Discrete-element investigation of influence of granular debris flow baffles on rigid barrier impact

2016 ◽  
Vol 53 (1) ◽  
pp. 179-185 ◽  
Author(s):  
Raymond Pak Hei Law ◽  
Clarence Edward Choi ◽  
Charles Wang Wai Ng
Keyword(s):  
Debris Flow ◽  
Discrete Element ◽  
Row Spacing ◽  
Dynamic Force ◽  
Flow Front ◽  
Flume Experiments ◽  
Rigid Barrier ◽  
Flow Energy ◽  
Slit Size ◽  
Peak Impact Force

Granular debris flow baffles are commonly installed in front of rigid barriers to dissipate flow energy and reduce the required barrier impact capacity. Despite the engineering value of baffles, their influence on rigid barrier impact is still not well understood. A previously calibrated discrete element method (DEM) model using a series of flume experiments was adopted to study the effectiveness of installing baffles in front of a rigid barrier. Froude scaling was used to characterize the flow front. Different baffle configurations were examined, namely number of rows, spacing between successive rows (L), and baffle height. Results reveal an optimum row spacing of L/D = 3 (D is the slit size). Row spacing less than L/D = 3 leads to increased peak dynamic force from overflow impacting the barrier, whereas row spacing greater than L/D = 3 results in increased peak dynamic force from the granular debris flow front. Increasing spacing greater than L/D = 3 allows the dispersion of debris between rows and decreases the effectiveness of the second row. Adopting baffle heights greater than 1.5 times the approach flow depth (h) reveals little influence on the peak impact force induced on the barrier.

Computational investigation of baffle configuration on impedance of channelized debris flow

2015 ◽  
Vol 52 (2) ◽  
pp. 182-197 ◽  
Author(s):  
C.E. Choi ◽  
C.W.W. Ng ◽  
R.P.H. Law ◽  
D. Song ◽  
J.S.H. Kwan ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Debris Flow ◽  
Interaction Mechanism ◽  
Back Analysis ◽  
Flume Experiments ◽  
Flow Energy ◽  
Mountainous Regions ◽  
Impact Forces ◽  
Flow Attenuation ◽  
Array Of Baffles

Channelized debris flows surge downslope in mountainous regions and have large impact forces. Arrays of debris flow baffles are frequently positioned in front of rigid barriers to engage torrents and attenuate flow energy. They are regularly designed on empirical and prescriptive basis because their interaction mechanism is not well understood. Numerical back-analysis of flume experiments using the discrete element method (DEM) is conducted to provide insight on flow interaction with an array of baffles. Varying configurations of baffle height, a second staggered row, and spacing between successive rows are examined. Upstream and downstream kinematics are monitored to capture and compare the Froude number, kinetic energy, and discharge resulting from each baffle configuration. Results from this study reveal that the height of baffles can be categorized relative to the initial approach flow depth (h), namely tall baffles (1.5h) and short baffles (0.75h). Tall baffles are characterized by the development of upstream subcritical flow conditions, whereas short baffles exhibit supercritical upstream conditions. Furthermore, tall baffles facilitate the suppression of overflow, and short baffles lead to excessive overflow that is supercritical in nature. Less flow attenuation occurs as the distance increases both upstream and downstream from each array of baffles. A second staggered row of short staggered baffles is ineffective in reducing debris kinetic energy, whereas tall baffles should be positioned as close as possible.

Debris flow impact on a flexible barrier: laboratory flume experiments and force-based mechanical model validation

2021 ◽  
Vol 106 (1) ◽  
pp. 735-756
Author(s):  
R. Brighenti ◽  
L. Spaggiari ◽  
A. Segalini ◽  
R. Savi ◽  
G. Capparelli
Keyword(s):  
Debris Flow ◽  
Model Validation ◽  
Mechanical Model ◽  
Flume Experiments ◽  
Flexible Barrier ◽  
Laboratory Flume

scholarly journals The Development of a 1-D Integrated Hydro-Mechanical Model Based on Flume Tests to Unravel Different Hydrological Triggering Processes of Debris Flows

Water ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 950 ◽  
Author(s):  
Theo van Asch ◽  
Bin Yu ◽  
Wei Hu
Keyword(s):  
Debris Flow ◽  
Mechanical Model ◽  
Debris Flows ◽  
Overland Flow ◽  
Slope Angle ◽  
Great Influence ◽  
Flume Experiments ◽  
Triggering Mechanisms ◽  
Bed Material ◽  
Triggering Process

Many studies which try to analyze conditions for debris flow development ignore the type of initiation. Therefore, this paper deals with the following questions: What type of hydro-mechanical triggering mechanisms for debris flows can we distinguish in upstream channels of debris flow prone gullies? Which are the main parameters controlling the type and temporal sequence of these triggering processes, and what is their influence on the meteorological thresholds for debris flow initiation? A series of laboratory experiments were carried out in a flume 8 m long and with a width of 0.3 m to detect the conditions for different types of triggering mechanisms. The flume experiments show a sequence of hydrological processes triggering debris flows, namely erosion and transport by intensive overland flow and by infiltrating water causing failure of channel bed material. On the basis of these experiments, an integrated hydro-mechanical model was developed, which describes Hortonian and saturation overland flow, maximum sediment transport, through flow and failure of bed material. The model was calibrated and validated using process indicator values measured during the experiments in the flume. Virtual model simulations carried out in a schematic hypothetical source area of a catchment show that slope angle and hydraulic conductivity of the bed material determine the type and sequence of these triggering processes. It was also clearly demonstrated that the type of hydrological triggering process and the influencing geometrical and hydro-mechanical parameters may have a great influence on rainfall intensity-duration threshold curves for the start of debris flows.

scholarly journals Effects of dynamic fragmentation on the impact force exerted on rigid barrier: centrifuge modelling

2019 ◽  
Vol 56 (9) ◽  
pp. 1215-1224 ◽  
Author(s):  
C.W.W. Ng ◽  
C.E. Choi ◽  
D.K.H. Cheung ◽  
Y. Cui
Keyword(s):  
Volume Fraction ◽  
Impact Force ◽  
Inertial Particles ◽  
Size Segregation ◽  
Centrifuge Modelling ◽  
Rigid Barrier ◽  
Flow Energy ◽  
Dynamic Fragmentation ◽  
Large Particles ◽  
The Impact

Bi-dispersity is a prerequisite for grain-size segregation, which transports the largest particles to the flow front. These large and inertial particles can fragment upon impacting a barrier. The amount of fragmentation during impact strongly influences the force exerted on a rigid barrier. Centrifuge modelling was adopted to replicate the stresses for studying the effects of bi-dispersity in a granular assembly and dynamic fragmentation on the impact force exerted on a model rigid barrier. To study the effects of bi-dispersity, the ratio between the diameters of small and large particles (δs/δl), characterizing the particle-size distribution (PSD), was varied as 0.08, 0.26, and 0.56. The volume fraction of the large particles was kept constant. A δs/δl tending towards unity characterizes inertial flow that exerts sharp impulses, and a diminishing δs/δl characterizes the progressive attenuation of these sharp impulses by the small particles. Flows dominated by grain-contact stresses (δs/δl < 0.26), as characterized by the Savage number, are effective at attenuating dispersive stresses of the large particles, which are responsible for reducing dynamic fragmentation. By contrast, flows dominated by grain-inertial stresses (δs/δl > 0.26) exhibit up to 66% more impulses and 4.3 times more fragmentation. Dynamic fragmentation of bi-disperse flows impacting a rigid barrier can dissipate about 30% of the total flow energy.

scholarly journals A theoretical model for the initiation of debris flow in unconsolidated soil under hydrodynamic conditions

2014 ◽  
Vol 2 (6) ◽  
pp. 4487-4524 ◽  
Author(s):  
C.-X. Guo ◽  
J.-W. Zhou ◽  
P. Cui ◽  
M.-H. Hao ◽  
F.-G. Xu
Keyword(s):  
Theoretical Model ◽  
Debris Flow ◽  
Surface Runoff ◽  
Slope Failure ◽  
Fine Particles ◽  
Field Investigation ◽  
Hydrodynamic Theory ◽  
Mechanism Analysis ◽  
Flume Experiments ◽  
Initiation Mechanism

Abstract. Debris flow is one of the catastrophic disasters in an earthquake-stricken area, and remains to be studied in depth. It is imperative to obtain an initiation mechanism and model of the debris flow, especially from unconsolidated soil. With flume experiments and field investigation on the Wenjiagou Gully debris flow induced from unconsolidated soil, it can be found that surface runoff can support the shear force along the slope and lead to soil strength decreasing, with fine particles migrating and forming a local relatively impermeable face. The surface runoff effect is the primary factor for accelerating the unconsolidated slope failure and initiating debris flow. Thus, a new theoretical model for the initiation of debris flow in unconsolidated soil was established by incorporating hydrodynamic theory and soil mechanics. This model was validated by a laboratory test and proved to be better suited for unconsolidated soil failure analysis. In addition, the mechanism analysis and the established model can provide a new direction and deeper understanding of debris flow initiation with unconsolidated soil.

Flume investigation of cylindrical baffles for dissipation of debris flow energy

2021 ◽  
Author(s):  
Chan-Young Yune ◽  
Beom-Jun Kim
Keyword(s):  
Energy Dissipation ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Flow Characteristics ◽  
Digital Camera ◽  
Major Effect ◽  
Small Scale ◽  
Design Guideline ◽  
Flow Energy

&lt;p&gt;A debris flow with a high speed along valleys has been reported to cause serious damages to urban area or infrastructure. To prevent debris flow disaster, countermeasures for flow-impeding structures are installed on the flow path of debris flows. Recently, an installation of cylindrical baffles which are open-type countermeasures has increased because of a low construction cost, filtering out rocks, and an increased hydraulic continuity. However, a comprehensive design guideline for specification and arrangement on cylindrical baffles has not yet been suggested. Moreover, the design of baffle installation is mainly based on empirical approaches as the influence of baffle array on debris mobility is not well understood. In this study, to investigate the effect of cylindrical baffles on the flow characteristics of debris flow, a series of small-scale flume tests were performed according to the varying baffle height and row numbers of installed baffles. High-speed cameras and digital camera to record the flow interaction with baffles were installed at the top and side of the channel. To reproduce the viscosity of debris flows caused by fine-grained soil in the flume, glycerin was mixed with debris materials (sand and gravel). After the test, the velocity and energy dissipation according to various baffle arrays were estimated. Test results showed that the installation of baffles reduced the frontal velocity of debris flows. Furthermore, taller baffles also increased the effect of the energy dissipation in debris flows, but additional rows of the baffle did not have a major effect on the energy dissipation. Thus, increasing the height of baffle led to an increased efficiency of energy dissipation of debris flows.&lt;/p&gt;

Spatial-temporal distribution of debris flow impact pressure on rigid barrier

2019 ◽  
Vol 16 (4) ◽  
pp. 793-805 ◽  
Author(s):  
Dao-chuan Liu ◽  
Yong You ◽  
Jin-feng Liu ◽  
Yong Li ◽  
Guang-ze Zhang ◽  
...  
Keyword(s):  
Debris Flow ◽  
Temporal Distribution ◽  
Impact Pressure ◽  
Rigid Barrier
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