Influence mechanism of strong seepage on the development of single-circle pipe artificial freezing curtain in gravelly soil layer

Artificial freezing model tests have been conducted to explore the influence of strong seepage on the development of frozen curtain. Compared with the low seepage velocities below 5.0 m/d, the strong seepage of 7.5 m/d has further extended the varying ranges of freezing front developing rates and temperature gradients, changing the temperature fields to be more asymmetric, and delaying the freezing stages. The freezing process experiences four stages including “first rapid decrease-gradual decrease-second rapid decrease-stabilizing”, and the initial frozen time has been extended to 2–4 times. The closure time is generally increasing exponentially with seepage velocity, and the frozen curtain may not close under a critical value (15 m/d). As for the morphology of frozen curtain, its thickness at the upstream side gets thinner and that at the downstream side gets thicker, and its asymmetry has been increased to 4–7 times. To describe the unfrozen water content variation with temperature, a Boltzmann unfrozen water content function is proposed considering the initial and residual unfrozen water content, as well as the varying characteristics. Additionally, a hydro-thermal coupling model has been derived to present the artificial freezing process considering the seepage flow states from laminar to transitional state, and its simulating results including temperature variations and the morphology of frozen curtain are well consistent with the model test data. This research reveals the influencing mechanism of strong seepage flow on the generating of frozen curtain, and it provides theoretical support for predicting its formation process.