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.

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This research deals with the improvement of the mechanical properties of expansive clay soils by silica fume. The expansive soil was prepared in laboratory by mixing natural soil brought from (Nahrawan) city with different percentages of Bentonite (30, 50 and 70% by weight). The test program included the effect of Bentonite on natural soil then study the effect of silica fume on prepared soil by adding different percentages of silica fume (3,5, and 7% by weight) to the prepared soils and the influence of these admixtures were observed by comparing their results with those of untreated soils (prepared soils). The properties chosen for this comparison were specific gravity, the consistency limits, swelling percent and swell pressure. The results show that the plasticity index, the optimum moisture content, swelling percent and swell pressure increase with increasing the Bentonite percent, and the maximum dry density, specific gravity decrease with increasing the Bentonite percent. When the prepared soil treated with silica fume, the results show that plasticity index, specific gravity, maximum dry density swelling percent and swell pressure decrease with increasing the silica fume percent, while optimum moisture content and unconfined compressive strength increased with increasing silica fume percentages. And the perfect percentage of silica fume was obtained to be 7% which where decreased the swell and swell pressure in large percent.The result showed that the addition of silica fume to expansive soils has in a positive effect to the geotechnical properties and these results will benefit the engineers or decision makers in using this additive.

The present work investigates the strength characteristics of sand stabilized with two additives (cement and lime) each alone at different percentages ranging between 1-10%. Sand mixed with different additive contents are statically compacted in perforated tubes, 38 mm in diameter and 200mm in length, the perforated holes are 2mm in diameter along the tube. Compaction is carefully controlled by compressing the sand to the required density by two plungers at top and bottom, two ends of the samples are waxed and soaked for 7 and 28 days in water. Unconfined compression test were performed, the strength and stiffness were determined for all the samples. Results referred to an increase in strength and stiffness of stabilized sand with increasing additives content, cement treatment improved strength significantly rather than lime and soaking time plays an important role in increasing compressive strength of sand treated with cement and lime. Also results showed that the type of failure behavior varied greatly from plastic to brittle. An empirical equation was derived for the unconfined compression strength depending on type of additive and soaking time.