Geotechnical Engineering State of the Art and Practice: Keynote Lectures from GeoCongress 2012

This paper describes key steps in the design process for water balance covers using a case history at a municipal solid waste landfill in Missoula, Montana, USA as an example. The intent is to illustrate how state-of-the-art concepts can be applied in the state-of-the-practice. The process begins by understanding the design objective (including regulatory requirements) and investigating lines of evidence indicating that a water balance cover is likely to function satisfactorily at the design location. Data from two other instrumented water balance covers in the region are used to evaluate efficacy along with historical meteorological data and information contained in a prior unsuccessful submittal for a water balance cover at the Missoula landfill. Site characterization is conducted to define properties of the soil resources and vegetation at the site for preliminary cover sizing and numerical modeling of the water balance. A numerical model is used with various design metrological conditions as input to evaluate whether the cover will meet the design goal under realistic conditions. The final design consists of a monolithic cover comprised of a 1.22-m storage layer overlain by a 0.15-m topsoil layer. A field test with a fully instrumented lysimeter was constructed and monitored to confirm that the cover performs as anticipated in the design.

Soils and rocks typically exhibit strongly nonlinear, inelastic load-deformation behavior. Capturing their mechanical response in numerical simulations requires elaborate constitutive models and robust numerical algorithms. Computational plasticity strives to strike a balance between complexity of the constitutive model and feasibility of numerical implementation. In this paper, we describe the applications of computational plasticity to four classes of problems in geotechnical engineering: (a) multiscale problems including bridging of different scales; (b) nonlinear contact mechanics; (c) multiphysics and multifield problems; and (d) seismic response of geotechnical structures.

Column-supported embankments (CSEs) can reduce settlements, improve stability, and prevent damage to adjacent facilities when embankments are constructed on ground that would otherwise be too weak or compressible to support the new load. Geosynthetic reinforcement is often used to help transfer the embankment loads to the columns in CSEs. This paper addresses three important design issues for CSEs: (1) the critical height above which differential settlements at the base of the embankment do not produce measurable differential settlements at the embankment surface, (2) the net vertical load on the geosynthetic reinforcement in the load transfer platform at the base of the embankment, and (3) the tension that develops in the geosynthetic reinforcement. Based on bench-scale tests, field-scale tests, and case history data, the critical height was found to be a linear function of the column spacing and the column diameter. The net vertical load that acts down on the geosynthetic reinforcement can be determined using the load-displacement compatibility method, including determination of the limiting stress distribution at the base of the embankment by a generalized form of the Adapted Terzaghi Method, which accommodates any column or pile cap shape, any repetitive column arrangement, and different soil types in the load transfer platform and the overlying embankment fill. The tension in the geosynthetic can be calculated using a generalized form of the parabolic method, which incorporates stress-strain compatibility and which accommodates rectangular and triangular column arrangements and biaxial and radially isotropic geogrids.

The paper will review the state-of-the-art in the use of finite element methods for modeling geotechnical engineering problems involving non-typical geometries and highly variable soil properties. Examples will focus on slope stability analyses in which traditional limit equilibrium methods, and even well-established probabilistic methodologies may lead to misleading results.

Basic concepts in the transition from allowable stress design (ASD) to reliability-based design (RBD) are reviewed. Critical issues related to RBD are noted, including their strengths and weaknesses. It is stressed that current simplified RBD methods need to be improved and expanded. Recommendations then are made for improving factor calibrations, addressing serviceability and economic limit states, and optimizing the foundation design process.

Assessing the stability of slopes is a difficult task that requires a rigorous approach. This paper starts by presenting a geotechnical characterization of slope movements that helps in classifying the information related to slopes. The paper then shows the tremendous progresses that have recently been made for monitoring slopes, understanding slope behavior, and for numerically simulating coupled hydro-mechanical problems in saturated/unsaturated soils. A methodology for assessing the stability of slopes is presented. It includes qualitative and quantitative approaches and, separately, the characterization of the post-failure stage. Finally, there is some discussion on the use of factor of safety, use of numerical models and consideration of risk.

Due to the inherent complexities of natural soil materials, a thorough geotechnical site investigation program requires an integrated testing program of geophysics, rotary drilled borings with sampling, in-situ measurements, and various laboratory test series in order to provide ample information for design and analysis. This is only possible on large projects or situations where critical structures receive sufficient funding. For routine site exploration, realistic limitations in cost and time would dictate that the seismic piezocone test (SCPTù) and seismic flat dilatometer test (SDMTà) with dissipation phases be adopted in practice since as many as five separate measurements are obtained in an economical, continuous, and expedient manner from a single sounding. The collection of multiple readings is necessary to provide adequate information on geomaterials for rational engineering evaluations.

This paper provides one person's perspective on flexible pavement analysis and design methodology since about 1960. Some developments during the past 50-plus years briefly summarized include: mechanistic analyses; materials characterization; mechanistic-empirical (M-E) pavement design methodologies; accelerated pavement testing; non-destructive pavement evaluation and overlay design; pavement management; and, improved construction practices. Some observations on education and training in pavement engineering are also included.

Surface wave method was introduced as a tool to the geotechnical and infrastructure engineering fields in the early 1980's. Since then, the method has been continuously modified and improved. The adoption of the method has accelerated in the last ten years because of the interest of the engineering community, and due to the development of affordable and portable hardware and software. Despite numerous studies that demonstrate its effectiveness in a wide spectrum of applications, the method has not been fully embraced by the engineering community mainly due to lack of standardization. The common attributes of different approaches in implementing the surface method from the point of view of the engineering applications are discussed, followed by the practical and theoretical strengths and limitations of alternative approaches. Different approaches should provide satisfactory results as long as the inherent limitations of each approach are matched with the requirements of the engineering objectives of a given project.

In principle, design 'practice' is represented by gradually evolving national and international design guidelines. In reality, most designs rely on more sophisticated analysis techniques and principles, informed by recent research publications that may take several years to be reflected in industry guidelines. This may be considered as 'art'. The more rapidly a sector of industry is developing, the wider will be the gap between practice (as represented by design guidelines) and art. In the offshore industry, the most rapidly changing sector is the move to increasingly deep water, with new developments now in water depths exceeding 2 km. In those conditions, the seabed typically comprises relatively soft fine-grained material, with very slow sedimentation rates. The challenges to be discussed in this state-of-the-art paper include characterizing the shear strength and other engineering properties of the sediments, and design approaches for a range of deepwater infrastructure including different forms of anchoring systems, shallow mat foundations, pipelines, flowlines and riser systems. Particular focus in the paper is on secondary characteristics of the seabed sediments that reflect effects of loading (or strain) rate and disturbance (or remolding) on the response of the infrastructure in question.

There exist a large number of ground improvement methods that can be employed to overcome poor soil site conditions, some in use many decades, others recently developed. The growth in ground improvement methods, products, systems, and engineering tools has been tremendous, resulting in a very large body of knowledge. The selection of the most appropriate ground improvement technology is a complex undertaking that depends upon integration of available knowledge and a number problem-specific and site-specific factors. These factors are summarized and discussed in relation to the essential elements for success of a ground improvement project. A new comprehensive, web-based ground improvement information and guidance system, developed to summarize and organize this knowledge to facilitate informed decisions, is introduced and illustrated. The system can be used for engineering and construction practice that incorporates these essential elements.

After more than half a century of increasing neglect, the nation's flood defenses are currently rated by the ASCE as having the very lowest levels of adequacy and reliability among all types of critical U.S. infrastructure, receiving a letter grade of straight "F" on the ASCE's Annual Infrastructure Report Card for the nation. Accordingly, the U.S. now finds itself at a crossroads in the wake of the recent catastrophic flooding of New Orleans by Hurricane Katrina, and the spate of other significant flood events of recent years. There is much to be learned from these recent events, and that learning opportunity has been seized upon at both the national and more local (State and regional) levels; and some promising changes have been initiated. This paper discusses key lessons learned from the Hurricane Katrina experience, and other recent flood disasters, and then presents a discussion of ongoing efforts to implement these lessons in effecting positive changes and improvements in U.S. flood protection practice.

The evolution of the methodology for the evaluation of seismic earth pressures on retaining structures and basement walls is reviewed together with observations of field performance. The case history data and data from recent experimental work are used to show that the currently used methods are quite conservative and lead to excessively conservative designs in regions where design PGA exceeds 0.4g. Specifically, the experimental data from seismic centrifuge tests shows that the seismic earth pressure distribution for moderate size retaining structures, on the order of 6-7 m high, is triangular, increasing with depth. Moreover, there is no significant increase in seismic earth pressure between unbraced and braced structures with fixed base, while the loads on free standing cantilever structures are substantially lower owing to their ability to translate and rotate. The significance of the observed seismic earth pressure distributions is that the dynamic force can be applied at 1/3H, as is done for static loading, which substantially decreases the design level seismic moments on the structures.

Site factors are used to modify ground motions from a reference rock site condition to reflect the influence of geologic conditions at the site of interest. Site factors typically have a small-strain (linear) site amplification that captures impedance and resonance effects coupled with nonlinear components. Site factors in current NEHRP Provisions are empirically-derived at relatively small ground motion levels and feature simulation-based nonlinearity. We show that NEHRP factors have discrepancies with respect to the site terms in the Next Generation Attenuation (NGA) ground motion prediction equations, both in the linear site amplification (especially for Classes B, C, D, and E) and the degree of nonlinearity (Classes C and D). The misfits are towards larger linear site factors and stronger nonlinearity in the NEHRP factors. The differences in linear site factors result largely from their normalization to a reference average shear wave velocity in the upper 30 m of about 1050 m/s, whereas the reference velocity for current application is 760 m/s. We show that the levels of nonlinearity in the NEHRP factors are generally stronger than recent simulation-based models as well as empirically-based models.

This paper deals with tunneling in squeezing conditions, and highlights different ways proposed to successfully drive a tunnel in such difficult conditions.

Even though geosynthetics are now a well-established discipline within geotechnical engineering, ingenuity continues to be significant in projects involving their use. This is probably because of the ability to tailor the mechanical and hydraulic properties of geosynthetics in a controlled manner to address design needs in all areas of geotechnical engineering. This paper focuses on specific advances involving the use of geosynthetics in a wide range of geotechnical projects. Specifically, this paper addresses the creative use of geosynthetics in the design of earth dams, resistive barriers, unsaturated barriers, veneer slopes, coastal protection systems, foundations, bridge abutments, retaining walls, embankments, and pavements.

With increased manufacturing and industrial prowess following World War II, the United States entered into a period of unprecedented economic growth and advancement of the quality of life for its citizens. Nevertheless, as had occurred before in Western Europe, and is now occurring in the developing world, economic expansion and industrialization outpaced advances with respect to environmental stewardship. As a result, the environment was significantly impacted - often in the form of vivid, high-visibility events and disasters, but far more often with little notice or directly observable side effects on the subsurface environment. Regardless, in all of these cases, the cumulative effect was enormous and presented a very real threat to the gains made in quality of life in the preceding years. This state-of-the-practice paper presents a chronology of the effects of over 60 years of rapid industrialization, economic expansion, the detrimental effects to the environment, and the resulting reactions from private citizens, the corporate sector, and local, state, and federal government. An overview of the evolving regulatory framework as well as site characterization and remediation technologies used in practice is presented. Finally, the emerging holistic approaches and technologies to achieve green and sustainable remediation of contaminated sites are discussed. Many challenges and opportunities still exist for the development of efficient, reliable, simple and cost effective technologies to characterize and remediate numerous contaminated sites.

The state of the practice of MSE wall design has become more complex as more and more systems, engineers and researchers have become involved in the practice. There are correct ways to design MSE walls, to apply traffic surcharge, to select design parameters and backfill, to assess service life, to address special design conditions such as bridge abutments, traffic barriers and earthquakes, and to select the wall design method itself. Yet the complexity persists, arising from policy changes and a multitude of design choices. This paper will discuss these and other areas of confusion and provide clarification regarding accepted, reliable methods of MSE design that have been proven in the field for more than forty years.

This paper presents the author's perspectives on the state of the industry with respect to U.S. private-sector businesses providing geotechnical and geoenvironmental services to clients. The paper discusses: the history and evolution of the business sector; size and attributes of the sector; business models and practice characteristics of companies in the sector; and operational, management, and personnel priorities and challenges of these firms. The paper also addresses career considerations for personnel in this business sector, and the topics of clients and competition, risk management and contractual liability, mergers and acquisitions, and the author's thoughts on future directions for the business sector over the next 10 to 20 years. Sustained business success is being achieved by both large and small firms practicing geoengineering that can recruit and retain great people, provide superior work deliverables and solutions to their clients, perform their work efficiently and at a reasonable cost, and navigate both the competitive and risk management landscapes. A significant and exciting challenge for the senior management teams of these firms now and in the future is to achieve and integrate excellence in technical practice development, project management performance, personnel development and retention, risk and quality management, financial performance, and equity and ownership management to continually improve their firms and, in so doing, improve the profession.

The construction and design of drilled foundations in recent years has been most significantly affected by developments in drilling techniques related to materials, equipment, and generally improved capabilities in construction. In addition, advancements in technology for testing and QC/QA have resulted in improvements in performance, reliability and design. This paper describes some of the most significant developments affecting drilled foundations, including large diameter drilled shafts, continuous flight auger piles, drilled displacement piles, and small diameter micropiles.

Computer monitoring and specialized equipment in the grouting industry has undergone multiple levels of technological advancement over the past two decades. The implementation of these technologies over recent years has greatly enhanced the industry's ability to more efficiently collect and evaluate pertinent data. This has subsequently resulted in more reliable and sound decision making, an increase in efficiency, and ultimately, cost savings to the owner. Dreese et al. (2003) discussed advances in the grouting industry and defined Levels 1 to 3 Technology for real time monitoring and data collection. Level 3 Technology (Advanced Integrated Analytical Systems) represents the current level of advancement in real-time monitoring of grouting in the industry today. The multitude of technical challenges faced during any grouting project, includes assessing the geologic formation and identifying characteristics most likely to impact the grouting program. This paper documents the progression of the industry in using state of the art technologies to not only collect data and make real-time assessments of the formations response to grout injection, but also the use of high resolution images to evaluate discontinuities with the formation prior to injection, the implementation of digital photogrammetry for assessing outcrops and/or structures in three-dimension, assessment of Monitoring While Drilling (MWD) information and its integration, and real-time monitoring of instrumentation data for evaluating the formations immediate response to grout injection.

The paper presents recommendations for conducting geotechnical site characterizations to obtain design parameters for settlement and stability analyses. It focuses on relatively uniform, saturated 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.

Design of foundations for expansive and collapsible soils is an important challenge facing engineers. The state of the practice in this area has been changing over the past decades. The standard of care and definitions of the state of the practice and the state of the art are discussed, followed by an in-depth treatment of the state of the practice. The authors present what they consider to be the appropriate practice for field investigation techniques, laboratory testing, and foundation design on expansive and collapsible soils. They then discuss the general practice that is being followed and present recommendations for change. The experiences of the two authors represent different viewpoints in some areas. When that is the case both viewpoints are presented and the reader is left to consider each one on its own merits.

The paper describes selected offshore geotechnical practices, from geohazards assessment in the early stages of a project, to the design of shallow and deep foundations, with a focus on deepwater applications and conventional siliceous sediments. The past and current recommendations of API and ISO are summarized and their differences are highlighted. The use of total and effective stress pile design methods is explored and recent developments in the design of piles in sands are discussed. Last, observations and lessons learned from the performance of offshore foundations during hurricanes are presented. In summary, worldwide industry design practices are broadly aligned through the use of API and ISO standards. Nevertheless, unusual or difficult basin-specific soil conditions require modified design approaches and foundation solutions.

This paper examines the state of practice of the design and construction of excavations in soft soils. The review is based primarily on the author's experience, published case histories, and discussions with colleagues involved in the design and construction of excavations in soft soils. It is not a survey of current practices, because such a survey would not be practicable, or even useful, because of many variations in local practices. The paper examines major milestones in the development of the design and construction of excavations in soft soils, and reviews recent developments and trends in design and construction practices. Traditionally, the design and construction of excavations is handled contractually as a design-build contract, with the responsibility for the design and construction of the shoring system delegated to the contractor. However, new developments in analytical design tools and construction methods, as well as wider recognition of the potential legal consequences of the impacts of excavation-induced deformations on existing structures, and the need to address these issues in advance of construction, is leading to new approaches in the design and construction of excavations in general, and for soft soils in particular. Recent innovations in construction methods, such as the introduction of deep-soil mixing and jet grouting, are providing greater flexibility in the design and construction of excavations for deformation control. This paper reviews these developments and summarizes data from case histories to illustrate practical application of these new methodologies and construction techniques for the design and construction of excavations in soft soils.

The notions of risk assessment, risk management, acceptable risk and risk mitigation are addressed, and the State-of-Practice of geo-risk assessment and risk mitigation is exemplified with case studies. The examples illustrate the assessment of hazard, vulnerability and risk, and the treatment (mitigation) of risk under different design situations, including underwater slopes subjected to earthquake hazard, the stability of quick clays, and the potential breach of embankment dams.

The practice of forensic engineering is one of the most interesting and challenging for geotechnical engineers. Geotechnical engineers are naturally drawn to failures as opportunities to increase our judgment by learning how applications of our knowledge may have failed to achieve the intended result. The challenge for many engineers is that these failure studies typically must be done within the context of a legal system where the primary objective is to assign or allocate responsibility for the failure. The adversarial process can be intimidating, especially for engineers not accustomed to the process. Engineers typically work together collaboratively in an atmosphere where they challenge each other to produce the best engineered result. In litigation, collaboration is displaced by criticism of even the most scientifically grounded professional opinions. Forensic engineering must therefore meld the best science of failure analysis to the art of conflict resolution, where the financial consequences of the resolution can be a matter of grave consequence to the responsible party.

This paper sets out the principles of a limit state design approach to design a pile or piled raft foundation system for tall buildings, and involves three sets of analyses: 1. An overall stability analysis in which the resistances of the foundation components are reduced by the appropriate geotechnical reduction factor and the ultimate limit state (ULS) load combinations are applied. 2. A serviceability analysis, in which the best-estimate (unfactored) values foundation resistances and stiffnesses are employed and the serviceability limit state (SLS) loads are applied. 3. An analysis to obtain foundation loads, moments and shears for structural design of the foundation system. The importance of appropriate parameter selection and load testing is emphasized. The approach is illustrated via its application to a high-rise building in Korea.

The current state of geotechnical engineering education in the United States is examined in this paper. K-12 outreach efforts, undergraduate and graduate education, continuing education opportunities, faculty demographics, the influence of the American Society of Civil Engineers (ASCE), and the challenges and changes facing geotechnical engineering education are examined. Several sources of data were used to develop this paper including results from a survey to members of the United States Universities Council on Engineering Education and Research (USUCGER), results from an informal survey provided to practitioners, university websites, and published literature. The K-12 outreach efforts appear to have been successful as enrollments in civil engineering have demonstrated strong growth over the past decade. Nearly all (93%) accredited civil engineering programs require soil mechanics and most (83%) require soil mechanics laboratory. Geotechnical engineers comprise 11% of the civil engineering faculty and about three quarters of all programs have two or fewer geotechnical engineering faculty members. Geotechnical engineering faculty are supportive of ASCE's Policy Statement 465 and The Body of Knowledge. The key challenges facing geotechnical engineering education are falling credit-hour requirements for the attainment of a bachelor's degree, time and resources needed to support laboratories, effectively incorporating complex topics into classes, and balancing the importance of hands-on practical experience with ever-increasing research demands.

A moderate earthquake in the Eastern United States (US) could affect millions of people and potentially impact the world economy. The region is home to many densely populated urban centers, including the nation's capital, Washington, DC, and the financial capital of the world, New York City. The anticipated moderate earthquake hazard places the region at high seismic risk because a significant portion of the infrastructure, including buildings, bridges, and public utilities, were not designed to accommodate seismic loading. Eastern US practice of geo-seismic engineering has a relatively short history. We will discuss engineering approaches presently followed to address common geo-seismic problems such as seismic hazard assessment, site response analysis, and liquefaction potential evaluation. Most of these approaches are based on developments and experiences from the Western US and other seismically active areas. Certain concepts and requirements from the seismically active areas may not be applicable due to unique geological and tectonic characteristics of the Eastern US such as: (i) very hard bedrock; (ii) sparse strong motion data; and (iii) unique regional geology of overburden soils. These unique characteristics affect geo-seismic analyses due to the high impedance contrast between the relatively soft overburden soils and stiff bedrock, and the vibrational differences between the predicted high-frequency bedrock motions and low-frequency deep soft sites. We will present an overview of the geology and regional aspects of geo-seismic design with some practical examples.