Geogrid bridging over existing shallow flexible PVC buried pipe – Experimental study

Abstract

Protecting existing utility lines in congested urban centers is considered a major challenge especially in cases of new construction bridging over these lifelines. Several innovative techniques have been proposed lately to bridge over existing pipes. This study discusses the use of stiff three-dimensional geogrids to reinforce sandy soils bridging over existing buried Polyvinyl Chloride (PVC) pipe at shallow depth subjected to strip static loading. Twenty-eight large scale laboratory tests were conducted with variable geogrid geometries using single and double layers of geogrid reinforcement. Tests were heavily instrumented to record longitudinal and transverse strains in the pipe wall and geogrids, pipe deflections, pressures within the soil and above the pipe crown, and footing settlement. Optimization of the geogrid geometry was conducted in order to reduce strains and stresses in the PVC pipe subjected to static loading. In general, introducing the geogrid reinforcement has reduced stresses transferred to the pipe crown below the center of the loading. For a given applied stress, the increase in geogrid width has resulted in a reduction in stress transferred to the pipe and longitudinal strains developed in the pipe. Up to 80% reduction in longitudinal strains was observed in the PVC buried pipe as a result of the geogrid reinforcement. Finally, the results have shown up to 150% improvement in soil bearing capacity and nearly 50% reduction in surface settlement as a result of introducing geogrid reinforcement. The main finding in this study is that three-dimensional geogrid reinforcement was effective in reducing the longitudinal strains in existing PVC shallowly buried pipes subjected to static loading.