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Ground temperatures monitored at four observation sites in permafrost regions on the Tibetan Plateau was analyzed. It was found that the ground temperature at the depth of 12～20 m increased 0.2～0.4 K and the permafrost thickness decreased 4～5 m from the base in Xidatan Site from 1975 to 1989; and the ground temperature at the depth of 6～15 m increased 0.2～0.4 K in Kunlun Pass Site from 1982 to 1997. Contrast observations show that a sand cover, 15～20 cm in depth, can result in a ground temperature decrease of 0.1～ 0.2 K in MS66 Site; and a removal of vegetation can result in a ground temperature decrease of some 0.2 K in Hoh Xil Site. The monitor demonstrates that many factors that control permafrost developing have duality, e.g., sand and vegetation are able to increase or decrease the ground temperature. These factors, in conjunction with permafrost behaviour, play different roles under different conditions. Therefore, it is necessary to study, understand and evaluate permafrost and its engineering geological properties taking the viewpoint of dynamic variation.
Ground was monitored at four observation sites in permafrost regions on the Tibetan Plateau was. The was found that the ground temperature at the depth of 12-20 m increased 0.2-0.4 K and the permafrost regions decreased 4-5 m from the base in Xidatan Site from 1975 to 1989; and the ground temperature at the depth of 6 ~ 15 m increased 0.2 ~ 0.4 K in Kunlun Pass Site from 1982 to 1997. Contrast observations show that a sand cover, 15-20 cm in depth, can result in a ground temperature decrease of 0.1-0.2 K in MS66 Site; and a removal of vegetation can result in a ground temperature decrease of 0.2 K in Hoh Xil Site. The monitor demonstrates that many factors that control permafrost developing have duality, eg, sand and vegetation are able to increase or decrease the ground temperature. These factors, in conjunction with permafrost behavior, play different roles under different conditions. Therefore, it is necessary to study, understand and eva luate permafrost and its engineering geological properties taking the viewpoint of dynamic variation.