Learning from Failures: A Geotechnical Perspective

Proceedings of the International Conference on Forensic Civil Engineering, Nagpur, India 21,22,23 January 2016

Learning from Failures: A Geotechnical Perspective Dr. Sherif W. Agaiby Director, Geotechnical and Heavy Civil Engineering Dept., Dar Al-Handasah (Shair and Partners), 15 Amr Street, Mohandessin, Giza 12411, EGYPT. E-mail: [email protected] Dr. Sayed M. Ahmed Associate Professor, Geotechnical Engineering, Department of Structural Engineering, Faculty of Engineering, Ain Shams University, 1 El Sarayat Street, Abbasseya, Cairo 11517, EGYPT. E-mail: [email protected]

ABSTRACT Engineering failures are hard to define. They may form catastrophic disasters that are serious threats to public safety; yet, at other instances, they may be a shortcoming in the behavior or function of structures. A functional shortcoming, unforeseen and unplanned for, of an engineered element, may sometimes be considered a failure while at other times seen as tolerable or even advantageous. Engineers always regard failures as their greatest enemy; ironically, failures may be considered as their foremost teacher as well. Without failures, much of the current advances in design would not have been gained. Studying welldocumented failures is important as the findings can be used to improve the designs and performance of structures. In this article, the different aspects related to failures and their prevention are explored. A conceptual model for the cost of failures is also presented. Additionally, some of the well-documented case histories of failures encompassing a wide range of geotechnical practices are highlighted and the learnt lessons are emphasized. It is demonstrated that failures may be substantially reduced by carrying out proper geotechnical site investigations, adopting flexible designs that incorporate observations during construction, applying strict site supervision, implementing geotechnical instrumentation programs and embracing risk management principles. INTRODUCTION “It is unwise to be too sure of one's own wisdom. It is healthy to be reminded that the strongest might weaken and the wisest might err.” Gandhi Engineering may be defined as a systematized human endeavour aiming at precluding possible failures especially catastrophic failure, which may result in great losses of properties, damages to the environment, and possibly injuries or loss of lives. The design and construction of an engineered item have to aim at the avoidance of failures under the expected loadings and/or loading conditions. The assumption of no failure in the design may only be proved by the successful construction of the engineered item and by the observations and measurements that confirm qualitatively and quantitatively that the design is accurate and complete (Petroski, 1992). Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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Notwithstanding the endless efforts of engineers to avert failures, the history of engineering, as one of the oldest humankind occupations, reports numerous serious failures. During the design and construction stages, some aspects may be overlooked particularly in newly developed technologies; yet, nature does not necessarily ignore what may have been overlooked by the engineers (Petroski, 2012). Indeed, geotechnical engineers have to acknowledge that the probability of geotechnical failures cannot be simply waived with detailed ground investigations, sophisticated calculations, strict site supervision and monitoring, as soils and rocks are complex engineering materials with properties and parameters that are commonly not linear in behavior, unique or constant. To date, some failures seem to be inevitable because of the complex nature of the geology and/or groundwater as well as the limitation of our understanding and capability to model geomaterials. The ignorance-failure cycle seems to be unavoidable especially with new techniques as there is no way to obtain complete and reliable knowledge in the face of errors, uncertainties, limited data and human imperfections (Szechy, 1961; Sowers, 1993; Bea, 2006). In most cases of geotechnical failures, it is anticipated that there are particular links between the failure and the prevailing geological and geotechnical aspects. There are always uncertainties underneath the Earth surface that may or may not be revealed to the geotechnical engineer. Sometimes, even the most brilliant minds cannot understand geo-secrets. Terzaghi once stated that “Unfortunately, soils are made by nature and not by man, and the products of nature are always complex”. Variability and unforeseen conditions are often the first to be “accused” when a ground failure occur. Yet, one may challenge the concept of unforeseen conditions; these unforeseen condition could have been identified if proper and adequate investigations, data reduction and interpretation have been adopted during the design stage; thus, the unforeseen conditions could be considered in this case more related to human errors. In fact, “unforeseen” is often a contractual tool used by contractors to claim conditions that are not considered in the pricing of a certain job. On the other hand, one may consider the unforeseen conditions are related to deficiency in the organizational procedures (i.e., company guidelines for the site investigation, the country code provisions for the investigations, etc.). As such, an unforeseen condition can be considered as a cause of failure itself but it should be put in the right category of failure causes (Baynes, 2010; Hanna, et al., 2014). If a failure occurs, it provides incontrovertible evidence that the engineering of this failed structure was improper or incomplete. Nowadays, forensic engineers thoroughly investigate occurred failures and come up with hypotheses of how the particular failure under investigation was initiated and progressed. Such investigations are puzzle-solving design and construction problems worked in reverse, in that the engineer must develop possible scenarios and then test them with analyses. In many cases, failures do not occur because of one deficiency but rather a misfortunate combination of factors, which adds to the difficulties in its prognosis (Greenspan, 1989; Day, 1999; Rao, 2015). Despite the recent technological advances, it is estimated that failure rates has increased in the last few decades and it is expected to continue to increase. This may be attributed to the increase of the human needs to utilize undeveloped problematic areas and to the recent environmental changes such as the Global Warming, which increase the rate of catastrophic events such as hurricanes. For example, more than 32,000 Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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landslide-related fatalities (not including those landslides caused by earthquakes) have been documented in the period of 2004 to 2011. (David, 2011; Love, et al., 2013; Petley, 2012). A recent example of the failures initiated by the Climate Changes due to the Global Warming is the failure of the flood defense system for the greater New Orleans area in August 2005. Approximately 75% of New Orleans became under water after the breaches (Fig. 1). Hurricane Katrina was initially held to be the main reason for the failures of levees and floodwalls protecting New Orleans. Yet, later, it was found that major breaches were caused by failure of the soils underlying the levees or failure of the levee embankments due to design and construction shortcomings that were revealed by studying the occurred failures (Kanning, et al., 2007; Sills, et al., 2008; and others).

Fig. 1: A satellite image for New Orleans on 31 August 2005(Source: FEMA) Understanding of the reasons of failures helps in averting such unfortunate incidents. A successful design teaches engineers only that that design is successful; it does not prove that another design like it, in every way but, one will also be successful. Conversely, a catastrophic failure may unfortunately occur but opportunely provides clear and unambiguous evidences that certain design assumptions were faulty and should have been avoided. (Petroski, 1994, 2006; Day, 1999; Shivashankar, 2013). MODERN CHALLENGES AND NEW FRONTIERS “The world is full of challenges, but with those come opportunity” H. Cantu According to UN (2015), the world population reached 7.3 billion in mid 2015. This implies that the world population has increased by about five folds since the end of World War II. Moreover, the projected world population is expected to range, with 95% confidence intervals, between 8.4 and 8.6 billion in 2030 and between 9.5 and 13.3 billion in 2100, as demonstrated in Fig. 2. The huge increase in the numbers of human Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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inhabitants necessitates, among other evolving essentials, unprecedented acceleration of construction. This can only be achieved through the utilization of undeveloped areas that were previously considered as problematic (e.g., areas with soft clays, high seismicity, arid problematic soils, etc.). Moreover, developed and rich countries built, and continue to build, higher and heavier buildings than ever before, as illustrated in Fig. 3. These nations dig deeper and wider excavations/tunnels than ever before in order to serve the planned mega constructions. The emerging huge constructions push the boundaries of our engineering practices beyond their present limits. Consequently, the number and frequency of failures are expected to increase in the forthcoming decades despite the accelerated technological advances.

Fig. 2: World Population 1950-2015 and the projected medium population with 80 and 95 per cent confidence intervals for the interval 2015-2100 (UN, 2015)

Fig. 3: Timeline for the World tallest buildings till the year 2010 (Source: Council of Tall Buildings and Urban Habitat, CTBUH) Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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THE PUBLIC PERCEPTIONS OF ENGINEERING FAILURES “Real knowledge is to know the extent of one's ignorance” Confucius Much of the reasons why we, as engineers, should carefully study engineering failures, besides averting them, has to do with the high public perception of the engineering profession practically in our knowledge-driven societies. Engineering inventions have become the main key to the survival of the human race starting from supplying the basic needs of electricity, potable water, sewage, roads and buildings and ending with the hightech new inventions such as the internet, computers, smart phones, three-dimensional television, etc. Engineers are nowadays leading modern technologies. Hence, the public opinion would certainly consider engineers’ successes as unquestionable and their failures as intolerable. Conversely, Brandl (2004) noted that recent medical statistics disclosed that in Great Britain, Italy and Germany about 100,000 people annually lose their lives because of medical mistakes. Additionally, about 300,000 patients annually suffer permanently from severe treatment mistakes. He also noted that despite the magnitude of these huge numbers, the public opinion would not react against them as fiercely as it would in case 10 lives are lost in a building collapse caused by a faulty design and/or construction. It is interesting to note that the engineering perceptions of failures in the pioneering works of Prof. Petroski has inspired the research related to biomedical failures (Schrenker, 2007). This, indeed, shows that engineers’ concerns and remedies related to failures deeply affect other science branches. SUCCESS EMERGING OUT OF FAILURES “It is an apparent paradox of science and engineering that more is learned from failures than from successes.” H. Petroski It is worth stating that some of the engineering failures undoubtedly paved the way to magnificent successes. A clear model is the Great Pyramids of Giza, Fig. 4, which stand long as examples of successful mega structures that were built by benefiting from previously failed pyramid trials (viz., Sneferu’s Meidum and Bent Pyramids). Similarly, but with a different outcome, the Ancient Egyptians learnt from the failure of their first flood control dam, El-Kafara Dam, Fig. 5, that was destroyed by a flood during its construction that their knowledge at that time would not allow then to control the mighty force of water. They abandoned the idea of building a similar flood-control dam and it was not till another eight centuries that the attempt was retried (Mays, 2010, Agaiby et al., 2013).

Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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The Meidum Pyramid

The Bent Pyramid

The Great Giza Pyramids Fig. 4: Success is born from the womb of failure: Top: The failed pyramids of Sneferu. Bottom: The Great Giza Pyramids

Fig. 5: El-Kafara Dam. Left: slope protection on the upstream face. Right: Close view showing the revetment masonry blocks (Mays, 2010) Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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FAILURE DEFINITION “If you cannot explain it simply, you do not understand it well enough.” A. Einstein Defining failure is not quite agreeable among the public. A well-known example of that is the Leaning Tower of Pisa (Fig. 6). The tilt of Pisa Tower began just during its construction more than 840 years ago due to the existence of soft soil on one side. The tilt increased in the decades before the structure was completed, and gradually increased until the structure was stabilized by the end of the 20th century. Although the tilt of the tower (about 4 o or 1/14.3 with the vertical after its stabilization between 1990 and 2001) may be considered a “failure” from an engineering point of view, it turned to be a touristic attraction for centuries and a great “success”. In fact, had it not “failed”, it may have never “succeeded” (Burland, et al., 1998, 1999, 2009 & 2013).

Fig. 6: The Leaning Tower of Pisa

Failures have conventionally been synonymous with limit states in modern codes. Failures resulting in loss of stability (and often causing gross losses and endanger lives) are studied as ultimate limit state and performance-based definitions of failures. Failures address serviceability as behaviour are studied through serviceability limit state analyses. Additionally, design codes often specify a minimum design lifetime to structures; hence, if a structure does not perform satisfactorily in the working environment during its anticipated exposure conditions during that lifetime, a limit state related to its durability is reached. Durability limit state is not related to the typical consideration of the working load, the


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ultimate load and the load–deformation behaviour but it is mostly relevant to the aggressiveness of the environment to the structure (Frank, 2004; Simpson, 2011). Although limits states are commonly applied in everyday design, yet, the boundaries between the ultimate limit state failures and the serviceability limit state failures are not so rigid. For example, Duncan (2000) discussed the case of sliding of a retaining wall, which is considered an ultimate limit state, and the effect of wall movement on this mode of failure. If the wall slides for a small distance away from the backfill side, then the earth pressure on the active side would decrease and the passive soil earth pressure on the other side would increase; accordingly, the wall may become stable again. The progress of the net resisting load with the increasing deformations may be considered unsatisfactory by some engineers, from a serviceability point of view, despite the fact that sliding is an ultimate limit state. Additionally, the definition of “failure” in the load-deformation and/or stress-strain relationships is not well-agreed on among geotechnical engineers. Fellenius (1980) and Kulhawy & Hirany (1997) demonstrated using the observed load-deformations relationship for deep foundations that the common methodologies for inferring failure loads as ultimate limits are highly variable and give a wide range of results. They concluded that the concept of failure is still not fully understood even at the very basic level of the interpretation of loading tests. Along with the above definitions and understandings, failure may also be identified from a contractual point of view. It is well-acknowledged that the largest source of claims and disputes in the civil engineering field is in the ground. In projects such as tunnels or dams, the predicted costs and time schedules are often exceeded due to the revealed differing ground conditions/unforeseen. Consequently, project managers and contract administrators may consider the resulting overruns as failures from their perspective especially if they substantially exceed the planned budget and/or schedule (Hoek & Palmieri, 1998; Reilly & Brown, 2004; Van Staveren, 2006 & 2009). COST OF FAILURES “Failure is the tuition you pay for success.” W. Brunell Failures always impose implications that may be defined in terms of added costs to the project budget. The costs related to failures can be divided into: 1. Costs due to failure occurrence, including the costs of financial losses, losses due to delays, damages to the owner properties, liquidated damages, third-party damages and fatalities; 2. Costs of prevention of failures, including the cost of proper investigation, competent materials, acceptable engineering, strict quality control, suitable installation/construction and any other factors that could be considered as preventive measures of failures. The total costs are the sum of these costs, they may be expressed using the following formulation: Total failure costs = costs due to failure occurrence + costs of failure prevention

(1)

Failure occurrence costs presumably are directly proportional to the probability of failure whilst costs for the prevention of failures are inversely proportional to the probability of failure as conceptually shown in the Fig. 7.


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Fig. 7: A conceptual model for the two components of the total costs of failure

It can be seen from Fig. 7 that aiming at no failures seems to be not in the best economic interest of contractors and owners. Allowing for a certain probability of failures may reduce the total costs; this is luxury that cannot be afforded for some projects or where lives are in danger. In this regard, the engineering of certain projects may be categorized into the following three categories: 1. Pragmatic engineering: This type of engineering seeks the lowest failure costs. This may be attainable at a certain point where the costs of failure occurrence and the costs of failure preventions are equal and hence the total costs are minimum. 2. Principled engineering - lower failure probability than pragmatic engineering: Some owners and design engineers (and contractors but to a lesser degree) would prefer to have lower probabilities of failure for ethical reasons such as the value of fatalities may not represent the true values of lost lives due to failures. Hence, engineers and contractors would overdo the required effort to avoid, as economically possible, failures. 3. Unprincipled engineering - higher failure probability than pragmatic engineering: The involved stakeholders in a certain projects (most probably contractors) may deliberately or unintentionally take a “risky” approach of reducing the costs and the quality of design, material and quality assurance measures in order to save their costs regardless of the implications which may entail higher costs. FAILURE CAUSES “Nine out of ten recent failures occurred not because of inadequacies in the state of the art, but because of oversights that could and should have been avoided.” R. Peck Ground is extremely variable. It is the most uncertain material that engineers need to assess. Geological anomalies, inherent spatial variability of soil properties, natural and induced anisotropy, changing Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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environmental conditions are all important factors that may hinder the improper characterization of sites and, consequently, failures. Yet, many studies showed that human errors are actually the major cause of engineering failures (particularly, in geotechnical failures) despite the recent advances in analysis, design and quality control of the engineering projects. Peck (1981) estimated that ninety percent of dam failures occurred because of oversights that could, and should, have been avoided. According to Brandl (2004) and based on European statistics, about 80 to 85 percent of all building failures and damages relate to problems in the ground. Nevertheless, he also stated that most failures are due to design or construction flaws. Sowers (1993) and Bea (2006) found that the dominant factor in geotechnical failures (about 80 to 90%) was due to the human, organizational and knowledge uncertainties. Similarly, Bea (2006) concluded that failures are, in many cases, directly related to engineers’ lack of knowledge. Van Tol (2007) shows that more than 60% deep excavations failures in the Netherlands were caused by not applying the existing knowledge. Gue and Tan (2004) reviewed 55 cases of failures in soft clays and found that nearly most of the failures are largely due to human errors in design and construction. Simpson (2001) indicated that human errors in geotechnical engineering design are not uncommon including arithmetic errors, lack of basic knowledge, miscommunications, misunderstanding of important information, etc. David (2011) concluded that very few failures occur due to the lack of existing knowledge, some occur due to misapplication of existing knowledge, while many failures could have been avoided by more control and management of the design and construction works. Shaffner (2011) noted that clear potential foundation problems posing significant risk may be kept unnoticed for long by many engineers. He considered that overlooking a possible failure pattern is similar to a cognitive bias called Dunning– Kruger effect (Kruger & Dunning, 1999) which illustrates how relatively unexperienced individuals suffer from mistakenly assessing their ability to be much higher than reality as illustrated in Fig. 8. In the following sections, some of the possible design and construction oversights that may lead to failures are explored along with possible approaches to overcome such deficiencies.

Fig. 8: A graphical illustration of the Dunning– Kruger effect. Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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APPROACHES TO OVERCOME OVERSIGHTS Proper Site Characterization “The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.” S. Hawking Geotechnical investigation is one of the most crucial geotechnical elements to obtain reliable ground and groundwater information for use in the design and construction. Unlike other engineering disciplines, geomaterials at a given site are generally not specified nor manufactured to have desired engineering properties within known confidence levels. Hence, the primary role of geotechnical site investigations is to gain knowledge about the soils and rocks and obtain good estimates of the ground properties and their variations to ensure safe and economic design and construction (Hunt, 2005). Investigation programs are carried out to define the geotechnical characteristics of the project sites. They may comprise boring, sampling and insitu testing, laboratory testing and geophysical surveys. The interpretations and analyses of the data should consider geology, site history and environment. Consequently, recommendations on the favorable/unfavorable locations, economic and safe design, and prediction of potential risks are inferred. Fig. 9 shows the relationships between site investigations and other geotechnical works (Nazir, 2014).

Fig. 9: Relationship between site investigations and other related geotechnical works (Nazir, 2014)


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ICE (1991) found out that 35-50% of the projects with cost and/or time overruns suffered from ground problems due to the unforeseen ground conditions that were met during construction. Goldsworthy et al. (2004) indicated that a site investigation scheme with limited testing may result in a more expensive foundation, when the cost of possible foundation failure is included. The consequences of inadequate investigations are not only severe for the design and construction phases of a project but may even be more serious if they continue into the full-life costing. In addition to failures, cost and time overruns are also serious concerns that may arise due to improper site investigations (Littlejohn et al., 1994). A proper site investigation work is carried out by the combined effort of a specialized geotechnical engineer and a competent ground investigation contractor. Geotechnical engineers should attempt to answer the following questions (Fig. 10) while envisaging the ground investigations (Nazir, 2014): 1. What is known about the site? 2. What is not known about the site? 3. What needs to be known?

Fig. 10: Circles of questions for site investigation (Nazir, 2014)

Based on the answers to the above questions, the following 1. What type of investigations are needed? 2. Why are they needed? 3. Where should the actual field work be performed? 4. How will the work is be done? Accordingly, the site investigation program is envisaged including the stages of investigation, the type of field work, the number and location of boreholes, type and number of sampling, type and number of testing, etc.


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Quantifying Uncertainties in the Design “Natural soil is never uniform. Its properties change from point to point while our knowledge of its properties are limited to those few spots at which the samples have been collected.” K. Terzaghi Uncertainty in geotechnical parameters necessitate the adoption of reasonably conservative values of geomaterials stiffness and strength. Reliability and probabilistic approaches constitute a key basis of limit states geotechnical design codes (e.g., Eurocode, AASHTO and others). The use of these statistical concepts is integral to the appropriate selection of characteristic value for geotechnical properties and design parameters. Characteristic parameters are the worst credible design values that are selected on the basis of a reasonable engineering assessment and design. Additionally, geotechnical engineers should consider the site’s geological setting, stress history, geomorphology, hydrology and other controlling geotechnical/geological features such as existence of buried channels, pre-sheared zones or slip surfaces, permeable bands within clays, etc. These aspects may significantly influence the geotechnical behavior of the ground; yet, they cannot be simply represented by the codes common approaches such as the partial factors analysis (Simpson, 2011). Validated Modeling “All models are wrong. Some models are useful.” G.E. P. Box Peck (1981) highlighted that the geotechnical problems are fundamentally non-quantitative and hence solutions are principally non-numerical. Yet, the recent unprecedented advances in software and hardware technologies allow geotechnical engineer to perform complex nonlinear three-dimensional analyses without much difficulties. These powerful tools may potentially lead to failures especially if the engineers who perform the modeling do not have the required engineering experience. Indeed, the currently available powerful geotechnical software is only as good as their user. The ideal approach to validate the computed results from advanced modeling is to perform calculations and/or assessment that do not involve the use of the numerical software. In some cases, closed form and hand solutions are available but in many cases, engineers can only resort to laboratory models or field observations and/or measurements for calibration. They may also validate the computer analyses by using two different software for the same model (Ong, et al., 2006; Ong, 2008). Engineering Judgment “Theory and calculation are not substitute for judgment, but are the basis for sounder judgment” R. Peck Engineering judgment has always played a predominant role in geotechnical engineering prior to the invention of modern computer-aided design. At that time, design was performed mainly based on the experience gained from previous similar works. Yet, at the current time where computer-based design and analysis is very common, engineering judgment is still indispensable to the successful engineering as geotechnical problems cannot yet be solved by the advanced numerical analysis without having reasonable input parameters is reasonable. The output of analyses from computers needs also to be judged wither to be accepted, or rejected on the basis of its reasonableness (Peck, 1981 & 2006).


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Peer Review “The man with insight enough to admit his limitations comes nearest to perfection.” J.W. von Goethe Geotechnical projects need the close cooperation of experts of various disciplines (e.g. geology, geotechnical engineers and geophysicists) in addition to the opinions and feedbacks of the structural and hydraulics engineers. It is expected that highly qualified experts usually arrive at rather similar opinions although the opposite is not infrequent. Diversity of opinion of experts have always been a spark for further development and innovations (Sowers, 1993; Bea, 2006). Monitoring and Risk Management “Residual risks are unavoidable, because ground is the greatest uncertainty in civil engineering” H. Brandl Uncertainty can be defined as an absence of complete information about a system under consideration. Uncertainty is always present, even when information is perceived as complete considering factors such as possible human errors. Risk is the combination of the probability of an uncertain event and its consequence. Consequences can range from positive to negative. ICE (1991) showed that in civil engineering and building projects the largest element of technical and financial risk lies normally in the ground. In other words, risk is the product of the probability or likelihood of an undesired event and the consequences of that event. Monitoring of structures during the construction stage is considered one of the most important tools for the mitigation of uncertainties in geotechnical engineering. It provide a quantitative tool for the geotechnical engineers to learn from the ongoing and completed projects and to ascertain the design assumptions. Monitoring also allows the back-analysis of the failure cases to determine the possible reasons and/or scenarios that caused the unexpected failure (Dunnicliff, 1993). Peck (1969) presented the Observational Method, which calls for a continuous re-assessment of the design parameters by utilizing the results of the monitoring programs. The possibility to modify the design and strengthen the structure during construction is a fundamental benefit of the Observational Method. Additionally, the Observational Method allows precautionary measures to be adapted in case the observations exceed predetermined thresholds that are defined for both stresses and deformations. The Observational Method establishes the general framework for the risk management procedure that should be considered to avert possible failures (Powderham, 2002). The concept of geo-risks has been widely adopted (Lacasse & Nadim, 1998; Chapman et al., 2007). Brinded (2000) defined the risk management as the processes of risk understanding (Risk Analysis) and compared it to the societal tolerated risks of a similar nature (Risk Evaluation), allowing a decision regarding the requirements to control of the risk. This staged approach has been adopted in geotechnical risk management for dams by Stewart (2000). Deltares (formerly known as GeoDelft) developed the GeoQ-method for risk management; it has been already adopted in many construction projects in the Netherland for controlling ground-related risks (Van Staveren, 2006).


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LESSONS LEARNT FROM SOME PREVIOUS FAILURES “All men make mistakes, but only wise men learn from their mistakes.” W. Churchill Geotechnical engineers used to accept the unescapable uncertainties that may cause serious complications and failures. Hence, upon occurrence of a failure, such unforeseen conditions are often the first to be blamed. Yet, numerous recent studies indicate that most of the geotechnical failures are caused by engineers failing to comply with the proper engineering practice or the misjudgment of a clear geotechnical data as previously discussed. Indeed, previous failures include numerous case studies where abundant geologic information was collected, but not properly understood or incorporated in the design. In some instances, sufficient geologic information was collected, but the failure mode was not understood by engineers at the time of failure. The study of past failures draws attention of the engineering community to the weak aspects in the design and construction states-of-the-practice. Engineering can undoubtedly be improved through the dissemination of the details of observed failures to the practicing engineers, contractors, code committees, public works officials and construction supervisors. The following sections describe some of the previous geotechnical failures that affected our profession profoundly. Failure of St. Francis Dam, California, USA, 1928 St. Francis Dam was a 57m high, 213 m long, curved concrete gravity dam built for the City of Los Angeles in 1924-1926. It stored 47 million m3 of water. Just before midnight of March 12, 1928, the dam collapsed and the resulting flood took the lives of 431 people. Fig. 11 shows the dam before and after collapse. The collapse of the St. Francis Dam is considered to be one of the worst American civil engineering disasters of the 20th century. It is also considered the second greatest catastrophe in California's history after the 1906 San Francisco earthquake and fire. This disaster marked the end of its designer's career (Grunsky & Grunsky, 1928; Outland 1963; and others).

Fig. 11: St. Francis Dam. Left: Before failure. Right: After failure (Grunsky & Grunsky, 1928; Outland 1963; and others) Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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There are many anticipated causes of failure that are believed to include the following (Rogers, 2002 & 2007): 1. The east abutment was founded on mica schist interspersed with talc with a greasy texture. This location had old landslides prior to the dam construction. 2. The western abutment of the dam was rested on a fault comprising red conglomerates which swelled upon wetting. A piping instability appeared to occur upon the water impoundment of the reservoir behind the dam. 3. The dam height was increased by 6m during construction without any increase in base width 4. The dam, after the increase of its height, became unstable in overturning. This failure lead to many dam safety and maintenance legislations and guidelines in California and other states. This failure also lead to the introduction of the professional engineering registration. Liquefaction Failures in Niigata Earthquake, Japan, 1964 The Niigata earthquake occurred on June 16, 1964 with a magnitude of 7.5 and an epicenter located about 50 kilometers to the north of the Niigata city. As a great part of the city of Niigata is built on the recent deltaic deposits from the Shinano and Agano rivers (mainly loose sands), the earthquake shaking caused substantial liquefaction. Subsidence of up to 140 cm was observed over the large areas that suffered from liquefaction. Fig. 12 shows a well-known example of the liquefaction failure of apartment buildings that were built on reclaimed land by the Shinona River. This failure occurred despite the relatively low levels of ground acceleration recorded by strong motion accelerographs placed in one of these buildings. The occurred failures demonstrated the importance of considering the liquefaction in design of structures in the seismic active zone. Nowadays, liquefactions analyses and checks are commonly applied in everyday design to avert the possible failures that were observed in earthquakes (Ohsaki, 1966; Seed & Idriss, 1967 & 1971).

Fig. 12: Failure of apartment buildings by tilting in Niigata due to liquefaction (Source: National Geophysical Data Center, NOAA) Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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Another aspect is also related to the observations in Niigata 1964 earthquake. Fig. 13 shows the collapse of the Showa Bridge in Niigata after the 1964 earthquake. The bridge had a length of 307m with spans of 28m. Each span was supported on nine 600mm diameter steel piles of wall thickness of 9 to 16mm. Some of the bridge girders rested on movable joints to allow for the thermal expansion. After the earthquake, lateral spreading was observed in the loose sands at the riverbanks and it is suspected that it caused the failure of the bridge (Fukuoka, 1966; Kramer, 1996; and others).

Fig. 13: Collapse of the Showa Bridge after Niigata Earthquake, 1964 (Source: National Geophysical Data Center, NOAA) Rissa Landslide, Norway, 1976 Quick clay is a highly sensitive marine clay that exists in Canada, Norway, Russia, Sweden, Finland, the United States and other locations around the world. When it is undergoes strain, its behavior changes from that of a soil to that of a fluid. Quick clay is believed to be the cause of many retrogressive landslides that often initiate at riverbanks and the edges of lakes and progress away from its starting point at slow walking speed to kilometers inland consuming everything in its path. One of the most welldocumented cases of landslides in quick clays is Rissa landslide which took place April 29, 1978 in Norway. The slide debris was about 6 million m3. There were 40 people within the slide area (about 330,000 m 2) when the sliding started; only one was killed while the others escaped. The slide is documented by a film that was taken by two amateur photographers. Fig. 14 shows the progression of the failure from the edge of Lake Botnen, Rissa. This failure substantially added to the knowledge of the engineering community about the quick clay behavior and associated landslides (Gregersen, 1981; TerStepanian, 2000; Torrance, 2012). Agaiby, S.W. & Ahmed, S.M. - Learning from Failures: A Geotechnical Perspective

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(a)

(b)

(c)

(d)

(e)

(f)

Fig. 14: Stages of the retrogressive Rissa quick clay landslide, Norway, 1976. The capital letters A through E represent the failure boundaries and observation locations. The failure chorology is shown in the small alphabetic sequence a to f (Gregersen, 1981)


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Failure of the Nicoll Highway, Singapore, 2001 On 20 April 2004, during the construction of the Circle MRT Line - Stage 1- Contract 824, a 100-m length, 30-m depth section of the cut-and-cover tunnel suddenly failed near Nicoll highway (Fig. 15) causing the loss of four lives and the collapse of a substantial part of the main highway running over the tunnel. The excavation support system included ten levels of preloaded cross-lot struts with two rafts of jet grouted piles (JGP) which was a novel excavation support system (COI, 2005).

Fig. 15: Photos of the collapse of Nicoll Highway in Singapore on 20 April 2004 (COI, 2005)


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Relatively large wall deflections occurred during the excavation; yet, the measured strut loads were smaller than the design calculated values. Accordingly, the project engineers were apparently unaware of the potential for a catastrophic failure. There are many possible causes for the collapse including (Magnus et al., 2005; Whittle & Davies, 2006; Corral & Whittle, 2010; Ishihara, 2011): 1. Overestimating the undrained shear strength of the lower marine clay, which appears to be still underconsolidated. 2. The design was based on the effective stress strength parameters (c’, φ’) for the undrained condition and Mohr-Coulomb constitutive model, which seems to have overestimated the undrained shear strength profile for the underconsolidated clays. 3. Underestimated the deformations for the mobilization of the passive shear resistance in the JGP. 4. Underestimating of the earth-pressure on the diaphragm wall. 5. Detailing errors for the structural bracing system and its connection. 6. The diaphragm wall was designed to extend 3m below the soft clay into much stronger alluvium. However, at the location of the failure, it seems that the surface of the clay had been eroded by a buried channel. This failure resulted in additional research regarding constitutive modeling of soft clays and the applicability of the Observational Method in deep excavations that may undergo sudden failures due to the failure of the structural strut elements. CONCLUSIONS “Everything behooves us to beware of the lure of success and listen to the lessons of failure.” H. Petroski Failures are not all evil; they can be more useful to engineers than successes if they are well-studied to answer the important questions of how to improve our performance and what are the patterns of erroneous thinking and generalizations that we should avoid. In fact, the most fruitful source of lessons in engineering judgment exists in studying case histories of failures and learning from the mistakes of others. As failures are mostly related to human errors, most failures can be avoided if extra care and input from engineers having the relevant experience in geotechnical engineering were consulted. The first and most indispensable tool to avoid failures is the proper engineering judgment that separates the significant from the insignificant details. Failure numbers could be reduced by implementing proper and adequate geotechnical site investigations, and adopting more flexible/conceptual designs together with the application of the Observational Method (as opposed to rigid, fully-engineered design) and by applying strict site supervision and quality control. REFERENCES Agaiby, S.W., El-Ghamrawy, M.K., & Ahmed, S.M. 2013. Learning from the past: the Ancient Egyptians and geotechnical engineering.” ISSMGE, TC 302: Forensic Geotechnical Engineering. 4 th International Seminar on Forensic Geotechnical Engineering. Sivakumar Babu, G.L., Rao, V.V.S. & Madhav, M.R. (Eds.). January 10-12, 2013 - Bengaluru, India. pp. 38-96.


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