Geogrid-reinforcement and the critical state of graded aggregates used in heavy-haul railway transition subgrade

The geogrid reinforced graded- aggregates are occasionally used as top geotechnical layer in heavy-haul railway transit subgrade, but the effects of geogrid reinforcement on critical state are rare. The current study considers effects of geogrid reinforcement on critical state line locations of aggregates. For this purpose, a series of consolidated drained triaxial tests were conducted using a large-scale apparatus. Large specimens with various geogrid-spacing were used and a critical state of each specimen was obtained at a relatively large axial strain. The experimental results reveal that the geogrids inclusion causes upward unparalleled shift of CSLs in p-q space where the critical state stress ratio Mc increases with increase in geogrid reinforcement coefficient, Rf. Mathematical expression for critical state stress ratio and geogrid reinforcement coefficient is proposed during monotonic shearing procedure; the similar upward and unparalleled shift of CSL are also produced due to geogrid presence in v-ln(p) space where slope of NCL, λn, keeps constant but the slope of CSL, λc, increases with increase in dilation angle. An empirical equation is set up to express the relationship between, λc/λn, and dilation angle. These experimental findings are helpful for modeling aggregates when considering geogrid reinforcement and dilative behaviors.