Abstract: To evaluate the effect of the proposed soil improvement, a series of tests has been performed on CementFlyashGravel (CFG) columns in the Gobi Desert of a rail road subgrade improvement project. These tests are: small strain integrity tests; coring through the CFG columns; axial loading tests on single column as well as column groups and settlement observations. The impact of the column spacing on the bearing capacity of the composite ground is studied. The objective of these tests and studies are for the later phase constructions and providing experience of subgrade improvement of railway in the Gobi Desert. The test results show: 1) Gobi soils have no obvious adverse effect on the quality of the CFG columns. Based on the integrity test results, a high acceptance ratio of 98.5% is observed. 2) Pumping concrete through a long distance using spiral pumping method is an appropriate technique for the CFG column installation. This has been verified through the sample cores from the installed columns. 3) The optimum column spacing in the Gobi Desert is 1.5 meter. When the spacing exceeds 1.5 m, a larger variation of composite capacity between the design and tested values are observed. 4) The composite ground has a small post construction settlement and a short duration for settlement stabilization is necessary.

Key words: CFG Columns, Gobi Desert, Railway Subgrade, Subgrade Improvement