Seismic Microzonation of the City of Winnipeg
RA: Mohammad Katebi (Ph.D. Candidate)
Project Duration: 2017 – Present
Collaborators & Partnerships: Dr. Ahmed Shalaby (Department of Civil Engineering & Municipal Infrastructure Chair – UofM) & Dr. Aftab Mufti (SIMTReC)
Financial Support: University Research Grants Program (URGP) – University of Manitoba
Local topographical and geological conditions of the site (seismic site effect) have a large influence on seismic amplification of the ground shaking. From the perspective of the seismic hazard, the seismic site effects should be considered for the seismic design and land use planning. Recently, Manitoba has adopted an amendment to the Manitoba Building Code (MBC) to take into account the seismic design for buildings. However, there is no available data regarding the dynamic properties of Winnipeg soil.
This study is a first attempt to establish the design spectra for the city of Winnipeg soils based on a database of stratigraphic and in-situ tests information from reconnaissance boreholes in different locations in the City of Winnipeg. Published correlations are used to estimate the shear wave velocity in each layer, and a nonlinear earthquake response analysis is carried out using NERA. Two different Canadian time-history ground movement measurements are used as input motions for the analysis. The input motions are scaled to the peak ground acceleration of 2,475-year earthquake of Winnipeg. This preliminary analysis showed that design spectra developed from NBCC 2015 are not reliable for structures with a fundamental period lower than 0.4 seconds. Depending on the depth to the bedrock, depth of the water table, and dynamic properties of the soil layers the spectral acceleration can reach a maximum of 0.45 g.
For design purposes, the design spectra is developed using an average of the spectral response of all the boreholes used in this study. The design spectra developed according to clause 1-6-2-1-4 of FEMA 356, is an estimate of the spectral response of the layered soil deposits of Winnipeg based on information from 20 boreholes.
The reliability of the design spectra developed in this study can be enhanced by increasing the number of boreholes. Also, due to the lack of dynamic properties of Winnipeg soils, published correlations are used to estimate the shear wave velocity of the layered soil and bedrock. Further investigations are needed to measure the shear wave velocity of soil and bedrock directly. Some of the common methods for measuring the shear wave velocity include Seismic Refraction Survey, Seismic Reflection Survey, Surface Wave Methods, Crosshole Method, Downhole Method and Suspension Logging.
Katebi M., Maghoul P., Shalaby A., Mufti A., 2018. The Seismic Site Response in Winnipeg Based on a Database of Borehole Information, 7th Geohazards Conference, Canmore, Canada.
Seismic Site Effects
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coming soon …
Software Development (FEM/BEM) for 2D Wave Propagation in Saturated and Unsaturated Soils
RA: Dana Amini (Visiting Researcher) & Hongwei Liu (Ph.D. Candidate)
Collaborators & Partnerships: Dr. Behrouz Gatmiri (ENPC, France)
I (Dr. Maghoul) developed analytical solutions (Fundamental Solutions) and numerical models (coupled Finite Element (FEM) and Boundary Element (BEM) techniques), during my Ph.D. program (2007-2010), to study the response of multiphase porous media (soils) under thermal, quasi-static and dynamic loadings. The applications in this regard include multiphase transfer of heat, moisture (water and vapor) and air in porous media, nuclear waste disposal modeling, and study of the combined effects of topography and sediments on the amplification of earthquakes.
For domains of infinite extensions, standard FE discretization leads to wave reflections at the edges of the FE mesh, which can be only partly eliminated for some cases, by using so-called transmitting, silent and non-reflecting viscous boundaries. The BEM, on the other hand, represents efficiently the outgoing waves through infinite domains, which is very useful when dealing with waves scattered by topographical structures. Before this research, the application of the BEM for solving problems of unsaturated porous media was limited, because no fundamental solution existed in the published literature, neither in the frequency nor time domain. This fact arises from the complexity of the coupled partial differential equations that govern the behavior of such media.
I established the first boundary integral equations (BIE) and associated fundamental solutions for unsaturated porous media subjected to transient loading for non-isothermal 2D and 3D cases, and dynamic loading for isothermal 2D and 3D cases. Then, the BEM based on the convolution quadrature method (CQM) concerning saturated and unsaturated porous media subjected to isothermal quasi-static and dynamic loadings were implemented via the in-house code HYBRID. Having integrated the BEM formulations for soils under dynamic and transient loading, I was able to obtain the first boundary element code that can model wave propagation and consolidation problems in saturated and unsaturated porous media.
In this research, we aim to add more feature to the near-field part (FEM) of this code including the elasto-plastic constitutive law.