An in-soil tensile test apparatus was developed to investigate the in-soil load-strain relationships of geosynthetics. The strain-controlled tests were performed to evaluate the influence of soil type, confinement pressure and vertical spacing on the reinforcement in-soil stiffness of the different geosynthetics. A nonwoven geotextile, a woven geotextile and a geogrid were tested under sand and gravel confinement. For all reinforcements used in this study, tests showed that reinforcement in-soil stiffness increases under soil confinement. The influence of confinement is greater in gravel. The stiffness increase depends on the type of geosynthetic, with the greatest increase observed for nonwoven geotextiles and the least for geogrids. Regression models were derived to represent the load-strain relationships of the geosynthetic. The segmental design of the test box enabled the placement of passive reinforcements both above and below the reinforcement to which the tensile load was applied. This was done to examine the effect of passive reinforcements on the load–strain behaviour of the geogrid at varying vertical spacings. The passive geogrid reinforcements caused an enhancement of in-soil stiffness when confined in gravel but showed minimal impact in sand. This was interpreted as due to the larger influence zone of the gravel-geogrid interface.
Yardimci et al. (Mon,) studied this question.