Experimental Study On Mechanical Properties Of Volcanic Slag Subgrade Mixture On Neima Railway

The Neima Railway traverses the Great Rift Valley of East Africa.The areas along the line are mainly subgrades.A large number of the silty clays with low liquid limit and the natural volcanic cinder with porous and lightweight are distributed along the line.Roadbed filling that meet the specifications are scarce.It is of great significance to carry out research on the application of volcanic cinder materials in railway subgrade engineering.It provide references for the design and construction of subgrade in this area.Based on the "Nairobi-Maraba" railway scientific research project in East Africa Kenya,the laboratory test method was adopted.The basic physical and mechanical properties and improved utilization of volcanic cinder were studied in this experiment.The main research contents are as follows:(1)The chemical properties,basic physical and mechanical properties and strength properties of the volcanic cinder are tested and analyzed.It was found that the natural volcanic cinder belongs to the group B material and has good water stability.The main chemical components are SiO2,Fe2O3,Al2O3,MgO and CaO.It has good chemical stability,low single particle strength and is easily broken.The compacted volcanic cinder has high strength.(2)Natural volcanic cinder and silty clay were blended according to different ratios.The mixtures with different blending ratios were subjected to compaction test and particle analysis test.It is found that compared with 100%silty clay,a certain percentage of mixture can reduce the water consumption of roadbed filling construction.According to the existing standards,the volcanic cinder mixtures with various blending ratios tested in this paper initially meet the requirements of subgrade filling for the bottom layer of the Class I railway subgrade in China.The blending ratio of 50%volcanic cinder mixed with 50%silty clay,40%volcanic cinder mixed with 60%silty clay and 30%volcanic cinder mixed with 70%silty clay is better.(3)A large-scale direct shear tests were carried out for the volcanic cinder and silty clay mixtures at different blending ratios and different degrees of compaction.The shear strength was obtained.It is found that the envelope of the shear strength of the volcanic cinder mixture is in a linear form.It conforms to the Mohr coulomb criterion.(4)Dynamic tests were carried out on three kinds of volcanic cinder mixtures with different mixing ratios at different frequencies.The particles of the mixture were screened before and after the test.The test results show that the particle breakage of volcanic cinder mixture particles mainly occurs in the process of sample compaction.The incorporation of silty clay has a obvious positive effect on the suppression of the crushing of volcanic cinder particles.The blending ratio of 30%natural volcanic cinder with 70%silty clay is the best.