土工格栅拉拔试验模型优化及加筋特性研究

目前土工格栅加筋提高工程的安全性广受关注,为研究土工格栅摩擦系数、网孔尺寸对其加筋特性的影响,采用PFC3D建立土工格栅拉伸试验模型和拉拔试验模型,并对2种试验模型进行优化。将土工格栅拉伸应力-应变关系按其应变量分段,开发了记录试验过程中土工格栅的应变并根据该应变与分段界限应变间大小关系来改变格栅的法向、切向黏结刚度的FISH程序。在保持土工格栅试样尺寸及各参数不变的条件下,分别开展不同格栅摩擦系数和不同网孔尺寸的数值拉拔试验。结果表明:按土工格栅应变量对其拉伸特性进行分阶段模拟的方法可使模拟结果更加准确;优化后的土工格栅拉拔试验模型计算结果与室内试验结果更加吻合;土工格栅的摩擦系数及网孔尺寸对加筋特性的影响明显,孔径比为5. 0左右时的加筋效果最佳。建议在选用加筋材料时应考虑土工格栅摩擦系数和网孔尺寸与填料粒径之间的匹配关系。

Approach to optimizing the pull-out test model of geogrid and the reinforcement features

The paper aims at tracing and discovering the influence of the friction coefficient and mesh size of the geogrid on the specific reinforcement features. For this purpose,the paper has formulated a tensile test model and a pull-out test model of geogrid with PFC3 Dso as to optimize the 2 testing models to promote the numerical test results up-closer to the laboratory testing results. To achieve the purpose,we have segmented the tensile stress-strain relationship of the geogrid gained from the laboratory tests according to its strain,and regarded those as the segment boundary strains in the numerical tests. Furthermore,we have also developed a program in FISH language to record the strain of the geogrid in the process of numerical test,which can change the normal and tangential bond stiffness of the geogrid according to the size relationship between the actual strain and the segment boundary strain in the process. The numerical results we have gained show that the program can make the numerical tensile test results basically consistent with the laboratory tensile test ones.In addition,keeping the geogrid sample size and the parameters unchanged,we have also conducted a series of pull-out tests with the different friction coefficients and various mesh sizes of geogrid. The results indicate that the testing results of the optimized geogrid pull-out test model can basically be kept consistent with the variation law of the pull-out forc-displacement curve gained from the equivalent laboratory tests,whereas the friction coefficient and mesh size of the geogrid keep obvious effect on the reinforcement features. Furthermore,with the decrease of the friction coefficient of geogrid,the peak strength of the pull-out force and its corresponding displacement may also in turn decrease. Among them,more significant can be found its influence on the corresponding displacement of the peak pull-out force than the influence of the friction coefficient of the geogrid on the peak pull-out force. Moreover,the peak pull-out force and its corresponding displacement have been found increasing first and then turning to decrease with the increase of the aperture ratio. And,when the ratio is getting to around 5. 0,the reinforcement effect of the geogrid should be regarded as being the best. The above results show that,to enhance the reinforcement effect of the geogrid in the engineering application,the surface friction coefficient of the geogrid can be made to increase appropriately. And,it is also necessary to take it into account the matching relationship between its mesh size and the particle size of the soil when the geogrid type has to be chosen.