Study On The Hydration Mechanism Of Nano-clay Modifie Grouting Material And Mechanical Model Of Surrounding Rocl Reinforcement

The increase of coal demand leads to the continuous development of deep mining,the complex geological environment in the deep is bound to cause more complex and severe challenges for coal mining.The stability control of roadway surrounding rock deformation has become one of the difficulties and emphases of the research.Grouting reinforcement plays a good governance effect on the stability control of surrounding rock and is widely used.However,the uneven development of cracks caused by the gradient failure of roadway surrounding rock results in the defects of traditional grouting materials,such as large particles,which cannot meet the requirements of grouting reinforcement for the stability control of surrounding rock.Moreover,the deep environment is more complex,which is faced with water rich and ion erosion environment,resulting in significant decline of mechanical properties of grouting materials.In order to solve the above problem,in this paper,the defects of traditional grouting materials were improved by laboratory tests,and nano-clay（NC）modified cement grouting material was proposed.The mechanical properties of cement materials were analyzed by macroscopic and microscopic means,and the evolution characteristics of macroscopic properties and microstructure of nano-clay grouting materials under complex environment were further studied.Meanwhile,laboratory tests were used to verify the reinforcement effect of grouting materials on surrounding rock.Combined with the property of cement grouting reinforcement material,according to the law of gradient failure of surrounding rock,the graded reinforcement mechanism of gradient support is put forward,and the mechanical model of gradient failure of surrounding rock is established by D-P criterion and elasto-brittle damage model,and the application is verified.The research has important guiding significance to the surrounding rock control of deep roadway.Through the above research,the research progress of this paper is as follows:（1）Firstly,the mechanical properties of nano-clay grouting reinforcement materials were studied.With the increase of NC,the initial setting time of the slurry became shorter,and the bleeding rate decreased obviously,but the retarder had little effect on the final setting time.The content of NC is inversely proportional to the flow time of slurry and has the exponential characteristic of high fitting degree.With the increase of NC,the compressional wave and shear wave of the stone first increased and then decreased,and NC changed the compactness of the cement sample.The change of compressional wave velocity is similar to the change of compressive strength,that is,the larger the uniaxial compressive strength of the sample is,the greater the corresponding compressional wave velocity is.Meanwhile,the law of capillary water absorption of the cement sample is obtained.（2）By means of microscopic experiments,the hydration mechanism was revealed.The MIP test showed that when NC≤2%,the number of harmless pores and less harmful pores increased,and the corresponding harmful pores and more harmful pores showed a decreasing trend.The hydration degree of cement material was higher,and the sample compaction was higher.When NC≥2%,the gel hole and transition hole generated by hydration of cement are reduced,the compactness is reduced,and the macroscopic mechanical properties of cement become worse.Microcosmic experiments showed that when NC≤2%,AFt products increased significantly and showed a "flower blossom" shape with relatively dense morphology.Meanwhile,CH consumption and C-S-H gel formed,and C-S-H gel could fill the pore structure of the material and improve the densification of the material.When NC continues to increase,ettringite is shorter in length and shows fine needle shape,and it is found that the flake CH,C-S-H gels are significantly reduced,and the formation of hydration products and ettringite are restricted,which affects the compactness and pore structure of cement samples.（3）In order to meet the complex geological conditions of the mine grouting material requirements The erosion characteristics of grouting materials in complex underground environment were studied.It was concluded that NC addition could improve the compressive strength of cement samples and reduce the mass loss rate under ion erosion.NC addition can not only fill the pores of cement grouting material,but also promote hydration reaction and reduce permeability.Theoretical models of permeability and immersion time were established and verified.Meanwhile,the microscopic test shows that when the content of NC is 2 wt.%,the peak strength of the hydration product ettringite is the highest.At this time,NC can promote the hydration reaction of cement material to the greatest extent and generate more hydration products.When the NC content is higher than 2%,the hydration reaction is inhibited,the main product ettringite and calcium silicate hydrate gel are reduced,the filling effect of the sample is weakened,the porosity is increased,and finally the compactness is reduced.The content and morphology of ettringite also changed with the change of NC content.Microscopic analysis shows that NC can effectively fill the crystal gap of cement material,promote hydration reaction and refine the pore structure of the material.（4）On the basis of the above analysis,the test and engineering verification of surrounding rock reinforcement are further completed.The strength of surrounding rock reinforced by NC materials can reach 63.4%（σ3=2.0 MPa）,58.3%（σ3=5.0 MPa）and 63.2%（σ3=10.0 MPa）of the peak strength of intact rock.The peak strength of the fracture reinforced by NC grouting material is 37.4%of that the intact specimen,and the peak strength of the fracture reinforced by HC material is 22.8%of that of the intact rock.It shows that the NC reinforcement material has the characteristics of small particle size and strong cohesive force,and can well penetrate into small cracks.（5）According to the crack distribution characteristics of surrounding rock,the graded control of gradient support is proposed,that is,the fractured area is reinforced by bolt and high strength grouting to realize the gradient confined shell around the roadway.Due to crack,pore diameter of the plastic zone along the radial stress direction of roadway gradually become smaller,open fractures also gradually transformed into a closed fractures,ordinary grouting material is very difficult to finish better consolidation and filling effect,thus in the plastic zone（crack area）,mickey grouting was adopted to realize hierarchical reinforcement,combined with anchor cable form within 3D gradient pressure hull,realize the stability of surrounding rock characteristics.（6）Combined with the grouting reinforcement material developed,the D-P criterion and the elasto-brittle damage model were adopted to establish the mechanical model of graded reinforcement.According to the characteristics of gradient failure,the graded gradient confined shell was established,and the control mechanism of the gradient confined shell was put forward to realize the recovery of the strength of surrounding rock.Based on the gradient stress solution of surrounding rock,the gradient coefficient K-_Δ is obtained:K_Δ=K._cΩ=|σ_θ/σ_r.c_Ω|;the parameters of surrounding rock were calibrated by numerical simulation,and the initial support verification was completed.Meanwhile,it is concluded that the gradient reinforcement technology changes the displacement of surrounding rock from local severe deformation to uniform slow global deformation,and the supporting effect mechanism is discussed.The study shows that the model provides theoretical and practical significance for surrounding rock control.