沙丘形态及表沙粒度特征对风况和地表植被变化的响应

以毛乌素沙地3种沙丘（新月形沙丘、抛物线形沙丘和反向沙丘）为研究对象,对其形态、表沙粒度特征和区域风况进行了量化分析,探讨了沙丘表沙物理运动过程及其形态对外界条件（风况和地表植被）变化的反馈,揭示了沙丘表沙粒度特征对不同沙丘形态的响应机制。结果表明：新月形沙丘表沙平均粒径由迎风坡底部向顶部逐渐变小,分选呈现逐渐变好趋势, 但粒径较小和分选较差的表沙样出现在沙丘迎风坡中部。随着地表植被覆盖度的增加,新月形沙丘逐渐向抛物线形沙丘转变,近地表输沙能力和沙丘上风向沙源的供应同样受到限制,致使抛物线形沙丘由迎风坡底部向顶部呈现表沙平均粒径变大,而分选逐渐变好的趋势。毛乌素沙地内季节性风况（春季盛行强劲西北风,夏季盛行较弱东南风）的变化不仅促进了反向沙丘的发育,并且重组了西北盛行风影响下的表沙粒度特征。在夏季反向风风蚀的作用下,沙丘落沙坡顶部出现反向堆积和脊线反向移动的现象,同时其顶部呈现平均粒径由小变大、分选逐渐变好的趋势。     

1321号台风“蝴蝶”强度变化特征和影响因素分析

利用NCEP/NCAR全球再分析格点资料（空间分辨率1°×1°）、台风实况资料及海南省气象台站观测资料,选取1321号台风＂蝴蝶＂为研究个例,从天气学原理高低空形势及动力、热力学物理量等多角度分析了＂蝴蝶＂强度演变特征及影响因素.研究结果表明,副热带高压与高空西风槽是影响此次台风的主要大尺度天气系统,弱冷空气南侵、南海海温偏高及越赤道气流强盛是＂蝴蝶＂迅速加强的重要原因.西风槽引导弱冷空气南侵使得台风外围环流气压梯度增加,斜压不稳定状态加剧;南海海温达到29℃,海温偏高使台风区域大气层结降低,深热对流发展;105°E越赤道气流强盛为台风提供了充沛水汽和能量.三者共同作用促使台风强度突然增强.另外,低层涡度、高层散度、湿位涡及水汽通量等物理量能够较好地表征＂蝴蝶＂强度变化特征.低层辐合流入、高层辐散流出为台风的加强提供了动力条件;湿位涡下负上正表明大气热力层结不稳定;水汽通量增加表明水汽条件充足.良好的动力条件、热力条件与水汽条件共同作用,使得＂蝴蝶＂在短时间内迅速加强为强台风.     

一种融合空间拓扑关系的室内无线定位方法

针对仅利用无线信号源和其发射信号强度定位会丢失待测位置与信号源之间固有空间关系的问题,提出了利用已知位置接收信号源发射的无线信号强度测量未知点的低成本室内定位方法。该方法深入分析了待定位点和无线信号源以及信号覆盖范围之间的空间关系,充分利用RCC-8空间关系模型进行无线定位。实验结果表明,采用这种融合空间拓扑关系的基于无线信号强度的室内定位方案能够优化定位流程,并在测得位置中反映待测点和信号源之间的相对空间关系。     

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硫酸侵蚀下水泥土的电阻率特性研究

通过室内试验模拟了水泥土试块受不同浓度硫酸（H2SO4）溶液侵蚀的过程,采用电阻率法研究了电阻率与各参数、无侧限抗压强度之间的关系。结果表明,受H2SO4侵蚀后,水泥土电阻率、孔隙水电阻率、水泥土抗压强度均随着溶液浓度的增加而减小,而水泥土的结构因子和重度均随着溶液浓度的增加而增加,水泥土抗压强度与水泥土电阻率成正比。在试验的基础上,考虑侵蚀因素对水泥土电阻率的影响,通过对Archie法则进行修正,得到了H2SO4侵蚀下水泥土电阻率模型。通过对无侧限抗压强度试验结果的分析,并结合试块表观变化,提出了利用电阻率来评价侵蚀程度的方法。     

Testing and evaluation of strength and deformation behaviour of jointed rocks

The objective of the paper is to derive the strength and modulus properties of rockmass as a function of intact rock strength and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. A study for the strength and deformation characteristics of jointed rock is done by conducting standard laboratory tests on cylindrical specimens of plaster of Paris after introducing artificial joints. The specimens having one to four joints at different inclinations which vary from 0° to 90° were tested at different confining conditions. The test results were examined to understand the effect of joint frequency and joint inclination on the strength and deformation behaviour of rock mass. Empirical correlations were developed for prediction of the uniaxial compressive strength and elastic modulus of jointed rocks. Results are compared with the earlier work on jointed specimens covering a wide variety of rocks. So, knowing the intact rock properties and the joint factor, the jointed rock properties can be estimated. These relations can be used for developing an equivalent continuum model for rock mass for handling boundary value problems. A failure criterion as proposed by Ramamurthy (1993 Ramamurthy, T. 1993. “Strength and modulus response of anisotropic rocks”. In Comprehensive rock engineering, Edited by: Hudson, J.A. Vol. 1, 313–329. Oxford: Pergamon Press.  [Google Scholar]) has been validated from these experimental results.     

Effects of Mudstone Particle Content on Shear Strength of a Crushed Sandstone–Mudstone Particle Mixture

The present study focuses on the shear strength, deformation, and particle crushing of sand which is mixed by crushed sandstone and mudstone particles. Two triaxial tests—one for unsaturated specimens and the other for saturated specimens—were performed, along with sieve analysis tests. Results obtained from the triaxial tests indicate that, with the increment of the mudstone particle content by weight, the angle of internal friction decreases, the cohesion increases and then decreases, and both the initial angle of shearing resistance at the atmospheric pressure and decremental angle increase and then decrease. Compared to the unsaturated specimens, the deviator stress or normalized deviator stress of the saturated specimens at the same axial stress may decrease due to the wetting action. Thus, the shear strength of the tested materials may be reduced by the wetting action. Results of sieve analysis tests indicate that the mixing of some mudstone particles into the sandstone particle mixture may reduce the amount of particle crushing, but the wetting action may increase the amount. The amount of the crushed particle may arrive at a minimum of 40% of mudstone particle content by weight.     

桩端沉降测量对试桩成果分析的意义

桩端沉降测量和试桩资料的分析结果表明,桩在传递上部荷载与地基土之间产生的应力应变过程,表现为桩的弹性杆件和地基土的弹—塑性变形特征。从而对受荷桩,尤其是长柱和超长桩的应力应变特征有了更切合实际的认识。     

不排水抗剪强度非平稳随机场模拟及边坡可靠度分析

边坡可靠度分析中通常假定采用平稳或准平稳随机场表征土体参数的空间变异性,然而大量现场试验数据表明,土体参数如不排水抗剪强度沿土体埋深常呈现明显的非平稳分布特征,即其均值和标准差均随埋深发生变化,因此亟需发展土体参数非平稳随机场模型及其模拟方法。针对目前不能有效单独模拟土体参数趋势分量和随机波动分量的不确定性,提出了一种有效的不排水抗剪强度参数非平稳随机场模型,并给出了土体参数二维非平稳随机场模拟方法计算流程,同时将新提出的模型与现有非平稳随机场模型及平稳随机场模型进行了系统比较。最后通过不排水饱和黏土边坡算例验证了提出模型的有效性,并揭示了不排水抗剪强度非平稳分布特征对边坡可靠度的影响规律。结果表明：提出模型能够有效地单独模拟土体参数趋势分量和随机波动分量的不确定性,考虑土体参数均值和标准差随埋深增加而增大的特性,可为表征土体参数非平稳分布特征提供了一条有效的途径。此外,与采用非平稳随机场模拟土体参数空间变异性相比,采用常用的平稳随机场模型会低估边坡失效概率,从而造成偏危险的边坡工程设计方案。     

兰州九州重塑黄土的抗拉变形破坏机理

通过对不同干密度及含水量的重塑黄土进行室内抗拉强度试验,探究轴向压裂法致使试样破坏的机理及一般规律。结果表明,黄土的抗拉变形破坏可分为4种类型：I类,高干密度低含水量（干密度大于1.65 g·cm^-3,含水量小于15%）,抗拉强度介于8~12 kPa;Ⅱ类,低干密度低含水量（干密度小于1.60 g·cm^-3,含水量小于15%）,抗拉强度介于4~8 kPa;Ⅲ类,高干密度高含水量（干密度大于1.65 g·cm^-3,含水量大于17%）,抗拉强度介于4~8 kPa;IV类,低干密度高含水量（干密度小于1.60 g·cm^-3,含水量大于17%）,抗拉强度介于3~4 kPa。I类、Ⅱ类破坏类型属于脆性破坏,Ⅲ类、IV类属于塑性破坏。重塑黄土抵抗变形最弱的含水量为15%。通过对比分析黄土、普通黄黏土、红黏土及膨胀土的抗拉强度发现,在最优含水量处,不同干密度下黄土的抗拉强度均最小。黏性土的持水能力远超过黄土。黏土及膨胀土的抗拉强度均在最优含水量处达到最大值,而黄土的抗拉强度随着含水量的增加持续减小。研究结果对黄土强度特性的理解具有一定的参考意义。