on the Important of kinematice in the analysis of (large) landslides - 2015 Spring CROSS CANADA LECTURE TOUR
by Dr. Nicholas Sitar, P.h.D., P.Eng., Thursday, May 14, 2015
The most convenient methods of slope stability analysis rely on limit equilibrium solutions which assume a pre-determined slide plane geometry and rigid body deformation. However, many, particularly very large landslides are composed of many individual blocks that may be toppling, rolling or otherwise moving downslope in a manner inconsistent with the above assumptions. Example results of discrete body deformation modeling will be used to show that in such cases the traditional limit equilibrium methods would lead to erroneous and possible very unconservative conclusions.
2014 SR 530 LANDSLIDE (OSO, WASHINGTON, USA) - A MECHANISTIC INTERPRETATION OF INITIATION AND MOVEMENT
by Timothy D. Stark, Ph.D. and Oldrich Hungr, Ph.D., Wednesday, April 15, 2015
This presentation will focus on current research regarding the March 22, 2014 SR530 Landslide in Washington, USA. This major, tragic landslide exhibited some particular aspects of geo-mechanical behavior. Its detailed study by several groups of specialists will contribute to better understanding of landslide mechanisms and to improved methods of hazard and risk assessment. The on-going research is focused on landslide triggering and runout of the slide mass. In particular, Professor Stark will focus on the field and laboratory investigations, slope stability analyses, and triggering aspects of the landslide and Professor Hungr will focus on the runout mechanism and distance.
by Tuna Onur, Ph.D., Wednesday March 25, 2015
There are broadly two questions that need to be answered in order to understand the potential for earthquake shaking regionally or at a specific site: 1) Where and how frequently do various types and magnitudes of earthquakes happen? (Seismic Source Characterization), and 2) When these earthquakes happen, how much does the ground shake in locations of interest? (Ground Motion Characterization). PSHA provides a quantitative solution to the problem of evaluating earthquake shaking potential by integrating across these two components (seismic sources and ground motion) in a probabilistic framework. It currently forms the basis for seismic provisions in most structural design codes, when conducted regionally; and underpins site-specific design ground motions for critical facilities at long return periods. This presentation will describe the overall PSHA methodology and its basic components, and provide examples of its utilization, both in a regional and site-specific manner.
FAILURE AND POST-FAILURE ANALYSIS OF SUBMARINE MASS MOVEMENT - THE GEOLOGICAL ENGINEERING 2015 DISTINGUISHED LECTURE
by Professor Jacques Locat, Wednesday March 11, 2015
Multibeam sonar and seismic (2D and 3D) surveys provide excellent tools to ascertain the morphology of the sea floor. By investigating the morphology of the starting zone and of the depositional zone one can use that information for estimating various parameters needed for both failure and post-failure analysis. In many cases, the required reduction in shear strength is linked either to the effects of earthquake, gas hydrates or pore pressures with a strong influence of layering. In order to provide a rationale for estimating the magnitude of these triggering mechanism, one must make sure that the consolidation state of the sediment before failure is evaluated in order to carry a relevant back analysis. However, geotechnical cores are not always available and one must extract as much information as possible from geomorphologic and lithological data. For example, this may involve reading the morphology of the failure zone and relating it to slope forming processes. It may also imply distinguishing between slopes formed by sedimentation from those generated by erosion. Similarly, a geomorphological approach can also be used to estimate the yield strength mobilized for observed debris flow deposits, and the run out morpho-stratigraphic characteristics of that mass flow deposit can also be used to evaluate the tsunamigenic potential of the original slide! This approach will be illustrated and discussed in the light of recent studies carried on mass movements in various marine environments in North America and in Europe.
by Dr. Joseph Wartman, P.E., Thursday, February 19, 2015
The Oso Landslide occurred on the morning of Saturday, 22 March 2014, and claimed the lives of 43 people, making it the deadliest landslide disaster in the history of the continental United States. The landslide initiated within an approximately 200-m-high hillslope comprised of unconsolidated glacial and colluvial deposits; it rapidly transitioned to a debris flow/debris avalanche that rapidly inundated a neighborhood of approximately 35 single-family residences. An intense 3-week rainfall that immediately preceded the event is believed to have played a major role in triggering the landslide. In this talk, I will present the findings of our Geotechnical Extreme Events Reconnaissance (GEER) Association scientific research team that performed a field reconnaissance of the Oso Landslide shortly after its occurrence. The talk will focus on observations made and data collected at the landslide site, but will additionally review regional and local geologic conditions, climate setting, eyewitness accounts, and land-use history. In addition, newly published findings and current debates on the landslide will be discussed.
Tuesday, February 3, 2015 from 1730 to 2100; Registration is limited to 100 participants with a deadline of January 23.
Dr. Peter M. Byrne was the 2014 recipient of the Canadian Geotechnical Society’s R.F. Legget Medal; the society’s most prestigious award. The award was given at the CGS annual conference in Regina in November. However, Dr. Byrne was unable to attend the ceremony. In light of Dr. Byrne’s significant contributions to local geotechnical practice, the Vancouver Geotechnical Society is holding this dinner in honour of Dr. Byrne and to present him with the award in person.
The agenda for the evening includes the award presentation and dinner with five short technical presentations by Dr. Byrne’s former graduate students.
A two-day workshop by Mr. Mike Jefferies and Dr. Dawn Shuttle, Friday & Saturday, January 16 & 17, 2015
The aim of this workshop is for all attendees to become confident in using CSSM across a spectrum of applications from assessing laboratory data through to developing design parameters. Confidence will be achieved by minimizing presentations in favour of participants being guided through developing their own spreadsheets to model soil behaviour – an approach insisted on three decades ago by Peter Wroth as the only way to grasp CSSM and still valid today. Once working spreadsheets have been created, participants will be guided through calibration of soil properties and onto modelling sample disturbance.
Laboratory data will be provided on Fraser River sand for use by workshop participants, but participants are encouraged to bring their own triaxial data (test requirements will be circulated to registered participants before the workshop). This workshop can be viewed as a further step from the May 2014 VGS short course by Professor Malcolm Bolton, and will focus on “how” rather than extended lectures about “what”. The models developed in the course will start with Original Cam Clay (the initial theoretical model) discussed by Professor Bolton, and then move on to NorSand (which works with real soils).
OFFSHORE FOUNDATION SYSTEMS - ROLE OF GEOTECHNICAL CENTRIFUGE MODELING - 2014 FALL CROSS CANADA LECTURE TOUR
by Ryan Phillips, Ph.D., P.Eng., FEIC, Thursday November 27, 2014 -- CANCELED DUE TO FLIGHT DELAY
A video of the same presentation can be downloaded here.
Offshore geotechnical engineering needs physical measurements to calibrate designs. Centrifuge modelling is increasingly accepted by industry to provide such a data source. An overview of centrifuge scaling principles and limitations will be presented. Several actual applications will be described, including jacket pile foundations, suction caissons, riser-seabed interaction and pipeline design against ice gouging. The results provided important insight into prototype behaviour and agree well with available full scale measurements.
by Dr. Mason Ghafghazi, P.Eng., Wednesday, November 12, 2014
Characterisation of cohesionless soils is of interest to a number of geotechnical problems, including liquefaction potential assessment. In gravelly soils found in most alluvial deposits, performance of conventional methods such as SPT and CPT are adversely affected by the presence of larger particles. The Becker Penetration Test (BPT) is a widely used tool for characterisation of gravelly soils in North America. The test is performed by driving a closed ended pile into the ground and reporting the number of blows per foot of penetration after correcting for the hammer energy. Interpretation of data obtained using the conventional BPT system to estimate soil properties below the driving shoe has significant challenges. The main source of the difficulty is that a large percentage of the energy delivered by the hammer is absorbed by the frictional resistance developed along the pile shaft. The instrumented Becker Penetrometer (iBPT) bypasses the shaft resistance issue by directly measuring the energy transferred from the driving shoe to the underlying soil.
The presentation slides are available here.
by Dr. P.K. Robertson, P.Eng., Tuesday, October 7, 2014
Evaluating the potential for soil liquefaction and the resulting consequences is often a major design issue for many geotechnical projects in seismic areas. This presentation will provide some brief background on the available methods and present examples to illustrate some key points. Practical issues that influence the results will be discussed and presented.
The presentation slides are available here.
by Tuna Onur, Ph.D., Thursday, September 18, 2014
Southwestern BC is situated in the Cascadia Subduction Zone and can be impacted by three distinct types of earthquakes: Deep earthquakes in the subducting Juan de Fuca Plate, shallow crustal earthquakes in the overriding North America Plate and giant earthquakes (Mw~9.0) at the interface of the two plates. Probabilistic seismic hazard assessments that form the basis of design ground motions in Canada take into account all these sources of seismic activity to produce a uniform hazard spectrum (UHS). After a brief overview of earthquakes in southwestern BC and calculation of design ground motions, this presentation focuses on various approaches to selecting and modifying time-histories to be compatible with the UHS. Related issues that are discussed include de-aggregation of hazard, use of artificial versus real records, sources of processed and unprocessed strong motion recordings that are appropriate for the tectonic setting in southwestern BC, and time-domain, frequency-domain and hybrid methods for scaling and modifying time-histories.
The presentation slides are available here.
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.
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.
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
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.
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.
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.
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.
by Dr. James McCalpin, Wednesday, May 8, 2013
Paleoseismology arose as a new field of study from nuclear power plant studies in the USA in the late 1960s. This talk covers the “invention” of paleoseismic trenching; the slow acceptance of paleoseismology by seismologists; the role it now plays in Seismic Hazard Assessment; and how paleoseismology can help reduce worldwide earthquake deaths, which have risen since the 1970s. The talk is based on my 35 years experience in paleoseismology, starting with USGS in Menlo Park and my first paleoseismic trench in 1977, through about a zillion trenches in the USA and many countries overseas, and several high-profile Seismic Hazard Analyses (Yucca Mountain, Los Alamos, South Africa.
Case Studies in Soil Parameter Selections for Clay Foundations - 2013 Spring Cross Canada Lecture Tour
by Bob Cameron, P.Eng., Thursday, April 18, 2013
The methodology developed over 29 years to pick design shear strength and pore pressure parameters for up to 6 different clays will be presented. Anyone who designs large foundations on clay knows it is often not easy to select soil design parameters. The case studies of failures and successes will show examples of how the same clay can have multiple pore water pressure design parameters depending on the whether loaded, or unloaded, and everything in-between. Field measured deformations and pore water pressures for two dump embankment foundations, two dam foundations, two failed slopes, two retaining walls and a mine pit wall will be discussed. It will be shown that one shear strength estimate and one pore water pressure selection for the same clay within even the same design, is not adequate for many of the case studies. Some of the clays noted have high shear strengths across bedding, but very low sliding shear strengths along bedding and weak planes. Trials and tribulations with peak and residual shear strength laboratory testing, total and effective stress considerations and field pore water pressure data will be discussed and shown to provide some very useful, but often misleading or misinterpreted input parameters, unless properly interrogated. Surprisingly, all the clays to be discussed, that act differently and also differ within themselves under different conditions, are all located in the same area.
How to try to reduce a 3 m^3/sec leakage in a 100 meter high natural dam using the Jet-Grouting Technology
by Paolo Gazzarrini, P.Eng., Thursday, March 14, 2013
The Zeballos Lake Hydroelectric project is an IPP "lake-tap" project on the West Coast of Vancouver Island. Since the power plant opened two years ago, the production of energy has been affected by important leakages in the natural dam that formed the lake more than 300 years ago. The water leakages didn't permit the utilization of the turbines at their maximum capacity resulting in a significant loss of revenue for the Owner. In September 2011 the Owner decided to carry out a grouting program to try to reduce the underground flow of water that was evaluated in the order of 2 to 3 m^3 per second.
This presentation will describe the problem, the possible solutions available, the solution adopted (atypical Jet Grouting), the logistical difficulties encountered, the instrumentation installed, the tests done on site, the results and the lessons learned in a very challenging grouting project, both from technical and logistic aspects.
Lessons learned from full-scale measurements of soil-structure interaction for
municipal infrastructure repair and renewal
by Dr. Richard Brachman, P.Eng., Wednesday, February 6, 2013
The Soil-structure interactions dominate an interesting class of geotechnical problems where the soil provides both loading to and support for the buried structure. Three examples are presented where full-scale physical experiments have been used to: quantify the three-dimensional ground displacements induced by a trenchless pipe installation technique called pipe bursting; evaluate the ultimate limit state of 10-m-span, deep-corrugated metal box culvert; and assess the long-term performance of buried polymer structures. With a practical focus on the measured soil and structure behaviour, the talk illustrates the useful role of carefully conducted full-scale experiments to resolve important buried municipal infrastructure issues.
Temporary Tower Foundations for the New San Francisco-Oakland Bay Bridge Self-Anchored Suspension Span
by Alex Sy, P.Eng., Tuesday, January 22, 2013
The new east span of the San Francisco-Oakland Bay Bridge, currently under construction, will become the world’s largest self-anchored suspension bridge when completed in 2013. This signature span, with its unique asymmetrical design, has a single main tower and one continuous main suspension cable anchored to the deck. During construction, temporary towers and trusses are needed to support the bridge deck consisting of box girders, until suspension cables are erected and the deck load is transferred to the suspension cables. The foundation condition varies from sedimentary bedrock outcrop with steep slopes at the west end of the span on Yerba Buena Island to deep, thick, soft marine sediments (Bay Mud) overlying bedrock at the east end in the Bay. The foundations for the temporary towers consist of micro piles, rock socketed drilled shafts, and large diameter steel pipe piles driven into bedrock and into deep marine sediments. This presentation will describe the challenges faced during the design and construction of the tower foundations, including pile relaxation during pile driving into sedimentary rock and pile set up for piles installed into the Bay Mud. Construction of the temporary foundations and towers began in 2008, placement of the box girders and construction of the permanent main tower occurred in 2010-2011, erection of the suspension cables and load transfer were completed by late 2012, and the bridge is scheduled to open to traffic in September 2013.
by David Siu, P.Eng., Tuesday, December 11, 2012
The John Hart Dam is located 9 km west of the town of Campbell River. It was constructed between 1946 and 1947. The main components of the John Hart Development consist of the Intake Structure, the North, Middle and South Earthfill Dams and the Concrete Main Dam. In 2010, BC Hydro decided to improve the seepage cutoff of the North Earthfill Dam by adding a backup seepage cutoff wall. In order to minimize the impacts on the operation of the John Hart Powerhouse and the drinking water supply to the City of Campbell River, construction must be carried out without reservoir drawdown.
This presentation focuses on the ECI process, the cement/bentonite grout mix design, various components of the field trial such as the jet grout methodology, instrumentation response during jet grouting, unexpected issues, verification testing etc., risk management measures during construction and lessons learned.
Influence of Ex-Solved Gases on Slope Performance at the Sarnia Approach Cut to the St. Clair Tunnel
by Paul Dittirch, P.Eng., Tuesday, November 20, 2012
In 1993, over 100 years after completion of the original St. Clair Tunnel and its approach cuts, work commenced on the new St. Clair Tunnel. The new tunnel used the existing approaches but required additional excavation to widen and deepen the original cuts. In Sarnia, the new work initiated unusual deep-seated deformations on the south slope of the approach. Effective stress finite element analysis (FEA) utilizing an elliptical cap soil model coupled with Biot consolidation theory is used to model the 1993 construction but initial predictions are unable to capture the trend of deformations noted in the field. Naturally occurring gases are frequently encountered near the base of the overburden in the Sarnia area and this phenomenon was observed during drilling investigations in the Sarnia approach cut. Including the effects of the presence of ex-solved natural gases in fine grained soils subjected to unloading in the FEA results in substantially better predictions in the trend of deformations on the slopes of the approach cut.
Flaws in the NCEER liquefaction assessment method and how to fix them - 2012 Fall Cross Canada Lecture Tour
by Mike Jefferies, P.Eng., Monday, October 29, 2012
"Understanding Liquefaction Through Applied Mechanics"; Mike Jefferies and Dawn Shuttle
Soil liquefaction is conventionally evaluated through an empirical framework based on accumulated experience from case histories - the "NCEER Method". An incorrect view has developed that because the NCEER method is based on case histories, then it must be correct. The reality is that the NCEER framework contains inconsistent physics and characterizations that are unrelated to modern understanding of soil behavior – the NCEER method can mislead, and is particularly misleading in the case of postliquefaction
This talk will present soil liquefaction (both cyclic mobility and static) within the context of a modern constitutive model, NorSand, to illustrate a proper approach to evaluating the effect of soil type ('fines content'), stress level and initial stress state on liquefaction. A Page 2 of 2 two-pronged approach is used with soil state in situ being inferred from the CPT, while the cyclic strength-state relationship is computed using measurable, standard, soil properties (compressibility, etc.). Computed liquefaction resistances are consistent with the case history record, but the approach now offers understanding as to how that case history experience should be extrapolated to other situations.
by Tim Little, P.Eng., Wednesday, September 12, 2012
British Columbia is situated in one of the more tectonically-complex regions of the world, with both a tectonic plate boundary and a subduction zone along the west coast and a diverse range of geological terranes inland from the coast. This setting has produced some very large magnitude earthquakes over the last few hundred years, although most of the major populated regions have not experienced strong seismic shaking in the last several decades. Scientific investigations have greatly advanced our understanding of the seismotectonics of BC and adjacent regions over the last several decades, but knowledge of the seismic potential and capability of many individual tectonic and geologic features remains incomplete. Given this situation, seismic hazard analyses, which are an important element of design for engineering projects in BC, must deal with large uncertainties and have proven to be challenging. This presentation will look back over the evolution of seismic hazard analyses in BC over the last several decades and how those uncertainties have been addressed. Several recently-applied innovative approaches to modelling uncertainties and opportunities for future research will be highlighted. Some comments will also be offered about key factors and potential pitfalls that should be considered prior to embarking on a seismic hazard analysis.
by Don J. DeGroot, P.E., Thursday, June 28, 2012
This presentation gives recommendations for conducting geotechnical site characterizations to obtain design parameters for settlement and stability analyses. It focuses on relatively uniform, saturated terrestrial cohesive soil deposits with near zero Standard Penetration Test blow counts and soft ground conditions, which means that construction will load the foundation soil beyond its preconsolidation stress. The site characterization program should select an appropriate combination of in situ tests for soil profiling (identify soil types and their relative state) and laboratory tests on undisturbed samples for strength-deformation-flow properties. Although the tools, procedures, and interpretation methods needed to conduct a reliable site characterization program are well developed, general practice often ignores this knowledge. Thus a prime objective of the paper is to provide recommendations for moving practice closer to the state of the art. Components of site characterization covered include site stratigraphy, drilling and undisturbed sampling, in situ testing, and laboratory consolidation and strength testing. Key recommendations include: fixed piston sampling using drilling mud and tubes with an appropriate geometry, piezocone testing for determination of site stratigraphy, radiography of sample tubes, debonding of samples from tubes, evaluation of sample quality, CRS testing to measure consolidation behavior, and anisotropic or K0 consolidated strength tests to measure undrained shear strength behavior.
Can we successfully reclaim Oil Sands Mine Closure Landforms? - 2012 Spring Cross Canada Lecture Tour
by S. Lee Barbour, April 26, 2012
The goal of reclamation at oil sands mines in Northern Alberta is the reconstruction of landforms following mining, which have an equivalent capability to those present prior to mining. This reclamation is occurring at unprecedented scales over extremely challenging parent materials. Syncrude, for example, has reclaimed nearly 3500 ha (2011) of disturbed land since 1978, approximately 17% of a total disturbance area of 20,000 ha. These reconstructed profiles have been placed over a range of parent materials comprised of saline/sodic overburden, sand and fine tailings, as well as refining by-products such as coke. The goal of these reconstructed profiles is to accelerate the development of soil profiles through the placement of an organic rich ‘A’ horizon of peat/mineral mix overlying a ‘B’ horizon of salvaged glacial lacustrine clay or till. It is anticipated that these reconstructed soil profiles and the associated ecosite characteristics (particularly available water, soil chemistry and nutrients) will then evolve along a trajectory towards that of comparable natural profiles.
This presentation will highlight the performance of several reconstructed soil profiles over different parent materials including saline-sodic shale, sand tailings and a refiner by-product, coke. Of particular interest will be the evolution of the hydraulic properties, the controls on water and salt transport within these cover profiles and the dynamic nature of the water balance over time. The evolution of shale chemistry due to pyrite oxidation and its impact on the reconstructed soil profile will also be highlighted. The research highlights the relatively long time frames that are required to demonstrate the trajectory and maturation of these reclamation cover profiles; decades (10s of years) for physical changes and water dynamics and longer (50-100 years) for chemical weathering and the re-establishment of upland forests.
by David J. Tara, P.Eng., Tuesday, March 6, 2012
The Pitt River Bridge is part of the Gateway Program, a long-term initiative to improve roads and bridges throughout Greater Vancouver. The project is a stand-alone component of the North Fraser Perimeter Road Project. The bridge is designed to accommodate different lane allocations and to allow for one lane to be added in the future. This additional lane could meet future demand for vehicle use (HOV, buses, and/ or other vehicles) or Light Rail Rapid Transit.
To validate the foundation design for the main piers of the new Pitt River Bridge, a conventional, head down, static pile loading test was carried out using production piles for both the test and reaction piles to minimize costs. The piles comprised driven 1824 mm diameter, open-toe, steel pipe. The 45 MN loading test was completed successfully in December 2007 by Peter Kiewit Sons. Design of the piles was based on information provided by the owner to the DB proponents and included results of test holes and static pile loading tests conducted in the 1970s on 36 and 55 m long, open toe steel pipe piles, CPT and SCPT profiling conducted in the 1990s and mid 2000s, and dynamic load tests (DLTs) conducted on an 100 m long, 1067 mm diameter, open toe indicator pile installed in 2005. Test pile installation records and Pile Driving Analysis (PDA) records and signal matching analyses for the 2005 test pile were used to calibrate the design and confirm pile installation requirements. Supplementary test holes, CPTs and SCPTs were conducted to over 100 m depth to calibrate pile resistance, particularly the pile toe resistance. DLTs were also conducted on several of the production piles to validate the design. This presentation is based on a upcoming paper and will present key aspects of the pile design and test loading.
by Kenneth H. Stoke (II), Thursday, February 2, 2012
Geotechnical engineers are continually faced with the problem of characterizing soil and rock materials and systems in the field. Over the past 45 years, seismic (stress wave) measurements have been employed at an ever increasing rate to an increasing diversity of applications. This measurement technique was originally adapted from exploration geophysics and was originally used in soil dynamics and geotechnical earthquake engineering. However, today geotechnical engineers are employing seismic measurements in a wide range of both static and dynamic applications. In this presentation, a brief background on seismic measurements in the field as well as in the laboratory is presented. A number of example applications are presented, ranging from investigations of a tunnel, an earth dam, hard-to-sample soils such as gravels and cemented alluvium, and deeper profiling (> 100 m) in soil and rock. Recent advances in field measurements of nonlinear shear modulus and soil liquefaction are also briefly presented.
by Bengt Fellenius, P.Eng., Tuesday, January 17, 2012
Vietnam is integrating into the world economy at an increasing rate, causing a rapid growth in the urban population with significant rural to urban migration. The development has brought enormous challenges to the society not least in creating the infrastructure to meet the increased transportation and trade demands. The Vietnam geology is characterized by vast areas with thick deposits of soft, deltaic soil, numerous rivers and streams, and frequent floods, where new highways, bridges, and ports are now being constructed. In early 2009, construction started for the Cai Mep Port, a new container terminal in the Mekong delta approximately 80 km southeast of Ho Chi Minh City. The site comprises about 35 m of very soft clay over sand. The mean water table lies at the ground surface, but it will seasonally be well above the ground. Construction requires raising the area by several meters and placing all structures on piled foundations.
The lecture will present the soil conditions, the original design of the wick drain site improvement, the measurements, aspects of the piling including results of static and dynamic tests, back-analysis of the observations, propose explanation of why the settlements continue, predict the magnitude of future settlement to occur at the site, and present the remedial measures undertaken.
by (Uthaya) M. Uthayakumar, P.Eng., Tuesday, November 29, 2011
The new five-lane William R. Bennett Bridge across the Okanagan Lake was constructed under a Design-Build-Finance and Operate contract and opened to traffic in May 2008. Subsurface soils along the bridge alignment include very soft to soft silts and clays and loose to compact sands. Key components of this new crossing include the light-weight fill west approach embankment; the west abutment and five piers supporting the fixed section of the bridge; a transition span; the floating section of the bridge supported on pontoons; the east transition span; the east abutment; and the east approach embankment. The west abutment, the five piers and the east abutment are supported on driven, 610mm and 914mm diameter steel pipe piles with embedment depths of 30m to 50m. This presentation will include description of the bridge and site conditions, an overview of the subsurface soil conditions, geotechnical design and analyses, construction of the bridge and approach embankments and post-construction monitoring of embankments and foundations.
The Science of Judgment - 2011 Fall Cross Canada Lecture Tour
by Steven J. Vick, P.E., Thursday, November 3, 2011
Since Ralph Peck asked in 1980 where judgment had gone, there has been little sign of its return, and engineering judgment is privately viewed in some circles as a metaphysics for the elderly or the analytically inept. This lecture seeks to revive the concept of engineering judgment by elaborating its principles and establishing its foundations in cognitive and behavioural research.
Inseparable from judgment then is the notion of probability, and the relation between the two has much to say about judgment’s cognitive basis. Within this framework, the lecture will develop a number of topics in a geotechnical context. For many, this framework will provide a new perspective on judgment. It does not merely assert, it establishes why judgment is a necessary component of all engineering problem solving, far from the nebulous accessory it has often been taken to be.
Investigation and Retrofit of the Roger Pierlet Bridge damaged by Failure of Adjacent Soil Stockpile
by Alex Sy, P.Eng., Thursday, September 15, 2011
The Roger Pierlet Railway Overpass in Cloverdale, built in 1975, was damaged in November 2004 by foundation soil movement caused by failure of a large soil stockpile placed adjacent to the bridge. The concrete bridge is supported on very long precast concrete piles driven through soft marine clay to toe bearing in very dense till-like soils. The soil failure displaced the pile-supported bridge piers by as much as 425 mm horizontally. Substantial cracking of pier columns, foundation tie beams, and piles resulted. Shortly after the damage was discovered, temporary support towers were erected to provide support for the bridge decks and to allow traffic to safely continue on the bridge. Permanent retrofit of the bridge included strengthening of columns and beam/column joints, extension of existing pile caps, and addition of steel pipe piles to replace the damaged concrete piles. This presentation will describe details of the damage, subsequent ground investigations, and the temporary and permanent retrofits of the bridge and its foundations.