Application Technology Of Phyllite In The Subgrade Structure

During the excavation of the tunnel and subgrade in the An Kang to Ping Li Expressway,An-Ping Highway for short hereinafter,a large amount of weathered phyllite waster was produced.The paper used the phyllite waster,which is poor in physical and mechanical properties,as the subgrade fillers,and successfully solved the difficult problems of bad stability of phyllite subgrade,which is significant to low the engineering cost,save the investment and the farmland,reduce the damage to the environment.Firstly,the related physical the mechanical characteristics of three kinds of typical phyllite along the An-Ping Highway line were analyzed,the weathered degrees of the phyllite were classified,according the apparent features,saturated uniaxial compressive strengths,point load strengths,disintegration resistance index,and softening coefficients,as the basis of the engineering application.Then,the compaction characteristics of the phyllite subgrade fillers were investigated,the maximum compaction degree in different compaction processes were analyzed,and the effects of heavy hammer and vibrating compaction methods were compared.The results show,the economic compaction ways are,normal rolling for 10 times,or drop hammer dynamic compaction for 3 times,or intelligent continuous dynamic compaction for 6 times.The vibrating compaction method is better than the heavy hammer method.The optimum parameters of the vertical vibration instrument are,static pressure 164.8kPa,vibration frequency 40 Hz,and the angle of eccentric block 0o.Next,the effects of soaking ways,soaking time and the overburden pressures to the CBR values of phyllite,as well as the relationships between the compaction degree of phyllite subgrade and the strengths of the subgrade fillers and the water-stabilities were studied.It is found,that sideway soaking is the better way to show the true strengths of the phyllite.With the elongation of soaking time and the reduction of overburden pressure,the CBR values of the weathered phyllite are reduced gradually.When used in the filling work of roadbed,upper and lower embankment,the suggested overburden pressure are 10kPa?20kPa and 30 kPa,respectively.Comprehensively considering the subgrade strengths and water-stabilities of the phyllite,in the standard compaction degrees,the CBR values of the weak weathering phyllite can only reach the standards of embankment and lower roadbed,and that of middle weathered phyllite can only meet the requirements of embankment,while that of the strong weathered phyllite can not meet the specifications.Further,the phyllite were modified with silicate cement according to the elastic multilayer theory and the performance characteristics of phyllite subgrade with different weathered degrees.It shows that,though the mechanical strengths and the water-stabilities of the phyllite modified by cement were largely increased,the permeability coefficients of it were decreased sharply,and the disintegration rates of it were largely slowed,to meet the property specifications,the compaction degrees should be raised if it is used to fill the subgrade.Finally,the construction technology and the key points of quality control were proposed,which provides the technical support to the construction of the An-Ping Highway and the theoretical basis to the revising of related standard and rules.