R.B.J. Brinkgreve

Wavelet-based evolutionary response of multi-span structures including wave-passage and site-response effects

Stochastic seismic wavelet-based evolutionary response of multispan structures including wave-passage and site-response effects is formulated in this paper. A procedure to estimate site-compatible parameters of surface-to-bedrock frequency response function (FRF) by using finite-element analysis of the supporting soil medium is proposed. The earthquake energy content is represented by a composite power spectrum density function contributed by the surface-to-bedrock FRF and bedrock power spectra. A long span multisupport structure is subjected to spatially varying differential support motions where the spatial-variability is represented by bedrock parametric coherency models and time-lags. In addition to the time-lags from wave-passage effects, the site-response effects from different soil conditions at the supports are characterized by frequency-dependent time-lags. In an illustrative case study, a three-span, two-dimensional hangar frame is analyzed using the proposed formulations. The time-lags resulting from site-response effects and computed by different FRFs show different variation in trends and frequency content. The site-response effect is found to introduce additional frequency nonstationarity and leads to an increase in the frame responses but with slower attenuation in time.

Tools for Predicting Damage to Archaeological Sites Caused by One-Dimensional Loading

Tools are developed to predict damage to archaeological remains caused by the construction of line infrastructure on soft soil. They are based on numerical modelling and laboratory testing supported by X-ray microcomputed tomographic observations, and micromorphological analyses of thin sections. They have been validated for one-dimensional (1D) loading at two sites in the Netherlands where soil has been placed on top of organic layers rich in ecofacts and overlaying Pleistocene sands. Numerical prediction of the deformation of soft layers underneath an embankment remains a challenge for geo-technical engineers. Errors on surface settlement prediction reach ±15% of the measured total settlement. Laboratory observations show that vulnerable artefacts can get crushed when packed loosely in pure assemblies under 1D loading equivalent to less than 5 m of sand. Fragmentation is assimilated to loss of archaeological value as it compromises recovery during sieving. Embedment in a sandy or a very compressible organic matrix has a beneficial effect on the resistance of ecofacts. Embedded ecofacts can resist a load of more than 12 m of sand. Flattening and re-orientation of soft plant remains occur during 1D loading without microscopic damage of tissues.

A parallel linear solver exploiting the physical properties of the underlying mechanical problem

The iterative solution of large systems of equations may benefit from parallel processing. However, using a straight-forward domain decomposition in “layered” geomechanical finite element models with significantly different stiffnesses may lead to slow or non-converging solutions. Physics-based domain decomposition is the answer to such problems, as explained in this paper and demonstrated on the basis of a few examples. Together with a two-level preconditioner comprising an additive Schwarz preconditioner that operates on the sub-domain level, an algebraic coarse grid preconditioner that operates on the global level, and additional load balancing measures, the described solver provides an efficient and robust solution of large systems of equations. Although the solver has been developed primarily for geomechanical problems, the ideas are applicable to the solution of other physical problems involving large differences in material properties.

Implementation, Validation, and Application of PM4Sand Model in PLAXIS

This paper presents the implementation, validation, and application of the PM4Sand model (version 3) formulated by Boulanger and Ziotopoulou (2015) in the PLAXIS finite element code. The model can be used for modelling geotechnical earthquake engineering applications, especially in the case liquefaction is likely to occur. The PM4Sand model represents an improvement of the elasto-plastic, stress ratio controlled, bounding surface plasticity model for sands formulated by Dafalias and Manzari (2004). The two-dimensional version has been implemented in PLAXIS and compared to the original implementation by Boulanger and Ziotopoulou (2015). The original implementation has been used in explicit finite difference simulations which can be sensitive to the size of the returned stress increment, based on the chosen time step size and loading rate. Therefore, the user needs to evaluate the sensitivity of the solution with respect to the chosen time step sizes. On the contrary, in the finite element method used here, the default time step together with the sub-stepping used at the constitutive model level provide a robust solution independent of the size of the returned stress increment.

Geotechnical Ultimate Limit State Design using Finite Elements

Displacement-based finite element calculations are primarily used for serviceability limit state (SLS) analysis, but the finite element method also offers possibilities for ultimate limit state (ULS) design in geotechnical engineering. The combined use of SLS and ULS calculations with partial safety factors according to the different design approaches in the Eurocode 7 can be time-consuming and prone to error. In this paper a Design Approaches facility is presented for an efficient use of partial safety factors in a finite element environment. In addition to a description of the methods used in this facility, an example is elaborated involving the geotechnical design of a sheet-pile wall supported excavation using different design approaches.