Monitoring Study of Shaft Lining Concrete Strain in Freezing Water-Bearing Soft Rock During Mine Shaft Construction Period in West China

Abstract

Abstract In the water-bearing soft rock strata of West China, a field measurement is carried out on the shaft lining in bedrock section. The shaft lining is built with freezing method. From the measurement, some changes of regularity in construction, thawing and post thawing period are obtained, including the temperature, freezing pressure and the vertical and hoop strain of the shaft lining. Measurement studies have shown that: during the plastic stage of shaft construction period, with the release of hydration heat, the thermal expansion occurs in the concrete and the strain gauge, leading to tensile strain. In the earlier stage, the elastic modulus and strength of concrete increases rapidly. When the shaft lining temperature reaches its maximum, the cooling and growth in the freezing pressure make the hoop strain increase sharply. However, the hoop strain is at lower tensile or compressive value. In the early stage and mature stage, the strain change is mainly affected by temperature. In the thawing and post thawing period, the concrete strain is also primarily influenced by temperature change. During the measurement, when the maximum compressive strain is less than ultimate value, the shaft lining is in a safe state. To ensure the security of the shaft lining, the concrete strength growth and sidewall temperature should be controlled in the similar shaft condition. In addition, the reinforcement ratio should not be too small for the shaft lining in frozen bedrock. And further, the fiber reinforced concrete, shrinkage-compensating concrete and low hydration heat concrete technology can also be adopted to reduce the cracks as much as possible and to avoid penetrating cracks. For the soft aquifers in West China, the further field measurement is still needed to obtain the stress and deformation regularities of the shaft lining, which can not only provide a basis for security assessment of the shaft, but also guide its design and optimization to improve the design theory.