تحليل رفتار شمع‌هاي توخالي با مقاطع غيريكنواخت در فرآيند كوبش

Analysis of Non-Uniform Cross Section Hollow Piles in Drivability Process

يكي از روش‌هاي اجراي شمع، استفاده از روش كوبش براي نصب شمع‌هاي بتني پيش‌ساخته به كمك ابزار خاص مي‌باشد. نحوه كوبش و كنترل اين فرآيند يكي از جنبه‌هاي مهم اجرايي اين شمع‌ها بوده، به‌طوري‌كه عدم دقت كافي به اين مسيله، علاوه بر كاهش راندمان عمليات كوبش، خاك و محيط اطراف را تحت تاثير قرار مي‌دهد. در اين مقاله، به بررسي رفتار شمع‌هاي توخالي استوانه‌اي و مخروطي شكل در فرآيند كوبش به كمك آزمايش واقعي در سايت و تحليل عددي پرداخته شده است. براي اين منظور، با استفاده از انجام آزمايش‌هاي واقعي و روش تفاضل محدود و معيار گسيختگي موهر-كولمب، رفتار شمع و خاك هنگام كوبش مدلسازي شده و شرايط استفاده و كاربرد اين‌گونه شمع‌ها در عمليات كوبش مورد ارزيابي قرار مي‌گيرند. اطلاعات و نتايج حاصل از اين پژوهش را مي‌توان در مراحل مختلف طراحي و اجراي شمع‌هاي كوبيدني و همچنين براي بهينه‌سازي آنها استفاده نمود. با مقايسه نتايج به‌دست‌آمده از بررسي رفتار شمع‌هاي با هندسه مختلف در آزمايش‌هاي واقعي و تحليل عددي، نتيجه‌گيري مي‌شود كه هندسه و شكل شمع در رفتار كوبشي آنها تاثير مستقيم داشته و با استفاده از اين‌گونه شمع‌ها در عمليات شمع‌كوبي، علاوه بر كاهش مصرف انرژي به ميزان بين 25 تا 60 درصد، افزايش راندمان و بهره‌وري عمليات كوبش نيز فراهم مي‌گردد. همچنين شرايط باز يا بسته بودن نوك شمع تاثير بسيار زيادي در فرآيند كوبش دارد و در شرايط اعمال انرژي يكسان در حين عمليات كوبش، شمع ته‌باز عملكرد بهتري نسبت به شمع ته‌بسته داشته و در مجموع شمع مخروطي ته‌باز عملكرد بهتري نسبت به ساير شمع‌ها با هندسه‌ي مختلف دارد.

Pile driving is one of the pile construction methods to install prefabricated concrete piles using special tools. Driving method and its process is one of the most important aspects of implementation of this pile, so that the lack of sufficient accuracy to this problem, in addition to reducing operation efficiency, affects the surrounding environment and soil. In this paper, the behavior of cylindrical and tapered hollow piles were investigated with real tests and numerical analyses using FLAC3D software. The efficacy of pile geometry such as cylindrical and tapered hollow piles is analyzed in pile driving under hammer impact. Pile T is fully tapered hollow pile, and pile C is cylindrical one. All piles made by steel have the same length (Lp = 250 cm) and volume. Their properties are in Table (1). The single acting hammer with a 300 kg weight falling through a distance of 1 m is used to install all piles to the embedded length of 0.5 m to 2 m. The pile driver is made by different parts such as mounting frame, hammer and electric motor for lifting the ram to the selected falling height, and the hammerhead falling to induce an impact on the hammer components. The sand deposit was located in Vardavard-Tehran with maximum specific weight, 2.16 kg/cm3 and relative density of about 93%. The pile driving analyser (PDA) with two accelerometers and strain transducers was used to record the induced pile velocity and strain. The PDA takes results from every impact velocity and force signals obtained by sensors attached to the pile. To measure forces and velocities at the pile, they were attached externally along the pile shaft at 32.4 cm from the pile head in two opposite directions. The driving records for all piles with different toe condition in terms of cumulative hammer blow count versus the penetration depth are illustrated in Figure (1). It can be seen that for achieving the same final penetration, the cylindrical hollow pile required more number of blows than tapered ones. Besides, velocity and displacement were measured as shown in Figure (2). By comparing the obtained results from experimental and numerical analyses, it has been found that the behavior of hollow piles was changed by varying of its geometry. It is also concluded that the hollow piles offer better drivability performance with used energy reduction from 25 to 60% than the filled ones of the same volume and length. The open or close-ended pile has also an effect on pile driving process. In the case of applying the same energy during pile driving, the open-ended pile has better performance than close-ended one, and tapered shape pile is also performed better than the ones with other different geometries. In this case, tapered pile has also performed better than cylindrical one by an increase in pile velocity and displacement.