Browsing by Author "Dreyer, Tashreeq"

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    Integral abutment bridges – continuum modelling of soil-structure interaction using finite element analysis with interface elements.
    (Stellenbosch : Stellenbosch University, 2024-02) Dreyer, Tashreeq; Van Zijl, Gideon P. A. G.; Fataar, Humaira; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: This thesis presents a computational study on the soil-structure interaction (SSI) behaviour stemming from cyclic thermal-induced movements of integral abutment bridges (IABs) using finite-element engineering software DIANA-FEA. An existing IAB, the Van Zylspruit Bridge in South Africa, is used as a template for the modelling presented in this study, with instrumented earth pressure and abutment displacement readings serving as validation of the models. The abutment-backfill section of the bridge is considered for the SSI modelling using continuum element methodology. The hardening soil model (HSM or HS model) is a numerical soil model that approximates real soil behaviour, including densification due to plastic deformation, stress-dependent stiffness, plastic straining (or yielding) in primary compression and deviatoric loading, isotropic hardening, and dilation. Soil failure is governed by a modified Mohr-Coulomb criterion in this model. The HS model is used to model the backfill, whereas the concrete and in-situ soil materials are assigned linear elastic models for simplicity. In continuum mechanics, ratcheting is the incremental build-up in pressure due to imposed cyclic loading. Ratcheting is prevalent in the backfills of IABs due to imposed cyclic thermal-induced displacements in the deck which are transferred to the abutments. Models presented in this thesis include interface modelling to allow separation between the integral abutment and retained granular (silica sand) fill to capture ratcheting and settlement behaviour in the backfill. The effective bridge temperature (EBT) with daily and seasonal cycles was measured on site from January 2016 to August 2017. This EBT “double cycle” is used to model imposed deformations on the abutment in order to capture ratcheting behaviour in the backfill. The Van Zylspruit bridge has a buried approach slab with one end fixed to the abutment (as a cantilever member). To evaluate the effect that approach slabs have on SSI behaviour, two models were created: one with an approach slab (Slab model) and the other without (No-Slab model). In the Slab model, interface elements were defined between the edges of the approach slab and the backfill to capture SSI behaviour stemming from the slab’s inclusion. The presence of the slab typically reduced settlements, but the development of a gap beneath the slab that grew with seasonal cycles prompts engineers to exercise caution with cantilevered slab designs. Results from both models showed reasonable agreement with measured data in terms of lateral earth pressure and abutment displacement. Two additional clay materials (one stiff and one soft) are used as alternative fill materials (with HSM parameters) to evaluate their effectiveness as backfill materials for IABs, with and without the approach slab present. The stiff clay was found to behave similarly to granular soil both in terms of stress ratcheting and backfill settlement. The soft clay was found to behave unfavourably, especially with the slab present, causing excessive backfill settlements over three times that of the stiff clay. A parameter study on the Mohr-Coulomb parameters (cohesion, friction angle, and dilatancy angle) of the HS model is conducted on the Slab model with granular fill. The values are modulated in reasonable ranges to provide settlement data on granular soils that might be considered as fill material in South Africa. It was observed that high dilatant granular materials with low friction cause excessive heave at the far end of backfill, in excess of 5mm after 5 cycles of ±5.5 mm abutment displacement amplitude. Low-friction and low-dilatant materials typically behaved unfavourably, with settlements across the backfill reaching 4 mm with the same aforementioned displacement criteria. The findings in this study may be beneficial to the current discourse surrounding IABs in the bridge engineering industry as well as the enhancement of modelling IABs using continuum mechanics methodology.