كليدواژه :
شمع كوبشي , گيرش خاك , مدلسازي فيزيكي , خاك رس نرم
چكيده فارسي :
تعيين ظرفيت باربري نهايي شمع در طراحي از اهميت ويژهاي برخوردار است.در اغلب اوقات آزمايش بارگذاري شمع در فاصله زماني كوتاه پس از اجراي آن انجام مي شود. نتايج حاصله بعنوان ظرفيت باربري نهايي شمع در طراحي لحاظ مي شود. كوبش شمع سبب تغيير شكل زياد خاك اطراف شمع و بوجود آمدن اضافه فشار آب حفره اي در پيرامون آن مي شود اين امر سبب كاهش مقاومت برشي و ظرفيت باربري شمع مي گردد. آزمايش استاتيك و ديناميك شمع بيانگر ظرفيت باربري شمع در زمان آزمايش مي باشد براي بررسي تاثير گيرش در ظرفيت باربري شمع، آزمايش ها بايد در زمان هاي مختلف انجام شود كه اين امر زمان بر و غيراقتصادي مي باشد. بنابراين بايد راه حل هاي عددي و تجربي توسعه يابد تا بتوان با توجه به تعداد محدودي آزمايش هاي استاتيكي و ديناميكي تاثير زمان در ظرفيت باربري شمع را بررسي كرد. محاسبه ظرفيت باربري شمع با زمان سبب كاهش قطر، طول و تعداد شمع و كاهش اندازه تجهيزات كوبش مي شود كه اين موضوع از ديدگاه اقتصادي قابل توجه است. هدف از اين تحقيق بررسي ظرفيت باربري شمع هاي كوبشي در خاك رسي نرم در زمان هاي مختلف پس از كوبش مي باشد. آزمايش ها براي ارزيابي افزايش ظرفيت بابري شمع كوبشي در خاك رس نرم شمال ايران در نظر گرفته شده است. چندين آزمايش بارگذاري بر روي شمع هاي آلومينيومي كوبشي در خاك زسي نرم انجام شد. نتايج نشان مي دهد 14روز پس از كوبش، ظرفيت باربري شمع نسب به زمان پايان كوبش تقريبا 80% افزايش داشته است. بخش عمده از افزايش ظزفيت باربري در سه روز پس از كوبش مي باشد و پس از آن نرخ افزايش ظرفيت باربري شمع كاهش مي يابد.
چكيده لاتين :
Determination of ultimate pile capacity is important for proper design and construction of pile foundations. Most of the time, the pile load test is carried out shortly after the installation of pile. The pile capacity obtained from the load test is often assumed to be the ultimate pile capacity in most of design methods. However, during pile installation, the soil around the pile experiences large deformations and changes in excess pore water pressure, which in turn reduces the shear strength and pile bearing capacity. After the completion of pile driving, the pile capacity increases as the strength of the surrounding soil increases mainly by reconsolidation, manifested by the dissipation of excess pore pressure at the soil-pile interface zone. the ultimate pile capacity could be underestimated if pile load test was carried out while excess pore water pressure still remains, which may lead to a conservative pile design. It should be noted that a pile static load test (SLT) and a dynamic load test (DLT) only measure the pile load–displacement relation and ultimate load at the time of testing; they do not provide any information on pile capacity variations over time. Pile load tests must be repeated at different times to evaluate any set-up effects, which can be time-consuming and costly during pile construction. Therefore, it is essential to develop empirical and numerical solutions to enable analyzing and estimating long-term pile set-up effects on the basis of limited numbers of SLT and DLT tests. Accurate estimation of pile setup, rather than measuring directly in the field, may reduce the cost of piling and still provide the required performance for the pile. Prediction of pile capacity gain with time after driving would certainly be advantageous from an economic standpoint. Incorporating the effects of setup into pile design is expected to reduce the general cost of piling project by reducing pile diameter, pile length, size of driving equipment, and subsequently piling duration. The major reasons for set-up can be categorised into the following two groups: (1) the generation of excessive pore water pressure during pile driving and subsequent dissipationover time, leading to soil consolidation, and (2) the aging process. The purpose of this research is to conduct experimental research aimed at developing an understanding of pile capacity in soft clays and to develop relationship between the pile capacity and elapsed time after the end of initial driving for cohesive soils. An experimental program was developed to study the evolution of pile capacity increase with time for piles driven into a type of soft clay in northern Iran. results of a series of pile load tests conducted on small-scale Aluminum pile foundations driven into soft clay. The piles were tested instantly after driving to measure their initial bearing capacities, and were tested repeatedly over different elapsed times to study the evolution of pile capacity over time. Results show pile capacity increases approximately 80% of initial value, 14 days after initial pile driving. A large proportion of this pile capacity increase over time, also known as setup, was generated within the three days due to fast excess pore water pressure dissipation, and afterward, the pile capacity increased at a lower rate.
