مطالعه‌ي آزمايشگاهي ضريب فشار جانبي مخلوط ماسه- بنتونيت غيراشباع در حالت سكون

Experimental Investigation of At-Rest Lateral Pressure of an Artificially Prepared Sand-Bentonite Mixture

معمولاً مخلوط ماسه- بنتونيت به ‌منزله‌ي پوشش اطراف مخازن دفع زباله‌هاي شهري مورد استفاده قرار مي گيرد. اين پوشش داراي طول زياد و ضخامت كم است و بنابراين، رفتار اديومتريك دارد. در اين نوشتار، يك اديومتر اصلاح‌شده براي تعيين ضريب فشار جانبي در حالت سكون خاك هاي آماسي اشباع و غيراشباع معرفي مي شود. رينگ صلب دستگاه با حكاكي سه ديافراگم با قطر 15 ميلي‌متر و ضخامت 35/0 ميلي‌متر اصلاح مي‌شود. اين ديافراگم‌ها با استفاده از فشار هيدرواستاتيك آب، كه مي توان آن را به تغييرشكل ايجادشده در ديافراگم مرتبط كرد، كاليبره مي‌شوند. روش ابتكاري جديدي براي به‌دست‌آوردن پارامترتنش موثر خاك غيراشباع با استفاده از رفتار تغيير حجمي آن، ارايه و ضريب فشار جانبي مخلوط ماسه- بنتونيت در حالت سكون و در گام‌هاي تنش مختلف تعيين مي‌شود. در نهايت، تاثير بارگذاري‌هاي هيدروليكي در ميزان فشار جانبي خاك مورد بحث و بررسي قرار مي گيرد.

Sand-bentonite mixtures are usually utilized as liners for municipal waste disposal facilities. These widespread liners are constructed in thin layers and, therefore, indicate an oedometric behavior. Experimental study of the at-rest lateral pressure of these soils is an important step in understanding the hydro-mechanical behavior of the abovementioned barriers. Despite the huge amount of research on the oedometric volume change of expansive clay, little work has been done to date on the K0-coefficient of these soils, and the effect of hydraulic loading on their mechanical behavior has been rarely studied. In this paper, a novel oedometer is introduced to determine the coefficient of the lateral pressure of soil. The almost rigid ring of the modified apparatus has three circular diaphragms, with a diameter of 15mm and a thickness of 0.35mm. Three LVDTs are installed in contact with these diaphragms to measure the horizontal deformation of the thin diaphragms induced by the horizontal pressures. The diaphragms are calibrated using the water hydrostatic pressure, and pressure and deformations are correlated. Adopting the osmotic method to impose the matric suction, the modified oedometer apparatus accommodates the circulation of the PEG solution beneath the soil sample. A semi permeable membrane is introduced between the sample and the PEG solution to prevent the PEG macromolecules from passing towards the sample. Twenty five percent of the studied material is composed of bentonite and the rest of the soil is well graded sand. The coefficient of the at-rest lateral pressure of the material is determined at various stress states, and the influence of hydraulic loading on the lateral pressure of the soil is discussed in detail. A single effective stress approach is employed to determine the at-rest lateral pressure of the soil particles. The outcomes indicate that the K0-parameter decreases significantly with suction increase. Furthermore, drying-wetting cycles harden the soil, reducing the amount of compressibility indices and the K0-parameter of the material.