Experimental Study On Controllable Cement Slurry Of Railway Foundation In Karst Area

With the development of the national economy,there is an increasing demand for railway construction in karst areas in China.Grouting is a common method to solve karst caves in subgrade.At present,the cement grouting fluid in the karst area mainly uses conventional cement slurry and cement-water glass double slurry.The former is low in cost and easy to use,but the gel time is too long,the fluidity is high,the bleeding rate is high,the slurry is easily lost,at the same time it is easy to cause pollution of groundwater environment;and the latter's gel time is too short,and the fluidity is poor,at the same time it is easy to cause pipe blockage.Therefore,this article hopes to obtain a cement slurry that can accurately control the gel time and the bleeding rate,that is,the cement slurry can be controlled: the formulation can be fine-tuned to meet the grouting requirements of the cement slurry at different cave depths,thereby avoiding grouting pollution to the environment.Now China is paying more and more attention to environmental pollution.During the grouting process,if the cement slurry flows into the underground river,it will cause huge pollution to the groundwater environment.At present,some of the hexavalent chromium content of cement produced in China still exceeds the standard.In order to prevent hexavalent chromium from polluting the groundwater environment,it is necessary to not only strictly control the contact of the grouting fluid and groundwater,but also control the hexavalent chromium dissolved in the groundwater after the cement block is formed.In this paper,the project background is the controllable cement slurry of DK40 + 256 ?DK40 + 400 section of Qianzhang-Changchang high-speed railway.After literature analysis,firstly,the admixtures were tested for single and mixed admixtures respectively,so as to obtain a controllable cement formulation that meets the requirements of railway foundation grouting in karst areas.Next,the total dissolution of hexavalent chromium in the controllable cement slurry is measured and the dissolution of hexavalent chromium is reduced by the chromium reducing agent.Finally,the controllable cement slurry was applied to the Qianzhang-Changchang high-speed railway,and the effect of the formulation selected in the laboratory test was checked.The main research results of this article are as follows:(1)In the single admixture test,the preferred quick setting agent sodium carbonate,water retaining agent silica fume,water reducing agent polycarboxylic acid water reducing agent and retarder sodium gluconate all have good effects.Among them,sodium carbonate can shorten the gel time of cement slurry to 11 min,water retaining agent can reduce the bleeding rate to 0%,and polycarboxylic acid water reducing agent can increase the degree of expansion by more than 35%.(2)In the blending test,the retarder is the main factor affecting the gel time,bleeding rate and later expansion of the cement slurry,and the water retaining agent is the main factor affecting the bleeding rate of the cement slurry.In addition,under the temperature conditions of 10 ?,20 ? and 30 ?,the controllable cement slurry test formulations with low bleeding rate,strong fluidity and control of gel time were selected.(3)When the blending amount is 0% to 3%,ferrous sulfate has a significant effect on reducing the total dissolution of hexavalent chromium in the controllable cement slurry;after the blending amount exceeds 3%,the increase in the blending amount will has little effect on the amount of hexavalent chromium dissolved.(4)According to the results of the application of controllable cement slurry on Qianzhang-Changchang Railway,the slurry has no extravasation phenomenon,and the grouting effect is good through visual grouting,simple water pressure test and geological radar detection method.