Field study on the use of gravelly tunnel muck for frost heave and thaw settlement prevention in soft subgrades, northwest China

摘要

Fine-grained valley sediments in cold mountain regions can cause frost heave and thaw settlement problems to infrastructure. These processes have caused major issues along a highway between Tanchang County and Diebu County in south Gansu province (the TDH), northwest China. A planned high-speed railway between Chengdu and Xi'ning, the capitals in the Sichuan and Qinghai provinces, will likely face the same problems. To mitigate the effects of frost heave and thaw settlement, new engineering techniques were tested in a valley region along the TDH. These included replacing frost-susceptible subgrade soils with gravels from a tunnel excavation as an anti-frost fill layer, and installing dewatering seepage drains. Two highway test sections were constructed, one with a 1.0-m fill layer and the other with 2.0-m fill layer, to test the performance of the coarse tunneling material as an anti-frost heaving technique. Ground temperature, water table, and deformation measurements indicated that the two sections experienced very limited post-construction settlement (1.5 mm and 1.7 mm). The maximum frost heave at the two sections was 4.0 mm and 10.7 mm, respectively, much lower than the admissible amount in the Chinese standards (50 mm). These results indicate that coarse-grained waste material from tunneling can be used to effectively control frost heaving. The dewatering measures, which served to lower the water table and thus limit the water supply for ice segregation, are also suggested as important implement in rainy valley regions with ground high water tables. The installation of an anti-frost fill layer and drainage measures are effective and economical techniques to mitigate frost heaving and settlement of infrastructure in cold mountain regions.