A study of the genesis mechanism and model of Longyao ground fissures in Hebei plain

The Longyao ground fracture is the tectonic ground fracture with a largest scale, which is one of the strongest activity and the most serious degree of disasters in North China Plain. However, the cause of formation between the Longyao ground fracture and faults were seldom examined and complete demonstration materials and systematic theoretical analyses are lacking. Based on field investigation, including trenching, physical exploration and joint borehole profile, etc, this paper analyses the planes, profiles and deep characteristics of ground fissures and discuss the genesis mechanism and mode of the Longyao ground fissures. The development location of the Longyao ground fissures (western part) coincides with the Longyao fault. The ground fissures trends in EW direction, dip south with 60~80 degrees, and is of normality. The ground fissure surface development scratches in the clay layer, the branch fissures in the hanging wall intersects with the main fissures to form a “y” shape, and the displacement between the hanging wall and foot wall increases with depth. The depth of the Longyao active fault upper break poin is 40~50 m by the interpretation of exploration, and the joint borehole profile reveals that the downward extension of the ground fissures coincides with the upper break point of the buried faults. The Longyao ground fracture is directly connected with the Longyao active fault. According to the above genetic theory, a genetic mode of structural ground fissures, fault direct shear type, is proposed. On the basis of regional stress strengthening or transformation, the hidden faults in the base began to creep and slide, the fault surface or fault zone extended to the surface, cut through the Quaternary rock and soil layers, and formed scarps on the surface. The formation, appearance and development of the Longyao ground fissures are analyzed. The results provide theoretical guidance for the study of the cause of ground fissures of direct shear type.