ارايه‌ي گراف‌هاي طراحي به‌منظور به‌كارگيري ستون هاي سنگي جهت تثبيت خاكريز راه آهن متكي بر بستر رسي نرم

DESIGN CHARTS OF STONE COLUMNS FOR STABILIZATION OF RAILWAY EMBANKMENTS OVERLAID ON SOFT CLAY SUBGRADES

كنترل پايداري و نشست خاكريزهاي راه‌آهن متكي بر بسترهاي رسي نرم از نظر حفظ ايمني اهميت ويژه‌‌يي دارد. در ميان روش‌هاي تثبيت، اجراي ستون‌هاي سنگي ضمن سهولت اجرا و كارايي قابل‌ملاحظه، سازگاري بيشتري را با محيط زيست از خود نشان مي‌دهد. در اين نوشتار تلاش شده است تا با استفاده از روش اجزا محدود و نرم‌افزار PLAXIS 2D، مناسب‌ترين شيب پايدار خاكريز در ارتفاعات مختلف و در شرايط متكي بر ستون‌هاي سنگي مشخص شود. سپس با توجه به نتايج تحليل عددي، به‌طور جداگانه روابطي تحليلي ميان بار محوري راه‌آهن و نشست خاكريز با پارامترهاي هندسي ستون‌ سنگي و مقاومت زهكشي‌نشده‌ي بستر استخراج شده است. همچنين كفايت شيب خاكريز و چيدمان ستون‌ها در شرايط اعمال زلزله به‌صورت شبه استاتيكي بررسي شده است. در پايان نيز با استفاده از رابطه‌هاي تحليلي استخراج‌شده، گراف‌هاي طراحي ستون‌هاي سنگي زير خاكريز ارايه شده است.

An important issue in the design and implementation of railways located on loose beds is to control the stability and settlement of the embankment through stabilization of the beds. Of the very large number of stabilization methods of loose beds, the stone column can be characterized as economically compatible with the environment. In this method, loose materials are replaced by stone material with notable shear strength. Stone columns increase the bearing capacity and control settlement of the embankment. Furthermore, it prevents slippage of the soil structure during application of service and earthquake loads. However, not many studies have been conducted on the interaction between surcharge railways and embankments located on stone columns, the mechanism of load transfer from the embankment to the columns and the amount of embankment settlement. This paper is aimed at determining the stability slopes of an embankment at different heights (5m up to15m) using the 2-D finite difference method and Plaxis Software. Then, through considering the bearing mechanism of stone columns, an analytical relation (root minimum square method) between the axial load of the railway, the geometric parameters of the stone column and the strength parameters of the clay bed has been derived. Due to the importance of the settlement control of a railway embankment, a relation has been derived between embankment settlement and mentioned parameters. Moreover, in order to examine the proper arrangement of columns and embankment conditions for different factors of earthquake acceleration, seismic analysis was performed. Also, the results of the pseudo-static analysis of an embankment indicated that by an increase in the horizontal coefficient of an earthquake, Kh, the safety factor decreases. However, all considered embankments relying on the stone column were stable in the horizontal acceleration coefficient within the range of 0.1 to 0.5. Finally, using the derived analytical relations, design graphs of stone columns have been presented on the basis of characteristics of a stone column and bed, and the axial load of the railway.