Mechanical Properties And Damage Constitutive Model Research Of Loess-Slag-Based Cemented Backfill Material

In China,open-pit coal mines are often limited by factors such as mining technology,geological conditions,and mining efficiency,resulting in a large amount of coal resources being buried under the end-slope and difficult to extract,leading to a huge waste of coal resources.In order to improve the extraction rate of coal resources in open-pit mines and ensure the stability of the end-slope,end-slope backfill mining technology is currently the most effective and feasible method.Traditional backfill materials such as cement have certain limitations in their use due to cost and environmental protection reasons.Therefore,this study used slag and loess from openpit mines as binder materials,waste rock from open-pit mining as filling aggregates,and water glass as a hardening agent to prepare a low-cost and high-performance cemented material suitable for end-slope filling mining in open-pit mines,and studied its mechanical properties and damage evolution during loading.Using theoretical analysis,rock mechanics experiments,electron microscopy scanning,acoustic emission,and other research methods,this study explored the mechanical properties and damage evolution of cemented backfill materials under different loess-slag ratios and curing time conditions from macro and micro perspectives.Finally,the damage constitutive model of the loess-slag-based cemented backfill body was derived.Specifically,the fluidity properties and curing time of the backfill slurry were analyzed by measuring the slump,expansion,and initial and final setting time of the backfill slurry under different loess-slag ratio conditions.The uniaxial compression mechanical properties of the cemented backfill body under different curing time and loess-slag ratio conditions were studied,and numerical models of compressive strength and elastic modulus were established.The mechanism of the effect of curing time and loess-slag ratio on its mechanical properties was studied from a microscopic perspective.Based on the characteristics of stress-strain curves,acoustic emission features,and energy evolution features,the damage evolution law of the cemented backfill body during loading was explained.Finally,the damage constitutive model of the cemented backfill body was derived based on the damage evolution law.The following research results were obtained:(1)With the increase of curing time,the uniaxial compressive strength and elastic modulus of the loess-slag-based cemented backfill material increased in the form of negative exponential functions.The macroscopic failure mode changed from plastic failure to brittle failure,and the microscopic structure became more compact,with an increase in the number of acoustic emission ringings and energy counts,and an increase in the proportion of elastic energy.(2)With the increase of the loess content in the cemented material,the bleeding and segregation of the cemented material slurry were improved,and the initial setting time gradually extended from 10 minutes(loess ratio of 10%)to 185 minutes(loess ratio of 90%),while the uniaxial compressive strength and elastic modulus of the cured cemented backfill body decreased in an "S" curve.(3)Scanning electron microscope experiments on the backfill material showed that the gel formed by loess is N-A-S-H gel,which has stronger plasticity,while the slag gel is C-(A)-S-H gel,which has higher deformation resistance.With the increase of the loess ratio in the cemented material,the macroscopic failure mode of the cemented backfill body changed from brittle to plastic,and the microscopic structure became more compact.(4)A "gap" backfill model was constructed,and the damage variable was defined using Weibull’s random distribution parameters.The concept of effective damage rate was introduced,and a damage constitutive model was established.The calculation method of each parameter in the model was given,and its correctness was verified using the stress-strain curve obtained from loading tests.This study used the slag and waste rock from open-pit mining and industrial solid waste slag as the main raw materials for cemented backfill materials,and prepared cemented backfill materials that meet the end-slope filling requirements and emit no greenhouse gases.This research has certain practical guiding significance for improving the recovery rate of overlying resources in open-pit coal mines,reducing waste rock emissions,and realizing green,safe,and efficient mining in open-pit mines.There are 60 figures,18 tables and 161 references in this dissertation.