Comparison of individual and sequential copper piping systems in an experimental artificial ground freezing model

Artificial ground freezing application creates a cementitious ice structure between grains in addition to shear strength parameters, such as internal friction angle or cohesion. Thus, settlement levels are minimized while the bearing capacity of soil is increased considerably. In this study, the effect of copper pipes in twenty different cases were realized, including four soil types, two piping systems, and four source temperatures with mono ethylene glycol circulation. Temperature/time graphs, horizontal and vertical isotherms, unit temperature changes, formations of frozen cylinders, and obtained peak values were presented to investigate the difference between individual and sequential piping systems in terms of efficiency. The cooling effect increases with a decrease in grain size and permeability parameters, while each soil type shows its specific freezing behavior. Although similar frozen cylinder formations were observed in same soils regardless of piping system, peak temperature values were differed. The most effective freezing process were obtained for MH and SM type of soils for individual and sequential piping systems in terms of average unit temperature drop during first 4 h called as a sudden fall zone, respectively. The largest frozen cylinder diameters proved these temperature results around 169 and 142 mm in the same order. However, the GP type of soil was cooled more easily through the remaining 20 h of linear decrease zone. As a result, the critical frozen sections should be regarded with respect to specific frozen formations of soils in the practical applications of artificial ground freezing projects.