Experimental And Numerical Simulation Research On Stability Characteristics Of Underwater Reinforced Gabion

Reinforced gabions are composed of manually edited steel grid filled with natural stones to form a stone integrated body.Natural stone is easy to obtain.The integrated reinforced gabion can restrain the crushed stone and increase the weight.Due to the good water permeability of the reinforced gabion,its impact stability is significantly better than that of concrete blocks of the same quality.However,up to now,there are few research results on the force characteristics of underwater reinforced gabion at home and abroad,which makes the design and construction of the closure project and the bank protection project lack the corresponding theoretical guidance,and brings inconvenience to the engineering practice.Therefore,further research is needed.In this paper,starting from the impact stability and force characteristics of underwater reinforced gabions,the critical velocity experiment and drag force experiment of a single reinforced gabion were carried out,the relationship between the shape and size of the reinforced gabion and the critical velocity was analyzed and discussed,and the influence of the flatness coefficient,the block Reynolds number,and the deflection angle on the drag force coefficient was studied;the numerical simulation method with porous media as a simplified model was applied,and the influence of porosity on the force characteristics of underwater reinforced gabions was studied.The main work and research results of this paper are as follows:(1)Considering the influence of flatness coefficient and deflection angle on the critical velocity of underwater steel gabions,the existing calculation formula for the stability of reinforced gabions has been revised;the force analysis of the gabion deduced a formula for calculating the critical velocity of the reinforced gabion with a undetermined coefficient(drag coefficient),and the value range of the drag coefficient under different Reynolds numbers and deflection angles was determined through the experiment.The experiment results showed that when the ratio of width to height remains unchanged,the critical velocity of the reinforced gabion increases with the increase of the flatness coefficient,the critical velocity of the reinforced gabion increases with the increase of the flatness coefficient,and the critical velocity was proportional to the 0.40 power of the flatness coefficient;the critical velocity of the reinforced gabions with length,width and height of a × a × a,a × a × c and a × b × c all decrease with the increase of the deflection angle,and the drag coefficient first decreases with the increase of the deflection angle,and then increases.(2)Considering the influence of the interaction between the block Reynolds number and the flatness coefficient on the drag coefficient of the reinforced gabion,the calculation formula of the drag coefficient of the reinforced gabion under the interaction of the two factors were fitted.The experiment results showed that the drag coefficient of the reinforced gabion was significantly smaller than that of solid blocks,generally between 0.54 and 0.84;the drag coefficient increases first and then decreases slowly with the increase of Reynolds number,which is approximately a quadratic function.When the Reynolds number is less than 2.0×104,the drag coefficient fluctuates greatly.When the Reynolds number is greater than 2.0×104,the drag coefficient decreases steadily and slowly;under the same aspect ratio,the drag coefficient of the reinforced gabion increases with the increase of the flatness coefficient,and the relationship is approximately linear.(3)The RNG k-ε model and porous media model was used to simulate the water flow characteristics inside and outside the reinforced gabion,and the calculation results were basically consistent with the experiment results.The calculation results showed that the drag coefficient of the reinforced gabion model with porous media was significantly lower than that of the impervious model;compared with the impervious model,the porous media model significantly reduced the average pressure of the front surface;the greater the porosity of the reinforced gabion,the smaller the drag coefficient.Compared with the existing drag force calculation model of reinforced gabion,the porous media model could better reflect the influence of the internal flow field of the reinforced gabion on its force characteristics.