Experimental Study On Physical And Mechanical Properties Of Grouting Consolidation Body Under Freeze-thaw Cycle

The key projects of Tibet Laluo Reservoir,Sichuan-Tibet Railway and its surrounding railway which are constructed in the 14th Five-Year Plan,need to remain or cross the seasonal frozen area.Under the action of freeze-thaw cycle,the damage and deterioration of macro and micro defects such as joints,cracks and pores rich in rock mass in seasonal frozen zone can reduce the structural stability of rock mass,and even cause the freezing damage of rock engineering.Grouting is the key technology to effectively strengthen joint fissures and improve rock mass stability.Therefore,it it is of great theoretical significance and engineering application value to study the physical and mechanical properties of grouting consolidation body under freeze-thaw cycle,which can improve the theory of grouting reinforcement and ensure the safe and efficient operation of rock mass engineering in seasonal frozen area.In this paper,the grouting consolidation body is taken as the research object,and the freeze-thaw cycle test is used to simulate the environment of the seasonal frozen zone.The change characteristics of the microscopic pore structure are analyzed by NMR,and the physical and mechanical properties are determined by laboratory tests.The failure mechanism of the grouting consolidation body under the action of freeze-thaw cycle is studied from macro and micro scales,which provide a theoretical basis for evaluating the grouting effect of fractured rock mass in the seasonal frozen zone and improving the stability of rock mass engineering.The following research results are obtained:(1)The ordinary cement slurry(P-type),ultra-fine cement slurry(C-type)and epoxy resin slurry(H-type)were injected into yellow sandstone to make grouting consolidation body samples.0,5,10,15 and 20 freeze-thaw cycles were carried out to observe the surface characteristics and water content changes of grouting consolidation body.The results show that with the increase of freeze-thaw cycles,the particle spalling,falling off and cracking appeared in different degrees on the surface of grouting consolidation body.Macro cracks appear on the interface of grouting rock of p-type and C-type specimens after 15 and 20 freeze-thaw cycles,respectively,while no cracks appear in H-type specimens.The moisture content of samples can be divided into a slow and a rapid increase stage.The increase of moisture content is positively correlated with the apparent freeze-thaw deterioration.(2)The evolution of the interfacial micro pore structure of the three samples under different freeze-thaw cycles was analyzed by the NMR layered test technology.It was found that the microscopic pore distribution at the slurry-rock interface was bimodal distribution,and the pore diameter in the peak was mainly micropores and macropores.With the increase of freeze-thaw cycles,micropores increase and transit to mesopores,and macropores gradually increased,and the bimodal trended to the right.The T2 spectrum curves of the three samples are similar,but there are differences in the cumulative NMR signal strength and T2 spectrum area,under the same freeze-thaw cycles,the two quantitative indexes of P-type sample are the largest in,C-type sample is the second,and H-type sample is the smallest.(3)The shear mechanical test of grouting consolidation body under different freeze-thaw cycles and different slurry types are carried out,the variation rules of macro shear mechanical parameters and shear failure mode are obtained.The results show that the shear strength(?p)and shear stiffness(Ks)of slurry-rock interface are affected by freeze-thaw cycle and slurry types.?p is negatively correlated with freeze-thaw cycle,and Ks is positively correlated.Under the same freeze-thaw cycle,among the three types of specimens the slurry-rock interface ?p and Ks of the H-type specimens was the largest,second was the C-type,and the smallest was the P-type.The shear failure modes of P type,C-type and H-type specimens after freeze-thaw cycle were sliding failure,shear sliding failure and shear splitting failure.(4)In order to explore the relationship between macro and micro parameters of grout-rock interface of grouting consolidation body under the action of freeze-thaw cycle,the grey correlation method was used to calculate the correlation degree between microscopic pore structure index of grouting consolidation body and macro shear parameters.It was found that the correlation degree between shear strength of grout-rock interface and T2 spectrum area was greater than 0.6.Based on the correlation between macro and micro parameters of the interface,the shear failure mechanism of the interface was obtained.