利用扫描电镜、压汞法、氮气吸附法评价近海黏土孔隙特征

Study of pore characteristics of offshore clay by SEM and MIP and NA methods

近海地区黏土的微观结构单元——黏土畴中含有大量的粒内孔隙,其孔径小至纳米级,这部分孔隙对黏土的物理指标、水稳性、膨胀性、收缩性等具有重要影响,一般方法很难准确地描述其孔隙特征。试验利用扫描电镜、压汞法、氮气吸附法对湛江黏土的微观孔隙特征及其孔隙发育的控制因素分析,建立微观结构与物理指标、力学行为的相互关系与灵敏性分析。结果表明,湛江黏土具有不良物理性质和良好力学特性指标的异常组合,是一种高灵敏性的强胶结结构性黏性土,其机制主要是:湛江黏土的微观结构为带有胶质联结特性的、定向性无序的开放式絮凝结构,孔隙结构为具有较高的强度和空间稳定性的边-面-角联结的空间网架系统。由于特殊的孔隙网架结构以及"墨水瓶"型孔隙的存在,导致退汞过程出现滞留现象及产生吸附回线。研究表明,联合扫描电镜、压汞法、氮气吸附法能够准确、完整地对近海地区黏土孔隙体系特征进行定性与定量的评价。

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.