Lecture 26 Flashcards
What are four examples of dense flows?
Hyper concentrated flows
Mud flows
Debris flows
Rock flows
What is the structure of a dense particle flow?
The top layers resembles a fluid dominated flow, with air mixed with fine particles.
The middle layer resembles a mudflow, with a high concentration of mud silt particles bulked out by incorporated and eroded sediments.
The bottom layer travels in circular motion, and is composed of gravel sands in a high energy multiphase flow.
How are dense flows classified?
Their classification is based on the concentration of solid material in the flow and the ration of fine to solid material
What are debris flows composed of and what is their behaviour dependant on?
They are a mixture of: mud,sand,soil,rock,air,water
Their behaviour is dependant on the makeup of their structure
What are the four mechanisms that cause debris flow, and how?
Moisture addition- adds weight and lubrication
Support removal (often by erosion)- undermines the stability of the system
Deforestation- loss of root structure holding materials together
Tectonic activity- cause increased instability, loosening material
What is rheology?
The study of the flow of matter
In grain flow models, what are the four acting forces?
Collision
Friction
Viscosity
Pore pressure
What is a non Newtonian fluid?
One that does not follow Newton’s law of viscosity, and changes viscosity over time
Describe sheer thinning fluids
Viscosity decreases as sheer stress decreases, meaning that deformation increases with shear forces. These stop flowing like a fluid and assume a solid position when the force is removed.
What is a shear thickening fluid?
Viscosity increases as shear stress increases, so the greater the force applied the more it behaves like a solid.
How does a thixotropic fluid differ from a rheopectic fluid?
Both receive constant pressure, however a thixotropic fluid has a decrease of viscosity over time whereas a rheopectic fluid has an increase
