Site characterization for cohesive soil deposits using combined in situ and laboratory

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.

Some Geotechnical Aspects of the Pitt River Bridge 2007 Static Pile Loading Test

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.

The increasing role of seismic measurements in geotechnical engineering

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.

Wick Drains and Piling for Cai Mep Container Port, Vietnam

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.

Geotechnical Design and Construction of the William R. Bennett Bridge, Kelowna,

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.