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971.
The determination of hydraulic properties in non-stationary experiments is suspected to be affected by dynamic effects. This is based on thermodynamic considerations on the pore scale displacement of wetting and non-wetting phase. But also macroscopic heterogeneities at the continuum scale may influence the dynamics of water during drainage and wetting. In this paper we investigate both aspects. Firstly, we present the results of typical multi-step outflow experiments in heterogeneous sand columns which are compared with two-step outflow experiments covering the same pressure range. The discrepancies caused by pressure steps of different size reveal the impact of dynamic effects due to the non-stationarity of the experiments. 相似文献
972.
The determination of hydraulic properties in non-stationary experiments is suspected to be affected by dynamic effects. This is based on thermodynamic considerations on the pore scale displacement of wetting and non-wetting phase. But also macroscopic heterogeneities at the continuum scale may influence the dynamics of water during drainage and wetting. In this paper we investigate both aspects. Firstly, we present the results of typical multi-step outflow experiments in heterogeneous sand columns which are compared with two-step outflow experiments covering the same pressure range. The discrepancies caused by pressure steps of different size reveal the impact of dynamic effects due to the non-stationarity of the experiments. 相似文献
973.
利用华东地区1970年以来的地震目录,对华东地区、郯庐断裂带100km范围、2007年度划定为地震危险区的苏鲁皖交界地区及安徽地区,以地震活动性参数群体异常变化项目数为参量,进行相应的均值之差与标准差统计分析,提取其变化率R(李永莉等,2003),即通过统计计算地震活动性参数异常项目月变化率R值,观察R值变化特征。结果发现,华东地区、安徽地区中强震前R值异常表现为中短期异常特征,郯庐断裂带100km范围内及本年度划定为危险区的苏鲁皖交界地区,R值异常表现为中长期异常特征。 相似文献
974.
以消除年变化等短周期变化后的数据做为当月正常值,利用实测的月均值与正常值之比即月干扰比率、偏差等指标,突出反映月观测值在当月受到综合干扰因素影响的大小。从而突出地震前短临地电阻率异常。 相似文献
975.
976.
本文利用随机介质模型对复杂岩性储层进行了非均质性描述.利用模型特征量即非均质纵横比、纵向谱指数、横向谱指数以及扰动标准差等来模拟不同的随机介质.在前人工作的基础上,由某油气田的两口井资料估计储层非均质性能谱,从能谱曲线上提取储层纵向大小尺度非均质谱指数.通过将二维随机介质模拟的合成井记录互相关系数与实际井记录互相关系数进行分析比较,分别得到大小尺度非均质情况下最佳拟合时的横向谱指数和非均质性纵横比.以上求得的各种特征量从不同角度定量分析了储层非均质性的纵横向变化,为储层横向预测提供了依据. 相似文献
977.
Behaviour of deep immersed tunnel under combined normal fault rupture deformation and subsequent seismic shaking 总被引:1,自引:0,他引:1
Ioannis Anastasopoulos Nikos Gerolymos Vasileios Drosos Takis Georgarakos Rallis Kourkoulis George Gazetas 《Bulletin of Earthquake Engineering》2008,6(2):213-239
Immersed tunnels are particularly sensitive to tensile and compressive deformations such as those imposed by a normal seismogenic
fault rupturing underneath, and those generated by the dynamic response due to seismic waves. The paper investigates the response
of a future 70 m deep immersed tunnel to the consecutive action of a major normal fault rupturing in an earthquake occurring
in the basement rock underneath the tunnel, and a subsequent strong excitation from a different large-magnitude seismic event
that may occur years later. Non-linear finite elements model the quasi-static fault rupture propagation through the thick
soil deposit overlying the bedrock and the ensuing interaction of the rupture with the immersed tunnel. It is shown that despite
imposed bedrock offset of 2 m, net tension or excessive compression between tunnel segments could be avoided with a suitable
design of the joint gaskets. Then, the already deformed (“injured”) structure is subjected to strong asynchronous seismic
shaking. The thick-walled tunnel is modelled as a 3-D massive flexural beam connected to the soil through properly-calibrated
nonlinear interaction springs and dashpots, the supports of which are subjected to the free-field acceleration time histories.
The latter, obtained with 1-D wave propagation analysis, are then modified to account for wave passage effects. The joints between tunnel segments are modeled with special non-linear hyper-elastic elements, properly accounting
for their 7-bar longitudinal hydrostatic pre-stressing. Sliding is captured with special gap elements. The effect of segment
length and joint properties is explored parametrically. A fascinating conclusion emerges in all analysed cases for the joints
between segments that were differentially deformed after the quasi-static fault rupture: upon subsequent very strong seismic
shaking, overstressed joints de-compress and understressed joints re-compress—a “healing” process that leads to a more uniform
deformation profile along the tunnel. This is particularly beneficial for the precariously de-compressed joint gaskets. Hence,
the safety of the immersed tunnel improves with “subsequent” strong seismic shaking! 相似文献
978.
Adem Dogangun Ramazan Acar Halil Sezen Ramazan Livaoglu 《Bulletin of Earthquake Engineering》2008,6(3):505-517
Almost all historical minarets in Turkey were constructed using cut stone, masonry blocks or combination of these two materials.
The structural and geometrical properties of each masonry minaret, or slender tower structure, depend on many factors including
the structural knowledge and applications at the time of construction, experience of the architect or engineer, seismicity
of the region, and availability of construction materials in that area. Recent earthquakes in Turkey have shown that most
masonry minarets in high seismic regions are vulnerable to structural damage and collapse. In this study, in order to investigate
the dynamic behavior of historical unreinforced masonry minarets, three representative minarets with 20, 25, and 30 m height
were modeled and analyzed using two ground motions recorded during the 1999 Kocaeli and Duzce, Turkey earthquakes. The modal
analyses of the models have shown that the structural periods and the overall structural response are influenced by the minaret
height and spectral characteristics of the input motion. The dynamic displacement and axial stress time histories are computed
at the critical points on the minarets. During recent earthquakes, most minaret failures occurred above the base of the structure.
Consistent with the observed response, the largest stresses were calculated at the same location. 相似文献
979.
This paper describes a nonlinear finite element (FE) analysis of high strength concrete (HSC) columns, and verifies the results through laboratory experiments. First, a cyclically lateral loading test on nine cantilever column specimens of HSC is described and a numerical simulation is presented to verify the adopted FE models. Next, based on the FE model for specimen No.6, numerical simulations for 70 cases, in which different concrete strengths, stirrup ratios and axial load ratios are considered, are presented to explore the effect of these parameters on the behavior of the HSC columns, and to check the rationality of requirements for these columns specified in the China Code for Seismic Design of Buildings (GB 50011- 2001). In addition, three cases with different stirrup strengths are analyzed to investigate their effect on the behavior of HSC columns. Finally, based on the numerical results some conclusions are presented. 相似文献
980.