The Research On Stability And Protective Measures Of Special Geological High Slope In KKH Ⅱ

With the construction of the second phase of the Karakorum Highway(abbreviated as KKH Ⅱ),a large number of phyllite high slopes were excavated along the route.The stability of the slope affects the normal operation of the highway.Therefore,this paper established the finite element numerical model focusing on the dominant failure mode of the phyllite high slope,analyzing the failure process based on the strength reduction method.Sensitive analysis of the slope parameters and anchoring parameters was conducted and the excavation process was simulated to provide a reference for slope construction and protection.Firstly,on the basis of the survey and design data of the KKH Ⅱ,the influencing factors of the stability of the phyllite high slope were analyzed.The dominant failure mode of the phyllite slope was bedding landslide along the weak interlayer.According to the data of twelve high phyllite slopes,the No.9 slope gained the highest score with 79 points by means of the slope engineering risk assessment method.Consequently,it was selected as the basis for the subsequent ABAQUS model.Secondly,a typical high slope model containing weak interlayer was generated in ABAQUS.The slope safety factor(Fs)was calculated as 1.092 employing the strength reduction method and the failure process of the slope was described.The rationality of the model was demonstrated by comparing with two model,one without weak interlayer and the other including multiple weak interlayers.Sensitivity analysis was conducted regarding the parameters of the weak interlayer and the geometric parameters of the slope,which affected the stability of the slope.It was found that all the parameters except the single grade slope ratio had a linear relationship with the slope safety factor.The order of the sensitive coefficient of the slope weak interlayer parameters was: interlayer dip angle > internal friction angle > cohesive force > thickness,and the value was 0.772,0.663,0.308 and 0.005 respectively;the order of the sensitive coefficient of the slope geometric parameters was: single grade slope ratio > slope height > single grade slope height > platform width,and the value was 0.971,0.396,0.093 and0.039 respectively.Then,the bolt support simulation was performed.The safety factor increased to 1.709 by57% and the maximum horizontal displacement decreased to 10.6cm by 70% when slope failed.The result indicated that bolt support functioned positively.Through the sensitive analysis of the bolt parameters,the order of sensitivity coefficient was: bolt spacing> bolt length> bolt angle,and the value was 0.512,0.448 and 0.123 respectively.According to the relationship between the bolt parameters and the safety factor of the slope,the optimized scheme was bolt length at 16 m,bolt angle of 15 degrees,and bolt spacing of 3.4m.Finally,the excavation process was simulated.It was indicated that excavation at the foot of the slope would cause a rapid increase on horizontal displacement.During the excavation,the appearance of the weak interlayer raised the plastic strain.The tensile stress of 46 to 91 k Pa was distributed on the slope surface,which was likely to promote surface crazing and the recommendation was strengthening the observation during construction.After that,by comparing four excavation anchoring schemes,it was found that the scheme of excavation and anchoring step by step could keep the slope safety factor always at a relatively high level,and this scheme should be adopted preferentially in the construction process.