运营期上硬下软型双层地基动力损伤评价

Evaluation of Dynamic Damage of Two-layer Subgrade with Upper Dry Crust and Lower Soft Soil Layer in Operation Period

为了给运营期上硬下软型双层地基(简称双层地基)工程设计提供参考依据,以河北省境内的邢台-临西高速公路(以下简称邢临高速)双层地基为研究对象,采用现场监测、动三轴试验、理论推导和数据统计相结合的方法,给出了动应力界面传递系数和硬、软土层间动应力水平的关联性。提出了一种改进的、适用于评价双层地基动力损伤特征的R-N非线性疲劳累积损伤模型。借助数据统计手段,对地基土损伤演化信息进行挖掘,给出了运营期双层地基设计的指标依据。研究结果表明:硬、软土层界面处具有动应力突变现象,硬壳层力学性能劣化导致界面效应减弱;硬、软土层动应力水平具有强相关性,导致硬、软土体的损伤模型计算参数产生关联;夹角转动、夹角增量是评价双层地基损伤的敏感指标,夹角转动由车辆荷载增幅决定,夹角增量平均值与硬、软土压缩模量比呈对数函数关系;相同工况下软土的运营期寿命短于硬土,软土层是诱发运营期地基失稳的关键土层;当硬壳层厚度超过2.3 m且硬、软土体压缩模量比大于4.6时,硬壳层具有显著降低软土层动应力水平的能力,有助于延缓双层地基运营期寿命。因此,当双层地基的力学指标满足上述条件时,建议在高速公路工程设计中优先考虑利用天然硬壳层作为地基持力层。

In order to provide reference for the design of two-layer subgrade with upper dry crust and lower soft soil layer(two-layer subgrade for short) during operation period, taking the two-layer subgrade of Xingtai-Linxi expressway in Hebei Province as the research object, by means of comprehensive method combining field monitoring, dynamic triaxial test, theoretical derivation and data statistics, the transfer coefficient of dynamic stress at interface and the correlation between dynamic stress levels of hard and soft soil are obtained. An improved R-N nonlinear fatigue cumulative damage model is put forward to evaluate the dynamic damage characteristics of two-layer subgrade. By means of data statistics, the damage evolution information of subgrade soil is mined, and the indicator basis for the design of two-layer subgrade in operation period is given. The research result shows that(1) there is a sudden change of dynamic stress at the hard and soft soil interface, and the mechanical property deterioration of the hard crust leads to the weakening of the interfacial effect;(2) the dynamic stress levels of hard and soft soil are strongly correlated, which leads to the correlation between the calculation parameters in the damage models of hard and soft soil;(3) intersection angle rotation and intersection angle increment are the 2 sensitive indicators for evaluating the damage of two-layer subgrade, the intersection angle rotation is determined by vehicle load increment, and the average intersection angle increment has a logarithmic function relationships with the compression modulus ratio of hard soil to soft soil;(4) the service life of soft soil is shorter than that of hard soil under the same working condition, and the soft soil layer is the key one to induce subgrade instability during operation period;(5)when the thickness of hard crust being more than 2.3 m and the compression modulus ratio being greater than 4.6, the hard crust has strong ability to reduce the dynamic stress level of the soft soil, which is helpful to postpone the life of two-layer subgrade in operation period. Therefore, when the mechanical indicator of two-layer subgrade meets the above conditions, it is suggested that the natural hard crust should be used as the bearing layer in the design of expressway project.