裂隙网络模拟与REV尺度研究   总被引：4，自引：2，他引：2  

张贵科  徐卫亚 《岩土力学》2008,29(6):1675-1680

研究了利用平面四边形模拟节理岩体三维裂隙网络的方法。在生成裂隙网络时,同时考虑结构面几何参数和力学参数的随机性。利用裂隙网络研究了确定岩体REV尺度的指标。在此基础上,编制了岩体裂隙网络模拟程序、裂隙网络图形输出程序和岩体REV尺度指标分析程序。通过算例分析,验证了研究成果及程序的合理性,并得出了岩体REV尺度约为各组裂隙中最大迹长期望值3~4倍的结论。研究成果为后续计算岩体等效力学参数奠定了基础。  相似文献   

用水位恢复数据反演越流承压含水层参数   总被引：1，自引：0，他引：1  

杨建民  郑刚 《岩土力学》2008,29(6):1602-1606

水文地质勘测中,由于水位恢复阶段没有人力和机械因素干扰,由测量数据可以画出平滑的曲线,更适宜于分析水文地质参数,但经典非稳定流Theis公式和Theis水位恢复法所依据的若干假设条件在实际中难以满足。针对越流承压含水层具有补给条件而很快稳定以及非稳定抽水阶段流量常“抖动”的特点,论证了利用稳定流量和Hantush-Jacob越流模型计算的可行性,并用扩展的卡尔曼滤波器反演水文地质参数,经文献中历史数据和实地抽水试验检验结果表明,由该方法反演的预测值和实测值吻合良好。  相似文献   

剪胀性砂土本构模型的研究   总被引：1，自引：0，他引：1  

迟明杰  赵成刚  李小军 《岩土力学》2008,29(11):2939-2944

对于中密砂和密砂,剪胀现象是一个比较显著的特征,相变线是描述剪胀现象的一条特征线,它比较容易确定。因此,以相变线作为状态参考线,提出并定义了一种状态参量,在已有弹塑性模型基础上,将状态参量引入剪胀方程和塑性硬化模量表达式中,建立了一个新的考虑砂土剪胀性的本构模型。该模型尤其适合于中密砂和密砂,对于松砂则退化为原弹塑性模型。模型形式较简单,包含9个材料参数,且比较容易确定。数值模拟结果与试验数据吻合较好。  相似文献   

岩土体物理力学参数对岩质滑坡稳定性的影响   总被引：2，自引：0，他引：2  

刘红帅  杨俊波  薄景山  刘德东 《煤田地质与勘探》2008,36(1):37-40

采用有限元-极限平衡法研究了含软弱滑动带的岩质滑坡滑动体、滑动带和滑床的密度、弹性模量和泊松比及滑动带的抗剪强度对滑坡稳定性的影响。结果表明:滑床密度、滑体及滑动带的弹性模量、滑动带及滑床的泊松比和滑动的抗剪强度指标与滑坡稳定性系数呈正相关关系,而滑体及滑动带土体密度、滑床的弹性模量和滑体的泊松比与滑坡稳定性系数呈负相关关系;软弱滑动带的抗剪强度对滑坡稳定性的影响最显著,其次为软弱滑动带的泊松比和滑床的弹性模量,其他参数的影响相对较小。   相似文献   

Influence of environmental, root, and stand parameters on soil surface CO₂ efflux in a Populus euphratica of desert forest in extreme arid region     

ZongQiang Chang  Qi Feng  YongHong Su  JianHua Si  HaiYang Xi  ShengKui Cao  Rui Guo 《寒旱区科学》2009,1(4):0348-0355

Spatial variation in soil surface CO2 efflux was measured in a stand of Populus euphratica in the Ejina Oasis of desert riparian forest in the extreme arid region in northwestern China from April 2007 through October 2007.Measurements were taken with a gas-exchange analyzer linked to a soil-respiration chamber.The mean soil CO2 efflux in the stand was 2.71 μmol/(m2·s) during the growing season and 1.38 μmol/(m2·s) in the nongrowing season.The seasonal maximum (end of May through early June) andminimum (October) CO2 efflux were 3.38 and 0.69 μmol/(m2·s),respectively.The diurnal fluctuation of CO2 efflux was relatively small (< 20 percent),with theminimum appearing around 05:00 and the maximum around 15:00.Linear regression analysis showed soil-surface CO2 efflux to be most highly correlated with soil temperature (R2=0.435) and soil moisture (R2=0.213).When all variables were considered simultaneously,only soil temperature (R2=0.378),soil moisture (R2=0.147),and root volume density (R2=0.021) explained a significant amount of variance in soil surface CO2 efflux.Stand volumes were not correlated with soil CO2 efflux on our sites.  相似文献   

New physical characterization of the Fontana Lapilli basaltic Plinian eruption,Nicaragua   总被引：1，自引：1，他引：0  

L. Costantini  C. Bonadonna  B. F. Houghton  H. Wehrmann 《Bulletin of Volcanology》2009,71(3):337-355

The Fontana Lapilli deposit was erupted in the late Pleistocene from a vent, or multiple vents, located near Masaya volcano (Nicaragua) and is the product of one of the largest basaltic Plinian eruptions studied so far. This eruption evolved from an initial sequence of fluctuating fountain-like events and moderately explosive pulses to a sustained Plinian episode depositing fall beds of highly vesicular basaltic-andesite scoria (SiO₂ > 53 wt%). Samples show unimodal grain size distribution and a moderate sorting that are uniform in time. The juvenile component predominates (> 96 wt%) and consists of vesicular clasts with both sub-angular and fluidal, elongated shapes. We obtain a maximum plume height of 32 km and an associated mass eruption rate of 1.4 × 10⁸ kg s⁻¹ for the Plinian phase. Estimates of erupted volume are strongly sensitive to the technique used for the calculation and to the distribution of field data. Our best estimate for the erupted volume of the majority of the climactic Plinian phase is between 2.9 and 3.8 km³ and was obtained by applying a power-law fitting technique with different integration limits. The estimated eruption duration varies between 4 and 6 h. Marine-core data confirm that the tephra thinning is better fitted by a power-law than by an exponential trend.  相似文献   

近断层地震动的频谱周期参数和非平稳特征分析     

杨迪雄  王伟 《地震工程与工程振动》2009,29(5)

分析地震动的频谱周期参数和频率非平稳特征,是地震危险性分析和结构抗震设计的重要内容.本文对近断层地震动记录按照不同的运动特征分组,进行了Hilbert-Huang变换分析.结合相关的定义得到了表征地震动频谱特性的7个周期参数,包括:Fourier幅值谱平均周期Tm、Hilbert边际谱平均周期Tmh、特征周期Tc、卓越周期等,并计算了地震动的Hilbert谱瞬时频率时程变异系数.计算结果表明,从整体上把握地震动频谱特性的三个周期参数Tm 、Tmh 和Tc适合于表征近断层地震动的频谱成份.近断层地震动的频率非平稳特征显著,Hilbert谱瞬时频率变异系数良好地反映了地震动的频率非平稳性质和程度.而且,考察了近断层地震动运动特征对地震动频谱周期参数和频率非平稳性的影响.  相似文献   

汶川8.0级地震前紫坪铺水库小震活动及震源参数研究   总被引：2，自引：0，他引：2  

张致伟  程万正  张永久  谢蓉华  傅莺 《中国地震》2009,25(4)

利用区域和水库地震台网记录的数字地震波资料,研究了汶川8.0级地震前的2000年1月1日～2008年5月11日紫坪铺水库区的地震活动及震源参数.结果表明:汶川8.0级地震前该区域小震活动持续,地震活动水平为M_L2～3,自2005年9月紫坪铺水库蓄水以来,特别是2008年2月地震活动明显增加,但从长期的序列来看,地震活动频次和强度仍在区域地震活动的正常起伏范围.汶川8.0级地震发生前近3个月内,中小地震的视应力差值△σ_(app)普遍大于0,计算得到的视应力总大于其拟合值.汶川8.0级地震震中位于低应力区,而相对较高的视应力差值分布在震中以东地区,局部出现视应力增加的现象.  相似文献   

Variability in rainfall threshold for debris flow after the Chi-Chi earthquake in central Taiwan, China   总被引：6，自引：0，他引：6  

C. L. SHIEH  Y. J. TSAI 《国际泥沙研究》2009,24(2):177-188

The purpose of this study is to analyze variability in rainfall threshold for debris flow （critical rainfall for debris flow triggering） after the ML 7.3 Chi-Chi earthquake in central Taiwan in 1999. Two study sites with different geological conditions were surveyed in the earthquake area. Streambed surveys were conducted to continuously monitor debris flows between 1999 and 2006. During the 7-year study period, every debris flow event was identified, and the streambed characterized. Results show that the rainfall threshold for debris flow was remarkably lower just after the Chi-Chi Earthquake, but gradually recovered. To date, this rainfall threshold is still lower than the original level prior to the earthquake. This variability in rainfall threshold is closely related to the mount of sediment material in the initiation area of debris flow, which increased rapidly due to landslides resulting from the earthquake. With the increase in sediment material, the rainfall threshold was lowered severely during the first year following the Chi-Chi earthquake. However, heavy rainfalls mobilized the sediment material, causing debris flows and transporting sediment downstream. With the decrease in sediment material, the rainfall threshold recovered gradually over time. Furthermore, debris flows occurred only in the subbasins that had sufficient sediment material to cause significant movement. Hence, these results confirm that the sediment material in the initiation area of debris flow is a crucial component of the rainfall threshold for debris flow.  相似文献   

Preliminary sensitivity study of eruption source parameters for operational volcanic ash cloud transport and dispersion models — A case study of the August 1992 eruption of the Crater Peak vent, Mount Spurr, Alaska     

P.W. Webley  B.J.B. Stunder  K.G. Dean 《Journal of Volcanology and Geothermal Research》2009,186(1-2):108

Ash clouds are one of the major hazards that result from volcanic eruptions. Once an eruption is reported, volcanic ash transport and dispersion (VATD) models are used to forecast the location of the ash cloud. These models require source parameters to describe the ash column for initialization. These parameters include: eruption cloud height and vertical distribution, particle size distribution, and start and end time of the eruption. Further, if downwind concentrations are needed, the eruption mass rate and/or volume of ash need to be known. Upon notification of an eruption, few constraints are typically available on many of these source parameters. Recently, scientists have defined classes of eruption types, each with a set of pre-defined eruption source parameters (ESP). We analyze the August 18, 1992 eruption of the Crater Peak vent at Mount Spurr, Alaska, which is the example case for the Medium Silicic eruption type. We have evaluated the sensitivity of two of the ESP – the grain size distribution (GSD) and the vertical distribution of ash – on the modeled ash cloud. HYSPLIT and Puff VATD models are used to simulate the ash clouds from the different sets of source parameters. We use satellite data, processed through the reverse absorption method, as reference for computing statistics that describe the modeled-to-observed comparison. With the grain size distribution, the three options chosen, (1) an estimated distribution based on past eruption studies, (2) a distribution with finer particles and (3) the National Oceanic and Atmospheric Administration HYSPLIT GSD, have little effect on the modeled ash cloud. For the initial vertical distribution, both linear (uniform concentration throughout the vertical column) and umbrella shapes were chosen. For HYSPLIT, the defined umbrella distribution (no ash below the umbrella), apparently underestimates the lower altitude portions of the ash cloud and as a result has a worse agreement with the satellite detected ash cloud compared to that with the linear vertical distribution for this particular eruption. The Puff model, with a Poisson function to represent the umbrella cloud, gave similar results as for a linear distribution, both having reasonable agreement with the satellite detected cloud. Further sensitivity studies of this eruption, as well as studies using the other source parameters, are needed.  相似文献