落石冲击棚洞结构冲切特性研究

HERTZ THEORY BASED STUDY ON PUNCHING CHARACTERISTICS OF ROCKFALL IMPACTING ON SHED-TUNNEL STRUCTURE

落石是一种严重的山区地质灾害,而棚洞作为主要防护落石的工程措施之一,研究落石冲击下棚洞结构动力响应特征具有重要的现实意义。以经典Hertz理论为基础,假设落石为球形刚性体,棚洞结构为梁结构,建立落石冲击力学模型,理论推导得到不同尺寸落石以不同速度冲击不同厚度砂土垫层材料下棚洞板的最大冲击力计算公式,并得出不同工况下棚洞板被冲切破坏时落石的极限冲切速度,结果表明:总体上,落石对棚洞板的冲击力随垫层厚度增加而减小,但垫层厚度不能无限增加,过厚的垫层自重较大,使棚洞板受力较大,垫层材料厚度在0.5~1.5 m厚之间较为合理;落石尺寸和冲击速度越大,棚洞板受力越大,有限厚度的垫层材料只能承受一定限度的冲击能量,当冲击能量超过垫层材料的极限承受强度时,垫层不再耗散能量;分析棚洞板冲切破坏条件可知,无垫层时,很小的落石冲击速度使棚洞发生破坏,可见,合理的垫层厚度对防治落石具有重要意义。

Rockfall is a serious geo-hazard in mountainous area. The shed tunnel is one of the main engineering measures to prevent rockfall. It has the great actual meaning to study the dynamic response characteristics of the shed tunnel under the impact of rockfall. Based on Hertz theory, the impact mechanics model of rockfall is established assuming that the rockfall is a rigid spherical body and the shed is a beam. Then the maximum impact force of rockfall impacting on the shed slab with different thickness cushion are derived at different speeds. Moreover the limit punching shear velocity of rockfall is obtained. The results show that the impact force of rockfall on the shed slab decreases with the increase of cushion thickness, while the cushion with finite thickness can only bear a certain limit of impact energy, The larger the rockfall size and impact velocity is, the greater the stress of the shed plate becomes. When the impact energy exceeds the ultimate bearing strength of cushion material, the cushion would no longer dissipate energy, furthermore, the small impact velocity of rockfall could cause the shed tunnel without cushion damaged, and the reasonable cushion thickness is of great significance to prevent rockfall.