Experimental Study On Elastic Modulus Of Sand Cushion Cushion In Shed Hole

China is a country with many mountainous disasters,nearly two-thirds of which is mountainous and hilly area.Rockfall hazards is a common natural calamity in the central and western mountainous areas of China,it has the characteristics of wide distribution,unpredictable occurrence of time and place,frequent happening,changeable Path,great im Pact of damage and so on.Along with the occurrence of rockfall movement,the complex process of energy transformation is accom Panied.Rockfall hazards poses a serious threat to the buildings,life and property of human beings which are within its influence area.Therefore,the study of preventing and controlling measures of rockfall hazards has long been the hot research target in recent years.Among the plenty of existing rockfall hazards preventing measures,shed tunnel project has been widely applied to the preventive works for its excellent function.Sand-gravel cushion,which serves as a Passive protective measure,is used with the shed tunnel project.And it is laid on the top of the shed tunnel to reduce the im Pact energy caused by rolling stone.Elasticity modulus refers to the Parameter reflecting the cushioning property of sand cushion,which plays an influential role in reducing the maximum im Pact force when rolling stones strike cushion.Currently,there mainly are two ways to study the elastic modulus of cushioning property of sand-gravel cushion and its influence factor,including model experiment and field experiment.Among which,the model experiment can be used to conduct the quantitative study to explore the influence of the characteristics of sand-gravel material on the elastic modulus of cushion for its preferable repeatability and controllability.The model experiment is employed in this thesis to study the relationship between the elasticity modulus and its influencing factors when rolling stone strike the sand-gravel cushion in the shed tunnel.Based on the previous researches on elasticity modulus,the author studies the optimal thickness of sand-gravel cushion,which provides more technical support for disaster prevention design of shed tunnel structure and other engineering facilities.Through the experimental research and the results of com Parison with other relevant researches,the major findings are as follows:(1)The analysis and selection of the factors that affect the elasticity modulus of cushion,three main factors are found affecting the elasticity modulus of cohesiveless soil,they are the relative Particle diameter of sand-gravel material“D”,the relative density of sand and gravel“C_m”and the non-uniformity coefficient of gradated sand and stone“C_u”.The three factors have significant influence on the effective stress of soil skeleton,which can further affect the elasticity modulus of the soil and the maximum impact force which is caused when the sand-gravel cushion is buffered by the rolling stone.(2)The analysis of the results of several groups of experiments and data reduction,the computing formula for calculating elasticity modulus of the cushion of sand-gravel class(0.0375?D?1)is obtained,it is“E=21D^0.9C_m^4.3C_u^0.64”.The research results show that:the elasticity modulus of the sand-gravel cushion increases with the increasing of the relative Particle diameter of sand-gravel material“D”,the relative density“C_m”and the non-uniformity coefficient“C_u”.(3)The computing formula for calculating elasticity modulus of the cushion of gravel-cobble class(1?D?15 is“E=22.7D^0.33C_m^4.3C_u^0.64”.The research result indicates that:the elastic modulus of the sand cushion also increases with the increasing of the relative Particle diameter of sand and gravel material“D”,the relative density“C_m”and the non-uniformity coefficient“C_u”.The different computing formulae for calculating elastic modulus of the cushion of sand-gravel class and gravel-cobble class reflects the influence of the cohesiveless soil with different Particle size range and the different Particle size range on the formation of the elasticity modulus value.Through the com Parison between the calculated results of the elasticity modulus of sand-gravel class and gravel-cobble class and the literature data,it is found that the formulae are in high goodness of fit.(4)By analyzing the factors affecting the elasticity modulus of the cohesive soil cushion and combining with the experiment results and data analysis,the formula for calculating the elasticity modulus of sandy clay cushion is gotten,it is“E=46C_m^3.6”;and the formula for calculating the elasticity modulus of montmorillonite(it belongs to cohesive soil)cushion is“E=10.8C_m^7.8”.The calculating results of this model are com Pared with the reference range value of elastic modulus of cohesive soil,the com Parison result is very close,which verifies the reliability of the formulae.(5)On the basis of research findings of elastic modulus of the sand-gravel cushion,the experiment result of the optimum cushion thickness and the data processing and analysis,the computing formulae for calculating the optimum cushion thickness are gotten as follows:when the elastic modulus of the gravel cushion is in the 1?100MPa interval,the formula for calculating the optimum cushion thickness“H_b”is“H_b=H_c/H₀=2.25(E/E₀)^-0.025(F/F₀)^0.26”;when the elastic modulus of the gravel cushion is in the 101?155MPa interval,the formula for calculating the optimum cushion thickness“H_b”is“H_b=H_c/H₀=2(F/F₀)^0.26”.In the formulae,“H_b”symbolizes the nondimensionalize optimum cushion thickness,the unit of“H_c”is“cm”;“H₀”refers to the constant and“H₀=1cm”;the unit of“F”is“N”and“F₀=1N”;the unit of“E”is“MPa”and“E₀=1MN”.The com Parison between the calculating model of optimum cushion thickness and data from the relevant literature shows that the formulas fit well with each other.