Fragility analysis of continuous pipelines subjected to transverse permanent ground deformation

The structural integrity of buried continuous pipelines can be jeopardized by transverse permanent ground deformation (PGD) induced by landslides. A probabilistic analysis can facilitate understanding the likelihood of damage to pipelines in landslide regions, further minimizing the risk. However, empirical fragility curves for the landslide-pipeline interaction problem are not available due to the lack of field data. The problem can be addressed by numerical approaches. In this study, a simplified two-dimensional numerical model is developed. It characterizes the pipes as beam-type structures and the surrounding soil as Winkler springs. It is compared here against three-dimensional continuum-based analyses, which could save extensively on computational efforts. All input parameters were sampled randomly and paired with the displacement demands to form a limited set of statistically significant, yet nominally identical, pipeline samples, and the demand models for the maximum tensile strain were evaluated. A supervised machine learning technique, called Lasso regression, was then used to establish a predictive relation between the input and the output using the limited dataset, based on which a large dataset (one million) was calculated for the fragility analysis. The use of a Winkler-based analysis and the supervised machine learning technique makes it possible to generate fragility curves for pipelines subjected to transverse PGD for the first time.     

Improvement of mechanical behavior of buried pipelines subjected to strike-slip faulting using textured pipeline

The present study investigates the mechanical behavior of a new generation of buried pipelines, dubbed the textured pipeline, which is subjected to strike-slip faulting. In conventional cylindrical pipelines, the axial and bending stresses brought about in their walls as a result of fault movement, lead to local buckling, which is construed as one of the major reasons contributing to pipeline failure. The present study has assessed 3-D numerical models of two kinds of buried textured pipelines, with 6 and 12 peripheral triangular facets, subjected to a strike-slip faulting normal to the axis of the pipelines, with and without internal pressure, with the two kinds of X65 and X80 steel, and with different diameter-to-thickness ratios. The results indicate that, because of specific geometry of this pipeline shell which is characterized by having lower axial stiffness and higher bending stiffness, compared to conventional cylindrical pipeline, they are considerably resistant to local buckling. The results of this study can be conceived of as a first step toward comprehensive seismic studies on this generation of pipelines which aim at replacing the conventional cylindrical pipelines with textured ones in areas subjected to fault movement.     

Performance and damage evolution of plain and fibre-reinforced segmental concrete pipelines subjected to transverse permanent ground displacement

This paper presents the results of three full-scale experiments performed on segmental concrete pipelines subjected to permanent ground displacement. The first pipeline was made of reinforced concrete pipes and the second pipeline was made of steel fibre-reinforced concrete pipes. The third pipeline was made of a combination of fibre-reinforced and reinforced concrete pipes. An array of sensing techniques was used to assess the damage evolution in pipelines and their overall performance. Three stages of damage were observed. In the first stage, damage was concentrated in the joints near the fault line. In the second stage, the damage occurred in all joints along the pipeline. While in the first two stages damage was mainly concentrated at the bell and spigot joints of the pipe segments, the third stage of damage was characterised by severe damage and rupture of the body of pipe segments located in the immediate vicinity of the fault line. The modes of failure for the plain and fibre-reinforced concrete pipelines were similar in the first and second stages of damage. However, in the pipeline constructed using both plain and fibre-reinforced concrete pipe segments, the damage was concentrated in the standard reinforced concrete pipe segments.     

盾构法施工隧道纵向地层移动与变形预计

将盾构法施工隧道开挖引起的地表下沉以及盾构挤压引起的地表隆起均视为随机过程,应用随机介质理论,对隧道施工所引起的纵向地层移动与变形进行了分析,推导了相应的计算公式。工程实例分析表明,该方法效果良好。     

最近邻抽样回归模型在纵向地表沉降预测中的应用

针对传统方法在盾构法施工地表沉降预测中过于形式化和数学化的缺点,本文引入最近邻抽样回归模型(NNBR)。将盾构法施工引起地表沉降的因素分为三类:结构类、地质类和施工参数类,结合NNBR模型的计算特点对不同种类的因素采取不同的处理措施:结构类因素视为常量;按照能否形成免压拱将地质土层分为两类,计算距离系数时同类地层中的地质类因素视为常量;施工参数类因素的影响近似用隧道埋深和盾构平均掘进速度来衡量。由于NNBR模型对纵向地表沉降进行预测时可忽略常量因素,从而大大简化诸多次要因素对预测结果的影响,最终可以隧道埋深和盾构平均掘进速度为预测因子来预测纵向地表沉降。结合工程实例,证明预测因子选择的合理性以及NNBR模型在纵向地表沉降预测中的实用性。     

GPS monitoring and analysis of ground movement and deformation induced by transition from open-pit to underground mining

To trace the potential hazards of open-pit slope in Longshou mine,global positioning system(GPS) is applied to monitoring ground movement and deformation induced by transition from open-pit to underground mining.Through long-term monitoring from 2003 to 2008,huge amounts of data were acquired.Monitoring results show that large-scale ground movement and deformation have occurred in mining area,and the movement area is ellipse-shaped.The displacement boundary of settlement trough is 2.0 km long along the exploratory line,and 1.5 km long along the strike of ore body.GPS monitoring results basically agree with the practical deformation state of open-pit slope.It is indicated that the long-term GPS monitoring is an effective way to understand the mechanism of ground movement and deformation in mine area.     

近断层脉冲型地震动作用下建筑结构的层间变形分布特征和机理分析

利用广义层间位移谱方法,将高层建筑等效化为一个弯剪型悬臂梁,从地面输入理想的简单脉冲,以及含破裂向前方向性效应脉冲、滑冲效应脉冲和无脉冲三组近断层地震动记录,然后对弯剪组合梁进行层间变形分析。获得了近断层地震动作用下建筑结构层间变形沿高度的分布规律。滑冲效应脉冲主要激起抗弯框架体系的基本振型响应,导致结构的最大层间变形发生在较低楼层;破裂向前方向性效应脉冲能够激起框架结构高阶振型的响应。而且,从脉冲型地震动的不同特征和层间位移谱分析出发,分析了建筑结构产生上述层间变形分布特征的机理。研究表明三组不同类型地震动的平均层间位移谱在整个结构基本周期段差别很大。