Investigation Of Granular Collapse Flow Behavior In The Presence Of Interstitial Liquid

Gravity-driven flow of discrete media is a widespread phenomenon in nature and in many industrial production areas.Such flows are generally dominated by the high-speed,transient motion of a large number of discrete solid particles,which are often accompanied by a certain amount of interstitial liquid and can exhibit extremely complex flow behaviors in different environments,which can pose a significant danger to the safety of engineering facilities and personnel within the flow direction.The deeper understanding of the triggering and flow behaviors of such complex multiphase systems is of great scientific importance and is also a fundamental issue of current interest to many disciplines and engineering fields.This dissertation begins with the mechanical properties of low-saturation wet granular materials and investigates the collapse,flow,and accumulation characteristics of wet particles under different configurations in the pendular state,as well as the collapse flow evolution characteristics of partially submerged granular columns,by independently building a state-controlled small-scale granular flow experiment and measurement device that under quasi-static conditions,a theoretical model for predicting collapse damage and flow expansion of a wet particle system was developed.The dissertation’s main work is as follows.1.An experimental setup with different initial configurations（quasi-two-dimensional single-channel configuration and three-dimensional non-channel configuration）and controlled state of collapse flow of wet granular particles has been built in-house.With the help of two high-speed cameras and an appropriate light source,a complete high-speed particle flow measurement system has been developed,allowing simultaneous filming of the collapse flow process of the particle system from different perspectives.With the help of digital pictures and PIV technology,a data analysis method of particle collapse transient flow behavior is constructed.2.A stress-shear expansion model of wet granular materials is established based on the friction theory of dry particles by trying to introduce cohesive yield shear stresses characterizing wet particles,which can accurately describe the shear dilatation characteristics of wet particles under the action of plane shear in the pendular state.On the other hand,based on the classical rate state friction law,the relationship between the macroscopic stress of the system and the power dissipated per unit volume is constructed by considering the shear dilatation and rotational characteristics of the wet granular material as well as the work done by capillary forces,while the stress balance relationship at the inter-particle contact is combined to establish a preliminary shear strength model applicable to the wet granular material in the pendular state.3.The collapse process and deposition morphology of wet particles on a horizontally channelized substrate in the pendular state were systematically investigated based on an experimental setup with a quasi-two-dimensional single-channel configuration.It is observed that the collapse of the wet granular column will show three different regimes,and it is found that the collapse mode mainly depends on the initial configuration of the column and the particle size,while it is almost independent of the moisture content of the material in the pendular state,and this is used to construct a state phase diagram describing the different collapse regimes.In addition,the microscopic mechanisms of the occurrence of different collapse regimes of the system were analyzed based on the evolution characteristics of the particle velocity fields under two collapse regimes;on this basis,the effects of moisture content on the collapse flow time and deposition morphology of wet particles were quantitatively analyzed;finally,a simplified theoretical model describing the front end of particle flow was proposed,which can predict the dependence of flow distance on particle size after collapse of wet particles in the pendular state.4.The flow and propagation behavior of the wet granular column on the horizontal substrate after collapse in the pendular state was investigated based on an experimental setup with a three-dimensional non-channel configuration.It is found that particle size and column aspect ratio lead to different collapse regimes of wet particles,while the moisture content only quantitatively affects the deposition morphology of the collapsed material.Considering the inter-particle capillary effect,a dimensionless number B₀^-1w^2/3,which includes particle size and physical properties,liquid viscosity and material moisture content,is proposed to quantitatively characterize the macroscopic cohesive effect of the granular material due to interstitial liquid,and a state phase diagram describing the different collapse regimes of wet particles is proposed in conjunction with the initial configuration of the granular column.The influence laws of factors such as particle size,moisture content and initial aspect ratio of the column on the dynamical behavior and deposition morphology of the wet particles after collapse were quantitatively analyzed.Finally,by considering the system’s macroscopic cohesion effect caused by the presence of interstitial liquid within the system,a generalized scalar law describing the deposition morphology of wet particles after collapse in the pendular state is constructed,and it is discovered that the characteristic quantities describing the deposition morphology of wet particles can be characterized by the results of the corresponding dry granular materials with the additional quantities.When the cohesive effect within the wet granular material is weak enough,the generalized scalar law can be degraded to the existing experimental results for dry granular materials.5.The collapse flow behavior of partially submerged granular columns in different initial configurations was investigated.By introducing the granular submergence rate,the evolution characteristics of the interface between dry and saturated particles during the collapse process were analyzed,and the effect of interstitial liquid on the granular collapse flow behavior was discussed,and it was found that the presence of interstitial liquid would hinder the movement of the particles,and this effect would depend on the submergence rate.By introducing the dimensionless submergence rate,different collapse regimes of partially submerged granular columns in different configurations were found and the corresponding state phase diagrams were constructed;the effects of the submergence rate on the propagation velocity along the longitudinal and transverse directions of partially submerged granular columns and the deposition morphology were discussed.Finally,based on the evolution characteristics of the failure angle at the initial stage of saturated granular collapse,a theoretical model for the evolution of the failure angle at the initial stage of partially submerged granular column collapse is established,and it is proven that the model can predict the evolution characteristics of the initial failure angle of partially submerged granular column collapse under different conditions by comparing with the experimental results.This dissertation focuses on the fundamental problem of mechanical behavior of granular matter containing interstitial liquids.The deformation and collapse flow behaviors of wet granular matter with different configurations and initial states are systematically investigated using two self-designed small-scale granular flow experimental devices.The investigation work has documented several novel and unusual macroscopic flow phenomena of wet granular materials,revealed the microscopic mechanisms underlying the occurrence of various collapse regimes,and also made an effort to develop theoretical models for projecting their associated mechanical behaviors.These studies have been conducted in order to provide a theoretical foundation and research methodologies for the description and prediction of more complex liquid-containing mass flow in engineering practice,as well as to help advance our understanding of how the presence of interstitial liquid affects the flow behavior of discrete media from the perspective of a mechanical mechanism.