If it takes one person 10 days to dig a ditch, how long does it take 10 people to dig the same ditch?

A simple question from primary school math class. If your answer was "one day" then you are wrong, if you said 10 days you are probably also wrong. If you said 5 you are getting warmer.

My first job after University was working on a Gold Mine. I eventually worked up to mine manager, and managed the largest Vat Leaching Gold Retreatment operation in Australia, so moving dirt is something I know a lot about. I am not sure how many people out there have to dig big holes in the ground, but I thought some of my gold mining experience may be useful for others that plan to dig a ditch in the near future.

This is the first of a series of Blogs to help people that plan to dig Ditches.

When one person gets down to dig a ditch, the job is very clear, you take a shovel you get a wheel barrow and you dig. You don't need to tell anyone what you are doing every hour; you don't have to worry about anything except digging the ditch.

But lets say we are in a hurry, and we need our hole dug faster, the only solution is either to dig faster, or get some people to help out. So lets look at the process of digging a hole for a paying customer and see how we can speed it up.

So the project plan:

  1. Discuss with the customer the plan of the hole.
  2. Decide how you will dig the hole.
  3. Mark out the area to dig.
  4. Get tools and start digging.
  5. Have customer check after about 1/4 of digging that the hole is being dug according to plan.
  6. Back to work and Complete the hole.
  7. Have customer accept and sign off that hole is correct.
  8. Clean up the area around the hole.
  9. Put away tools and write up an explanation of any issues found whilst digging the hole.
  10. Send invoice to customer.

The Design Process:

Now since its just you, the customer takes you to the spot where they want the hole dug, you both sit down with you mug of coffee, and decide the best way to dig the hole, and draw up a plan:



The Implementation process:

Next you look at where the hole is, and what tools you have, and where the dirt needs to be move to, and you work out the details, such as how do you get the dirt up the 2.4m, how far you cart the dirt etc.


The Quotation Process:

Now I have dug a lot of ditches, and I am very good at getting a full shovel load each time and can dig very straight, so I know that I can dig about 1.6-1.8 meters per day for a ditch of this depth and width, and I know that the ditch will be square and the sides of the ditch smooth. So it will take about 8.5 – 9 days of digging, which includes wheel barrowing the dirt 50m or so to where I dump it, and it gives me 1-1.5 days to handle the issues with getting the ramp setup, clearing and dirt that falls back in etc. I told the customer, that if there is any water in the ditch, then we have to re-discuss this, because I am basing this on a dry ditch with no drainage issues.

Now because I am a very good ditch digger, and very fast (someone else would probably take 20 days) I have given the customer a quote at my rate for 10 days work. The customer came back and said that the cost is OK, but they really need the Ditch dug much faster, so can I propose options. So now I look at ways to speed this up.

Of course the first thing I can do it to get an assistant to do some of the less complex work. For example I could have someone with limited ditch digging experience Take the dirt away in the wheel barrow. So lets look at that.

Wheel Barrow Assistant:

This person will take the dirt away, so that I can spend more time digging. Since pushing a wheel barrow is much simpler, I can get someone with much less experience (AKA Cheap). But I also now need a second wheel barrow, and more importantly how do we now get the empty wheel barrow down the ramp when we have a full wheel barrow at the bottom of the ramp. So the first issue is that we have now added technical complications and that requires extra Ditch digging planning. So probably we need to take the full wheel barrow out before bringing the empty one down. Also working by myself every time I go up with a full barrow load, I stop on the way back, review the overall progress of the ditch, take a drink of water and clear my head out a bit. So really have I gained anything just by having a wheel barrow assistant.

Furthermore any minor changes I make like this may cut the time from 10 days to 9 days, no where near what the customer wants. What the customer wants is to have ten ditch diggers to dig the ditch in one day.

Use 10 diggers for the job:

So lets see how this would look.


This is starting to look good. Clearly we can see that the 10 diggers can dig this ditch much faster. The first glance of this plan shows one immediate issue. Where do we find 10 top notch A grade ditch diggers, that are all going to be available to dig this ditch. In fact that is not a big problem, because the Elbonian Off Shore Ditch Digging Company can provide me with as many fully certified Ditch diggers as I need. So let's get down to practicalities and see if we can make this work.

Taking a closer view, I can see one thing missing, and that is wheelbarrows. Each digger has 1.5 meters of space, and that does not leave much room for the wheel barrows and of course we seem to have totally missed out the fact of how we get the wheel barrows out of the ditch full or dirt. Hmm odd, it looked good on paper, why is it not looking so good in the real world.

The net issue is that the Diggers are going to be getting in each other's way, 1.5 meters is not a lot of room to heave a shovel full of dirt, and its too deep to throw dirt 2.4 meters high. So let's look at getting some more wheel barrow assistants to do that work. In that case, I know that about 20% of my time is spent wheel barrowing, so let me get 8 diggers and 2 wheel barrowers, and that should work, in fact since wheel barrowers are cheap, let me get 3 of them to make it even faster.

Next we probably need to work a new way of getting the dirt out of the ditch into the wheel barrows, so we will need to set up some stations with buckets and pulleys to get the dirt out. In fact let's get 4 wheel barrowers, 2 on the barrows, and 2 on the pulley/bucket set ups. Next I see that each digger has a different preference for the tools they use, form Round nose shovels to square spades, picks to breaking bars. So to avoid having all that stuff in the ditch, let's get a Tool getter to get the diggers the tools they need. Since Diggers are the most expensive, it makes sense to optimize their time.

Also I am thinking that instead of them taking breaks for water and food, better will to be have someone to do that also. And after talking with the new manager, it seems that even though these Ditch diggers all have years of experience, and certifications for everything, most of them though they can dig a basic ditch, aren't really able to dig the ditch straight, and the walls tend to cave in a lot, so we will need a surveyor with a theodolite to keep the ditch straight, and we will need 2 people to manage trench boxes and keep the walls from collapsing. Also lets pick the best two from the eight diggers and have them as leaders to coordinate them, to save time from the manager.

Now my job will be to manage and coordinate all this, but to be honest, this is going to run pretty smooth, so I could go out and be looking for more work, and I could get in a manager to look after the job and make sure it's running smoothly. In fact I probably only need to be there at the first kick off meeting, then I can get out and sell more ditches.


Revised plan with 10 Ditch Diggers:


Now this looks much better. And it looks like we can have the ditch now dug very fast. So let's revise our implementation plan.

Revised project plan:

  1. Discuss with the customer the plan of the hole.
  2. Develop project plan with the job manager and the surveyor and customer.
  3. Review plan with the trench boxers, and revise as required
  4. Have customer sign off on plan.
  5. Work out testing and acceptance points so that we manage expectations.
  6. Mark out the area to dig.
  7. Have project meeting with the whole team.
  8. Work out logistics getting to and from the site
  9. Setup the pulley/buckets
  10. Map out the path to carry dirt so we are not crossing paths.
  11. Setup food and drinks stations.
  12. Test out communications channels.
  13. Organize all the tools required, have spares of each type as required.
  14. Have customer check after about 1/4 of digging that the hole is being dug according to plan.
  15. Have follow-up management meeting to review discrepancies and determine plan for getting back on track.
  16. Back to work and continue digging the Ditch.
  17. Have review meetings at each mile stone or target point.
  18. Have customer accept and sign off that hole is correct.
  19. Clean up the area around the hole.
  20. Put away tools
  21. Have team meeting and create core issue list from the digging of the ditch.
  22. Write up an explanation of any issues found whilst digging the hole.
  23. Send invoice to customer.
  24. Pay salaries

The next Blog in this series will look at what we learned when we scaled the operation from one Digger to ten, and how much faster we got the ditch dug.

For now, I would like to ask those with experience digging ditches, what issues can you see that our team had in digging the ditch with 10 diggers, and how long do you think it actually took us to dig the ditch.



Comment List
  • As someone who has dug many ditches (with the army), you can only get so many people working in the same hole. Where the gains come is by taking breaks. Digging is hard work. The people digging can work faster and then take breaks to rest. For a ditch this size, you can probably get half the people working at once. They can dig straight down for most of the way, if you don't mind re-scooping the spoil to move it away.

    As a cynical engineer, I'd say it will still take 10 days but cost 10 times as much.

  • Yes that is also a common issue, where the ditch is already there, but they just didn't see it.

    often the biggest job is filling in the existing ditch so the client does not know they just paid for something twice.

  • How long time does it take 10 diggers to dig a ditch, that has already been dug?

    (maybe my english skills are too limited to understand the question :D)

  • Thanks Kamil, its an interesting suggestion, and its actually one of the things I will discuss in my next Blog. To give you a hint did you see the "20 deg" angle on the ramp Wink

  • Sorry, the ASCII art is screwed up with the proportional font in my previous post...

  • Ok, these problems is possible to solve in traditional ways, but do not forget that there are other solutions:

    Start digging the ditch in the upright direction of the ditch - it means you can do something like that:

             Direction of digging

    |  Ramp     ||    |  Depth = 0


    |  Your ditch     |  Depth = 2.5m


      Width = 15m

    In this way you can have one digger per 1.5 m of ditch length, with one assistant, withou the problem of empty/full wheel barrow, because the assistant can use the wide ramp to take the full wheel barrow out... :-)

    It means the whole ditch is digged in a time, in which the one digger can dig the 1.5 wide ditch with a ramp. But after digging the ditch there is another problem - what to do with the ramp - you can do some boarding to make the second "wall" of the ditch and fill the ramp with the dirt. And this is additional time... :-)

  • Wow I am quite surprised that so many people have experience digging ditches. Thanks for all the feedback. I wont address any of the comments yet, since I want to hear peoples opinions without me biasing them, so please keep  the feedback coming, and the next installment in this blog will be lessons learned.

  • Sorry, I mean finding the point between "negative" return and dimishing return has been a challenge of businesses.

  • I remember learning this in my Micro Economics class back when I was in college. This can be charted in a graph. Essentially, every miner you add to a certain point will net you greater returns than the cost incurred, which is called the point of Increasing Return.

    At some point, the cost increasing another resource will be below of rate of the increased production from the additional resource. This is called Diminishing Returns.

    Then if you keep adding resource, you'll hit the point Negative Return, meaning each additional resource you add will not only increase your cost, but will have adverse effect in your production.

    Find the point between point of increasing return and diminishing returns has been a challenge of businesses since mankind began...

  • I found a graph on this:


    The blue line is important on this one.  On the X, you have the number of ditch diggers, the Y gives you the profit.  You see that until some point, there is a maximum "efficienty", but over that ... the graph falls down dramatically.

  • Having been in charge for several Ditch Diggings, I can add something, too:

    1. Elbonian Ditch diggers and Surveyor speak different languages - Translator comes in to explain what means "straight walls" - another Translator is required between Customer and Surveyor, hence they speak different languages, too;

    2. at 1/4 phase Customer says OK, but at 3/4 he comes again and says - yes, its just as we agreed, but when I see it in material, I understand I actually need the far end at straight angle to the right BUT don't know exactly at which point the turn should be;

    and the worst cames at end - you agreed with Customer that corners should be rounded at 15" radius and slopes should look "nice". Yes, corners are exactly 15", but Customer meant "nice" is gold-plated with diamonds...

  • How about half the time, and ten times as expensive :) You may get Elbonian certified ditch diggers for half price, but you will also need to get a high price project coordinator that is much more expensive. Then all the lunches, hotel cost, travel expenses will add to the cost as well.

  • In our language, this is called "wet van de niet evenredige meerproductie" ...

    literaly translated it would be: "law of the not proportional more production" ... but I'm sure there is another better description for it.

  • Hi David,

    Biggest issue digging a hole with 10 diggers is often the communication.

    Digging a hole with 2 diggers already requires quite a bit communication. Let alone with 10 diggers..