Improving the punching capacity of footings using geocell, geogrid and granular soil replacement.

Punching failure in footings occurs in thin pads that is subjected to heavy concentrated loads, such as concrete pads below racks' supports in heavy storage facilities. Since the punching capacity depends on the stress distribution beneath the footing, it could be enhanced by improving the soil stiffness beneath the footing. This research examines the effects of geocell layers, geogrid layers, and base soil stiffness on the punching capacity of isolated footings. Seven identical footings were subjected to experimental testing until failure, with continuous monitoring of load, settlement, strain in rebars, and contact pressure. The control footing was rested on pure sand; two footings were rested on one and two geogrid layers, two footings were rested on one and two geocell layers and the last two footings were rested on pure crouched stone and mixture of sand and crushed stone. The results indicated that all footings exhibited pure punching failure. In addition, enhancing the base granular soil stiffness through geocell confinement, geogrid reinforcement, or replacement with stiffer soil concentrated contact stress under the load, thereby increasing punching capacity, reducing settlement and increasing the subgrade reaction at the center while decreasing it at the mid-edge and corners. The efficiency of geocell and geogrid layers depends on their proximity to the footing; the closest geocell layer was most efficient, while the closest geogrid layer was least efficient. Implementing geocell layers, geogrid layers, and soil replacement improved punching capacity by 20%, 11%, and 17%; subgrade reaction values at the center by 90%, 65%, and 200%; and reduced settlement at the center by 70%, 75%, and 45%, respectively.