Earthquake Engineering

Seismic hazard analyses

Development of seismotectonic model

We integrate available geological, seismological and geodetic data to develop a seismotectonic model for use in a subsequent site-specific PSHA. This model includes characterisation of the location and geometry of seismic sources, style of faulting, earthquake magnitude distributions, and earthquake recurrence parameters. We have developed an approach to implement the UCERF3 source model for site-specific applications.

Probabilistic Seismic Hazard Analyses (PSHA)

We can conduct a PSHA with a range of different software (e.g., EZ-FRISK, FRISK88, HAZ). Adequate ground motion prediction equations are selected based on the seismotectonic setting of the site. Seismic hazard deaggregation is conducted to estimate the controlling scenarios in terms of earthquake magnitude, source-to-site distance, and epsilon. If warranted, directivity and fling effects are incorporated in the analyses. We systematically update our software to incorporate the latest advances in this field, and stay at the forefront of the state of practice.

Time histories selection and modification

Our engineers develop design ground motion time histories compatible with a target acceleration response spectrum using spectral matching or scaling methods. The ground motion selection is based on the controlling earthquake magnitude and site-to-source distance, site conditions, peak intensity measures, frequency content, directivity effects, and duration. If warranted, static fault displacement or fling effects can be incorporated. If spectral matching is performed, we take particular care to preserve the non-stationary characteristics of the seed ground motions.

Design ground motions

We provide recommendations for seismic design levels for any engineered facility. This includes buildings where the design is governed by local building codes; critical facilities (e.g., nuclear power plants and dams) governed by specific requirements; and facilities where the owner wishes to achieve design levels that meet a certain performance criterion.

Integrated site characterisation using gis

Our GIS capabilities include integrated 3D site characterisation and development of 3D models of subsurface conditions, parameter plots to develop engineering design parameters, liquefaction analyses, maps for various geohazards, seismicity catalogues and seismic source models.

When handling large amounts and different types of data (e.g., geophysics, geological, geotechnical), the use of our GIS platform and tools allows for efficient compilation, integration, and interpretation of all data, and the development of 2D and 3D subsurface models, which can be directly incorporated in subsequent engineering evaluations.

Site response analyses

Site response analyses should be considered to develop near-surface design ground motions for sites underlain by soft to medium stiff/dense soils which tend to modify the “stiff-soil/rock” ground motions as they propagate through the soil column. Fugro routinely conducts 1D, 2D and 3D equivalent linear and nonlinear site response analyses. If liquefiable soils are present, we also conduct nonlinear effective stress analyses with appropriate effective stress constitutive models. Fugro conducts the site response analyses using a variety of software such as DEEPSOIL, FLAC, OpenSees, and SHAKE.

Slope stability evaluations

We employ advanced approaches to assess the potential for dynamic slope instability at a project site. Numerical analyses offer an alternative, refined response model, compared to widely used simplified methods. Key aspects of soil behaviour captured by the soil constitutive models used in these analyses are: 1) first time monotonic loading defined by the backbone curve; and 2) nonlinear stress-strain behaviour under cyclic loading. The constitutive models are validated against soil-specific laboratory tests and observations from centrifuge experiments from the existing literature. When warranted, the effect of strain-softening or strain rate effects are also modelled.

Liquefaction triggering hazard assessment and liquefaction-induced demands

We have developed unique GIS-based tools to automate liquefaction triggering hazard analyses using boring and CPT data and the latest state of practice and art methodologies. These tools allow for visual interpretation of the vertical and lateral extent of liquefaction and associated ground deformations. For important structures founded on or surrounded by liquefiable soil, we can conduct numerical evaluations using advanced soil constitutive models appropriately calibrated against laboratory cyclic simple shear tests, centrifuge model tests, and actual case histories. We perform evaluations of liquefaction-induced demands using a variety of software such as FLAC and OpenSEES.

Fault rupture hazard assessment

Probabilistic fault displacement hazard analyses (PFDHA) can be performed to estimate surface displacements associated with direct fault rupture during the design earthquake. We use both a displacement approach using fault displacements during earthquakes from in-situ observations, and an earthquake approach using the seismotectonic model for the site. We also conduct numerical analyses modelling the fault rupture propagation through the soil and simulating the foundation under the direct fault rupture displacements.

Soil-structure interaction effects

Soil-Structure Interaction (SSI) effects modify both soil and structural response during dynamic shaking compared to free field. We routinely perform analyses incorporating SSI effects to allow for more realistic modelling of the structural response. Depending on project needs, we can conduct both de-coupled and fully coupled SSI analyses using a variety of finite element and finite difference software. Outputs can include foundation-specific nonlinear springs, depth-varying nonlinear p-y and t-z springs, cyclic degradation and strain-rate effects on pile skin friction, quantification of large pile group effects, etc. We also conduct fully coupled dynamic SSI analyses, simulating both foundation and surrounding soil in one single model

Fugro’s comprehensive earthquake engineering services combine wide-ranging, state-of-the-art analysis and modelling techniques to predict the effects of seismic activity on foundations and structures and to inform appropriate geotechnical design and engineering solutions.

Customers benefit from:

• Our extensive knowledge and experience in geotechnical earthquake engineering
• Advanced numerical modelling services to address the most complex of challenges in seismically active areas
• Access to a complete spectrum of integrated seismic assessment and evaluation services