The collapse and creep beheviour of kaolin with double porosity structure

Despite several studies and researches already carried out on secondary consolidation in fine-grain soils, there is no consensus among researchers about the changes of the coefficient of secondary consolidation versus stress. The present research specifically aims to discuss the trend of these changes in soils having double porosity and undergoing stress. The behavior of kaolin has been investigated un this work. Samples with a double porosity structure have been compacted. In order to make sure of the preparation procedure as well as the existence of double porosity in them, prosimetry experiments were also carried out by mercury intrusion method which finally confirmed the existence of double porosity structure in the samples. The samples were put in a consolidation apparatus. Saturation was done in two ways; the first group samples were saturated and then loaded. In the second group, the samples were loaded and then saturated under a constant load. The results indicate that the order of saturation process has no effect on the porosity of the samples after they have been saturated (Collapse). Over the long time of measuring the secondary changes in soil volume, the samples were put under a constant load, and value of increase in settlement versus time after the completion of initial consolidation was measured. The experimental data shows that in the stress range of 100 to around 300 kPa, the coefficient of secondary consolidation has had an increasing trend reaching its maximum and has descended after passing the 300 kPa. This result is in compliance with the past researchers’ results trend. So, given that the soil used by the past researchers has been of simple-porosity type, it can be inferred from the results of the present research that double porosity structure has no effect on trend of changes in secondary consolidation coefficient. The main purpose of this research is to present experimental data on the changes of coefficient of secondary consolidation under stress in an aggregated soil,. One-dimensional consolidation tests were performed and analyzed. The effect of net stress and initial porosity on changes in secondary consolidation coefficient was also studied. The paper is divided into four major parts; after the first part of the paper, introduction, the second part presents details of the experimental plan including characteristics of the soil under study, sample preparing technique, and experiment procedure (method of applying loads). Results and their interpretation are discussed in the third part, and finally, the main findings of the research are summarized in the fourth section. The tests indicated that path of collapse of structure and transposition of loading and saturation processes have no effect on porosity of sample after collapse at a certain stress value, and end of the primary consolidation line is a unique line.