道砟大型直剪试验颗粒破碎定量分析

Quantitative analysis of particle breakage in large-scale direct shear test of ballast

铁路道砟在受荷载作用时易发生破碎,影响道床的力学特性。为研究道砟集料在直剪条件下的破碎情况及破碎规律,利用大型直剪试验设备对新建铁路一级道砟开展不同法向压力(15,35,55和75 kPa)下的直剪试验。通过对试验后剪切面上下60 mm区域内的道砟进行筛分,分析剪切对道砟试样级配的影响规律。采用Marsal破碎指标,Hardin破碎指标以及BBI破碎指标对道砟试样在剪切后的破碎情况进行定量分析。研究结果表明:在直剪试验中,道砟在剪切面区域会发生明显的尖角破碎,大粒径颗粒减少,小粒径颗粒明显增加;随着法向压力的增加,3种破碎指标均有明显增加,表明道砟破碎加剧。

Ballast particles are apt to break under loads,thus affecting the mechanical behavior of railway ballast bed.In order to study the breakage status and breakage laws of ballast particle under direct shear conditions,a large-scale direct shear apparatus was developed and a series of direct shear tests were conducted on the Class I ballast from newly-built railway under different normal pressure levels(i.e.,15,35,55 and 75 kPa).Through the mechanical sieve analysis on the ballast within the region of 60 mm above and below the shear plane after the test,the influence of shearing on the gradation variation was analyzed.Marsal’s breakage index,Hardin’s breakage index and Ballast breakage index(BBI)were adopted to quantitatively evaluate the breakage status of ballast particles after shearing.The results show that distinct ballast particle corner breakage occurs around the shear plane after direct shearing,as evident from the decrease of the amount of large sized particles and the obvious increase of the amount of small sized particles.It is also found that all three breakage indices increase with the increase of normal pressure,indicating escalating ballast particle breakage.