Particle obstruction and crushing of dredged calcareous soil in the Nansha Islands, South China Sea

The bearing capacity of the dredged calcareous soil in the Nansha Islands, South China Sea typically exceeds that of terrigenous dredger fill. Furthermore, the shear strength of calcareous soil exceeds that of siliceous sand under identical conditions. It is mainly caused by the interparticle obstruction between calcareous soil particles. To explore the obstruction mechanism of calcareous soil particles, a series of triaxial tests were performed on calcareous soils under both consolidated undrained (CU) and consolidated drained (CD) conditions, respectively. Particle shape characteristics and particle crushing were also investigated to study the formation mechanism of obstruction force. Test results indicate that irregular particle shape is the prerequisite for the emergence of particle obstruction in calcareous soils. A simple obstruction-dilatation model was developed to describe the relationship among particle obstruction, dilation and particle crushing. The obstruction force varies greatly during the shearing process, which is mainly influenced by particle size and stress level. Under low confining pressure, particle obstruction results in dilatation and increases internal friction angle. In contrast, obstruction causes particle breakage, increases the apparent cohesion, and ultimately decreases the effective internal friction angle under high confining pressures. The particle obstruction of calcareous soil noticeably improves shear strength. Therefore, the effect of particle obstruction on strength should be considered in coral reef engineering design work.