Experimental analysis of compression bearing characteristics of multi-layer geogrid-encased aggregate column based on digital image measurement technology

Abstract

Multi-layer geogrid-encased aggregate column(GEAC) has enhanced bearing performance, cost-effectiveness, and eco-friendliness for soft ground treatment due to the extra lateral confinement from the multi-layer geogrid encasement. To analyze the bearing behavior of GEAC, indoor compression tests were conducted on GEAC with different aggregate sizes, aspect ratios, and encasement layers, using digital image measurement and other techniques. The effects of these parameters on the failure mode, load capacity, and aggregate displacement of GEAC were investigated. The results indicate that: among the aspect ratio, encasement layer, and aggregate size, the encasement layer is the most influential factor on the bearing performance of GEAC, and increasing the number of encasement layers can significantly enhance the load capacity of GEAC; the failure mode of GEAC is buckling when the aspect ratio exceeds 5.33, and is bulging when the aspect ratio is equal to or less than 5.33; in the local region of GEAC, the remarkable horizontal relative displacement of the aggregates is the main cause of the shear band formation; under unconfined compression, the “net pocket effect” of the multi-layer geogrid encasement layer prevents the local stress concentration in GEAC, which helps to resist local failure and delay the yielding and failure of GEAC. Under confined compression, the overlapping part of the multi-layer encasement also increases the lateral contact area between GEAC and the surrounding soil, enhances the radial confinement and the lateral friction of the soil on GEAC, effectively improves the ultimate load capacity, and reduces the compression of GEAC.