Experimental Study On Improved Roadbed Fillings Of Fully Weathered Argillaceous Sandstone ——In The Case Of The Project Of The Chengdu’s Urban Main Line Along The East-west Direction

Weathered argillaceous sandstone belongs to weathered soft rock,which is widely distributed in Chengdu area of Sichuan Province,China,especially in the excavation of Chengdu’s urban main line along the east-west direction,where there exists a large amount of weathered argillaceous sandstone.Due to the shortage of high quality stone filled roadbed filler,the reasonable use of weathered argillaceous sandstone becomes an important research topic.Therefore,the direct use or improved use of fully weathered argillaceous sandstone as roadbed filler was considered,and the engineering characteristics tests of weathered argillaceous sandstone and its improved soil were carried out.The main research work and conclusions are as follows.（1）Based on the project of the Chengdu’s urban main line along the east-west direction,the fully weathered argillaceous sandstone was collected on site and its engineering properties,including the study of basic physical properties and basic mechanical properties,were studied.The results show that the subsoil has low strength,is easy to disintegrate and soften when encountering water,and has poor water stability,so it cannot be directly used as roadbed filler.（2）The improvement ratio scheme was designed with cement,powder and liquid as improvement materials.The powder includes LFJ soil improver and HAS soil improver,and the liquid includes EFS soil stabilizer and CG soil stabilizer.The improved materials were mixed into plain soil in accordance with the ratio of the test program and the improvement test was carried out.The research results show that the improved soil samples have different degrees of improvement in mechanical properties,water stability and deformation resistance,and the improvement effect increases with the increase of blending amount.Among them,the addition of HAS soil improver or LFJ soil improver has the most significant effect in improving the strength and deformation resistance of soil samples,and the soil stabilizer plays an important role in water stability.（3）The microstructure and mineral composition of the improved soil samples were obtained by SEM electron microscopy scanning test and X-ray diffraction test to realize the improvement mechanism analysis of the improved soil samples.The results showed that all the improved soil samples produced hydrated calcium silicate and other hydration products,and the soil integrity was improved compared with that of the plain soil.The cement-amended soil could not achieve strong consolidation effect,but the addition of LFJ improver and HAS improver generated calcium hydroxide and calcium carbonate,which enhanced the compactness of the soil.The specimens with the addition of EFS soil stabilizer and CG soil stabilizer have more hydration products and higher strength and water stability of the soil compared with the cement specimens.（4）Considering technicality,economy and construction convenience,a hierarchical fuzzy comprehensive evaluation model of the improved soil samples was established and the improvement scheme was optimized and studied.The results showed that the better improvement effect of the powder improvement scheme was the FJ2-3 group（mixed with 7%HAS）,and the better improvement effect of the liquid improvement scheme was the YJ2-2group（mixed with 3% cement + 0.02% CG）.