基于模糊综合评判的机械零件材料选择方法

针对在选择机械零件材料时采用传统方法所具有的主观性缺陷,本文结合设计实例,运用模糊数学理论,建立了零件材料选择的模糊综合评判的数学模型,能从多种可用材料中较客观、合理地确定出最适用的一种材料,从而提高了设计质量.     

Mantle Mush Compaction: a Key to Understand the Mechanisms of Concentration of Kimberlite Melts and Initiation of Swarms of Kimberlite Dykes

Kimberlite pipes or dykes tend to occur in clusters (a few kilometresin diameter) within fields 30–50 km in diameter. Theyare generally considered to originate from low degrees of partialmelting of carbonated peridotite within zones of ascending mantle.Numerical modelling shows that at the depth of formation ofkimberlite melts (>>200 km), mantle compaction processescan result in the formation of melt pockets a few tens of kilometresacross, with melt concentrations up to 7%. The initiation ofswarms of kimberlite dykes at the top of these melt pocketsis inevitable because of the large excess pressure between themelt and the surrounding solid, which exceeds the hydraulicfracturing limit of the overlying rocks. After their initiationat mantle depth the swarm of dykes may reach the surface ofthe Earth when the entire cratonic lithosphere column is inextension. We propose that kimberlite fields represent the surfaceenvelope of dyke swarms generated inside a melt pocket and thatkimberlite clusters represent the discharge of melt via dykesoriginating from sub-regions of the pocket. This model reproducesthe worldwide average diameter of kimberlite fields and is consistentwith the observation that some of the main kimberlite fieldsdisplay age ranges of c. 10 Myr. It is deduced that, at thescale of the Kaapvaal craton, different fields such as Kimberley,N. Lesotho and Orapa, dated at 80–90 Ma, probably resultfrom synchronous melt pockets forming inside an ascending mantleflow. The same model could apply to the fields of the Rietfontein,Central Cape and Gibeon districts dated at 60–70 Ma. Itis suggested that the same mantle flow that produced the Kimberley,N. Lesotho and Orapa fields migrated over 20–30 Myr afew hundred kilometres westward to form the Rietfontein, CentralCape and Gibeon fields. KEY WORDS: kimberlites; mantle; compaction; convection; volcanism     

振冲挤密加固深厚吹填珊瑚礁砂地基试验研究

针对沙特吉赞新建的围海造陆货物堆场的地基处理,基于珊瑚礁砂的疏浚工程特性,开展了用两种振冲挤密法加固该处不良级配疏松礁砂地基的有效性及确定其相应工艺参数的现场试验。先完成选定小区试验,后由SPT检验其效果,再分析确定最优振冲工艺并指导了大面积工程施工。通过比对场区地基加固前、后的CPT检测结果,用Iwasaki液化指数法对振后地基做进一步液化判断,同时采用极限法(基于CPT)和施莫法(基于SPT)对加固地基进行了沉降分析并对比两种计算结果,验证本试验研究所确定的加填料振冲方案与施工工艺合理性,加固后地基的承载及抗液化能力得到有效提高且完全能满足工后沉降控制要求。研究成果可供珊瑚礁海域的类似工程参考或借鉴。     

内嵌式法兰连接预制拼装双柱墩参数分析

本文基于实际工程对内嵌式法兰连接预制拼装双柱墩参数进行了分析,将法兰设置在塑性铰区以外,设计1∶3缩尺模型,通过分析不同法兰强度等级、混凝土强度等级、轴压比和配筋率的内嵌式法兰连接预制拼装双柱墩模型,得到不同情况下推覆曲线和损伤破坏状态,分析各参数的影响。研究结果表明,法兰强度等级对结构的影响较小,配筋率对结构承载力和延性的影响较大,结构最终失效主要表现在塑性铰区域,法兰存在一定程度的翘起。     

浅谈挤密碎石桩的施工方法

挤密碎石桩施工法是一种振动成桩法,即先用桩管振动成孔,然后填入足够数量的碎石,最后振动密实成桩体。通过振动、挤密的成桩过程,将原地基土振动夯实,桩体与桩间土形成复合地基,达到既处理可液化地基又增强地基的效果。介绍了挤密碎石柱的施工方法和质量检测方法。     

Effects of rainfall intensity and compaction on water transport from opencast coal mine soils: An experimental study

The use of heavy machinery during opencast coal mining can result in soil compaction. Severe soil compaction has a negative impact on the transport of water and gas in the soil. In addition, rainfall intensity has traditionally been related to soil surface sealing affecting water transport. To assess the effects of rainfall intensity and compaction on water infiltration and surface runoff in an opencast coal mining area, the disturbed soils from the Antaibao opencast mine in Shanxi Province, China, were collected. Four soil columns with different bulk densities (i.e., 1.4 g cm^-3, 1.5 g cm^-3, 1.6 g cm^-3, and 1.7 g cm^-3) were designed, and each column received water five times at rainfall intensities of 23.12, 28.91, 38.54, 57.81, and 115.62 mm hr^-1. The total volume of runoff, the time to start runoff, and the volumetric water contents at the depths of 5 cm, 15 cm, 25 cm, 35 cm, 45 cm, 55 cm, and 65 cm were measured. Under the same soil bulk density, high rainfall intensity reduced infiltration, increased surface runoff, and decreased the magnitude of change in the volumetric water contents at different depths. Under the same rainfall intensity, the soil column with a high bulk density showed relatively low water infiltration. Treatments 3 (1.6 g cm^-3) and 4 (1.7 g cm^-3) had very small changes in volumetric water contents of the profiles even under a lower rainfall intensity. Severe soil compaction was highly prone to surface runoff after rainfall. Engineering and revegetation measures are available to improve compacted soil quality in dumps. Our results provide a theoretical basis for the management of land reclamation in opencast coal mine areas.     

Simulation of drilling‐induced compaction bands using discrete element method

Rock failure is observed around boreholes often with certain types of failure zones, which are called breakouts. Laboratory‐scale drilling tests in some high‐porosity quartz‐rich sandstone have shown breakouts in the form of narrow localized compacted zones in the minimum horizontal stress direction. They are called fracture‐like breakouts. Such compaction bands may affect hydrocarbon extraction by forming barriers that inhibit fluid flow and may also be a source of sand production. This paper presents the results of numerical simulations of borehole breakouts using 3D discrete element method to investigate the mechanism of the fracture‐like breakouts and to identify the role of far‐field stresses on the breakout dimensions. The numerical tool was first verified against analytical solutions. It was then utilized to investigate the failure mechanism and breakout geometry for drilled cubic rock samples of Castlegate sandstone subjected to different pre‐existing far‐field stresses. Results show that failure occurs in the zones of the highest concentration of tangential stress around the borehole. It is concluded that fracture‐like breakout develops as a result of a nondilatant failure mechanism consisting of localized grain debonding and repacking and grain crushing that lead to the formation of a compaction band in the minimum horizontal stress direction. In addition, it is found that the length of fracture‐like breakouts depends on both the mean stress and stress anisotropy. However, the width of the breakout is not significantly changed by the far‐field stresses. Copyright © 2013 John Wiley & Sons, Ltd.     

The application of satellite differential SAR interferometry-derived ground displacements in hydrogeology

The application of satellite differential synthetic aperture radar (SAR) interferometry, principally coherent (InSAR) and to a lesser extent, persistent-scatterer (PSI) techniques to hydrogeologic studies has improved capabilities to map, monitor, analyze, and simulate groundwater flow, aquifer-system compaction and land subsidence. A number of investigations over the previous decade show how the spatially detailed images of ground displacements measured with InSAR have advanced hydrogeologic understanding, especially when a time series of images is used in conjunction with histories of changes in water levels and management practices. Important advances include: (1) identifying structural or lithostratigraphic boundaries (e.g. faults or transitional facies) of groundwater flow and deformation; (2) defining the material and hydraulic heterogeneity of deforming aquifer-systems; (3) estimating system properties (e.g. storage coefficients and hydraulic conductivities); and (4) constraining numerical models of groundwater flow, aquifer-system compaction, and land subsidence. As a component of an integrated approach to hydrogeologic monitoring and characterization of unconsolidated alluvial groundwater basins differential SAR interferometry contributes unique information that can facilitate improved management of groundwater resources. Future satellite SAR missions specifically designed for differential interferometry will enhance these contributions.     

水-岩化学作用对岩体变形破坏力学效应研究进展

水—岩化学作用对岩体变形破坏力学效应的研究涉及力学和化学两方面,也即为地球化学与岩体力学两个研究领域的交叉。针对水化学作用对岩体力学性质的影响机理,较系统地总结了该研究领域中的现状和研究新进展,分析了其研究方法,指出了今后的研究方向和主要研究内容,并认为此方面的研究将在工程地质学中占重要地位。     

瞬态瑞雷波法在工程检测中的应用研究

本文简要介绍了瞬态瑞雷波法的工作原理,野外观测及数据采集系统,并总结出了资料处理解释流程图,同时从工程实践出发,探讨了该项新技术应用于高速公路建设中的优点,存在问题及未来发展趋势。