Study on the Mechanism and Prevention Method of Frozen Wall Maldevelopment Induced by High-Flow-Rate Groundwater

Abstract

In order to solve the engineering problem of the increase in closure time or even the failure of closure of the frozen wall in the high-velocity permeable stratum, the maldevelopment mechanism of frozen walls induced by high-flow-rate groundwater was studied by a similar physical model test. The results show that the flowing groundwater reduced the heat transfer efficiency of the freezing pipes and changed the spatial distribution of the frozen area. The closure time of the frozen wall and the non-uniformity coefficient of the frozen wall thickness increased with the increase of the groundwater velocity. Based on the maldevelopment mechanism of frozen wall induced by groundwater, the artificial freezing scheme of permeable stratum with high seepage velocity was optimized. For the scheme of single-circle freezing holes, the optimization method of reducing the spacing between freezing holes and adding auxiliary freezing holes upstream of water flow was proposed. For the scheme of double-circle freezing holes, the optimization method of local variable pipe spacing was proposed. The optimization effect of several schemes was predicted and analyzed by numerical calculation, the results show that: in the optimized design scheme of single-circle freezing holes, both methods of local compaction and adding auxiliary freezing holes upstream could effectively shorten the closure time of frozen walls, and increase the maximum velocity at which the frozen wall can be closed. The optimum spacing of auxiliary freezing pipes under different groundwater velocity was obtained by calculation. In the optimized design scheme of double-circle freezing holes, the spacing of freezing holes in different regions was optimized and adjusted according to the degree of influence of water flow on freezing temperature fields under the condition that the number of freezing holes was kept constant. After adopting this optimization scheme, the limit flow velocity of frozen walls can be closed increased significantly. This study could provide reference for the arrangement of freezing holes in high-velocity permeable formation.

Keywords

• artificial ground freezing
• high-flow-rate groundwater
• optimization of freezing holes layout
• similar model test
• numerical calculation