Study On High Ductile Concrete Materials For Roadway Side Support In Gob-side Entry Retaining Under High Geo-stress

Gob-side entry retention technology has been applied more and more widely in the field of mining engineering,but its application is limited by structural problems such as the failure of roadway supporting concrete filling body to form effective coordination with overlying strata.High ductile concrete has the advantages of good strength,toughness and plastic deformation,and can be used as an ideal supporting and filling material for gob-side entry retaining.In this paper,based on the ratio of C40 ordinary concrete,selection of mineral admixture of fly ash,high toughness and good cushioning performance of ethylene vinyl acetate copolymer(EVA)and are commonly used to improve the concrete ductility of steel fiber on concrete material modification,according to the concrete mechanics performance test method of national standard,produced 100 mm * 100 mm * 100 mm cube specimens,used for uniaxial compressive strength and splitting tensile test;A prism specimen of100mm×100mm×300mm was fabricated for the calculation of axial compression and elastic modulus.A prism specimen of 100mm×100mm×400mm was fabricated for compressive and three-point bending tests.Through laboratory physical property test,digital speckle technology and numerical simulation,the mechanical properties and failure process of the modified concrete are analyzed and studied.The main work and results completed in this paper are as follows:(1)The mechanical properties of concrete were tested according to the national standard for the test method of mechanical properties of concrete,and the modification mechanism of fly ash,ethylene-vinyl acetate copolymer emulsion and steel fiber on ordinary concrete was analyzed based on the test results.The results show that the substitution of fly ash and the incorporation of polymer make the concrete crack and less broken by enhancing the cohesiveness and integrity inside the concrete,and the use of steel fiber with good tensile performance can enhance the service time of concrete by limiting the development of concrete cracks.Due to the low compressive strength and elastic modulus of the polymer itself,with the increase of the polymer content,the compressive strength of concrete gradually decreases,but the plastic deformation capacity will gradually increase.The toughness of steel fiber itself is large,adding into concrete can improve the ductility of concrete very well,in the concrete flexural test,shows very good toughness,greatly enhanced the mid-span deflection of concrete and after the peak ductility;The addition of polymer and steel fiber can improve the size effect of concrete.With the addition of steel fiber,the strength of concrete in the early stage is guaranteed,which can better adapt to the mining speed of the working face.When the polymer content is 15%,the film and network structure generated will take shape in about 7days,showing its bearing effect when compressive resistance.The substitution of fly ash increases the compressive strength of concrete mainly in the later stage.(2)Digital speckle technique was used to study the uniaxial compressive failure process of concrete specimens with the size of 100mm×100mm×300mm at the meso level,and the localization zone theory was applied to analyze the results.The crack of ordinary concrete expands faster when it is pressed,it was found that the development speed of concrete cracks was greatly limited after steel fiber was added.With the increase of dosage of polymer,transformation of localization band and fracture strain threshold value are increased,the crack extension speed decrease again,and the specimen overall stress is relatively uniform,tiny fractures are distributed throughout the specimen surface,the tension fracture and dislocation displacement curve more slow,finally displacement of tension or rupture of two opposite directions will appear in a localization band.Through the proportion analysis of concrete specimens at various stages,it is concluded that the incorporation of steel fiber and polymer enhances the homogeneity of concrete,which is consistent with the results of macroscopic analysis.(3)By FLAC 3D numerical simulation,the simulation of concrete filling body along the empty left even compression destruction,filling body measurement parameters using F15S1 mechanics parameters measured,by filling in the plastic zone,the roof and floor closer and filling body vertical stress analysis and expounds the concrete filling body after rotary roof subsidence damage rule,to study other modified the related mechanical performance and failure process of concrete to provide effective way.