| With the global climate change and engineering activities affecting the degradation of frozen soil in the Qinghai-Tibet Project Corridor,the thermal stability of frozen soil-rock mixture caused the structural stability to decline is a major problem that the cold region project construction needs to face.The characteristics and mechanism of the strength deterioration of the soil-rock mixture and structure interface induced by hot melting under different engineering conditions are the core scientific issues of this study.The thesis carried out the test of the deterioration of interface strength under positive melting with the samples of frozen soil-rock mixture and concrete combination,and clarified the law of the change of interface temperature with time of different parameters during positive melting;based on the macroscopic shear strength of the interface,make the analysis of rock content,water content and positive degradation characteristics of shear strength at the interface between frozen soil-rock mixture and structure during the thawing process under the normal stress.Through NMR,it is clear that the interfacial strength degradation is intrinsically related to the change in unfrozen water content.Combined with the mechanical test results,it is revealed that the effect of rock content and initial water content on the strength degradation of the frozen soil-rock mixture-structure interface.And it provides a theoretical reference for the structural load of the frozen soil-rock mixture under hot melting.Aiming at the temperature change problem of frozen soil-rock mixture and structure interface during positive thawing process,based on the temperature calibration test of frozen soil-rock mixture and structure interface under different engineering conditions during positive thawing process,explore different rock content ratios of the temperature change rate of the interface in the same time.Clear the internal relationship between the phase transition time of the interface of frozen soil-rock mixture and structure and the ice content under heat melting,and summarize the law of heat conduction of the frozen soil-rock mixture by the gravel medium.It was found that the difference of required time to defrost the sample interface with different rock content in the negative temperature range of-15??-5? is small.In the temperature change range of-5? to 0?,as the large particles in the soil-rock mixture form a stable framework and the secondary particles fill the voids of the large particles,the crushed rock as the main heat transfer material participates in the entire heat transfer process,the higher rock content of frozen soil-rock mixture is characterized by a higher thermal conductivity in terms of heat transfer.That is,in the same period of time,the faster the rate of temperature rise of the soil-rock mixture with a higher rock content.Aiming at the problem of the strength loss characteristics of the soil-rock mixture-structure interface induced by hot melting under different conditions,a series of tests of the interface degradation law of the combined body with different engineering condition parameters(including rock content,water content,normal stress)was carried out to obtain the interface damage law corresponding to engineering working condition during the positive melting process.Analyzes the interface degradation behavior characteristics of each interface trait at different temperature stages,clarifies the positive melting characteristic threshold corresponding to the significant interface degradation response,and reveals the relationship between the positive melting characteristic threshold and the interface rock content,water content,and normal stress.Based on the law of shear strength of rock content,water content and normal pressure on the interface with temperature rising,the three stages of strength change are summarized:(-5??-3?)reduction stage,(-3??0?)extreme speed reduction stage and(0??15?)flat stage,based on the influence of water content on the interface strength,a "watershed" of strength changes in two dimensions is proposed.Finally,through the analysis of the change law of interface strength in the whole phase transition phase,it is found that the increase of normal pressure reduces the influence of shear strength and aggregates.It can be seen that the interface is in an extremely unstable state at this time.In view of the inherent relationship between the degradation response of the soil-rock mixture-structure interface and the change of unfrozen water content,this paper establishes the correlation between temperature-unfrozen water content shear strength based on the NMR nuclear magnetic stratification test technology,which can completely correct the frozen soil-structure interface.The melting process is divided into three stages(freezing stage ?,phase transition stage ?,and melting stage ?).When the interface temperature is defrosted from-15? to-5?,the unfrozen water content at the interface increases by 1.7%,the unfrozen water content at the interface rises little,and the interface ice crystal content is high.It can be seen that the frozen soil-structure is still frozen in the early stage of thawing.The unfrozen water content at the interface of the sample changed little at the beginning of the thawing,but as the thawing degree deepened,the unfrozen water content began to rise rapidly,and the unfrozen water content of the sample only increased by 80.4%from-5? to 0?.At the same time,the shear strength of the interface is greatly reduced.As the melting degree of the sample continues to deepen,the unfrozen water content at the interface gradually stabilizes after the sample is thawed to 0?.At this time,the ice crystals at the interface are completely melted.The unfrozen water sample enters the complete melting stage,and the corresponding shear strength decreases.It also gradually decreases and gradually stabilizes.Aiming at the problem of the morphology and deterioration mechanism of the fracture and displacement zone of the frozen soil-rock mixture and structure interface,through the analysis of the macro-characteristics of the damaged concrete interface and the shear displacement zone of the soil-rock mixture,the interface of the broken rock content and the shear failure are clarified.Consider the feedback effect of the combined impedance on the degradation of the interface between the soil side and the concrete side of the failure surface to the deterioration of positive melting,the embedding characteristics of crushed rock in cast-in-place concrete are proposed.It was found that with the increase of the rock content,the surface state of the sample gradually changed from smooth and to the state of uniform distribution of gravel,and the shear dislocation zone changed from a smooth shear plane to an irregular shear zone,and internal cracks gradually developed and penetrated.Based on the generalized analysis model of the strength of the frozen soil-rock mixture during the positive thawing process,the Mohr Coulomb criterion was revised.Comprehensive analysis of interface strength degradation and positive melting temperature,interface properties make the test correlation analysis of meso-strength degradation mechanism.Based on the mechanical results and deformation analysis of the thermal-induced frozen soil-rock mixture-structure interface,the effects of the crushed rock content and initial water content on the interface strength degradation mechanism were summarized.The above research results are not only a useful supplement to the research system of frozen soil-rock mixture,but also provide effective guidance for the construction of Soil-rock mixture engineering in cold region. |
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