بررسي آزمايشگاهي و عددي كارايي ريزشمع‌ها جهت تقويت خاكريزهاي بلند راه‌آهن

Experimental and Numerical Investigation of Efficiency of Micropiles for Reinforcing High Railway Embankments

در اين پروژه به منظور افزايش باربري استاتيكي و ديناميكي خاكريزهاي بلند راه‌آهن، به بررسي چگونگي تقويت شيرواني‌هاي آن با استفاده از ريزشمع‌ها پرداخته شده است. بدين منظور در بخش اول با ساخت يك نمونه‌ي آزمايشگاهي از خاكريز راه‌آهن متكي بر بستر ماسه‌يي با مقياس 1 به 20 و در ادامه با انجام تعدادي آزمايش بارگذاري بر خاكريز تقويت‌شده با ريزشمع به بررسي كاربري اين روش مقاوم‌سازي پرداخته شده است. سپس در حين انجام آزمايش‌هاي بارگذاري و با استفاده از ابزار دقيق، مقادير نشست خاكريز و كرنش محوري ريزشمع اندازه‌گيري و در مرحله‌ي بعد مدلي عددي و سه بعدي طراحي و با استفاده از نتايج ابزاربندي آزمايشگاهي كاليبره شده است. در پايان، تحليل حساسيت روي پارامترهاي مختلف ريزشمع صورت گرفته و بهينه‌ترين چيدمان جهت تقويت خاكريزهاي بلند راه‌آهن ارايه شده است.

Construction of the railway embankments on loose foundations without using reinforcing elements leads to reduction of the embankmentsʹ slope, which significantly increases the volume of soil operation. Hence improving such loose foundations is an essential part for the aim of increasing bearing capacity of the embankments. One of the solutions for static - dynamic stabilization and the axial load enhancement of the rail lines constructed on high embankments (with the height more than 5m) is use of micropiles in embankments slope to transmit the applied loads to the tenacious layers of subgrade. Generally, micropile, as a supporting element in the soil with the main characteristic of improving the mechanical-experimental properties of the soil, is a proper methodology for the purpose of improving such loose earth with low load capacity and intensive settlement characteristics. It should be mentioned that micropile is a pile with less than 30 cm diameter, light reinforcement and impacted grout injection. Review of the literature indicates that there are no comprehensive studies on micropiles performance to reinforce the high railway embankments. So, this paper presents a model of high embankment in laboratory scale of 1 to 20 in order to setup some experimental tests on non-reinforce and reinforced embankments. It should be mentioned that the experimental tests are based on a non-reinforced embankment and two reinforced ones strengthened with two different arrangements of micropiles. Moreover, by the use of instrumentation tools during the experimental tests, the data such as load-bearing capacity of embankments, displacements of different points and axial strain of micropiles have been measured. In the next step, a 3D numerical model was developed based on the finite element method and the load-deformation behavior was simulated in the two mentioned experimental states with two different micropiles arrangements; then, the numerical model was calibrated. In the numerical analysis procedure, the behavior of embankment materials and elasto-plastic bed were considered with the Mohr-Coulomb failure criterion and other structural components of rail line and micropiles were regarded as linearly elastic. At the end, the numerical model was developed by improving it with different arrangements of micropiles in order to verify their effects on magnitude of providing safety factor of slope stability and find the optimum arrangements to reinforce the high railway embankments on loose foundation. By using this methodology can determine the efficiency factor of each geometrical parameters of micropiles group, too.