Grain breakage in shear bands and its effect on the permeability decrease of granular material specimens during Triaxial loading

This paper aims to achieve an experimental study on changes in permeability of non-cemented soils during shear.In petroleum engineering applications when fluid is injected under pressure in unconsolidated oil reservoir sands, it alters the stress state, particularly near the injection site, potentially increasing permeability due to dilatancy.Strain localization in shear bands near the injection well can affect porosity, which may either increase in the case of a band dilating or decrease due to grain breakage.The present study examines the effect of several parameters on grain breakage and permeability of sheared specimens using Triaxial loading on sieved sand (opening of 125m) with varying densities (medium density ID = 0.5, moderately dense ID = 0.7, and dense ID = 0.9).The experimental results showed a reduction in permeability after shearing despite the increase in the total void ratio in the dilatancy phase.This decrease in permeability was attributed to grain breakage specifically within the shear band.A key methodological advancement of this study is the use of specimen freezing after shearing to preserve the internal structure.This technique enabled precise cutting of the shear band, allowing for conducted necessary tests and investigate more closely the factors influencing the recorded responses.The grain size distribution analysis carried out on the three parts of the specimen (the bottom, the shear band and the top of the specimen), clearly indicates that the production of fine particles is primarily localized at the shear band.Permeability tests conducted on this same band after triaxial test revealed a decrease in the permeability despite the increase in the global void ratio.These findings have important practical implications for petroleum engineering and geotechnical applications.Understanding how grain breakage affects permeability can improve predictions of fluid flow in reservoir sands, optimize injection strategies, and mitigate potential permeability losses due to fine particle migration.This study provides a more comprehensive framework for evaluating permeability evolution in unconsolidated formations under shear stress, offering valuable guidance for reservoir management and enhanced oil recovery techniques.