A linear model for surface mining haul truck allocation incorporating shovel idle probabilities

We present models of trucks and shovels in oil sand surface mines. The models are formulated to minimize the number of trucks for a given set of shovels, subject to throughput and ore grade constraints. We quantify and validate the nonlinear relation between a shovel’s idle probability (which determines the shovel’s productivity) and the number of trucks assigned to the shovel via a simple approximation, based on the theory of finite source queues. We use linearization to incorporate this expression into linear integer programs. We assume in our integer programs that each shovel is assigned a single truck size but we outline how one could account for multiple truck sizes per shovel in an approximate fashion. The linearization of shovel idle probabilities allows us to formulate more accurate truck allocation models that are easily solvable for realistic-sized problems.     

A probability density function of liftoff velocities in mixed-size wind sand flux

With the discrete element method (DEM), employing the diameter distribution of natural sands sampled from the Tengger Desert, a mixed-size sand bed was produced and the particle-bed collision was simulated in the mixed-size wind sand movement. In the simulation, the shear wind velocity, particle diameter, incident velocity and incident angle of the impact sand particle were given the same values as the experimental results. After the particle-bed collision, we collected all the initial velocities of rising sand particles, including the liftoff angular velocities, liftoff linear velocities and their horizontal and vertical components. By the statistical analysis on the velocity sample for each velocity component, its probability density functions were obtained, and they are the functions of the shear wind velocity. The liftoff velocities and their horizontal and vertical components are distributed as an exponential density function, while the angular velocities are distributed as a normal density function. Supported by the Key Project of the National Natural Science Foundation of China (Grant No. 10532040)     

Formation of Calcareous Deposit during CathodicProtection and Its Properties

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The application of power ultrasound to the surface cleaning of silica and heavy mineral sands

Power ultrasound may be used in the processing of minerals to clean their surfaces of oxidation products and fine coatings, mainly through the large, but very localised, forces produced by cavitation. Results of the application of power ultrasound to remove iron-rich coatings from the surfaces of silica sand used in glass making and to improve the electrostatic separation of mineral sand concentrates through lowering the resistivity of the conducting minerals (ilmenite and rutile) are presented. Parameters affecting ultrasonic cleaning, such as input power and levels of reagent addition, are discussed. In particular, we present data showing the relationship between power input and the particle size of surface coatings removed. This can be explained by the Derjaguin approximation for the energy of interaction between a sphere and a flat surface.     

Bacteria transport through goethite-coated sand: effects of solution pH and coated sand content

This study investigated the transport of bacteria through goethite-coated sand, focusing on the effects of solution pH and coated sand content on the transport of Escherichia coli ATCC 11105. The first set of column experiments was performed in columns (length 30 cm, diameter 5 cm) packed with quartz sand coated with goethite in solution having a pH in the range of 6–9. The second was carried out in columns (length 30 cm, diameter 2.5 cm) with varying coated sand contents ranging from 0 to 100%. Results indicate that the bacteria transport in the coated sand was influenced by solution pH. Around pH 6 and 7, bacterial mass recoveries were low at 2.4–6.7% while they were high at 76.3–81.6% around pH 8 and 9. Around pH 8, the positively charged coated sand may convert to being negatively charged, causing an electrostatically repulsive interaction between the coated sand and bacteria, thus effecting a sharp change in the mass recovery. Results also reveal that the mass recovery decreased from 76.7 to 2.7% as the coated sand content increased from 0 to 100%, showing the nonlinear dependency of mass recovery on the content of coated sand. This study demonstrates the importance of the solution pH and coated sand content in the adhesion of bacteria to goethite-coated sand and furthermore contributes to the knowledge of bacterial removal in positively charged porous media.     

冻融循环次数和含水率对尾细砂力学性质的影响研究

为研究冻融循环次数和含水率对尾细砂力学性质的影响,利用GDH-2005B型高低温试验箱对尾矿砂试样进行冻融循环,并通过FST-200型应变控制式三轴剪力仪开展五种冻融循环次数(1次、3次、5次、7次、9次)和五种含水率(11%、13%、15%、17%、19%)尾矿砂试样常规三轴试验。研究表明:(1)相同含水率时,随着冻融循环次数的增大,变形模量逐渐减小,内聚力和内摩擦角均呈现降低的趋势;经历9次冻融循环后,内聚力降低至17.4kPa,内摩擦角降为14.82°。(2)相同冻融循环次数条件下,随着含水率的增大,尾矿砂的峰值应力降低,对应峰值应变增大;围压100kPa时,含水率19%的尾矿砂在经历9次冻融循环后应变为18.21%,应力为139.37kPa;各冻融循环次数下的尾矿砂抗压强度均呈现下降的趋势,内聚力和内摩擦角均随着含水率的增大而减小。研究成果可为尾矿砂物理力学性质理论的丰富以及尾矿砂相关工程的安全运营提供参考。     

火焰原子吸收法测定铬质引流砂中铁镁含量

建立了火焰原子吸收光谱法连续测定铬质引流砂中铁、镁含量的分析方法。试样以碳酸钠-硼酸混合熔剂熔融,以盐酸浸取,在校准溶液中加入重铬酸钾和二氧化硅进行基体匹配,抵消基体影响。对熔剂、熔融温度等进行讨论,确立了最佳分析条件,对样品多次测定,其测定结果与国家标准测定方法测定的结果基本一致,相对标准偏差(RSD,n=11)小于0.3%,加标回收率在98.7%~101%。方法具有操作简便、准确性好、速度快、成本低等特点。     

地震液化问题研究进展

概括了地震液化问题研究的框架和主要内容.从液化的机理、液化可能性分析, 液化稳 定分析、液化变形分析及液化分析的数值方法等几个方面, 总结了液化问题的主流研究思路 和近期进展, 指出了目前的不足和应着重研究的方向.随着对地震液化问题研究的深入, 液 化问题研究的重心逐渐由液化可能性分析、液化稳定分析转向液化引起的变形评价.在液化 变形的评价方法中, 基于震害调查的经验统计方法的预测精度较差, 且不能考虑土与结构的 相互作用;而基于数值模拟的方法可以考虑复杂的边值问题, 显示出广泛的前景.在以后对 地震液化问题的研究中, 除了进一步收集分析已有震害资料提高液化可能性分析及液化变形 分析的现有方法的可靠性以外, 应着重深入研究饱和砂土液化变形的基本规律及物理机制, 在此基础上建立能够合理模拟饱和砂土整个液化过程中(包括液化前和液化后)的应力应变 行为的本构模型, 发展能有效地预测实际边值问题中液化变形的数值模拟方法.     

Centrifugal experimental study of suction bucket foundations under dynamic loading

Centrifugal experiments were carried out to investigate the responses of suction bucket foundations under horizontal and vertical dynamic loading. It is shown that when the loading amplitude is over a critical value, the sand at the upper part around the bucket is softened or even liquefied. The excess pore pressure decreases from the upper part to the lower part of the sand layer in the vertical direction and decreases radially from the bucket’s side wall in the horizontal direction. Large settlements of the bucket and the sand layer around the bucket are induced by dynamic loading. The dynamic responses of the bucket with smaller height (the same diameter) are heavier. The project supported by the fund of Chinese Ocean Oil Co. and Chinese Academy of Sciences(KZCX2-YW-302-02).     

含粘粒砂土抗液化性能的试验研究

通过对含粘粒砂土所作的试验研究, 包括: 粘粒矿物成分不同、粘粒含量不同的重塑土样所作的室内动三轴试验; X光衍射试验, 试验结果对比分析后, 得出了含粘粒砂土抗液化性能的特性。并得出以下结论: (1)粘粒矿物成分不同, 也引起砂土动力稳定性的变化; (2 )动剪应力强度与粘粒含量并非呈单调增加关系, 而呈抛物线型, 并给出回归方程; (3)含粘粒的砂土, 其抗液化能力最低点总是在粘粒含量 8.5～ 9.5 %之间。