| Soft and hard strata interbedded is a common type of layered rock mass,which has strong structural effect in engineering,and is one of important rock masses that are studied in the exploitation of coal and shale gas.However,due to the limitation of core taking technology and the influence of rock structure,such layered rock mass is faced with the problems of sampling and mechanical properties test in the field.Therefore,it is difficult to get systematic parameters and deformation analysis results through field and sufficient indoor experiments.At the same time,the physical and mechanical parameters obtained by the test of the local complete rock through indoor test are difficult to reflect the overall mechanical parameters of the soft and hard interbedded rock mass.Considering above problems,this paper selects finite element software ABAQUS as tools for analysis,firstly designs a fast modeling method of layered rock mass by Python and INP file.Then,combining with the extended finite element method(XFEM)and damage mechanics theory,the Brazilian spliting experiment in laboratory is conducted to verify the failure path of rock in numerical simulation.Finally,the strength and deformation characteristics of the rock mass with different dip angles,rock thickness and random distribution of strata in different thickness are analyzed under uniaxial compression.The quantitative relationship between the micro unit strength,internal friction angle,cohesion,elastic modulus of the soft rock and the macro elastic modulus and uniaxial compressive strength of the rock mass is obtained.At the same time,the influence of the four kinds of microscopic parameters on the macroscopic failure of rock mass is discussed.The results show that:(1)By comparing the results of Brazilian splitting test in laboratory and numerical simulation,the direction and shape of cracks in both cases are basically the same,which verifies the accuracy of XFEM method in simulating rock mass fracture.(2)Under the same mechanical parameters,dip angle is the main factor affecting the strength and failure of layered rock.The failure of 45 ° layered rock mass is mainly controlled by the sliding of soft rock,and it's macroscopic strength of rock mass is lower than micro strength of soft rock;while the dip angle is less than 45 °,the failure type of rock mass mainly is "X",and it's the macro strength is between the unit strength of soft and hard rock.However,the macroscopic elastic modulus of rock mass in different dip angles is all lower than that of soft rock element.(3)For the layered rock with the same thickness of soft and hard rock,when the dip angle of rock is less than 45 °,the macro elastic modulus and uniaxial compressive strength are positively correlated with the thickness of rock,but When the dip angle is equal to 45 °,the macroscopic strength and elastic model of rock mass will increase first and then decrease with the increase of rock thickness.(4)For layered rock with random distribution of strata in different thickness,the macro elastic modulus and uniaxial compressive strength of rock mass have little response to the distribution of soft and hard rock position,but the macro strength and deformation are greatly affected by the dip angle and thickness of strata.(5)When the dip angle is equal to 45 °,the shear stress of monitoring points of layered rock mass fluctuates slightly with time;While the dip angle is less than 45 °,the shear stress of monitoring points of layered rock mass fluctuates in varying degrees with time,which is mainly reflected in the changes of shear stress peak value,direction and frequency.(6)The linear fitting relationship between the macro uniaxial compressive strength of layered rock mass and the strength of microscopic element,internal friction angle,cohesion and elastic modulus is good and positive.Among them,the linear relationship between the micro cohesion and the USC,the micro and macro elastic modulus is the best,and the influence of micro parameters on the macro parameters varies with the change of rock structure and dip angle in other condition.(7)The four Microscopic parameters have obvious influence on the deformation and failure of layered rock,but the influence range is related to dip angles and thickness of rock.When the dip angle of rock strata is 45 °,the failure mode is basically unchanged,which is controlled by the sliding failure of soft rock.When the dip angle is less than 45 °,the deformation and failure of rock mass is obviously different,including single "X" type,double "X" type,single shear plane and multiple shear planes crossed.The results provide quantitative relations for the macro and micro parameters of layered rock mass with different geological characteristics,which can provide reference for understanding the influence of dip angle,thickness of rock layer,soft rock parameters and the distribution of soft and hard rock strata on the strength and deformation law of layered rock mass,and also provide guidance for the stability analysis of layered rock mass under similar geological conditions in engineering.The paper has 144 diagrams,7tables and 80 references. |
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