AbstractThis thesis examines the seismic behaviours of isolated (in consideration of soil-structure-interaction, SSI) and adjacent structures (in consideration of structure-soil-structure interaction, SSSI) with shallow foundations on liquefiable soil. Consideration is given to the influence of foundation types, relative dynamic characteristics of adjacent structures, and the influence of soil liquefiability. Dynamic centrifuge testing was used as the primary method of investigation on behaviours of liquefied soil, and finite element modelling was used for comparisons on non-liquefied soil.
For the site response analysis in the free-field, lower intensity ground shaking was observed at the ground surface when liquefaction occurs. The amount of reduction in soil amplification can be derived. The peak excess pore water pressure profile can be predicted by a modified simple liquefaction susceptibility analysis. The reduction in ground intensity can also be correlated an ru-index ranging from 0 to 1 describing the degree of liquefaction which can be useful for linking intensity measures (e.g. Housner Intensity) and resulting engineering demand parameters (e.g. inter-storey drift) with site response.
For a beneficial shallow foundation type on liquefied soil, separated strip foundations are favourable when in the building is in isolation due to the reduced structural response; a one-piece raft foundation is favourable when adjacent to another structure (e.g. in an urban area) due to reduced structural response. In both cases, greater foundation deformation is a price to pay for reduced structural response. The change of beneficial foundation type from strips in isolation to a raft in the adjacent case is explained by changes in effective natural period and damping ratio, determine using measured transfer functions.
In terms of the influence of soil liquefiability (from fully non-liquefied to completely liquefied) on SSI effects, correlations of engineering demand parameters and ground intensity indictors in the free-field was derived, which can be further linked to an ru-depth index and the depth of the liquefaction front. Where there are adjacent structures, a strongly beneficial SSSI effect on settlement and detrimental effect on drift in non-liquefied soil, reduce towards a null-effect in both cases with increased liquefaction, with liquefaction appearing to isolate the structures from each other. This has also been linked to ground intensity measures.
For effects of relative dynamic properties of adjacent buildings, SSSI effects in terms of structural response is found to be increasingly beneficial with period ratio between adjacent structures increases in liquefied soil and are generally detrimental irrespective of period ratio in the non-liquefied soil. In both soils, the effects are most detrimental when the period ratio is only slightly different. SSSI in non-liquefied soil can provide a safe assessment (upper-bond) in terms of SSI and SSSI effects. A simplified equivalent single-degree-of-freedom response is used to estimate the storey accelerations and shows a generally good match in both soils. SSSI effects is found detrimental in terms of foundation deformation, so that SSSI case on non-liquefied soil cannot provide a safe design any more.
|Date of Award||2020|
|Sponsors||China Scholarship Council|
|Supervisor||Jonathan Knappett (Supervisor) & Ioannis Anastasopoulos (Supervisor)|