饱和土沉积谷场地对平面P波的散射

把沉积谷软土场地用饱和多孔介质的Biot动力学理论模拟 ,周围的场地用单相介质弹性动力理论模拟 ,利用波函数展开法 ,在频域内给出了不同土层界面条件 (透水条件和不透水条件 )下具有饱和土沉积层的圆弧形沉积河谷场地对平面P波散射问题的解析解。利用该解分析了不同土层界面条件 ,以及饱和土层的孔隙率和饱和度在不同入射角下对地面运动的影响     

半球形凹陷谷场地对Rayleigh波的三维散射

利用半空间场地用单相介质动力学理论模拟，并略去阻尼项的影响，首次推导出了三维半球形凹陷谷场地在平面Rayleigh波入射下散射问题的解析解。确定局部场地的三维波场分布，给出半球形沉积谷场地地表位移分量，分析了入射波频率对场地震动的影响，并进一步与单相弹性介质情况下的地表运动进行了对比。     

软硬交互横向不均匀场地地震反应分析

软硬交互横向不均匀场地十分常见,其在强震作用下的地震反应对工程结构的安全有着重要影响,然而目前还很少有针对该场地地震反应分析的研究。基于精确动力刚度矩阵和均布荷载动力格林函数的间接边界元方法,经快速傅里叶逆变换,在时域内求解了层状半空间中软硬交互横向不均匀场地的地震反应问题。求解中将模型分解为含较硬介质的层状半空间域和较软介质域,同时将总波场分解为自由波场和散射波场两部分,通过在相应边界上施加斜线和水平线虚拟均布荷载,进而求解动力格林函数以模拟散射波场,自由波场可由直接刚度法方便求得。验证了方法的正确性,检验了求解模型的收敛性,进而开展了相应的数值计算分析,着重讨论了介质参数和软硬交界面倾角对场地地震反应的影响。研究表明:软硬交互场地中,较大的地表地震动响应发生在较软介质侧;软硬交界面的存在使得场地地表加速度响应发生突变,突变程度受介质参数和交界面倾角的影响显著;随着介质参数差异和交界面倾角的增大,地表加速度峰值增大,反应谱曲线显示短周期成分变得更为丰富,对基岩地震动的放大作用增强;软硬交界面对场地地表地震反应的影响主要在交界面外的两倍介质层厚度范围。     

流体饱和层状半空间中沉积谷地对地震波的散射— IBIEM求解

针对流体饱和层状半空间中任意形状沉积谷地对地震波的散射问题,基于单层位势理论,建立一种新的间接边界积分方程法（IBIEM）：首先推导饱和层状半空间中两类膨胀波源和剪切波源动力格林函数,进而由分布在沉积谷地和层状半空间交界面附近两虚拟波源面上的P_I、P_II和SV波源分别构造沉积内外的散射波场。由交界面连续性条件建立方程并求解确定虚拟波源密度,总波场即可由自由波场和散射波场叠加而得。然后通过边界条件验算、退化解答与现有结果的比较,验证了方法的计算精度。通过一组典型算例,初步探讨了平面SV波在饱和层状半空间中沉积谷地周围散射的基本规律。研究表明：饱和层状沉积对地震波的散射和相应干土情况存在显著差异,边界渗透条件对沉积内部地震响应具有重要影响;饱和层状场地中波的散射和均质半空间情况有着本质不同,总体反应体现了饱和土层的共振放大效应和沉积谷地对波的散射效应。实际场地中地震波传播的精确模拟需考虑岩土介质的多相性和层理特征。     

复杂介质对地震波传播的影响

本文基于两相介质动力学方程组,利用显式集中质量有限元结合透射人工边界,研究了水平自由场地单相土、欠饱和土和饱和土及不同模量的土层排列结构对地震波传播的影响。结果表明介质的性质对P 波传播有明显的影响;而土层结构对SV 波传播有明显影响。同时,本文还研究了横向不均匀场地地震反应,结果进一步表明,仅用一维模型研究横向不均匀场地会引起较大误差。     

圆弧状多层沉积凹陷在平面SV波入射下的动力响应

利用波函数的Fourier-Bessel级数展开法,推导了含任意多个圆弧状沉积层的凹陷地形在平面SV波入射下动力响应的解析解。通过与单一沉积凹陷条件下所得结果的比较,验证了该解析解计算结果的正确性。利用该解析解,研究了凹陷地形上覆沉积介质的成层性,包括沉积层的层数、排列顺序、以及软弱夹层的厚度和刚度等,对地面运动的影响效应。     

饱和软土动力响应的弹粘塑性有限元分析

采用基于混合物理论的多孔介质模型,将饱和软土的固体相视为弹粘塑性体,建立了饱和软土的弹粘塑性模型。根据饱和软土两相多孔介质的控制场方程,利用罚参数法和Galerkin加权残值法,推导得到饱和软土动力响应的有限元基本方程,采用了Hughes隐式－显式的求解算法。通过相关理论编制了有限元程序,模拟分析了桩基对饱和软土作用的动力响应,指出了土动力响应的一些特点,揭示了桩基对饱和软土作用的相关机理。     

DNAPLs在低渗透性夹层影响下的迁移和分布特征研究

重非水相流体(DNAPL)在地下介质中的运移分布受多种因素影响,包括DNAPLs的物化性质、泄漏速率、地下水流速、介质非均质性等。本文基于T2VOC程序对DNAPLs在非均质地层(含低渗透性夹层)中的迁移和分布特征进行了数值模拟,分别采用三相毛管压力函数Parker模型和二相毛管压力函数van Genuchten模型,研究了夹层的饱和渗透率、地下水流速对DNAPLs运移和分布的影响。研究表明,地下水流速的增大显著促进了DNAPLs的水平和垂向运移;相同流速情况下,非均质层(低渗透性夹层)饱和渗透率的减小使得DNAPLs污染羽形态及空间路径出现了明显蓄积和绕流。模拟结果可为DNAPLs污染场地识别与修复提供了理论基础与技术支持,便于进一步研究其在地下饱和非均质介质中的运移。     

液化场地桩-土地震相互作用振动台试验数值模拟

基于动力Biot理论将饱和砂土模拟为两相介质,正确考虑水和土颗粒之间变形关系,采用完全耦合u-p有限元公式模拟土体位移和孔压,选用多屈服面弹-塑性本构模型模拟黏土、砂土,砂层划分为20-8节点六面体单元,桩处理为梁-柱单元,建立三维有效应力振动台试验分析模型。通过振动台试验结果,验证该模型的正确性,显示该方法能够准确地模拟可液化场地桩-土-结构动力相互用的重要特征,这对于实际工程设计具有一定的参考意义。     

盆地场地远场长周期地震动输入的确定

盆地场地的长周期结构在远场长周期地震动作用下震害明显,目前国内设计规范尚未将低幅值的远场长周期地震动记录纳入统计范围。研究盆地场地远场长周期地震动输入方法,可用于国内盆地建筑的抗震补充验算。文中针对日本沉积盆地台站地震动记录数据进行统计,拟合出盆地效应与沉积层厚度的关系曲线。结合国内板壳内地震下的基岩地震动衰减关系、盆地效应与沉积层厚度关系曲线以及局部工程场地放大作用,给出适用于国内的盆地场地远场长周期地震动输入方法。基于渭河盆地内的西安市区以及周边地震环境,进行了远场长周期地震动输入方法的案例分析。分析结果表明：盆地效应对加速度反应谱的放大作用和对地震波到达时刻的影响,均随盆地沉积层厚度的增加而变得更显著。文中方法综合考虑了震源分布、震级、震中距、盆地效应和局部工程场地的影响,可用于估计国内盆地场地远场长周期地震动加速度反应谱及其地震动时程,其模拟的加速度反应谱与地震动时程符合实际远场长周期地震动记录的特征。     

Performance of a road embankment on soft clay supported on a Geocell mattress foundation

A five kilometre-long road was constructed in the New Territories of Hong Kong between 1989 and 1992. Part of the road crossed an alluvial plain on an embankment, and at two locations on the alluvial plain this embankment was underlain by soft clay deposits. A geocell mattress was used as the means of supporting the embankment on these soft clay deposits. Wick drains were installed beneath the embankment to speed up consolidation of the soft clays, and using staged construction the embankment was built up to a maximum height of 10 m.

The embankment was fully instrumented with pneumatic piezometers, inclinometers, hydrostatic profile gauges, settlement plates, surface settlement markers, and lateral movement blocks. This paper presents the results of the instrumentation monitoring and the performance of the geocell mattress foundation during the construction of the embankment. At one section, unusually high excess pore water pressures and a slight heave of the toes of the embankment were recorded. The accompanying small lateral extension and the deflected shape of the geocell mattress indicated that it had behaved as a raft foundation to the embankment.     

沪蓉西高速公路拓宽软土地基高路堤施工技术

沪蓉西高速公路贺家坪连接线K2+710～K2+890段为软土地基上老路拓宽高路堤.半幅路基为稳定性较好的老路利用,而另半幅路基位于河谷冲击沉积的水田内,上部有3.0～6.5m的淤泥层,路堤最大填筑高度约40m.工后沉降、差异沉降、路堤失稳是本路堤质量控制的关键.介绍施工中采用抛石挤淤、开挖台阶、分层铺设土工格栅等措施综合处治措施,并加强稳定性和沉降动态监测.确保了路堤填筑质量和进度,保证了整个工程顺利完成.     

圆弧形沉积谷地对平面SV波三维散射解析解

采用大圆弧面来模拟半空间表面,利用波函数展开法和有限项Fourier展开技术,在频域内给出了圆弧形沉积谷地对平面SV波三维散射的一个解析解。并以此解答为基础,进一步分析了入射波频率和入射角度对圆弧形沉积谷地场地反应的影响。研究表明,圆弧形沉积谷地对平面波的三维散射比二维散射更加复杂;将三维散射问题分解为两个主平面入射的简化处理存在较大的误差;入射波的频率和入射角度对圆弧形沉积谷地场地反应均有重要影响。     

圆弧形层状沉积河谷场地在平面SH波入射下动力响应分析

利用Fourier Bessel级数展开法在频域内给出了圆弧形层状沉积河谷场地对平面SH波放大作用的一个解析解 ,并利用该解分析了河谷中沉积土层排列顺序对放大作用的影响     

EPB tunneling challenges in bouldery ground: a new experience on the Tabriz metro line 1, Iran

Underground construction of the Tabriz metro line 1 involved boring twin tunnels with two earth pressure balance machines in alluvial deposits. Although this type of machine is recommended for excavation in fine soils, its performance was evaluated in this project where part of the ground consists of alluvial deposits with particle size ranging from silt to boulder and even rock blocks. It was found that the tunnel boring machine (TBM) performance was highly reduced due to the variation in ground conditions. Many types of problem were observed during the excavation in coarse grained alluvial deposits including high cutter-head torque, excessive wear of tools, breaking of TBM parts and ground instabilities in the form of large settlement and ground collapse. A trial effort was implanted to stabilize the overburden ground by the injection of cement grout, but this proved to be unsuccessful. In both cases, the excavation operation was delayed. With the experience gained from the excavation of the first tunnel and use of foam with a high foam expansion ratio as a soil conditioner in closed mode, the performance of the TBM in the second tunnel improved.     

High-mountain landslides in the Atlantic Pyrenees: their relationship with the geology and geomorphology

This paper discusses the importance of high mountain landslides and their sliding mechanisms using a case study in the Aspe Valley of the Pyrenees. The first part of the paper considers the influence of geology including the lithology and complex structural history of the area. It notes the weak resistance of the Carboniferous substratum to glacial erosion. The second part describes the impact of the glaciation of the area, during which a pronounced morphology was created, frequently with a different orientation to the main valleys. The valleys were commonly infilled with till deposits resting on a hidden topographic bedrock surface referred to as the "cryptorelief". Failures most frequently occur where glacial deposits remain, generally at the junction between the till and the underlying strata which have often experienced stress relief. The paper provides a methodology for the study of unstable slopes in such environments and discusses the characteristics of some triggering factors.      

北京市延庆区石窑村南地沟泥石流特征及发展趋势预测

本文以北京市延庆区石窑村南地沟泥石流为研究对象,通过野外调查与GIS统计分析,研究该流域降雨条件、地形地貌和沟道条件、物源条件等形成条件特征,针对流域内松散堆积物转换,开展了流域分区特征分析;通过14个因子分析,建立了该泥石流的发育阶段识别模型,对其发展趋势进行了预测;利用单沟泥石流堆积区公式开展了最大危险区预测研究,提出相应的防治措施建议。研究表明:石窑村南地沟泥石流内松散堆积物动储量达18.36×10~4 m~3,物源类型划分为冲洪积物源、残坡积物源、人工堆积物源和崩滑塌物源4种,其中残坡积所占比重最大。该泥石流属于暴雨-沟谷型-支沟群发型、中易发泥石流,泥石流发展阶段处于发育期,最大危险区面积为0.413 km~2,对沟口堆积区的石窑村及村民的生命财产安全造成威胁,建议采用局部物源平整与疏理排导渠相结合的综合治理措施。本文为该区地质灾害防治提供基础依据。     

沉积河谷-衬砌隧道体系对平面P波的散射

沉积河谷对地震动的放大效应已为地震观测和理论研究所证实。现实中有大量隧道穿越河谷情况,而河谷中隧道地震反应规律尚不明确。为此,本文建立沉积河谷-衬砌隧道整体二维平面应变模型,基于一种高精度边界间接积分方程法,对河谷中隧道地震响应及动应力集中进行模拟分析。大量参数计算结果表明:沉积河谷中隧道地震反应更为剧烈,动应力集中更为显著,应力峰值可达到入射波应力幅值的数十倍。随隧道埋深加大,应力频谱振荡加剧且峰值频率发生明显变化。部分频率段,隧道对河谷地表位移同样有较大的扰动。穿越河谷隧道的抗震设计需考虑河谷中地震动放大效应对隧道内力和变形的显著影响。     

Seismic isolation effect of a tunnel covered with coating material

A method to cover a tunnel lining with a soft and thin coating is discussed herein as a possible measure for mitigating seismic damage to tunnels. Long-term earthquake observations at different tunnel sites within a variety of alluvial soil deposits have demonstrated that a circular tunnel is liable to deform in such a way that its two diagonal diameters crossing each other expand and contract alternately. Narrowing down vibration modes for discussion to this particular and the most important mode, any of the essential items of the soil-tunnel system—namely the soil, the coating and the tunneling lining—had only one degree of freedom, allowing the isolation effect to be simply evaluated in terms of a limited number of key parameters.