Static And Dynamic Interface Shear Properties Of Soil/Geosynthetics Systems

Since the intruction of reinforced soil technique in the1960’s, it has been usedwidely for its remarkable economical benefit by saving25%~65%of total cost andsignificant advantages such as quick construction, beautiful shape, smaller areaoccupation, etc. The interaction characteristics of soil-geosynthetics interface directlyeffect the stabilization of reinforced structure and play a critical role in designingreinforced soil structures. Therefore, a series of large-scale direct shear tests,including interfaces of some frequently used geosynthetics against Fujian standardsand, have been conducted to investigate the interface behavior systematically. Themain conclusions are as follows:1. For the reason that soil as subgrade filling has different characteristics, Aseries of large scale direct shear tests, involved three kinds of sand with geogrids andgeotextiles, were performed to investigate the interface shear strength and dilatancy ofsoil against geosynthetics.The effect of particle-size distribution, dense degree, typesof geosynthetics and vertical stress on interface shear strength and dilatancycoefficient were investigated. The test results show that coarse sand and finesand/geosynthetics interface have significantly higher shear strength than mixed sand.Loose sand-geosynthetics interface displays only shear contraction during the shearprocess while dense sand-geosynthetics interface presents obvious dilatancy. At highstress level, sand-geosynthetics interface has larger shear displacement when itreaches peak shear strength than that of low stress. Coarse sand-geogrids interface haslarger shear displacement when reaching peak strength than that of coarsesand-geotextile, while fine sand-geosynthetics interface shows the opposite results.2. A series of large scale direct shear tests are performed to investigate theinfluence of longitudinal/transverse ribs and aperture pattern on the interface shearbehavior of soil against geosynthetics. The test results show that both the longitudinaland transverse ribs play an important role in improving the interface strength througha different course of inaction. The shear force of interface will be shared by passiveresistance of transverse ribs and friction resistance of longitudinal ribs when sheardisplacement is small, while the longitudinal ribs present the role of framework toimprove the geogrid stiffness with the increasing of transverse resistance due to the ofshear displacement increasing. Therefore, coordinate work of transverse and longitudinal ribs will help advance the interface shear strength.3. A series of large scale interface cyclic shear and monotonic shear tests wereperformed to investigate the dynamic behavior of interface between soil andgeosynthetics. The effect of normal stress level, shear amplitude and cyclic number onthe interface shear strength and dilatancy were investigated, including the comparisonof cyclic and monotonic shear tests to analyse the post-cyclic interface behavior. Thetest results show that the growth rate of cyclic strength becomes more flat with theincreasing of normal stress, that is to say the increase of cyclic shear stress is moresensitive under lower normal stress. The shear dilatancy/contraction of interfaceincreases with the shear amplitude. Interface strength and vertical displacementimproves with the increasing number of cycle.4. Based on the test results, a combined constitutive model has been presentedfor predicting sand-geogrid interface behavior. The model is composed of fourrelationships:(1) the peak/residual shear strength envelope;(2) a hyperbolicrelationship model of shear behavior in pre-peak region;(3) a displacement-softeningmodel for post-peak region;(4) modeling for shear dilatancy of sand-geogrid interface.The predictions made by the proposed model are found to be in good agreement withother experimental results obtained from direct shear tests, so it is considered to bereasonable.