用GPS时间序列获取中国大陆微动态应变场

基于中国大陆GPS观测在国际地球参考框架（ITRF）获得的站点位置,由三角形法通过反演逐年推算中国大陆年微动态应变场. 结果显示,研究区年微动态应变场大致以南北地震带为界. 西部地区存在方向大体一致的年主压应变优势分布方向, 方向自西向东、 由近南北向转为北东向,与近代应变场的方向一致,表明西部地区变形主要是由印度板块向北推进和西伯利亚地块相对南推形成的,且整体上仍是新构造运动的继承;东部大部分地区不存在年主应变的优势分布方向.年最大剪应变在不同地区差别很大,变化范围从4.13times;10-8~7.0times;10-10, 总体上西部大于东部. 同一区域年最大剪应变的多年变化表明,西部变化大,东部变化平缓. 年面膨胀显示,研究区大部分为压缩区,且同一区域的多年变化平缓.      

GPS地壳形变监测网应变解算方法与程序设计

分析了在平面直角坐标系和大地坐标系内解算应变的方法及其特点,并以Matlab为开发平台,研制出一套在平面直角坐标系和大地坐标系中解算应变的程序GPSstrain。利用GPS监测网测站位移(速率),该程序能够解算剪切应变(γ1、γ2)、面应变、块体旋转、主应变及其方向、最大剪切应变及其方向,同时也可解算出这些应变分量的误差。另外该程序还具有高斯投影解算功能,根据各测站坐标能够自动形成所有的Delaunay三角形,并以图形方式显示。最后以实际算例给出了该解算程序的部分结果,并进行了初步的分析和讨论。     

用GPS位移资料计算应变方法的讨论

目前使用相同或类似的GPS资料求应变,不同研究者给出的结果会有显著差别。为此,对用GPS位移(或速度)资料计算应变(或应变速率)的方法进行了研讨。分析后认为,应变计算可以归结成两大类第一类是利用测点附近资料直接求微分或微分的加权平均值的直接计算法;第二类是用解析曲线拟合观测的位移,然后根据该曲线提供的总的趋势求测点的微分值的位移拟合法,这类方法在拟合中又可以分成整体拟合和分片拟合两种。应变计算应该在球面坐标系下进行,根据研究对象和要求,选择适当的方法。     

四川地震辐射能量和视应力的研究

利用成都数字地震台网的波形记录资料,研究了四川地区地震辐射能量〖WTHX〗E〖WTBZ〗s、σapp视应力等震源参数及相互关系.对时域波形数字记录首先进行数据处理,包括带通滤波,快速富氏变换,扣除仪器幅频特性;经反变换,回到时间域,给出数字波形时间序列,选取所有方向的整个p波和s波段数据;二次变换到频率域内计算速度和地动位移的功率谱积分,进而求得各台站记录的地震波辐射能量和视应力等震源参数.研究了2000年5月到2004年8月成都数字地震台网记录的224个3级以上地震的震源参数.四川地区地震辐射能量〖WTHX〗E〖WTBZ〗s与地震矩M0,应力降Δσ与视应力σapp,视应力σapp与震级ML大体成正比.其中地震视应力σapp与震级分布数据较宽,地震视应力与破裂尺度ra的关系也较分散.同时研究了四川地区近年视应力σapp的空间分布.方法是将计算的σapp值在一定空间邻域内作平均,从而绘出等值线.分析结果表明,σapp值的相对高值区分布在四川南部的川滇交界和北部的川甘交界一带.同时研究了四川地区地震视应力值的时间分布.最后对中小地震视应力σapp及其他震源谱参数的意义作了讨论.     

地震荷载下土层变形等级预测方法研究

以计算结果可靠的土层反应结果为基础数据,基于随机森林算法(Random Forest,简称"RF"),建立地震动、场地土层参数特征量与土层变形特征的关系,提出一种依据常规地震动和场地土层参数为特征量的地震荷载下土层变形等级预测新方法,给出了典型场地土体发生大应变的地震动阈值.结果表明:基于RF模型对土体的变形程度预测结...     

New formulae for capacity energy-based assessment of liquefaction triggering

Abstract

Liquefaction of loose saturated soil deposits is a hazardous type of ground failure occurring under earthquake excitations. Therefore, an accurate estimation of liquefaction potential is extremely important in geotechnical engineering. In the current study, a new model is proposed which estimates the level of strain energy needed for liquefaction initiation. A compiled database containing cyclic tests gathered from previously published works was used to develop new models to predict liquefaction potential. M5′ algorithm was used to find the best correlation between parameters. It was shown that not only the derived formulas are acceptably accurate but also they feature a very simple structure in comparison with available formulas in the literature. The proposed equations are accurate, physically sound and uncomplicated. Furthermore, safety factors were given for different levels of risk, which can be useful for engineering practice. In addition, the influence of different predictors on the liquefaction potential was evaluated and also the significance of input variables was assessed via sensitivity analysis. Finally, a new model was introduced for preliminary estimation of liquefaction potential.     

Dynamic characteristics of marine soft clay under variable phase difference and initial static shear stress

Abstract

Under seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress.     

北部湾地区海砂填料的动力特性分析

为研究北部湾地区海砂填料的动力特性,采用高级动态三轴测试系统开展循环荷载下的动三轴试验,研究不同围压及不同动应力幅值对海砂动力特性的影响规律。试验结果表明：轴向累计应变随围压增加而减小,围压150 kPa时振次10 000后应变仅为3%;随着动应力幅值的增大轴向累积应变随之增大,且达到破坏标准的时间越短。动弹性模量随着动应力幅值和围压的增加而增大,不同围压下动弹性模量随动应变的增加出现先骤减再略减后稳定的发展趋势,ε_d>0.3%后开始趋于稳定;不同动应力幅值下动弹性模量出现先增后减直至稳定的趋势,其中动应力幅值对动弹性模量有明显的影响,围压影响相对较小。孔压比随动应力幅值增加而减小,随围压增加而增加。     

西太平洋台风对上海地区钻孔应变的低频扰动特征分析

基于上海佘山台四分量钻孔应变仪在6次西太平洋台风期间的观测记录,利用小波分解、优势振动方向等处理方法提取出台风所激发的显著低频扰动信号,并详细分析扰动信号在时频域及空间域的表现特性.结果显示:在低频区间,台风激发的扰动信号优势周期为2～4 min,信号能量随台风进程而变化,并主要与台风量级、台风中心的位置(海上或陆域)...     

Effects of long-term cyclic horizontal loading on bucket foundations in saturated loose sand

A 1-g model experimental study was conducted to investigate the accumulated rotations and unloading stiffness of bucket foundations in saturated loose sand. One-way horizontal cyclic loading was applied to model bucket foundations with embedment ratios 0.5 and 1.0. Up to 10⁴ cycles of loading were applied at a frequency of 0.2 Hz varying load amplitudes. The accumulated rotation of the bucket foundations increased with the number of cycles and the load amplitudes. Empirical equations were proposed to describe the accumulated rotation of the foundations. The unloading stiffness of foundations increased with the number of cycles but decreased with an increase in load amplitude. The initial unloading stiffness of L/D = 1.0 (L is skirt length; D is foundation diameter) was approximately twice that of L/D = 0.5. Excess pore water pressure difference of 50% was observed between L/D = 0.5 and 1.0. The suction and static capacity of the bucket increased with increase of bucket embedment ratio with a difference of 69.5% and 73.6% respectively between L/D = 0.5 and 1.0.