Experimental Study On Damage Of Cement-sodium Silicate Reinforced Jointed Sandstone Under The Condition Of Cyclic Pore Water Pressure

With the formulation of China's"14th Five-Year Plan"national strategy,a series of major national infrastructure constructions related to the national economy and people's livelihood have been carried out one after another.The problem of engineering rock mass fracture has increasingly become a major problem and challenge restricting the safety and long-term stability of engineering construction.And the grouting reinforcement technology is an effective measure to solve this engineering problem.Since the construction of the Three Gorges Project,the water level of the reservoir has been repeatedly raised and lowered all the year round.The slope-reinforced rock mass has been in the state of loading and unloading cyclic load for a long time.Therefore,it is particularly important to study the long-term stability of the reinforced rock mass during the operation stage.Taking the slope sandstone in the Three Gorges reservoir area as the test object,the mechanical properties of the joint sandstone under different filling conditions and the damage characteristics of the cement-sodium silicate(referred to as C-S double grouting)reinforced joint sandstone under the condition of cyclic pore water pressure.The conclusions are as follows:(1)It is pointed out that as the joint inclination angle increases,the peak strength,crack damage threshold,elastic modulus,deformation modulus and peak strain of jointed sandstone are the smallest at the inclination angle of 30°and the largest at the inclination angle of 90°,and generally show a trend of"?"type change trend which first decrease and then increase.(2)A three-factor and three-level orthogonal experiment was designed to determine the optimal C-S double grouting ratio as water-cement ratio 0.6,C/S volume ratio 1:0.8,and retarder 1%.The mechanical properties test of natural mud filled and C-S double grouting filled jointed sandstone was carried out,and it was pointed out that the peak strength,elastic modulus,and deformation modulus of C-S double grouting filled jointed sandstone were respectively increased by 124%,123%,and 119%compared with unfilled jointed sandstone,which is respectively 67%,74%,and 45%higher than the natural filled jointed sandstone,which proves that C-S double grouting filling has a good reinforcement effect on jointed sandstone.At the same time,the evolution law of crack damage threshold,elastic modulus,deformation modulus and peak strain with joint inclination angle of natural filling and C-S reinforced jointed sandstone was obtained.(3)Based on nuclear magnetic resonance spectroscopy and acoustic testing methods,the damage evolution law of C-S reinforced jointed sandstone is quantitatively analyzed.(1)It is pointed out that with the increase of water pressure cycle value under the same joint dip,the density and wave velocity of C-S reinforced jointed sandstone gradually decrease,whose maximum reduction are 0.3g/m~3and 710m/s respectively.And the porosity gradually increases,whose maximum increment is 0.67%.(2)Under the same water pressure cycle value,with the increase of the joint dip,the attenuation rate of density,wave velocity and porosity of C-S reinforced joint sandstone all increase first and then decrease,and the maximum is at60°inclination angle,which is 83%,26%,24%.The minimum is at 90°inclination angle,which is 41%,15%,and 3%.(3)In addition,the damage evolution law of the strength and deformation parameters of the C-S reinforced jointed sandstone by the condition of cyclic pore water pressure is obtained.(4)Research on damage constitutive model of jointed sandstone reinforced with cement-sodium silicate under the condition of cyclic pore water pressure.(1)Selecting the deterioration degree of the elastic modulus of the jointed rock mass as the initial joint damage value.And according to the equivalence principle,physical equation,generalized Hooker theorem and Misses yield criterion,the damage constitutive model of C-S reinforced joint sandstone was established.(2)Considering the effects of degradation under the different condition of cyclic pore water pressure,the ratio of the volume of the damaged cell to the total volume was defined as the damage variable,and the damage caused by the joint inclination angle was combined to obtain the comprehensive damage variable.Combined with the H-B strength failure criterion,generalized Hooke's law,and Weibull statistical distribution theory,the damage constitutive model of C-S filled joint sandstone under the condition of cyclic pore water pressure was established,and the rationality and feasibility of the model were verified.