ENGINEERING GEOLOGICAL FEATURES FROM BOREHOLE CORES FOR TYPICAL LOESS SECTION IN BAOJI REGION OF LOESS PLATEAU

A new complete loess profile has been found in Baoji region of the Loess Plateau in recent years.Based on this profile,this paper presents a study of the features of loess engineering geology.The loess is about 200m thick and formed from Holocene epoch to Lower Pleistocene epoch.The study is based on a detailed field investigation of typical loess section at Jiacun Terrace in Chenchang of Baoji region.Borehole drilling in the typical loess layer was conducted.Approximately undisturbed cores were obtained for the entire borehole depth.Subsequently,a systematic laboratory tests were carried out for the physical and mechanical parameters and material formation of the cores.The data was for the analysis of landslide mechanism and prevention.The test results show that 1)there is an inverse correlation between density and porosity ratio,2)there is a positive correlation between liquid limit and plastic limit along with the borehole depth, 3)there is an inverse correlation between modulus of compression and compressibility factor,and 4)there is an inverse correlation between internal cohension and internal friction angle with large variation range along the borehole depth.The analyses on the grain size analysis,carbonate content and major clay minerals of the typical loess show that a)there is a positive correlation between the 0.075mm to 0.010mm grain contents and the carbonate content,b)the grain and carbonate contents have an inverse correlation with the internal cohesion and a positive correlation with the internal friction angle,and c)there is a positive correlation of the less than 0.002mm colloid particle contents with the mixed-layer mineral of illite and montmorillonite,illite,kaolinite and other major clay minerals,and d)the less than 0.002mm colloid particle contents also have a positive correlation with the internal cohesion and an inverse correlation with the internal friction angle.The systematic test results presented in this paper will have an important significance to increase the scientific degree and reliability of loess landslide risk assessment.