Time effect of secondary consolidation coefficient of over-consolidated soil

In order to explain the phenomenon that post-construction settlement of highway subgrade reinforced by surcharge preloading is still greater than prediction, the time effect of secondary consolidation coefficient of over-consolidated soil was analyzed based on Bjerrum's creep diagram and the tangent definition of secondary consolidation coefficient, and then a corresponding hyperbolic theoretical model of secondary consolidation coefficient which increased along with time was established. As the secondary consolidation characteristics of actual soil were more complex than those revealed by Bjerrum's creep diagram, this theoretical model was modified by soil tests and a more generalized time-growth model of secondary consolidation coefficient was proposed, and a formula of post-construction secondary settlement corresponding to it was also established to estimate the post construction settlement in surcharge preloading engineering. The results show that secondary consolidation coefficient of over-consolidated soil is not only related to the effective stress defined over consolidated ratio, but also related to the development time of secondary settlement. When the effective stress defined over consolidated ratio is relatively small, the secondary consolidation coefficient of the soil increases quickly along with time in early period, and it could be approximately regarded as a constant in late period. When the ratio is relatively large, the secondary consolidation coefficient of over-consolidated soil increases slowly along with time, but it will have a significant development in late period. So its long-term time effect cannot be ignored, which must be taken seriously into account in evaluating the post-construction settlement of surcharge preloading ground. © 2016, Editorial Department of China Journal of Highway and Transport. All right reserved.