Study on the deformation behavior of slope by considering cohesion degradation and friction mobilization

• Main Authors: Chien-He Lee, 李建和
• Other Authors: Zon-Yee Yang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/98992555025718731091

碩士 === 淡江大學 === 土木工程學系碩士班 === 101 === In slope stability analysis, the coefficient of friction angle and cohesion adopted in Mohr-Coulomb failure criterion are kept constant. The friction angle and cohesion are assumed simultaneously to reach the peak value. However, the experimental result show that the cohesion (C) is decreasing rapidly after shearing from the maximum value to a constant residual value. The friction angle is increased to the peak gradually. In this thesis, FLAC is used to study the slope stability by considering the degradation in cohesion strength and the mobilization in friction strength according to the plastic shear strain of slope deformation. The following conclusions are drawn: (1) Using ‘C then ϕ’ concept to obtain C and ϕ value during shearing, it is found that C value is decreasing with shear displacement, but ϕ value is gradually increasing. The value of C and ϕ is not always kept as constant during shearing. The shear strength of soils by shearing is contributed first by the cohesive effect between soil grains and followed by the grain friction effect. (2) The value of friction angle is mobilized to the peak (ϕ p) after several displacement, but the initial value of cohesion is the maximum. At the peak shear strength state, the friction angle of soils reaches to the peak and the cohesion decayed to a residual value. The delayed friction effect in shear strength for cohesive soil is more obvious than that for cohesionless soil. (3) The maximum value of cohesion intercept using ‘C then ϕ’ concept is greater than the value of cohesion used in Mohr-Coulomb criterion. However, these two peak values of friction angle are very close. (4) The lateral displacement of slope in FLAC modeling using ‘C the ϕ’ concept is greater than that keeping C and ϕ as constant value. The fracture propagation of slope to form the failure surface is remarkable in FLAC modeling using ‘C the ϕ’ concept. The safety factor of slope stability obtained by using the ‘C the ϕ’ concept is smaller than that keeping C and ϕ as constant. This difference is more significant in sandy soils with high fraction angle and low cohesion. However, there is little difference in clayey soils with high cohesion and low frictional angle.