Investigation of Parameter Uncertainties Inherent to the Geotechnical Design of Bank Revetments at Inland Waterways

Abstract

This paper describes the effects of uncertainty inherent to the choice of hydraulic load and soil parameters on the geotechnical revetment design. As for the practitioner, the effect of uncertainties on the required armour layer thickness is studied. Uncertainties inherent to revetment design mainly result from the load and resistance parameters employed in the design. At present, design loads are obtained from empirical equations and worst-case 'design vessel passages'. Characteristic soil parameters are defined on the basis of a limited number of field and laboratory tests. Thus, uncertainties arise with regard to the choice of characteristic values. In order to investigate the effects of parameter uncertainty on the revetment design, distributions and correlations of loads are assessed using vessel passages observed in the field. In ensuing uncertainty analyses it is found that at present available data does not allow approximating loads by means of probability functions, whereas for the soil parameters the results indicate that the minima of the soil parameters govern the design. However, it is also found that when considering more than one soil parameter as random variable, a less conservative design can be achieved as with the individual minima. As a conclusion, recommendations regarding parameter choice and design procedure are provided.

Assessment of maintenance efforts and probabilities of failure at German inland waterways to advance the design of bank revetments

“…The majority of damages at riprap embankment is observed along the shore close to still water level, e. g., Sorgatz (2021). The maintenance of riprap revetments commonly encompasses the (re-)placement of armor stones to fix minor to moderate discontinuities.…”

“…It is assumed that the Ultimate Limit State (ULS) is only reached when the filter layer or soil is exposed locally. This condition is avoided by (re-)placing armor stones in time (PIANC, 1987;Oumeraci et al, 1999;Sorgatz, 2021). The main advantage of this methodology is that a complete loss of stability (slope failure) does not have to be considered.…”

“…a) Extrapolated data, the measurement location DEK(S)-1 was located at km 81.6, whereas the elicited maintenance measures refer to km 84.0-89.0. For the probabilistic analyses the following distributions and correlations are employed: The analyses of various measurements at different canals by Sorgatz (2021) indicates that Hstern is lognormally distributed. The present data supports these findings.…”

“…Particularly at the lower end and the body of the distribution, it can be noticed that the Lognormal distribution provides a slightly better fit to the data than the Gaussian distribution. A sieving analysis with more than 1000 armor stones and two different armor stone classes indicated that the mean µ of D50 varies depending on the armor stone class and delivery batch, whereas the standard deviation σ is constant at 12 mm for larger armor stones (D50 ≥ 150 mm) and 10 mm for smaller armor stones (Sorgatz, 2021). The armor stone density ρs is assumed to follow a Gaussian distribution with µ = 2650 kg/m³ independently of the investigated canal.…”

“…While the hydraulic design defines the minimum armor stone diameter necessary to withstand (shipinduced) waves and currents, the geotechnical design evaluates the armor layer thickness required to ensure embankment stability. Expert interviews (Sorgatz et al, 2018) have shown that armor stone displacement is the most significant damage from the point of maintenance, but also in terms of possible failures as they are the most frequently observed. Thus, this paper focuses on armor stone displacements or, in other words, the hydraulic design.…”