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.

Hulme Prize 2017

This year, I was privileged to get two of my papers shortlisted for the annual competition for the best technical papers from young engineers on subjects  associated with tunnelling and underground construction. The three papers shortlisted for this year are:

• Large Diameter Pipe Roof Box Excavation For Passenger Linkway Tunnel 
• By Ms F. Saffiyah Badurdeen, Ed. Zublin AG Singapore & Mr G. T. Senthilnath, Geoconsult Asia Singapore 

• Mined Tunnel Monitoring as a Part of Observational Approach – a Case Study 
• By Mr G. T. Senthilnath, Geoconsult Asia Singapore  

• Latest Development in Horizontal Grouting for Cross Passages in Thomson East Coast Line C1-C2 
• By Ms Jasmine Lim, Land Transport Authority

Presentation of the shortlisted papers were held on 17th August 2017 at the SMRT Auditorium and prizes for the winners were distributed during TUCSS Annual Lecture at Stephen Riady Auditorium At One Marina Boulevard, Singapore. The first paper was presented by my co-author and I presented the second paper (summary of the paper is available in my previous post).

The Hulme Prize was set up by TUCSS in 1999 in honour of Mr. Terry Hulme, Honorary Member of  TUCSS,  for  his  outstanding  contribution  to  TUCSS  and  Tunnelling  in  Singapore. It  is  an  annual competition  for  the  best  technical  paper and the winners are presented with a cash prize and citation.

SCL / NATM tunnel lining displacement monitoring - Case Study

The observational method is widely used in tunnelling works. For a successful implementation of observational method in tunnelling, an efficient monitoring, data evaluation and interpretation on site is of prime importance. Reviewing the common practice on sites in Singapore, it could be said that, there is a potential for improvement in the data collection and interpretation techniques employed for mined tunnelling works in Singapore. Although there are several advanced tools available in the market for data handling, evaluation and interpretation; there is a scope for development of simple and easy to use tools, to properly handle the spatial displacement measurements. With the adoption of Eurocode 7 in Singapore, it is further more important to evaluate the mined tunnel movements, continuously update the geotechnical model & adjust the excavation/support system to suit the actual ground conditions.

This post presents simple implementation of absolute tunnel displacements visualization in the ubiquitous spreadsheet software. A practical procedure for predicting and comparing displacement behind the face in relation to face advance and time is presented with a case study of mined tunnel in shallow overburden condition. The case study considers a mined tunnel which is in overburden ranging from 6m to 8m under a road with significant traffic as well as major utilities and services. The design included temporary excavation support using staggered piperoof,  sprayed concrete with lattice girder and wire mesh. Observations & insights provided by spatial visualization of the tunnel displacements are presented.

A custom-built spreadsheet macro was prepared for this case study project to visualize the displacement vectors at each monitoring array and deflection curve along the tunnel alignment at any point in time based on the latest raw data obtained from the instrumentation and monitoring contractor. Below figure shows the monitored displacement characteristic of the mined tunnel as vector plot in a plane perpendicular to the tunnel axis. The displacement plot in this figure is for the lattice girder location “S3-5” (which could be selected from the option button on left side. List indicates the location of all monitoring array locations). The displacement pattern can be described as almost symmetrical in the cross section with slightly increased displacement on the right side. In a homogenous, isotropic ground, the crown prism movement is expected to be vertically down however the movement is towards left side which could indicate a possibility of singularities near the face. In case there was any fault / singularities on the right side of the tunnel face, the readings on the right side (instrument P3 and P5) would register larger movements. In this manner, features outside the excavation area (faults, slickensides etc), change in stress situation and kinematics could be predicted based on these displacement vector plots. 

Custom built spreadsheet VB script to visualize displacement vector

Below figure shows the monitored displacements vectors in a plane parallel to the tunnel axis. The plot in longitudinal direction shows displacement vectors tending against the excavation direction. Influence of foliation modifies the longitudinal settlements. Using the knowledge about the influence of the anisotropy orientation on the displacement development, the geological structure encountered on site can be used to predict the expected spatial displacement vector orientation. Any significant deviation from this “normal” behaviour will thus reflect an abnormal behaviour. In case the reason for the abnormality does not originate from a failed support system, the type of deviation can be used to predict changes in the ground condition ahead of the tunnel.

Custom built spreadsheet VB script to visualize 3D prism movements

Ground settlements at different stages of excavation

Monitoring methods along with above interpretation methods could improve short term prediction in tunnelling. The information, which can be extracted from displacement monitoring data, is enormous. This insight plays a crucial role in difficult geotechnical conditions or in sensitive environments. In order to meet the requirements of a Eurocode 7 compliant “observational method” design, dedicated design preparation work prior to construction and organized monitoring system is required. This case study proves that this could be achieved easily on site without the need for any special software. 

Reference:

[1] Senthilnath G T, Mined tunnel monitoring as a part of observational approach - A case study, Tunnelling and Underground Construction Society (Singapore), 2017

ITACET Training Course, KL - Lecture on Singapore Case Studies

Recently I had the pleasure to deliver a lecture during ITACET training course in Kuala Lumpur, Malaysia.

Speakers & participants of the ITACET training course

Receiving token of appreciation from Dr. Ooi Teik Aun

The two-day training session on the "Principles of Tunnel Design" was held on 20th & 21st April 2017 at the P J Hilton, Petaling Jaya, Selangor, Malaysia. This short course was organized as a post conference event of the SEACETUS 2017. The training session was organised by The Institution of Engineers, Malaysia (IEM) and the Foundation for Education and Training on Tunnelling and Underground Space Use (ITACET).

The training session provided an introduction to the principles of tunnel design throughout a project cycle, from planning, design and construction, through to implementation of a tunnel or underground project. Contents of the course is available at: link. Official report of the training course is available in IEM wesbite: Link

My presentation was on Case history studies from Singapore. I was able to present case histories from the projects I have been involved in Singapore, which includes:

• Thomson Line MRT tunnels
• Power transmission cable tunnels
• Other LTA projects involving underground linkway construction.

Summary of my presentation brief is available at: link