开河期冰盖横向冰缝形成机理

Mechanism of transverse-crack formation during river-ice breakup

春季随着流量或水位增加,冰盖底部受水流上举力作用发生弯曲,首先在岸壁附近形成纵向冰缝,破坏冰盖与岸壁的冻结,导致冰盖体中间部分与岸壁脱落分离。采用弹性基础梁的理论及计算方法,通过对冰盖体弯矩及弯曲应力分析,针对平面弯曲和垂直弯曲两种弯曲形式导致冰盖体横向冰缝形成机理进行了研究,并提出了横向冰缝间距的计算表达式。计算结果得到了实测资料的验证。研究结果表明,横向冰缝间距与开河初期冰盖宽度、厚度、冰的抗弯强度及地貌特征有关。

During the river-ice breakup, the longitudinal cracks near banks are firstly formed due to the rtmoff increase, resulting in the detachment of central part of ice cover from both banks. Subsequently, as a result of horizontal bending or vertical bending of ice cover the transverse cracks will be further formed, and the continuous ice-cover is finally fractured into floes with cerain sizes. Based upon the theory and calculation method of elastic-foundation, the mechanism of transverse-crack formation is fully investigated. By means of studying on the bending moment and bending stresses of ice cover, the analytical expressions of the crack-spacing due to both horizontal bending and vertical bending are presented, and validated with the field measurements. The study indicates that the transverse-crack spacing depends on the ice-cover width, thickness, bending strength and topography.