Mechanical Behavior Of Geogrid Reinforcing Soil

Based on the review of existing tests and calculated methods, ultimate pullout force of geogrid is studied by pullout test, FEM method and theory analysis.Firstly, application and research of geogrid are summarized in this thesis.The importance of study on geogrid is expounded.Secondly, pullout tests of geogrid under different normal pressure are carried out. Lateral pressure on frontal wall of pullout box is measured during pullout process. Qualitative analysis is brought forward to influence of 'squeeze effect' on ultimate pullout force. Influences of 'squeeze effect' on geogrids in different lengths are identical, so errors induced by 'squeeze effect' are cancelled by calculated differences between different long geogrids. Ultimate resistance of transverse bar is obtained by geogrids with same length and different number of transverse bar.Thirdly, single bar in soil induced by horizontal force is simulated with plain strain FEM. The Yang's modulus and Poisson's ratio have little influence on ultimate resistance of single bar, but normal pressure and internal friction angle significantly influenced on it. Expression of ultimate resistance of single bar is proposed and validated by experiment data.Fourthly, Prandtl's mechanism is applied to analyzed the ultimate resistance of single member in soil, a theoretical equation is attained and compared to expressions of former researchers. Influence of cohesion on ultimate resistance is not significant and could be neglected.Finally, the calculated method of friction between geogrid and soil is proposed, and ultimate pullout load capacity of geogrid is proposed at last and validated by test results.The pullout resistance of geogrid which is an important parameter normally obtained from laboratory pullout test. It is diffusedly believed that the pullout resistance of geogrid is induced from two sources. One is the friction and cohesion between the surface of geogrid and surrounding soil, and the other is the transverse bar resistance of the geogrid. With the results of FEM, expression of ultimate resistance of single bar is fitted and equation of pullout resistance of geogrid is proposed at last.