| In the field of geotechnical engineering,practical engineering such as engineering blasting,large-scale section excavation,landslide instability treatment,and advanced earthquake prediction all involve the disturbing influence of dynamic stress waves on rock masses.Joints are a very common form of rock fractures,which have an important impact on the propagation characteristics of stress waves.The rock mass in nature contains a large number of joints,and these natural joints are often composed of filling materials that are different from rock materials such as mud,sand,rock soil,and gravel.No matter the strength or deformation characteristics,the filling medium and the rock material are relatively different.In view of the advantages of simple and fast numerical simulation methods,this paper uses PFC2 D particle flow software to carry out a numerical simulation study on the propagation characteristics of stress waves in filled jointed rock masses.The main research work of this paper includes:(1)Based on the PFC numerical theory,PFC command flow,FISH programming language and contact model constitutive relationship,the rock model is created and the "particle string boundary" that similar to the non-reflective viscoelastic boundary is set.Using PFC to simulate the propagation process of stress waves in rock mass media and analyzing the contact force chain between particles and the particle velocity-time relationship.The result presents that it is feasible to simulate the propagation characteristics of stress wave by PFC.(2)Based on PFC program,the propagation characteristics of stress wave in single filled jointed rock mass are simulated,and the numerical solution of transmission coefficient PFC is obtained,which is compared with the theoretical solution of thin layer theory and equivalent wave impedance theory.The comparison results indicate that the error between PFC numerical solution and the above two theoretical solutions is small and the coincidence is good,which indicate that it is reasonable to use PFC program to simulate the propagation characteristics of stress wave in jointed rock mass.(3)Based on PFC model of single filled joint rock,the influence law of incident wave frequency,amplitude,wave shape and filling thickness on the propagation characteristics of stress wave is studied.Results show that when the filling thickness increases continuously,the transmission coefficient gradually decreases,and the “filtering effect”becomes stronger;The transmission coefficient decreases as the frequency of the incident wave increases.As the frequency of the incident wave continues to increase,the transmission coefficient will gradually approach 0,that is,it has the characteristics of “passing low frequencies and blocking high frequencies”.When the filling thickness is larger,the frequency of the incident wave has a stronger influence on the attenuation of the stress wave.When the thickness of the filling joint is constant,the transmission coefficient will increase with the increase of the incident wave amplitude.The greater the filling thickness,the stronger the influence of the incident wave amplitude on the transmission coefficient.Rectangular waves have the best propagation effect in filled jointed rock masses,followed by sine waves,and triangular waves are lower.(4)PFC model of rock with two filled joints is established,and the influence of the ratio of filling joint spacing on the propagation characteristics of stress wave is studied.Results illustrate that when the ratio ? of the filling joint spacing is small(?<2%),the transmission coefficient of the two filled jointed rock masses is not equal to the simple multiplication of the transmission coefficient of the single jointed rock mass;when the filling joint spacing ratio ? is small(?<2%),the transmission coefficient is related to the "thickness" transmission sequence of the stress wave at the two filling joints.There are two limit values ?1 and ?2 for the filling joint spacing ratio ?.When ?<?1,the transmission coefficient will increase with the increase of the filling joint spacing ratio;when ?1< ? < ?2,the transmission coefficient will decrease with the increase of the filling joint spacing ratio.When ? > ?2,the transmission coefficient tends to a stable value.(5)The PFC model of rock with multiple filling joints is established,and the influence of the distribution of filling joints on the propagation characteristics of stress wave is studied.Results present that for multiple filling joints with the same spacing and the same filling thickness,when the filling joint spacing ratio is small(?<2%),the number of filling joints has little effect on the transmission coefficient.At the same time,when ?<5%,for multiple filling joints with different spacing and the same filling thickness,the transmission coefficient is related to the density of the filling joints.When the filling joints are in a "sparse-dense" distribution,the transmission coefficient is the largest,when the filling joints are in a "dense-sparse" distribution,the transmission coefficient is second,and when the filling joints are in a "sparse-dense-sparse" distribution,the transmission coefficient is the smallest.(6)On the basis of the PFC model of filling jointed rock mass,the damage mechanism of the filling joint distribution state on the explosive stress wave in the rock mass is studied,and the damage mode and crack evolution of the rock mass under the action of the explosive stress wave by the filling joint are analyzed in detail.During the process,the study found that when the filling joint intersects the minimum resistance line and leads to a free surface,the weak layer of the filling joint produces shear and tensile failure.The existence of the filling joint changes the force path of the stress wave,and the explosion energy follows the filling.The joint direction "escapes",the effective action time of the explosion wave is extremely short,the explosion energy attenuation amplitude is the largest,and the blasting effect is the worst. |
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