明棚洞落石冲击荷载计算方法研究

A method for calculating rockfall impact load on shed tunnel

根据落石冲击回填土明棚洞过程中的基本力学和运动学规律,采用Laplace变换,从落石冲击半无限土体、落石冲击有限厚度土体、考虑回填土与下部结构相互作用3个方面推导了落石冲击荷载的理论计算公式,通过数值模拟和相关试验数据对理论公式进行了验证,并与目前常见落石冲击荷载计算公式进行了对比研究。研究表明:所提出的公式理论计算结果与数值模拟结果和相关试验结果均有较稳定的规律,理论计算值比数值模拟值大6%~41%,与Pichler现场试验的95%分位值差值仅在6%以内;尽管所提出的公式计算值比目前所有公式计算结果均偏大,但与数值模拟和试验数据更吻合,更能反映出真实的落石冲击荷载;所提出的计算公式可以反映缓冲层厚度和缓冲层性质的影响,缓冲层厚度越小,落石冲击荷载越大,缓冲层厚度影响系数可根据h/r查表确定;缓冲层和结构的动力相互作用导致结构承受冲击荷载相较缓冲层顶部冲击荷载增大,结构动力放大系数与缓冲层厚度相关,缓冲层厚度越大,结构动力放大系数越小。所提出的计算公式可以反映落石大小、落石形状、落石冲击能量、缓冲层厚度、缓冲层性质等因素对冲击荷载的影响,计算荷载值可直接用于明棚洞结构设计。

According to the basic mechanics and kinematics laws of rockfall impacting backfilling shed tunnel,the theoretical calculation formula of rockfall impact load is derived from three aspects using Laplace transform:rockfall impacting semi-infinite backfill,rockfall impacting finite thick backfill,and considering the interaction between backfill and substructure.The theoretical formula is verified by numerical simulation and relevant test data,and is compared with the other calculation formulae.The research shows that the theoretical value obtained from the proposed formula and the results of numerical simulation and laboratory tests all have a relatively stable law.The theoretical values are 6%−41%larger than the numerical values,and the difference between the theoretical value and the 95th percentile value of Pichler test is within 6%.Although the theoretical value in this paper is larger than that of all the other formulae,it is more consistent with numerical data and test data,thus it can better represent the real rockfall impact load.The formula can reflect the influences of thickness and properties of backfill,i.e.the smaller the thickness of backfill,the greater the impact load,and the thickness amplification factor can be determined according to the h/r table.The dynamic interaction between the backfill and the structure leads to the increase of the impact load on structure,which can be defined as dynamic amplification factor;the larger the thickness of backfill,the smaller the dynamic amplification factor.The proposed theoretical formula can consider the influence of many factors such as rockfall size,rockfall shape,rockfall energy,and thickness and properties of backfill.Therefore,the theoretical value can be used to design structure of shed tunnel directly.