Abstract: Loess joints are the places where groundwater exists and migrates. They break the soil, and affect the stability and strength of loess, causing enormous losses on both economy and human lives. Joints are the structural basis of all kinds of loess disasters. Accurate analysis of its development characteristics and distribution rules is crucial to understanding the frequent occurrence of loess disasters. Through systematic field investigation, mathematical statistics and topological analysis of loess in Longxi, we found that: (1) The dominant strikes of loess tectonic joints in Longxi are NNW,NWW and NE, which is influenced by strike-slip fault and reverse tilting fault.(2) The occurrence of dominant tectonic joints group obeys the Gaussian normal distribution, with the dip angle mostly within 60-80°. The occurrence of vertical joints are more randomly distributed and highly discrete. (3) The average spacing of both tectonic and vertical joints is wide, the opening of joints belongs to “crack” in standard, and the continuity medium, except that the spacing of vertical joints is more concentrated, while the opening of tectonic joints is smaller by comparison. (4) Topological analysis shows that I-node is the majority. Joints extension process is easily interrupted. Branch ratio is at a low level below 3. Topological analysis is more simple and intuitive to describe connectivity, especially under the help of powerful toolbox in software, and has been discussed for decades in the world, yet is rarely used in relative research in China. The research results provide basic data for the recovery of Neotectonics stress fields, for understanding the basic laws of joints development and the numerical modeling of joints network.

Key words: loess, joints, geometrical features, topological analysis, connectivity