土工格栅在季节性冻土中的加筋机理及长期工作特性研究

Geogrid is proposed to prevent freezing-thawing hazard which always occurs at the subgrade in cold regions. But most of geogrid-reinforced subgrades were designed and built based on contraction experience. There is no suitable standard and typical design theory for reinforced subgrade in seasonal frozen area. This project,focusing on the problem，plans to do some researches as follows：1) A series of tests investigating physical and mechanical parameters of frozen soil are conducted in the laboratory,then pullout test will be done to get the interface mechanical model between geogrid and frozen soil. Three factors will be considered in details, such as temperature, moisture and freeze-thaw cycles. 2) 1/4 scale reinforced and unreinforced subgrade model test will be conducted in constant temperature and humidity laboratory. The inhibitory effect of geogrid on freezing-thawing hazard will be clarified by contrastive analysis. Based the data under several freeze-thaw cycles, the law of stress inside and deformation outside subgrade will be further revealed, and the long-term performance of geogrid-reinforced subgrade in seasonal frozen area will be derivated. Finally, instability mechanism and failure modes of reinforced and unreinforced subgrade will be obtained by doing failure load test. This reseach can improve the basic design theory, and provide technical support to construction of the geogrid-reinforced subgrade in seasonal frozen ground.

国内外工程界已在冻土区初步尝试采用土工格栅对路基的冻融灾害进行防治，但目前大多数工程仅依靠经验型建议，尤其对于季节性冻土地区更为复杂和频繁的冻融交替现象，尚缺乏独立的设计理论和技术导则。针对上述问题，本项目拟开展如下研究：1）将冻土强度特性试验和冻土中土工格栅拉拔试验相结合，从冻土本构关系研究逐步开展到筋土界面力学计算模型研究，重点分析温度、土体含水率和冻融循环次数三个因素对土工格栅加筋效果的影响。2）建立室内小比尺冻土路基模型对比试验，明确土工格栅对路基冻融灾害的抑制作用，并基于长期试验数据，进一步分析加筋路基的内部应力与外部变形随冻融循环次数的变化规律，揭示土工格栅在季节性冻土路基中的长期工作特性；最后通过破坏性载荷试验研究冻土路基在加筋前后的失稳机理及破坏模式。相关研究成果可完善现有加筋结构的设计理论，并为季冻区加筋冻土路基的设计与施工提供技术支持。

国内外工程界已在冻土区初步尝试采用土工格栅对路基的冻融灾害进行防治，但目前大多数工程仅依靠经验型建议，尤其对于季节性冻土地区更为复杂和频繁的冻融交替现象，尚缺乏独立的设计理论和技术导则。针对上述问题，本项目开展了如下研究：1）本项目采用直接剪切试验和三轴试验两种方法对土体的抗剪强度指标及峰值强度进行了针对性试验，获取了温度、含水率和冻融次数对土体强度指标的影响特征；并进一步实施了冻融循环作用下的加筋土体变形对比试验，重点针对多次冻融情况下加筋前后土体的冻胀量和融沉量变化进行了定性和定量分析。2）本项目采用冻土中土工格栅拉拔试验对冻土-格栅界面特性进行了研究，重点分析了含水率和冻融循环对格栅加筋效果的影响。研究发现冻融循环作用对高应力下的格栅加筋效果影响不大，低应力下加筋效果出现波动趋势；含水率对格栅与土体界面间的摩擦效果存在一定影响，而对横肋产生的被动阻抗作用几乎没有影响。对于整体的等效拉拔摩擦系数而言，加筋土体并没有由于冻融循环而产生明显的强度下降。3）本项目借助步入式环境模拟实验室进行了小比尺冻土加筋路堤的对比模型试验，在路堤内部布置了含水率、温度、应力等微型传感器，重点观测了路堤内部的温度场、应力场、以及含水率和地表沉降变化等数据。从加筋前后的数据对比中可发现加筋作用可显著抑制冻融循环作用下路堤表面变形；在最后的破坏性加载对比试验中发现，土工格栅也大幅提高了加筋路堤的极限承载性能；且本次模型试验也总结并形成了一套有效的冻土数据监测和采集办法，为后继开展冻土加筋工程的应用与评价奠定坚实的基础。相关研究成果可完善现有加筋结构的设计理论，并为季冻区加筋冻土路基的设计与施工提供技术支持。