There are three special cases of out-of-sequence or out-of-logic work that are of distinct importance in LBMS projects. Subcontractors working in multiple locations at the same time instead of working in sequence cause issues with forecasting. Finishing 95% of a location and then moving to the next location is also typical. The third important issue is starting too many subcontractors at the same time in the same location.
Working in multiple locations at the same time instead of focusing resources on fewer locations results in locations taking longer to release to the next trade. Figure 1 at the bottom of this article shows this behavior with number 1. This requires either larger buffers or overlapping work with a successor trade which, in turn, leads to slowdowns. The reason of this behavior is that typically crew sizes are not considered in CPM and additional resources are always assumed to work in a separate crew that works in a different activity. The default action of subcontractors when required to add more people is to open up new locations. It requires training and active management to focus resources to finish work in one location only.
Current production control methods such as CPM pay more attention to starting than finishing. Locations often progress to 90% or 95% completion and then get suspended. If the successor tasks can start, the issue falls quickly out of production management’s radar. These small amounts of work in each location for each trade result in a large amount of manhours required in the end of the project to finish all partially finished locations. This contributes to the end of project rush. Suspended locations also make forecasting difficult. It is hard to know what the subcontractor is going to do next with all the open, partially finished work. Figure 1 at the bottom of this article shows this behavior with number 2.
To solve this issue we have had success with having subcontractors explain any suspended locations and committing to a continuation date. A more complete solution can be achieved if payment structures can be changed to be by location instead of paying for percentage completed.
Finally, letting too many subcontractors work in parallel in the same location causes a lot of inefficiency and slowdowns. In general, if the locations are small enough, two tasks with large space or lay-down area requirements should not be ongoing in the same area, even if they are not technically dependent. It has been empirically shown that overlapping work can result in 30%+ productivity decreases (for both the predecessor and the successor). This basically negates the benefit of starting the successor early because both the predecessor and the successor will take longer than needed. It is better to wait for a completely free location and then work faster. Figure 1 below shows this behavior with number 3.
Figure 1: Example showing overlapping work (1) uncompleted locations (2) and overlapping work causing slowdowns (3).
Best sure you are caught up with all the articles in this series:
Part 1: Beyond Start Dates
Part 2: Get the Subs Involved
Part 3: Manpower and Suspensions
Part 4: Control Actions
Part 5: Planning the LBS
Part 6: Clarifying Scope
Part 7: Look-Ahead Plans
Part 8: Running Parallel Schedules
Part 9: Resource Graphs
Part 10: Production Rates and Location Sequence
Part 11: Using 5D with LBMS in Subcontractor Meetings
Part 12: Deliveries and Lay-Down Areas
Part 13: Starting As Early As Possible Will Hurt Your Project
Part 14: Buffers Are Important for Production Control
Part 15: Implement Control Actions as Soon as Possible
Part 16: In LBMS It Is Possible to Work Too Fast!
Part 17: Keep Chaos Out of the Construction Schedule