Abstract: The ultimate stress of subsea pipeline calculated by applying current seismic design methods is higher than the real stress and independent of the geometric parameters and the buried depth of the pipelines.Theoretical analysis taking the properties of the surrounding soil into account shows that soil acting on the pipelines is easy to turn into plastic slippage state under the condition of light earthquake intensity,which indicates that the current seismic design methods based on elastic constraint state are unsuitable for the design of subsea pipelines.Therefore,a new calculation method for ultimate seismic stress was developed on the basis of the plastic slippage theory for soil-pipeline interaction.The new method for calculating the ultimate constraint force of unit length includes the unit length friction force method,the amend method and the weighting average method.The above three methods were applied to two engineering projects.The application results demonstrate that the ultimate seismic stress methods can accurately reflect the soil-pipeline interaction during earthquake waves and overcome the shortcomings of the current methods.

Key words: seismic wave, subsea pipeline, friction force, ultimate stress, plastic constraint, design methods

摘要： 目前工程设计中使用的海底管线抗震设计方法给出的地震应力值偏大,计算结果与管线结构参数和埋设深度等几乎没有关系。理论分析及海底管线的实际埋设环境证明,在一般海底管线工程的设计地震条件下,约束海底管线的土壤很容易进入塑性滑移状态,已超出现用抗震设计方法的前提条件,即管土之间的约束为弹性约束。对于约束土壤进入塑性滑移状态,给出了新的地震应力计算方法———极限地震应力计算法,并根据决定极限应力大小的单位长度管线极限约束力的计算方式,把极限地震应力计算法分为单位长度摩擦力法、修正法和加权平均法。两个实际工程算例的比较分析结果说明,极限地震应力法能准确地反映海底管线的实际地震应力状况,解决现用抗震设计方法中存在的问题。

关键词: 地震波, 海底管线, 摩擦力, 极限应力, 塑性约束, 设计方法