网孔尺寸对格栅-尾矿界面特性的影响

Effects of mesh size on interface characteristics between geogrid and tailings

目前加筋尾矿结构中土工格栅的选用未考虑网孔尺寸的影响,仅考虑格栅的极限抗拉强度,致使格栅网孔尺寸的选用还存在较大的主观性。为了研究土工格栅加筋尾矿的网孔尺寸,也就是格栅-尾矿界面与剪切面面积比对格栅-尾矿界面强度参数的影响规律。选用5种网孔尺寸(12.7 mm×12.7 mm,25.4 mm×25.4 mm,38.1 mm×38.1 mm,50.8 mm×50.8 mm,63.5 mm×63.5 mm)相同规格的土工格栅,分别通过直剪试验和拉拔试验对格栅-尾矿的界面特性进行分析,探求土工格栅加筋尾矿的合理网孔尺寸。试验结果表明:两种试验条件下,随着土工格栅网孔尺寸增大,格栅-尾矿界面强度指标似黏聚力减小,似摩擦角增大;格栅网孔尺寸的变化对似黏聚力的影响显著,对似摩擦角的影响较小;随着格栅网孔尺寸的增大,界面似摩擦因数逐渐降低,降低幅度越来越慢,且法向应力越大,界面似摩擦因数变化范围越小;相同条件下,拉拔界面似黏聚力约为直剪界面似黏聚力的0.7倍,拉拔界面似摩擦角约为直剪界面似摩擦角的0.45倍。为了更准确分析土工格栅加筋尾矿的效果,应该将格栅-尾矿界面摩擦作用从界面综合摩擦作用中分离出来,得到格栅-尾矿界面摩擦因数比;随着格栅-尾矿界面与剪切面面积比的减小,格栅-尾矿界面摩擦因数比先轻微上升,后发生陡降,格栅加筋作用迅速消失。土工格栅加筋尾矿的合理网孔尺寸应控制在格栅-尾矿界面与剪切面面积比为0.4左右,即所用格栅网孔尺寸为38.1 mm×38.1 mm时,此时土工格栅加筋尾矿的效果最佳。

At present,the selection of geogrid in reinforced tailings structure does not consider the influence of mesh size,but only consider the ultimate tensile strength of geogrid,which makes the geogrid selection more subjective in practical engineering.To study the influence law of mesh size on geogrid reinforced tailings,i.e.the area ratio between geogrid-tailings interface and shear surface,on the interface strength parameters of geogrid-tailings,five geogrids of the same specification with different mesh size(12.7 mm×12.7 mm,25.4 mm×25.4 mm,38.1 mm×38.1 mm,50.8 mm×50.8 mm and 63.5 mm×63.5 mm)were selected to analyze the interface characteristics of geogrid-tailings through direct shear test and pull-out test respectively to explore the reasonable size of geogrid reinforced tailings.The test results show that under the two test conditions,with the increase of mesh size of geogrids,for the geogrid-tailings interface strength index parameters,the pseudo-cohesion decreases and the pseudo friction angle increases.The change of mesh size of geogrid has a significant effect on the pseudo-cohesion,but has little effect on the pseudo friction angle.With the increase of mesh size of geogrids,the interface pseudo-friction coefficient decreases gradually and the decreasing range becomes slow.The larger the normal stress is,the smaller the variation range of pseudo-friction coefficient is.Under the same condition,the pseudo-cohesion of pull-out interface is about 0.7 times of that of direct shear interface,and the pseudo friction angle of pull-out interface is about 0.45 times of that of direct shear interface.In order to analyze the effect of geogrid reinforced tailings more accurately,the interface frictional effect of geogrid-tailings should be separated from the interface comprehensive frictional effect,and obtain the interface friction coefficient ratio of geogrid-tailings.With the decrease of the area ratio between geogrid-tailings interface and shear surface,the interface friction coefficient ratio of geogrid-tailings increases slightly at first,then decreases sharply,and the reinforcement effect of geogrids disappears rapidly.The reasonable mesh size of geogrids reinforced tailings should be controlled about 0.4 of the area ratio between geogrid-tailings interface and shear surface,i.e.when the mesh size of geogrid used in this paper is 38.1 mm×38.1 mm,the effect of geogrid reinforcement tailings is the best.