Study On The Crack In Permafrost Embankment Of Qinghai-Tibet Railway

Constructions of roadbed in permafrost areas have changed the thermal distinction of original natural ground surface and the distinction of water-heat transportation within seasonal thawing layer of permafrost,as well as the water-heat environmental distinction of original ground surface.All these changes have led to a new two-dimensional heat-transfer process between the new structures and the environment at both vertical and horizontal directions.Roadbed deformation associated with such heat-transfer process influences the occurrence and development of crack of roadbed. After the permafrost roadbed construction of Qinghai-Tibet railway completion, vibrating load from the constructional trains made the mechanical expression of the new heat-transfer process more complex.The permafrost test roadbed construction of Qinghai-Tibet railway was built in 2001 and cracks occurred at different places of roadbed after first cycle of freezing and thawing.It is valuable to study the mechanics and engineering solutions to ensure the safety of long-period operation of Qinghai-Tibet railway.Based on classic theory of cryopedology and research achievements of roadbed cracks,the crack of Qinghai-Tibet railway roadbed was studied in this dissertation.Its main contents are generalized as follows.1.Engineering geological conditions,environmental geological conditions and water-heat environmental conditions were determined as influential factors of crack occurrence by field survey.Changes of water-heat environmental conditions caused by roadbed construction were analyzed,and key problems that control the crack of roadbed were presented.2.Cracks were classified according to its location and shape.Distinctions of different development stages of roadbed crack were studied.Also influential factors and occurrence locations were analyzed.3.The mechanics of occurrence of roadbed cracks was studied from phases of soil mechanics,permafrost cooling mechanics and water-heat environmental influence mechanics by field survey of ground temperature field,roadbed deformation and the development of crack shape.Regulating measures were presented.4.Numerical simulation was accomplished to evaluate the long-period effect of regulating measures for cracks.Finally key preventive and regulating techniques and suggestions were presented.