The Study On The Genetic Mechanism Of The Paleo Channel Ground Fissures In The North China Plain

The north China plain is widely developed in the ancient rivers.There are many rivers such as the yellow river,Zhang river and Chaobai river disturbed in the area.The tectonic fault and secondary block distribution,tectonic activity and the uplift and decline of the secondary block make the ancient river Diversion,which caused the ancient river to change,and then caused the rich old river bed landform in north China plain.The ancient river is the dependent carrier of ground fissures,because of its special formation property,shape and burial depth,it produces a kind of atectonic fissure which called the old channel fissure.Taking the ground fissure of Daming county as an example,this paper discusses the cause mechanism of ancient paleochannel fissure,not only enriches the genetic mechanism of cracks in north China plain,but also provides theoretical basis for disaster prevention and reduction.By consulting and collecting relevant geological data,the distribution law,lithology characteristics and geological structure of the shallow buried river in the north China plain are found.Taking the ground fissure of Daming county as a typical example,through field geological investigation,the distribution characteristics of paleochannel fissure are basically found out.Using drilling and trenching exploration as a technical means,the section structure characteristics of ancient paleochannel fissure are revealed.On this basis,the influencing factors and genetic model of old channel fissure are discussed.Finally,through the numerical simulation study,the influence of the buried depth of the overlaying soil and the initial underground water level on the formation of ground fissures in the old river channel under pumping action is discussed and analyzed,and the development regularity and genetic mechanism of the fissures in ancient river channel under pumping action are summarized.The main findings of the study are as follows:(1)By consulting and collecting the geological data related to the north China plain,the geological tectonic activities and the geological and geomorphological environment of the ancient river in north China plain are analyzed,and the formation characteristics and development rules of the ancient river channel are explained.(2)Through the field geological survey of north China plain,according to the existing ground fissures investigation data,combining the development of ancient river channel and ground fissures,the fissure distribution map of ancient river channel in north China plain is drawn.(3)Taking the ground fissure of Daming county as an example,according to the profile characteristics of trenching exploration and drilling,and combining the distribution of ground fissures and the development regularity of strata,the plane and section characteristics of paleochannel fissure are analyzed.(4)Based on the correlation between the occurrence of ground fissures and the space-time correlation of pumping,earthquake and rainfall,combined with the special geological characteristics of ancient river channel,the three genetic models of paleochannel fissure formation are discussed,and the formation differential settlement of pumping formation is the main cause of formation.(5)Through numerical simulation of ground fissure mode caused by differential settlement of water pumping in ancient river channel,the development characteristics and formation mechanism of the fissure in old channel under pumping action are analyzed,and the influence of buried depth and initial groundwater level on the formation of ground fissures is discussed.