Influence of seismic motions on behavior of piles in liquefied soils

In the present study an analytical procedure based on finite element technique is proposed to investigate the influence of vertical load on deflection and bending moment of a laterally loaded pile embedded in liquefiable soil, subjected to permanent ground displacement. The degradation of subgrade modulus due to soil liquefaction and effect of nonlinearity are also considered. A free headed vertical concrete elastic nonyielding pile with a floating tip subjected to vertical compressive loading, lateral load, and permanent ground displacement due to earthquake motions, in liquefiable soil underlain by nonliquefiable stratum, is considered. The input seismic motions, having varying range of ground motion parameters, considered here include 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj, and 2011 Sikkim motions. It is calculated that maximum bending moment occurred at the interface of liquefiable and nonliquefiable soil layers and when thickness of liquefiable soil layer is around 60% of total pile length. Maximum bending moment of 1210 kNm and pile head deflection of 110 cm is observed because of 1995 Kobe motion, while 2001 Bhuj and 2011 Sikkim motions amplify the pile head deflection by 14.2 and 14.4 times and bending moment approximately by 4 times, when compared to nonliquefiable soil. Further, the presence of inertial load at the pile head increases bending moment and deflection by approximately 52% when subjected to 1995 Kobe motion. Thus, it is necessary to have a proper assessment of both kinematic and inertial interactions due to free field seismic motions and vertical loads for evaluating pile response in liquefiable soil.     

太行山淇河流域2000-2015年土壤侵蚀和水源供给变化研究

山地生态系统的土壤侵蚀和水源供给变化对评估区域生态环境质量有重要意义。基于2000-2015年四期土地利用数据,借助InVEST模型对淇河流域近16年间山地生态系统的土壤侵蚀和水源供给变化进行评估。结果表明：① 研究区主要土地利用类型为耕地、草地和林地,共占流域总面积的90%以上。近16年间淇河流域的耕地面积显著减少,草地和水域面积大幅增加,建设用地扩张明显。② 平均土壤侵蚀模数显著降低,2000年土壤侵蚀模数为154.27 t/（hm²·a）,2015年减少到32.09 t/（hm²·a）;强度侵蚀、极强侵蚀和剧烈侵蚀由9.03%、12.19%和25.96%分别减少到7.17%、6.36%和4.21%,微度侵蚀、轻度侵蚀和中度侵蚀由24.31%、16.96%和11.57%增加到41.89%、27.71%和12.68%;退耕还林、还草措施优化了土地利用格局,促进植被恢复,对治理土壤侵蚀起到了显著效果。③ 水源供给量整体呈现先增加后减少的趋势,2005年达到峰值（1.79亿m³）。相邻两期水源供给量增减变化不一,2000-2005年水源供给量增加的面积大于减少的面积,其水源供给的量值也呈增加趋势,水源供给能力整体增强;而2005-2010年、2010-2015年的水源供给能力随之减弱,其中,2010-2015年水源供给减少的较小;林地和草地面积的增加造成水源供给量降低,土壤水源涵养能力增强。土壤侵蚀和水源供给是山地生态脆弱性响应的重要指标,制定合理的水土保持措施对增强山区生态系统的服务能力具有重要意义。     

Laboratory and field performance of recycled aggregate base in a seasonally cold region

The objective of this project was to characterize the freeze-thaw properties of recycled concrete (RCA) and asphalt (RAP) as unbound base and to assess how they behaved in the field for nearly 8 years. This paper includes an examination of existing information, laboratory studies of freeze-thaw behavior, and evaluation of data from MnROAD field-test sections in a seasonally cold region, i.e., in Minnesota, USA. Test sections were constructed using recycled materials in the granular base layers at the MnROAD test facility. One test section included 100% RAP, another 100% RCA, a third one a 50/50 blend of RCA/natural aggregate, and a fourth one only natural aggregate (Class 5) as a control. The stiffness (i.e., elastic modulus) was monitored during construction and throughout the pavement life by the Minnesota Department of Transportation, along with the variation of temperatures and moisture regimes in the pavement to determine their effects on pavement performance. The resilient modulus of each material was determined by bench-scale testing in accordance with NCHRP 1-28a, as well as by field-scale tests incorporating a falling-weight deflectometer. Specimens were subjected to as many as 20 cycles of freeze-thaw in the laboratory, and the change in their resilient modulus was measured. In the field-test sections constructed with the same materials as the base course, temperature, moisture, and field modulus (from falling-weight deflectometer tests) were monitored seasonally for nearly 8 years. From the temperatures in the base course layer, the number of freeze-thaw cycles experienced in the field was determined for each test section. Inferences were made relative to modulus change versus freeze-thaw cycles. Conclusions were drawn for long-term field performances of the recycled base (RAB) in comparison to natural aggregate.     

Experimental investigation on static and dynamic resilient moduli of compacted fine soil

To investigate the static and dynamic resilient modulus of fine soil, and adapting to the new design code and maintenance system of highway subgrade in China, a series of static and dynamic tests were carried out according to the standard laboratory test methods (JTG E40-2007 and JTG D30-2015, respectively). The effects of initial water content, compactness and freeze-thaw cycles on the static and dynamic resilient moduli of fine soil were investigated and analyzed. Experimental test results show that with increasing water content, dry density and freeze-thaw cycles, the static moduli reduces about 10.2%~40.0%, 14.4%~45.5%, and 24.0%~50.3%, and dynamic moduli reduces about 10.9%~90.8%, 2.5%~38.4%, and 0.0%~46.0%, respectively. Then, the empirical mathematical relationship between static and dynamic resilient moduli was established under different water content, dry density and freeze-thaw cycles. The investigation results can be used to determine the dynamic modulus of fine soil by widely used static modulus, which could meet the requirement of adopting dynamic modulus index in new specification.     

GRAPES全球切线性和伴随模式的调优

伴随技术是四维变分同化（4DVar）系统中计算代价函数梯度的最佳办法,切线性和伴随模式的效果和效率直接影响着4DVar系统的发展。基于GRAPES（Global and Regional Assimilation PrEdiction System）全球切线性和伴随模式1.0版本,利用GRAPES全球模式2.0版本在并行框架和性能等方面的改善,重新优化和设计了GRAPES全球切线性伴随模式2.0版本,提高了GRAPES全球切线性和伴随模式的效果和效率,优化了切线性模式程序结构,使其计算时间最优可控制在非线性模式的1.2倍以内;采用在切线性模式中保存基态的方法,重构了伴随模式的程序结构,使其计算时间最优控制在非线性模式的1.5倍以内;在GRAPES全球切线性物理过程的设计中,将线性物理过程的轨迹基态计算和切线性扰动计算解耦,提高了GRAPES全球切线性和伴随模式的计算效果和效率。     

冰力学参数的超声波测试研究

利用非线性高能超声测试设备及超声波(纵波、横波)波速与物体力学参数的关系,对人造冰样进行了冰样力学参数(杨氏模量、泊松比、剪切模量、体积模量)随温度变化的研究。通过MATLAB进行所测数据曲线拟合,得到超声波波速在人造冰样中随温度的变化规律,进而由理论公式推导所测人造冰样力学参数随温度的变化规律。结果表明:冰样中超声波波速随温度降低而升高,冰样的杨氏模量、泊松比、剪切模量、体积模量也都随温度降低而升高。本研究有助于超声波检测法在冰样物理力学性质测量中的应用,为开展南极冰盖、海冰以及终年冻土等力学及流动特性研究提供理论模型和实验数据。     

基于比值均方根的杨氏模量反演方法

杨氏模量和泊松比是表征岩石脆性、评价储层可压性以及描述储层流体特征的重要参数,叠前地震反演是从地震数据中得到此类参数的有效手段.常规的叠前地震反演方法多使用Zeopppritz方程的近似式计算反射系数,近似式的误差影响了反演结果的精度.针对这个问题,推导了比值均方根形式的杨氏模量、泊松比和密度的Zoeppritz方程,并基于广义线性反演构建了杨氏模量和泊松比直接反演方法,有效地避免了使用近似式的局限性,提高了反演的精度.模型测试和实际资料试算结果表明：采用比值均方根形式构建的反演流程稳定,能够从叠前地震数据中获得可信的杨氏模量、泊松比和密度,提供了一种可靠的杨氏模量和泊松比直接反演方法.     

盾构隧道下穿管道施工引起的管-土相互作用研究

采用Loganathan公式研究了盾构隧道下穿管道施工引起的地下管道处土体竖向位移,利用考虑土中剪力传递的Pasternak模型模拟管-土相互作用,运用修正Vlasov模型中的迭代流程计算出Pasternak模型的关键参数——弹性系数k与剪切系数gs。将计算结果与已有文献结果及工程监测数据进行对比,深入分析了迭代求解k、gs值的Pasternak模型与传统模型的计算差异,并进一步研究了土中剪力、管道与隧道的夹角、土体弹性模量及隧道半径的变化对管-土相互作用的影响。研究结果表明：迭代求解的k、gs值能提升Pasternak模型的精确度;土中剪力对管道竖向位移计算值的影响可达15.3%;随着管道与隧道夹角的减小,管道的竖向位移增大、弯矩减小;土体弹性模量与隧道半径的增大均会增加管道的竖向位移和弯矩。     

重载铁路水泥改良膨胀土路基填料动弹模量及阻尼比研究

动弹模量与阻尼比是土动力学分析中的重要力学参数,考虑重载铁路荷载特征定量分析水泥改良膨胀土的动模量和阻尼比的较少。依托蒙西至华中地区铁路煤运通道(简称蒙-华铁路)工程为背景,采用南阳邓州市大山寨膨胀土,通过在不同频率、围压、固结比及动应力幅值下的持续振动三轴试验,研究了水泥掺量3%和5%水泥改良膨胀土的动弹模量及阻尼比,并与膨胀土素土进行对比分析。结果表明:水泥掺量3%和5%改良膨胀土的最大动弹模量约为膨胀土素土的3~4倍;在动弹模量-应变曲线中,动应变小于0. 002时表现为陡降段,动弹模量随动应变增长降幅达70%,而动应变大于0. 002时降幅较小,动弹模量随动应变增长趋于稳定;动弹模量随围压、频率、水泥掺量增加而增大,阻尼比随围压、固结比增加而减小;低应变水平下,固结比与动模量成正相关关系,高应变水平下,固结比与动弹模量成负相关关系。同时,对动弹模量及阻尼比进行了归一化分析,建立了估算动弹模量及阻尼比的经验公式。     

结构性参数在黄土地基沉降计算中的应用研究

弦线模量法建立了考虑黄土基本物性指标及附加应力综合影响的弦线模量函数,应用分层总和法计算黄土地基的变形量,并在陕西关中黄土地区工程实践中获得良好的预测结果,而在分析兰州等其他黄土地区地基沉降时,结果出现偏差,究其原因,与计算中忽视了天然状态下黄土的结构性特征有关。以弦线模量法为基础,通过西安近郊4处土样试验和大量载荷试验资料,分析黄土的构度指标与压缩模量、孔隙比、含水量的关系,并将构度指标引入弦线模量表,深化结构性参数在地基沉降变形计算中的理论。