英文摘要 |
The debris-flow dam is caused by debris flow, which carries a great amount of
sediment into the main river. It is the most serious secondary disasters caused by
debris flow. After the Ms 8.0 Wenchuan Earthquake, many debris flows have occurred
in the quake-stricken area and more than 10 dams formed and blocked the mainstream
rivers, resulted in great disasters and greatly influenced the reconstruction and
economic development of the area.
Field surveys of three typical cases indicate that the velocity (vd), discharge (QB),
density ( d ), yield stress ( d ) and total volume (Vd) of debris flow, and flow velocity
(vw) and discharge (QM) of main river, are the major factors controlling the dam
formation. In the following, we conducted 42 groups of experiments simulating the
dam formation by debris flow and 6 groups of experiments measuring the yield stress.
The influence of each single factor on debris-flow dam formation and typical
phenomenon of deposit in confluence are explored. In the finally, the formulas of
morphological parameters of the debris-flow dam are established and determination
conditions are proposed. In this paper, it was found that:
1. We analyze the influence of each single factor on debris-flow dam formation
Ⅰ)the velocity and average discharge of debirs flow have a positive effect on
the debris-flow dam formation. But the angle of dam decreases with the increase in
debris-flow velocity.
Ⅱ)because the influence of yield stress, which changes in diffierent way , on the
debris-flow dam isn’t consistent, the yield stress dosen’t used to be only parameter for
the dam-formation measurement and the influence of maxium-size particles in
composition can not be ignored.
Ⅲ)the total volume of debris flow has a positive impact on morphological
parameters including length and height of dam. But when the total volume reaches a
certain level, this influence is not significant.
Ⅳ)the ratio of debris flow in tributary to water in main river characterize their
interactions. The more ratios lead to the more prone to block the main river.
2. The changes of surface resistance, are caused by water in the main river, are so
important. By the way of energy and dimensional analysis, combining with the data of
the 20 experiments, the formula of debris-flow acceleration force (F阻) by water is
established.
3. Using energy analysis, the law of conservation of momentum and the
information of indoor experiments, the formulas of maximum impact height ( I h ) and
maximum wallop( I max F( )) are established.
4. The formulas of the mixing density ( (d w) ) of debris flow and yield stress
( c d ) are established.
5. The formulas of length of debris-flow dam are established. And it is found that
the formula has a higher accuracy to verify data of 40 experiments.
6. Debris-flow dam height depends on the processes of deposition, i.e., the
deposition en masse, or deposition by multi-surge accumulation. The formulas of
debris-flow dam height are established and verified by information of 40 experiments.
7. It is proposed that three determination conditions whether the debris-flow dam
form. |
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