National Academies Press: OpenBook

Service Life of Culverts (2015)

Chapter: CHAPTER SIX Inspection

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Suggested Citation:"CHAPTER SIX Inspection." National Academies of Sciences, Engineering, and Medicine. 2015. Service Life of Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22140.
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Suggested Citation:"CHAPTER SIX Inspection." National Academies of Sciences, Engineering, and Medicine. 2015. Service Life of Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22140.
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Suggested Citation:"CHAPTER SIX Inspection." National Academies of Sciences, Engineering, and Medicine. 2015. Service Life of Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22140.
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Suggested Citation:"CHAPTER SIX Inspection." National Academies of Sciences, Engineering, and Medicine. 2015. Service Life of Culverts. Washington, DC: The National Academies Press. doi: 10.17226/22140.
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39 CHAPTER SIX INSPECTION The LRFD Bridge Construction Specifications (AAS- HTO 2010) provides excellent baseline recommendations for inspection requirements for the three main categories of pipe materials (Metal Pipes in Section 26, Reinforced Concrete Pipes in Section 27, and Thermoplastic Pipes in Section 30). These recommendations can also be applied to other flexible and rigid pipe material systems. INSPECTION OF PIPE MATERIALS AT DELIVERY In general, state agencies have well-developed and well- documented policies for evaluating and ensuring the quality of pipe materials delivered to project sites. These policies often include: • Qualification of manufacturer and manufacturing facility, and review of mill certificates. • Inspection of deliveries, which may include inspection of: – Identification markings – Date of manufacture – Shipping papers – Diameter – Net length of fabricated pipe – Evidence of poor workmanship – Identification of damage during shipping and handling – Measurement of surface cracks (for example, with leaf gages). • Taking pipe samples for additional testing (chemical, mechanical, coatings, etc.). INSPECTION DURING CONSTRUCTION Inspection of the pipe system materials and workman- ship during construction allows corrections to be made in assembly and backfill practices before construction is complete, and is of particular importance for deeply buried, high-traffic, or other critical or costly-to-repair installations. The timing and frequency of such inspec- tions depends on the structure’s significance and the fill depth. In general, inspections would be conducted when materials arrive at the job site, during pipe installation, during backfilling, and before construction of final fin- ishes (e.g., paving). Experience has shown that one of the critical issues affect- ing the performance (short and long term) of pipe systems is the quality of the installation. Appropriately designed and properly installed drainage systems will generally perform well throughout the pipe system’s design life, and it is on this basis that design service lives are assigned. Post-installation inspection of a buried pipe system is one phase of a comprehensive quality assurance program. Mill certificates for all pipe materials are to be checked in advance, and conformance to relevant project specifi- cations and reference standards (e.g., ASTM, AASHTO) confirmed. Source acceptance test results for all imported materials should be checked against project specifications. Inspections are to be performed on the pipe, bedding, and backfill materials before and during installation. The agen- cy’s specifications for compaction and general require- ments and for workmanship during construction need to be enforced. Some agencies conduct periodic routine, systemwide inspections for in-service pipe systems as part of an asset management program. While this practice is not consid- ered essential, it can identify potential future serviceabil- ity problems that can be addressed by routine maintenance rather than by emergency repairs. Early detection of dete- rioration may allow a low-cost intervention, such as invert paving, that may defer full pipe replacement for 10 years or longer. The inspection of drainage system materials before instal- lation and during construction will be summarized briefly in this section, followed by a more detailed discussion of post- installation inspection procedures. Guidelines for routine systemwide inspection programs of in-service pipe systems can be found in the FHWA Cul- vert Inspection Manual (1986). As new pipe products (e.g., materials, coatings, and rehabilitative liners) and remote- access inspection technologies have been introduced since the Culvert Inspection Manual was developed, a need has arisen for updated culvert inspection guidelines. An update and review of inspection procedures and technologies is proposed to be addressed through NCHRP Project 14-26, Culvert and Storm Drain System Inspection Manual, which is due to be released in 2015.

40 Inspections during construction may include examina- tion of: • Foundation material • Trench geometry and dimensions • Groundwater conditions • Bedding material • Line and grade • Assembly techniques • Structure backfill and compaction methods • Joint assembly and materials • Pipe deflection (during construction) • Damage to pipe coatings. POST-INSTALLATION INSPECTION Post-installation inspection allows for timely identification of potential installation problems and allows for corrective action to be taken, if needed, within the scope of the construc- tion contract. The LRFD Bridge Construction Specifications (AASHTO 2010) recommends that final post-construction inspections for culvert approval be completed no sooner than 30 days after completion of installation and final fill such that defects under initial conditions can have time to present themselves. The AASHTO construction specifications com- mentary expands on this recommendation by stating, “Soil consolidation continues with time after installation of the pipe. While 30 days will not encompass the time frame for complete consolidation of the soil surrounding the pipe, the period of 30 days is intended to give sufficient time to observe some of the effects that this consolidation will have.” However, occa- sionally pavement is placed over the pipe sooner than 30 days. Although the 30-day time limit needs to be maintained, a brief inspection of the pipe before paving over it, particularly for the first few joints, may be prudent to ensure that good construc- tion practices are being applied. The most frequent distresses identified from comprehensive pipe inspection are leaking joints, joint gaps, deflection, and cracking. Post-installation inspection can be carried out in a num- ber of ways. The most common methods are (Figure 35): FIGURE 35 Laser profiler and CCTV used in tandem for pipe inspections. • Visual inspection performed manually (usually for larger-diameter pipes, typically greater than 36 in.) • Visual inspection performed remotely by video inspec- tion using closed-circuit television (CCTV) • Mandrel testing • Laser profiling (forthcoming ASTM F36 method) • Nondestructive inspection/testing (NDI/NDT) techniques. Across state agencies, post-installation inspection require- ments for pipe systems vary more significantly than practices for the other stages of inspection. This difference is due in part to the continued introduction of new pipe materials, design methods, and remote-access inspection techniques within the industry. Improving the consistency of post-installation inspection practices will help to deliver more consistent and predictable pipe performance and service life. POST-INSTALLATION INSPECTION TECHNIQUES Post-installation inspections can be broadly categorized into three main groups: visual inspection, installation deflection testing, and joint inspection. Visual Inspection Visual inspections are typically performed using one of the following techniques: • Manual pipe entry (for larger pipe diameters) • Video testing (using CCTV) • Optical scanning (obtaining a full circumferential optical scan of the pipe interior) • Laser profiling (combined visual and deflection testing technique, available in 2D and 3D). Installation Deflection Testing Confirmation that the original shape of the pipe is not dis- torted beyond an acceptable tolerance level (referred to as “ovalisation” in a circular pipe) is used as a key indicator of post-installation quality. Inspection of post-installation deflection is typically conducted no sooner than 30 days fol- lowing installation [as per the LRFD Bridge Construction Specifications (AASHTO 2010)] and is typically performed using one of the following techniques: • Mandrel testing • Physical survey (manual entry into pipe, measurement of diameter using rod or tape) • Laser profiling (combined visual and deflection testing technique). Mandrels are devices that are pulled through the pipe to determine if the deflection is acceptable. They do not pro-

41 vide quantitative information. Installation deflection testing performed by mandrel can typically identify only the first occurrence of excessive deflection, because a test mandrel cannot be pulled past sections failing the deflection criteria. When possible, either laser profiling or physical surveys (in the case of larger-diameter pipes) are preferred because they provide more quantitative and complete information, potentially allowing any required repairs to be completed more efficiently. Since laser profiling is usually performed in conjunction with video, the engineer can inspect the nature of the nonconformance. Additional information on the physical survey require- ments can be found in the LRFD Bridge Construction Speci- fications (AASHTO 2010). Joint Inspection Joint inspection typically occurs after installation and involves one of the following techniques: • Manual pipe entry (for larger-diameter pipes) • Video recording (using CCTV) • Laser profiling (combined visual and deflection testing technique) • Joint leak testing (typically not conducted for highway drainage systems, although leaking joints can be iden- tified from video inspection). NCHRP Web-Only Document 190: Structural Design Requirements for Culvert Joints (Moore et al. 2012) reports that movements during culvert installation are typically signif- icantly larger than movements measured during any of the sur- face loading tests examined in the field. As such, installation plays an important role in creating permanent deformations in pipes and in causing such potential problems as leakage at the joints. In addition, soil stiffness increases after years of service and this leads to substantial reductions in incremental response under repeated vehicle loads. The main concern with open joints is the potential either for backfill fines to enter the pipe or for water to flow outside the pipe, both of which can lead to the formation of voids along the outside of a pipe and a reduction of structural support for the pipe overall. AASHTO LRFD BRIDGE CONSTRUCTION SPECIFICATIONS Standard post-installation inspection recommendations are found in the following sections of the LRFD Bridge Con- struction Specifications (AASHTO 2010): • Metal Pipes (Section 26) • Reinforced Concrete Pipes (Section 27) • Thermoplastic Pipes (Section 30). AASHTO Visual Inspection Recommendations for Flexible Pipe Systems The recommended inspections for flexible pipe system installations include checks for: • Alignment • Joint separation • Cracking at bolt holes • Localized distortions • Bulging, flattening, and racking • Minimum cover levels (for shallow installations) • Deflection testing. AASHTO Visual Inspection Recommendations for Reinforced Concrete (and other rigid) Pipe Systems Reinforced concrete pipes do not deflect appreciably before cracking or fracturing, so deflection testing is of limited value. Visual inspection of pipe interiors and joints is the primary means of inspection for rigid pipes. During a visual inspection, observations of the following should be made: • Misalignment • Joint defects • Longitudinal cracks • Transverse cracks • Spalls • Slabbing • End-section drop-off. OTHER INSPECTION TECHNIQUES A wide range of other, less commonly used culvert inspec- tion techniques are available, including: • Destructive core sampling and evaluation • Ground-penetrating radar (applied from ground sur- face and from within pipes) • Impact echo testing • Infrared thermography • Mechanical impedance testing • Microdeflection testing • Natural frequency measurement • Pigs (basic mandrels through Instrumented “Smart” Pigs) • Spectral analysis of surface waves • Ultrasonic testing • Ultra-wideband radar. SUMMARY OF INSPECTION TECHNIQUES Two ongoing NCHRP projects—14-19, Culvert Rehabili- tation to Maximize Service Life while Minimizing Direct

42 Costs and Traffic Disruption, and 14-26, Culvert and Storm Drain System Inspection Manual—are proposed to provide updated summaries of culvert inspection techniques. The interim draft literature review summary report for NCHRP (2010) Project 14-19 provides an excellent sum- mary (Table 11) of techniques for culvert inspection, outlin- ing their applicability (culvert pipe type and flow) and ability to find defects. SUMMARY OF CURRENT INSPECTION PRACTICES The following observations were made based on the results of the NCHRP 10-86 survey completed in 2012: • For rigid pipe systems, visual inspection is the most com- mon, followed by video inspection and laser profiling. • For flexible pipe systems, mandrel testing is the most common, followed by visual inspection, video inspec- tion, and laser profiling. • Leak testing is performed equally (although infre- quently) on flexible and rigid pipe systems. • Video inspection and laser profiling are performed equally on rigid and flexible pipe systems. • Video inspection is approximately 60% more common than laser profiling. • Rigid pipe systems are less likely to be inspected than flexible pipe systems. In recent decades, the procedures for conducting and doc- umenting highway culvert condition surveys have benefited tremendously from significant improvements in inspection technologies. Most notably, improvements in CCTV, remote control robotics, laser profiling, optical scanning, and other remote techniques make inline inspections of culverts easier, less expensive, and more reliable than ever before. Many agen- cies routinely use a range of remote and man-entry inspection techniques during installation and post-installation, and for long-term monitoring and inventory management. Inspector training is provided by the National Associa- tion of Sewer Service Companies, and a number of DOTs have developed their own training courses, including Florida and Ohio DOTs. TABLE 11 METHODS OF CULVERT INSPECTION Technique Culvert Type Flow in Pipe The inspection will find: Visual inspection of man- entry culverts Any culvert type No Visible surface defects and defective joints; also, pipe misalignment, shape, or uniformity of curvature with additional field measurements Pigs Any culvert type Not important Pipe-shape deformations over allowed tolerances CCTV Any culvert type No Visible surface cracks, deformation, defective joints, stains from corrosion, shape distortion Optical scanning Any culvert type, pref- erably not corrugated No Visible surface cracks, deformation, defective joints, stains from corrosion, shape distortion Laser profiling Any culvert type No Ovality, alignment, diameter; also, defects such as surface cracks, corrosion of pipe inner surface, deposits Impact-echo Concrete culvert No Pipe-wall thickness, delamination conditions within reinforced con- crete pipe Spectral analysis of sur- face waves Concrete culvert No Conditions inside the concrete pipe and soil conditions (density, voids) outside of the pipe Mechanical impedance Any culvert type No Soil conditions outside of the pipe (voids or over-compaction in the soil around culvert) Natural frequency No Changes in overall pipe condition over time Microdeflection Concrete culvert Yes Damaged areas in pipe wall Ultrasonic, pipes empty Any culvert type No Ultrasonic, pipes full Any culvert type Yes Pipe surface conditions and anomalies, deposits Infrared Any culvert type Not important Soil conditions outside of the pipe (voids, leakage from pipes) Ground penetrating radar (GPS) from surface Any culvert type Not important Soil conditions outside of the pipe (location, depth of voids) GPR, from pipe Any nonconductive culvert type No Defects behind liners Source: NCHRP 14-19 (2010).

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 474: Service Life of Culverts explores the time during which a culvert is expected to provide a desired function with a specified level of maintenance established at the design or retrofit stage.

This study is an update of NCHRP Synthesis 254: Service Life of Drainage Pipe (1998), which itself was an update of NCHRP Synthesis 50: Durability of Drainage Pipe (1978). Developments in plastic pipe, fiber-reinforced concrete pipe, polymeric-coated metal pipe, recycled materials, larger and more diverse structures, and sophisticated analytical soil-structure interaction modeling within the past 15 years led to the development of this report.

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