| The construction of Qinghai-Tibet Railway from Geermu to Lasa is a symbol project for the development of economy in the west district of China. There are three worldwide problems for the construction of the railway such as permafrost, lack of oxygen, and frail ecology, and furthermore, there is no successful experience from which could be drawn lessons. The Qinghai-Tibet railway lies in the severe frozen area of the plateau, where there is serious coldness, rare air, and mutable climate. The four elements including temperature (air temperature and low temperature), water (surface water and ground water), soil (granule status), force (frozen-heave force) and the dynamic reason of increasing economical activities impact directly the variety and frozen heave of frost earth. It has a great effect on the bearing force of bridge foundation, so that it becomes the research subject for ecological balance and environmental protection in the construction. There is a long history of the development of frozen soil technology. With the economic construction and the recourse exploitation in the permafrost regions, the construction of the railway, road and pipeline for the petrol and gas delivery in this area will make a swift progress. So the research on frozen soil is quite urgent.In this article, we adopt plenty of research productions about secular frozen area on plateau, which are provided by the very scientific research units. According to the geology, climate condition and design requirement of the VI and XI foundation in the high temperature instable area, an exploratory research is carried out on the construction techniques in this area, such as the mixture ratio of concrete, dry boring method by twist drill machine, drilling pedestal pile, drilling insert pile, fast excavation for open-cut foundation, and etc. The main content is as follow:(1) The construction tech research on endurable concrete of foundation in this frozen area. Adding with the series of DZ high performance concrete admixture and fly ash I ,through indoor experiment and casting practice of the concrete structure on spot, the proportion of the raw material was adjusted. The workability of fresh concrete in the low or minus temperature was improved, and the water cement ratio was decreased efficiently. The development of the early strength of concrete was accelerated, and the hole structure of harden concrete was improved, that makes the concrete used in the minus temperature reach 8 durability targets, such as anti-circulation of freezing and melting, anti-penetration of C1-, anti-corruption and so on. The gelation material with low hydrating heat and specific compound admixture was chosen, the proportion ofthe raw material was adjusted, the self-compact concrete for cast-in-place pile with high fluidity used in the low temperature was made, that can ensure the casting quality of concrete in cast-in-place pile, and decrease the thermal disturbance of concrete to frozen layers.(2) Drilling pile method in high temperature secular frozen area. In this area, we adopt the twist drill machine to construct by dry drilling method. Because it has fast drill velocity with small location deviation, less environment pollution, low cost, good mobility, wide adaptability, and safe construction condition. In the drilling process, we could switch to use smaller diameter twist drill when being faced with hard rock interlayer. Then, we can resume the drill's diameter to enlarge the hole. If there is a great construction quantity in hard interlayer, we should use high power drilling machine, equipped by 3-4 rock short twist drill with different tapers, to accelerate the drilling. And as for non-uniform hardness of geology, high strength steel plates are fixed outside the drills to lead direction, and it can solve the drill-hole deflection problem.(3) In order to construct pedestal pile with a length of 2.45m in 1.0~1.5h, a tool named "gravity open-close pedestal drilling device" is researched and designed. Because of the pedestal pile, it could increase the bearing resistance and withdrawal capacity. And it can prevent the crack caused by frost heave, so that the pedestal pile is more suitable for bridge construction in high temperature and ice-contain secular frozen area.(4) Construction tech of drilling insert pile in secular frozen area in plateau. A study about calculation and craft of insert pile is achieved to ensure the quality of the clay mortar surrounding piles. In cold season, the temperature of casting concrete should be kept in 0-5 °C when casting the central concrete. Insert pile should be constructed in dry or less water condition, so the warm season and low temperature is suitable. Compared with cast-in-place pile, the insert pile has less bearing capacity, so it can be used in the structure that asks lower bearing ability.(5) Simple back frozen testing tech for driven cast-in-place pile in secular frozen area of plateau. Depending on the simple testing method, 4 cast-in-place piles, which are casting in warm season, are surveyed to make sure the back frozen time is 43~45d. It can support the back frozen monitoring of pile foundation in construction.(6) Fast excavating technique for the open cut foundation of bridge culvert in high temperature and instable frozen area. In this area, there is construction principle for fast excavation, which is "one time of explosive for shaping foundation ditch, one minute of excavation by mechanical device". According to the geology condition of ground, we should choose reasonable season, andexcavate one section by another, so that it can prevent collapsing and heat transmission. Corresponding to the section with dry ground and good foundation, it is good for construction from June to September. As far as the section with wet ground and ice-contain foundation is concerned, it is the best to choose the alternate season as April ~ June and September ~ October. And as for the section with thick underground ice, ground swamp, and surface stream, we 'd better construct in winter.
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