雷电冲击下土体应力及弹塑性界面时程分析

Time Course Analysis of Soil Stress and Elasto−Plastic Interface Under Lightning Impact

雷电作为自然界一种极端天气的表现形式,常给地基、地面、高耸建筑等造成严重破坏。工程防雷措施依赖于土体雷电冲击特性。现阶段,研究人员大多从电气工程角度探究雷电冲击土体造成的危害,但因学科间的差异与局限,雷电作用下岩土工程与电气工程的交叉融合方面的研究十分欠缺。本文构建土体雷电冲击模型,基于电弧通道能量平衡方程计算雷电放电产生的冲击波压力,将冲击波压力作为外加荷载作用在土体中,并通过修正Mohr-Coulomb屈服准则考虑动荷载下土体应变硬化,利用土体的理想锁定状态方程(Idealized Locked Equation of State)和动态扩孔方法考虑冲击波非稳态加载,探究雷电冲击下土体的弹塑性界面及应力时程变化规律。研究表明:在雷电冲击下,土体应力随时间变化呈现先陡增后迅速衰减的趋势,应力突变点表明土体此时正处于弹塑性交界面;在应力突变点之前,土体附加应力趋于0,处于弹性状态。任一时刻下,随着逐渐远离雷电冲击点,土体应力呈现迅速衰减的趋势,应力发生突变骤降表明此处土体正处于弹塑性交界面;在突变点之后土体附加应力趋于0,处于弹性状态。土体压缩系数对土体的弹塑性界面变化具有显著影响,随着压缩指标增大,土体塑性区半径逐渐减小;随着土体黏聚力逐渐增大,土体塑性区半径逐渐减小;增大土体弹性模量可以增大土体塑性区半径,但变化幅度相对较小;电流波形对土体塑性区中的应力会产生较大影响,而对土体弹性区影响较小。

Lightning is a form of extreme weather in nature,often causing serious damage to foundations,ground,towering buildings,etc.Engin-eering lightning protection measures depend on the lightning impact characteristics of soil.At this stage,the hazards caused by lightning impact on soil are mostly explored from the perspective of electrical engineering,but the cross-fertilization research between geotechnical engineering and electrical engineering under lightning action is very lacking due to the differences and limitations between disciplines.This paper constructs a lightning shock model for soil,calculates the shock wave pressure generated by lightning discharge based on the arc channel energy balance equa-tion,applies the shock wave pressure as an applied load to the soil,and considers soil strain hardening under dynamic load by modifying the Mohr−Coulomb yielding criterion.The ILEOS(Idealized Locked Equation of State)and dynamic reaming methods are used to consider the un-steady loading of shock waves and to investigate the elastic−plastic interface and stress time course change law of soil under lightning impact.The study shows that under the lightning shock,the soil stress changes steeply with time and then decays rapidly,and the sudden change point of stress indicates that the soil is at the elasto-plastic interface,before the sudden change point,the additional stress of the soil tends to zero and is in an elastic state.At any moment,the soil stresses show a rapid decay as one moves away from the lightning impact point,and when the stress sud-denly decreases,it indicates that the soil is at the elasto−plastic interface,and after the sudden change point,the additional stress of the soil tends to zero and is in an elastic state.Soil compression coefficient has a significant effect on the elastic-plastic interface change of the soil,with the in-crease of compression index,the radius of the plastic zone of the soil gradually decreases.As the cohesive force of the soil gradually increases,the radius of the the plastic zone of the soil gradually decreases.Increasing the modulus of soil elasticity can increase the radius of soil plastic zone,but the change is relatively small.