冲击地面过程中落石特征参量的理论分析

根据落石与地面碰撞过程中落石加速度、冲击力的曲线特征,利用动量定理推导正面碰撞时法向冲击力的理论计算公式;在假设切向冲击不影响法向冲击的前提下,提出一种新的摩擦力模型,基于该模型推导切向冲击力和切向恢复系数的理论公式。最后研究不同入射速度大小、不同入射角时的碰撞时间、恢复系数和最大冲击力的变化规律,分析结果表明:(1)当入射角一定时,随着入射速度增加,冲击力近似呈线性增加,切向恢复系数逐渐增加,但增加幅度很小,而法向碰撞恢复系数和碰撞时间逐渐减小;(2)当入射速度一定时,随着入射角的增加,法向恢复系数和切向恢复系数均增加,但前者增幅远小于后者,碰撞时间也呈增大趋势,而最大冲击力呈先增加后减小的变化规律;(3)地表覆土厚度与落石半径比值越大,碰撞时间越长,法向恢复系数随之递增,切向恢复系数随之递减,而最大冲击力随之呈上凹型曲线递增。

CHARACTERISTIC PARAMETERS THEORETICAL ANALYSIS OF ROCKFALL IMPACT ON GROUND

In accordance with the character of rockfall acceleration or impact force curve,impact force computation theory formulas of front impact are derived using momentum law.Supposing normal impact force is not affected by tangential impact force,a new friction model is proposed,using which tangential impact force and coefficient of restitution both are induced.Finally the change law of impact time,impact force and coefficient of restitution are analyzed when incidence speed,incidence angle or the ratio of the thickness of surface soil to rockfall radius are changed.It showed that:(1) With the impact velocity increasing and the incident angle fixed,the impact force increases linearly,the tangential restitution coefficient ascends with a small amplitude,while the normal restitution coefficient and impact time both descend.(2) With the augment of incidence angle,normal and tangential coefficient of restitution both are getting larger,the increment of tangential restitution coefficient is greater than that of normal restitution coefficient,and the collision time longer,while maximum impact force rise and then drop.(3) With the ratio increase of the thickness of surface soil to rockfall radius,the longer the collision time is,the larger normal coefficient of restitution is while the smaller tangential coefficient of restitution is,and maximum impact force goes up like a concave curve.