客货共线铁路路基基床底层承载力分析

在客货共线铁路路基设计中,经常遇到填土高度小于路基基床厚度的低路堤、挖方路堑,现行设计规范规定了基床底层范围内的天然地基静力触探比贯入阻力、天然地基基本承载力两项判定指标,如不满足该两项标准,就应进行换填、改良或加固处理。很多设计者在使用该标准时提出了疑问,本文旨在对此问题进行分析落实。通过计算Ⅰ、Ⅱ级铁路不同设计速度对应的动荷载和轨枕底部应力,采用布辛尼斯克公式算出了基床底层顶面及其以下不同深度处的应力,并根据动强度与静强度的关系确定出了基床底层的基本承载力新标准值,建议设计规范采用该新值后取消静力触探比贯入阻力指标。

Analysis on Bearing Capacity of Bottom Layer of Subgrade Bed of Mixed Passenger and Freight Railway

When designing the subgrade of mixed passenger and freight railway,it is not unusual to face the problem of a low embankment or an excavation cutting in which the filling height is less than the thickness of subgrade bed. Considering this reason,for the natural subsoil within the range of the bottom layer of subgrade bed,there are two evaluation indexes in the current design code: the specific penetration resistance of static sounding,and the basic bearing capacity of natural subsoil; still more,if not meeting the two evaluation indexes,the methods of earth replacement,earth improvement or earth strengthening treatment should be utilized. However,these evaluation indexes were questioned by many designers when using them. The purpose of this paper was to analyze and solve this problem. This paper calculated the dynamic load and the stress at the sleeper bottom corresponding to different design speeds of class I and class Ⅱ railways. And then this paper worked out the stresses at different depths above and below the top surface of bottom layer of subgrade bed by using Boussinesq formula. Finally a new standard value of basic bearing capacity of the bottom layer of subgrade bed was determined in this paper according to the relationship between dynamic strength and static strength. It is suggested that the index about specific penetration resistance of static sounding should be abolished after this new standard value has been adopted in design code.