The Study On The Formation Mechanism Of Ground Fissures By Irrigation Action

Beibao village is the intensive distribution of ground fissure disasters in the town ofFengcun,the causes of the cracks are complicated,in fact,are also essentially a variety offactors under the action of a comprehensive effect.By the study of the spatialdistribution,profile features and failure characteristics of the cracks,combine with thegeological background,analyse the main factors of formation of cracks,and on the basis ofthese,discuss the inherent formation mechanism of the cracks.Firstly,though-the-spot investigation,and on-site visit to the trenching,explorationwells,drilling,seismic-prospecting,and so on,revealed the Beibao village had two maindevelopment direction of ground fissures,the four esat-west and three north-southcracks.Ground fissure is mostly present in the form of discontinuous shape sinkhole,on theprofile most cracks are nearly vertical,on a wide and below narrow.East-west fracturedistribution and concealed basement tectonic activities with obvious corresponding relation,and north-south cracks mostly distribute in the loess gully,or near the canal.Secondly,through the analysis of survey data and research,about the causes of crackshave the following understanding:first of all,on the northern side of east-west cracks DBf1isthe secondary breakdown formed the tray of Yanjiazhuang—Shuangquan—Jinshuigou activefaults in tensile stress concentration,fracture structure has mainly control function with theformation of cracks,and these are the tectonic transition zone controlling ground fissures;inthe second, DBf2～DBf4mainly controlled by regional tectonic stress field,the author thinksthat,the intersection of the NEE fracture(Yanjiazhuang—Shuangquan—Jinshuigou activefaults) and the NW fracture(Pucheng—Dali concealed fault) easily form a few EW cracks;inthe third,infiltration of surface water caused by heavy rainfall or irrigation have induced effecton activity of the ground fissures,and can cause ground fissrue repeated opening andclosing;fourthly,North-South cracks,because of the particularity of its position ofdevelopment,are non tectonic ground fissures caused by the loess collapsibility deformation.Finally,the section of cracks in the study area has the appearance of the surface water,andreflect the ground fissures certainly correlate with the earthquake activity,but restricted by siteconditions and a shallow groove excavation,on the profile unseen the phenomenon of sandblasting,failed to give accurate interpretation about seismic activity on the influence of theground fissures.As you see,the study of beibao cracks would need more detailed analysis.