Study On Shear Strength Monitoring Model Of Loess Based On AHFO-FBG Method

With the strategic goals of"carbon peaking and carbon neutrality"put forward,the development and utilization of clean energy has become a top priority,so pumped storage power stations have been built in large numbers.However,in the construction of pumped storage power station in the northwest cold and arid loess area,it is necessary to solve the problem of prediction and early warning of reservoir bank loess slope landslide.As one of the main mechanical parameters of loess,the shear strength parameters of loess play an important role in the stability of loess slope on reservoir bank.Therefore,by studying the relationship between the shear strength parameters and temperature eigenvalues of loess and the moisture content and dry density,the calibration model between the shear strength and temperature eigenvalues of unsaturated loess with different dry densities is obtained.Finally,this paper combines the calibration model with the active heating fiber Bragg grating(AHFO-FBG)technology to propose a distributed in-situ online monitoring method to realize the in-situ monitoring of loess shear strength.In addition,this paper also uses nuclear magnetic resonance(NMR)to measure the saturated and unsaturated samples of loess,and studies the influence of the pore structure of loess and the occurrence state of water(bound water and free water)on the shear strength monitoring model of loess from a microscopic perspective.The main research contents are as follows:(1)Firstly,by analyzing the shortcomings of the existing shear strength measurement and monitoring methods,this paper proposes to use AHFO-FBG technology to monitor the shear strength of loess.Then,after comparing and studying different shear strength theories,this paper chooses to combine the shear strength theory into which water content is introduced with the technology of measuring soil moisture content based on AHFO-FBG method,and puts forward the theoretical monitoring model of unsaturated loess shear strength based on AHFO-FBG technology.(2)On the basis of the existing research on the measurement of soil moisture content based on AHFO-FBG method,this paper considers the influence of loess pore structure,further improves the traditional experimental scheme,controls the pore structure of loess samples unchanged when the moisture content changes,and obtains an improved calibration formula between loess moisture content and temperature characteristic value.The formula is more suitable for in-situ monitoring of loess moisture content.(3)By studying the variation law between the shear strength parameters and water content of the existing loess,this paper compares the effects of pre-wetting and humidification-dehydration on the relationship between shear strength and water content of loess.It is pointed out that the unsaturated compacted loess obtained by humidification-dehydration is similar to the undisturbed loess,and its shear strength parameters decrease linearly with the increase of water content,and its linear fitting formula is obtained.(4)Through NMR test and analysis of saturated loess samples with different initial water content and unsaturated loess samples made by two sample preparation methods,this paper explains the influence of different sample preparation methods on the calibration model between temperature characteristic value and shear strength and water content of loess from the perspectives of pore structure change and water occurrence in soil.(5)In order to realize the distributed in-situ on-line monitoring of heterogeneous unsaturated loess slopes,based on the above relationship model of shear strength parameters and temperature eigenvalues with water content,this paper further considers the influence of dry density on shear strength parameters and temperature eigenvalues of unsaturated loess,and obtains the binary relationship model between shear strength parameters and temperature eigenvalues of loess and water content and dry density of loess.Then,the above two relational models are combined to obtain the calibration model between the shear strength parameters of unsaturated loess with different dry density and its temperature characteristic value,and the calibration model between the shear strength of loess and its temperature characteristic value is further obtained by combining Coulomb’s law.Finally,the AHFO-FBG technology is introduced into the calibration model to obtain the loess shear strength monitoring model based on the AHFO-FBG method.