水分迁移及交通荷载作用下路基土体损伤变形机理研究

The pavement water damages may weaken the bearing capacity of deep soil subgrade. If resurface only, soon the damage will appear again. Gross feature and mesoscopic mechanism of water damage in subgrade is the emphasis of project. Firstly, exploration pit will be excavated around water damage. Soil samples from subgrade under water damage center, edge and well segments, their mechanical properties and mesoscopic structure will be tested by in-situ tests and CT. According to results, we will find the differences between damage and well segments. Secondly, the dynamic stress induced damage will be measured. The dynamic soil pressure sensors will be buried while backfilling the test pit. Dynamic signal analysis system is adopted to measure the stress and deformation response in subgrade when the vehicles pass with different velocity and different load. From Fourier analysis of the results of tests, we can know dynamic stress amplitude, vibration wave’s spectrums, propagation rules and influence range in subgrade. Thirdly, the degradation mesoscopic mechanism of soil influenced by single factor will be studied. The compaction samples are made from clay, silt, fine sand soil, soil containing fine sand. Through three axial tests and CT scanning of soil samples with different water contents, the mesoscopic mechanism of soil damaged by water infiltration will be analyzed. Meanwhile, dynamic shear tests of saturated soil will be done. According to CT scanning picture of original and broken samples, the mesoscopic mechanism of soil damaged by stress will be analyzed. Finally, model tests are simulated the development process of water damage. The mechanical properties of affected soil are tested to study the extent of the damage. Traffic loads just like the external cause, and the reduction of bearing capability caused by water migration is the internal cause, internal and external combination will reach the acme, and pavement will damage. The results will enrich the theory and practice of unsaturated soil, and guide highway maintenance and management departments to treat the damage by water.

调研发现道路水损和交通荷载对路基土体的损伤主要集中在路床。课题拟首先采用坑探配合原位试验、CT扫描对比研究水损病害中心处、边缘处及未发生病害处的路基宏观力学性能和细观结构的差异。探坑回填时布设动态土压力传感器，检测不同轴重、不同速度车辆通过时路基的附加动应力，分析不同深度处路基附加动应力的幅值、频谱特性、衰减规律，研究病害产生的力学机理。其次进行单因素作用下土体损伤的细观机理研究，选择常用填料击实模拟路床土体，选取最优含水率状态、自然浸润状态和饱和状态进行CT扫描和三轴试验，研究水分浸润作用对土体力学性能损伤的细观机理；同时对饱和状态的土样进行动剪试验和CT扫描，分析土体受动力损伤前后细观结构的变化。最后，采用模型试验研究动载、水分浸润耦合作用下路床土体病害形成及发展的细观机理。课题从受力状态及水分迁移两方面探讨路基土体的损伤机理，可进一步推动非饱和土力学在实践中的应用。

水分迁移和交通荷载双重作用是路基土体损伤的主要原因，有必要研究二者耦合作用下路基土体宏观力学特征的变化规律和损伤变形的发展机理。课题首先采用原位试验对江西水损道路进行了调研，并通过XRD衍射试验、颗粒级配试验、液塑限试验等室内试验对路基填料的力学参数进行了研究。在此基础上，开展填筑路基室内模型试验，分析降雨入渗及交通荷载耦合作用下对路基的应力状态及沉降变形的影响。研究表明：一般公路路基工作区深度大约在100cm到110cm左右，且随着交通荷载的增大有小幅度增加；降雨入渗及交通荷载耦合作用下可以明显弱化路基的承载能力，表现为基层上表面的动应力减少约17%，沉降增大约20%。研究发现土工格室加筋路基对整治水损病害具有十分重要的意义，通过动三轴试验，研究了加筋土单元体的应力应变曲线、滞回曲线及动弹性模量等力学特性指标及其在不同加筋工况、不同含水率及不同外部荷载下的变化规律。通过缩尺寸模型试验，对交通荷载及降雨入渗作用下的土工格室加筋路基的变形特性进行了系统性的研究。从微观角度探究土体宏观力学性能改变的原因，对不同工况的路基原状土土样作电镜扫描，探究在细观状态下土颗粒之间的组团排布和孔隙结构，发现在降雨入渗和交通荷载耦合作用下，路基土颗粒呈明显的片状形式分布，片状组团之间有较多的角面、角边接触，且各片状组团排列松散，各颗粒组团间有明显的孔隙结构。压缩荷载是路基颗粒材料最为常见的受力形式，通过光弹实验可视化的特性，观察有侧限单轴压缩试验过程中的力链演变，发现应力的分布与连续介质的材料的内部分布区别很大，所形成的应力网格中分成强弱力链，并表现出明显的局部化特征。根据以上研究成果，采用数值模拟的方法建立全尺寸道路模型，对降雨入渗、交通荷载耦合作用下土工格室加筋路基的承载性状进行模拟研究，对路基的应力和变形进行了系统的分析。课题成果将进一步提高我国非饱和土力学的研究水平，同时为处治水损病害提供理论支撑，具有一定的学术价值。