水库围堤地基液化有效应力动力分析

利用基于Biot方程耦合场分割算法的ANSYS有限元软件二次开发形成的岩土工程有效应力分析模块,对某水库围堤坝基进行了液化震陷分析。计算中选取具有代表性的堤坝断面建立二维有限元模型,并采用上海50 a超越概率10％的人造地震波加速度-时程作为基底输入地震。计算得到围堤孔隙水压力与有效应力比的分布情况以及震陷分布情况。分析结果表明,坝基中心部位的孔隙水压力比要比坝脚两侧的孔隙水压力比小,坝基中心部位可以不进行地基处理。该方法可为今后其他类似工程的设计和施工提供参考。     

汶川地震前后都江堰山区滑坡滑动距离影响因素变化分析

滑坡滑动距离作为滑坡防灾减灾的主要评价指标之一,不仅受滑坡体积和落差的影响,还与滑坡运动的地质环境作用相关。本文在对都江堰地区51个地震滑坡、16个降雨滑坡详细调查编目的基础上,采用数理统计方法分析了斜坡原始坡度、滑坡前后缘高差、滑坡平面形态、体积、滑体平均厚度及坡面摩擦系数等6个因素与滑坡水平滑动距离的相关性,借此厘清了汶川Ms8.0级大地震前后不同因素对不同类型滑坡运动的贡献大小,进而构建了不同成因类型滑坡的滑动距离预测关系式,可为龙门山区的滑坡防灾减灾工作提供参考。研究表明:影响都江堰地区地震滑坡运动距离的主要因素有滑坡体积(lg V)、斜坡原始坡度(α)、滑坡平面形态(R)和滑坡前后缘高差(ΔH);而控制降雨滑坡运动距离的主要因素为滑坡前后缘高差(ΔH)、滑坡体积(lg V)、斜坡坡度(α)和斜坡表面摩擦系数(μ);汶川地震后,影响该地区降雨滑坡滑动能力的因素发生了变异,各因素与滑坡滑动距离的相关性较弱,显示出其贡献率在急剧减弱,仅滑坡体积(lg V)与滑动距离的相关性较强。     

Effects of cross-correlated multiple spatially random soil properties on wave-induced oscillatory seabed response

The evaluation of seabed response under wave loading is important for prediction of stability of foundations of offshore structures. In this study, a stochastic finite element model which integrates the Karhunen-Loève expansion random field simulation and finite element modeling of wave-induced seabed response is established. The wave-induced oscillatory response in a spatially random heterogeneous porous seabed considering cross-correlated multiple soil properties is investigated. The effects of multiple spatial random soil properties, correlation length and the trend function (the relation of the mean value versus depth) on oscillatory pore water pressure and momentary liquefaction are discussed. The stochastic analyses show that the uncertainty bounds of oscillatory pore water pressure are wider for the case with multiple spatially random soil properties compared with those with the single random soil property. The mean pore water pressure of the stochastic analysis is greater than the one obtained by the deterministic analysis. Therefore, the average momentary liquefaction zone in the stochastic analysis is shallower than the deterministic one. The median of momentary liquefaction depth generally decreases with the increase of vertical correlation length. When the slope of the trend function increases, the uncertainty of pore water pressure is greatly reduced at deeper depth of the seabed. Without considering the trend of soil properties, the wave-induced momentary liquefaction potential may be underestimated.     

波浪作用下粉质土海床液化界面波压力的研究

波浪作用下粉质土海床的液化是影响海上平台、海底管线等海洋构筑物安全的灾害之一。在进行构筑物设计中应考虑海床液化的深度问题,而液化土体对下部海床的界面波压力是计算海床孔隙水压力增长以及液化深度的重要参量。本文基于波致粉土海床自上而下的渐进液化模式,利用双层流体波动理论,推导了考虑海床土体黏性的海床界面波压力表达式,并与不考虑黏性时的界面波压力进行了比较分析。结果表明,计算液化后土体界面波压力时,是否考虑液化土体的黏性对结果影响较大,进而可能影响粉质土海床液化深度的确定。     

基于动三轴试验和土层地震反应对地震液化的判别

以汉口某场地典型钻孔剖面为研究对象,结合动三轴试验成果,采用等效线性化方法考虑土层的非线性特征,利用一维波动方法进行场地土层地震反应分析,探讨场地内埋深10~36 m范围内的各土层在不同地震作用下的液化可能性。结果表明,汉口地区埋深超过20 m的砂土层在Ⅶ度、Ⅷ度地震作用下有液化的可能性;土层液化的可能性随着埋深的增大而减小;输入地震动的频谱特性及平稳段持续时间等因素可影响液化判别结果。该方法可为深层液化判别提供参考。     

Earthquake imprints on a lacustrine deltaic system: The Kürk Delta along the East Anatolian Fault (Turkey)

Deltas contain sedimentary records that are not only indicative of water‐level changes, but also particularly sensitive to earthquake shaking typically resulting in soft‐sediment‐deformation structures. The Kürk lacustrine delta lies at the south‐western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault, which has generated earthquakes of magnitude 7. This study re‐evaluates water‐level changes and earthquake shaking that have affected the Kürk Delta, combining geophysical data (seismic‐reflection profiles and side‐scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water‐level changes provides a temporal framework for the depositional record. In addition to the common soft‐sediment deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake‐induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a palaeoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the East Anatolian Fault. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (¹³⁷Cs and ²¹⁰Pb), two major sedimentary events were attributed to the ad 1874 to 1875 East Anatolian Fault earthquake sequence. Their sedimentological characteristics were determined by X‐ray imagery, X‐ray diffraction, loss‐on‐ignition, grain‐size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post‐seismic sediment reworking of earthquake‐triggered landslides.     

厦门砂土的动力特性研究

为了探讨厦门砂土的动力特性,对厦门金秋豪园场地的中粗砂和细粉砂做了一系列振动三轴试验,并对同一场地的含泥中砂做了4个共振柱试验。根据试验结果,确定了中粗砂与细粉砂的液化曲线和动本构关系,提出了相应的动孔压模型,得到了含泥中砂在小应变条件下动剪切模量和阻尼比的变化规律。     

饱和粉土振动液化分析

液化是造成场地地震破坏的首要原因之一。自Casagrande的经典工作以来,对地震液化的研究已经取得了很大的进展。然而这些研究大多是针对于砂土而进行的,对于粉土液化研究的相对较少,且粉土的液化特性也有别于砂土。因此,在已有研究的基础之上利用粉土液化试验得出的结果,分析了粉土液化的机理、影响因素以及在振动过程中粉土中孔隙水压力的增长规律,认为粉土中的粘粒含量、密实度以及土的结构性对其抗液化能力有较大的影响。考虑到试验中振动次数的离散性,引入了时间参数的概念,根据动三轴试验结果提出了孔隙水压力增长的经验公式,可以比较方便地应用于计算液化的有限元程序中去。     

杭州钱塘江防洪堤抗震分析

通过动力试验研究了杭州钱塘江防洪堤基的动力特性,并用原位和室内分析法判别了堤基液化的可能性,在有限元分析时,改进了工程上常用的排水有效应力动反应分析方法,在地震期间采用Biot动力固结方程进行动力分析,可以同时考虑地震期间孔压的上升及固结消散对防洪堤的抗震液化和稳定性进行分析。采用非线性成层地基反演技术,反演分析基岩地震加速度曲线,对堤坝地震反应进行分析。地震响应的各种结果对于了解今后防洪堤在地震期间的运行状态具有一定指导意义。     

饱和砂砾料振动孔压与轴向应变发展模式研究

利用自行研制、开发的高精度中型动三轴仪,对文选定的砂砾料液化过程中的孔隙水压力增长和轴向应变发展模式进行了研究。同时,对剔除粒径大于5 mm后的模拟料,采用相似级配法,运用DS-2T型动三轴仪进行了一组平行试验。着重比较了砂砾料和模拟料在振动荷载作用下孔压、应变发展模式的区别。结果表明：在均压固结条件下,砂砾料在循环应力作用下,其孔压的发展模式与模拟料不同,可以用修正的反正弦进行拟合,而模拟料振动孔压的发展模式可用反正弦拟合;二者振动孔压均达不到初始有效固结围压,约为初始围压的90 %左右。模拟料与砂砾料在振动荷载作用下,应变发展模式不同。前者在初始液化前应变幅值较小且无明显增长,临近初始液化时应变大幅度增加导致试样突然破坏;后者在循环荷载作用过程中应变幅值一直稳定增加。