برآورد ضرايب ظرفيت باربري لرزه‌يي پي نواري مجاور شيرواني با روش خطوط مشخصه‌ي تنش

ٍEstimation of Seismic Bearing Capacity Coefficients of Strip Foundations Adjacent to Top of the Slopes by the Stress Characteristic Method.

برآورد ظرفيت باربري استاتيكي و خصوصاً لرزه‌يي پي نواري متكي بر روي زمين افقي يا شيب‌دار با استفاده از روش خطوط مشخصه‌ي تنش از جمله موضوعاتي است كه به سبب سادگي و بي‌نيازي به مش‌بند‌ها و مدل‌هاي رفتاري پيچيده، طي ساليان اخير توجه پژوهشگران حوزه‌ي ژيوتكنيك لرزه‌‌يي را به خود جلب كرده است. اين نوشتار موضوع ظرفيت باربري استاتيكي و لرزه‌‌يي پي نواري مستقر در مجاورت بالاي شيرواني را با استفاده از روش خطوط مشخصه‌ي تنش مورد بررسي قرار داده و پاسخي جديد را بر مجموعه‌ي بسيار محدود پاسخ‌هاي تقريبي موجود افزوده است. نتايج بررسي‌ها بيانگر آن است كه اولاً هر قدر شيب شيرواني بيشتر باشد، ضرايب ظرفيت باربري استاتيكي و لرزه‌يي پي‌هاي نواري مستقر در مجاور شيرواني كمتر خواهد بود؛ ثانياً در محيط وزين، ظرفيت باربري پي نواري مستقر در مجاور شيرواني از ظرفيت باربري پي مشابه متكي بر شيب كمتر است. در انتهاي نوشتار، برخي نمودارها و جداول كاربردي ارايه شده‌اند كه ضرايب ظرفيت باربري استاتيكي و لرزه‌‌يي پي نواري مجاور شيرواني را براساس روش خطوط مشخصه‌ي تنش به دست مي‌دهند.

Structures such as buildings, walls and towers are often located on sloping grounds, which may involve the construction of shallow foundations adjacent to top of the slope. The literature concerned with evaluation of bearing capacity factors of foundations is mostly limited to horizontal ground surfaces as well as static cases. Assessment of seismic bearing capacity of strip foundations has been the concern of only few researchers in the field of geotechnical earthquake engineering during the last decades. This paper presents the seismic bearing capacity factors N?, Nq and Nc of a rigid strip foundation resting adjacent to the top of a slope obtained by the stress characteristic method, commonly referred to as the slip-line method. The effects of the earthquake on body forces as well as on overburden surcharges are incorporated. It is assumed that the soil behaves rigid perfectly plastic and obeys the well known Mohr-Coulomb failure criteria under plane strain conditions. It is assumed that the state of the stress everywhere in the neighborhood of the foundation is at failure. It is also assumed that everywhere along the surface of the foundation, the ratio of the shear to the normal stress is equal to the horizontal earthquake acceleration coefficient (kh). The N? parameter was calculated based on the both-sides failure mechanism, whereas the Nq and Nc parameters were calculates based on the single-side failure mechanism. The Nc parameter for cohesive media was calculated using the rule of equivalent states. Some graphs and tables are presented that could be used in order to assess the seismic bearing capacity factors of foundations resting adjacent to top of a slope evaluated by the stress characteristic method. It is shown that all the seismic bearing capacity factors reduce considerably with increase in either the ground inclination or in kh. It is also shown that in weighty media, the seismic bearing capacity of a foundation adjacent to the top of a slope is less compared to the one resting on a similar infinite slope, whereas in weight-less media, they are equal. The values of the seismic bearing capacity factors calculated by the stress characteristic method are compared with those obtained by the upper bound theorem reported in the literature. It is observed that the stress characteristic method gives less value of the seismic bearing capacity factors than those estimated by the upper bound theorem.