تعيين ظرفيت باربري شمع با استفاده از تحليل هاي عددي سيستماتيك آزمايش بارگذاري شمع بر مبناي روش تاگوچي

Determination of Bearing Capacity for Piles Using Systematic Numerical Analyses of Pile Load Testing Based on Taguchi Method

آزمايش بارگذاري شمع روشي قابل اعتماد ولي گران در تعيين ظرفيت باربري شمع است. عملاً مي توان با انجام تعداد محدودي آزمايش صحرايي، در كنار به‌كارگيري مدل‌سازي هاي عددي، ظرفيت باربري شمع را با دقت خوبي تعيين كرد. در اين پژوهش، با استفاده از روش سيستماتيك تاگوچي، طرح مناسبي براي نحوه‌ي تغيير تمامي پارامترهاي موثر در نتايج تحليل عددي به‌منظور انطباق نتايج آن با نتيجه‌ي آزمايش بارگذاري شمع ارايه شده است. با اين‌كار پارامترهاي تدقيق‌شده‌ي خاك و اهميت نسبي هريك بر ميزان ظرفيت باربري مشخص مي ‌شود. در اين پژوهش، با داشتن پارامترهاي مكانيك خاك آزمايشگاهي و همچنين نتايج آزمايش بارگذاري شمع در يك محل، با روش تاگوچي ضمن تدقيق پارامترهاي خاك، عامل مقاومتي فصل مشترك، زاويه‌ي اصطكاك داخلي و چسبندگي مهم‌ترين و نسبت پواسون و زاويه‌ي اتساع كم اهميت‌ترين عوامل تشخيص داده شدند.

Determination of the bearing capacity of piles is an important subject which has always challenged geotechnical engineers. The factors which affect the bearing capacity of a pile in compressive, tensile or lateral loading consist of the geometrical characteristics of the pile, such as length and shape of cross section, execution methods (cast in place, driving) and also geotechnical specifications. Due to these numerous factors, a direct estimation of the pile baring capacity based on in-situ testing is the most precise and reliable method. However, this method is expensive, time consuming and troublesome. In this regard, geotechnical engineers usually utilize classic formulations proposed by some soil mechanics pioneers, such as Meyerhof, Hansen, and Vesi?, to estimate the ultimate bearing capacity of piles. However, these relationships may lead to conservative or unsafe designs. Numerical methods, on the other hand, are a powerful but relatively cheap approach, which help engineers to obtain a reasonable estimate of the ultimate bearing capacity, based on existent soil mechanics parameters. Nevertheless, a wrong determination of geomechanical parameters can lead to a wrong estimation of pile bearing capacity. To overcome those difficulties, a combination of pile loading tests and numerical modeling is able to submit a precise and reasonable cost solution to the problem. In this method, the geometechnical parameters are varied in the numerical modeling in such a way that the results of the load-settlement curve obtained by a number of numerical analyses find good agreement with the same curve recorded during in-situ pile testing. In this study, a suitable arrangement of all parameters affecting the numerical analysis is introduced, based on the Taguchi systematic method, to allow good agreement between the results of numerical analysis and pile load testing. Hereby, accurate soil parameters and the relative importance of each factor governing the bearing capacity are determined. In this research, laboratory soil mechanics parameters and the results of pile load testing in a specific site are incorporated into a group of Taguchi analyses to improve the mechanical parameters of soil. The results indicated that the soil-pile interface factor, frictional angle and cohesion of soil are major factors in the bearing capacity, while the Poisson ratio and dilation angle play minor roles.