粉煤灰湿陷变形的三轴试验和计算

采用双压力室三轴仪对粉煤灰试样进行了单线法湿陷试验,研究了在静水压力作用以及在不同应力状态和应力水平下粉煤灰湿陷变形的规律,得出了粉煤灰湿陷变形的经验计算公式.提出了计算粉煤灰地基湿陷变形的"全应变曲线"增量有限元法.基于本文的试验结果,对一个粉煤灰地基的湿陷变形进行了有限元计算.     

太行山东麓北拒马河冲积扇结构探测及地震砂土液化判别

北拒马河冲积扇及邻近地区位于太行山东麓,地表覆盖全新世(Qh)松散砂土与粉土,该区域地下水埋深较浅,潜在地震最大震级达6.5级,在地震作用下存在发生砂土液化危险性.通过野外地质调查、工程地质钻探和高密度电阻率法勘探揭示北拒马河冲积扇地层结构特征.在此基础上,采用原位标准贯入试验和室内动三轴试验评价北拒马河冲积扇饱和砂土...     

剪切-体积应变耦合的孔压增量模型试验

以南京细砂为对象,通过共振柱试验及应变控制的排水/不排水分级和单级加载循环三轴试验的系统性研究,建立了能够描述饱和砂土孔压增长规律的新模型。该模型遵循Martin和Byrne提出的基本理论框架,孔压的增长是由循环剪切作用下体积改变所引起的。提出的孔压模型属于应变控制的孔压增量模型。基于排水循环单级加载试验,通过引入体积门槛剪应变γ_(tv)的概念,以具有代表性的15周体应变(ξ_(vd))15为基准点,归准化体应变发展与循环剪应变之间的关系,建立了三参数的体应变增量模型及其参数标定方法。基于排水和不排水循环单级加载试验结果,揭示了体应变与孔压比之间的内在联系,进而导出回弹模量表达式。通过耦合新的体应变增量模型及回弹模量公式,建立了新的剪应变-体应变耦合的孔压增量模型。验证性试验表明,新的孔压增量模型的预测值与试验结果的吻合度较高。     

应力路径和干湿状态对堆石料颗粒破碎的影响研究

堆石料颗粒破碎是引起高土石坝变形的重要因素。在大坝填筑、蓄水期,堆石料的应力路径和干湿状态均是变化的。通过大型三轴试验,系统地研究了应力路径和干湿状态对堆石料颗粒破碎规律的影响。试验结果表明：（1）相同初始条件下,按不同应力路径达到同一轴向应变停机时测定的颗粒破碎率是不同的,等围压?3试验产生的颗粒破碎最大,等平均主应力p试验的次之,等最大主应力?1试验的最小,但不同应力路径下的颗粒级配演化规律是一致的。（2）相同初始条件下,湿样的颗粒破碎率明显高于干样,且二者的差距随着围压的增大而增大,不同干湿条件下的颗粒级配演化规律同样是一致的。（3）建立的考虑母岩强度的颗粒破碎率与塑性功的关系可以较好地统一描述不同应力路径及干湿状态下的颗粒破碎。该研究成果可为建立复杂应力路径及干湿变化条件下考虑颗粒破碎的堆石料弹塑性本构模型提供依据。     

循环脱吸湿与加卸载耦合作用下土体持水性能试验研究

土体所经历的干湿循环和应力历史,对其孔隙结构和持水性能影响明显。为进一步深入研究二者耦合作用的影响,开展了先竖向固结再循环脱吸湿以及先气压脱湿再反复竖向加卸载两种不同加载路径的水分变化测量试验,探索土样持水性能和变形能力的演化规律。研究结果表明:(1)脱湿与吸湿路径对比,土体的持水能力具有明显的差异性,且土体越密实,这种差异性越强烈;(2)随着脱吸湿循环次数的增加,土样的进气值略有增大,减湿段和吸湿段的斜率都会减小,但影响趋势随循环次数增多而减弱;(3)对于气压减湿后的非饱和土样,其前期固结压力随气压值增加而增大,而加卸载形成的滞回圈的面积却随之减小,土体的持水性能和变形能力也降低;(4)重塑土样从不同加载路径首次达到同一应力状态时,先固结再脱湿路径下土样的体积收缩更多,而先施加气压再加载路径下土样持水性能减弱的更多。     

砾钢渣抗液化特性试验研究

陈化的钢渣作为土工回填材料是废弃钢渣循环利用的主要途径之一。按土的工程分类方法,将废弃钢渣划分为砾钢渣、粗钢渣和细钢渣。针对砾钢渣,考虑固结应力比、振动频率、围压和含砾量等影响因素开展动三轴试验研究。分析了砾钢渣的应力、应变和动孔隙水压力的特性,分析了砾钢渣试样的动强度与振动次数、动应变与振动次数、孔隙水压力与振动次数和动应力与动应变关系。采用Seed和Finn提出的饱和砂土动孔压计算模型分析砾钢渣的动孔压曲线类型,并与传统砂砾土的抗液化强度进行比较。得出砾钢渣的抗液化特性较好,工程中可以用砾钢渣替代传统的砂土、砂砾土、砂砾料和砂卵石作为回填料,解决砂砾资源日渐短缺的问题。     

红层软岩压缩破坏的分形特征与级联失效过程

基于不同围压条件下的红砂岩三轴压缩试验结果,采用数字图像相关技术对岩样外表面破坏形态进行全程观测,获得不同阶段岩样外表面破坏图像,分别对岩样破坏后阶段的图像进行分析。通过分形盒维数表征岩样外表面裂纹的变化情况,发现岩样破坏越严重,裂纹分形维数越高,且在最后破坏阶段裂纹分形维数出现突变,揭示岩样的破坏特征。引入级联失效数学模型,结合红层软岩内部的矿物成分与细观结构分布特点,概化出其结构的随机连接模型与破坏方式,分析红层软岩加载作用下的内部节点颗粒“容量-荷载”重分配原则以及节点颗粒失效后其初始荷载传递路径。结果表明,红层软岩在受载时为一个级联失效的分阶段破坏过程,级联因子通过级联路径不断传播、增多,级联失效越发明显,同时结合岩石破坏的变形损伤过程与其轴向应力-应变曲线分段特征,揭示该类岩石破坏的级联失效分级标准,为拓展该领域的研究具备一定的参考价值。     

The influence of turbidity currents and contour currents on the distribution of deep‐water sediment waves offshore eastern Canada

Sediment waves are commonly observed on the sea floor and often vary in morphology and geometry according to factors such as seabed slope, density and discharge of turbidity currents, and the presence of persistent contour currents. This paper documents the morphology, internal geometry and distribution of deep‐water (4000 to 5000 m) bedforms observed on the sea floor offshore eastern Canada using high‐resolution multibeam bathymetry data and seismic stratigraphy. The bedforms have wavelengths of >1 km but fundamentally vary in terms of morphology and internal stratigraphy, and are distinguished into three main types. The first type, characterized by their long‐wavelength crescentic shape, is interpreted as net‐erosional cyclic steps. These cyclic steps were formed by turbidity currents flowing through canyons and overtopping and breaching levées. The second type, characterized by their linear shape and presence on levées, is interpreted as net‐depositional cyclic steps. These upslope migrating bedforms are strongly aggradational, indicating high sediment deposition from turbidity currents. The third type, characterized by their obliqueness to canyons, is observed on an open slope and is interpreted as antidunes. These antidunes were formed by the deflection of the upper dilute, low‐density parts of turbidity currents by contour currents. The modelling of the behaviour of these different types of turbidity currents reveals that fast‐flowing flows form cyclic steps while their upper parts overspill and are entrained westward by contour currents. The interaction between turbidity currents and contour currents results in flow thickening and reduced sediment concentration, which leads to lower flow velocities. Lower velocities, in turn, allow the formation of antidunes instead of cyclic steps because the densiometric Froude number (Fr′) decreases. Therefore, this study shows that both net‐erosional and net‐depositional cyclic steps are distributed along channels where turbidity currents prevail whereas antidunes form on open slopes, in a mixed turbidite/contourite system. This study provides insights into the influence of turbidity currents versus contour currents on the morphology, geometry and distribution of bedforms in a mixed turbidite–contourite system.