scholarly journals Effects of coarse grain size distribution and fine particle content on pore fluid pressure and shear behavior in experimental debris flows

2016 ◽  
Vol 121 (2) ◽  
pp. 415-441 ◽  
Author(s):  
Roland Kaitna ◽  
Marisa C. Palucis ◽  
Bereket Yohannes ◽  
Kimberly M. Hill ◽  
William E. Dietrich
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Debris Flows ◽  
Fine Particle ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Coarse Grain ◽  
Pore Fluid Pressure ◽  
Particle Content

scholarly journals Effect of Density and Total Weight on Flow Depth, Velocity, and Stresses in Loess Debris Flows

Water ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1784 ◽  
Author(s):  
Heping Shu ◽  
Jinzhu Ma ◽  
Haichao Yu ◽  
Marcel Hürlimann ◽  
Peng Zhang ◽  
...  
Keyword(s):  
Normal Stress ◽  
Debris Flows ◽  
High Speed ◽  
Goodness Of Fit ◽  
Flow Behavior ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Flow Depth ◽  
Pore Fluid Pressure ◽  
Mixture Density

Debris flows that involve loess material produce important damage around the world. However, the kinematics of such processes are poorly understood. To better understand these kinematics, we used a flume to measure the kinematics of debris flows with different mixture densities and weights. We used sensors to measure pore fluid pressure and total normal stress. We measured flow patterns, velocities, and depths using a high-speed camera and laser range finder to identify the temporal evolution of the flow behavior and the corresponding peaks. We constructed fitting functions for the relationships between the maximum values of the experimental parameters. The hydrographs of the debris flows could be divided into four phases: increase to a first minor peak, a subsequent smooth increase to a second peak, fluctuation until a third major peak, and a final continuous decrease. The flow depth, velocity, total normal stress, and pore fluid pressure were strongly related to the mixture density and total mixture weight. We defined the corresponding relationships between the flow parameters and mixture kinematics. Linear and exponential relationships described the maximum flow depth and the mixture weight and density, respectively. The flow velocity was linearly related to the weight and density. The pore fluid pressure and total normal stress were linearly related to the weight, but logarithmically related to the density. The regression goodness of fit for all functions was >0.93. Therefore, these functions are accurate and could be used to predict the consequences of loess debris flows. Our results provide an improved understanding of the effects of mixture density and weight on the kinematics of debris flows in loess areas, and can help landscape managers prevent and design improved engineering solutions.

Laboratory studies of subaqueous debris flows by measurements of pore-fluid pressure and total stress

2004 ◽  
Vol 213 (1-4) ◽  
pp. 403-414 ◽  
Author(s):  
Trygve Ilstad ◽  
Jeffrey G. Marr ◽  
Anders Elverhøi ◽  
Carl B. Harbitz
Keyword(s):  
Debris Flows ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Laboratory Studies ◽  
Total Stress ◽  
Pore Fluid Pressure

scholarly journals Runout Characteristics and Grain Size Distribution of Large-scale Debris Flows Triggered by Deep Catastrophic Landslides

2012 ◽  
Vol 5 (1) ◽  
pp. 16-26 ◽  
Author(s):  
Yuki NISHIGUCHI ◽  
Taro UCHIDA ◽  
Nagazumi TAKEZAWA ◽  
Tadanori ISHIZUKA ◽  
Takahisa MIZUYAMA
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Debris Flows ◽  
Large Scale

Laminar-turbulent transition in debris flow: measurement of basal pore fluid pressure in an open channel flow experiment

2020 ◽  
Author(s):  
Yuichi Sakai ◽  
Norifumi Hotta
Keyword(s):  
Reynolds Number ◽  
Debris Flow ◽  
Turbulent Flow ◽  
Debris Flows ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Transitional Flow ◽  
Flow Depth ◽  
Pore Fluid Pressure ◽  
Relative Flow

<p>The fluidity of a debris flow varies by grain size. Flows containing principally coarse grains are considered to be laminar and those featuring largely incohesive fine grains turbulent. The transition from laminar to turbulent flow depends on the ratio of flow depth to grain size (i.e., the relative flow depth). Debris flows with relative flow depths of approximately 10 are entirely laminar; those with relative flow depths over approximately 20 exhibit transitional flow behavior from entirely laminar to partially turbulent. This transitional flow has been investigated in the laboratory using the resistance law and the vertical distribution of streamwise velocity. The flow exhibits a two-layer structure; the lower layer remains laminar but the upper layer becomes turbulent. However, transition modeling remains incomplete given the lack of data on the internal stresses associated with transitional flow. Here, we studied the laminar-turbulent transitions of debris flows by measuring basal pore fluid pressures using flume tests.</p><p>We flowed saturated monodisperse granular materials over an open-channel rigid bed; we used sediment particles of diameters 2.9, 2.2, 1.3, 0.8, 0.5, and 0.2 mm. When the debris flow attained the steady state, the flow depth and basal pore fluid pressure were measured using an ultrasonic sensor and pressure gages respectively, and the basal total normal stress estimated using the bulk density of the debris flow assessed at the downstream end.</p><p>The relative flow depths ranged from 5 to 130. Comparisons among the measured pore fluid pressures and the hydrostatic and total normal stresses indicated that a pore fluid pressure of 0.2 mm differed greatly from the hydrostatic pressure, equaling, in fact, the total normal stress, and indicating fully turbulent flow. In contrast, pore fluid pressures of 2.9, 2.2, and 1.3 mm were slightly higher than the hydrostatic pressures, indicating that the Reynolds stresses of the pore fluid due to the strong shears imparted by the sediment particles were in play; flow was entirely laminar. Pore fluid pressures of 0.8 and 0.5 mm were intermediate between the hydrostatic and total normal stresses, indicating the transition from fully laminar to partially turbulent flow.</p><p>By analogy with the Reynolds number for Newtonian fluid, we investigated the transition based on the non-dimensional number for debris flows (thus, the ratios of inertial to dynamic stresses caused by interparticle collisions and the Reynolds stresses of the debris flow pore fluid). This identified the critical Reynolds number in terms of transition commencement. We describe the transitional flow behavior of monodisperse granular debris flows using a two-layered model in which the position of the between-layer interface is estimated based on that critical Reynolds number.</p>

Downstream evolution of grain size in extremely mobile post-earthquake debris flows, China

2021 ◽  
Author(s):  
Erin L. Harvey ◽  
Tristram C. Hales ◽  
Daniel E. J. Hobley ◽  
Xuanmei Fan ◽  
Jie Liu ◽  
...  
Keyword(s):  
Grain Size ◽  
Debris Flow ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Debris Flows ◽  
Fine Fraction ◽  
Excess Pore Pressure ◽  
Extreme Rainfall Event ◽  
2008 Wenchuan Earthquake ◽  
Grain Sizes

<p>Large, catchment transitioning debris flows are an important mechanism for transporting sediment from hillslopes into higher order channels. Extremely large flows can exceed volumes of 10<sup>9</sup> m<sup>3</sup>, however even flows with volumes of  ~10<sup>3</sup> m<sup>3</sup> can lead to fatalities and extensive damage. Few processes transport a wider range of grain sizes than debris flows, which can transport grains from clays to 10 m boulders. While the structure of debris flows can often be inferred by their deposits, the range of grain sizes presents a challenge for their interpretation. Debris flow grain size distributions can be used to constrain debris flow runout due to their effect on excess pore pressure dissipation. Currently, there is limited data available for the entire grain size distribution of debris flow deposits in the field.</p><p>We constrained the entire grain size distribution for two extremely large (>1 km in length) post-earthquake debris flows in Sichuan Province, China. These debris flows were triggered in August 2019 after an extreme rainfall event occurred close to the epicentre of the 2008 Wenchuan earthquake. We sampled the debris flows in November 2019 at intervals of 200 m and 500 m, respectively. At each site, we used a combination of field and laboratory sieving to obtain the coarse and fine fraction for both the surface and subsurface. We dug 1 m x 1 m x 0.5 m pits, excavating each layer at 10 cm depth increments. We sieved these increments into five size fractions in the field, including < 1 cm. We sieved 1 kg of the <1 cm fraction in the laboratory to estimate the distribution of the finest grains. The coarse surface fraction was then independently constrained using photogrammetry. Preliminary results for one debris flow show that the distribution of fine grains (~<4 mm) is consistent both laterally and vertically across the runout. This suggests that the processes occurring vertically and laterally during deposition result in the consistent distribution of fines.</p>

In-situ measurements of stress anisotropy in natural debris flows 

2021 ◽  
Author(s):  
Georg Nagl ◽  
Johannes Hübl ◽  
Roland Kaitna
Keyword(s):  
Debris Flows ◽  
Stress Ratio ◽  
Vertical Wall ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Gravitational Mass ◽  
Analytical Models ◽  
Pore Fluid Pressure ◽  
Stress Anisotropy ◽  
Mass Flows

<p>Stress anisotropy affects the motion of gravitational mass flows, including debris flows, rock and snow avalanches. Though widely used in analytical models and numerical simulation tools, direct measurements of stress anisotropy in debris flows are not yet available. The present study aims to investigate the ratio of longitudinal to normal pressure exerted by two natural debris flows impacting a monitoring structure in the Gadria creek, IT. The fin-shaped structure in the middle of the channel is equipped with a force plate upstream of the barrier and load cells on the vertical wall of the barrier, continuously recording forces in flow and bed-normal direction. Additionally, the flow height and basal pore fluid pressure were measured. Here we present data from surges of two debris-flow events with peak flow heights of 2.5 m and velocities up to 4 m/s. The ratio of pore fluid pressure to normal stress (often termed liquefaction ratio) reached values up to 0.8. We find an anisotropic stress state during most of the flow event, with stress ratios ranging between 0.1 and 3.5. Video recordings reveal complex deposition and re-mobilization patterns in front of the barrier during surges and highlight the unsteady nature of debris flows. We find a correlation of the stress ratio with flow depth. There is a weak correlation between stress ratio and liquefaction ratio during the falling limb of the surge hydrographs.  Our monitoring data confirm the assumption of stress anisotropy in natural debris flows and support the earth-pressure concept used for gravitational mass flows.</p>

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