| Frost decay of rocks in cold regions under temperature differences of seasonal change and circadian cycle for a long time has induced a series of engineering problems.With the development of China's western development strategy and the growth of energy demand,It is necessary to study the freeze-thaw properties of the rock for the security of cold regions rock mass engineering.As it is the dir ect guidance of rock mass engineering projects for analysis and prevention of freezing-thawing disaster in high altitude cold regions,which provides some theoretical support and has important practical significance.The study of rock-like materials has important engineering significance for the design and construction of rock engineering,for it is difficult to take samples due to the losses and damages in delivery and machining process and more suitable for the basic research under the ordinary experiment condition.Using the shale as the original rock and the cement,sand,fly ash made out the rock-like materials to study the freezing-thawing test,the thermodynamics test,the uniaxial compression test,the triaxial compression test,the uniaxial creep test and the SEM test,wich can obtain the characteristics of strength,damage and creep varing with freeze-thaw cycles and fly ash and analyze the damage mechanism.Thus,basing on above to carry out the numerical analysis under multiple physical fields by ABAQUS.The main research content and research findings are as follows:(1)The interaction between water,heat and force of rock under freezing-thawing are analyzed and the mathematical model about rocks coupling of temperature,moisture and stress field is summarized.A calculation model for frost heaving force of rock mass in the process of water freezing is established,which obtain that the frost heaving force is determined by the volume modulus and the frost heaving force is nonlinear positive correlation with elastic modulus.(2)Rock-like materials with cement,river sand and fly ash are configured into four type containing different fly ash(m=0%?m=10%?m=20%?m=30%)and made out specimen.The thermodynamics experiment is conducted to measure the laws of thermal conductivity,specific heat capacity,thermal diffusivity and thermal resistance varing with temperature after freeze-thaw experiments of different cycles(n=0?n=5?n=10?n=20?n=40?n=60)under full water.(3)After the uniaxial compression test,the triaxial compression test with 1MPa for four types rock-like materials is conducted and consider:(1)The stress-strain curves can be mainly divided into four stages: compaction stage,linear elastic stage,plastic deformation stage and damage stage under different freeze-thaw cycles and fly ash,and the strain softening stage is less obvious for the increasing of overall brittleness of rock mass later.(2)With the increasing of freeze-thaw cycles and fly ash,the average elastic modulus,the secant elastic modulus,the freezing-thawing coefficient and the peak strength show a decreasing trend.While the peak strain show a decreasing trend with the increasing of freeze-thaw cycles and the decreasing of fly ash.(3)The failure mode of the specimen has a splitting surface along the axial direction and is not completely through and has low degree of breakage under less freeze-thaw cycles,while whose is mainly the vertical rupture and oblique shear failure that has greater degree of breakage under more freeze-thaw cycles.(4)With the increasing of freeze-thaw cycles and fly ash,the triaxial compressive strength,the elastic modulus,the cohesive force is continuously decreasing and the internal friction has a first descending and then rising trend.(4)The rock-like materials are conducted the damage micromechanical properties and found:(1)Defining the damage mechanics as basic state,the damage evolution equation is established considering freeze-thaw and loaded effect.(2)The damage degradation mode of specimen under different freeze-thaw cycles is scaling mode,and the freeze-thaw damage of rock is from the outside to the inside.(3)The effect of freeze-thaw is first faster and then slower by the calculation and analysis of the freeze-thaw damage variables.(4)The micro pore structure and fracture morphology characteristics varing with freeze-thaw cycles and fly ash are obtained by scanning the morphologies using SEM magnifying 5000 times.(5)The rock-like materials are conducted uniaxial creep experiment by test machine and found that:(1)The creep change law in general is deceleration and uniform speed,and begins accelerating change with the increasing of freeze-thaw cycles and fly ash.Thus the steady creep rate is gradually increaing,and the stready creep rate adding fly ash is greater than without fly ash of that.(2)The average creep modulus and anti-deforming capability decreases with the increase of freeze-thaw cycles.While the average creep modulus has a first decrease and then increase trend with the increase of fly ash,but has less change in the whole.(3)Based on the material rheological mechanics and damage mechanics,the nonlinear viscoelastic plastic rheological model is established to describe the rheological properties law of rock-like materials when freezing-thawing,and the corresponding constitutive equation and creep equation are derived.(6)By numerical simulation,it is found that:(1)The freeze-thaw destruction of the specimen is from the outside to the inside and gradually deep into the inside.The stress and strain extend from two sides to the middle after the compression of the freeze-thaw specimen.(2)The temperature change near the wall of the tunnel surrounding rock is more greater.The intersection in the vault and side wall and in the arch bottom and side wall are the maximum stress of creep rupture,and the destruction of the vault-side wall-arch bottom is coupled with each other,and thus obtain the distribution law of frost heaving force under the coupling of thermal stress and the seasonal freezing-thawing.Therefore,relevant engineering measures should be taken to effectively control the range of temperature change. |
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