模拟基坑开挖过程的试验研究

采用三轴剪切试验对基坑开挖过程中土体卸荷的应力路径进行模拟，研究了由于侧向卸荷对土体抗剪强度指标产生的影响，并从土的微观结构角度分析了产生这一现象的原因。试验结果表明，经过侧向卸荷过程土样的抗剪强度指标与常规三轴试验明显不同。     

动水中含污染物冲击射流横向高浓度聚集区的形成机理和特性分析

采用RNG湍流模型对动水中含污染物冲击射流滞止点下游区域的横向浓度分布特征进行了详细的数值研究,并与相应的实验结果进行了比较。分析了下游过渡区内横向高浓度聚集区的形成机理和扩散特性。计算结果表明,冲击效应和横流绕流对冲击射流下游过渡区内的横向浓度分布具有重要的影响。当流速比相对较小时,在靠近对称面以及底层壁射流与环境横流的横向边界附近出现较为明显的横向高浓度聚集区,计算结果表明,冲击效应产生的横向逆压梯度以及横流绕流导致的Scarf涡结构对横向高浓度聚集区的形成起主导作用。     

绿片岩三轴流变力学特性的研究(I):试验结果

为了解锦屏一级水电站坝基绿片岩的流变力学特性,采用岩石全自动流变伺服仪对绿片岩进行了三轴压缩流变试验。基于试验结果,研究了绿片岩在不同围压作用下的轴向应变以及侧向应变随时间的变化规律,讨论了流变特性对岩石应力-应变曲线的影响,探讨了不同应力水平下的轴向以及侧向流变速率变化趋势,分析了不同围压下流变的破裂机制,掌握了绿片岩三轴流变的基本规律,从而为该水电站工程流变数值分析时参数的辨识提供了可靠的依据。     

An Approximate Method to Determine Lateral Force on Piles or Piers Installed to Support a Structure through Sliding Soil Mass

Piles and drilled shafts are commonly used to stabilize potentially unstable natural and engineered slopes. Estimation of lateral pressures on piles or shafts used to stabilize potentially unstable sites continues to be a fundamental problem in geotechnical engineering. Several methods are available to estimate the lateral force on piles or drilled shafts used to stabilize a site. An approximate procedure to estimate the lateral force on drilled shafts supporting structures, i.e., installed at relatively large spacings on a potentially unstable site with a fixed slip surface is proposed, which is based on a widely referred theory of plastic deformation. Lateral pressures estimated using the method proposed show good agreement with a more rigorous method, which in turn has been reported to provide results close to field measurements. An approximate procedure to estimate a limiting (maximum) value of lateral pressure on shafts or piles when they are installed at close spacings is also proposed. Although, the limiting pressures estimated using the approximate procedure are in agreement with the pressures calculated using more rigorous method, verification of both methods with field measurements is recommended.     

Study on stability of thin-walled circular pipe piles embedded shallowly under lateral loads

The interaction between soil and rigid piles loaded laterally is analyzed with finite difference method. There is a little difference between computational and experimental value of bearing capacity of rigid piles. Effects of embedding dimensions of piles and mechanical parameters of soil on lateral bearing capacity of rigid piles are studied. It is found that the lateral bearing capacities of rigid piles have important relation with the elastic modulus of soil, have approximate linear relations with the cohesion of soil and the friction coefficient of pile-soil interface and increase obviously with the internal friction angle of soil. But the effects of dilation angle on the lateral bearing capacities of rigid piles are negligible. The relations of bearing capacities of rough piles with smooth piles and the friction coefficient of pile-soil interface are also obtained.     

Long-period seismic source inversions using global tomographic models

We investigate the effect of laterally varying earth structure on centroid moment tensor inversions using fundamental mode mantle waves. Theoretical seismograms are calculated using a full formulation of surface wave ray theory. Calculations are made using a variety of global tomographic earth models. Results are compared with those obtained using the so-called great-circle approximation, which assumes that phase corrections are given in terms of mean phase slowness along the great circle, and which neglects amplitude effects of heterogeneity. Synthetic tests suggest that even source parameters which fit the data very well may have large errors due to incomplete knowledge of lateral heterogeneity. The method is applied to 31 shallow, large earthquakes. For a given earthquake, the focal mechanisms calculated using different earth models and different forward modelling techniques can significantly vary. We provide a range of selected solutions based on the fit to the data, rather than one single solution. Difficulties in constraining the dip-slip components of the seismic moment tensor often produce overestimates of seismic moment, leading to near vertical dip-slip mechanisms. This happens more commonly for earth models not fitting the data well, confirming that more accurate modelling of lateral heterogeneity can help to constrain the dip-slip components of the seismic moment tensor.     

Effect of no-flow in the Lower Yellow River on groundwater formation and usage in areas along the banks

Frequent flow cutoff has a serious effect on the eco-environment of the region along the Lower Yellow River. The authors study the impact on lateral seepage quantity and groundwater cycling caused by cutoff of the Yellow River and compare it with that of the year 1999 through the numerical simulation model of groundwater flow system of the affected zone. The lateral seepage quantity decreased 53.8% on flow cutoff stage from Huayuankou to the river entrance and breaking time of 300 d. The lateral seepage quantity will decrease 46.3% if flow cutoff is from Jiahetan to the river entrance and breaking time is 300 d, and it will decrease 75.2% if flow cutoff occurs throughout the year. The lateral seepage quantity will decrease 19.8% if flow cutoff is from Luokou to the river entrance and breaking time is 300 d, and it will decrease 25.1% if flow cutoff occurs throughout the year. The lateral seepage quantity will decrease 4.7% if flow cutoff is from Lijin to the river entrance and flow cutoff occurs throughout the year. Flow cutoff of the Yellow River has a minor effect on the shape of groundwater flow domain of the affected zone. Thus, the boundary condition of the shallow groundwater system will not change. Although flow cutoff has a major influence on the riverside source fields in the Lower Yellow River, it will not have a significant effect on groundwater resources macroscopically in the affected zone of the Yellow River due to its large storage capacity. __________ Translated from Journal of Jilin University (Earth Science Edition), 2007, 37(5): 937–942 [译自: 吉林大学学报(地球科学版)]     

雅砻江锦屏水电站交通辅助洞施工控制与精度分析

本文围绕雅砻江锦屏水电站辅助洞17.5 km交通隧道工程重点介绍洞内施工导线测量的精度,分析了其中两次复测结果产生较大偏差的原因,采用加测陀螺方位角的方法改善导线的点位精度,削弱旁折光等因素可能产生的误差影响,实测数据的处理结果与分析表明加测陀螺方位角大大提高了导线的精度和可靠性。     

勒夫波群速度频散与太平洋地壳及上地幔三维构造

应用现代适配滤波频时分析技术对SRO/GDSN长周期面波记录进行处理,获得穿过太平洋盆地的117条波路径的勒夫波频散数据。我们用改进的分格频散反演方法,从混合路径频散数据中提取出对应于构成整个太平洋盆地的10°×10°分格的纯路径频散数据。所获得的18s到215s范围内的28个周期的太平洋勒夫波群速度的横向分布,揭示了速度随海底年龄的增大而逐渐增加的总趋势,以及其它变化细节。例如,对于同一等年龄线区而言,北太平洋及南太平洋的群速度要比中太平洋的低0.1-0.3km/s。在分格模型反演的基础上得出的深至300km的三维剪切波速度结构提供了太平洋盆地地壳及上地幔横向不均匀性的详尽的描述。