محاسبه‌ي تحليلي اثر سربار در فشار فعال خاك در ديوارهاي حايل با استفاده از روش قطعات افقي

Analytical calculation for effect of surcharge on active earth pressure of retaining walls

در بسياري از مسايل ژيوتكنيكي لازم است كه فشار فعال ايجادشده در يك ديوار حايل، با توجه به سربار وارده بر خاكريز پشت ديوار محاسبه شود. در اين تحقيق بر مبناي روش‌هاي تحليلي، روش قطعات افقي مورد بازنگري و تدقيق قرار گرفته و فرمول‌بندي كامل آن براي به‌دست‌آوردن اثر سربار در ديوارهاي خاك مسلح براي خاك‌هاي اصطكاكي و چسبنده‌ي اصطكاكي ارايه شده است. بر مبناي اين فرمول‌بندي جديد، فشار خالص ناشي از اثر سربار وارد در ديوارهاي حايل محاسبه و با نتايج به‌دست‌آمده از روش‌هاي ديگر مقايسه شده است. بررسي‌هاي صورت‌گرفته نشان مي‌دهد كه روش پيشنهادي قادر است به خوبي تاثير چسبندگي و زاويه‌ي اصطكاك داخلي را در فشار فعال ناشي از سربار برآورد كند.

Retaining walls are one of the most common approaches for construction of retaining soil structures across the world. These walls have remarkable flexibility against the earthquake loads and also they are less sensitive against settlements. In many retaining walls problem, it is necessary to determine additional earth pressure produced by surcharge loads acting on the soil surface behind the wall. Considering the application of various surcharge loads on the backfill in such systems, the necessity has been felt in the last decades to an appropriate method for calculating the effect of surcharge on the active earth pressure in retaining walls. In this study, based on analytical methods, previous formulation of horizontal slices method are improved and a new formulation has been proposed for estimating the effect of surcharge on active earth pressure of retaining walls with cohesive-frictional backfill. A comparison of the analytical results obtained from the proposed method with those of previous research. It was concluded that the analytical procedure proposed reliably calculates the active earth pressure due to surcharge in cohesive-frictional soil. The variations of angle of failure wedge versus intensity of surcharge indicate that increase in the intensity of surcharge causes increase in the angle of failure wedge but change in the distance of surcharge from the wall does not affect the angle of failure wedge significantly. Also, the results show that by increase in the distance of surcharge from the wall, the lateral pressure decreases and moving the surcharge out of failure wedge has no effect on the active earth pressure. Comparisons show that the results from the suggested method are a lower bound for the values obtained by recommended methods in ASHTOO (2007) and U.S Army Crops (2005) codes. However the suggested method is of good agreement with that of Motta (1994).