6.8.2.1 Initial Impact of a Temperature Gradient -- 6.8.2.2 Current Cyclic Wetting and Drying -- 6.8.3 Mechanisms in Migration and Percolation of Clay Liners -- 6.8.3.1 Migration-Controlling Factors -- 6.8.3.2 Geotechnical Properties of Fully Water-Saturated Top Clay Liners -- 6.8.3.3 Role of Smectite Content -- 6.8.3.4 Migration of Rainwater and Meltwater into and through Clay -- 6.8.3.5 Impact of Temperature and Temperature Gradients -- 6.8.3.6 Role of Microstructural Changes -- 6.8.3.7 Dispersion of Infiltrated Water -- 6.8.3.8 Evaporation -- 6.8.3.9 Transpiration -- 6.8.3.10 Conclusive Summary of Cyclic Wetting and Drying -- 6.8.3.11 Freezing and Thawing -- 6.8.3.12 Gas Penetration of Clay Liners -- 6.9 Function of the Bottom Clay Liner -- 6.9.1 Microstructural Constitution -- 6.9.2 Issue of Slope Stability of Clays -- 6.9.2.1 Stress-Strain Mechanisms in Slopes -- 6.9.2.2 Shear Strength -- 6.9.2.3 Long-Term Shear Strength -- 6.9.2.4 Liquefaction -- 6.10 Special Cases: Ideal Conditions for On-Ground Disposal of LLW and ILW -- 6.10.1 Options -- 6.10.2 Deserts -- 6.10.3 Clay Liners of Natural Smectite Soils in Arid Climate -- 6.10.3.1 An Iraqi Case -- 6.10.3.2 Clay Materials -- 6.10.3.3 Compaction Characteristics -- 6.10.3.4 Swelling Pressure and Hydraulic Conductivity -- 6.10.3.5 Shear Strength -- 6.10.3.6 Creep Behavior -- 6.10.3.7 Comments on the Iraqi Case -- 6.11 Design, Construction, and Performance of Underground Repositories for Disposal of LLW and ILW -- 6.11.1 Site Investigations and Location -- 6.11.2 Cases Considered -- 6.11.2.1 Disposal in Crystalline Rock -- 6.11.2.2 Disposal in Salt Rock -- 6.11.2.3 Disposal in Argillaceous Rock -- 6.11.2.4 Disposal in Clastic Clay