Research On Seismic Reinforcement Method Of Bridge Pile Foundation In Liquefiable Soil Based On Slag Powder

Previous seismic damage investigations have indicated that earthquake-induced soil liquefaction can cause large lateral deformation or even damage to piles,which in turn can cause the failure of the superstructure.The effect of materials such as cement,fiber,and rubber particles on the seismic reinforcement of bridge pile foundations in the liquefiable ground has been investigated by domestic and foreign scholars to address this issue.However,the current reinforcement methods have problems such as construction difficulties,high costs,and poor environmental friendliness.Meanwhile,China has a large amount of slag powder surplus every year due to steel production,and its stockpiling problem needs to be solved urgently.In light of this,this paper proposes two methods of seismic reinforcement of bridge pile foundations in the liquefiable ground using slag powder as new reinforcement material and based on indoor tests and the finite element method.The research contents and main insights of this paper are as follows:(1)The effect of slag powder content on the liquefaction resistance of saturated sands(Dr=40%)was studied by indoor undrained cyclic triaxial tests.The results show that: the higher the slag content,the slower the sample failure speed,the more loading cycles required for the sands to liquefy,and the better the inhibition effect on the growth of excess pore water pressure;When the slag powder content is certain,the larger the cyclic stress ratio is,the faster the sample is destroyed,and the fewer times of shaking for the sands to reach liquefaction.(2)The numerical model of the cyclic triaxial test was established based on the finite element method,and the calculation parameters of the sand-slag powder mixture were calibrated.And then a numerical analysis model based on slag powder reinforcement of bridge pile foundations in the liquefiable ground was established,and the effect of employing slag powder for seismic reinforcement of pile foundations in the liquefiable ground was discussed.The results show that slag powder can effectively reduce the lateral deformation of piles in liquefiable ground,and an empirical formula to predict the reinforcement effect of slag powder is proposed.(3)The mechanical properties,construction feasibility,and micro-mechanism of sandalkali-activated slag cementitious material mixtures were carried out.The results show that the increase in the content of slag powder and the decrease in the relative density of sands would increase the compressive strength of sand-alkali-stimulated slag cementitious materials.The sand-alkali activated slag cementitious material mixture has a better fluidity,but when the relative density of sands is low and the content of slag powder is high,its setting time is short.In addition,microscopic analysis showed that the porosity of the sand-alkali-activated slag cementitious material mixture increased with the decrease of the slag powder content and the relative density of the sands.Furthermore,the compressive strength of the sand-alkali-activated slag cementitious material mixture was much greater than that of the sand-cement mixture under the same mix ratio.(4)Based on the grid-type deep mixing technology,a new sand-alkali-activated slag cementitious material is used,and the seismic reinforcement effect of the material on the pile foundation in the liquefiable ground is studied by combining numerical simulation methods.The calculation results show that the sand-alkali-activated slag cementitious material mixture can effectively slow down the pore pressure growth of the soil around the pile and reduce the lateral deformation of the pile,and the larger the reinforcement area ratio is,the more obvious the reinforcement effect is.(5)Based on the numerical simulation method,the seismic response of pile foundations in the liquefiable ground under three reinforcement methods of slag powder,alkali-activated slag cementitious material,and cement were compared and analyzed,and the seismic fragility curves of pile foundations in the liquefiable ground under different reinforcement methods were obtained with the maximum displacement of pile top as the seismic demand.The results show that all three reinforcement methods can effectively reduce the seismic failure probability of piles,and the reinforcement effect of alkali-activated slag cementitious material is the best.In this study,two methods of seismic reinforcement of bridge pile foundations in the liquefiable ground are proposed based on industrial waste slag powder.The research results have expanded the application of slag powder in the field of geotechnical earthquake engineering,improved the utilization rate of industrial by-product slag powder,and perfected the seismic reinforcement methods for bridge pile foundations in liquefiable ground,which have important theoretical and practical implications for the seismic reinforcement of bridge pile foundations in the liquefiable ground.