Experimental Study On The Process Of Collapse-Deposit-Impulse Wave Generated By Columnar Dangerous Rock Mass

As the golden channel of our country,the Three Gorges channel of the Yangtze River has great tourism resources and important navigation significance.Channel safety is the lifeline of the stable development of the Yangtze River economic belt.Since the Three Gorges Dam impoundment,a large number of new columnar dangerous rocks have emerged on the slopes of both sides of the reservoir area,which will lead to the collapse of dangerous rocks.Therefore,the assessment and prevention of disaster points have become an important work to maintain the safe operation of the channel.The collapse disaster in the reservoir area has the characteristics of strong outburst,intense energy and wide range of influence.At present,the research on the collapse of dangerous rock mass in the reservoir area is mainly based on the qualitative analysis,lacking the corresponding quantitative research.Therefore,quantitative analysis is an important method to accurately reflect the collapse failure of columnar dangerous rock mass.In this paper,a general physical model with scale of 1:200 is established to study the unstable failure mode,accumulation form and wave height of the columnar dangerous rock body in the reservoir bank of the Three Gorges reservoir.The shape coefficient a(height width ratio of the columnar body)and the water depth h m are introduced as the test variables It provides a reference for the delimitation of the dangerous area and the prevention and control of the disaster when the pillar dangerous rock mass collapses in the flat area and near the water.The main research contents and conclusions are as follows:1)Six groups of tests were carried out under the condition of no water.Six height gradients(0.2m,0.4m,0.6m,0.8m,1m and 1.2m)were designed respectively,that is,the collapse test was carried out for six kinds of granular columns with different shape coefficients.It is found that there are two typical failure mechanisms due to the difference of shape coefficient in the process of column instability.When a is less than 2,the failure process is mainly energy storage stage,failure stage and post failure stage;when a is more than 2,it is divided into energy storage stage,failure stage I,failure stage II and post failure stage.It is found that in the failure stage I of a ? 2 test,the bottom of the column appears obvious crushing failure.At the same time,the characteristics of collapse duration,accumulation slope angle,farthest moving distance,residual height and vertical moving distance of center of mass are studied quantitatively,and the prediction formula is obtained.The formula shows that with the increase of the shape coefficient a,the collapse duration,the farthest moving distance,the vertical movement of the center of mass and the residual height will increase,while the slope angle of the final accumulation body formed by the particles will decrease.2)At the same time,11 groups of wading tests were carried out on the granular column with submergence less than 0.5.The failure process of the water-related granular cylinder mainly includes: energy storage stage(failure surface formation),failure stage I(collapse into water-surge formation),failure stage II(shear slip-push water body)and post failure and surge propagation stage(surface current-surge propagation).The results show that the complex "solid water" interaction in the process of the collapse of the particle column under the condition of wading is the internal cause of the difference of the movement and accumulation of particles in the wading test and the water free test,in which the particles entering the water lead to the irregular rolling,flow and displacement of the water body,on the contrary,the resistance,buoyancy and flow of the water body react on the particles.The "solid-liquid" interaction mechanism was found out.3)A large number of test data are obtained through multiple collapse tests.Taking the shape coefficient a of the cylinder and the wading depth h m as the independent variable and the maximum surge h as the dependent variable,the maximum surge prediction formula is obtained,and compared with the test results,it has a good correlation.The formula is applied to the prediction of collapse and surge of columnar dangerous rock mass under the actual working condition.The results are compared with Noda method,Panjiazheng method and the formula method of the Academy of water sciences,and the results are similar to those of the prediction method of the Academy of water sciences.The prediction formula in this paper has good prediction results.