اثر تراكم خاك در رانش ديناميكي وارد بر كوله‌ي پل‌هاي يكسره و مجزا

Density Effects on Dynamic Earth Pressure behind Integral Bridge Abutments under Traffic Loading

حذف مفاصل انبساطي و بالشتك‌ها در محل اتصال عرشه و كوله‌ي پل، به منزله‌ي يك مزيت قابل توجه از دو منظر اقتصادي و اجرايي، ساخت پل‌هاي يكسره را بسيار متداول كرده است. در اين نوشتار، براي تعيين رانش خاك وارد بر كوله‌ي پل، از مدل‌سازي عددي با نرم‌افزار FLAC استفاده شده است. رانش خاك پشت كوله‌ي پل‌هاي يكسره، تحت سربار سيكلي ترافيك، در تراكم‌هاي مختلف به‌دست آمده و با رانش وارد بركوله‌ي پل‌هاي متداول (پل‌هاي با بالشتك‌هاي ارتجاعي در محل اتصال عرشه به كوله، كه در اين نوشتار پل‌هاي مجزا ناميده شده‌اند) مقايسه شده است. نتايج تحليل عددي با نتايج يك تحليل آزمايشگاهي مقايسه و اعتبارسنجي شده است. بررسي اثر ميزان تراكم خاك در رانش سيكلي، مبين تفاوت قابل ملاحظه در توزيع و مقدار رانش بين پل‌هاي يكسره و مجزاست.

Integral bridges are gaining increasing popularity because of economics and their fast construction process, associated with the omission of bearing supports and expansion joints. In the present study, two objectives are followed: First, investigation of cyclic earth pressure behind integral bridge abutments being compared with that induced behind the abutment of traditional bridges (with isolated deck and abutment, which are called separated bridges in this study). Cyclic traffic load is used as the surcharge in the analysis. Second, investigation is undertaken of changes in the distribution and total thrust of earth pressure, due to different soil densities. Three numerical models are developed using the FLAC package. The first model is a retaining wall. The characteristics of this model are the same as a physical model made in the soil laboratory to study the earth pressure on retaining walls under cyclic surcharges. The first model is used to compare the results of numerical and experimental modeling and in validating the process of the numerical model. The second and third models are models of integral and separated bridges. The induced earth pressure is evaluated on the abutment of both bridges, under static and cyclic conditions of traffic surcharge. Pressure distribution behind the wall, as well as the point of application of the total thrust, was determined and compared between two bridges. The results have shown significant changes in both the quantity and distribution of earth pressure behind the abutment, in the case of integral bridges. In addition, the effect of soil density on cyclic earth pressure is investigated and compared between the two bridges. Three different states of sand, including loose, medium and dense, are used for modeling the granular backfill behind the abutment. Results of earth pressure behind the separated abutment show a similar trend to retaining walls, which experience increasing pressure due to increasing density. Unlike retaining walls and separated abutments, the integral bridge experiences less lateral pressure due to increasing density. More details of the findings and their causes will be discussed in the next sections.