莫斯科-喀山高速铁路沿线季节性冻土冻融特征

在莫喀高铁沿线770余公里的季节性冻土区内, 依据地貌单元、微地貌、地层岩性与水文地质条件等特征设置了14个监测场, 对季节性冻土的岩性、密度、含水率、地下水位、地温、近地面气温及雪盖的厚度和密度进行了频率为10天1次, 持续时间为7个月(2016年10月1日~2017年4月26日) 的监测, 依据监测数据分析了莫喀高铁沿线季节性冻土的冻结融化特征。分析结果表明: 莫喀高铁沿线季节性冻土区的雪盖主要存在于10月下旬至翌年4月, 雪盖厚度为20.2~38.2cm, 平均值为27.3cm, 最大积雪厚度为25~60cm, 平均值为44.4cm, 出现在2月上、中旬; 莫喀高铁沿线季节性冻土的起始冻结时间为11月中、下旬, 全部消融时间在翌年3月上旬~4月中旬之间, 存活时间为100~165d, 平均时间为122d;季节性冻土的冻结速率为0.27~1.20cm·d-1, 平均为0.50cm·d-1, 融化速率为0.27~2.52cm·d-1, 平均为1.14cm·d-1; 在土体的冻结期间, 雪盖减小了地层的冻结速率, 在土体的融化期间, 雪盖推迟了季节性冻土自上而下融化的起始时间与融化量, 并且会使季节性冻土在无雪条件下的双向融化变为自下而上的单向融化; 莫喀高铁沿线土体在自然状态(积雪覆盖) 下的季节最大冻深为0.19~0.90m, 平均为0.45m, 出现在2月上、中旬; 雪盖会减小土体的最大冻深, 在雪盖平均厚度为26.1~28.6cm时, 雪盖可以使季节最大冻深减小22.2%~32.6%;在莫喀高铁沿线的季节性冻土区, 雪盖在形成初期和消融末期保温与降温效果并存, 但主要以降温效果为主, 而在积雪稳定期, 主要以保温效果为主; 雪盖对季节性冻土热状况的影响深度和程度取决于土体含水率, 土体含水率越大, 雪盖的影响深度和程度就越小, 反之则亦然。 

Freezing and thawing characteristics of seasonal frozen soil along Moscow-Kazan High-Speed Railway

According to the geomorphologic unit, micro-geomorphology, stratigraphic lithology and hydrogeological conditions and other factors, 14 monitoring sites were established in seasonal frozen soil areas along the Moscow-Kazan High-Speed Railway, which is 770 km long. FromOctober 1, 2016 to April 26, 2017, the lithology, density and moisture content of seasonal frozen soil, groundwater level, earth temperature, air temperature near the ground surface, snow thickness, and snow density were continuously measured once every 10 days. Based on the measuring data, the freezing and thawing characteristics of seasonal frozen soil along the railway were studied. Research result shows that in the seasonal frozen soil region along the MoscowKazan High-Speed Railway, snow cover lasts from late October to following April. Snow cover thickness varies from 20.2 to 38.2 cm and the average value is 27.3 cm. The maximum snow cover thickness varies from 25 to 60 cm, occurs in early to middle February, and the average value is 44.4 cm. The soil starts to freeze from middle November to late November, and thaws completely from early March to following middle April. The unfrozen time lasts from 100 to 165 days, and the average time is 122 days. The freezing rate of the soil changes from 0.27 to 1.20 cm·d-1, and the average value is 0.50 cm·d-1. The thawing rate changes from 0.27 to 2.52 cm·d-1, and the average value is 1.14 cm·d-1. In the freezing period of the soil, snow cover reduces the freezing rate of the soil. In thawing period of the soil, snow cover delays the thawing beginning time of the soil from the top to the bottom, also reduces the thawing thickness of the soil from the top to the bottom, and changes the double-direction thawing between the top and the bottom into the single-direction thawing from the bottom to the top. Along the Moscow-Kazan HighSpeed Railway, the maximum average freezing depth of the soil is 0.45 m within the range of 0.19-0.90 munder natural conditions, which generally occurs in early or middle February. Snow cover can reduce the seasonal freezing depth of the soil, and the reduction is 22.2%-32.6% when the thickness of snow cover is 26.1-28.6 cm. Snow cover has both cooling and insulating effect on the soil in the periods of early snow formation and late snow melting, but the cooling effect is major. However, in the stable period of snow cover, the insulating effect is major. Snow cover has a substantial insulating effect on the soil temperature, and the influencing depth and extent depend on the moisture content of the soil. The higher the moisture content is, the less the influencing depth and extent are, and vice versa.