Influence of non-plastic fines and density state on stress-dilatancy behavior of coral sand: an experimental investigation

Understanding accurately the influence of non-plastic fines on stress-dilatancy of coral sand mixture-packing is crucial for marine engineering in various geotechnical applications. This work experimentally examined the effects of non-plastic fines and initial test conditions on stress-dilatancy behavior of mixture. Based on test results, equivalent void ratio (\({e}^{*}\)) was determined to quantify the global effect of fines on shear behavior across different shear stages. Test results show that \({e}^{*}\) exhibits a reduction as the mean effective stress (\({p}{^\prime}\)) increases, following a power function relationship. Besides, \({e}^{*}\) variation under phase transformation, peak state, and critical state can be described by a normalized curve. Reduced fines content and increased relative density can contribute to the enhancement of both peak strength and internal friction angle within the mixture. However, the smooth shape and lubrication function facilitated by fines actively contribute to initiation of shear contraction. Furthermore, the stress paths observed in the CD shear tests manifest as a sequence of parallel straight lines within the \(q\)-\({p}{^\prime}\) plane. The length of these lines progressively extends as the stress level escalates. Moreover, deviator stress in \(q\)-\({p}{^\prime}\) curves under character state presents lower and upper limits which are 0.334 and 0.639 corresponding to tested samples determined by fines content and relative density. Elevated fines content combined with reduced relative density can lead to a reduction in both peak-state friction angle and maximum angle of dilation.