DYNAMIC PULLOUT RESISTANCE OF SOIL REINFORCEMENTSUSING STRESS CONTROL APPARATUS

摘要

Heavy structures on weak soils may cause failures. Some modern heavy structures may warrant soilimprovement measures even for strong soils. Reinforcing earth increases strength, elastic moduli, andrange of stresses with elastic behaviour and reduces strains. Tensile failure of geotextile reinforcementsleads to catastrophic failures, especially under dynamic loads, which may be avoided if ultimate pulloutresistance of geotextiles is less than its tensile strength. It makes pullout resistance an important designdata. Geotextiles under pullout forces exhibit ductility, which is important in earthquake engineering.Equipment cited in present day state of the art to determine pullout resistance of geotextiles is of straincontrol type, which overestimates pullout resistance. This is unsafe. Stress control apparatus are superiorand have not been reported in the state of the art. This presentation deals with a stress control apparatus toobtain pullout resistance of geotextiles embedded in sand placed in a 300 mm x 300 mm direct shear box.Sustained pullout force is applied by suspending dead weights to a string attached to geotextile. Dynamicpullout forces are created by exciting test box with an eccentric drive powered by a DC motor-speedcontrol unit. The apparatus can control frequency and amplitude of vibrations, apply desired normalstress, measure pullout forces, displacements and accelerations using suitable transducers and dataacquisition system. Results indicate that for a given displacement amplitude of test box, pulloutdisplacement increases nonlinearly with reducing normal stress, reducing sustained pullout stress,increasing frequency of excitation, increasing dynamic pullout stress and increasing number of cycles ofdynamic pullout force, which are expected. Angle of mobilized dynamic pullout resistance is significantlylower than angle of shearing resistance of soil from direct shear tests. Pullout displacement dependentdata obtained this way has important applications in designs of reinforced earth structures under static anddynamic loads.