رفتار كائولين با ساختار تخلخل دو گانه در فروريزي و خزش

The Collapse and Creep Behavior of Kaolin with Double Porosity Structure

اين پژوهش به صورت خاص به بحث چگونگي اين تغييرات در خاك هايي كه داراي تخلخل دوگانه هستند و تحت اثر تنش قرار مي گيرند پرداخته است. براي انجام اين پژوهش از خاك كائولينيت استفاده گرديده است. براي اطمينان از روش ساخت نمونه و وجود تخلخل دوگانه در آنها، آزمايش تخلخل سنجي به روش تزريق جيوه نيز انجام گرفت كه وجود تخلخل دو گانه در نمونه ها را تاييد نمود. نمونه ها در دستگاه تحكيم قرار داده شده و بارگذاري انجام گرفت. اشباع به دو شكل انجام پذيرفت؛ در دسته اول ابتدا نمونه اشباع و سپس بار گذاري انجام گرديد و در دسته دوم نمونه بار گذاري و سپس تحت بار ثابت اشباع شد، نتايج بدست آمده حاكي از عدم تاثير ترتيب اشباع بر ميزان تخلخل نمونه ها پس از رمبندگي است. در طول زمان قابل توجهي به منظور اندازه گيري تغيير شكلهاي ثانويه خاك؛ نمونه ها به مدت زيادي تحت بار ثابت قرار داده شدند و افزايش نشست در برابر زمان پس از تكميل تحكيم اوليه اندازه گيري گرديد. داده هاي آزمايشگاهي نشان مي دهد ضريب تحكيم ثانويه در بازه تنش هاي 100 كيلو پاسكال تا حدود 300 كيلو پاسكال سير صعودي و به ماكزيمم خود رسيده و پس از آن روند نزولي را طي مي كند كه با روند نتايج محققين گذشته انطباق دارد. بنابر اين نظر به آنكه خاك استفاده شده توسط محققين گذشته داراي تخلخل ساده بوده است. عدم تاثير ساختار تخلخل دوگانه بر روند تغييرات ضريب تحكيم ثانويه از نتايج اين پژوهش قابل استنتاج مي باشد.

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.