Significant geological features 215 7.3 Geology and mode of slope failure 218

Planar or two-dimensional failure mode 219 7.4 Landslide classification 220

Fall 221 Topple 221 Slides 222 Flow 225 Rate of movement 227 Additional classifications 227

7.5 Landslide triggering mechanisms 228 Creep 228 Rainfall 228 Rainfall intensity and rainfall amount 229 Antecedent rainfall 235 Infiltration 239

7.6 Stability analyses 242 Why do landslides occur? 242 Types of stability analyses 242 Factor of safety definition 243 Factor of safety calculation 244 Semi-infinite method 245 Limit equilibrium method of slices 248 Total cohesion method 250 Extended shear strength method 251 Factor of safety with respect to moment equilibrium condition 252 Factor of safety with respect to force equilibrium condition 253 Inter-slice force function 253 Assessment of slope stability during rainfall 254

7.7 Remedial measures for soil and rock slopes 257 Drainage and surface protection 257 Capillary barrier 264 Parametric study of capillary barriers 268 Physical laboratory scale model study of a capillary barrier 268 Field scale capillary barrier 271 Cut back 272 Access and means of transportation to job site 272 Retaining walls and soil nailing 272 Slopes with a rock to soil interface 275 Measures for stabilisation of rock slopes and rockfall 276 Summary of stabilisation methods and remedial measures 276

References 278


This chapter focuses on the geological factors and their effect on slope stability, landslip type, effect of relict structures, rainfall and suction and finally addresses the stabilisation and remedial measures to soil slopes. The authors’ experience covers a wide range of tropical regions including the Far East and Central and South America.