| The environment of deep soft rock mass is more complex than that of shallow rock mass.Under the action of temperature field,chemical field and stress field,the large deformation and rheological characteristics of underground soft rock mass are significantly enhanced,which has a great influence on the normal development of underground rock engineering.Aiming at the complex coupled environment underground,the physical and mechanical behavior of real soft rock in underground environment is simulated by using soft rock-like materials which based on comparatively mature similar theory system.Research on the interaction process and mechanism of multi-field coupling simply,efficiently and accurately,and the variation law of strength and rheological characteristics of soft rock-like material under different coupling conditions is obtained.It will provide reliable basis for excavation,support and stability analysis of surrounding rock in deep soft rock engineering.Firstly,the fabrication method and equipment of soft rock-like material are optimized and improved by comparing a large number of experimental results,and then The coupling control theory of temperature,chemistry and stress is analyzed and deduced based on the Heat Transmission Science,Chemical Kinetics and Damage Mechanics.The influence of different environmental factors on the strength,deformation and creep characteristics of soft rock-like materials is studied through uniaxial compression,triaxial compression and uniaxial creep test under the influence of temperature,chemistry and stress.Based on the above theoretical and experimental results,the multi-field coupling is simulated and analyzed by using the multi-physical field simulation software COMSOL Multiphysics.The main research contents and conclusions are as follows:1)Explore the forming quality of specimens under different manufacturing methods by comparing the experimental research methods.It is found that the demoulding quality of open die is better than that of cylindrical die.The specimens obtained by one-time loading have less fluctuation of compressive strength and elastic modulus and the forming quality of machine compacted specimens is better.On this basis,the specimen making tools were improved.The Vertical screening mechanism with horizontal screen,the small size weighing stirring integrated machine for laboratory and Hand-operated bilateral synchronous feed of cylindrical specimen die were designed respectively.2)The soft rock-like material specimens are made using cement and river sand as raw materials based on the improved method of specimen preparation and the analysis of original rock properties.The coupling effects of different temperatures,acidity and alkalinity are experimented,and the effects of coupling environment on the physical properties of soft rock-like material are analyzed by taking mass increment as the object.Composition identification of soft rock-like materials under different environmental fields were carried out by means of XRD technology.3)The effects of temperature field,chemical field and stress field on the mechanical properties of soft rock are analyzed.On the premise of basic hypothesis,the energy exchange of chemical reaction is taken into account in temperature control theory,combining thermal expansion and thermal damage,and then the governing equation of temperature effect is established.Based on the damage theory,the constitutive equation of soft rock under multi-field action is established by taking temperature,chemistry and stress damage into account.The governing equations of multi-field coupling of rock mass under the influence of temperature and chemistry are put forward.4)Uniaxial and triaxial compression tests were carried out on soft rock-like specimens under coupled conditions.The results show that:(1)Under the action of temperature,chemistry and stress,soft rock-like materials change from elastic deformation to elastic-plastic deformation,and the plastic and ductility characteristics increase,which makes the stress-strain curve fluctuate.With the increase of temperature,the compression stage of stress-strain curve in the three kinds of pH environments tends to increase gradually,correspondingly,the characteristics of elastic deformation gradually weaken.(2)With the increase of temperature,the ductility of soft rock-like materials in neutral solution increases and the rheological properties become more obvious,while the acidic and alkaline solutions gradually change to brittleness.(3)The elastic modulus of specimens in three kinds of pH solutions decreases first and then increases with the raise of temperature.The average change rate of secant modulus affected by temperature in different acidity and alkalinity environments is higher than that of elastic modulus.The elastic modulus and secant modulus of soft rock-like materials are relatively stable in alkaline environment.(4)The effect of confining pressure on compressive strength varies with the pH value.In neutral environment,the effect of confining pressure on compressive strength increases with the raise of temperature,while in acidic and alkaline environment,the effect on compressive strength of soft rock-like materials decreases with temperature.With the increase of temperature,the cohesion increases gradually in neutral and acidic environments,while in alkaline environments,it increases first and then decreases.The internal friction angle of soft rock-like materials in acidic and neutral environments decreases with the increase of temperature,while in alkaline environments,it increases.5)Through step loading creep experiments,the effects of temperature,pH value and stress on creep properties of soft rock-like materials are analyzed,and a creep model considering coupled environmental damage is established.It is considered that:(1)with the increase of stress level,the steady creep rate of soft rock-like materials increases gradually,and the slope of stress-strain curve straight section decreases gradually at different creep time.With the increase of temperature,the effect of pH value on creep properties of materials gradually weakens.(2)based on the Satin-Thomson model and considering the effect of coupled environmental damage,a new creep model is obtained,which can describe the accelerated creep stage and take damage into account.The effects of various parameters in the model on creep curves are analyzed,and the experimental data are fitted and validated by the model.6)Through numerical simulation,it is found that:(1)The change of temperature has a certain effect on the chemical reaction,and the increase of temperature can accelerate the reaction rate.With the extension of reaction time,the concentration of the same chemical composition tends to be the same in different temperature environments;chemical action also has a certain effect on temperature,and before t=100h,the endothermic and exothermic effects of chemical reactions make the temperature gradient fluctuate obviously.(2)The stress on the center of the cylinder and the edge of the end face of the specimen is larger,and the area presents an "X" shape distribution in the specimen.(3)The effect of stress field on creep characteristics of soft rock-like roadways is still dominant.The maximum stress and creep strain are mainly distributed at the contact between the two sides and the bottom of the roadway.With the passage of time,the deformation continuously diffuses to the surrounding area.Different temperature and chemical action also have certain influence on the creep law of soft rock-like roadway.When the pH value,stress and creep time are the same,the creep deformation of roadway increases with the raise of temperature,while the creep strain of roadway under alkaline environment is smaller with the same temperature,stress and creep time. |
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