Research On Cast-in-place Construction Technology Of Red Mud Lightweight Roadbed

In recent years,the problem of red mud hoarding has become increasingly serious in China,and a new type of roadbed filling material is urgently needed due to the scarcity of conventional roadbed backfill resources.Therefore,it is necessary to try to use red mud as roadbed filling material for road construction engineering and natural environment protection in China.Taking shandong Linzi Highway roadbed project as the carrier,this paper explores the feasibility of red mud light roadbed by means of theoretical analysis,laboratory test,construction test and engineering verification,combined with relevant specifications and engineering requirements.The main research results are as follows:(1)The unconfined compressive strength and flow performance of 64 groups of test pieces of light red mud soil with a wet density of 700~1000kg/m3,red mud content of45~55% and water-solid ratio of 0.9~1.2 were studied.Through range and variance analysis,it is found that the unconfined compressive strength of light red mud soil increases with the increase of wet density,and decreases with the increase of red mud content and water-solid ratio.The flow value of light red mud soil increases with the increase of wet density and water-solid ratio,and the red mud content has no significant effect on the flow value.The optimal mixing ratio of light clay in red mud is 45%,activator 55%,water-solid ratio 1,and wet density 800kg/m3 and 1000kg/m3 respectively.With the development of hydration reaction,acicular ettringite and calcium hydroxide interlace with each other to form strength framework of light red mud soil under the action of flocculent C-S-H gel and C-A-H gel.At the microscopic level,the red mud content,water-solid ratio and wet density affect the compressive strength of the light red mud soil by affecting the pore wall structure.(2)It was found in the project that the light red mud soil appeared alkaline seepage in the natural conservation stage.Therefore,a single control test was designed to analyze the average pore size fraction and porosity of light red mud soil with different densities through Image Pro Plus,and to explore the principle of alkali flooding of light red mud soil combined with the immersion test and site construction.The results show that the phenomenon of alkali-flooding is caused by the precipitation and accumulation of alkaline substances carried by red mud on the surface of light red mud soil through stomatal channels following water evaporation.The phenomenon of alkali-flooding can be solved as long as the curing strip time of light red mud soil is appropriately extended and the water is not lost,and the relatively stable surface structure of light red mud soil can be formed.(3)According to the curing temperature and humidity,seven different curing methods were designed to study the changes of light clay in red mud.The compressive strength,apparent morphology and microstructure of light clay in red mud and the related changes of reaction products were analyzed by unconfined compressive strength experiment,scanning electron microscope and X-ray diffraction.It is found that the curing mode of high temperature or low humidity is not conducive to the growth of ettringite,and then affects the later strength of light red mud soil,while appropriately increasing the curing temperature and ensuring the humidity can accelerate the strength development of light red mud soil.The best curing method is to wrap red mud light soil with plastic film at 40?.(4)In order to prevent the occurrence of temperature cracks during mass pouring,the pouring height of light red mud soil was tested on the construction site,and the development form of cracks and temperature changes were monitored.The experimental results show that the heat dissipation effect is significant at the edge of light red mud soil,and the contrast is most obvious at the bottom.When the thickness of single pouring layer increases from 60 cm to 90 cm,the maximum temperature in the center of pouring body increases by 4?.If the pouring height is greatly increased,there will be the risk of temperature crack and even depression.(5)Monitoring and comparison of plane and lateral earth pressure of light roadbed with red mud by embedding earth pressure box.The maximum pressure of foam light clay from red mud on retaining wall is 23 k Pa when it is not solidified after pouring,but the soil side pressure tends to zero after the hydration reaction of light clay from red mud is completed,which provides engineering monitoring basis for the later vertical construction without retaining wall.At the same time,in order to observe the influence of roadbed construction on the surrounding environment,the project set up a groundwater monitoring well to observe the influence of heavy metal seepage and alkali spreading on the p H of water in the light roadbed of red mud.The monitoring results showed that the concentrations of mercury,lead,cadmium,selenium,arsenic and hexavalent chromium in the monitored water were all below the detection limit,so the amount of heavy metals exuded was very small.However,p H value continued to rise during the construction period,and gradually returned to the original value after the completion of the construction,and only fluctuated in the range of 7.0~8.0.Therefore,the phenomenon of alkali-spreading in light red mud soil has no significant impact on the surrounding environment.The bending test meets the engineering requirements.