Abstract: Zhanjiang formation formed in early Pleistocene is widely distributed in Leizhou peninsula in China. The most typical gray clay of Zhanjiang formation is known as its strong structural performance and had produced a series of geotechnical engineering problems in actual engineering. According to the stratigraphic research, this typical gray clay of Zhanjiang formation has different sedimentary environments and compositions in different areas of Leizhou peninsula. Thus, the differences of geologic origin make the engineering properties of gray clay changing with the area. In the actual projects, it is difficult for engineers and researchers to master the engineering mechanics effect of gray clay due to its regional characteristics. Some tests by X-ray diffraction and scanning electron microscope (SEM) are carried out to study the microstructure characteristics of gray clay such as mineral composition and its content, and microstructure in different areas. The results show that there are differences of mineral composition and its content. Different proportions of mineral composition compose different microstructures of gray clay which have obviously regional characteristics. The revelations of micromechanism of gray clay which lead to its strong structural performance and the analysis of its regional characteristics make for cognition and use of this clay.

Key words: Zhanjiang formation, structural clay, strong structural performance, microstructure, regional characteristics