مدلسازي آزمايشگاهي - عددي رفتار لرزه اي شيب هاي ماسه اي خشك مسلح شده با رديف شمع

Experimental-Numerical modeling of seismic behavior of dry sandy slopes reinforced by piles row

در اين مقاله رفتار ديناميكي شيب خاكي متشكل از مصالح ماسه اي خشك سست توسط مدل هاي كوچك مقياس فيزيكي و عددي مطالعه مي شود. رديفي از شمع هاي شناور مدل آلومينيومي درون شيب ماسه اي ساخته شده در جعبه ي صلب و شفاف مدلسازي فيزيكي روي ميز لرزه نصب شده اند. ميز لرزه ي كوچكمقياس دو درجه ي آزادي با منشا ارتعاش الكتروديناميك به كمك سنسورهاي اندازه گيري شتاب و تغييرمكان ابزار بندي شده است. در اين تحقيق به شكل نوآورانه اي، بارگذاري لرزه اي هارمونيك يك بار در راستاي طولي شيب، يكبار در راستاي عرضي شيب و بار ديگر به طور همزمان در هر دوي اين راستاها اعمال شده است. مقادير پاسخ هاي نشست تاج شيب كه به كمك سنسور lvdt در هر يك از اين حالات بارگذاري اندازه گيري شده اند، به عنوان منحني هاي خروجي ارائه شده اند. در پايان مقاله، جهت صحت سنجي نتايج مدل فيزيكي كوچك مقياس، مدل عددي تفاضل محدود سه بعدي نظير آن ايجاد شده است. هماهنگي و توافق مناسبي بين نتايج عددي و آزمايشگاهي بدست آمده است. نتايج اين مطالعه نشان مي دهد كه افزايش راستاي بارگذاري شيب از حالت مرسوم يك محوري به دو محوري و نيز عدم تسليح شيب با رديف شمع، باعث افزايشي چشمگير و بيش از 100% در مقادير تغييرمكان هاي قائم خواهد شد.

In this study the behavior of floating piles row with circular cross-section were installed inside the dry sandy slope by help of three-dimensional numerical analyses and physical modeling have been simultaneously studied. The three-dimensional numerical modeling was used for conducting the parametric studies about effects of directions of imposition of harmonic seismic loading on the main geotechnical parameters of floating piles row-sandy slope problem. The seismic loading of harmonic sinusoidal waves in the form of seismic motions in the in-plane and out-of-plane directions along the longitudinal and transverse directions of slope model and both of them were imposed on the slope physical and numerical models. Moreover, the physical modeling of the investigating problem was implemented for validation of numerical results by imposing the sinusoidal harmonic loading in the longitudinal and transverse horizontal directions of micro-scale slope model by help of small-scale geotechnical shaking table. Reinforcing of a dry sandy slope by a row of floating piles (similar to reinforcing of slope by end-bearing piles row) results in significant decrease (to about more than 50 percent) in slope’s vertical displacements. Out-of-plane components of seismic loading such as transverse component of earthquake, T component, (productive of horizontal shear waves, i.e., SH waves) also in the presence of site’s effects such as “directivity effects” can produce the responses as large as the in-plane motion components such as earthquake longitudinal contained component, L (productive of P and SV seismic waves). The motion of slope sliding wedge in the strong ground motions is a rigid block motion while the failure wedge displacement under weak ground motions is a negligible motion and occur in a flexible block manner. Simultaneous seismic loading along two-axes of three coordinate axes in contrast to the current slope seismic loading that the seismic loading are imposed along one axis and in the longitudinal direction of slope failures surface, have great effects on the slope displacements values and internal efforts generated in the reinforcing piles row. Studying and solving the classic problem of in-plane and out-of-plane seismic-waves propagations in the combination with the existence of slope in the ground and piles row interaction (i.e., adding the piles row-slope seismic interaction to the initial classic problem) by help of present available analytical and mathematical solutions will be a very difficult problem. By combining of the in-plane and out-of-plane seismic motions the complexity of the piles row-sandy slope dynamic interaction problem will increase and in the some cases presenting analytical and closed-form solutions can be impossilble. The alternating solutions for solving these complex problems proposed by the present paper are the simultaneous using of numerical and shaking table physical modeling for understanding the precise details and ambiguities of the problem in the complete scientific and practical-empirical frameworks. The results of present study show that installing a row of floating piles similar to the end-bearing piles row can reduce the displacements of loose dry sandy slope and through this manner the seismic stability of slope against the local and general failures increased. In the present paper despite of increasing the directions of seismic loading from one-direction to the two-directions the installed floating piles row sufficiently played their roles in the reducing seismic displacements of slope. Indeed, according to the experimental-numerical results of the present paper, decreasing of slope crest settlements by installing a row of floating piles in the seismic loading cases are more than 50 percent. The results of small-scale 2DOF geotechnical shaking table physical model were used to verification of the obtained 3D numerical results. There is a good agreement between the numerical and physical models results.