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Earthquake Induced Residual Displacements of Shallow Foundations

Michael Pender, Tom Algie, Liam Wotherspoon, Michael Davies and Jeremy Toh

The particular aspect of performance based design considered in this paper relates to shallow foundations on cohesive soils. The work discussed is part of a larger project in which we are promoting the acceptance of brief instances of bearing strength failure beneath the foundation during the course of an earthquake as long as the post earthquake permanent residual displacements are acceptable. Herein we compare three different methods of estimating post earthquake residual displacements. The calculations are checked against the displacements and actions measured in a centrifuge test. Our conclusion is that the three methods, although very different, produce results that are generally comparable.

Paper P42: [Read] [Presentation]

Effects of SSI on the Seismic Response of Older Structures Before & After Retrofit

M.J. Arefi, Stefano Pampanin and Misko Cubrinovski

Comprehensive experimental and analytical studies have been conducted to understand the behaviour of frame buildings constructed before the introduction of modern design codes. This usually has been done assuming a fixed-base structure while ignoring the flexibility of soil.

The interaction between the super-structure and sub-structure (SSI) is investigated by modelling the soil as simple as possible to capture the overall response of the system.

As new analytical hysteresis rules and more advanced tools of analysis have been developed in recent years, and as part of a more comprehensive investigation on the response of older structures before and after retrofit, focus will be herein given on the response of SDOF systems representing a broad range of existing, newly designed and, retrofitted structures, while allowing for flexibility of the soil-foundation system.

The results of this study suggest that the compliance of simply modelled soil for typical building structures have in average beneficial effects in terms of structural demand especially in the case where as a consequence of implementing a retrofit strategy, the stiffness of the structure might increase. On the other hand, the governing component of these effects, i.e. rocking of foundation, can result on average in higher absolute displacement of floors.

Paper P43: [Read] [Presentation]

Effect of Lateral Stress on the Liquefaction Resistance of SCP-improved Sandy Soils

Rolando Orense, K Harada, J Mukai and K Ishihara

When the sand compaction pile (SCP) method is implemented to improve loose deposits of sandy soils, its effect is evaluated generally in terms of increase in density which is beneficial for reducing the liquefaction potential of the deposits during earthquakes. Additional advantage can be expected to occur due to a concurrent increase in lateral stress. When the resistance to liquefaction is evaluated on the basis of SPT N-value or CPT q_c -value, the increased resistance to penetration due to the sand compaction has been interpreted conventionally as being associated mainly with the increase in density. Therefore, in order to properly evaluate the effectiveness of ground improvement in compacted soils, it is necessary to quantify the effect of lateral stresses on the penetration resistance and liquefaction strength. In this paper, charts incorporating the effect of various lateral stress ratios proposed earlier by the authors are used to quantitatively analyze the contributions of the increased lateral stress and increased penetration resistance on the resulting liquefaction resistance. Results indicate that if the increase in penetration resistance due to SCP implementation is larger, the effect of increased lateral stress becomes smaller and such trend is more pronounced in denser deposits.

Paper P44: [Read] [Presentation]

Resistance From Bridge Abutment Passive Soil Pressure in Earthquakes

John Wood

This paper summarises the results from recent experimental and analytical research on the force resistance available from passive soil pressures on wall type and bridge abutment structures translated against the backfill in earthquakes, and shows how the results can be applied in bridge seismic assessment and design.

Paper P45: [Read] [Presentation]

Sensitivity Analysis of Simplified Methods for the Design of Piles in Laterally Spreading Soils

Jenny Haskell, Misko Cubrinovski and Brendon Bradley

The simplified analysis of piles in laterally spreading soils is burdened by uncertainties. Key parameters affecting the pile response, such as the stiffness degradation and lateral displacement of the liquefied soil, cannot be uniquely defined, but rather vary over a wide range. In this paper we explore the effect of variations of model parameters on the pile response by means of a deterministic sensitivity analysis, and demonstrate that the relative importance of the most critical parameters depends on the mechanism of soil-pile interaction. It is clear that without an understanding of the scale of variation of the model parameters and the effect of parametric variations on the predicted pile response, the consistent and reliable use of simplified pile design and analysis methods cannot be expected.

Paper P46: [Read] [Presentation]

A Macro-element for Pile Head Response to Cyclic Lateral Loading

Norazzlina Sa’don, Michael Pender and Abdul Razak Abdul Karim

The simplified analysis of piles in laterally spreading soils is burdened by uncertainties. Key parameters affecting the pile response, such as the stiffness degradation and lateral displacement of the liquefied soil, cannot be uniquely defined, but rather vary over a wide range. In this paper we explore the effect of variations of model parameters on the pile response by means of a deterministic sensitivity analysis, and demonstrate that the relative importance of the most critical parameters depends on the mechanism of soil-pile interaction. It is clear that without an understanding of the scale of variation of the model parameters and the effect of parametric variations on the predicted pile response, the consistent and reliable use of simplified pile design and analysis methods cannot be expected.

Paper P47: [Read] [Presentation]

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