Experimental investigation on dynamic properties of muddy sand from Pearl River Delta of China

Abstract

Muddy sand, which comes from a sea-land cross sedimentary layer containing a large number of skeletal residues from marine organisms, has different internal structures compared with other types of sand. The dynamic characteristics of the muddy sand needs to be studied owing to a great risk of earthquakes, which are prone to liquefaction and large ground deformation. In this study, a series of undrained cyclic loading tests were carried out on both undisturbed and remolded saturated muddy sand, which was excavated from Pearl River Delta of the South China Sea. A concept of pore entropy (PE) was taken based on microscopic tests, to analyze the liquefaction characteristics of saturated muddy sand from the perspective of the microstructure. The results show that the inflection point appears in axial strains for both undisturbed and remolded saturated muddy sand, but the stress and strain path of the undisturbed specimens shows better plasticity and ductility due to the structure of undisturbed soil. In the stage of initial liquefaction, the strain is 0.5–2% and the damping ratio (λ) is 0.35–0.55. When the relative density (Dr) exceeds 0.7 and the cyclic stress ratio (CSR) is <0.1, no liquefaction occurs in muddy sand. Due to the existence of mud, the particles in the soil appear stationary. CSR and loading frequency (f) are sensitive to the change of particles in soil. This study provides a theoretical and experimental results to reveal the relationship between the microstructural evolution and liquefaction properties of muddy sand. It can provide a useful reference for the safety of submarine engineering design and construction.