Properties And Diffusion Mechanism Of Alkali-activated Industrial Waste Residues-based Backfilling Grouts For Shield Tunnel

Backfill grouting is a key process in the construction of shield tunnels,and the selection and use of grouting grout is partially important.With the increasing number of shield tunnel projects in our country,the engineering geological conditions are becoming more and more complex,and higher requirements are put forward on the performance of the grouting grout for the shield tunnel.Therefore,in view of the shortcomings of the traditional ordinary Portland cement(OPC)-based grout with high energy consumption,poor engineering performance and durability,the development of a high-performance backfilling grout with a strong resistance to water dispersion,excellent impermeability,good durability,low carbon and environmental friendly is of great significance to the development of shield tunnel engineering.In addition,for the emergence of a new type of grout,often due to the insufficient understanding of the filling&penetration diffusion mechanism of grout in the shield tail void,the refined construction control in the backfill grouting process is not accurate enough to achieve a desired grouting effect.In view of this,this paper was supported by the National Natural Science Foundation of China(No.42072297)and National construction of high-level university public graduate projectand(No.201906090223),and took the industrial waste residues-based grouting grout as the research object.Through the laboratory tests and theoretical model construction,the engineering properties and durability of the industrial waste residues-based grouting grout and its filling&penetration diffusion mechanism during the shield tunnel synchronous grouting process was systematically studied.The main research content and main research results obtained in this paper are as follows:(1)Through the laboratory tests,the effects of the mixing amount of ground granulated blast-furnace slag(GGBS)and steel slag(SS)in the form of single and double blending with fly ash(FA)on the fresh,hardened and microstructural properties of the resulting alkali-activated pastes(AAP)was systematically studied,and the raw material composition of industrial waste residues-based AAP was optimized.When GGBS and SS were double-added,the two can produce a synergistic effect,which can effectively promote the increase of the compressive strength of the hardened samples without shortening the setting time of reducing the flowability of fresh AAP.Single addition of GGBS will increase the brittleness of hardened samples,while double addition of GGBS and SS can effectively alleviate the brittleness of hardened samples.Under the condition of the same dosage,the promoting effect of double addition of GGBS and SS on the flexural strength of the hardened sample is stronger than that of single addition of GGBS.Single addition of GGBS can effectively promote the formation of early C-(A)-S-H gel in the matrix of alkali-activated materials and accelerate the dissolution of solid powder particles,while single addition of SS will affect the formation and expansion of gel products.When GGBS and SS were double-added,the presence of GGBS can activate the activity of SS particles and promote their dissolution.The resulting C-(A)-S-H and N-A-S-H gels coexist in the matrix to bond the remaining particles into a whole,so as to achieve the microstructure of the same dense level as the sample obtained by single addition GGBS.(2)The industrial waste residues-based backfill grouting grout was prepared by using alkali-activated industrial waste residues cementing materials as the main body,supplemented by fine sand and water reducing agent.Through a series of laboratory tests,the effects of the ratio of liquid to solid,concentration of alkaline activator solution and water reducing agent on the basic physical properties,operating properties,hardened properties and pore structural properties of the prepared industrial waste residues-based grouts were studied.The easy pumping period of the grout controlled by the dual indicators of consistency and flowability can be adjusted in the range of several minutes to several hours.In the actual grouting construction,the grout can be flexibly selected and used according to the specific engineering conditions and construction conditions.By adjusting the proportioning parameters of the grout,the water/land strength ratio of the hardened sample can reach above 0.80 and the impermeability pressure can reach above 0.8 MPa while the grout has good operating properties.Therefore,the industrial waste residues-based grout has excellent water dispersion resistance and good impermeability.Through the comparison of the multiple performance indexes of the representative industrial waste residues-based grouts and the traditional OPC-based grout,it can be found that when the operating properties of the industrial waste residues-based grout are basically the same as that of the traditional OPC-based grout,its hardening properties including strength,elastic modulus,water dispersion resistance and impermeability are significantly better than those of the traditional OPC-based grout.Therefore,the industrial waste residues-based grout can be considered as a grout with higher performance.(3)According to the requirements of the construction quality of the backfill grouting for shield tunnel on the durability of the grout and the actual situation that the grout may encounter in the actual service environment,the dry shrinkage characteristics,the water corrosion resistance and sulfate erosion resistance of the industrial waste residues-based grout and the traditional OPC-based grout hardened samples were tested and studied.When the age is 90 days,the dry shrinkage strain of two representative industrial waste residues-based grout samples is slightly larger than that of OPC-based grout samples,but the difference is not significant,which is considered to be reasonable.In the water corrosion test,the increase in the pH value of the maceration water of the industrial waste residues-based grout hardened sample is mainly caused by the residual alkaline activator in the matrix,while the increase in the pH value of the maceration water of the traditional OPC-based grout hardened sample is mainly due to the decomposition of gel products.In addition,the quality and strength loss of the industrial waste residues-based grout hardened sample is also obviously better than that of the traditional OPC-based grout hardened sample,so the industrial waste residues-based grout has better water erosion resistance.In the sulfate resistance test,the apparent damage of industrial waste residues-based grout hardened samples is obviously better than that of traditional OPC-based grout hardened samples.The erosion effect of Mg SO₄ solution on hardened samples of grout is stronger than that of Na₂SO₄ solution.At the same age of sulfate attack,the quality and strength loss rate of industrial waste residues-based grout hardened samples are lower than that of traditional OPC-based grout hardened samples and have better sulfate resistance.(4)The flow pattern,rheological parameters and time-varying characteristics of two representative industrial waste residues-based grouts were tested through laboratory tests.The flow pattern of the industrial waste residues-based grout does not belong to a single flow pattern,and is usually related to the specific formulation parameters of the grout.The flow pattern of the grout does not change with time,but the rheological parameters are time-varying.According to the characteristics of shield tunnel synchronous grouting construction,the whole diffusion process of the synchronous grouting grout is regarded as a three-dimensional diffusion mode of circular filling,axial filling and radial penetration.Based on the time varying Bingham fluid rheological equations and the power-law fluid rheological equations,the model of circular generation and distribution of grout pressure during circular filling,the time-space dissipation model of grout pressure during axial filling,and the permeation diffusion model during radial permeation were derived and established.The parameters involved in the constructed theoretical model are shield tunnelling parameters,grout characteristic parameters,grouting construction parameters and soil characteristic parameters.The reliability of the theoretical model is verified by comparing the calculated values with the monitoring data and grouting test data.In addition,a single factor analysis of multiple influencing parameters of the theoretical model is carried out through calculation examples.This theoretical model can provide certain theoretical guidance for the parameter design of shield tunnelling and grouting construction.