Study On Cause Of Formation And Mechanism About Ground Fissures Of Hejian District In The North China Plain

The North China Plain is a rift basin formed from Mesozoic Era. So far, there are many ground fissures having developed in The North China Plain, which is another region of ground fissures developing following Fen-Wei basin. These ground fissures have caused damage to all kinds of subaerial buildings, the subterranean engineering of pipelines, agricultural irrigation facilities. At the same time these ground fissures constraint the planning of urban-rural construction and land resource. Therefore, it is very important to perform the research on cause of formation and disaster-causing mechanism about ground fissures. Then this reseach will be help to work out effective counter measures. All this work will make very important social and economical sence to the effective prevent the people's life and property security from ground fissure geologic disaster.This paper, based on field investigation and indoor research, combined with numrical simulation analysis, summarizes the following main conclusions on cause of formation and mechanism about Ground Fissures of the North China Plain:1) The north China plain ground fissures'advantage extension direction mainly concentrated in NW85, NW55°, NE5°, NE30°, NE60°etc, which has obvious correspondence and consistency with the overall extension directions of the active faults formed in the north China plain;2) These ground fissures'regional activity is characterized with belt-like or forest-like-gathering characteristic in local area. Usuaslly, there where theground fissures hanppened is not a single ground fissure, but it is an ground fissures belt, constituted by one main ground fissure and several subprime ground fissures;3) The formation and development position of ground fissure is closely related to regional faults activities. Usually along active faults or nearby active faults zones, the ground fissures formed. At the same time, in the area where active faults intersect or active faults tempestuously developed, ground fissures happen, and the developing strength of ground fissures are related to the corresponding fault activities. These ground fissures have obvious regional characteristics; 4) According to its developmental mechanical mechanism, the ground fissures in the North China plain can be divided into two types:fault controled ground fissures and basal controled ground fissures:①Fault controled ground fissures are caused by the relative motion of broken block existing in the north China plain. The fault controled ground fissures are the upper soil response that the deep fault activities transmitted to the surface of the ground or fault activities caused the upper soil stress concentration.②In addition to the typical fault controlled ground fissures, there are many basal controled ground fissures, which are under the action of regional stress field, in a certain distance away from faults zone. The cause of formation and mechanism about this type ground fissures is:due to the basal pulling and shearring movement of the basal. This movement caused the crust changing thinner and made the upper soil overall thinning and rupture.