尾砂胶结充填体蠕变模型及在FLAC3D 二次开发中的实验研究

关于岩石蠕变特性的研究已有诸多成果,但对胶结充填体的蠕变特性还缺乏系统地研究。在室内充填体单轴蠕变试验的基础上,利用Hoek-Kelvin模型表征充填体的蠕变特性,运用粒子群优化算法,对选用的蠕变模型的参数进行辨识,并研究各蠕变参数对应力水平的敏感程度。研究结果表明,在不同分级应力水平加载下,弹性模量EH和黏滞系数η变化较小,而参数EK对应力水平变化较敏感。利用FLAC3D软件二次开发所建立的蠕变模型,用开发的模型进行分级加载蠕变的数值模拟,计算结果与试验数据吻合。     

Further insight into the behaviour of Pleistocene Osaka clays at KIA Phase 1 island

The behaviour of the Pleistocene Osaka clays at Kansai International Airport Phase 1 island is investigated by FEM analyses using an elasto-viscoplastic constitutive model which replicates the destruction processes occurring in the microstructure of the clay. Excellent predictions are obtained by 2D analyses carried out using the actual soil profile and the characteristic values of soil parameters, confirming the validity of the methods proposed for characterizing and modelling structured clays. Unlike 1D analyses, where partially effective drainage layers occur, 2D analyses do not require arbitrary pre-definition of the model drainage scenario and of the ‘equivalent’ permeability of interlayered clays to account for macrostructure. In these conditions, 1D analyses must be validated with reference to 2D or 3D prototype analyses and/or well documented experience of comparable work. Once thus validated, 1D analyses are used to investigate the relative merits of possible measures (relief wells, preloading, lightweight fill) aimed at reducing in-service settlement. For future reclamation works at sites where structured clays extend to great depth, filling with lightweight material shows the greatest promise, but it is unlikely to remove the need for designing the superstructure to accommodate the inevitable settlement, which requires accurate prediction.     

Characterizing the climatic water balance dynamics and different runoff components in a poorly gauged tropical forested catchment,Nicaragua

ABSTRACT

The water balance dynamics and runoff components of a tropical forested catchment (46?km²) on the southwestern Pacific coast of Nicaragua were studied combining hydrometry, geological characterization and hydrochemical and isotopic tracers (three-component hydrograph separation). The climatic water balance was estimated for 2010/11, 2011/12 and 2012/13 with net values of 811?mm year^-1, 782?mm year^-1 and –447?mm year^-1, respectively. Runoff components were studied at different spatial and temporal scales, demonstrating that different sources and temporal contributions are controlled by dominant landscape elements and antecedent rainfall. In forested sub-catchments, permeable soils, stratigraphy and steep slopes favour subsurface stormflow generation contributing 50% and 53% to total discharge. At catchment scale, landscape elements such as smooth slopes, wide valleys, deeper soils and water table allow groundwater recharge during rainfall events. Groundwater dominates the hydrograph (50% of total discharge) under dry prior conditions. However, low soil infiltration capacity generates a larger surface runoff component (42%) under wet prior conditions which dominates total discharge. Our results show that forested areas are important to reduce surface runoff and thus soil degradation, which is relevant for the design of water management plans.

Editor D. Koutsoyiannis Associate editor D. Gerten     

Modeling of self‐desiccation in a cemented backfill structure

After placement of cemented tailings backfill (CTB), which is a mixture of tailings (man‐made soil), water, and binder, into underground mined‐out voids (stopes), the hydration reaction of the binder converts the capillary water into chemically bound water, which results in the reduction of the water content in the pores of the CTB, thereby causing a reduction in the pore‐water pressure in the CTB (self‐desiccation). Self‐desiccation has a significant impact on the pore‐water pressure and effective stress development in CTB and paramount and practical importance for the stability assessment and design of CTB structures and barricades. However, self‐desiccation in CTB structures is complex because it is a function of the multiphysics or coupled (i.e., thermal, hydraulic, mechanical, and chemical) processes that occur in CTB. To understand the self‐desiccation behavior of CTB, an integrated multiphysics model of self‐desiccation is developed in this study, which fully considers the coupled thermal, hydraulic, mechanical, and chemical processes and the consolidation process in CTB. All model coefficients are determined in measurable parameters. Moreover, the predictive ability of the model is verified with extensive case studies. A series of engineering issues are examined with the validated model to investigate the self‐desiccation process in CTB structures with respect to the changes in the mixture recipe, backfilling, and the surrounding rock and curing conditions. The obtained results provide in‐depth insight into the self‐desiccation behavior of CTB structures. The developed multiphysics model is therefore a potential tool for assessing and predicting self‐desiccation in CTB structures.     

基于电流变化的水泥土损伤统计模型

为了把电阻率法引入水泥土的损伤研究中,首先把水泥土试块浸泡在清水、生活污水和造纸厂污水中,待龄期为90 d时进行无侧限抗压强度试验,并结合照片将试验过程得到的电流-应变曲线和应力-应变曲线进行了对比分析,然后以“有效电流”作为度量损伤的基准,通过统计得到了水泥土损伤模型,最后进行了归一化。研究表明,电流的变化易于测量,电流随着应变的增加而有规律的变化;电流-应变曲线与应力-应变曲线相互对应,都可以划分为4个阶段,这4个阶段很好地描述了水泥土损伤发展的全过程;本模型将全应变范围都统一成一个4次多项式方程,且方程形式与水泥类型、污染类型无关;这充分说明借助电流的变化来反映水泥土的结构损伤过程完全可行     

静钻根植竹节桩桩端承载性能试验研究

静钻根植竹节桩是由预制竹节桩和桩周水泥土所构成的一种新型组合桩基,它主要通过桩周水泥土改善桩-土接触面摩擦性质以及桩端水泥土扩大头改善桩端承载性能。通过现场静载试验对静钻根植竹节桩桩端承载性能进行研究,并采用传统桩端沉降计算公式对其桩端沉降进行计算;通过模型试验对竹节桩桩端与水泥土扩大头相对位置不同的试桩桩端承载性能进行研究。结合现场和模型试验可以得到：桩端水泥土扩大头可以改善静钻根植竹节桩桩端承载性能;当竹节桩桩端位于水泥土扩大头中间位置时,静钻根植竹节桩桩端承载性能最好;可以用传统桩端沉降计算公式对静钻根植竹节桩桩端沉降进行计算,且当竹节桩桩端位于水泥土扩大头中间位置时,理论计算与实测曲线几乎完全吻合。     

Experimental research on variation of porosity in destruction process of cement stabilized soil

Based on the process of reinforcing soft soil using cement in laboratory, the porosity of test samples under different pressures conditions were determined through mercury intrusion porosimetry. The experiment was introduced and the law of porosity variation was summarized. The results show that when stress is between 0 and 0.15--0.2 qu, porosity decreases along with the pressure, then porosity has increased in the wake of the pressure until the sample damaged. It can provide an experimental basis for exploring the failure mechanism of cement stabilized soil from the microscopic view and the study to establish the microcosmic constitutive model of cement stabilized soil.     

结构性砂土海床管道上浮破坏的离散元模拟

借助离散单元法（DEM）建立海底管道上浮模型,模拟分析了不同胶结强度下胶结试样的力学特性;通过微观力学响应（局部变形、胶结点破坏分布和位移场）对海底管道上浮破坏机制进行分析;对比分析了海床砂土胶结强度对管道上浮土体破坏的影响（上浮抗力和地表隆起量）。结果表明：伴随土体变形和胶结破坏,上覆土体的渐进破坏主要集中在上覆土体区域内;土表隆起量随着管道上浮位移的增长而增长;胶结强度较高时,管道周围土体无回填行为,上覆土体有拉裂带形成,仅管道附近土体产生胶结破坏,峰值上浮抗力随海床砂土胶结强度的增加有显著提高     

侵蚀影响下水泥土的力学性质试验研究

港珠澳大桥拱北隧道地处沿海地区,其地下水与海水相连,隧道基底采用粉体喷射搅拌法和高压喷射注浆法等方法进行加固,加固产生的水泥土在海水侵蚀性离子作用下其强度和稳定性会发生变化,从而对工程安全产生影响。根据上述两种施工工艺,制作内部含侵蚀物质和不含侵蚀物质的两种水泥土试块,配制多种不同浓度的单组分的化学溶液来模拟海水侵蚀环境,将制备的水泥土试块置于侵蚀溶液中进行预定时间的短时（≤28 d）浸泡,通过无侧限抗压试验、电镜扫描以及离子色谱测定,分别得到了单组分侵蚀溶液短时浸泡下水泥土试块无侧限抗压强度、微观结构随侵蚀溶液浓度和侵蚀时间的变化规律,以及侵蚀环境中离子浓度随侵蚀时间的变化规律。基于海水化学成分,配制多种不同浓度的双组分的化学溶液来模拟海水侵蚀环境,将制备的内部含侵蚀物质的淤泥质土水泥土试块置于侵蚀溶液中进行预定时间的长时（≥90 d）浸泡,通过无侧限抗压试验得到了双组分侵蚀溶液长时浸泡下水泥土试块无侧限抗压强度变化规律。试验结果可为临时性及长期性水泥土工程的设计及安全维护提供一定参考依据。     

天然胶结钙质土强度及微观结构研究

自20世纪80年代起,国内就开展了关于岛礁钙质土岩土工程性质的研究工作,至今已经取得了大量的研究成果,但上述研究工作均是针对松散钙质土进行的,针对岛礁上广泛分布的胶结钙质土的研究工作尚未系统开展。而国外大量工程实践表明,胶结钙质土具有完全不同于松散钙质土的工程性状。针对天然胶结钙质土的空间各向异性,从微观角度研究影响其强度的主要参数,为今后的胶结钙质土的分类研究提供理论指导。文中采用多种试验研究方法,最后建立了天然胶结钙质土的密度、胶结度、孔隙度、颗粒大小等参数与强度间的对应关系,当前的研究结果表明,天然胶结钙质土的密度及胶结度与强度间存在良好的相关性。