REINFORCEMENT OF PASSIVE AREA AGAINST THRUST FORCE FOR BURIED BEND USING GEOSYNTHETICS

Thrust forces can be generated at the bend of a pipeline due to internal water pressure. Commonly, the thrust force is resisted by passive resistance acting on the bend. A concrete block can be installed at the bend when the thrust force is larger than the passive resistance. However, the heavy concrete block can become a weak point during an earthquake, because the concrete block moves largely due to inertia force. Therefore, new methods for thrust restraint are required. In this paper, new backfill methods for thrust restraint using geogrids are proposed. The new method comprised geogrids, installed in the passive area to improve the strength of the ground. In addition, gravel was used as backfill material in the passive area of the bend. In order to verify the effect of the proposed methods, lateral loading experiments were carried out using a model pipe with a diameter of 114 mm. The model pipe was backfilled with dry sand. After backfilling, the model pipe was laterally loaded at 0.5 mm/min. using a jack. The lateral resistance and lateral displacement acting on the model pipe were both measured. It was confirmed that the lateral resistance increased when using the proposed methods.