Study On Construction Aggregate Preparation And Synchronous Grouting Materials Of Mud Cake From Sand-Mud Separation Of Shield Muck

With the rapid development of China’s subway tunnel industry,a large amount of shield muck is produced in the process of subway shield tunneling.Taking Shenzhen city as an example,the mud cake separated from the shield muck by sand-mud separation technology was mainly disposed by landfill.This traditional treatment method not only leads to high transportation costs and waste of land resources,but also hinders the development of cities.According to the field investigation,shenzhen needed a large amount of low-strength construction aggregate in municipal and transportation construction,and a large amount of synchronous grouting materials in shield construction.Therefore,in view of the differences of mud cakes in different shield construction areas in Shenzhen,the study analyzed the physical and chemical characteristics of mud cakes through field sampling,according to different properties of mud cake,through a lot of research,two different paths successfully realized the recycling utilization of mud cake.The first way was to use the shield mud cake cement sodification method to prepare building aggregate,the other is to use the shield mud cake as the raw material for the preparation of grouting slurry.Physical and chemical analysis of mud cake showed that the increase of clay content in mud cake would increase the Atterberg limit value of mud cake.The influence of the type of mud cake on the strength of prepared aggregate and the properties of synchronous grouting slurry was further studied.The results showed that the increase of clay content in shield mud cake will reduce the curing effect of cement on mud cake.Therefore,low liquid limit silt shield cake with low clay content and low Atterberg limit value was suitable for the preparation of low strength construction aggregate.On the other hand,clay can stabilize grout due to its high hydrophilicity.Therefore,high liquid limit clay shield mud cake with high clay content and Atterberg limit value is suitable for preparing synchronous grouting grout.In view of silt shield mud cake with low liquid limit,anionic dispersant was used to disperse and pretreat the mud cake,and then mixed with cement,sand and other raw materials to form the mixture.After external pressure forming process and natural curing,low strength construction aggregate was prepared.The effects of cement/mud cake mass ratio,sand/mud cake mass ratio,dispersant/cement mass ratio,molding pressure and molding time on the compressive strength of solidified samples were investigated by orthogonal experiment.The results showed that the cement/cake mass ratio is the most significant factor affecting the compressive strength of solidified samples.At the same time,the maximum compressive strength of the cured sample can reach 43.2 MPa in 28 days by the optimal ratio and process conditions obtained by orthogonal experiment.Atterberg limit and Zeta potential test results of low liquid limit silt shield cake showed that after anionic dispersant modification,the negative Zeta potential value and Atterberg limit of shield cake decreased,the dispersity of shield cake was enhanced after"liquification",and the degree of mixing with cement was improved.The solidifying effect of cement on shield mud cake was enhanced.Pore size analysis results of cured samples showed that the pore structure of cured samples was optimized with the increase of molding pressure and the extension of molding time during external pressing process,thus improving the compressive strength of cured samples at 7 days and 28 days.Using high liquid limit clay shield mud cake as the raw material of synchronous grouting grout,water reducing agent and early strength agent as additives,under the condition of fixed water-binder ratio,cement-sand ratio and cement-fly ash ratio,the properties of the configured grout were adjusted,and the synchronous grouting grout meeting the requirements of grouting performance was prepared.Based on the principle of maximizing the utilization of mud cake,the optimal ratio of raw materials was obtained through proportioning design experiments,in which the ratio of baked mud cake and cementing material was up to 0.3.Under this ratio,the bleeding rate of synchronous grouting slurry was 1.1%,stone rate was 98.6%,consistency was 10.2cm,fluidity was 25.9cm,corresponding time loss was 4.5mm/h,setting time was 13 h.The slurry density is 1955 kg/m³,the 3-day and 28-day compressive strength is 3.54 MPa and 14.33 MPa,respectively.All properties meet the T-CECS 563-2018 standards.The experimental result showed that polycarboxylic acid superplasticizer（PCE）destroyed the cement floc structure in grout,releases free water,and improved the fluidity and consistency of grout.The experimental result of early strength agent regulation experiment showed that the addition of Na₂SO₄ consumed the cement hydration product-Ca（OH）₂,accelerated the cement hydration and pozzolanic reaction,increased the formation rate of C-S-H gel and calcium sulphoaluminate crystal,shortened the setting time,and enhanced the compressive strength of 3-day and 28-day curing test blocks.The two resource utilization methods for different kinds of mud cakes are proposed in this research,which broadens the utilization way of shield mud cake and provides a new idea for the resource utilization of mud cake in Shenzhen.