Investigation on the concrete strength performance of underlying tunnel structure subjected to train-induced dynamic loads at an early age

Abstract

The strength tests of vibrated concrete were carried out to investigate the influences of train dynamic loads on the later strength performance of concrete in the underlying tunnel structure. This study is based on a cast-in-place tunnel project subjected to the dynamic loads from the upper railway. With the measured data from the project site and the analysis results of numerical simulation, the primary train-induced vibration spectrum was determined and applied on concrete. At an early age, e.g. within the first 48 h after pouring, the concrete in the mold was subjected to gap vibration by imitating the actual train running interval. Compressive and tensile strength tests, as well as the internal ultrasonic inspection, were conducted on C40 concrete of 0.5, 1, 2, 3, 7, 14, and 28 days old which had been subjected to different levels of dynamic loads. The experimental results show that the strength of C40 concrete under train-induced dynamic loads with a basic frequency of approximately 114 Hz and a peak acceleration of approximately 0.2 g at an early age is the same as that of the specimen without vibration. Loads lower than the acceleration benchmark (frequency of 114 Hz and peak acceleration of 0.2 g) increase the strength in the later stage, while larger loads resulted in irreparable damage inside the specimen and reduced the strength. The peak acceleration value of 0.2 g can be regarded as the quasi-critical point of C40 concrete performance affected by the train dynamic load at the basic frequency of 114 Hz.