Investigation on Artificial Ground Freezing in cross passage construction by multiphysics coupling

Abstract

In cross passage construction in soft soils with high water content, Artificial Ground Freezing has been widely adopted to generate frozen walls to act as temporary support for excavation. Freezing of soil is a complicated process that involves multiphysics of temperature, water flow, stress and the coupling thereof, and which brings on significant alteration in thermophysical properties. Work of this paper is based on laboratory efforts and field observation of cross passage #1 in Shanghai Yangtze River Tunnel. Variation of soil properties with temperature including specific heat, thermal conductivity, and modulus of elasticity were obtained and adopted in the coupling analysis, which studied the growth of temperature field and frost heaving during the period of 40-day active freezing. Enclosure of ice columns occurred on the 14th day. Temperature and thickness of frozen soil wall developed quickly in the first 20 days and later the inner surface expanded more quickly while the outer surface very slow. Final thickness of the frozen wall could reach 5.14m. because of the frose heaving effect, the center of cross passage had a displacement of 2.35cm upward. Compressive stress within the frozen wall was remarkably concentrated, counting 2 times that of the adjacent unfrozen soil.