THE EFFECTS OF SOIL REINFORCEMENT WITH GEOGRID AND GRID-ANCHOR SYSTEMS ON UPLIFT CAPACITY OF BURIED PIPELINES

Reinforcing soils with geosynthetics is an effective method for improving the uplift capacity of buried pipelines.The pullout resistance of the reinforcing elements is one of the most notable factors in increasing the uplift capacity. In this paper, a new reinforcing element including the anchors attached to the ordinary geogrid, namely grid-anchors, was used for increasing the pullout resistance of the geogrid. An experimental study was performed to investigate the uplift resistance of the pipelines buried in sand reinforced with this system. Then, 37 experimental models and 33 numerical models were conducted to investigate the effect of pipe diameter, soil moisture content, soil type, pipe burial depth, the location of reinforcement layers installation, as well as the number of reinforcement layers and the width of reinforcement layers on the uplift resistance of granular soils. The PIV method reveals that due to a developed longer failure surface, inclusion of grid-anchor system in a soil deposit significantly increases the uplift capacity. Therefore the grid-anchor system of reinforcing can increase the uplift capacity 2.5 times greater than that for an ordinary geogrid and 4 times greater than that for non-reinforced sand. Compared to the multilayer reinforcement, the single layer reinforcement was more effective in enhancing the uplift capacity. Besides, the efficiency of reinforcement layer inclusion for uplift resistance in lower embedment ratios is higher. In addition, by increasing the pipe diameter, the efficiency of the reinforcement layer inclusion will be lower. There appears the efficiency of reinforcement layer inclusion for uplift resistance in the single layer reinforcement with higher width and installed in the pipe bottom; lower embedment ratios and lower pipe diameter are higher. To verify the experimental results and completion of research, the finite deference software FLAC-3D was used. It was found that experimental and numerical results were in good agreement.