Quality control in civil engineering projects
ENGINEERING ACTIVITIES
This section reviews the extent to which early defects prediction in on- site activities can play a part in achieving efficiency gains in construction projects.*
A significant factor contributing to cost/schedule blowout is construction defects. In line with defects is perhaps the construction industry’s overlap- ping tasks within on-site work programmes as part of an integrated criti- cal path, work breakdown–structured approach. The discussion reviews *Input from Abdullah Almusharraf,88–110 received with thanks.
the mechanisms for the identification and mitigation of installation defects resulting from concurrent work packages during the construction phase. A main challenge here is an accurate means and method to predict, at the early preconstruction planning stage, cumulative deficiencies and better manage overlapping tasks and, in turn, avoid negatively influencing project cost and duration.
The identification of actual defects during the construction phase might go towards a prediction of future defect susceptibility for specific activi- ties. In addition, the identification of key overlapping task(s) variables and examination of the behaviour of each variable and its effect on the overall project quality in general are important for civil engineering projects. The following discussion highlights how defects appear principally as a result of design stage factors (≈33%) and engineering installation stage factors (≈66%); summarising the work discussed, it can be said that
On-site observations and analyses determine the stage at which defect occur, namely,
• The ‘design stage’ contributes to one-third of civil engineering defect occurrences.
• Whereas, on-site activities during the ‘construction phase’ con- tribute to a significant two-thirds of defect occurrences in civil engineering works.
In addition to a discussion of the stage at which defects appear, the fol- lowing discussion also explains how both ‘project process/methods’, and ‘people on-site’ are predominately responsible for all on-site defects; both contribute to approximately 40% (respectively) of the material installation defects on a civil engineering work-site, whereas the remaining 20% or so of the defects noted stem from ambiguities such as design/documents.
Generally, it might be stated that an investigation of error and defect in the civil engineering and building design process can begin to make con- struction more efficient. On-site, there are opportunities to, on the one hand, examine multiple factors related to overlapping tasks during the con- struction phase and then, on the other hand, try to predict (resultant) defect occurrence and related efficiency levels.
A number of previous studies have sought to address and explore defect at the early stages in construction processes; the ideas can be summarised along the following lines:
Overlapping activities
There is a suggestion that one way to seek a reduction of sequen- tial defects is by examining overlapping processes (termed by some in the manufacturing sector as concurrent engineering, although this
technique is somewhat uncommon in civil engineering). Preceding task and succeeding task activity pair overlap is determined through the nature and range of information exchanges, with links termed as dependent, semidependent, independent and interdependent.
Activity pair sensitivity
The concept of overlapping activities evolves by presenting a num- ber of frameworks that determine overlapping parameters in preced- ing (so-called upstream) and succeeding (so-called downstream) task activities. Evolution is a function of overlapping activities as an evalu- ator for information over upstream activity time, generating initial information. Sensitivity of information downstream is then ‘rework’ needed as a result of a change in upstream activities.
Concurrent and overlapping task activities strategies
Generally, overlapping activities are well acknowledged as a project tool and as a means to reduce project duration and cost; however, it has been argued that overlapping, although useful, can produce errors, defects and rework, increasing project risks. To overcome this, construction defects need identification and distribution into execution phase activities and tasks to measure susceptibility for specific defect exposure and give appropriate overlapping between activities.
Defects description
Terminology such as error, fault and failure are commonly used to describe technical problems and construction defects. Not all, how- ever, necessarily lead to rectification or rework; this variation in defect description affects the understanding of the problem and may lead to inappropriate reactions. Design phase defects occur due to quality deficiencies/omission/change. Although construction defects at the execution phase often occur due to workmanship/supervision, where rework reinstallation to allow compliance and certificate of practical completion sign off.
Defect effect
Construction mistakes, errors or defects usually reduce project satis- faction levels and often create conflict and dispute between stakehold- ers; the search for monetary and nonmonetary compensation becomes common to address deviations from originally forecast costs, sched- ules and quality that can, in some cases, increase a project sum by up to 5%.
Defect classification
Quality problems might be assessed in terms of their respective devia- tion from compliance with design and construction drawings and specifications, as a result of variables such as supply chain noncom- pliance and worker installation noncompliance.
Case studies can help understand and identify which activity or task has low or high sensitivity in relation to defects and rework towards distribut- ing effort, improving quality and simultaneously controlling cost and time. Activities and tasks are categorized based on susceptibility to exposure to defects.
Figure 4.4 gives a hypothetical classification. In this example, if the rate of exposure to defects of an activity ‘A’ is 25%, and defect is classified as exposure to a defect ‘X’ is 70%, defect ‘Y’ is 20% and defect ‘Z’ is 10%.
The degree of overlapping between activities A, B and C is identified based on susceptibility to defect exposure and rates of defects for each activity. Activity A has the highest susceptibility to defect exposure.
The following work develops this approach (links susceptibility and defect) towards an early indication of when progress reaches a critical point in overlapping tasks (a critical point representing a probability that defects will occur increasingly). It is suggested that perhaps understanding this behaviour begins to mitigate defect effect.
Civil engineering defect distribution
Building on work identifying the traditional design-bid-build stages— concept, preliminary design, detailed design, construction and start- up—defects may be distributed appropriately, where potential sources become applicable, namely, structure, people, process, internal uncer- tainty and external uncertainty.
30 25 20 15 10 5 0
Activity A Activity B Activity C
Defect Z Defect Y Defect X
After which the main steps to distribute the factors of construction defect are to
• Review causes of construction defect from secondary research and distribute construction defects into project phases and sources for each defect
• Classify susceptibility for specific activities and related exposure to defects, and measurement of a rate of each activity defect based on exposure times
• Identify all variables of overlapping activities (from secondary research) that will affect work positively or negatively, then develop a formula that measures overlap through least squares regression and multiple regression analysis
• Prepare an overarching estimation to predict and send an early alarm signal to a site manager and the respective foreman of the (increasing) probability of defects occurrence(s) in that range of specific on-site tasks
• Validate the defects prediction approach by further detailed case study Groups of variables in two fields were assessed: (a) construction defects in the execution phase and (b) overlapping activities processes. For the first field variables, parameters and appropriate classification techniques for construction defects were based on existing previous work.
From the residential/construction industry, 342 construction defects cases and factors were assembled (causes and factors at design, construc- tion, start-up and the like were generated from sources related to variables such as people and processes). This database was organised in terms of distributing construction defects across the project phases.
• Three hundred and forty-two defects were distributed in construc- tion project phases (concept, preliminary/detailed design, build and start-up).
• Construction defects (for specific rankings) were divided into differ- ent sources causing the defects (structure, people, process and internal/ external uncertainty).
• The rate of construction factors for each project phase and the source that caused the defects.
Generally, critical path methods allow a task B to start with A; resul- tantly, construction defects may increase, thus ongoing work will develop formal measurement (and validation) of the range of work progression(s) for both A and B, to predict an amount of cumulative construction defect(s) through a least squares regression and multiple regression analysis to mea- sure a critical point of maximum overlap.
Table 4.3 presents the rate of the defect appearance in each project (sub) phase.
• The greatest rate of defect appearance occurs at the construction phase (67%), followed by the design phase.
• Interestingly perhaps, although previous studies stated that the ‘design phase’ causes most of the construction defects, this ongoing study is beginning to suggest that most of the defects occur in the construc- tion phase.
Table 4.4 describes ‘processes’ and ‘people’ as being responsible for 43% and 38% of defects, respectively.
Overcoming construction defects and work undertaken to remedy defects during overlapping activities in the execution phase is a key problem for construction and civil engineering.
As mentioned previously, the ‘construction phase’ seems to be the stage at which most defects are attributed (contributing to 67% of defects) fol- lowed by the ‘design phase’ (to which 30% of the defects can be attributed). ‘Process’ causes the most defects (attributed as 43%) followed by ‘people’ (38%).
Mechanisms able to help mitigate defects during the construction phase will always be welcomed by civil engineers, site managers and foremen, especially if they allow a relatively easy way to identify (the specific factors of) a specific task or series of work tasks that are most at risk from cost and time blowouts.
In general terms then, despite quality management systems (as part of the project documentation required by standard forms of general conditions
Table 4.3 Defects appearance (%) and subphase
Subphase Defects appearance (%)
Project concepts 1 Design 30 Preliminary design 7 Detailed design 93 Construction 67 Late design 10 Site management 70 Production management 2
Materials and equipment 14
Fabrication 3
Transportation 1
of contract, such as clause 29 of AS4000) to improve project processes, defects do still occur throughout both design and construction.
Having recognised the place of project and contract documentation in attempting to address quality, quality compliance, occupational health and safety, continuous improvements through modularisation and prefabrica- tion, as well as defect occurrences (see previous discussions), it is now per- haps pertinent to examine the contract documentation explicitly. Chapter 5 discusses contract documentation in detail.
Table 4.4 Percentages of defects and sources (contributions)
Subphases Structure (%) People (%) Process (%) internal (%)Uncertain external (%)Uncertain
Project concepts — 100 — — — Design 5 37 40 19 — Preliminary — 72 29 0 — Detailed 5 34 41 20 — Construction 3 36 44 7 8 Late design — 45 41 9 5 Site manager 2 38 43 9 8 Production — 100 — — — Material 10 21 62 — 6 Fabricate — 43 29 — 29 Transport — 25 50 — 25 Start-up — 28 57 14 — Total (%) 4 38 43 11 5
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