بررسي تاثير قطر شمع در مدول و ضريب عكس‌العمل افقي بستر با درنظرگرفتن اثرات بار محوري و ناهمگني خاك

Investigation of Pile Diameter Effect on Modulus and Coefficient of Horizontal Sub-Grade Reaction, Considering Axial Load and Soil Heterogeneity

در روابط تيوريك موجود، مدول عكس‌العمل افقي بستر شمع، كه با استفاده از يك سري فنرهاي كشسان خطي و غيرخطي مستقل تعيين مي‌شود، مستقل از قطر شمع و يا تابعي خطي از آن در نظر گرفته مي‌شود. اما در واقع، رفتار واقعي شمع به‌ويژه با سر آزاد، به دليل بروز رفتار خميري در خاك، از روابط به مراتب پيچيده‌تري پيروي مي‌كند. در اين پژوهش، اثر ميزان قطر شمع در مدول عكس‌العمل افقي بستر شمع با استفاده از روش تفاضل محدود غيرخطي مورد بررسي قرار گرفته است. در تحليل‌هاي انجام‌شده نيز اثرات ناهمگني و بار محوري بررسي شده است، كه انجام اين امر در روابط تيوريك موجود ممكن نيست. نتايج حاصله، بيانگر افزايش مقدار مدول و كاهش ضريب عكس‌العمل بستر با افزايش قطر و تاثيرات قابل ملاحظه‌ي ناهمگني و بار محوري در اين روند هستند.

The modulus of horizontal sub-grade reaction is one of two important stiffness parameters. This modulus defines the relationship between the soil reaction, p, and the pile deflection, y. Thus, knowing the exact amount of horizontal sub-grade reaction will lead to a more accurate pile design. In the theory of a sub-grade modulus, soil stiffness is defined by a series of independent elastic springs, while, in reality, they are interrelated in a complex fashion. Also, in cases where plastic soil behavior will most likely be initiated at the ground surface, especially for pile heads, the effect of pile diameter on the sub-grade modulus will be more important. Furthermore, in the classical sub-grade problem of Vesic, a flexible beam supported on an elastic half-space, the effect of heterogeneity has not been taken into account. Thus, in this study, the real behavior of a sub-grade modulus with pile diameter, the effect of heterogeneity and the existence of axial loads on the variation of sub-grade reaction, are investigated using a traditional computer code, namely FLAC (accounted for the Fast Lagrangian Analysis of Continua). The validation of the modeling procedure is carried out using a laterally loaded pile case, in which, the behavior of a driven pile was experimentally studied on over-consolidated clay in Houston. To take the heterogeneity effect into account, the elasticity modulus of the soil was considered to be a linear function of depth. The results obtained by numerical modeling were compared to the traditional Vesic and Bowel equations. As results, in spite of Terzaghi, Vesic and Bowel methods, it is obtained that the horizontal modulus of sub-grade reaction increases with the pile diameter. Also, a higher heterogeneity factor leads to a higher rate of increase in the value of sub-grade reaction. In the case of larger pile diameters, this increase in the sub-grade reaction value will be more reasonable. In addition, in homogenous clays, axial loads have no significant effect on the value of the sub-grade reaction. Nevertheless, in heterogeneous clays, this modulus increases with the degree of heterogeneity.