Guide for Conducting Forensic Investigations of Highway Pavements (2013)

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60 Data analysis and hypothesis testing are carried out once all the relevant observations and test results have been doc- umented and assessed. This part of the study relates these observations and results to the issues being investigated and needs to provide sufficient data to address them, as well as to support/justify any conclusions and recommendations that are made. 8.1 Data Analysis and Hypothesis Testing The method and approach followed will depend on the issues being investigated. Specific details on approaches to and methodologies for data analysis are not discussed in this guide, but the following items should be considered: • Check the data and observations for reasonableness and correctness, and if necessary, compare to agency norms. If satisfied with the reasonableness, continue with the analysis. – Reasonableness checks are especially important for calculated data such as backcalculated stiffnesses from FWD deflection measurements, IRI from profile data, layer thickness from GPR, etc. For example, an effec- tive modulus backcalculated from deflection data of 2,000 ksi (14 GPa) is reasonable for a cracked concrete layer but a much higher value (double or more) would be expected for a sound concrete layer. • Focus on the issues being investigated and analyze the data with consideration to the objectives of the investigation (see Sections 0 and 3.5.1). All observations and test results should be considered because both good and poor performance are often the result of a number of factors (e.g., the presence of punchouts in a CRCP pavement may be attributed to poor subgrade resulting from inadequate drainage during high- er than average rainy conditions, but other factors such as heavier than anticipated traffic loadings and/or poor con- struction quality may also have contributed to the problem). • Consider the fundamentals of pavement performance, namely pavement structure (including pavement type, pavement layers and construction); subgrade soil; traffic; drainage (including subsurface); and environmental con- ditions; and how each of these influences the result. • If applicable, compare as-designed/as-specified with as- built pavement structure information. – Determine whether any differences have influenced pave- ment performance. Deviations in construction require- ments (e.g., compaction), layer thickness, substitution of layers with others, the addition of leveling courses, actual strengths and stiffnesses, etc., could explain both excep- tional and poor performance. – Compare pavement performance (e.g., stiffness, profile, noise, permeability, etc.) against agency norms. If there are deviations, account for them from the observations and results and link them to the issues being investigated. • If applicable, link any key climate, environmental, and/or traffic events to the issues being investigated. Determine whether the pavement design considered the effects of the events and/or whether the as-constructed pavement was adequate to accommodate these events. Examples of such events include flooding; freezing; abnormal traffic loads; higher or lower than design traffic; actual traffic mix (volumes, loadings, or both); and periods of exces- sive heat, etc. • If applicable, assess any variability in construction or structure (e.g., layer thickness) across the entire project and its relationship to the issues being investigated. Local- ized problem areas may be explained from these observa- tions and QC/QA documentation. • Assistance or an outside opinion with interpretation of specialized test results may be necessary if that expertise is not on the team. Newly developed tests may not have a proven track record in pavement forensic investigations and their use may need to be justified. Specialized tests are useful for confirming other observations. C h a p t e r 8 Data Analysis, Hypothesis Testing, and Final Report

61 8.2 Forensic Investigation Report A final report is prepared at this point to document the findings of the study and to make recommendations based on these findings. The report will be a continuation of the ini- tial investigation report discussed in Section 5.3 and should include the following: • Executive summary. – Summarizes reasons for undertaking the forensic inves- tigation, the key findings, implications of the findings, and recommendations on actions that need to be taken. • Introduction. – Lists the reasons for continuing with the investigation. • Objectives and hypothesis. – Refines the issues being considered and potential hy- pothesis investigated. • Final investigation plan. • Observations and measurements. – Includes tables of key observations, measurement loca- tion, and measurement results that support the findings. • Analysis and interpretation. – Summarizes test data interpretation in terms of address- ing the investigation issues/questions. – Justifies that the investigation has satisfactorily addressed the investigation issues/questions. • Findings/Conclusion. • Recommendations. – Provides recommendations on using the findings from the investigation, for example: 77 Changes to design manuals, construction and qual- ity control procedures, specifications, test methods, and/or contractual documentation. 77 Dealing with contractual claims. 77 Corrective actions on premature failures. 77 Calibration factors for mechanistic models. • Lessons learned. • Dissemination of findings. – Details of the findings that need to be disseminated and recipients. • Costs of the investigation and if applicable, cost-benefit analysis comparing the costs of undertaking the investiga- tion against the benefits of implementing the findings. • Location of data files (e.g., website address for forensic inves- tigation database). An example final report cover sheet is provided in Appen- dix C (example Form #24 in Appendix C). 8.3 Record of Decision The forensic investigation coordinator obtains approval of the final report and recommendations from the investiga- tion director and adds a record of decision to proceed with implementation of the recommendations and dissemination of findings in the project file.