Failure mechanism of unsaturated landslide dam under seepage loading – Model tests and corresponding numerical simulations

Due to the rapid cracking, sliding and packing of its geomaterials, a landslide dam (LD) is usually weaker in structure than the undisturbed ground and is more vulnerable to seepage loading. In addition, since the naturally packed geomaterials of an LD are mostly in an unsaturated state, it is necessary to use a suitable constitutive model that can describe the mechanical behaviour of the soils under an unsaturated/saturated state in a unified way and whose material parameters can be determined in a rational way in order to accurately simulate the failure mechanism of the LD. In this paper, water retention tests and flume tests were conducted on model LDs prepared with three different ground materials. An unsaturated soil constitutive model was selected for the corresponding numerical simulations. Based on the results of water retention tests and triaxial tests, the parameters of the LD materials were properly determined. Using these parameters, soil-water-air coupling finite element analyses were conducted to simulate the flume tests on the model LDs. By comparing the calculated results with the test results, it was found that the numerical method used in this paper has satisfactory accuracy for describing the different failure mechanisms of the model LDs under seepage loading. The results indicate that the material properties of the LDs, especially the strength and the difference in void ratio between the unsaturated and the saturated states, play important roles. In addition, the influence of the rate of the rise in water head was also investigated by numerical tests. The purpose of this research is to provide a scientific basis for decision-making in the disaster mitigation process of LDs with a comprehensive method for understanding the failure mechanism of these LDs.     

聚焦波浪对哑铃型跨海桥梁围堰作用的试验研究

台风引起的巨浪将严重威胁跨海桥梁施工期围堰的安全,台风波浪较普通规则波浪具有周期更长、波高更大特点,正好符合聚焦波浪的特征。为更好地指导跨海桥梁围堰抵抗极端台风浪设计,开展聚焦波浪与哑铃型桥梁围堰相互作用的波浪水槽试验研究,探讨围堰吃水深度、聚焦波最大波幅、入射角度对测点波面位移及波浪力的影响。其中,分析结果表明,围堰吃水深度及入射角度的变化对测点波面位移的影响不大。随着吃水深度增加,垂直波浪传播方向的有效投影面积增大,围堰顺波向波浪力明显增大。由于波浪能量沿水深衰减,底部浮托力随之减小。随着入射角度增加,有效投影面积增大使得围堰顺波向波浪力非线性增大,而围堰底部浮托力则变化较为平缓。当入射角度和波幅均较大时,围堰顺波向和垂向浮托力的正、负向幅值差异均较大,呈现较明显的不对称性,若按对称受力设计施工方案可能偏危险。与同波幅的聚焦波浪相比,长波条件下若按线性波考虑作用于结构的波浪力将偏不安全,实际跨海桥梁工程设计时有必要按聚焦波浪考虑台风波浪作用。     

冬季扣塑料棚进行混凝土施工

论述了冬季扣塑料棚进行混凝土施工的方法，并作了经济效益分析。     

漕河渡槽裂缝成因及温控措施

对南水北调中线京石段应急供水工程中的漕河渡槽的裂缝成因、防裂措施进行了阐述.分析结果表明,采用骨料冷却技术、水管冷却技术、保温措施等具有良好的降低温度应力的作用,既可以有效地防止在施工早期和后期出现温度裂缝,亦可为类似工程提供借鉴.     

预应力混凝土在水工渡槽中的应用

结合工程实例,详细介绍了预应力混凝土在水工渡槽施工中的方法、步骤和采取的相应措施,有推广应用价值.     

景电二期向民勤调水工程5号渡槽风积沙地基特性及处理方法

通过对正在施工的景电二期向民勤调水工程５号渡槽地基特性与处理方法的论述，阐明了沙漠地基研究中应注意的问题及地基处理方法，对风积沙地基加固处理具有一指导意义．     

水压定向控制爆破在水塔拆除中的应用

详细介绍了水压爆破用于定向拆除２４m高水塔的设计及施工体会。     

Erosion properties of cohesive sediments in the Colorado River in Grand Canyon

Cohesive sediment deposits characterized by a high fraction of mud (silt plus clay) significantly affect the morphology and ecosystem of rivers. Potentially cohesive sediment samples were collected from deposits in the Colorado River in Marble and Grand Canyons. The erosion velocities of these samples were measured in a laboratory flume under varying boundary shear stresses. The non‐dimensional boundary shear stress at which erosion commenced showed a systematic deviation from that of non‐cohesive sediments at mud fractions greater than 0.2. An empirical relation for the boundary shear stress threshold of erosion as a function of mud fraction was proposed. The mass erosion rate was modelled using the Ariathurai–Partheniades equation. The erosion rate parameter of this equation was found to be a strong function of mud fraction. Under similar boundary shear stress and sediment supply conditions in the Colorado River, cohesive lateral eddy deposits formed of mud fractions in excess of 0.2 will erode less rapidly than non‐cohesive deposits. Copyright © 2008 John Wiley & Sons, Ltd.     

明渠量水槽的水力学分析

运用水力学理论分析了明渠量水槽的水流现象与计算方法，并给出实例。     

A STUDY OF DRAG COEFFICIENT RELATED WITH VEGETATION BASED ON THE FLUME EXPERIMENT

This study is focused on the effects of ecological factors (diameter and flexibility) and vegetation community composition on the drag coefficient related with vegetation. The single leafy shrub and three mixed communities (including shrub-grass, shrub-reed and reed-grass community) were studied. The flow velocity and water level were measured and used to calculate the drag coefficient based on the Bernoulli's equation, Darcy drag formula and the expression for the drag coefficient related with Darcy drag factor. The trend of the drag coefficient in the vertical direction was analyzed against flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height in different discharges. The results show that beside the dense leafy shrubs community, the vertical trend of the drag coefficient among other cases against flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height can be approximately expressed by power law functions under different flow discharges. Moreover, in a mixed community with two plants with distinctly different ecological factors, the one with the most distinct variations of ecological factors determines the vertical trend of the drag coefficient; the other one only affects the magnitude of the drag coefficient. Furthermore, if the ecological factors of the vegetation in the vertical direction are kept almost not changed, the drag coefficient can be approximately regarded as a constant.