土工格栅与砂土相互作用的单剪试验研究

Study of interaction behavior between geogrids and sand with simple shear test

利用大型循环单剪试验仪,进行30组大型单剪试验,综合研究分析不同类型的土工格栅,不同的格栅数量和格栅分布形式对加筋土力学特性的影响。研究3种不同类型的土工格栅,分别是矩形截面和椭圆形截面的双向格栅,以及三向土工格栅。试验结果表明,土工格栅的截面肋条以及节点厚度和相对开孔面积与加筋砂土的抗剪强度呈正相关,肋条长度和宽度与加筋砂土的抗剪强度呈负相关。进一步试验表明,格栅的布置层数对砂土的力学性能产生影响。当向纯砂中加入土工格栅时,其整体纯剪切强度降低。砂土的剪切破坏面集中在试样上部,试样下部各高度处的相对剪切位移较小。加入土工格栅后,整体试样的表观黏聚力增加,摩擦角降低。因此,在单剪模式且筋材铺设方向与剪切方向一致时,筋土界面成为软弱界面,降低了抗剪强度,同时筋材对砂土有一定的约束作用,因此出现了表观黏聚力。

Under various vertical stresses and number of geogrids layers,three types of geogrids were used,respectively,and 30 groups of simple shear tests were conducted on geogrids reinforced sand to study the change of shear behavior of soil. The three geogrids used were rectangular and elliptical bidirectional geogrids along with a tridirectional geogrids. The experimental results show that the thickness of the ribs and nodes as well as the relative opening area positively correlated with the shear resistance while the length and width of ribs negatively correlated with the shear resistance. Besides,the number of layers of geogrids influenced the mechanical properties of sandy soil. The strength decreased when geogrids were added with their laying directions corresponding to the shear direction. The shear failure surfaces were in the upper part of the specimens while in the lower part showed small relative displacement. Meanwhile,the cohesion appeared but friction angle reduced. Therefore when adding geogrids to the same direction with the shear direction of sandy soil will result in a weak soil-geogrid interface,and thus the shear strength decreases. However,the reinforced sandy soil shows an apparent cohesion due to the restriction from the geogrids to the sand.