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Topic 65: Excavation Work in Onshore Pipeline Crowded Areas - Risks and challenges

Oghenekevwe Ovbije's picture

Excavation is the most fundamental and important element in the construction industry, whether brownfield or greenfield. Basically, four excavation methods are employed during pipeline construction: vertical excavation; horizontal excavation; step trenching and cofferdams.


haroon latif's picture

Onshore excavation poses many risk and hazards to workers and the general public. Depending on the location, whether its urban or rural, the main risk of onshore excavation is damaging underground cables. Underground electrical cables look like ordinary pipelines, making it harder to tell if they are live or not.  

The risk posed from this is electrical shock resulting in severe burns or even death. An electric cable can easily be damaged during excavation, from either being crushed or cut partially. Cables that are damaged from excavation work and not reported can cause incidents also. 

According to the HSE, the risks from excavation work can be controlled and mitigated. This can be done by: 

  • Planning the work
  • Using cable plans
  • Cable locating devices
  • Safe digging practises

Haroon Latif
MSc Oil and Gas Engineering

Dike Nwabueze Chinedu.'s picture

Using an excavator, swamp buggy, pay-loader, bulldozer and other heavy duty equipment for onshore pipeline construction activity is a common feauture. The pipes are layed in trench foundations on the pipeline right-of-way (ROW). During this activity, personnel invovled in the construction are susceptible to the risk of being injured by falling object if not well protected with the necessary personal protective equipment (PPE). In crowded areas, there is the risk of damage to other facility within the location if the heavy duty equipment is not used properly. the most dangerous of it all is the risk of electric shock if the equipment touches an overhead or underground cable. Another risk that could result to increased cost or schedule over-run is when the excavator meets with ground rock formation which was not originally identified from the initial stage. The risk of equipment breakdown by virtue of strong environmental conditions is another obvious challenge which can impair the project execution.

In all of these, Proper project management and site supervision will go a long way in ensuring that these risks are identified, evaluated and mitigated. 

Connie Shellcock's picture

According to Adeeb et al, more than 50 % of pipeline failures in the US and Europe
are caused by mechanical interference and contact with excavation machinery. However
sometimes to maintain the pipelines , it is necessary to undergo excavation of
the pipelines.  Adeeb suggests that one
way to analyse any unwanted effects of interference with the pipe is to examine
the effects of the internal pressures of high pressure gas pipelines. This
source suggests that a safe working pressure could be established which would
allow operators to stay in a safe working bracket of pressure therefore reducing
the possibility of pipline failure while excavating. This involves the energy
needed to cause the rupture of a pipeline to be calculated (Adeeb, Horsley 2006).

and HORSLEY, D.J., 2006. A numerical procedure to establish a safe working
pressure during excavation of a pipeline in a rock ditch. International
Journal of Pressure Vessels and Piping,
83(7), pp. 488-497.


Catriona Ogg's picture

I have just watched a video of a pipe being laid in an urban area and have made the following observations regarding safety: 

1) Site security: The trenching takes place over a number of days which means that the trench is left exposed during non-working hours.  This poses a risk to the general public of falling into the trench should they permeate the site's perimeter.  In the video I watched, the trench was approximately 15ft deep which is sufficient to cause serious injury were someone to fall in.
2) Conditions within the trench: Several inches of water at the bottom of the trench.  This muddy water could conceal potential trip hazards or sharp objects.
3) Risk of trench collapse:  This is obviously more serious the deeper the trench as there is a heavier mass of soil that could cave in, potentially crushing workers.  The sides of the trench are reinforced with side support walls, but there is a risk that vibrations from the heavy machinery and pneumatic drills could cause resonance and hence structural damage to the supporting wall.  

A trench located in a crowded area would have an even higher risk of collapse with the added load of people and traffic on the soil surrounding the trench. 

AndrewRCarss's picture

Hello Catriona, 

Yes, without a doubt, excavations are one of the greatest hazards posed to construction workers in pipe laying operations. Sadly excavations still account for 10% of all deaths in the construction industry in the UK. However, that said, all of the risks that you have mentioned can be mitigated against and, in the UK, there is proven legislation to protect against the hazards you mention.  

1)     Any construction company involved in the excavation of a trench has a duty, under the health & safety @ work act 1974 (UK), to protect the general public from their activities. This means sealing off their worksite from the general public during non working hours. Non compliance can lead to prosecution. 

2)     Water in a trench can be dangerous for a number of reasons. But to make it safe to work in, there is a requirement under construction Design Management Regulations (CDM) to carry out daily inspections on the trench. If the trench is not safe to work in it should have been dewatered. 

3)     Trench collapse is the worst case scenario. Through proper planning, risk assessment and proper engineering this scenario can be avoided. There are shoring solutions for all kinds of trenches. Obviously dynamic loading on the trench walls from vehicle movements is not ideal but can be managed through a more robust shoring solution. Trench shields for example can provide much more support to the trench walls than a proprietary shoring solution.Stop blocks can be used to keep construction traffic a safe distance away from the trench walls. 

It seems to me that the mitigations in place in the video you watched were wholly inadequate. Perhaps you could send me the link to the video so I can sugesst some improvements?

Andrew Carss - MSc Subsea Engineering (DL)

Catriona Ogg's picture

Hi Andrew,

Thank you for your insight.  The videos I watched were for a pipe excavation in Sri Lanka. It's quite possible that for the most part, the safety measures that you've mentioned were implemented here; my observations were purely speculative and I'll admit this isn't an area that I know much about.  The trench does in fact flood at one point and they do use pumps to dewater it.

  With regards to public access and traffic, the trench has been excavated directly alongside a low speed railway line. In videos 2 and 3 you can see people dangling out of the windows and doors and one man actually demounts the train to give a thumbs up to the camera.  I believe the trains are carrying freight and workers, although the same line may be used for public trains in which case it would appear that in this instance, it is not possible block public access. 

Video 1

Video 2 (watch your volume on this one!)

Video 3

Mostafa Tantawi's picture


As I come
from an offshore background, I noticed that any new installation or even
intervention in crowded field have higher risks. In onshore, everything is
visible for the operator. However in Offshore unless you have the required
information of the subsea structure and their exact locations, it isn’t
possible to do any work. The threat of an anchor hitting a pipeline is relatively
higher in a crowded field. I have seen that before. When you have a convention
3 points mooring anchor ship an approved anchor pattern should be in place
before starting the positioning process. There are a lot of risk mitigation
procedures can be carried out to protect subsea structures in crowded are:

Trenching and backfilling of the pipeline

Rock dumping of crossings and exposed areas.

Concrete Mattresses for spool and riser arrangements

structures for subsea structures has become a convention.

Mostafa Tantawi
Masters Of Subsea Engineering, University of Aberdeen

AndrewRCarss's picture

Hello Mostafa,

If I understand you correctly, I believe that you are saying that you believe that the risks are greater in a crowded subsea environment than the risks that you might find onshore when installing a gas or oil line.

I cannot agree with your opinion. 

I believe that risks are relative to the environment in which they are in. Granted, intervention work in a crowded subsea field may be hazardous on the face of things. However, with the correct planning and mitigation factors in place the work can be made safe.

Planning the work by writing procedures, risk assessing the work and using approved transit corridors the risks can be brought down to as low as reasonable practical (ALARP).  

Onshore work if not planned properly can be just as, if not more, hazardous than offshore working. You mention in your post that for subsea intervention you need the information of the structure and its location before you do any work. Yes this is true, but the same principles apply when working onshore.

To give an example, you wouldn’t just start digging up the road in Central London looking for a gas main unless you had the correct information and controls in place. This may be a permit to dig and some confirmation of isolation for example.

My point is that safety engineering and risk management principles stay the same no matter what industry we are working in.

Andrew Carss - MSc Subsea Engineering (DL)

Abiaziem Davidson's picture

Excavation work in onshore pipeline crowded areas poses noise population to the environment. The noise coming from all the heavy duty equipment being used for operation is a big challenge to the host community as it makes the host community uncomfortable and most times the community is advised to relocate to another place far from the the pipeline right of way (ROW).

Another risk is destruction of existing pipeline during excavation operation, this poses the danger of exposion or destruction of investment. Pipeline excavation which invove road crossing operation tends to obstruct traffic, this is because the trench is left for days before backfilling of the trench. It also causes underground cable destruction resulting to power shortage in the area. 


Ikechukwu Onyegiri's picture

As recent comments have mentioned the risks varies from place to place. These factors depends on what we define as an "urban area". Different countries and different set of laws as regards onshore pipeline laying and excavation have been passed but I'll like to take this up from the vandalism aspect as is the case in most devloping countries.

Surely we are to say that safety laws don't extend to vandals who in the sense are commiting a crime but the dangers might not affect only them. In countries like Nigeria, vandalism is a major issue and has accounted for a lot of fatalities and land pollution over the years. Yes, companies comply with regulations as set to carry out any pipeline work but the truth is that the security of these pipelines should also draw attention to the safety bodies. Vandalism is involves illegal excavation of pipelines either to destroy them or steal from their transport and in a country like Nigeria costs the government 105billion naira yearly. Apart from this cost, the risks of explosions and pollution is highly eminent.

To quote HUSNAA "Peoplel vandalize oil pipelines because they can. It is also a possibility that though it is a hazardous venture for those who risk their lives to do it, it seldom results in tragedy and that is why you never get to hear about it until there is some really horrendous accident. Given this premise, then it becomes a calculated but highly lucrative risk".

The risks associated with excavation are eminent but it becomes a death trap when excavation occurs via vandalism.

Ikechukwu Onyegiri

Msc Oil and Gas Engineering

AndrewRCarss's picture

This is a very valid discussion you have just opened up and one that I would never have thought of before you brought it to my attention.

It is unfortunate, but in this day in age the threat of theft and vandalism of our infrastructure is a very real one. It is a threat that we as engineers will have to take into consideration in our safety engineering and risk management.

I recall the last pipe African pipe explosion that hit the headlines in the UK. It was in Nairobi, Kenya, back in 2011where 61 people were killed trying to tap into a diesel pipeline in a built up area.

We can draw comparisons between the vandalising of pipelines in Nigeria the theft of copper cable in the UK. Besides being extremely dangerous to the perpetrators, cable theft in the UK is costing the economy some £770million / year.

When the pipelines were built in Africa the designers could not have reasonably predicted the problems from vandalism. Likewise when Network rail designed the railway, they did not take into consideration the problems of theft..a reasonable assumption in my view.

Today though, things are different. Unfortunately it is the case that pipelines and railways will have to be designed to protect the public [thieves or not] and more importantly the economies of the countries in which they are in.

Network rail are already taking measures to prevent cable theft by deigning cables that are harder to steal and increased security.

There are measures that can be taken to protect oil pipelines in Africa too. New pipelines must be diverted away from urban communities. Where this is not practical, protection must be installed onto the pipes and as a final resort the pipelines must be monitored.

Unfortunately, because of the world we live in, this is a problem that is not likely to go away and as engineers we must manage it.

Andrew Carss - MSc Subsea Engineering (DL)

Thomas Ighodalo's picture


i would like to added a fifth method under pipeline construction Directional boring, commonly called horizontal directional drilling or HDD. it is a steerable trenchless
method of installing underground pipes, conduits and cables in a
shallow arc along a prescribed bore path by using a surface launched
drilling rig, with minimal impact on the surrounding area. It is suitable for a variety of soil conditions and jobs including road,
landscape and river crossings. Pipes can be made of materials such as PolyVinylChloride PVC, Polyethylene (PE), PolyPropylene (PP), ductile iron and steel. provided the strienght of material of the pipe is sufficient to be pulled through the drilled hole.

advantages of H.D.D

  • Reduce construction time
  • Saves expensive or historic landscapes and structures
  • Reduce impact on resident and business around construction site
  • Decrease overall surface disturbance
  • relatively safer than trenching


it 4-8 times more expensive than coventional open cut/ trench pipeline construction[1]





3. Willoughby, David (2005). Horizontal Directional Drilling, p. 1-263. Mcgraw-Hill, New York. 



"Everything we hear is an opinion not a fact"

Oghenekevwe Ovbije's picture

Hi Haroon,

The main risk involved in the excavation of onshore pipeline cannot be damaging underground cables. This is simply because before approvals are given for such a construction job, a subsurface/pre-entry survey must be done and the Right of Way (ROW) or pipeline track/route must be clearly defined then an Environmental Impact Assessment (EIA) is carried out by the company representative and a member of the awarding body to obtain the EIA certificate. With this measures in place, damage to electrical cables and properties are minimized.

Excavations for onshore pipeline in urban or restricted areas can be environmentally sensitive and requires a lot of planning and continuous supervision. The risks involved are [1]:
•Excavation collapse/landslip
•Overhead electrical cables
•Working on inclines/slopes
•Slinging loads and side boom operations
•Poor weather conditions
•Health issues from welding, use of chemicals and radiography
•Lack of competent resources
•Unplanned  breaks due existing scenarios like roads, railways, river crossing etc that leads to delay in project
•Difficulty in organizing an emergency response system in remote regions.
•Obstruction from host communities.

These are just a few of the risks that are associated with the excavation of onshore pipelines.

[1] Barber S, Allison P, Allinson J, Morgan B. Improving the Safety Performance of Large Scale Onshore Pipeline Projects. 2002 20-22 March 2002.

ikenna_ekekwe's picture

I would also like to add that in oil and gas processing facilities, designated pipeline corridors frequently contain more than one buried pipeline and this is the MAJOR concern. Therefore, there is always a risk of external impact to existing lines during excavation to install new pipelines either due to uncertainty of exact location or due to the use of heavy equipment in the vicinity where the excavation is to take place. This external impact is usually the biggest cause of leakage in live pipelines and this presents a major risk. Buried cables and other essential services can also be impacted during excavation works.

It is therefore necessary to ensure that the existing pipelines are accurately identified and marked ahead, prior to excavation. It is also necessary to establish an exclusion zone for heavy machinery while allowing only the use of hand tools in the vicinity.

Ekekwe Ikenna


Adejugba Olusola's picture

Persons working during an excavation can be injured or killed if they break an underground cable or pipe when digging, or if the walls of a hole or trench collapse.Steps that can be taken for safe excavation is to ensure that:

·    Check if a Permit to Work or confined space entry certificate is needed for the task

·    Find and mark the location of underground hazards

·    The sides of a trench or hole can collapse without warning. People must be protected by either:

·         Keeping the excavation shallow, sloping the sides, away from the people at the bottom of the hole; or

·         stepping the sides by cutting a series of different levels into the sides; or

·         using shoring to reinforce the sides

·         People must be kept away from the area using warning signs and barriers

·         Place removed soil well away from the sides of the hole

·         Keep a clear route to the exit

·         Stop work if weather conditions get worse and the task is assessed to no longer be safe

·         If digging goes into anything unexpected (including cables and pipes), stop work immediately

·         Erect signs and barriers around the excavation and ensure that they are highly visible

·         A competent person must inspect the excavation before and after each shift

Adejugba Olusola

ikenna_ekekwe's picture

Excavation is a very critical element of construction as it is almost always the first scheduled activity in any construction work. Every year, people are killed or seriously injured when working in excavations. Excavation work has to be properly planned, managed, supervised and carried out to prevent accidents. Before digging any excavations, it is important to plan against the following risks: collapse of the sides; materials falling onto people working in the excavation; people and vehicles falling into the excavation; people being struck by plant; undermining nearby structures; contact with underground services; access to the excavation; fumes; and accidents to members of the public.

It is also necessary to make sure the necessary equipment needed such as trench sheets, props, baulks, etc, is available on site before work starts.

Ekekwe Ikenna


Edwin Lawrance's picture

is an important part when construction is considered. Usually these construction
workers are involved in 20% of all the work related accidents. With 200 deaths annually
due to trenching accidents related to excavation. These deaths are mainly due
to cave-in, here the trapped victim suffocates to death.

Improper planning,
failure to detect the possible safety problems, failure to provide safe access,
lack of emergency rescue equipment .etc are the reason for accidents. To
prevent these accidents all the workers must be aware of the nature of work to
be done, the procedures to follow and the possible risks to face on the way. Precautions
like the use of standalone rescue equipment and monitoring of possible contaminations
must be made available, to assure the safety of the worker.


carrying out excavation work onshore a major challenge is the risk of collision
of excavating equipment with pipeline structures.

collisions could activate any of the failure mechanism of the pipelines which
could include fracture, fatigue or crack. As earlier pointed out, most pipe systems
today are installed with protection casing and additional protective sheaths
with an option of wrapping Kevlar tapes between the two sheaths to offer higher
resistance to impact loads on them. These measures however do not totally
remove the effect of impact loads on the pipelines. Excavation activities
around onshore pipelines have led to several accidents with some resulting in rupture
and hence explosions and thereby fatalities. According to US Department of
transport (PHMSA 2012), “excavation damage continues to be a leading cause of
all U.S. pipeline failures and is the single greatest threat to the safety,
reliability and integrity of the natural gas distribution system”.

calls for necessary care when excavation work is to be done onshore. The use of
work permits, Joint Safety Assessment systems, EIA’s and other such mechanisms
could ensure thorough evaluation is done before any such activity is carried
out onshore.



United States Department of
Transport, 2012. “Pipeline Safety Rule Proposes Stronger Damage Prevention

Programs, Increased
Accountability for Violators”. PHMSA, March 2012.
[Assessed online on 7th December 2012]

Agba A. Imbuo's picture

In excavating a pipeline crowded area, there are some inherent issues we will consider. We will consider the risk of damage of pipe due to lack of knowledge of the soil types, the cutting edge of the excavator could cause a pipeline to burst which might result in explosion. Also it is advisable to work with maps as maps would provide a pathway of pipe arrangement and distribution. There could also be a cave in as a result of poor filling of formerly excavated trenches. There could be accidental contact with utility lines and could lead to electrocution. All these could be avoided if there is a proper pre-job survey carried out before the job begin. 


Emmanuel Mbata's picture

Excavations as rightly mention above is one of the most hazardous construction operations no matter the location where it is carried out. Major risks includes, cave ins, collapse of spoil soils, accidental severing of underground utility lines, falling into excavated pit, flooding etc.

Employing suitable systems like the excavation permit to work to control these risks and the use of competent people and also continious risk assessment during the course of the project will help to mitigate these hazards 

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