青藏铁路北麓河试验段冻土工程地质特征及评价

Engineering Geological Characteristics and Evaluations of Permafrost in Beiluhe Testing Field of Qinghai-Tibetan Railway

冻土问题是青藏铁路建设的难题之一 ,为良好的解决这一问题 ,详细了解线路通过地区的冻土工程地质特征并对其做出工程地质评价至关重要 .在目前完成的青藏铁路北麓河试验段的冻土勘察工作表明 ,该试验段的土层以富含厚层地下冰的细粒土为主 ,试验段地下水丰富 ,全段高温与低温多年冻土都有分布 ,冻土上限深度一般为 2～ 3m .综合上述特征 ,该试验段综合评价为不良和极差冻土工程地质地段 .在类似地区进行铁路建设 ,工程措施设计和采用中要充分考虑冻土工程地质特征 ,否则可能导致工程建设的隐患甚至所采取工程措施的失败 .

The Qinghai-Tibetan Railway is the highest and longest railway on plateau in the world. The railway will cross 550 km of permafrost. Under global warming and permafrost degradation, many engineering difficulties will occur to the construction of the railway. In order to efficiently solve the problems caused by permafrost, it is necessary to deeply prospect and evaluate the engineering geological characteristics of permafrost, over which the railway will cross. In this paper the permafrost in the Beiluhe Test Field of the Qinghai-Tibetan Railway is analyzed from geological aspect. In fieldwork, as the present classification system of frozen soil has application difficulty, a practicable classification is put forward based on visible ice content in soils. Through practice and comparing with classical system, it is proved the practicable classification is reliable. Surveying shows that the soil is dominated by granule soil, and ground water is rich in the field. There are both high temperature permafrost and low temperature permafrost with rich ground ice layers, and the permafrost table is 2～3 m in depth. Such geological conditions are susceptive to engineering construction. From the above characteristics, the Test Field is classified into bad and very bad engineering geological sections. In these sections, special engineering treatment depending on geological conditions must be applied to the railway construction, otherwise potential failure might appear.