Effect of Geogrid Layers on the Behavior of Unskirted and 0.4B-Deep Skirted Square Footings over Weak Dry Sand under Central Loading

Due to the limited clarification of the combined effect of geogrid layers and a 0.4B skirt on square footings over weak dry sand, this paper summarizes the bearing capacity of a square shallow footing with dimensions of 10 × 10 cm under central loading, with the footing resting on weak dry sand with a relative density of 30%. The experimental program compared a footing without a skirt and the same footing supported by a skirt with a length of 0.4B, where B represents the footing width. The soil was studied in five cases: unreinforced soil, one geogrid layer, two geogrid layers, three geogrid layers, and four geogrid layers. A skirt length of 0.4B was adopted to evaluate its effect on bearing capacity and settlement. The results showed that the footing supported by a 0.4B skirt without soil reinforcement increased the bearing capacity and reduced the settlement. Adding geogrid layers further improved the footing response; however, the improvement became limited after the third geogrid layer. Therefore, the use of three geogrid layers can be considered the most effective arrangement. The highest bearing capacity ratio (BCR) was obtained when three geogrid layers were used with a 0.4B skirt length, reaching about 3.50 times the reference case, which corresponds to an improvement of approximately 250%. For settlement, the settlement reduction factor (SRF) reached 0.790 for the skirted footing case. Therefore, the combined use of geogrid layers and a 0.4B skirt length provided a noticeable improvement in bearing capacity and settlement behavior compared with the untreated unskirted footing.