Study On Fracture And Damage Behavior Of Frozen Soil

As basement of foundation of various buildings in cold regions, frozen soil plays an important role for building safety and utility. Study on characteristics of failure for frozen soil is one major component of frozen soil mechanics. To investigate the characteristics, fracture mechanics and damage mechanics have been introduced into the studies.In the first part of this dissertation, theory of fracture mechanics of the frozen soil has been presented. A general strength theory based on fracture mechanics was proposed, and the validity of the theory using in frozen soil was discussed. The fracture toughness values for different kinds of cracks extension were determined, such as the plane strain fracture toughness for mode I cracking(KIC), fracture toughness for mode â…¡ cracking of frozen soil and the intersectionof frozen soil and concrete. The relations of fracture toughness versus environment parameters (e.g. temperature, water content, loading rate etc) were investigated. Then a criteria of cracking propagation for mixed mode â… -â…¡ and the size effects of samples for mode I crack extension were studied. In the end of this part, some application examples of fracture mechanics for the frozen soil have been given out.In the second part, continuum damage mechanics has been introduced to study the characteristics of the frozen soil. On base of additional damage concept, a judging model for initial and additional damage for frozen soil was proposed. Using CT NDT, the inner-structure characteristics of samples of the frozen soilunder uni-axial compression were investigated, and the process of damage isseparated into two regions: e.g. plastic damage and cracks extension damage. The determination methods of damage values for different levels were proposed and the damage values were calculated. Subsequently, a constitutive including damage value for the frozen soil was set up, and the evolution equations for saturation and unsaturated frozen soil were given out based on the damage distinguish. At last, an effective stress were calculated and compared with the really stress using the theory mentioned above.The third part is a discussion and prospect on the frozen soil study using fracture mechanics theory and continuum damage mechanics.All of the work are supported by NSF and SKLFSA.