Abstract:

A basinshaped freezing waterstopping technology is proposed to control groundwater in underground engineering of fullsection sandy gravel strata. First, the compression and creep mechanical properties of the frozen sandy gravel are examined using a triaxial test. Second, the developing pattern of the temperature field in basinshaped freezing is investigated using largescale physical model tests and numerical simulations. Finally, a layout method for the freezinghole group during the freezing period and a precision control technology during the maintenance period are proposed. The following conclusions are obtained: (1) The triaxial compressive strength of the sandy gravel is positively and linearly correlated to the confining pressure under a confining pressure of less than 3 MPa, but remains unchanged when the confining pressure is increased. The whole process creep model of frozen sandy gravel is established on the basis of the damage theory. (2) Load has the greatest influence on the frost heave rate and melt sink coefficient, followed by fine soil content. The original saturated sandy gravel is a nonfrost heave material, and a threedimensional prediction model for the frost heave rate and melt sink coefficient of saturated sandy gravel is established. (3) The results of largescale physical model experiments and numerical simulations indicate that basinshaped freezing can form a complete basinshaped waterproof structure under groundwater seepage conditions, effectively stopping the water. (4) During the freezing process, the bottom freezing pipes exhibit a "superposition effect", which is completely different from that of a single pipe. A layout method for the freezing pipes during the active freezing period, including the spacing of the freezing pipes, thermal conductivity of the soil, and seepage velocity, is proposed on the basis of the experimental results. (5) To save cooling energy during the maintenance period, two schemes of freezing pipe cutting every other row and freezing pipe cutting at the bottom are proposed to finely control the freezing area.

Key words: basinshaped freezing method, underground engineering, waterproof technology, sandy gravel strata, temperature field, groundwater seepage, superposition effect