مطالعه‌ي ميداني رفتار پايه‌هاي سنگريزه‌يي كوبشي (RAPs) نسبت به تغيير قطر

A FIELD STUDY ON THE BEHAVIOR OF SINGLE RAMMED AGGREGATE PIERS TOWARDS CHANGES IN DIAMETER

مزيت‌هاي فني و اقتصادي پايه‌هاي سنگريزه‌يي كوبشي (سيستم RAP) در تقويت خاك‌هاي نرم موجب توسعه‌ي كاربرد آنها در مهندسي عمران شده است. وجود اين مزايا، انگيزه‌ي اصلي توسعه‌ي تحقيقات در اين زمينه طي دو دهه‌ي اخير بوده است. در اين تحقيق، تاثير قطر پايه‌هاي سنگريزه‌يي كوبشي روي ظرفيت باربري، نشست، مدول سختي و نسبت بار پايه‌ها مورد مطالعه قرار گرفته است. در مجموع 8 آزمايش بارگذاري در محل بر روي دو گروه پايه‌هاي سنگريزه‌يي با طول ثابت 1 متر و قطرهاي مختلف از 105 تا 185 ميلي‌متر انجام شده است. تفسير نتايج آزمايش‌ها به‌طور خاص روي رفتارهاي بار- نشست، مدول سختي و نسبت بار برحسب تنش بالاي پايه متمركز شده است.

The technological and economic advantages of rammed aggregate pier systems (RAPs) in stabilization of soft soils are due to development of their applications in civil engineering. Over the last two decades, these benefits are the main motivation behind developing research in this field. In this study, the effect of the RAP diameter on the bearing capacity, settlement, stiffness modulus and load ratio of RAP has been studied. In total, eight in situ loading tests have been undertaken on two groups of single RAPs. The nominal length of RAPs is 1 m and their nominal diameters vary from 105 to 185 mm. The testing area consisted of relatively uniform saturated soft alluvial clay overlain by a 1-m-thick, wet, soft-to-stiff, silt layer. In order to load the rammed aggregate piers, mobile reaction beams, in the form of a loading cart and a modular rail system, were used, both to speed up the tests and to make them more economical. The results show that the rate of increase in load ratio (tip to top) in RAPs with bigger diameters is considerably higher than the rate of increase in load ratio (tip to top) in RAPs with smaller diameter. In addition, by increasing applied stress at the top of the RAP, the difference is also raised. In fact, RAPs with smaller diameter are more likely to experience bulging deformation, and RAPs with bigger diameter are more likely to experience tip deformation. So, in a two-layer soil system, in which the strong layer is on the weak layer, the use of RAPs with smaller diameters is desirable. Interpretations of the test results are particularly focused on the load-settlement behavior of single RAPs, the stiffness modulus and the load ratio, in terms of stress at the top of the RAPs.