Investigating Hydration Heat and Thermal Properties of MJS Treated Soil

Abstract

Both metro jet system (MJS) and artificial ground freezing (AGF) techniques can be utilized and sometimes combined to reinforce the area during the tunnel construction for critical projects. The hydration heat released by the MJS treatment inevitably extends the active freezing time due to the introduction of cement paste. Consequently, before the implementation of two techniques, a numerical simulation is often conducted to determine the setup of the AGF system and the for AGF initiation. The rationality of the setup is highly dependent on the accuracy of the simulation results. In this paper, laboratory tests were conducted on soils with different cement contents and curing periods to measure the initial freezing point and hydration heat. Measurement of thermal conductivity and volumetric heat capacity on cemented soils was conducted under frozen and unfrozen conditions. Measurement results revealed that the initial freezing point, the thermal conductivity and volumetric heat capacity of cemented soil were highly dependent on curing period and cement content. By taking advantage of an ongoing project and the laboratory measured hydration heat and thermal parameters, a numerical simulation was also conducted to predict ground temperature variation after MJS treatment. The simulation results were found to be in agreement with the on-site temperature measurement results. The adoption of laboratory measured thermal parameters and hydration heat improved the accuracy of the numerical simulation, which is beneficial for the design and planning of MJS and AGF techniques.