Abstract: With the rapid development of industrialization and urbanization, a large quantity of solid wastes have been produced, the groundwater and subsurface soils are seriously contaminated, and the environment which peoples rely on is getting worse. The researchers in geotechnical engineering make efforts to use the theories and approaches of geotechnical engineering to study and solve these environmental problems, and a new branch of geotechnical engineering discipline—environmental geotechnics has come into being. The problems of environmental geotechnics involve many processes including biochemical reaction, physical change and mechanical motion. A unified framework of the basic theories for environmental geotechnics has not been established currently. The mechanisms of biochemical reaction, soil skeleton deformation, pore water and gas transport and solute migration in soils are described. A coupled model and the relevant governing equations for biodegradation, mechanical deformation, fluid flow and contaminant transport in soils are established. The parameters in this model and their measuring methods are also addressed. The phenomena, serious acid inhibition caused by biochemical degradation, skeleton weakening and liquid-gas mutual blocking in the landfills of municipal solid wastes with high food content, are revealed. The mechanisms, including compression deformation and liquid/gas generation and transport in municipal solid wastes, interaction between pollutant migration and soil consolidation, pollutant penetrationof barrier and prevention of water infiltration and gas escape in landfill covers, are demonstrated. Based on nearly twenty-year researches and practical works by the author's research group in environmental geotechnics, the proposed assessment approaches for the degradation degree of municipal solid wastes, leachate production, collection efficiency of landfill gas, landfill settlement and capacity, landfill stability and serving time of barriers in landfills are summarized, and the proposed techniques, including three-dimensional leachate and gas drainage system, new pattern of barriers and TDR survey technology for contaminated soils are validated.