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- Beijer Lundberg, Anders, et al.
(författare)
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Risk management and risk acceptance regarding the stability of slopes: Case study
- 2021
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Konferensbidrag (refereegranskat)abstract
- Most earthworks result in an alteration of the stress state in the ground, either throughthe excavation of soil or the placement of surcharge on the ground surface. These stress changeshave the potential to cause a slope collapse or failure, often with large consequences for theconstruction project or the immediate environment. Slope stability calculations are thereforefrequently carried out for various load and excavation stages in the design phase to reduce therisk in the construction phase. Nevertheless, slope collapses sometimes occur, both small oneswith minor consequences, as well as larger ones with significant consequences for society. In thecurrent paper, a case history of a slope from Scandinavia is examined to assess how the risk ofslope stability was managed and allocated among the various agents, and how the slide coulddevelop. Was the risk acceptable for society on an aggregate level? The soil conditions and theconstruction process for the case studies are elaborated in detail with respect to the riskmanagement principles in ISO 31000 and the recently published guidelines from the SwedishGeotechnical Society. The risk acceptance and the concept of the risk owner, i.e. the entity thatowns the specific risk, is discussed for the case study, as well as the consequences of the specificconstruction contract. The acceptable aggregate risk, i.e. the risk the local and national authoritiescan permit, is elaborated.
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- Bismut, Elizabeth, et al.
(författare)
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Optimal adaptive decision rules in geotechnical construction considering uncertainty
- 2023
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Ingår i: Geotechnique. - : Emerald. - 0016-8505 .- 1751-7656.
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Tidskriftsartikel (refereegranskat)abstract
- To optimally design a geotechnical engineering structure, an iterative decision-making process is required due to the prevailing uncertainty of the ground conditions. At present, these decisions are taken based on simple deterministic rules and models. This paper proposes a risk-based decision-theoretic framework to the optimal planning for geotechnical construction. This framework combines geotechnical probabilistic models, cost analysis using Monte Carlo simulation and the observational method. The framework is illustrated on the design of the surcharge for an embankment on soft soil, whereby the optimal preloading sequence of added surcharge is adapted to the observed settlement. The approach balances the cost of surcharge material against financial penalties related to project delays and insufficient overconsolidation, which causes damage due to residual settlement. The result is a preloading strategy that optimally accounts for information obtained from settlement measurements under uncertain ground conditions. The findings highlight the potential of using risk-based decision planning in geotechnical engineering, in particular in combination with the observational method. For the investigated case-study, we observe a reduction in the expected cost in the order of 25%.
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- Bjureland, William, et al.
(författare)
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Challenges in applying fixed partial factors to rock engineering design
- 2017
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Ingår i: Geotechnical Special Publication. - Reston : American Society of Civil Engineers (ASCE). - 0895-0563. ; :283, s. 384-393
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish national guidelines for design of the main structural support system in road and railway rock tunnels have been adjusted to cohere with Eurocode 7. In the design guidelines, the limit states that the designer should consider are specified. The main method to account for uncertainties in the Swedish guidelines is similar to the method preferred in Eurocode 7: the partial factor method. For each limit state, fixed partial factors retrieved from different sections of the Eurocodes are specified. However, fixed partial factors may not correspond to the same structural reliability for all design situations. In this paper, we show for a common design situation in rock engineering design how partial factors in theory should vary with design geometries and uncertainties. The derived partial factors are compared to the Eurocodes’ fixed values. We find that using fixed partial factors to ensure structural safety in these limit states might not be suitable. The implications are discussed along with suggestions of other more suitable methods to account for uncertainties in rock engineering design.
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- Bjureland, William, 1987-, et al.
(författare)
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Dimensionering av sprutbetongförstärkning för lösa block med sannolikhetsbaserade metoder
- 2020
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Användning av sannolikhetsbaserade metoder för dimensionering av bergförstärkning är ett tillvägagångssätt som är accepterat i Eurokoderna. Vid dimensionering med dessa metoder beaktas osäkerheter stringent genom att ansätta sannolikhetsfördelningar för relevanta parametrar. Konstruktionens säkerhet säkerställs genom att verifiera att sannolikheten att överskrida bärförmågan är lägre än den i Eurokoderna kravställda brottsannolikheten. För tillämpning av sannolikhetsbaserade metoder för dimensionering av sprutbetongförstärkning för lösa block har ett problem varit att data saknats för att kunna beskriva relevanta parametrar med representativa sannolikhetsfördelningar. Dessutom samverkar de olika brottmoderna och måste därför betraktas ur ett systemperspektiv, vilket inte beaktats i tidigare studier. I denna artikel presenteras resultatet av ett doktorandprojekt med finansiering av SBUF, BeFo, SVC och SKB. Baserat på ovanstående aspekter presenteras en metodik för dimensionering av sprutbetongförstärkning för lösa block med sannolikhetsbaserade metoder. Inledningsvis presenteras sannolikhetsfördelningar för sprutbetongens parametrar baserat på en stor mängd analyserade data från Citybanan. Därefter presenteras den utvecklade dimensioneringsmetodiken, vilken bygger på att en initial dimensionering av sprutbetongen utförs innan tunneldrivningen påbörjas och att den applicerade sprutbetongens bärförmåga därefter verifieras med hjälp av kontrollmätningar från fält och Bayesiansk statistik.
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- Bjureland, William
(författare)
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On reliability-based design of rock tunnel support
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tunneling involves large uncertainties. Since 2009, design of rock tunnels in European countries should be performed in accordance with the Eurocodes. The main principle in the Eurocodes is that it must be shown in all design situations that no relevant limit state is exceeded. This can be achieved with a number of different methods, where the most common one is design by calculation. To account for uncertainties in design, the Eurocode states that design by calculation should primarily be performed using limit state design methods, i.e. the partial factor method or reliability-based methods. The basic principle of the former is that it shall be assured that a structure’s resisting capacity is larger than the load acting on the structure, with high enough probability. Even if this might seem straightforward, the practical application of limit state design to rock tunnel support has only been studied to a limited extent.The aim of this licentiate thesis is to provide a review of the practical applicability of using reliability-based methods and the partial factor method in design of rock tunnel support. The review and the following discussion are based on findings from the cases studied in the appended papers. The discussion focuses on the challenges of applying fixed partial factors, as suggested by Eurocode, in design of rock tunnel support and some of the practical difficulties the engineer is faced with when applying reliability-based methods to design rock tunnel support.The main conclusions are that the partial factor method (as defined in Eurocode) is not suitable to use in design of rock tunnel support, but that reliability-based methods have the potential to account for uncertainties present in design, especially when used within the framework of the observational method. However, gathering of data for statistical quantification of input variables along with clarification of the necessary reliability levels and definition of “failure” are needed.
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- Bjureland, William, et al.
(författare)
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Probability distributions of shotcrete parameters for reliability-based analyses of rock tunnel support
- 2019
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier. - 0886-7798 .- 1878-4364. ; 87, s. 15-26
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Tidskriftsartikel (refereegranskat)abstract
- A common support measure for underground excavations in jointed rock masses to support loose blocks is to apply a thin shotcrete layer to the periphery of the excavation and systematically install rockbolts into the surrounding rock mass. In this support system, large blocks are carried by the rockbolts and small blocks are carried by the thin shotcrete layer. To verify the shotcrete layer's load-bearing capacity and to stringently account for the large uncertainties incorporated in the variables involved in determining its capacity, analytical calculations in combination with reliability-based methods can be used. However, a lack of knowledge exists regarding the magnitude and uncertainty of shotcrete characteristics (thickness, adhesion, flexural tensile strength, residual flexural tensile strength, and compressive strength), making it difficult to apply reliability-based methods. A statistical quantification of these characteristics is therefore important to facilitate reliability-based methods in design and verification of shotcrete support. In this paper, we illustrate how shotcrete support against small loose blocks can be viewed as a correlated conditional structural system and how this system can be analyzed using reliability-based methods. In addition, we present a unique amount of data for the aforementioned variables, which are all incorporated in the design and verification of a shotcrete layer's ability to sustain loads from small loose blocks. Based on the presented data, we statistically quantify and propose suitable probability distributions for each variable. Lastly, we illustrate how the proposed probability distributions can be used in the design process to calculate the probability of exceeding the shotcrete's load-bearing capacity. Both the probabilistic quantification and the defined correlated conditional structural system along with the illustrative calculation example are followed by a discussion of their implications.
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