| A large amount of seasonal frost boiling diseases will occur in the road engineering of Gansu province during spring thawing period, which affects driving safety and couldn’t ensure road unblocked. And even the new road engineering also exists subgrade frost heaving-boiling diseases, which is particularly serious in Gannan, Hezuo, Linxia, Longnan, Dingxi, and Wuxiaoling etc. Quantities of manpower, materials and financial resources are invested on the treatment of road frost heaving-boiling diseases in Gansu province every year. Gansu province, located in the cross belt that converges the winter monsoon climate zone, the northwest arid areas and the Qinghai-Tibet plateau climate zone, is situated in the northwest of China. The winter of this area is cold and road frost heaving-boiling diseases are common, which seriously affects the road engineering construction and development of our province.In seasonal frozen ground areas, along with freezing and thawing of the water in the soil, a series of strange and unique phenomenon of frozen soil occur. In the following is an example: with the decrease of the atmospheric temperature, when the soil temperature drops to the crystallization point of pore water in soil, soil freezing occurs and ice crystals appear, which leads to road frost. In the spring, with the rise of temperature, frozen soil begins to melt from the upper, but the lower layer of the permafrost hasn’t melt. Water failing to infiltrate makes the moisture content of the soil increase, which leads to strength reduction. Once the ice intrusion in the soil melts into water, while soil drainage consolidation has not fully completed, when the pore water pressure, generated under the upper load, is large enough to make the subgrade soil flow, the subgrade soil will move towards the upper coarse particles in the form of mud and emerge from the pavement cracks, which leads to the deformation of the upper structure and road frost boiling mud phenomenon etc. The emergence of boiling greatly reduces the stability of subgrade and increases the deformation of road.Now the more commonly used measure for prevention and treatment of subgrade frost heaving-boiling is replacing and filling coarse-grained soil of less frost heaving. However, the existing indoor experiment and practical engineering practice have proved that the method through the replacement with the coarse grained soil could only reduce frost heave, but could not eliminate the moisture migration. Vertical and lateral water migration and accumulation will occur in subgrade in the case of repeated freezing and thawing, which turns out to be that there still exists a larger water content in the subgrade. So the boiling phenomena still occur under the effect of freezing and thawing and the upper load. Subgrade structure, widely used currently, can not fundamentally eliminate the occurrence of the subgrade frost heaving diseases, there is an urgent need to seek a new embankment structure to change the subgrade moisture migration conditions and prevent the occurrence of subgrade frost heaving-boiling.Based on theoretical analysis and laboratory test, failure mechanism and influencing factors of road boiling in seasonal frozen soil area are researched; the new bidirectional waterproof and water-insulation subgrade structure to prevent the destruction of road frost boiling is put forward through the indoor model test research on moisture migration regularity and deformation law of the subgrade in seasonal frozen soil region, which is of great practical significance for construction, operation and maintenance of the road project in seasonal frozen area. |
