Theoretical Prediction of High-Risk Zone for Early Temperature Cracks in Well Walls in Deep-Frozen Shafts

The cracking of deep-frozen shaft walls in mines, caused by temperature stresses, has been a frequent occurrence in recent years. To study the evolution of early-age temperature stresses in the inner wall after pouring concrete (0 to 240 h), a mechanical model that considered thermal–mechanical coupling conditions was developed. The changes in early-age temperatures from the center to the outer edge did not follow a monotonically decreasing pattern due to the instability of the thermal boundary conditions and the complexity of the heat transfer pattern of the well wall. We report an improved method to determine the temperature distribution that could predict the temperature with an error of no more than 6.02%. The evolution of the components for each temperature stress with time and space was obtained. Circumferential tensile stresses of 1.24 MPa arose (10 h) at the inner edge of the wall before the maximum temperature of the concrete (36 h) was reached, which could potentially cause a circumferential rupture in the shaft wall. The thickness: diameter ratio and expansion pressure of the well wall could significantly affect the magnitude of early temperature stresses, where the expansion pressure enhanced the turbulence of the temperature field inside the well wall, resulting in severe oscillations in temperature stresses. This study provides theoretical support for a technical approach to predict the timing and location of early wall cracks in deep-frozen shafts.