Ebook: Geotechnical Safety and Risk V

It is our great pleasure to present to you the proceedings of the Fifth International Symposium on Geotechnical Safety and Risk (ISGSR2015), which is held in Rotterdam, the Netherlands, 13–16 October 2015. This 5th ISGSR is a continuation of a series of symposiums on geotechnical safety reliability and risk assessment and management. These symposiums started 15 years ago with LSD2000 in Melbourne, Australia and continued with IWS2002 in Tokyo and Kamakura, Japan; LSD2003 in Cambridge, United States of America; Georisk2004 in Bangalore, India; Taipei2006 in Taipei; 1st ISGSR2007 in Shanghai, People's Republic of China; 2nd ISGSR2009 in Gifu, Japan; 3rd ISGSR2011 in Munich, Germany and 4th ISGSR2013 in Hong Kong, People's Republic of China. All of these symposiums have been organized and attended by a truly international and dedicated group of geotechnical academics and professionals. In addition, all of these symposiums proved the great value of sharing knowledge and experiences from research and practice between the international geotechnical engineering communities.

This 5th ISGSR symposium has been organized by KIVI Geotechniek, the Netherlands Society of Soil Mechanics and Geotechnical Engineering (SMGE), which is a member society of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE), together with the Geotechnical Safety Network (GEOSNet) and the Dutch Geo-Impuls innovation program. GEOSNet has been formed in 2006 in Taipei in view of the increasing interest and need to rationalize the concept of risk in new geotechnical design codes using reliability, risk analysis and risk management methods.

This 5th ISGSR is even more special, because it is combined with the presentation of the results of the Dutch Geo-Impuls innovation program in the Netherlands. Geo-Impuls is a five year long, joint industry programme. It has been executed from 2010 to 2015 and aims to reduce geotechnical failure in construction and infrastructure projects substantially by 2015. Implementing Geo Risk Management (GeoRM) and the tools developed by the Working Groups in projects and organizations are the key objectives for reaching this ambitious goal. The Dutch geo-engineers and managers are truly honoured to present and discuss their results with the international geo-community during ISGSR2015.

Managing geotechnical safety and risk during and after completion of construction and infrastructure projects became over the years essential to satisfy the already high and ever growing expectations in our societies. Therefore, ISGSR2015 selected the following seven conference themes:

1. Geotechnical Risk Management and Risk Communication

2. Variability in Ground Conditions and Site Investigation

3. Reliability and Risk Analysis of Geotechnical Structures

4. Limit-state design in Geotechnical Engineering

5. Assessment and Management of Natural Hazards

6. Contractual and Legal Issues of Foundation and (Under)Ground Works

7. Case Studies, Monitoring and Observational Method

In total 139 peer reviewed and accepted papers from 31 countries are included in these proceedings. Each of these papers has been allocated to one of the conference themes. The proceedings contain also seven keynote lectures, of which the Wilson Tang Lecture is the most prestigious one. This lecture was inaugurated during the 2nd ISGSR in Gifu, Japan, for recognizing the valuable and remarkable contributions of the late Professor Wilson Tang. We are very honoured that Professor Kok Kwang Phoon of the National University of Singapore provided the 4th Wilson Tang Lecture during ISGSR2015, with the title “Is there anything better than load and resistance factor design for simplified geotechnical reliability-based design?”

This symposium has been well-supported by the following Technical Committees (TCs) of ISSMGE:

• TC304 Engineering Practice of Risk Assessment & Management

• TC205 Safety and Serviceability in Geotechnical Design

• TC212 Deep Foundations

• TC302 Forensic Geotechnical Engineering

Moreover, substantial financial contributions have been delivered by a considerable number of sponsors. The premium sponsors are Rijkswaterstaat of the Dutch Ministry of Infrastructure & Environment and the Municipality of the city of Rotterdam. The main sponsors are Deltares and Prorail. The regular sponsors are Antea Group, Arcadis, Crux, Fugro, Grontmij, Movares, Royal HaskoningDHV and Witteveen+Bos.

Finally, the editors are grateful to all dedicated members of the Local Organizing Committee. They provided and organized the right conditions. Nevertheless, at the end of the day the credits for these proceedings go to the many authors and reviewers, who found the time and energy to provide their excellent contributions. Many thanks to all of you!

The editors

Timo Schweckendiek, Frits van Tol, Dirk Pereboom, Martin van Staveren and Paul Cools

October 2015, Delft, Netherlands

Geotechnical design codes, be it reliability-based or otherwise, must cater to diverse local site conditions and diverse local practices that grew and adapted over the years to suit these conditions. One obvious example is that the COVs of geotechnical parameters can vary over a wide range, because diverse property evaluation methodologies exist to cater to these diverse practice and site conditions. Another example is that deep foundations are typically installed in layered soil profiles that vary from site to site. These diverse design settings do not surface in structural engineering. If the performance of geotechnical RBD were to be measured by its ability to achieve a more uniform level of reliability than that implied in existing allowable stress design over these diverse settings (which is recommended in Section D.5, ISO2394:2015), then LRFD and comparable simplified RBD formats widely used in structural design codes are not adequate. While it is understandable for geotechnical RBD to adopt structural LRFD concepts at its initial stage of development over the past decades, it is timely for the geotechnical design code community to look into how we can improve our state of practice in simplified geotechnical RBD. This paper demonstrates that improved formats such as the Quantile Value Method coupled with an effective random dimension (ERD-QVM) can cater to a more realistic and diverse range of design scenarios. Specifically, ERD-QVM can maintain an acceptably uniform level of reliability over a wide range of COVs of geotechnical parameters and a wide range of layered soil profiles. It can achieve this while retaining the simplicity of an algebraic design check similar to the traditional factor of safety format and LRFD. ERD-QVM is a step in the right direction to develop geotechnical RBD for geotechnical engineers. More research is urgently needed for geotechnical RBD to gain wider acceptance among practitioners.

In the Netherlands more and more attention is paid on reducing geotechnical failures in civil engineering projects. This paper focusses on describing the contractual measures and procedures Rijkswaterstaat as a client has developed and implemented in recent years for this purpose. The principles of Geotechnical Risk Management are leading.

This paper presents an overview on how uncertainty and variability of mechanical soil properties are dealt with in offshore site investigation and presents some ideas for utilizing the reliability tools in a more optimal manner for this purpose. Two types of problems are addressed. First, how to extract the maximum amount of information from geotechnical site investigation, which is often constrained by high costs. Second, how to establish characteristic or representative soil properties for design while taking into account the uncertainties caused by the natural variability of soil properties and the interpretation of the in situ and laboratory tests.

Important engineered slopes are often heavily instrumented and their performance routinely monitored through these instruments. The evaluation of the safety of the slopes based on the monitored information is however a challenge. A systematic method is presented in this paper for evaluating the slope safety by combining multi-source monitoring information with underlying physical mechanisms. First, a Bayesian network with continuously distributed variables for a slope involving the factor of safety, multiple monitoring indexes and their influencing soil or rock model parameters is constructed. Then the prior probabilities for the Bayesian network are quantified considering model and parameter uncertainties. After that, multi-source monitoring information is used to update the probability distributions of the soil or rock model parameters and the factor of safety or failure probability using Markov Chain Monte Carlo simulation. Two rock slope examples are worked out to illustrate the proposed methodology. A non-intrusive stochastic numerical method is used in the reliability analysis in the examples.

This paper presents and overview of advances in flood risk and levee reliability analysis in the Netherlands. It is described how new safety standards – in the form of a target failure probability – have been derived on the basis of nationwide flood risk assessments which taken into account both economic risk and risk to life. The process for derivation of semi-probabilistic design codes (i.e. factors of safety) for various geotechnical failure mechanisms of flood defences is described and it is shown how these semi-probabilistic requirements are consistent with the target probabilities of failure and ultimately with the underlying flood risk acceptance criteria. The newly introduced approach also raises challenges like the introduction of fully reliability based design and assessment techniques, but it also provides opportunities such as the use of reliability updating and data assimilation, which will be highlighted after discussing the framework and its overall coherence.

To date, the tunneling in China is experiencing an age of fast development for decades. The potential risks behind the huge amount of construction and operation works in China was first formally realized and managed after 2002. The transition of risk assessment from a qualitative manner to a quantitative manner is on the way from the research gradually to the practice. This paper tries to share some experiences in the quantitative risk management for tunneling in China by introducing novel techniques and associated practical applications. The fuzzy fault tree analysis is used for hazard identification, the conditional Markov chain for probability analysis of soil spatial uncertainty, the quantitative vulnerability analysis for consequence evaluation and the field data based statistics for environmental impact risk analysis. All these novel methods have been validated successfully by applying into real cases shown in the paper. The dynamic feature of risk management is appreciated due to the different stages and scenarios of a tunnel project. The real-time monitoring technique developed using the LEDs and MEMS coupled with WSN could visualize the risk to the worker on site timely. The resilience analysis model to incorporate the high-impact low-chance risk for tunnel lining structure is introduced in the end of paper, which could assist the engineers to make the decision on performance recovery strategies once the tunnel goes through a significant disruption.

For all types of construction works the aspects safety, serviceability and sustainability have to be focused during the planning phase, the design phase, the construction phase and in the service phase. Particularly this has to be considered for complex deep foundation systems like the Combined Pile-Raft Foundation (CPRF). The basis for a successful realisation of a project is an adequate soil investigation and a high-level design. For risk mitigation an independent peer review and special technical solutions are necessary. In geotechnical engineering Eurocode 7 (EC 7) defines the scope of necessary measures in relation to the complexity of the project. The complexity of the project is described by the Geotechnical Category GC 1 to GC 3. For the Geotechnical Category GC 3, this is the category for projects with a very high complexity, for risk mitigation comprehensive measures are necessary. The paper explains risk management and risk communication by several examples of realized CPRFs. All examples belong to the Geotechnical Category GC 3.

In the preparation and construction stages of the underground car park beneath Kruisplein with diaphragm walls, risk management played an important role. After a description of the structure and the construction, the preventive measures that were invented and carried out are summarised. These relate to the organisation of the project (experienced advisors, consequent risk management), the preparation of the construction stage (detailed plan of action, lessons learned from other projects, analysis of the environment and physical conditions), environment management, monitoring and the supervision of the construction process. The monitoring process and a new method to detect anomalies in the joints of diaphragm walls are presented in more detail.

Hong Kong faces a unique long-term slope safety problem due to its dense urban development in a hilly terrain combined with high seasonal rainfall. Its slope engineering practice and landslide risk management have evolved in response to experience and through continuous improvement initiatives and technology advances. The application of state-of-the-art slope engineering practice and quantified landslide risk management has reduced landslide risk to an as low as reasonably practicable level that meets the needs of the public and facilitates safe and sustainable developments. This paper will give an overview of the slope safety system that serves to manage landslide risk in a holistic manner through an explicit risk-based approach and strategy and provide an update on the recent initiatives undertaken as part of the continuous efforts to enhance landslide risk management. These initiatives include identifying new candidates of vulnerable hillside catchments, developing a territory-wide rainfall-based landslide susceptibility model and assessing potential implications to the risk profile of natural terrain due to extreme rainfall events.

Ground, building and utility deformation monitoring is a well-accepted and required practice for underground construction works in urban environments. The availability of real-time monitoring data during construction allows stakeholders to stay ahead of potential problems, to make decisions prior to damage occurrence, and ultimately to reduce damage and cost risk. This paper presents the analysis of a comprehensive monitoring program carried out during the East Side Access Queens bored tunnels project in New York City. The project involved the construction of four near surface, closely spaced metro transit tunnels beneath the rail yards and mainline railroad tracks. The close proximity of the tunnels provides a unique opportunity to examine the influence of multiple closely spaced tunnel openings on ground deformation, particularly the accumulation of vertical surface deflection due to consecutive tunnels. The project also allows for a direct comparison between deformation monitoring techniques as both manual survey based monitoring and automated total station monitoring were used on the project. This paper will provide an overview of the monitoring program as a component of the risk management process on the project. The monitoring program will be described in detail and results will be presented. The paper also addresses potential improvements to risk-reduction through monitoring.

In The Hague, a 2 storey parking garage was built beneath a reinstated canal at the Veenkade with 160 parking places. The canal and the parking garage were installed at minimum 3 - 6 m distance from old houses with a shallow foundation by means of a 10 m deep building pit. A risk analysis was undertaken and major risks were identified, resulting in mitigating measures, e.g. compensation grouting in combination with very accurate monitoring. The structure was completed in 2014.

This paper proposes a seismic risk management scheme for long continuous geotechnical structure, such as road embankment, water canal and so on. In this scheme, the continuous variation of responses, the failure probability and the risk, 50m intervals for instance, of the structure can be estimated with using response surface method. The detail of the proposed scheme and its applicability to the seismic risk management of continuous geotechnical structures are described from an application example to a more complex canal system model in this paper.

Rijkswaterstaat has recently stated that the use of GeoRM is obligatory for projects with major geotechnical risks. Underground construction of freeway's in high-profile areas, such as the business district Zuidas in Amsterdam or railway links in densely populated areas, always introduce major geotechnical risks. It is not uncommon for these locations to have all the facets that require strong geotechnical risk management: underground construction occurs adjacent to high-rise structures, locations have a very busy surface area, there are financially dependent stake-holders and concerns prevail after issues on earlier projects.

Rijkswaterstaat and their consultant firms are tackling this by forming a strong bridge between engineering and management using geotechnical risk management (GeoRM). In this article its main focus is translating the language of technical risks into managerial terms of cost, delay and reputation. Then actions are translated back again into countermeasures, which are often technical in nature. With a unique approach of subdividing and quantifying risks into sub-risks all the way down to a construction activity level, engineers have the ability to talk directly to the decision makers. To this end a visualization tool has been developed to assess and evaluate risk and counterfeit measures with management staff. The teams involved believe risk reduction is about real-life measures that require a level of detail and knowledge of the actual construction activities to be performed.

This approach has led to real risk-reduction activities, for example: additional investigations into underground obstacles (e.g. existing steel anchors) and actions for removing them beforehand, preventing stagnation later. But also: site investigation activities associated with specific construction methods like soil injection which may turn out to be unfeasible if soil parameters don't come out as expected.

Geo-Impuls is a Dutch nationwide programme with the aim to reduce geotechnical related failures in projects. During the last 5 years, a large number of teams have been working within three themes (techniques, communications and contracts) on a procedure for coping with the natural uncertainties of the Dutch subsoil.

The large variation in the mainly soft subsoil in the Netherlands involves geotechnical risks. These risks need to be managed and controlled. The main focus of one of the themes of Geo-Impuls – theme ‘Geo-Engineering in Contracts’ – is how to deal with these risks during the different phases of a project and especially during the drawing up of the contract. Which party is able to manage geotechnical risks most effectively in which phase of the project? In addition, which party is responsible for which risks? Moreover, how can this responsibility be reduced, allocated and established?

These questions are of current interest due to a shift in the methods of contracting. Nowadays the traditional form of contracting changes towards a more integrated form. Several parties are responsible for the project design or realization instead of only one party. Furthermore, the way of selecting the contractors is also changing. All this makes it difficult to make clear-cut agreements on how to deal with the geotechnical risks. It is no longer the responsibility of only the geotechnical consultant, but of the whole project team.

Within ‘Geo-Engineering in Contracts’, research has been done on how to determine a method to deal with geotechnical risks in all phases of the project. Eventually, the following topics were identified and researched by different teams. 1. The determination of a risk controlled approach for the executing of soil investigation during all phases of the project. 2. The awareness of geotechnical risks and how to allocate these risks to the parties involved during all phases of the project. 3. The presentation of guidelines on how to successfully integrate geotechnical aspect in different contract forms. The article outlines the activities and results of these three topics of the Contracts-teams.

As part of the Dutch national research program GeoImpuls an inventory has been made of the state of the education at Dutch institutes of higher education and post-graduate education in so far as this education concerns geotechncial engineering and geotechnical risk management. Significant differences have been found in the amount of time allotted and detailed technical knowledge taught at different levels and different institutes. Given the limited technical background and limited knowledge of GeoRM for most civil engineering graduates, a split is perceived between the actual and necessary skill set of starting engineers. The impact of this split is discussed in light of international standards for professional engineers.

In the urban area of Rotterdam many different groundwater extractions take place, which affect the groundwater system. Urban groundwater management is a tool to prevent the risk of non-intended effects of these extractions and unsustainable use of groundwater. The main goal is to exchange information and knowledge for a better understanding of the groundwater system and an integrated approach when regarding and authorizing the different functions of groundwater.

During a design process the risk profile of a project continuously evolves. Often a project progresses through a diamond shaped risk envelope. The initial concept is simple, but during the engineering process several risks are defined and mitigated, making the design increasingly complex. With additional investigations and calculations, some of the identified risks can be better defined. As a result, the design should evolve into a matured design in which only a few risks remain. These risks should be manageable. If uncontrollable risks remain, even though the chance of occurrence may be small, this could render the project unfeasible. This paper will show how the risk profile of a bridge foundation adaptation has evolved.

The paper describes the geotechnical design and execution challenges in underground construction in the historical center of Amsterdam. The geotechnical design and risk management approach of the total works will be presented in detail, with special attention to the specific geotechnical conditions in Amsterdam and the GeoRM risk document. The design results, using FEM calculations will be mentioned shortly and the risk control during execution of the works will be presented and discussed. The design contains special geotechnical features such as trenching to remove underground obstacles, special retaining walls and measures to prevent instability of the excavation floor. Through a sophisticated geotechnical and structural design, and by applying Geotechnical Risk Management in the design and during execution the Museum was constructed successfully without any significant damage or delay.

This paper investigates the spatial variability characteristics of geologic profiles, including variations in thickness of marine clay deposits and rockhead levels, based on borehole data obtained from four sites in Hong Kong. The numbers of boreholes are approximately 100 in two cases, while the other two cases comprise more than 300 boreholes each. The large volume of data allows comprehensive statistical analyses to identify the spatial correlation/variability in subsurface profiles using the Restricted Maximum Likelihood (REML) method. The Matérn Autocorrelation model is adopted for its flexible functional form, with the parameters optimized using the Differential Evolution algorithm, in order to maximize the log likelihood value in REML. This technique is used to evaluate the spatial variability characteristics of geologic profiles, including parameters such as the spatial dependence and scale of fluctuation at the four sites. The effects of irregular sampling pattern, sample domain scale and sampling density on these parameters are also discussed based on the analyses. In addition, the existence of faults in two of the sites is found to significantly affect the spatial variability of rockhead level, as indicated by the reduced scales of fluctuation and spatial dependence in areas intersected by faults.

Settlement of problematic soils constituting the roadway subgrade may result in pavement distress and structural failure, requiring periodic pavement patching and resurfacing. Many of these problems occur as a result of the settlement of soft cohesive and organic soils. Due to the extent of roadway projects and the limited frequency of boring locations, spatial variability of subsurface soil conditions, and sometimes due to an inadequate extent of exploration, these problematic soils may not be identified suitably during subsurface explorations. An extensive subsurface exploration program was implemented for detailed characterization of subsurface conditions for a relatively short section of an existing roadway experiencing continuing settlements. This paper presents some of the exploration results, assesses the spatial variability of the subsurface soil conditions, and comments on the effect of spatial variability of subsurface conditions on the roadway's performance.