Abstract
Effective design of mitigation measures against debris flow hazards remains a challenging geotechnical problem. At present, a pseudo-static approach is commonly used for the calculation of impact load acting on a rigid debris-resisting barrier. The impact load is normally calculated based on the maximum velocity observed in the transportation zone under free-field conditions without considering debris-barrier interaction. In reality, the impact load acting on a barrier varies with the change of debris momentum flux but this is seldom considered in barrier design. To provide a scientific basis for assessing debris momentum flux during impact, this paper presents results from a study of debris-barrier interaction using physical flume modelling. This study showed that, following the first stage of impact, the accumulated debris behind a barrier formed a stationary zone and caused the remaining debris to slow down in a run-up process. In the experiments, the peak debris momentum was 30 % lower compared to that observed under free-field conditions. A new momentum-based model was developed to take into account attenuation of momentum flux for predicting debris impact load on rigid barriers. The new rationalised model was assessed using data from the notable Yu Tung Road debris flow in Hong Kong. The assessment showed that the design bending moment at the base of the barrier wall could be reduced more than 30 % using the proposed model, compared with the current design approach. The adoption of the proposed model could offer a new opportunity for practitioners to optimise the design of rigid barriers.
Similar content being viewed by others
Abbreviations
- α :
-
Dynamic pressure coefficient
- β :
-
Empirical factor to account for the dynamic effect of flow impact
- ρ :
-
Debris density
- θ :
-
Channel slope angle
- θ d :
-
Deposition angle
- ϕ :
-
Internal friction angle
- δ :
-
Basal (interface) friction angle
- g :
-
Gravitational acceleration
- h :
-
Free-field debris thickness
- h d :
-
Debris run-up height
- h ret :
-
Design retaining height of debris
- m :
-
Mass of debris
- t :
-
Time
- v :
-
Debris velocity
- v p :
-
Peak debris velocity
- v :
-
Free-field debris velocity (no barrier)
- w :
-
Barrier width
- BM:
-
Bending moment per unit width of barrier
- E R :
-
Energy loss due to frictional resistance
- F :
-
Total force acting on a barrier
- F d :
-
Dynamic impact force
- Fr:
-
Froude number
- F ru :
-
Run-up impact force
- F s :
-
Static force due to lateral earth pressure of the deposited materials
- L :
-
Debris’ travel distance during the run-up process
- M :
-
Momentum flux
- N :
-
Weight of debris acting on slope surface
- R :
-
Frictional resistance between moving and stationary debris
- R m :
-
Momentum reduction factor due to debris-barrier interaction
- R ru :
-
Velocity reduction factor due to frictional resistance between moving and stationary debris and conversion from kinetic to potential energies during run-up
References
AECOM (2012). Detailed study of the 7 June 2008 landslides on the hillside above Yu Tung Road, Tung Chung. GEO Report No. 271, Geotechnical Engineering Office, Hong Kong, 124 p.
Armanini A (1997) On the dynamic impact of debris flows. In: Recent developments on debris flows, vol 64, Lecture notes in earth sciences. Springer, Berlin, pp 208–226
Armanini, A., Larcher, M. & Odorizzi, M. (2011) Dynamic impact of a debris flow against a vertical wall. Proceedings of the 5th International Conference on Debris-Flow Hazards Mitigations: Mechanics, Prediction, and Assessment, Padua, Italy, 14–17 June 2011, pp. 1041–1049
Ashwood, W. (2014) Numerical model for the prediction of total dynamic landslide forces on flexible barriers. Master’s Thesis of Applied Science, Geological Engineering, The University of British Columbia, 162 p
ASI (2013) ONR 24801 protection works for torrent control—actions on structures (draft). Austrian Standard Institute, Austria, p 25
Choi CE, Ng CWW, Song D, Kwan JSH, Shiu HYK, Ho KKS, Koo RCH (2014) Flume investigation of landslide debris-resisting baffles. Can Geotech J 51(5):540–553
Fitze, P. (2010) Runout analysis of rapid, flow-like landslides. Master’s Thesis, Hochschule für Technik Rapperswil, 101 p
Hong Y, Wang JP, Li DQ, Cao ZJ, Ng CWW, Cui P (2015) Statistical and probabilistic analyses of impact pressure and discharge of debris flow from 139 events during 1961 and 2000 at Jiangjia Ravine, China. Eng Geol 187:122–134
Hubl, J., Suda, J., Proske, D., Kaitna, R., Scheidl, C. (2009) Debris flow impact estimation. Proceedings of the 11th International Symposium on Water Management and Hydraulic Engineering, Ohrid, Macedonia, 1–5 September 2009, pp 137–148
Hungr O (1995) A model for the runout analysis of rapid flow slides, debris flows and avalanches. Can Geotech J 32(4):610–623
Hungr O (2008) Simplified models of spreading flow of dry granular material. Can Geotech J 45(8):1156–1168
Iverson R, Logan M, LaHusen R, Berti M (2010) The perfect debris flow? Aggregated results from 28 large scale experiments. J Geophys Res 115:F03005
Kwan, J.S.H. (2012). Supplementary technical guidance on design of rigid debris-resisting barriers. GEO Report No. 270, Geotechnical Engineering Office, Hong Kong, 88 p.
Kwan, J.S.H. & Koo, R.C.H. (2015). Enhanced technical guidelines for design of debris-resisting barriers. Technical Note No. TN 2/2015, Geotechnical Engineering Office, Hong Kong, 33 p.
Kwan JSH, Koo RCH, Ng CWW (2015) Landslide mobility analysis for design of multiple debris-resisting barriers. Can Geotech J 52(9):1345–1359
Kwan JSH, Sun HW (2006) An improved landslide mobility model. Can Geotech J 43(5):531–539
Law, P.H. (2014) Computational study of granular debris flow impact on rigid barriers and baffles. PhD thesis, The Hong Kong University of Science and Technology, 252 p
MLR (2006). Specification of geological investigation for debris flow stabilization. DZ/T 0220–2006, National Land Resources Department, China, 32 p (in Chinese).
NILIM (2007). Manual of technical standard for establishing Sabo master plan for debris flow and driftwood. Technical Note of NILIM No. 364, Natural Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure and Transport, Japan, 18 p. (in Japanese)
Peng C, Chao Z, Yu L (2015) Experimental analysis on the impact force of viscous debris flow. Earth Surf Process Landf 40(12):1644–1655
Proske D, Suda J, Hübl J (2011) Debris flow impact estimation for breakers. Georisk 5(no. 2):143–155
Tiberghien, D., Laigle, D., Naaim, M., Thibert, E. & Ousset, F. (2007) Experimental investigations of interaction between mudflow and an obstacle. Proceedings of the 4th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment, Chengdu, China, 10–13 September 2007, pp 281–292
VanDine DF (1996) Debris flow control structures for forest engineering. Ministry of Forests, British Columbia, p 68
Wendeler, C. (2008) Murgangrückhalt in Wildbächen – Grundlagen zu Planung und Berechnung von flexible Barrieren. PhD thesis, ETH Zürich, Switzerland (in German)
White DJ, Take WA, Bolton MD (2003) Soil deformation measurement using particle image velocimetry (PIV) and photogrammetry. Geotechnique 53(7):619–631
Acknowledgments
This paper is published with the permission of the Head of the Geotechnical Engineering Office and the Director of Civil Engineering and Development, Hong Kong SAR Government. The work described in this paper was supported by a grant from the Research Grants Council of the Hong Kong SAR (HKUST 06/CRF/12R and T22-603/15N). The authors would also like to acknowledge the support of the HKUST Jockey Club Institute of Advanced Study.
Author information
Authors and Affiliations
Corresponding author
Additional information
An erratum to this article is available at http://dx.doi.org/10.1007/s10346-016-0730-6.
Rights and permissions
About this article
Cite this article
Koo, R.C.H., Kwan, J.S.H., Ng, C.W.W. et al. Velocity attenuation of debris flows and a new momentum-based load model for rigid barriers. Landslides 14, 617–629 (2017). https://doi.org/10.1007/s10346-016-0715-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10346-016-0715-5