Design Of Super Gravity Internal Erosion Device And Preliminary Experimental Study

Internal erosion may be treated as on of the important reasons that induce the destruction of embankment dams.It has the characteristics of a long period,a large spatial scale,and high hazard level.High-speed rotation of the centrifuge can produce the same self-weight stress field as the prototype.It is of great significance to conduct centrifuge hydraulic model tests on dams under the same stress conditions,to reveal the hydraulic-induced dams failure mechanism.Clearly,the mechanism of the seepage and subsequent internal erosion under high g-level needs to be characterized to understand the initiation of dam failure process,also provide validations for further centrifuge-based dam model.The one-dimensional soil column test is a common method to study the characteristics of seepage and internal erosion.The scientific challenges of applying it to the centrifuge test research include:the lack of a device that can perform a one-dimensional seepage and internal erosion test under supergravity,and the lack of research experience of internal erosion’s supergravity effect.This thesis carried out a preliminary study on the internal erosion characteristics of gap-graded soil under normal gravity and supergravity.Conclusions can be made as follows::1.Based on ZJU-400 centrifuge,a set of one-dimensional internal erosion soil column test device that can be used in the centrifuge environment was designed and developed.Tests for various functions were carried out on the test device developed.The test results show that the device can provide a constant head for soil samples under a supergravity environment of up to 80g,achieve the precise adjustment of mm-level water level difference,axial loading,and large-scale flow measurement.Various one-dimensional soil column tests including seepage and internal erosion can be completed.2.Gap-graded sand suffusion tests under normal gravity and 30g supergravity with a relative density of 90%were carried out.The results show that the development process of the soil mass under supergravity is the same as that under normal gravity.With the gradual increase of hydraulic load,the soil body firstly experienced sudden erosion locally.Then,soil erosion entered a stable overall development stage,and a seepage channel composed of soil skeleton was gradually formed from top to bottom,and the permeability gradually increased.Eventually,a certain critical hydraulic condition is reached,and the seepage channel of this soil skeleton is opened,which leads to piping.3.This paper analyzes the development process of internal erosion and the effect of hypergravity on it from the single-particle level.The analysis results show that the process of internal erosion is that the fine particles in the soil skeleton are driven by the penetration force to continuously overcome the gravity force of the particles and the interaction force between the particles,and gradually flow out of the soil body.Under the same geometric hydraulic gradient,when Darcy seepage occurs in the soil sample,the development of internal erosion is not affected by hypergravity;but when the seepage is converted to a non-Darcy state,the penetration force is greatly improved,so that the development of internal erosion will be affected by hypergravity.Based on the analysis results,this paper proposes the concept of fluidized normalized hydraulic gradient.Under the same fluidized normalized hydraulic gradient,the development status of soil in hypergravity and normal gravity is the same.4.Internal erosion is a complex process,whoes local development inside the soil is uneven.The traditional test methods are increasingly unable to satisfy the analysis and evaluation of the internal conditions of the soil during the development of internal erosion.To solve this problem,a transparent soil material is synthesized by using fused quartz sand and mixed oil.Affected by factors such as fluid viscosity,particle size,particle size distributions,and porosity,the permeability characteristics of transparent soil and natural soil are very different.This paper introduces a particle morphology theory to modify the Kozeny-Carman model.This modified model can effectively predict the permeability of transparent soil,thus guiding the similarity design of the permeability characteristics of the supergravity transparent soil internal erosion model.