Soft soil improved by stone columns and/or ballast layer

Abstract

Iraq has the oldest railway network in the region. Currently the Iraqi railway company is rehabilitating the existing network in different regions and planning to expand it for the future. About 30–40% of the total length of the network is located in the southern part of Iraq, passing over soft, saturated, sedimentary deposits and in many areas close to the marshland. Stability and settlement are the major challenges to the safety and serviceability of rail tracks in these areas, thus ground improvement is essential to achieve the required level of performance. The paper presents results of tests of three treatment patterns. The first investigates the presence of a ballast embankment overlying a bed of soft, saturated clay. The second pattern focuses on the improvements achieved in load-carrying capacity and settlement as a result of eight stone columns added at an area replacement ratio of 0·196. The third pattern investigates the improvements achieved when patterns one and two are combined. In all tests, the ballast model embankment is loaded gradually by stress increments up to failure and stress deformation measurements are recorded and analysed in terms of bearing improvement ratio and settlement reduction ratio. Optimum outcomes are deducted from the third pattern, revealing bearing improvement ratio of 2·3 and settlement reduction ratio of 0·17.

Multi-Scale Analysis of Geotechnical and Physicochemical Changes in Loess Caused by Nano-SiO2 Pile Migration

“…Pile treatment techniques have been used to improve the slope, Earth embankment, and clay soils (Rogers and Glendinning, 1997;Rajasekaran and Narasimha Rao, 2002;Larsson et al, 2005;Barker et al, 2006Barker et al, , 2007Gallagher et al, 2007;Saoudi et al, 2013;Abiodun and Nalbantoglu, 2014;Helle et al, 2017;Selvakumar and Soundara, 2019). According to the nature of the stabilizing agent, pile treatment techniques can be divided into two different types.…”

“…The improvement mechanism of chemical pile-treated soils is mainly attributed to ion migration, which generates a chemical reaction with the surrounding soil. The second type is for physical piles, which are currently made up of stone or colloidal silica grout without a chemical reaction with neighboring soil (Gallagher et al, 2007;Saoudi et al, 2013). The reinforced effect of the stone pile comes from its own mechanical properties Saoudi et al (2013), Castro (2017), while stabilization from colloidal silica can also be attributed to silica nanoparticle migration (Gallagher et al, 2007).…”

“…The second type is for physical piles, which are currently made up of stone or colloidal silica grout without a chemical reaction with neighboring soil (Gallagher et al, 2007;Saoudi et al, 2013). The reinforced effect of the stone pile comes from its own mechanical properties Saoudi et al (2013), Castro (2017), while stabilization from colloidal silica can also be attributed to silica nanoparticle migration (Gallagher et al, 2007). On the whole, chemical piles are still more generally practiced in soil improvement, but the interest in physical piles such as silica nanoparticle has increased due to its eco-friendly characteristics and effectively stabilized effects.…”

Editorial

“…The second paper (Al Saoudi et al, 2015) is from Iraq and outlines the problems of constructing new railway lines or upgrading existing ones situated on the country's soft saturated sedimentary deposits and considers improving the bearing capacity and stiffness of the soils with ballast and stone columns. A useful summary is given of previous research work around the world on ground improved by stone columns.…”