مطالعه‌ي ميداني مقايسه‌ي رفتار پايه‌هاي سنگريزه‌يي كوبشي (RAPs) با پايه‌هاي بتني درجاريز (CPs) تحت بار بركَنش

A Comparative Field Study of the Behavior of Rammed Aggregate Piers and Concrete Piers under Uplift Loads.

در اين نوشتار به ارايه‌ي مقايسه‌ي رفتار و پارامترهاي حد طراحي اندازه‌گيري‌شده‌ي پايه‌هاي سنگريزه‌يي كوبشي و پايه‌هاي بتني درجاريز تحت بار بركنش در محل پرداخته شده است. در اين مطالعه، دو گروه متناظر چهارتايي از پايه‌هاي سنگريزه‌يي كوبشي و پايه‌هاي بتني درجاريز منفرد با مقياس كوچك در محل ساخته و آزمايش شده‌اند. ناحيه‌ي آزمايشي شامل يك لايه لاي مرطوب يكنواخت بوده است. نتايج نشان مي‌دهند به طور ميانگين، بار بركنش و جابجايي اندازه‌گيري‌شده در حد طراحي پايه‌هاي سنگريزه‌يي كوبشي، حدود 3/1 برابر مقدار نظير در پايه‌هاي بتني است. رفتار پايه‌هاي بتني نيز به ازا طول‌هاي مختلف به صورت صلب و رفتار پايه‌هاي سنگريزه‌يي كوبشي به ازا نسبت‌هاي لاغري كمتر از 4، مشابه پايه‌هاي بتني و به ازا نسبت‌هاي لاغري بيشتر از 4، به صورت شكل‌پذير هستند.

This paper aims to compare the behavior and design limit parameters of rammed aggregate piers (RAPs) and of cast-in-place drilled concrete piers (CPs) under in situ uplift loading. Usually, RAPs and CPs are two new and common systems for strengthening foundations against uplift loads used in buildings with braced frames. In this research project, two groups of small scale RAPs and CPs were constructed and tested on site. The single piers had a fixed diameter of 135 mm and variable lengths of 300, 550, 650 and 850 mm. The test site was the Bushehr Special Economic Zone, where the testing area was made up of a uniform layer of moist silt; 1.2 meters thick and stiff. The trial piers were constructed and loaded in a linear row at a safe distance from each other. For uplift loading, a mobile reaction beam system, made up of a heavy cart, modular rails and an uplift loaded frame, was utilized. Results show that on average, the measured load and pier deflection at the design limit of RAPs were 1.36 and 1.32 times the corresponding values in CPs, respectively. The behavior of CPs was rigid at various lengths. The behavior of RAPs with slenderness ratios of less than 4 was similar to that of the CPs, and the behavior of RAPs with slenderness ratios of higher than 4 was ductile. There was better agreement between the results of the calculated and measured uplift loads in CPs than in RAPs. The stiffness modulus of both types of pier was the same at different lengths under uplift loads. In general, it seems that these technical merits, including the fact that RAPs (unlike CPs) do not need cement, has convinced engineers to use RAPs under uplift loading and do more research in this area.