous variable (SCIS continuous variable). Four realizations of an SCIS (category variable) showed that on the average, 60 percent of the data was simulated in the same class and over 90 percent of the data within one class difference. A comparison with field samples showed that IK estimates of calcite content were within 20 percent accurate. The SCIS (continuous variable) does not perform as well with differences between –45% and +26% calcite; however, simulation reproduces the spatial variability better.     

循环荷载下土石混合体力学特性野外试验研究

土石混合体是一种物理、力学性质非常复杂的不连续介质。以云南某高速公路土石混合体边坡为例,分别对选取的3个试验点进行了单调加载、循环加载一次及多次循环加载试验,获取了其相应的剪切位移-剪切应力关系曲线,并对其曲线特征进行分析研究。通过对试样三维滑动面的形态分析,指出由于土石混合体三维滑动面的不规则性,利用传统的二维计算方法难以得到较为准确的强度参数。基于三维极限平衡理论,提出了土石混合体水平推剪试样强度参数的三维数据计算方法。并利用该方法得到了研究区土石混合体的相应的强度参数及残余强度参数。     

蓄水后土石坝应力变形有效应力算法

水库蓄水后,土石坝应力变形较之施工填筑阶段更为复杂,其计算方法可分为总应力算法和有效应力算法。总应力算法简便直观,将心墙作为一个大单元仅宏观上符合总应力加面力的组合,而在微观上对于心墙具体单元而言却不符合;有效应力算法是采用有效应力加渗流力的组合,再考虑浸润线以下坝壳和心墙每个单元受到的浮托力及湿化变形引起的等效结点力（等效荷载）,因此,不论是在宏观上,还是微观上,有效应力算法将更趋于合理,没有总应力算法所存在的缺陷。