Abstract
Increasing rockfall activity in the European Alps raises the need for designing systems protecting Alpine infrastructure. So far, layout of rockfall protection layers was carried out in a quasi-deterministic manner. This paper is concerned with the extension towards a semi-probabilistic design of the thickness of gravel layers covering steel pipelines. Quantities with little scatter such as geometric dimensions and elasto-plastic material constants of steel and gravel are treated as deterministic. By contrast, strongly scattering quantities such as the indentation resistance of gravel, R, and rockfall characteristics including boulder mass m and height of fall h f are considered as probabilistic variables. While 5 and 95% quantiles of R (obtained from statistical evaluation of a series of real-scale impact tests onto gravel) represent probability-based interval bounds for designing the gravel layer thickness, the lack of statistical data from rare rockfall events motivates to follow the philosophy of EUROCODE 1, i.e., to define a design rockfall: m = 10,500 kg and h f = 80 m. Based on this input, a standard burying depth of steel pipelines (H = 1 m) is assessed, by comparing estimates of (i) boulder penetration depth into gravel and of (ii) the maximum impact force, respectively, with corresponding quantities related to a suitable real-scale impact test. This comparison shows the need to increase the height of the gravel overburden. In order to prove that a gravel layer thickness H = 2.7 m is sufficient to prevent the pipeline from inelastic deformations when the structure is hit by the design rockfall, several structural analyses with different values for R are carried out. This is done by means of a validated Finite Element model. As a by-product of the proposed semi-probabilistic design procedure, three different deformation modes of the hit pipeline are identified.
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Abbreviations
- a :
-
acceleration of boulder
- d :
-
outer pipe diameter
- d c :
-
characteristic size of boulder
- g :
-
gravitational acceleration
- E :
-
Young’s modulus of steel
- E imp :
-
impact energy
- F :
-
maximum impact force
- F D :
-
F related to the design rockfall
- F exp :
-
F related to a real-scale impact test
- H :
-
height of gravel overburden
- h f :
-
height of fall
- I :
-
dimensionless impact function
- I D :
-
I related to the design rockfall
- m :
-
boulder mass
- n :
-
statistical sample size
- R :
-
indentation resistance of gravel
- R 5% :
-
5% quantile of R
- R 95% :
-
95% quantile of R
- s :
-
co-ordinate following the inner surface of the pipe
- t :
-
time
- t p :
-
pipe thickness
- V :
-
boulder volume
- v 0 :
-
impact velocity
- w :
-
boulder penetration depth at maximum impact force
- w D :
-
w related to the design rockfall
- X :
-
boulder penetration depth after completed impact
- X D :
-
X related to the design rockfall
- X exp :
-
X measured in a real-scale impact test
- Δt :
-
impact duration
- ν:
-
Poisson’s ratio of steel
- ρ b :
-
mass density of boulder
- ρ g :
-
mass density of gravel
- σ vM :
-
equivalent von Mises stress
- σ y :
-
uniaxial yield stress of steel
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Pichler, B., Hellmich, C., Eberhardsteiner, J. et al. Semi-probabilistic design of rockfall protection layers. Comput Mech 42, 327–336 (2008). https://doi.org/10.1007/s00466-007-0207-5
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DOI: https://doi.org/10.1007/s00466-007-0207-5