Project Risk Assessor Model for Underground Corridor Construction

Dr. Debasis Sarkar, Assistant Professor, Construction and Project Management Dept., Faculty of Technology, CEPT University, Ahmedabad

Project Risk Assessment is an integral part of Project Risk Management which primarily comprises of cost and schedule uncertainties and risks. These risks can be assessed or measured in terms of likelihood, impact and consequences. Depending upon the severity of each of the risks obtained after the assessment, specific risk mitigation measures have been proposed. The decision making authorities of the project should take appropriate decision pertaining to the adoption of the mitigation measures for reducing the likelihood of occurrence of the identified risks involved in the project. In this paper Case Study of Metro Corridor MC 1B (Delhi Metro Rail) has been considered for development and formulation of the Project Risk Assessor Model (PRAM). This PRAM will be effective for ongoing projects of Delhi, Kolkata and Bangalore metro rail, and future anticipated projects of Mumbai, Chennai and Ahmedabad metro rail.

Introduction

For a complex mega infrastructure project like construction of an underground corridor for metro rail operations, risk assessment should be mandatory during the conceptual and feasibility phase of the project. For effective risk assessment, proper investigation and identification of the sources of risks need to be carried out by the risk management team. These risks can be assessed or measured in terms of likelihood, impact and consequences. The most appropriate way of dealing with the project risk is treating it as a function of likelihood and impact [Risk = f (likelihood, impact)]. Finally, as risk is a component which cannot be eliminated, suitable risk mitigation measures are to be suggested which will enable to reduce the identified project risks.

The major activities of the underground corridor construction consist of feasibility studies, design, traffic diversion, utility diversion, survey works, soldier piling and king piling works, timber lagging works, soil and rock excavation, construction decks, steel struts, rock anchors, subfloor drainage, waterproofing, permanent structure works, mechanical and electrical installations and backfilling and restoration works. For a complex infrastructure project like construction of underground corridor for metro rail operation, risk identification should be done as perfectly as possible to formulate a proper risk assessor model. Identification of the risks at the various phases of the project (feasibility phase to execution phase) has been carried through personal working experience and interaction with experts involved in and associated with underground corridor projects of Delhi and Kolkata metro rail and also similar complex infrastructure projects. The responses from the experts have been obtained through a questionnaire survey and the consistency of the responses has been ensured through Delphi technique.

Literature Survey

For an infrastructure project there is always a chance that things would not turn out exactly as planned. Thus project risk pertains to the probability of uncertainties of the technical, schedule and cost outcomes. Jannadi and Almishari (2003) developed a risk assessor model for assessing the risk associated with a particular activity and they tried to find out a justification factor for the proposed remedial measure for risk mitigation. Peterson et al. (2005) worked on risk and uncertainty identification, risk and uncertainty analysis and decision analysis which as per them are all integral to any responsible and respectable risk management process. A thorough risk management process combines two defined forms namely qualitative and quantitative analysis. Qualitative risk analysis mainly focuses on prioritizing the risks for which action needs to be taken. It is also a pre-requisite for quantitative risk analysis. Quantitative risk and uncertainty analysis can consist of deterministic methods such as decision trees or risk matrices and stochastic methods such as Monte Carlo simulation. As per them, Monte Carlo simulation helps to assess the probability to achieve project objectives. It helps in identifying realistic and achievable cost, schedule and scope targets. Also it helps in determination of the apparent best project decision when some conditions or outcomes are uncertain. Diekmann and Featherman (1998) developed a cost uncertainty assessing model based on influence diagramming and Monte Carlo simulation.

Complex projects like construction of underground corridor for metro rail operations involve risks in all stages / phases of the project starting from the feasibility phase to the operational phase. These risks have a direct impact on the project schedule, cost and performance. Reilly (2005), Reilly and Brown (2004), Sinfield and Einstein (1998) carried out their research on underground tunnel projects. Reilly and Brown (2004) stated that infrastructure underground projects are inherently complex projects with many variables including uncertain and variable ground conditions. As per Reilly (2005) for a complex infrastructure project like underground construction it is very important to identify the risk events in early phases of the project. A proper risk mitigation plan if developed for the identified risks, it would ensure better and smooth achievement of project goals within specified time, cost and quality parameters. It would also ensure better construction safety throughout the execution and operational phase of the project.

Dey (2001) developed an Integrated Project Management Model for Indian petroleum industry where he incorporated risk management into the conventional project management model and cited it as an integral component of project management. But the analysis carried out by finding out the respective likelihoods of the identified risks were found to be having a summation of 1 for the respective work packages on local percentage (LP) basis and the summation of the likelihoods of all the concerned work packages to be equal to 1 on global percentage (GP) basis. Nehru and Vaid (2003) carried out the risk analysis with similar concepts. As per Nicholas (2007) the likelihood of the identified risks can have a value ranging from 0 to 1, which indicates 0% chance of occurrence and 100% chance of occurrence. But the weightages associated with all risk sources for a work package / activity is always equal to 1. The product of the likelihood and the respective weightages equals to cumulative likelihood factor (CLF).

Conceptual Framework

The Base Time Estimate (BTE) and Base Cost Estimate (BCE) of all the major activities of the project and also for their work packages have been calculated as per the detailed construction drawings, method statement and specifications for the works collected from the project. The corresponding expected failure time or Corrective Time (CT) for each activity and their expected failure cost or Corrective Cost (CC) has been tabulated. The Likelihood of failure (L_i) of each activity as per the feedback from the questionnaire survey from the experts has also been tabulated. This value ranges from 0 to 1. The corresponding Weightage (W_i) of each activity has also been obtained from the feedback of the questionnaire survey circulated among the experts. The summation of the weightages should be equal to 1. ie. “W_i = 1. The weightages can be based on Local Priority (LP) where the weightages of all the activities of a particular work package equals to1. For Global Priority (GP) the weightages of all the interrelated work packages of the project equals to 1. The Risk Cost (RC) and Risk Time (RT) of the activities of the different work packages of the project can be obtained from the following relationship:

Risk Cost (RC) = Corrective Cost (CC) x Likelihood of failure (L_i) -----------(1)

Risk Time (RT) = Corrective Time (CT) x Likelihood of failure (L_i) -----------(2)

(Note: Total Risk Time for a work package is the summation of risk time of all the activities along critical path) The Likelihood (L_i) of risk sources of all the activities of a work package can be combined and expressed as a single Composite Likelihood Factor (CLF). The Weightages (W_i) of the risk sources of the activities are multiplied with their respective Likelihoods to obtain the CLF for the work package. The relationship of computing CLF as a weighted average is given below:

Composite Likelihood Factor (CLF) = L₁(W₁) + L₂ (W₂) + L₃ (W₃) + ……… + L_n (W_n) = Σ L_i W_i -----------(3)

(i = 1,2,3, …. n)

Where L_i and W_i are the Likelihoods and Weightages respectively of the i^th risk source of the activities of a work package. The values of L_i ranges from 0 to 1 and Σ W_i = 1.

The impact of a risk can be expressed in terms of the effect caused by the risk to time and cost of an activity of the work package. This time impact and cost impact can be considered as the risk time and risk cost of the activity of the work package. Risk impact can be expressed as qualitative rating as high, medium or low and can also be expressed as a numerical measure between 0 and1, where 0 is “nil impact” and 1 is “most serious” impact. A similar computation as that of likelihood can be done for obtaining a single combined Composite Impact Factor (CIF) by considering the weighted average as per the relationship given below:

Composite Impact Factor (CIF) = I₁(W₁) + I₂ (W₂) + I3 (W₃) + ……… + I_n (W_n) = Σ I_i W_i ----------(4)

(i = 1,2,3, …. n)

Where I_i and W_i are the Impacts and Weightages respectively of the i^th risk source of the activities of a work package. The values of I_i ranges from 0 to 1 and Σ W_i = 1.

Risk Consequence or Severity can be expressed as a function of Risk Likelihood and Risk Impact. Thus the numerical value will range from 0 to 1. This severity can also be expressed in terms of qualitative rating as “no severity” for value 0 and “extremely high severity” for value 1. The numerical value of the Risk Severity is obtained from the below mentioned relationship:

Risk Consequence / Severity (RS) = L_i x I_i ----------(5)

Here L_i and I_i are Likelihood and Impact respectively of the i^th risk source of a work package.

Risk Consequence / Severity can also be expressed as:

Risk Consequence / Severity (RS) = CLF + CIF – CLF (CIF) ----------(6)

The Risk Consequence derived from this equation measures how serious the risk is to project performance. Small values represent unimportant risks that might be ignored and large values represent important risks that need to be treated.

The Probable Cost (PC) and Probable Time (PT) of each activity of the work package are calculated using the following relationships:

Probable Cost (PC) = BCE + RC + Opportunity Cost -----------(7)

Probable Time (PT) = BTE + RT ----------(8)

Some basic assumptions were considered during the analysis. These assumptions are that, the maximum cost overrun permissible is 25 % of the basic cost beyond which the project becomes less feasible. Also the maximum permissible time overrun for infrastructure projects is about 30% to 50%.

Case Study

Details of the project of underground corridor of metro rail taken as case study for Project Risk Management is described as below:

1. Scope of work: Design and construction of underground Metro Corridor MC1B from Inter State Bus Terminus (ISBT) to Central Secretariat (Delhi) with 6 underground stations and twin tunnel system. The underground stations include Delhi Main, Chawri Bazzar, New Delhi, Connaught Place, Patel Chowk and Central Secretariat.
2. Client: Delhi Metro Rail Corporation (DMRC)
3. Contractor: International Metro Civil Contractors (IMCC JV) This is a joint venture of five companies as stated below: DYWIDAG (Dykerhoff & Widman AG, Germany) with 9% shares. L&T (Larsen & Toubro Ltd, India) with 26% shares SAMSUNG (Samsung Corporation, South Korea) with 26% shares IRCON (IRCON International Ltd, India) with 9.5% and SHIMIZU (Shimizu Ltd, Japan) 9.5% shares.
4. Consultant: General Consultants (GC)
5. Type of contract: Design Build Turnkey Contract
6. Contract Period : April 2001 to March 2006
7. Total project cost: Rs. 1800 Crores.
8. Length of route : 6569 m
   1. Tunnel (by Tunnel Boring Machine [TBM] ) – 3811m
   2. Tunnel (by Cut & Cover method) – 937m
   3. Station boxes – 1821m
9. Depth of stations: 15 – 20 m below ground level
10. Typical width of stations : Average 20m
11. Typical length of stations: 275m to 300m
12. Design life: 120 years for underground structures and 50 years for super structures
13. Major scope:
    1. Excavation (soil) : 10,90,000 cu‎m.
    2. Excavation (rock): 2,15,000 cu‎m.
    3. Concreting : 3,00,000 cu‎m.
    4. Reinforcement : 47,500 MT
    5. Strutting : 24,500 MT

The sample stretch under analysis consists of 530m cut and cover tunnel connecting Patel Chowk and Central Secretariat Station, 290m Central Secretariat Station Box and 180m cut and cover over run tunnel. Central Secretariat Station being the terminal station, the down trains towards this station after leaving Patel Chowk Station will travel through the 530 m cut and cover tunnel and enter the platforms of Central Secretariat Station. After the commuters vacate the train in this terminal station, this down train will travel through the 180m over run tunnel and will be converted into up line train which will travel from Central Secretariat to Delhi Main Station.

The activities of the sample stretch under analysis consists of installation and erection of temporary supporting and retaining structures to enable construction by cut and cover technology and for construction of permanent structures like tunnels and station box which are RCC single box / twin box for tunnels and RCC box with intermediate concourse slab for station box.


The risks identified at each phase of the project and its subsequent work packages and activities are classified as follows:

1. FPR : Feasibility Project Risk
2. PEPR 1: Pre execution Project Risk – Design Risks
3. PEPR 2: Pre execution Project Risk – Technology Risks
4. EPR 1: Execution Project Risk – Risks in traffic diversion works
5. EPR 2: Risks in utility diversion works
6. EPR 3: Risks in survey works
7. EPR 4: Risks in soldier piling and king piling works.
8. EPR 5: Risks in timber lagging works.
9. EPR 6: Risks in soil excavation works
10. EPR 7: Risks in rock excavation works
11. EPR 8: Risks in installation of construction decks
12. EPR 9: Risks in installation of steel struts
13. EPR 10: Risks in installation of rock anchors
14. EPR 11: Risks in shotcreting and rock bolting works
15. EPR 12: Risks in subfloor drainage works
16. EPR 13: Risks in waterproofing works
17. EPR 14: Risks in diaphragm wall construction
18. EPR 15: Risks in top down construction
19. EPR 16: Risks in permanent structure works
20. EPR 17: Risks in mechanical and electrical installation works
21. EPR 18: Risks in backfilling and restoration works

The risks identified under each activity have been listed and a detailed questionnaire consisting of all the identified risks as per the classification stated above has been framed. This questionnaire was circulated amongst about 67 experts having adequate experience in underground construction projects or similar infrastructure projects. These experts were required to respond about the likelihood of occurrence and the weightage associated with each risk as per their experience. The methodology for receiving the filled up questionnaire from the respondents were personal approach, telephonic conversation, emails and couriers. The experts were Designers, Consultants, Dy. Project Leader, Project Managers, Dy. Project Managers, CEO, MD, Area Managers, QA /QC Incharges, Safety Incharges, Senior Engineers and Project Engineers of IMCC JV (Delhi Metro), Delhi Metro Rail Corporation (DMRC), General Consultants (GC), Kolkata Metro and Ahmedabad – Gandhinagar metro feasibility studies team. Of about 67 experts 45 had responded to this study and the mean of all the responses of respective risk likelihoods and their associated weightages in the related activities have been considered. Delphi technique was used to ensure the consistency ratio of the responses is kept within 8%.


Similarly for Feasibility, Design, Development and Execution Phase, tables have been formulated for identification of the risks involved in the respective work packages along with their likelihood and weightages as obtained from the questionnaire survey. Considering all the work packages, the major type of risks identified for the underground corridor project can be grouped and listed as follows:

1. Delay in Approval of Detailed Project Report (DPR)
2. Land Acquisition risks
3. Design Risks
4. Technology Selection Risks
5. Approval and Permit Risks
6. Joint Venture Risks
7. Financial and Investment Risks
8. Political Risks
9. Environment Related Risks
10. Geo-technical Risks
11. Major / Minor Accidents during Execution
12. Unforeseen Heavy Rains
13. Force Majeure Risks like Flood, Fire, Earthquake etc.
14. Labor Agitation and Strikes
15. Inflation Risk
16. Delayed Payment from Client
17. Delayed Payment to Subcontractor

Application of EVM for Risk Analysis

The network diagrams consisting of the major activities of respective work packages have been drawn and their early and late event times have been calculated by forward and backward pass and then their critical path was tracked out. The duration along the critical path is the longest duration path and is considered as the duration of the project. The Base Cost and Base Time of each activity for a particular work package have been calculated as per the actual site data. The Corrective Cost and Time for each activity have been assumed as a certain percentage (25% - 75%) of Base Cost and Time respectively depending upon the severity and casualty caused by that risk.


As a demonstrative example a sample analysis of the work package of soldier and king piles installation (Execution phase) of the project is presented in Table 2. The corresponding network diagram is presented in Fig. 1.


Figure 1 represents the network of the activities of work package of soldier and king piles installation of the underground corridor construction project. The critical path of the network is A-B-C-D-E-G-J-K-L-M-N and the duration for completion is 530 days. The analysis of this network has been carried out in Table 2. Activity “A” which is traffic diversion, takes a Base time (BTE) of 60 days and the Base cost (BCE) to complete this activity is Rs. 95,00,000. The likelihood of failure (L_i) of this activity is 0.1 with a Weightage (W_i) of 0.04. The Corrective Time (CT) or the failure time of this activity due to risks is 50 days. The Corrective Cost (CC) or the cost of failure of this activity due to risks is Rs. 42,75,000. The BCE, BTE, CT, CC have been calculated as per the actual data collected including drawings and specifications from the construction of the underground corridor of Delhi Metro Project. L_i and W_i have been obtained from the questionnaire survey responded by the experts associated with the underground construction. The Risk Cost (RC) and Risk Time (RT) can be calculated by using the relationship as per equation (1) and (2) respectively. Thus for activity “A” RC and RT is calculated as follows:


RC = L_i x CC = 0.1 x 42,75,000 = Rs. 4,27,500. RT = L_i x CT = 0.1 x 50 = 5 days.

Similarly the Risk Cost (RC) of the entire feasibility phase or work package can be calculated as the summation of the RC of all the activities of the work package ie Rs. 4,27,500 + 12,15,000 + …… + 26,512.5 = Rs. 2,63,62,888. The Risk Time (RT) for this feasibility phase or work package is the total risk time along the critical path ie. 5 + 6.9 + 11.25 + 6.25 + 1.3 +22.8 + 29.25 + 24 + 12.25 + 3 + 0.5 = 122.5 days. Thus for this work package, Probable Cost (PC) = BCE + RC + Opportunity Cost = 22,00,00,000 + 2,63,62,888 + 44,00,000 (assumed 2% of BCE) = 25,07,62,888. Further, the Probable Time (PT) = BTE + RT = 530 + 122.5 = 652.5 days. Thereby it is observed that the PC is about 13.98 % higher than BCE and PT is 23.11 % higher than the BTE.

Similar computations are carried out for all the other work packages of the project.

Risk Cost and Time Analysis of the Entire Project

The entire project of underground corridor construction has been analyzed by considering the risks involved in the individual work packages. The network diagram of the entire project is presented in Fig. 2. The work packages of the network diagram of the entire project as presented in Fig. 2, are as follows: A–Feasibility studies; B-Design; C-Technology selection; D-Traffic diversion; E- Utility diversion; F-Survey works; G- Soldier / King piles; H-Timber lagging; I- Soil excavation; J-Rock excavation; K-Fabrication and erection of construction decks; L-Fabrication and erection of steel struts; M- Rock anchor installation; N- Shotcreting & rock bolting; O-Subfloor drainage; P-Water proofing; Q-Diaphragm wall construction; R-Top down construction; S-Permanent structure; T-Mechanical / Electrical installations & services; U-Backfilling & restoration works.


Probable Cost (PC) of the entire project of underground corridor construction is calculated as follows:

Probable Cost (PC)_Project = PC_FPR + PC_{PEPR 1} + PC_{PEPR 2} + PC_{EPR 1} + PC_{EPR 2} + …… + PC_{EPR 18} = Rs. 401,45,02560.

Base Cost Estimate (BCE)_Project = Rs. 324,00,00,000.

Probable Time (PT)_Project = Base Time Estimate (BTE)_Project + Risk Time (RT)_Project = 3786 + 884.47 days = 4670.47 days

Thus as per the analysis, Probable Cost (PC) of the project is 23.90% higher than the Base Cost Estimate (BCE) of the project. The Probable Time (PT) of the project is 23.36% higher than the Base Time Estimate (BTE). As per the basic assumptions considered for risk management analysis the cost overrun should not exceed 25% of the estimated base cost and the time overrun should not be more than 30 - 50% of the estimated base time. Exceeding these limits would increase chances of the project becoming less feasible. The risk management analysis predicts probable cost of the project which is 23.90% higher than the estimated base cost which is highly alarming as it almost touches the upper limit of the permissible cost overrun. It requires meticulous planning and proper risk mitigation measures to enhance the probability of success of the project. The probable time predicted from the analysis is 23.36% higher than the estimated base time which is nearing the upper limit of permissible time overrun (30-50%), thus making it essential to judiciously follow the risk mitigation measures to ensure that the project is completed within scheduled time frame.

Risk Severity Analysis using Concept of CLF and CIF

Risk severity can be computed from equations (5) and (6). The product of likelihood and impact of a risk can be considered as the severity of that risk. This concept can be extended for multiple risk sources in a work package the likelihood and impact of which can be expressed in terms of CLF and CIF respectively. Thus for underground corridor construction project, risk severity of each work package of the project is computed as presented in Table 5.


The scale for classification of risk severity is expressed as

Risk severity analysis has also been carried out by PERT analysis and the outcome of both EVM and PERT analysis in terms of severity of the major work packages of the project is presented in table 6.

Proposed Risk Assessor Model

Generalized Project Risk Assessor Model (refer Fig.3) for underground corridor construction is proposed on the basis of the detailed analysis carried out. This model can be effectively implemented in the upcoming metro rail projects in Indian cities like, Chennai, Mumbai, Ahmedabad and also on the ongoing metro rail projects of Delhi Kolkata and Bangalore.


As a part of formulation of risk mitigation strategies, following risk response planning can be adapted by the project authority:

1. Transfer of risk
   For a complex infrastructure project, risk can be partly or fully transferred from the client to contractor, subcontractor and users of the project. This can be done using contractual incentives, warranties, or penalties attached to project performance, cost or schedule measures. It is to be noted that entire transfer of risk is impossible and transfer of one kind of risk may inherit another kind of risk. Risk sharing between the concerned parties so that proportionate burden of uncertainties is born by the client, consultant, designer, contractor, sub contractor and also the users seem to be an effective risk mitigation strategy.
2. Avoid risk
   Some of the identified risks can be avoided by altering the original project concept (eg. attempting to eliminate risky activities, minimizing system complexity etc.), changing contractors and subcontractors, using tested and certified construction equipments particularly cranes, hydraulic excavators, hydraulic rigs, hydraulic breakers etc. The risk management team should make the project authorities aware that it is always better to reduce risk to an acceptable level than to attempt to completely avoid the risk.
3. Reduce Risk
   Risks for a complex infrastructure project like underground construction can be reduced by (a) employing most capable contractor, consultant and designer (b) establishing a standard safety department and ensuring that the safety rules and regulations are religiously followed by project personnel and workforce. Violation of safety rules should be treated seriously and in some cases heavy penalties should be imposed. (c) as a matter of policy the client should always give priority to safety than to work progress (d) using mature, computer-aided system engineering tools (e) establishing a fully equipped quality control / quality assurance department (f) providing the project team with adequate incentives for success and providing good amount as safety awards (g) hiring experts for critical review and assessment of work (h) performing extensive tests and evaluations (i) using effective management information systems for project monitoring and control (j) minimizing system complexity (k) using proper design margins and risk free designs (l) All concrete used for temporary or permanent should be Ready Mixed Concrete (RMC) (m) All formwork used should be of latest safe formwork type like Doka Formwork System
4. Risk Contingency Planning
   In risk contingency planning the consequences of the identified risks are anticipated and detailed plan of action is prepared for mitigating these risks. Contingency funds should be taken into consideration along with the base cost of the project to calculate the expected project cost. Contingency action can also be an action taken parallel to original project plan or it can be a preventive action initiated by preliminary risk symptoms to mitigate the risk impact.
5. Accept Risk
   For risks for which impacts or consequences are not severe, and if the cost of avoiding, reducing or transferring the risk exceeds the benefit, then it may be advisable to accept the risk. But risks with severe consequences should not be accepted and always risks with severe impacts should be carefully treated, no matter how small is the likelihood of occurrence of the risk.

Flow chart of the proposed Project Risk Assessor Model (PRAM) is presented in Figure 3.

Conclusions

In present research work it has been found that the numbers of major and minor risks involved during the construction of the project from the feasibility to completion of the execution, are large and if not treated or mitigated properly, the probability of successful completion of the project within stipulated time and cost frame will reduce. This will have a direct impact on the efficiency and profitability of the organization.

As per the analysis carried out by EVM based on the expert questionnaire survey the probable project cost for the sample stretch under analysis (530 m, cut and cover tunnel connecting Patel Chowk to Central Secretariat station, Central Secretariat Station Box and 180m cut and cover over-run tunnel) is about 23.90 % higher than the base cost estimate of the project. According to basic assumption made for the analytical procedure adopted, the maximum permissible cost over-run for the project is 25 %, thus if proper Project Risk Management is not carried out by the authority, the project will result in cost over-run and time over-run which will ultimately reduce the feasibility of successful completion of the project. The probable project time as obtained by the analysis is about 23.36 % higher than the base time estimate of the project, the maximum permissible time over-run as per basic assumptions being 30–50 % of the base time, this figure is also highly alarming making the concerned authority feel that the need for carrying out proper Risk Management for such type of complex infrastructure projects.

Hence considering the results of all the analysis carried out in this research work it can be concluded that for complex infrastructure projects like that of an underground corridor construction about Rs. 8.8 lakhs per day per station would be incurred extra if proper risk management is not followed to mitigate the anticipated risks. Thus for six underground stations for this 6.8 km MC 1B package approximately Rs. 53 lakhs per day have to incurred extra by the project authorities. Though at present a very nominal percentage of identified risks can be insured under the existing “Contractors All Risk Policy” but potentiality of insurance and means of making insurance as a strong risk mitigation tool for construction industry will be a future scope of research.

The proposed Risk Management Model will definitely benefit the future anticipated metro projects in Indian cities like Chennai, Mumbai, Chandigar, Ahmedabad and ongoing projects of Delhi, Kolkata and Bangalore metro.

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Acknowledgement

The author (former Senior Engineer of IMCC JV, Delhi Metro) highly acknow- ledges the support and cooperation of IMCC JV for carrying out this research work.