Short Course - A Fresh Perspective on Soil Mechanics With Applications to Geotechnical Design

by Professor Malcolm Bolton, Cambridge University

The Vancouver Geotechnical Society will be offering a 2-day short course presented by Professor Malcolm Bolton of Cambridge University.  The short course will take place on May 22 & 23 at the Coast Coal Harbour.  The course brochure, which has the outline and registration form can be found here.

Embankment Deformations Include Creep in Compression and Shear - 2014 Spring Cross Canada Lecture Tour

by Jim Graham, Ph.D., D.Sc., FEIC, P.Eng. - Wednesday, May 7, 2014

Clays exhibit creep at all stages of loading; not only after primary consolidation is complete. When a normally consolidated clay ‘ages’ under constant effective stress it develops an apparent preconsolidation pressure that affects creep rates. Creep is experienced, for example, in delayed compression and long term settlements. Elasticviscoplastic modeling based on (1) an ‘instant’ elastic component and (2) a plastic component which contains viscous non-recoverable strains, has produced improved modeling of vertical and horizontal deformations. The model is expressed in terms of stress, stress rate, strain, and strain rate. It can accommodate tests at different constant strain rates, different load durations, creep and aging, and relaxation. The model is based on an extension of Modified Cam Clay and is easily calibrated using only simple, readily available oedometer and triaxial tests. Equations have been written so that strain rates vary with overconsolidation ratio, even though the creep coefficient  is defined as a soil constant like kappa and lamda. It does not vary with stress level like the traditional coefficient of consolidation cv.

Less is more: Step Zero and back of the envelope calculations

by David Muir Wood, Wednesday, April 16, 2014

Before embarking on complex numerical modelling or physical modelling, Step 0 is ‘to write down the answer’. If you have no idea what answer to expect then you will not recognise when the modelling has gone awry. Step 0 estimates are best supported by ‘back of the envelope’ calculations which may be based on simplified modelling which manages to include the important mechanisms of response. ‘System’ as opposed to ‘element’ treatment is often possible.

The presentation slides can be downloaded here.

Earthquake-Induced Landslides - Lessons from Taiwan, Pakistan, China and New Zealand - The UBC Geological Engineering 2014 Distinguished Lecture

by Dave Petley, Tuesday, March 4, 2014

Landslides are an important secondary hazard in large earthquakes in upland areas. In high mountains, landslides typically cause about a third of the fatalities; they impede rescue and recovery operations; and they create a long term legacy as slope failures continue to occur after the aftershock sequence has decayed. Unfortunately, our understanding of the processes occurring within slopes during large earthquakes remains poor. Based on field visits and research by the presenter, this talk will explore some of the landslides triggered by the 1999 Chi‐Chi earthquake in Taiwan, the 2005 Kashmir earthquake in Pakistan, the 2008 Wenchuan earthquake in China and the 2011 Christchurch earthquakes. In each case, the talk will focus on some case studies of very large landslides triggered by the earthquake, describing the nature of the failures and the impacts that they caused. This information is then used to explore how and where landslides are triggered by earthquakes. In the final part of the talk, the presenter will outline scenarios for potential earthquakes in New Zealand and Nepal, and the landslides that they would be likely to trigger.

Critical State Soil Mechanics: 125 years of history to current engineering use

by Mike Jefferies, Thursday, February 6, 2014

The talk will be in two parts. The first part – slightly more than an hour - will be of general interest as a synthesis of the history underlying everyday consulting practice (unappreciated as it may be...): very much “the ideas” not “the math”. After a short break, the second part – also of about an hour - will be for aficionados of the subject and discuss using critical state soil mechanics within practical consulting including: numerical integration of the equations (an Excel worksheet will be provided); needed aspects of laboratory testing; evaluation of insitu state from SCPTu; and, using NorSand within FLAC.

The NorSand soil model can be downloaded here.

Understanding Liquefaction Through Applied Mechanics by Mike Jefferies and Dawn Shuttle

South Fraser Perimeter Road Project

by Dr. (Uthaya) M. Uthayakumar, Wednesday, January 22, 2014

South Fraser Perimeter Road project includes the design and construction of an approximately 40 km long, 80 km/hr four-lane divided highway along the south side of Fraser River, from Deltaport Way in southwest Delta to Highway 15 and the Golden Ears Bridge Connector in Surrey, BC.  The project is delivered through a Design-Build-Finance-Operate contract between the BC MoTI and the Fraser Transportation Group.  Poor ground conditions extending to great depths, peat deposits, environmentally sensitive areas, existing municipal landfill sites, existing unstable hill slopes and numerous creek crossings presented challenge to the design and construction of the SFPR project.

The presentation will include the following:
  • an overview of the project;
  • subsurface soil and groundwater conditions;
  • description of geotechnical and seismic design criteria;
  • geotechnical design and analyses;
  • preload treatment, ground densification and embankment design;
  • foundation design and tests to verify foundation capacities.

Estimation of Parameters for Seismic Design in Peru

by Dr. Manuel Monroy, Wednesday, December 4, 2013

Peru is situated in one of the most seismically active regions in the world.  However, parameters for the seismic design of structures in the country are scarce.  The presentation will discuss site-specific 0.2-second and 1.0 second spectral accelerations (Sa), earthquake magnitude (M), source- to-site distance (D) and epsilon parameters suitable for seismic design.  The parameters are quantified for a return period of 475 years for cities located along the coast and the Peruvian Andes.  Comparisons between the site-specific seismic design spectra with those specified in the 2003 Peruvian Seismic Code will be highlighted and implications to seismic design in those cities will be presented.  Fundamentals of probabilistic seismic hazard analysis, challenges faced by the practice in subduction environments and a comparison with the seismotectonic setting in BC will be commented.

Critical Role of Laboratory Characterization in Geotechnical Modeling and Practice

by Dr. Yogi Vaid, Professor Emeritus, University of British Columbia - Wednesday, November 13, 2013

Great advances have been made over the last three to four decades in numerical solution of boundary value problems of continuous media.  Their applications to geotechnical problems, in particular, has far outpaced our abilities to characterize realistically the mechanical properties of geomaterials – the key input required for meaningful results from the analysis.  Idealized material models, with increasing degrees of complexities are being frequently used, with little experimental verifications as to their validity.  Often the mechanical parameters derived from triaxial compression tests are used to calibrate the model, which is also assumed valid under generalized stress systems.

This presentation is intended to show that the soil response is much more complex than that revealed by the triaxial compression test. Among the many factors that influence soil behaviour include: (i) initial state variables, which are comprised of void ratio, effective stress state, soil fabric, and any prior stress/strain history experienced by the soil; (ii) the stress path during loading, and also; (iii) the consequence of the tacit undrained assumption in problems of rapid loading.

Evaluating the Seismic Coefficient for Slope Stability and Retaining Wall Design - 2013 Fall Cross Canada Lecture Tour

by Dr. Edward Kavazanjian, Jr., Ph.D., P.E., NAE - Monday, October 21, 2013

A performance based approach has been developed for establishing the seismic coefficient, ks, for use in pseudo-static analyses of slope stability and retaining walls.  While the seismic coefficient is one of the most important parameters in these types of analyses, relatively little guidance is available on the appropriate value to use in design.  Furthermore, most existing guidance is based upon work done over 30 years ago.  However, work on a recent US National Cooperative Highway Research Program project has led to development of a new method in which the seismic coefficient depends upon the acceptable permanent seismic displacement as well as on factors representing the seismic environment and the spatial incoherence of the ground motions.  Factors considered in this approach includes the seismic environment, amplification of ground motions by local site conditions, spatial and temporal attenuation of ground motions over the potential failure mass or retaining wall backfill, and acceptable permanent seismic displacement.  Analyses using this new method demonstrate that in earthquakes of magnitude up to 8.0 a seismic coefficient equal to no more than 50% of the free-field PGA at the site, and in some cases less than 25% of the free-field PGA, is appropriate for retaining walls and slopes over 100 ft in height if 1-2 inches of permanent displacement can be accommodated in the design event.  Even smaller values of the seismic coefficient are appropriate in small magnitude earthquakes or if greater seismic displacement can be accommodated.

The presentation slides can be found here.

Rock Falls - Developments in modelling and design of protection Structures

by Duncan Wyllie, P.Eng. - Wednesday, September 25, 2013

The talk will address two recent developments related to the design of rock fall protection structures.  First, it will be shown that values of the normal coefficient of restitution eN, used in modelling of rock falls are more dependent on impact conditions than on the properties of the slope materials.  That is, for steep angle (i > 40 degrees) impacts, the values of eN are low, while for shallow angle impacts, eN can be greater than 1.   Second, attenuator-type rock fall fences will be discussed.  Attenuators are fences that deflect and redirect rock falls rather than stop falls.  Observations of the behaviour of actual rock falls, and the results of model testing, show that attenuators reduce impact velocities such that only a portion of the impact energy is absorbed by the fence, with the remaining energy being retained in the moving rock. This behaviour means that attenuators can be designed for higher impact energies compared to conventional fences that stop falls.