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Buckling of End-Bearing Retaining Walls in Clay
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
2018 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The design of back-anchored retaining walls in Sweden has traditionally not included global elastic instability of the retaining wall as a possible failure mode. Eurocode 3 part 5 (SS-EN 1993-5) requires design of steel structural members for retaining walls to assess the risk of buckling if the normal force exceeds 4 % of the critical buckling load of the retaining wall.

The geological conditions in Eastern Sweden are characterized by the intersection of very hard Precambrian rock and very soft Holocene clays. Thus often ground anchors anchored in rock at a 30-50 degree angle to the vertical plane are used to support retaining walls, resulting in a very high utilization of the ground anchor and a significant normal force in the retaining wall. The threshold value for buckling risk is consequently frequently exceeded and the specific failure mode, of global buckling, is often limiting the use of the structural members in practical design.

The buckling load can either be calculated using Euler’s second or third buckling mode, or by modelling the soil-structure interaction by a suitable model. Since no such model is specified in the code, the aim of this thesis was to develop a model which takes into account the stabilizing effect of the soil for the calculation of the buckling force and to model the soil-structure interaction with a beam-spring model connected to Winkler springs.

The model simulations show that the soil has a significant influence on the critical load, especially when the retaining wall base is driven to depths greater than 2 meters below excavation depth. The model simulations suggest that higher utilization, with up to 4 times greater critical load, of the steel members is possible for some specific cases and an idealized design factor is also elaborated.

Abstract [sv]

Dimensioneringen av bakåtförankrade spontväggar har traditionellt sett i Sverige inte tagit hänsyn till risken för global knäckning. I och med införandet av Eurokod 3 kapitel 5 (SS-EN 1993-5) som styrande dokument vid dimensionering av sponter måste risken för knäckning nu mera beaktas när normalkraften överstiger 4 % av den kritiska knäckningslasten.

De geologiska förhållandena i de östra delarna av Sverige, med lösa leror som täcker hårt berg, leder till att bakåtförankrade sponter med brant lutande stag ofta används. Detta leder till en hög utnyttjandegrad av ankaret och också stora normalkrafter i sponten, vilket leder till att knäckning ofta blir dimensionerande brottmod för sponten.

Metoden för att beräkna knäckningslasten kan enligt SS-EN 1993-5 göras med Eulers andra eller tredje knäckningsfall eller med en modell som tar hänsyn till jordens stabiliserande effekt. Idag finns ingen sådan numerisk modell att hitta i litteraturen, varför målet med detta arbete har varit att finna en lämplig modell för att ta hänsyn till jordens inverkan vid bestämning av knäckningslasten. För att modellera samverkan mellan jorden och sponten användes en balkmodell med Winkler fjädrar.

Simuleringarna visar att jorden har en signifikant inverkan på den kritiska knäckningslasten, särskilt när nedslagsdjupet är större än 2 meter. Flera simulerade geometrier har gett drygt fyra gånger högre knäcklast jämfört med den knäcklast som erhålls om SS-EN 1993-5 följs. Om jorden tas hänsyn till i dimensioneringen av en spont skulle således slankare konstruktioner kunna användas.

Place, publisher, year, edition, pages
2018. , p. 85
Series
Examensarbete Jord- och bergmekanik, ISSN 1652-599XTRITA-ABE-MBT ; 18250
Keywords [en]
Berliner walls, Critical loads, buckling, finite element model, Eurocode 3
Keywords [sv]
Berlinerspont, Rörspont, kritisk knäckningslast, knäckning, finit element modell, Eurocode 3
National Category
Geotechnical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-229808OAI: oai:DiVA.org:kth-229808DiVA, id: diva2:1218160
External cooperation
ELU Konsult AB
Subject / course
Soil and Rock Mechanics
Educational program
Master of Science in Engineering - Urban Management
Supervisors
Examiners
Available from: 2018-06-15 Created: 2018-06-14 Last updated: 2018-06-15Bibliographically approved

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