“The best laid schemes o’ mice an’ men / Gang aft a-gley.”
-Robert Burns
Few construction schedules ever go according to plan. For that reason their baselines should not be presented as immutable perfections of logic, but approximations of the highest likely trajectory. Resequencing should then not necessarily be thought of as schedule manipulation, but a measure of control intended to refine project logic that was either unanticipated, or otherwise could not have been represented in the baseline. Accordingly, proper resequencing is an examined and educated guess at optimal outcomes, and improper sequencing a hypothetical guess at idealistic outcomes.
Once the first out of sequence activity appears, if it is not soon adjusted, it can drive successor activities out of sequence, as well, creating a cascading path of disrupted project logic that corrupts the critical path. Fortunately, most scheduling program alert users to out of sequence activities as a matter of front-line diligence, however, they don’t predict upset logic in the forward pass.
Best practice and experience dictates that the baseline is revised and optimized somewhere between the preliminary baseline and the first update, so as not to disrupt any milestones. By such time it is hoped that the contractor has realized most, if not all, of the necessary adjustments that need to be made for a more refined representation of project logic.
In itself, resequencing is a necessary and valuable tool that only becomes suspect when used for ill purpose – such as to conceal or obfuscate delays, float shortfalls, oversights or other shortcomings. Resequencing may be a measure of correcting work out of sequence, or a reordering of reconsidered projected networks. It is up to the reviewer to use keen discernment in assessing the true nature of resequencing.
There’s nothing intrinsically wrong with a logic path unfolding out of sequence. It is when such disruptions go unattended to, or go unreconciled, that they may become problematic. The longer and more disrupted project logic becomes, the harder it will be to resequence, and the higher the likelihood that the critical path becomes skewed, and the forward-pass loses relevance.
“CPM Construction Schedules and work-in-place too often exist in parallel universes.
It is in the reordering or resequencing of disrupted logic paths that diverge from the baseline that schedulers and contractors struggle coming to terms with. The success of any resequencing effort is contingent on whether it is merely artifice or a scientific endeavor that most oversight consultants would not be able to discern: no scheduler wants to be second-guessed by an academic who’s never swung a hammer. It’s easy for the theoretician to stagger several trades start-to-start + lag, but more complicated to visualize the consequences in real time, such as trade congestion, lower production rates, increased mistakes, and more accidents.
If a baseline schedule is not based on a properly calculated or scientific method, it follows that resequencing logic introduced into the baseline cannot be plausible either. This defect may be owing to ineptitude, poor reasoning, or misrepresentation. Why would a contractor do that? Simply to mollify a client with a static turnover date that miraculously remains undisturbed by lack of progress or delay.
Activities run out of sequence for a variety of reasons, all of which dictate different approaches and resolutions. For example, drywall installation may change its relationship with compound coat applications from finish-to-start to start-to start with lag, but seldom start-to-start (sans lag), or finish-to-finish. A scheduler might try to squeeze these relationships not so much as to represent actual work in place, but as a means to reduce the critical path.
However, most resequencing isn’t performed to correct out of sequence activities, but as a means of compression: once float paths begin their southern trajectory, contractors begin paring away at finish-to-start relationships by changing them to start-to-start. If such plans are introduced with due diligence, they may actualize into reality, yet very few seem to do so.
For example, if a contractor is pouring concrete at a rate 50% slower than he needs to meet a milestone, he would have to triple his output no later than 50% of the activity duration to keep on schedule. As we know, concrete activities don’t lend themselves well to compression – no pun intended. Moreover, the likelihood of completely reversing a severe downward trend has a small likelihood of success.
Returning to the drywall example, if the contractor had met with his installer trades and arranged for enhanced resources to achieve a calculated 150% production rate (from 50%) for a given quantity of work, that would be a more scientific approach then merely clapping one’s hands and saying “make it so.” Sadly, it is this latter method that is the popular choice. The reality is that a contractor would prefer to have a dust free environment for his tapers or plasterers, as opposed to working around debris and gypsum installations. Carpenters do not enjoy working around billowing clouds of plaster dust either. This overlap of resources we call ‘trade stacking.’
‘Concrete pour schedules don’t lend themselves well to ‘compression’
An owner is unlikely to challenge a contractor’s claim that he can make certain egregious reversals of fortune until the bank recalls his construction loan, which is, of course, too late. Moreover, they are ill-equipped to deconstruct and quantify such claims. This task is often left to oversight consultants who are no better positioned, owing to experience limited to the classroom: ‘float ninjas.’
‘Most schedule compression exercise are contingent on egregious reversals of fortune that never materialize.
It doesn’t take a genius to validate resequencing plans, in fact it is the humble field managers who are best positioned to make such assessments, however, they generally are only apprised after the fact, if they are considered at all. They should be the first line of push-back. When a schedule is tinkered with in this way, it loses its relevance in the field, and becomes a mere red-herring for executive managers to wrestle with in the boardrooms. For this reason, copies of the schedule are scarce in most any field office.
It’s not hard to identify schedules that have been doctored or tinkered with, as opposed to being judiciously modified. A layperson can easily compare the angle of the forward pass trajectory of the base-line to remaining work using a simple visual exercise and scenic analogy: the base-line of a GANTT chart early-finish bar will flow freely at a 50% slope, like a gentle waterfall. As updates are logged, this slope slackens to show slip of work in place – think of it as soil erosion that causes friction to the flow of water. The forward pass must recover the slip. It is resequenced such that the slope of the GANNT is now nearly perpendicular, as a cliff might be. It is the edge of this figurative cliff that too many schedules approach to closely or fall off of.
‘Float ninjas are unsuitable as oversight consultants or reviewers. Their place is in the classroom or anywhere else they won’t get their hands dirty.
An intermediate skier may traverse a 50% slope, but he would have grave concerns about negotiating a vertical precipice. This same hesitation and caution should be the measure of any compression resequenced construction schedule. For example, a vigorous risk assessment would out the likelihood of potential calamity, alerting the contractor and owner to vulnerabilities. However, this assumes that risk assessments are employed at all on any given project.
If risk profiles were known, it would be a simple exercise to reassess them. For example, if a given activity was resquenced to finish 50% sooner, or half baseline duration, its risk assessment would also increase proportionately. If an owner knew of the risk, he would be in a better position to assess whether or not he accepted the revised plan. As we now know, an RA is not exigent to assess risk, only to more accurately quantify it. Barring any such risk assessment, an owner can simply overlay the GANTT charts, and compare the slope of the forward pass.
