研究目的：(1)处理多年冻土地基有被动保护、主动降温、被动保护结合主动降温、两种主动降温相结合、以桥代路等多种工程结构，各种处理多年冻土地基结构的功效不同。为合理使用处理多年冻土的工程结构，需统筹考虑影响多年冻土工程地质条件的主要因素，对多年冻土的工程地质条件进行分级。(2)根据多年冻土工程地质条件分级及对应的工程结构，估算工程费用，为多年冻土区工程地质选线提供科学依据。
研究结论：(1)青藏铁路多年冻土的工程地质条件划分为良好、一般、差、极差四级，分别采用普通路基、单一主动降温措施、两种主动降温措施组合、以桥代路等工程结构通过。青藏铁路自2006年7月通车后，多年冻土区列车以100 km／h速度的平稳运行，证明r多年冻土工程地质条件分级的设想可行，对应采用的工程结构稳定可靠。(2)多年冻土区极筹地段以桥代路，估算造价为4 000万元／km，为其他等级地段多年冻土工程费用的4．4～15．4倍，青藏铁路多年冻土区选线时，对多处不同类型的极差地段进行了绕避或以最短的距离通过。
Research purposes: (1)The treatment measures for the subgrade in permafrost area include passive protection，active cooling，passive protection along with active cooling，combining two kinds of active cooling，building bridge and SO on，and each measure has the different effect．In order to reasonably use the measures，the main factors that affect the engineering geological condition should be considered together and the engineering geological condition should be classified in permafrost area．(2)Based on the classification of engineering geological condition and its corresponding engineering structure，the cost was estimated for providing the scientific basis for engineering geological route selection in permafrost zone．
Research conclusions: ：(1)The engineering geological conditions in permafrost area along Qinghai—Tibet Railway are divided into four grades，namely good，general，poor and very poor．The corresponding measures for them are to adopt ordinary embankment，take a single active cooling measure，take two active cooling measures and build bridge．The safe running of train with 1 00 km／h on the Qinghai—Tibet Line in permafrost zone since open to traffic on July，2006 shows that the classification of engineering geological condition is feasible and the respective engineering structures are stable and reliable．(2)The cost of building bridge in very poor section Was 40 millions per kilometer，that was 4．4～15．4 times than the other section in the permafrost area．Therefore，railway route bypasses some very poor areas or passes it with the shortest distance．
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