Abstract: Based on the special properties of loess, such as structure, water sensitivity and fissure, the systematic frame of engineering geological research on loess mass is established, including its research object, basic theory, contents, route and methods. It is pointed out that the research object is loess mass and the characteristics of structural planes and their associated engineering geological problems are studied little in engineering geological research on loess mass. Some problems, such as sort and grade of structural planes, structural types, surrounding rock classification and water sensitivity of loess mass, are also discussed. According to the scale and activity of structural planes in loess mass and their effect on the stability of engineering, loess mass structural planes are classified into 6 grades. And loess mass structures are divided into four types as homogeneous, stratified, columnar, blocky and cloddy pulverescent structures based on the sedimentation characteristics of loess, features of structural planes and range of engineering loess mass. To emphasize and strengthen research on those problems will be helpful to know the characteristics and solve the engineering geological problems of loess mass.

Key words: engineering geology of loess mass, systematic frame, loess mass, grading of structural planes, loess mass structure, surrounding rock classification