Abstract
This paper proposes a method for improving the design of rockfall protection fences and accounting for the variability of loading cases. It is based on a probabilistic reliability analysis and can combine loading cases from rockfall propagation simulations with numerical simulations of the structure response to the block impact. The advantage of such a reliability-based approach is that statistically relevant results can be obtained concerning the fence’s efficiency in stopping the block with a limited number of simulations. This method was employed in a study case, involving a low-energy tree-supported fence placed on a forested slope. The trajectory simulations were conducted using Rockyfor3D and the fence was modelled using a three-dimensional discrete element method model. For demonstration purposes, two parameters were considered: block velocity and the block’s angle of incidence before impact. The probability of the fence stopping the block was evaluated accounting for the variability of these two parameters separately and together, either considering these variables as non-correlated, or as correlated. The value of this approach is demonstrated in terms of computation cost. In addition, the results revealed the importance of accounting for both these parameters in designing the structure as well as in estimating the residual hazard downslope from the protective structure.
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Abbreviations
- Cv i :
-
Coefficient of variation of random variable X i
- E c, max :
-
Estimated maximum block impact energy
- F slip :
-
Cable clips sliding force
- G :
-
Performance function, associated with the limit state G = 0
- \(\tilde{G}\) :
-
Approximation of G
- L i :
-
Lagrangian polynomial
- m rock :
-
Block mass
- P f :
-
Fence failure probability, equals Prob(G > 0)
- p y :
-
Probability density function of \(\mathbf{Y}\)
- T :
-
Gaussian standardization function
- V r :
-
Block translational velocity at impact
- V r, max :
-
Estimated maximum block translational velocity at impact
- V z, out :
-
Norm of the block translational velocity after contact with the fence
- V z, in :
-
Norm of the block translational velocity before contact with the fence
- \(\mathbf{X}\) :
-
Vectorial Gaussian standard variable, related to \(\mathbf{Y}\) such as \(\mathbf{Y}\) = T (\(\mathbf{X}\))
- X i :
-
Components of Gaussian standard random variable \(\mathbf{X}\)
- x i :
-
Realization (chosen value) of component X i of vector \(\mathbf{X}\)
- \(\mathbf{Y}\) :
-
Vectorial random variable associated with the loading parameters
- Y i :
-
Random variables
- y i :
-
Uncertain parameters associated with the block properties and its trajectory
- \(\mathbf{Z}\) :
-
Vectorial random variable associated with the fence reponse
- α r :
-
Impact angle
- \(\lambda_{\epsilon}\) :
-
Reduction factor for the strain at rupture of double-twisted wires vs. single wire
- λ k :
-
Reduction factor for the stiffness of double-twisted wires vs. single wire
- μ i :
-
Mean value of the random variable Y i
- \(\rho_{Y_i Y_j}\) :
-
Correlation coefficient between the random variables Y i and Y j
- \(\sigma_{Y_i}\) :
-
Standard deviation of the random variable Y i
- ω r :
-
Norm of the block rotational velocity
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Acknowledgments
This research was conducted within the framework of the Natural Hazards and Vulnerability of Structures (VOR) research network. This network is funded by the French Ministry of Research and joins different laboratories in the Rhônes-Alpes region.
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Appendices
Appendix 1: Roots of Hermite Polynomials
The values of x i , corresponding to the roots of Nth-degree Hermite polynomials, denoted H N , should be computed numerically or found in tables (Press et al. 1994). For instance, Table 6 provides points x i for N = 3, 4, 5, where H 3(x) = x 3 − 3x, H 4(x) = x 4 − 6x 2 + 3, H 5(x) = x 5 − 10x 2 + 15x. Such values are classically deduced from quadrature formulas (see also Baroth et al. 2007).
Appendix 2: Gaussian Standardization of Two Correlated Log-Normal Random Variables
Let \(\mathbf{Y} =(Y_1, Y_2)\) be a 2D lognormal random variable with given mean μ Y = (μ Y_1, μ Y_2) and standard deviation σ Y = (σ Y_1, σ Y_2) and coefficient of correlation ρ Y_1 Y_2. In this case, the Gaussian standardization of \(\mathbf{Y}\) is written (Baroth et al. 2006):
with:
where \({\rm Cv}_{Y_i}=\frac{\sigma_{Y_i}}{\mu_{Y_i}}, i=1,2\) are the coefficients of variation of Y 1 and Y 2.
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Bourrier, F., Lambert, S. & Baroth, J. A Reliability-Based Approach for the Design of Rockfall Protection Fences. Rock Mech Rock Eng 48, 247–259 (2015). https://doi.org/10.1007/s00603-013-0540-2
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DOI: https://doi.org/10.1007/s00603-013-0540-2