Research on key technologies for tunnel concrete crack prevention of Dianzhong Water Diversion Project

Abstract

The secondary lining of water conveyance tunnels is a typical thin-walled, strongly constrained reinforced concrete structure. Currently, there is no specific technical code for crack prevention in thin-walled, large-volume concrete structures. Preventing cracks in tunnel secondary linings has long been a key technical challenge. Based on the Dianzhong Water Diversion Project, this study conducted experimental investigations and computational analyses on crack prevention technologies for tunnel lining concrete, focusing on crack formation mechanisms, concrete performance optimization, and temperature control measures. The result indicate that the primary causes of circumferential and irregular horizontal cracks in some tunnel sections are excessive concrete water content and significant temperature gradients between the concrete and its foundation. To reduce concrete water demand, the MB value of manufactured sand should not exceed 1.0 g/kg. If this threshold is exceeded, washing or adding antimud agents is recommended to mitigate the adverse effects of clay content in the sand. The crack resistance safety factor of tunnel lining concrete should be no less than 1.65. Among influencing factors, temperature during construction has the most significant impact on crack resistance. Under standard construction conditions, the minimum crack resistance safety factor typically falls below 1.65; therefore, it is necessary to control both the pouring and peak temperatures to minimize cracking risks. During construction in high-temperature seasons or when structural joints are excessively long, micro-expansion concrete with added magnesium oxide can be used. This ensures that the autogenous volume change at 28 days exceeds 30 × 10^-6, raising the crack resistance safety factor above 1.65 and effectively reducing the risk of cracking.

Keywords

tunnel lining concrete / thin-walled reinforced concrete structure / crack prevention / Dianzhong Water Diversion Project