Characteristics And Stress Analysis Of Joints In The Longgang Area Of Pingchang Country, Central Sichuan Basin

The tectonic deformation is relatively weak and rock strata are nearly horizontalin Longgang area of PingChang county within central Sichuan Basin. The authorob- served more than 4200 joints in the surface strata, and found the geometric characteristicsof joints are: the joint surfaces are straight and the opening degree of joints'is small , the EW-trending is the dominant orientation of joints', the high dip angleis predominant of joints', the extended distance of joints'is generally less than 7m,and the horizontal distribution characteristic of joints'is sparse alternate with dense.Ba- sis for the development characteristics and the movement properties of the joints',and followed the mating principle of conjugate shear joints, and divided them intofour sets of conjugate joints, characterized by NE-SW and NW-SE trend, NNWNNEand NEE-SWW trend, NW-SE and NE-SW trend, and NNE-SSW and NWWSEEtrend. The movement of joints'is mainly with the trust motion; the strike- slipmovement takes the second place. The principle of determination of conjugate joints,the method of structural analysis, and the cutting relation of the joints, were appliedto the study of the paleo-stress of 100 conjugate joints. It was indicated that the principlecompressive stress field in the Longgang area had shifted from EW to NW-SE,NS, and finally NE-SW.Interpreted the faults of 3-D seismic data of Long Gang area, by using software'Discovery 2004'and'Kingdom'. On the basis of fault interpretation result, throughsettiing up rational geological model, mechanics model and mathematics model, using2-D finite element method, a numerical simulation of modern tectonic stress fieldof the second member of Shehejie Formation has been realized in Longgang area.The level maximum principal stress, minimum principal stress, and shear stress valuewere calculated, the distributing characteristics of the maximum principal stress distribution have an obvious nonuniformity. The zones of predicated tectoclase developmentare mainly controlled by faults, and distributed along the area of fault.