Study On The Measures To Guarantee The Stability Of The Permafrostal Roadbed In Wudaoliang Region Of The Qinghai-Tibet Railway

Based on the in-site tests derived from the experimental segment of the spall revement and the rubble berm in the region of Wudaoliang.of Qinghai-Tibet railway, in this paper, the effect of the spall revement and the rubble berm cooling the the ground temperature and stabilizing the permafrostal roadbed is detailedly studied.Based on the illustration of the engineering geological conditions, the author analyzes and discusses the factors that can affect the existence and changing of the natural permafrost including air temperature, terrestrial heat, lithofacies, snow cap, cloudage and sunshine, and that can affect the perennial permafrost underlying the roadbed including the height of the backfill soil, the sunlit slope and the sunless slope. The factors above always give effect to the permafrost by changing the ground temperature field.By elucidating the mechanism of the frost heaving and the thawing subsidence, the author points out the main factors that effect the deformation of the permafrostal roadbed caused by the frost heaving and the thawing subsidence are the temperature and the moisture content of the permafrost.Elementarily, the author analyzes the engineering measures that can protect the permafrost underlying the roadbed and elucidates the principle of the spall revement and the rubble berm cooling the ground temperature and stabilizing the roadbed.By analyzing detailedly the test data of the ground temperature and the deformation of the roadbed carried out on the test segment, the conclusions were drawn as below:(l)The features of the natural perennial permafrost and the behaviors of the natural ground temperature field in this region are that: the annual average ground temperature is -2.35-2. 4C;the thickness of the perennial permafrost is 45~50m; the maximum depth of seasonal thawing is 2.5m. The changing of the ground temperature lags with the increasingof the depth; the annual temperature span decreases with the increasing of the depth; the lowest temperature of the permafrstal active layer is -6.74-7. 59C, which appears at the end of December.(2)The features of the perennial permafrost underlying the roadbed and the behaviors of the artificial ground temperature field in this region are that: the isotherm of the stratum always protrudes upward and biases to the sunless side of the roadbed; the stratum on the sunless side freezes earlier than that on the sunlit side; the maximum seasonal thawing depth is 1. 6~3. 9m.(3)The effect of the spall revement and the rubble berm cooling the ground temperature and maintaining the stability of the roadbed varies with their structure and size, mainly revealed by as below:(1)When the thickness of the spall revement on the sunlit side is less than 1.3m, the function is very bad; if the thickness reach to 1. 3"-1. 6m, then it is sure to prevent the ice layer from thawing; but if its thickness more than 1.6m, not only can it prevent ice layer from thawing but also can uplift the upper. limit obviously.(2)The soil berm is capable of cooling the ground temperature field, but the time the practice is taken at is imperative to its cooling function. The most optimal time is the turning point when the air temperature varies from cold to warm.(3)The cooling function of the rubble varies with its grain diameter. When the thickness of the berm is uniform, the cooling function of the rubble diametered 10cm has no obvious difference with that diametered 20cm, but the latter is a little more effective; otherwise if the grain diameter more than 30cm, the effect is very bad.(4)The reasonable structure of the rubble berm are that: the diameter of the rubble is 10cm or 20cm; the thickness on the sunlit side and the sunless side are either 6m and 3m respectively, or 5m and 2. 5m respectively. The height of the rubble berm on the sunlit side may be increased properly so that its cooling function can reach the roadbed shoulder.(5)By analyzing the tested ground temperature, the author forecasts that when the ground temperature underlying the roadbed is attained to the equilibrium,...