WANG Shuang-jie, LI Zhu-long, WU Jing-min
In this paper, the state-of-the-art of the research on highway construction in permafrost regions of China is analyzed, and the research works in the permafrost regions along the Qinghai-Tibet Highway are introduced. State the results of the research in the east of the Tibetan Plateau, where permafrost is degenerating, also guide the research work in island-permafrost regions in the Xiao Hinggan Mountains. Based on the studies and practice for many years, some new topics and new ideas are put forwards to the highway construction in permafrost regions. There are more than 600 km of the Qinghai-Tibet Highway passing through permafrost regions. Since 1973, more attention has been paid on them. From that time, research works were completed thrice, the first one carried out from 1973 to 1978, the second one from 1979 to 1985, and the third one from 1986 to 1999. Furthermore, since 2001 a new project about the whole technique for the highway construction on the permafrost regions of China has been undertook, not only for the permafrost regions in the Tibetan Plateau, but for the permafrost regions in Northeast China. In the first research on the Qinghai-Tibetan Highway, a design standard was put forward, which is used today in a certain condition. The main result of that time was using black pavement on the plateau, which was the first time to use black pavement on permafrost region in the world. Several experiences about black pavement were obtained, such as asphalt volume, requirements of materials, and methods of construction. Nine types of pavement were recommended. In the second period, there were four main aspects studied, the underground ice along the Qinghai-Tibet highway, the stability of subgrade under an asphalt pavement, the selection and construction of asphalt pavement, and the base of bridge and culvert.In the third period, the main studies involved the engineering geology of plateau permafrost, the stability of highway, the usage of asphalt and modified asphalt pavement, and the culvert engineering, such as using corrugated steel pipe and heat pipe, and the database of engineering and permafrost. The problems about the stability of highway included subgrade temperature fields, subgrade deformation, design principle of subgrade, and methods to keep subgrade stable, such as elevating fill height of subgrade, using steel-fiber cement concrete pavement and using thermal insulation layers.In the east of the Tibetan Plateau, permafrost is degenerating. The Cold and Arid Regions Environmental and Engineering Research Institute, CAS, and the Qinghai Highway Research and Design Institute have studied the engineering and the permafrost in the Xining-Zhangye Highway (National Highway No.227) and Qinghai-Kangding Highway (National Highway No.214). It was found that some results are the same or similar to the discovering in the Qinghai-Tibet Highway, some results are different. The main results and differences are presented in this paper.In the Xiao Hinggan Mountains, permafrost is distributed as many islands. In the National Highway No.202, permafrost is found in the section from Heihe to Beian. The two cities are in Heilongjiang Province. After thrice surveying and checking, distribution and rule of permafrost are now mastered, and research on highway construction in the island-permafrost regions is doing. The methods and some ideas are described in this paper.In the end of this paper, many new topics are put forwards. First, in the construction and research, environment protection shall be paid more attention, not only on air, water and plants and animals, but also on permafrost. The later is more important sometimes, and which cannot be recurred. Secondly, the relation between engineering and permafrost should be studied continuously to insure subgrade and pavement stable. Furthermore, checking or surveying in great scale should be arranged to establish a permafrost database. After the database setup, the distribution, rule and features of the subgrade or diseases of the pavement, as well as their degeneration and stability, can be mastered. Thus prediction of permafrost changing can be made,and the troubles in engineering before they comes can be prevented.
Singular perturbation method is used to solve unsteady phase change temperature question. The perturbation parameter ε used in the expansion solution is as ε=cs(Tf-Tw)/L. The zero-order expansion term of frozen and thawed phase and interface equation are solved. Because the factor of the term ∂v/∂t in the zero-order thawed phase equation is a function of |dw/dz|, Galerkin’s method is used to solve the perturbation equation. Besides researching the temperature field of oil-pipeline system, the thermal parameter relating to temperature and numerical examples are also discussed.
