Paleoseismology; Has it Reduced Seismic Hazards, and if not, How Do We Change Course?

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.

A Case History – John Hart North Earthfill Dam Jet Grout Wall Construction

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
strength.

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.

Seismic Hazard Analysis in British Columbia: Where Have We Been? Where Are We Headed?

by Tim Little, P.Eng., Wednesday, September 12, 2012

Links to presentation slides & seismic references.

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.