Study On Dynamic Disturbance Characteristics And Simulation Reproduction Of Soft Sediment Deformation In Diexi Ancient Dam Lake

The upstream of the Minjiang River is located in the north-central part of themiddle section of the"North-south seismic tectonic belt".The area is affected by the Minjiang Fault Zone,the Huya Fault and the Longmenshan thrust nappe structural zone.Not only is seismic activity very frequent in this area,but geological disasters caused by external forces are also extremely significant.A series of barrier lakes have developed in the upper reaches of the Minjiang River,and a large number of soft sediment deformation structures have been found in the ancient barrier lake soft deposits,of which the Diexi ancient barrier lake is the most typical.This article takes the soft sedimentary deformation in the ancient barrier lake in the upper reaches of the Minjiang River as the research object.Based on the previous data,detailed geological survey and on-site sampling work were carried out on the deformation structure of soft sediments exposed in the Diexi ancient barrier lake.By analyzing the sedimentary environment and disturbance conditions of lacustrine sediments,the process of indoor simulation test was designed.This simulation test deeply analyzes the influence of vibration frequency,vibration acceleration,vibration frequency and consolidation time on disturbance and deformation characteristics of lacustrine sediments.Then the results are verified by numerical simulation using discrete elements.Finally,the deformation characteristics of lacustrine sediments under different dynamic disturbance conditions are summarized,and their specific causes are analyzed.Through the above research methods,the main understandings are as follows:?1?On the basis of on-site investigation and previous data,the basi characteristics of soft sedimentary deformation were obtained,and a series of tests were carried out after fully comparing similar materials.The results show that the talc powder has a particle gradation,density and physical characteristics that are similar to lacustrine sediments.Therefore,talc powder was determined as the comparative layer in the simulation experiment of sedimentation disturbance.?2?Using the shaking table model test technology,a soft sediment disturbance simulation test was carried out on the lacustrine sediment model,which revealed the dynamic disturbance law under different seismic wave frequencies,the seismic evolution process of the sediment and the response to acceleration of vibration.The following results were obtained through experiments:?1?During the early production process of the test model,through real-time monitoring of the thickness of the sediment layer,after the consolidation time reaches24h,the thickness of the soft sediment will not change substantially and enter the"creep"state.?2?In the vertical direction,the acceleration of the sediment has a decreasing effect,that is,the vibration response amplification factor increases as the elevation increases.?3?The characteristic of soft sediment deformation disturbance at different frequencies is that as the frequency increases,the dynamic disturbance response of the sediment decreases,that is,5Hz>10Hz>15Hz.?4?The evolution process of soft sedimentary deformation under the action of multiple seismic forces.After the initial vibration disturbs the sediment,it will accelerate the consolidation of the sediment,resulting in very small disturbance deformation of the consolidated sediment by the later vibration force.?5?Through the monitoring of the two observation surfaces of the model box,the disturbance characteristics of the soft sediment deformation are found to be different in the parallel vibration direction and the vertical vibration direction,but the response law is basically the same.?3?Using PFC^2Dto numerically model the deposition model,on the basis of loading sine waves of different frequencies,analyze the cloud map of the displacement of the particles,and then summarize the deformation characteristics and process of the deposition model,and get the following conclusions:?1?The particle displacement area of the deposition model is mainly concentrated on the contact surface of different particle layers,showing a"strip-like"distribution characteristic.?2?The disturbance characteristics of the sedimentation model under different vibration frequencies show a certain similarity,but the size of the particle displacement decreases with the increase of the sine wave frequency,that is,5Hz>10Hz>15Hz.?3?Under the same sine wave,the disturbance change degree of the deposition model increases with the height of the sediment layer,indicating that the sequence before and after deposition has a direct relationship with the disturbance deformation of the sediment.?4?Based on the characteristics of laboratory tests and the results of numerical simulation,by observing the microstructure of soft sedimentary deformation and the direction of seismic wave transmission,the stress characteristics during the process of soft sedimentary deformation are analyzed,and the main cause of the disturbance characteristics is:?1?when the vibration occurs,the sine wave is transmitted from the bottom to the top,generating pore water pressure,which causes the sediment to liquefy;?2?there is a horizontal shear force in the horizontal direction,which causes the shear layer to deform.