| Author | Nguyen Huy Phuong |
| Call Number | AIT Thesis no. WM-00-07 |
| Subject(s) | Debris avalanches
|
| Note | A thesis submitted in partial fulfillment of the requirements
for the degree of Master of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | The debris flow is a flowage of mixture of all sizes of sediment. It is frequently observed
that debris flows, especially mudflows, consist of waves or successive surges. While it is
known that a number of large rocks gather at the surge front, which causes strong, destructive
power of debris flows, the mechanism of the wave or surge formation has not been
completely clarified. In this study, a mathematical model to describe the surge formation is
presented based on the idea that the debris flow surges are physically identical to the roll
waves observed in water flows.
Roll waves are commonly observed in sheet flows on comparatively steep slopes. The roll
waves are characterized by a series of waves each of which has a strongly discontinuous
surge front and the subsequent mildly-varied portion. The generation of roll waves has been
described by the linear stability analysis with the use of the long wave approximation and the
depth-averaged shallow water equations. According to the existing theory, however, the
characteristic wavenumber associated with the maximum growth rate of disturbance turned
out to be infinitely large; thus, infinitely small wavelengths should be dominant in waves. In
this study, a new theo1y with the use of non-depth-averaged flow equations is presented to
explain the generation of roll waves. The theory is, then, extended to apply to the fonnation
of debris flow surges with the use of the Newtonian fluid formulation.
In the analysis of roll waves in water, it is found that the critical Froude number beyond
which uniform flows destabilized to evolve into a series of waves takes a value between 1.2
and 2.4 dependently on the condition of bottom friction. It is also found that the uniform
flow is stabilized against the waves with wavenumbers larger than 1.0-5.0. The angular
frequency derived from the theo1y is found to agree well with experimental results.
In the analysis of debris flows, the critical Froude number is found to be 0-1.0, which is
considerably smaller than the case of water. Theory shows that the largest possible
wavenumber beyond which waves do not appear is 1.0-5.0. The relation between angular
frequency and wavenumber (dispersion relation) is found to be explained by the present
the01y reasonably well. This strongly suggests that the debris flow surges are generated due
to the same instability that causes roll waves in water. |
| Year | 2001 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Izumi, Norihiro |
| Examination Committee(s) | Gupta, Ashim Das ;Babel, Mukand Singh ;Sutat Weesakul |
| Scholarship Donor(s) | Swedish International Development Cooperation Agency |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 2001 |