Application of Line of Balance (LOB) in construction projects using Excel

I was always asking myself, why the line of balance method is not widely used in construction projects. Then I realized that because it is mainly used in repetitive projects such as roads, pipelines, and other projects with fewer dependencies. Furthermore, I saw a few graphs of the scheduling using a Line of Balance, and my first impression was it looked complicated. Accordingly, I decided not to proceed and study further about this planning technique. However, during one of my training sessions with new engineers, we discussed the line of balance method, and I asked them to explain it to me as they understood. To be honest, at this point, my information about the LOB method was very generic and I never thought it could be a useful planning method.

Surprisingly, the fresh engineers explained this method to me, and I found it very simple. Then, I started thinking and researching how we can use this simple method in our complicated projects. There is some software like TILOS which deals with the LOB method similar to Oracle Primavera which deals with the Critical Path Method (CPM). However, I wanted to start my investigation using my favorite planning tool Microsoft Excel. Accordingly, I would like to share with you my results in this article, the application of the LOB method in construction projects using the Excel tool.

What is the Line of Balance (LOB) Planning Technique?

According to designing, “Line of balance (LOB) is a management control process used in the construction where the project contains blocks of repetitive work activities, such as roads, pipelines, tunnels, railways, and high-rise buildings. LOB collects, measures, and presents information relating to time, cost, and completion, and presents it against a specific plan.”
According to my understanding, LOB is a very simple method, it converts the dates into lines, you need to maintain these lines not crossed and near to each other as you can. Let us start with this example. We have 10 similar buildings, and we want to create the schedule using a line-of-balance method.

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LOB Step one

We will draw the Plain concrete works under footings, each building will take 10 days to be completed, so it is a straightforward process.

LOB Step 2

The X-axis represents the unit number, and the Y-axis represents the Time. So now we know each unit when the PC under footings should start and when it should finish. For example, Unit No. 7 should start on 31-May-17 and should finish on 9-Jun-17. Now we want to add reinforced concrete for footings, but it will take 15 days to complete one unit. So, here is the first role for the LOB method, if the successor activity takes longer time for execution, then start from the bottom. In our case, the reinforced concrete for footings should start immediately after the Plain concrete finishes. I.E 11-April-17, see the Line of Balance graph below after adding the reinforced Concrete for footings.

LOB Step 3

Ok, now we want to start the foundation waterproofing and let us assume that a subcontractor will come to do it for us, but in the subcontractor contract, the unit will take only 3 days to finish. If the work is not available, the subcontractor will claim idle time. So, the question here is when the subcontractor should start to maintain continuous work without stoppage. This is one of the main benefits of the Line of line-of-balance method, in this case, we will start our calculation from the top. I.E., we will start from when the waterproofing work should be finished and make backward calculations. In our case, the waterproofing should finish after the last unit of the RC foundation finish + waterproofing duration = 7-Sep-17 + 3 days = 10-Sep-17. See the figure below to know what it will look like.

LOB Step 4

As you can see, the perfect start timing (LOB) for the waterproofing sub-contractor is 12-Aug-17, this will ensure the work continuity and will finish just after the last unit foundation. This is great, but not practical, it does not make any sense to wait 109 days (between the first unit RC completion and the first unit waterproofing start). Construction projects are rapid, and we want to start the successor activities such as backfilling, columns, and so on. So, we can reach an agreement with our subcontractor (If applicable) to work in patches. Let us say, 3 units, 3 units, and 4 units. In that case, we need to modify our line for waterproofing as per the following chart.

LOB Step 5

Now we have made the planning more reasonable. The waterproofing subcontractor can visit the site three times on 20-May-17, 4-July-17, and 30-Aug-17. Every time will do 3 units except the third time will do 4 units, and the graph above shows the schedule of each unit and the buffer time. Even if you are not going to use a subcontractor, and you have several projects in your company, you can schedule your teams like this. Now we can schedule the backfilling team/equipment to follow the waterproofing.
The backfilling is executed in layers, each layer is 25 cm, and we have 1 meter to backfill, so we need 4 days to finish 1 unit. In that case, from where should we schedule? Top or bottom? Of course, bottom because the 4 days’ duration of backfilling is more than the 3 days required for the previous activity waterproofing which is 3 days. So, we can start immediately after the first unit waterproofing completion. i.e., 23 May 2017. See the figure below:

LOB Step 6

Ok, now our construction site is safer with the backfilling (no excavation is left for a long time), so we want to start the slab on grade as soon as possible and keep it going smoothly without stopping. In that case, we need to find the best crew size to fit this situation and estimate the optimum duration for the slab-on-grade activity. Accordingly, the information we have is.
1-The First Slab on grade (S.O.G) can start on 27-May-17
2- The Last Slab on grade can start on 15-Sep-17
The duration between the first start and the last start is 111 days, if we divide it by the number of units, we get 11.1 days per unit. So, we will make the duration for the unit 12 days, draw the line, and see what it looks like. (see the figure below).

LOB Step 7

As you can see, we have two intersections between S.O.G. and Backfilling in units 4 and 7. Unit 7 has the biggest intersection, so if we solve this one our line will be fine. So, we need to start the S.O.G in unit 7 on 6-Sep-17 instead of 13-August-17 and recalculate all other units’ dates accordingly. (see figure below)

LOB Step 8

Now we have the Slab on Grade perfectly aligned with our overall schedule. Let us think now of reusing the PC foundation team to start the columns. This team will finish the PC footings on 9 July 2017 so I can add to them steel fixers and establish a new team for the R.C. columns, what would be the optimum size of this team to finish the unit in the best duration I want? The team size who would finish the PC footings in 9 days, could finish the R.C. columns in 6 days, but the slope of the S.O.G. is 12 days which means that there will be an intersection between these two teams. What are the options we have here?
Option 1: delay the start date of R.C. columns.
Option 2: increase the duration of the R.C. columns.
My choice: is a mixture between option 1 and option 2. Let us think together, what if I can find the R.C columns slope which will make the columns finish just on time, increase the duration of the columns with the same percentage I decrease the PC concrete productivity to end up with the PC footings team finish the footings and start the R.C columns immediately (without impacting the RC footings team)?
Since I am using an Excel template that calculates the dates based on simple formulas, changing any date will not be a problem because all the relevant dates will be changed automatically. So, I need the R.C. column’s last unit to start around 28-October-17 and the first start after the PC completion date. So, I am going to increase the PC footings duration by 2 days which gives me the start date of the R.C Columns on 30 July 2017 and the Perfect Finish date. (see the figure below).

LOB Step 9

Similarly, I can re-use the same crew of the R.C. footings to execute the R.C. slabs. In this scenario, I will wait one month after executing the columns for the R.C. footings crew to finish their work. However, starting from 16-Nov-17 the R.C columns crew will join the R.C slabs crew to finish faster, can we do this scenario?
Yes sure, from 11-Sep-17 to 16-Nov-17, the R.C. slabs will take 15 days to finish 1 unit. However, after 16-Nov-17, the duration should be reduced to 10 days only for 1 unit. 16-Nov-17 was during the execution of unit no. 5, so I will start the new duration (10 days) from unit 6. See the figure below:

I hope my example is clear and useful for you. You can now fine-tune your line of balance schedule by giving the start and finish line the same color for each activity and adding a note on how your manpower will move across project different activities. Also, do not forget to make the dates clear by moving dates that overlap with each other, then you can print this schedule in A0 size and explain to your team how easy and effective the line of balance is. The figure below is the final output of our schedule:

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