Book Review: Trapped Under the Sea

This book has been in my "To Read" list for a very long time. Only when the Breakthrough Magazine (current issue) wrote a review about this book, it gave me the final push to read this book without any delay. But once I started reading, it was so gripping and thrilling that I had to complete the book within a week.

The book describes the tragedy which occurred during construction of a waste treatment plant in Boston Harbor, USA. As with the most sewage outfall tunnels, this project has diffuser lines installed towards the end of the tunnel to disperse the treated sewage. The book describes about an incident where divers were sent into ~15km long un-ventilated tunnel (with individual breathing system) to  remove the safety plugs installed at the tunnel and diffuser connections.

Deer Island Treatment Plant and Sewage Outfall tunnels (source)

The author describes the the dangers faced by the workers due to the inability of the tunnel designers, constructors, and management who could have worked together to solve the issue. Rather they tried to insulate themselves from liabilities and to push the risks on to the other parties which made their relationship thoroughly dysfunctional. At the end, the dangerous cocktail of time, money, stubbornness and frustration (near the end of over budget , long delayed project) has caused the lives of workers.

Having a bit of experience myself in working for mines, tunnels and claustrophobic hyperbaric chambers, I have some idea of the "adventure" and risk that the job entitles to the people working in such conditions on a daily basis. Even then, I found the book baffling and I found it hard to digest the fact that these divers were exposed to such extreme risks.

Entering a hyperbaric chamber 

But this seem to be the reality of lump-sum low bid construction. The company bids the bare minimum and can make profit only when the cost turn out to be unusually low. In order to do so, the company weighs in too much on the responsibility that it assigns to a third party and the farther the managers are from the actual decision making, the greater is their tolerance for risk. In such an arrangement, as the problem arrives, the priority is not on solving them but to figure out who's is to blame and who is going to pay. Hence the problem gets a lot harder and more expensive to fix. Once relationship gets poisoned, the parties become so fixed in their position that they could no longer trust the intention of the other side.

If there is any incident, it is usually caused by a series of small bad decisions made by many individuals, none of which on its own would have been enough to produce a failure.The author draws the comparison with "Swiss cheese" model of failure which is often used by safety scientists. When the holes in organizational defects line up in ways that had not been foreseen, the problem require rapid interpretation and responses and here it is when that things can go wrong. 

I got to learn very good lessons for my professional as well as personal life based on the narrative presented in the book. I could immediately relate to some of my projects where opposing sides become fixed in their positions, relying on cognitive shortcuts as they are locked in adversarial contest. Some of my take away points are:

• Accidents do happen when confidence runs high and tolerance for delay dips low. This should not let people accept looser standards in the name of greater speed. The more people do something without suffering bad outcome, the harder it could become to remain aware of the risks associated with that behavior.
• Engineer should have a good sense and strong stomach to say no whenever he/she ethically believes so. An engineer has to plan to follow proven protocols rather than panic gut decisions.

Overall, a very interesting story documenting the heroism of the workers and mis-management of design and contract administration.

The Italian Art of Tunnelling

Literature survey will show that the fundamentals of modern tunnelling were already well understood during 19th and 20th century. The basic processes were almost completely understood by then and the only actual innovations have been in the use of new materials (shotcrete, high-strength steel, steel fibre reinforcements, admixtures, etc).

Based on the country of origin and underlying principles, there have been many classification of "tunnelling methods". It is quite obvious that differentiation of various "tunnelling methods" is sometimes difficult and they often overlap with each other. More often, a combination of "methods" offers an optimal solution for the problem at hand. However, for the case of classification, the classical tunnelling methods can be broadly divided into:

• German Tunnelling Method - Core method
• The English Tunnelling Method - Longitudinal beam/ trestle method
• Belgian Tunnelling Method - Underpinning method
• The (old) Austrian Tunnelling Method - Upraise tunnelling
• The New Austrian Tunnelling Method (NATM) - Thin-walled support to relieve ground pressure
• The Italian Tunnelling Method - ADECO-RS (Lunardi Method)

This post covers some salient points of the Italian tunnelling method.

Italian - Packing method in squeezing condition [4]

Traditionally, the Italian tunnelling method referred to packing method. It is used to overcome very difficult geological conditions (strongly squeezing rock with water ingress). Excavation is done in parts with immediate installation of packing material (even within the finished dimension of tunnel) and later broken out after ring closure. Later, the tunnelling method developed by Dr. Lunardi and Prof. Pelizza was referred as New Italian method, which was called ADECO-RS (Analysis of COntrolled DEformation in Rocks and Soils). The intention was to develop a process, which can conter the disadvantages of the NATM in regard to safety and cost-effectiveness in squeezing ground conditions.

While the Austrian method calls for partial excavation to increase face stability, the Italian method advocates full face excavation but with advance face support using methods like glass fibre anchors, jet grouting etc. This results in early ring closure than with the excavation of the entire cross-section in parts and keeps the deformation of the rock mass low. In addition, it also permits the use of large and powerful machines and hence faster production rates.

Lunardi [3] summarizes that the ADECO-RS approach emphasis to:

• Analyse the deformation response of the ground both ahead of and down from the face (using experimental, full scale, numerical, empirical tools etc)
• Controlling the susceptibility to deformation of the ground ahead of the face (advance core) by using appropriate stabilization techniques (various face stabilization techniques proposed in Dr. Lunardi's paper are shown below).

Choice of face stabilization methods [4]

While it may seem very similar to the New Austrian Method of measurement and control, Lunardi [3] clearly summarizes the difference in design and control using the pictures below:

Difference in analysis approach

Difference in control approach

Elaborate explanation about ADECO-RS method is given in Dr. Lunardi's book [1].

References:
[1] P. Lunardi, Design and Construction of Tunnels: Analysis of Controlled Deformations in Rock and Soils (ADECO-RS). Springer, 2008.

[2] Pelizza, S.; Peila, D.: Soil and Rock Reinforcements in Tunnelling. In: Tunneling and Underground Space Tech. 8 (1993), No. 3, S. 357–372.

[3] P. Lunardi, “The design and constrution of tunnels using the approach based on the analysis of controlled deformation in rock and soils,” Tunnels & Tunnelling International, no. May, pp. 3–30, 2000.

[4] Maidl, Bernhard, Markus Thewes, and Ulrich Maidl. Handbook of Tunnel Engineering I: Structures and Methods. Vol. 1. John Wiley & Sons, 2013.

Book Review: NATM - The Austrian Practice of Conventional Tunnelling

NATM book by Austrian Society of Geomechanics,
ISBN: 978-3-200-01989-8

NATM - The Austrian Practice of Conventional Tunnelling is the book released by the Working Group "Conventional Tunnelling" of The Austrian Society of Geomechanics in the year 2010. I had a chance to go through this book and want to share my impression through this blog post.

As described by Professor Robert Galler, during the release of this book, this book contains all the topics concerning NATM with the necessary references. Although the topics are not covered in-depth, this book acts as a primer to all the disciplines of engineers/stakeholders to start understanding about conventional tunnelling / NATM.

First four chapters covers the general definitions, applicability of the method and explains the typical stages in design phase. Chapter 3 on "Application of NATM" briefly explains the construction sequence clearly with the help of illustrations and site photographs. I found it very useful in relating with site conditions and visualization of the construction sequences. For the soft ground conditions, three examples of Tunnels (Road tunnel with shallow overburden, Metro tunnel in urban area with shallow over burden and Railway tunnel with shallow overburden) are explained with typical excavation sequence & tunnel cross sections.

Chapter 5, 6 and 8 covers the details about Geotechnical investigation, geotechnical design and geotechnical monitoring along with flowchart for design process at different stages of project.

The remaining chapters gives a general overview about safety management, contracts and risk management. Since the target audience for this book is varied (which includes engineers, geologists, owners, decision makers, etc.) specific topics like Rock mechanics, rock classifications, numerical modelling, design of supports etc, are not discussed in this book. Very good book to start understanding about Tunnelling and allied aspects.

-Senthil Nath G T

Risk Management in Tunneling

This article is a brief summary of Chapter 2 of Mechanized Tunnelling in Urban Areas by Vittorio Guglielmetti et. al by Taylor and Francis Publications and Guidelines for Tunnelling Risk management proposed by International Tunneling Association (WG No. 2), published in Tunnelling and Underground Space Technology 19 (2004) 217–237 (doi:10.1016/j.tust.2004.01.001).

“No construction project is risk free. Risk can be managed, minimized, shared, transferred, or simply accepted, but cannot be ignored”^[1]. Due to inherent uncertainties, including ground and groundwater conditions, there might be significant cost overrun and delay risks and as well as environmental risks and hence Formal Risk Management is becoming more common for underground projects to systematically and continually conduct formal risk management evaluations at all stages of underground projects. Risk Management Plan (RMP) can be broadly divided into the following steps:

• Step 1: Hazard Identification
• Step 2: Assigning probability of occurrence (P)
• Step 3: Assigning consequence/impact of hazard (I)
• Step 4: Risk Analysis
• Step 5: Risk response & monitoring

Probability-Impact pair (from step 2 and step 3) defines “Initial risk level”. In cases where “Initial risk level” is above acceptable risk level, step 5 is performed to bring it down to “Residual risk level”. Figure 1 illustrates this concept of initial risk and residual risk.

Figure 1 Risk Level Definition

Following sections brief each of above steps of Risk Management Plan (RMP).

Risk Identification (Step 1, 2 & 3)

Types of hazards depend on the type of project and the method of construction. However, in any tunneling project, the main risk stages would be:

1. Data collection stage (Geology, Hydrogeology, Geotechnics, Hydraulics, etc.)
2. Design stage (insufficient experience, difficult solution, lack of design flexibility, etc.)
3. Construction stage (method, technology, human factors, etc.)

For each of the above design stages, project specific objectives and project tolerances are to be identified and documented in Reference Design Scenario. Once the Reference Design Scenario is defined, workshops with experts, desktop study and engineering judgment based on past experiences are used for identifying associated risks, likelihood, impact etc. and are compiled in Risk Register. Risk register would also include identification of specific strategy to reduce each initial risk and quantification of residual risks.

Risk Analysis (Step 4)

In the early stage of project, qualitative risk analysis is used. The timing of the qualitative risk assessment should be such that major design changes are still possible. Probability (P) and Impact (I) are assigned using qualitative scales that are prepared using engineering judgment, brainstorming, etc. Risk, R is defines as the product of P & I. P and I can be defined on 3 point scale or 5 point scale depending on the requirements. I can be further divided based on specific project requirement. Typical example of a qualitative scale (on 5 point scale) is shown in Figure 2.

Figure 2 Qualitative scale of Risk­­­­

A preliminary estimate of project vulnerability to different types of risks is achieved if qualitative evaluation methods are used while a more reliable estimate can be provided if quantitative methods (probabilistic analysis) are used.

Quantitative risk analysis is performed by substituting qualitative P & I with quantitative estimates of P & I. Probability associated with data regarding the ground characteristics, construction variables and unpredictable events can be treated statistically to identify the most appropriate probability distribution function for each variable. Quantifying the impact of a hazard is mainly done to quantify its consequence in terms of project time and cost at different stages of the project. At the end of Quantitative risk analysis, following key parameters are arrived at:

1. Normal cost of project                    : Calculated using deterministic design
2. Variance in project cost                  : Calculated using foreseen variations
3. Base cost                                        : Normal cost (item no. 1) + Variance cost (item no. 2)
4. Sum of all individual risk events (calculated using quantitative risk analysis). Assuming that all risk will act together
5. Range of probable cost                   : Base cost (item no. 3) + Summed risk cost (item no. 4)

The above process of probabilistic estimation of time and cost can be performed using the software system DAT (Decision Aids in Tunnelling). DAT not just calculates the above parameters but also simulates the construction cycle of a tunnel by following a proposed construction sequence along a probabilistic geological profile that stochastically changes for each simulation process for probabilistically significant number of runs. Using the computational effort, it is possible to make a comparative evaluation of the performance of the project alternatives.

Risk Response and Monitoring (Step 5)

The authors opine that for effective use of Risk Management Plan (RMP), the designer can assume two important roles in construction phase:

• Interact with TBM Manufacturer and contractor in order to contribute new ideas of technological innovations
• Validate the design hypothesis by observation and monitoring during construction

Elaborating on the monitoring point, the author describes about “Plan for Advance of Tunnel” (PAT). The PAT is a live document that provides a dynamic link between design and construction and facilitates the management of residual risks.  A PAT is updated as the tunnel progresses (say every 200-500m stretch). It summarizer both the design and construction requirement in order to achieve a safe performance and is based on the content of the initial design, construction feedback from previous PAT and on new input data.

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[1] Sir Michael Letham, 1994 also reported in Clayton, 2001

Book Review: Soil Improvement - PVD Technique

Book Review: Soil Improvement - Prefabricated Vertical Drain Techniques by M.W.Bo, J.Chu, B.K. Low and Choa. V, Thomson Publishers 2003.

I had become Dr. B.K.Low's fan immediately after reading his papers on Geotechnical reliability analysis and probabilistic approach to geotechnical problems. I liked the way he solves a complicated problem with an easy-to-understand numerical model in the form of spreadsheet. So when I came across this book, I was really curious to go through it. 

This handy book, entitled Soil Improvement, gives the reader an account of case studies of projects where PVDs are installed for ground improvement, along with the theoretical background behind it. Authors present a spreadsheet template for computation of degree of consolidation using the implicit finite difference solution. The computed settlements are then compared with field measurements from case studies. Case studies presented are Changi Airport, Changi East Reclamation Project, Chep Lap Kok Airport, Tianjin East Pier Project & Oil Storage Station Project.

What is particularly interesting in this book is that it discusses, in-detail practical aspects of installation, quality control, field instrumentation and assessment procedures. In absence of any International code for implementing Ground improvement using PVDs, this book proves to be a treasure of knowledge for practicing geotechnical engineers. Every engineering firm involved in PVD design/installation should have at least one copy.