بررسي عددي پايداري شيرواني ماسه‌يي روي رس نرم بهسازي‌شده با ستون سنگي

Numerical Investigation of Sand Embankment Stability over Soft Clays Retrofitted with Stone Columns

در اين پژوهش با استفاده از نرم‌افزارPlaxis ، پايداري شيرواني ماسه‌يي ساخته‌شده روي رس نرم مسلح به ستون سنگي به دو روش نوار معادل و ناحيه‌ي معادل بررسي شده است. با انجام تحليلهاي عددي اثر پارامترهايي نظير: قطر، زاويه‌ي اصطكاك و فاصله‌ي بين ستون سنگي، چسبندگي خاك رسي، ارتفاع و زاويه‌ي اصطكاك خاكريز در ضريب اطمينان شيرواني ماسه‌يي مورد بررسي قرار گرفته‌اند. نتايج حاصل نشان داده است كه از بين پارامترهاي مورد بررسي، مقاومت ستون سنگي و رس نرم در ضريب اطمينان پايداري تاثير بيشتري دارند. همچنين بر مبناي نتايج عددي و با توجه به متداول‌بودن روش طراحي ناحيه‌ي معادل نسبت به نوار معادل و براي تعديل تفاوت موجود بين نتايج حاصل از روش‌هاي مذكور، يك ضريب كاهش پيشنهاد شده است كه براي كل پارامترهاي بررسي‌شده در محدوده‌ي 74/0 تا 99/0 قرار گرفته است. توصيه مي‌شود كه ضريب اطمينان حاصل از روش ناحيه‌ي معادل با ضريب كاهش ذكرشده تعديل يابد.

Various techniques have been adopted to enhance the stability of embankments constructed over soft soils. One of the most appropriate methods for this purpose is the application of stone columns. In this study, finite element analyses were carried out using PLAXIS 2D to consider the stability of sandy embankments over a soft clay bed reinforced with stone columns. To estimate the factor of safety (FS) against the deep-seated failure of the embankments, both common approaches of equivalent strip and equivalent area methods were used as a comparative investigation. The numerical analyses were focused on the effects of parameters on embankment stability, such as the diameter as well as the spacing of stone columns, the friction angle of the stone columns, the cohesion of the clay bed, slope height and friction angle. The analyses results show that the enhancement values of the embankment safety factor, due to an increase in the stone friction angle and the cohesive strength of the clay, were more pronounced in comparison to the effects of other parameters. Thus, an increase of 12kPa in the cohesive strength of the clay bed caused 34.2% and 15.8% enhancement in the safety factor of the embankment, respectively, through the equivalent strip and area methods. As modeling equivalent strips is a tedious task, especially when the number of columns is high, geotechnical designers prefer to use the equivalent area method. Hence, a reduction factor was proposed here to apply to the safety factor of the equivalent area method. The analyses results show that the reduction factor varies between 0.74 and 0.99. The FS values obtained from the equivalent area method may be adjusted using such reduction factors.