Research On Shear Behavior Of 3D Printed Three-dimensional Geogridsand Interface

The interface parameters between the geogrid and soil are the key indicators to characterize the reinforcement and determine the safety and stability of the reinforced soil engineering.In order to enhance the interaction between geogrid and soil,the thicknesses of transverse ribs in conventional geogrids can be increased to form three-dimensional geogrids.However,the three-dimensional reinforcement materials in the past research mostly appeared in the form of pasting,binding or splicing vertical members on traditiongal planar geogrid,and the manufacturing process was complicated and difficult to apply in actual engineering.3D printing technology was used to design and produce the three-dimensional geogrid of different specifications,and the mechanism of the interaction between geogrid and sand were studied.The main contents of this paper are as follows:Four geogrids with different thicknesses of transverse ribs were fabricated by 3D printing technology.The effects of the thicknesses of transverse ribs,vertical stress(20,40,60 k Pa)and shear rate(1.0?2.5?5.0?10.0 mm/min)were investigated through a large-scale direct shear test.And adding the test results of the plane geogrid as a comparison were studied.A theoretical calculation formula for the passive resistance of transverse ribs is established.And the contribution of transverse rib thickness to passive lateral resistance is quantified.The results show that the three-dimensional geogrids has a stronger reinforcement effect compare with the plane geogrid.The apparent cohesion and friction angle are improved by the existence of the strengthened transverse ribs,both of which are promoted with the increasing of thicknesses of the transverse ribs.The thickness of transverse rib is the key factor to effect the passive lateral resistance,but the reinforcement effect cannot be fully exerted when the thickness is too large.Considering the reinforcement effect and economy,the thickness range of the strengthened transverse rib is between 12 mm and 15 mm is the best.Based on 3D printing technology,four kinds of three-dimensional geogrid with different transverse rib spacing and longitudinal rib spacing were designed respectively.Direct shear tests under different vertical stresses(20,40,60 k Pa)were carried out.The mechanism of threedimensional geogrid-sand interface was discussed,and the shear strength model was proposed.Compared with the test results,the correctness of the model was verified.The results show that three-dimensional geogrid-sand interface shows shear hardening in the middle and late shear period.With the decrease of transverse and longitudinal rib spacing,the dilatancy characteristics are enhanced.However,the effect of transverse rib spacing on dilatancy is more obvious than that of longitudinal rib spacing.The frictional resistance between sand and geogrid surface of theoretically calculated is about 15% to 30% of the horizontal shear force,and internal resistance of sand in opening area of geogrid is about 15%?35% of horizontal shear force.The passive resistance of the transverse ribs accounts for 37%?68% of horizontal shear force,and the contribution of passive resistance increases with the decreasing of the transverse rib spacing.Three kinds of sand with different particle diameters and three-dimensional geogrid with different aperture size were selected to conduct a series of monotonic direct shear tests.And the effect of particle size,vertical stresses,the percent open area of geogrid on the chage rules of friction angle,dilatancy angle and interface shear strength coefficient were analyzed.The interface dilatancy coefficient model was established,and effect of the average particle size and the percent open area of geogrid were quantitatively analyzed on the three-dimensional grid-sand interface dilatancy.The results show that the particle size has a more significant effect on apparent cohesive of the three-dimensional geogrid-sand interface,and has little effect on the friction angle.The maximum dilatancy angle decreases with the increase of vertical stress.It is found that when the particle size is larger and the percent open area of geogrid is smaller,the shear dilatancy is stronger.The shear strength coefficient is promoted with the increasing of particle size,indicating that the coarse particle has a better reinforcement effect with three-dimensional geogrid.