Abstract: Microstructure unit of the offshore clay— clay domains contains a large amount of intragranular pores, of which the diameters are small to nanoscale. These pores have an important influence on the physical indices, water stability, expansion and shrinkage characteristics. However, general methods are difficult to accurately describe intragranular pore characteristics. The scanning electron microscopy (SEM), mercury porosimetry(MIP), nitrogen adsorption(NA) are used on the Zhanjiang clay to study its microscopic pore characteristics and control factors of pore distribution. The relationship and sensitivity analysis of the microstructure and physical parameters, mechanical behavior are established. Results show that the Zhanjiang clay has the unusual combination of poor physical properties and good mechanical properties; it is a kind of high sensitivity and strong cementation structural clay, the main mechanism was disorderly orientation and open flocculation structure with cementation bond; furthermore , pore structure is a space frame system which has higher strength and stability of the side-surface-angle connection. Therefore, the retention phenomenon of mercury-ejection curve and hysteretic loop in adsorption-desorption isotherm occurring because of special space frame system and ‘ink bottle’ type pore. In addition, the research shows that, the combination of SEM, MIP, NA methods can accurately , qualitatively and quantitatively evaluate overall pore system characteristics of offshore clay.

Key words: Zhanjiang clay, scanning electron microscopy(SEM), mercury intrusion porosimetry(MIP), nitrogen adsorption(NA), microscopic pore；pore size distribution