Experimental Study On Improving The Compaction Character- Istics Of Cohesive Soil Subgrade By Magnetized Water

Starting with the microscopic mechanism in compaction of cohesive soil and the systematic analysis on interaction of water-soil-salt (ions), this paper puts forward to soften soil structure and to strengthen compaction effect during construction period, then decreases the amount of compression and increases the strength of subgrade soil during operation period. Based on the micro-mechanism analysis of magnetized water used in the fields of concrete engineering, desalination of saline soil and boiler cleaning, this article proposes an assumption of using magnetized water in the treatment of subgrade soil, around which a lot of laboratory experimental study have been done. The results show that it is feasible to increase the strength and dry density of subgrade soil by using magnetized water in the treatment, and a preliminary design scheme about improving subgrade soil with magnetized water is given in this paper. Due to the correlative research work on improving subgrade soil which has not been reported at home and abroad, this study is just an explorative subject, and some valuable achievements are presented as follows:(1) According to the special function of magnetized water in the interaction of water-soil-salt (ions), this article proposes a thought about optimizing the micro-structure of soil. Magnetized water weakens the structure strength of contact points between soli particles during construction period, thus will collapse soil’s structure which is wetted by magnetized water under the same exterior load (compaction work), and the arrangement of soil particles is going to be more tightly. So the void ratio of soil will be decreased greatly, and the compaction performance will be improved.(2) Compared to common water, the physical and water-physical property indexes of soil samples which are processed by magnetized water have changed in different degree. Among them, free swelling ratio somewhat increases, and plastic index decreases, because plastic limit content increases while water limit content decreases. The results of aggregate analysis show that soil particles of coarse grain group (aggregates) are transformed into silt group and clay group by magnetized water, and it explains that magnetized water disrupt the aggregates of soil. But the grain size analysis experiments added with dispersant show that soil particles of clay group are also transformed into slit group, which illustrates that agglutination and dispersion can occur at the same time.(3) The permeability tests, compaction tests and shear tests further confirm the optimizing function of soil structure processed by magnetized water. Because of the disintegration of aggregates, the particles of soil samples processed by magnetized water become more disperse, and the permeability coefficient of cohesive soil processed by magnetized water becomes smaller under the same dry density. Using the same compaction work, the maximum dry density of soil samples which are wetted by magnetized water increases, and the corresponding optimum water content slightly decreases. The shear tests show that the cohesion and friction angle of soil samples under the same dry density which are processed by magnetized water somewhat increase compared to common water, so as to improve the shear strength of cohesive soil.(4) The tests using different magnetic induction, temperature, flow velocity and soil show that the improvement of cohesive soil’s properties by magnetized water is influenced by very complicated factors. The best magnetic parameters and the type of soil which is applicable to this method need to be confirmed in the further study.