| As a bulk solid waste,asphalt aggregate dust has adverse effects on the ecological environment such as soil,air and water quality.At present,most of the treatment measures in my country are to bury it on site,discharge it into water,or mix it into the asphalt mixture as a substitute for mineral powder for recycling.The resource recycling method is single and the reuse rate is low,which is easy to cause secondary pollution to the ecological environment.In this paper,it was innovatively used as a substitute for mineral admixtures in simultaneous grouting material components,and the microscopic properties and physicochemical properties of asphalt aggregate dust were studied to verify its feasibility as a mineral admixture.The mechanical properties of the grouting consolidated body when mixed with asphalt aggregate dust alone and mixed with fly ash were explored,which provided a basis for the practical application of dust.Aiming at five influencing factors,the prediction models and optimal mix ratios of different performance indicators were obtained by means of multiple regression and multi-objective linear programming.Finally,a three-dimensional numerical simulation model of the whole process of shield construction was established based on the principle of slurry time-varying,and the surface settlement law considering the optimal mix ratio of asphalt aggregate dust and slurry was obtained,which can be used in the grouting slurry for fine dust in the later stage.This study has good environmental,social and economic benefits.The main conclusions reached are as follows:(1)Asphalt aggregate dust is mainly oxides of Ca,C,Si,Al,Fe,Mg,and its chemical composition mainly includes CaCO3,SiO2,Ca Mg(CO3)2,K2SO4,Mg2SiO4.The particles in the aggregate dust are unevenly distributed and densely distributed,the coarse particles are mostly in the form of gravel,and the fine particles are in the form of broken glass.The physical properties such as specific surface area,fineness,density,and water demand ratio of the dust all meet the requirements for the use of cementitious materials.(2)For the asphalt aggregate dust-based grouting body,with the increase of the powder-ash ratio and the mixing ratio of asphalt aggregate dust,its compressive strength and flexural strength decrease,the triaxial compression curve conforms to the elastic-plastic model.The main failure modes are as follows:vertical splitting and oblique shear failure.The peak pressure decreases with the increase of the fly-ash ratio and the asphalt aggregate dust content,The peak strain decreases with the confining pressure,fly-ash ratio and asphalt aggregate dust mixing ratio.The shear resistance decreases with the addition of asphalt aggregate dust and large amount of fly ash.The stress-strain empirical equation and the calculation formula of key mechanical indexes of asphalt aggregate dust-based grouting under triaxial stress were obtained by fitting.(3)The multiple regression prediction model of synchronous grouting mixed with asphalt aggregate dust under the influence of five independent variables:water-binder ratio,cement-sand ratio,swelling water ratio,powder-ash ratio and dust mixing ratio was established,and the corresponding indicators were obtained.On this basis,the multi-objective linear programming method was used to obtain the optimal mix ratio suitable for engineering applications:the water-binder ratio was 0.661,the mortar ratio was 0.519,the swelling water ratio was 0.245,the powder-ash ratio was 2.482,and the dust mixing ratio was 0.144.(4)An improved three-stage changing process of slurry consolidation-hardening was proposed,and a three-dimensional numerical simulation model of the whole shield tunneling process based on the time-varying slurry was established.Through the optimized numerical calculation method,it can be seen that the reasonable selection of slurry material properties,grouting pressure and grouting amount have positive effects on the control of formation settlement,but the latter two have more significant effects.And based on this,the control measures of the surface subsidence can be put forward to guide the shield construction reasonably. |
