The first step in any repair, rehabilitation, or replacement project is assessment and evaluation of the structure in question. This starts with proper inspection, along with a key understanding of the features of the culvert type and material. During such an evaluation, it is essential to consider the major structural and geometric characteristics unique to the particular type of culvert product and material under investigation. There are a number of references available to assist the engineer or inspector in this process. However, some of the key factors are discussed here.
A critical step in proper evaluation of any culvert structure is determining the type of material used in its manufacture and installation — for example, stone and masonry, reinforced (or unreinforced) concrete, corrugated metal (steel or aluminum), solid-wall steel or iron, or plastic (PVC or HDPE). Each of these culvert material types has a unique set of design and installation standards, along with applicable criteria used for proper inspection and evaluation.
Understanding the nuances and differences relevant to each culvert material type is important to accurately assessing structural adequacy, estimating service life, and determining whether a culvert is a candidate for rehabilitation.
Ideally, there exists a set of plans or other documentation pertinent to the specific culvert that is being evaluated for repair, rehabilitation, or replacement. Previous inspection reports prove invaluable in determining whether a culvert has experienced any changes or deterioration in physical condition, shape geometry, structural performance, or hydraulic capacity since the last time it was inspected. The prior inspection history should include those criteria that are relevant to the particular type of culvert product being evaluated. Not all of these criteria apply to each type of culvert product. Therefore, familiarization with the relevant criteria is important to a thorough and accurate assessment of each culvert.
Adhere to applicable OSHA requirements and related agency guidelines relevant to confined space entry and inspector safety precautions. Evaluate the risks associated with factors such as water flow surges, air quality, fall protection, and worker accessibility prior to undertaking culvert inspections.
Compare inspection data — changes in shape, invert clogging, loss of wall section, perforations, cracking, settlement, joint separation or related problems, pavement distress, et cetera — to that found in previous inspection reports to help indicate any pattern of change or worsening conditions. This aids the inspector and the engineer in determining the proper course of action and assessing the relative urgency for any action required.
Measure, record, and compare the cross-sectional, geometric shape dimensions of the culvert to shape measurements from previous inspections for any significant change and to establish a pattern of movement or deflection.
Note and investigate cracks in the culvert wall, spalled or deteriorated wall sections, problems with seams, missing bolts or rivets, and buckling or other visible distortions to the culvert wall for potential effects on structural performance.
Note and investigate changes to the road surface, guardrail, shoulders, and adjacent side fill embankments, along with any changes to the end slopes associated with the culvert site. Changes that could affect the integrity of the roadway should, in the interest of public safety, be considered in such an inspection.
Since the primary purpose of a culvert is to convey flow, an inspection must consider the hydraulic performance and efficiency of the culvert. Any buildup of debris that would affect the ability of the culvert to carry flow should be noted and addressed. Undermining of the pipe invert at either the inlet or outlet ends should be noted, as should the loss of fill along the end slopes. Either situation can lead to loss of fill and support for both the culvert and the roadway above and may require attention in the form of cut-off walls, slope collars, or paving or other suitable modifications to the end protection.
Inspect joint integrity and alignment. Open joints that allow for significant exfiltration of water or infiltration of backfill should be noted and marked for possible repairs. Misaligned sections of pipe affect the efficiency and rate of flow, as well as provide the means for infiltration/exfiltration to occur.
Note and evaluate abrasion loss, effects of corrosion, perforations, and similar damage to the culvert material itself or to the coatings for the potential effects on long-term service life and structural performance. Record the presence of abrasive materials — such as rocks, gravel, sand, and other debris — representing a potentially abrasive bed load situation. Note that corrosion may appear to be much worse than is actually the case because of the voluminous nature of rust products associated with corroded steel. Often, after using an abrasive pad to remove such apparent rusting, it is discovered that the "rust" is actually staining of the culvert wall, and the metal and coating underneath is performing as intended. Conduct core sampling to verify the extent of actual metal loss. Any perforations should be noted for size, location, and frequency in order to quantify their severity.
It is recommended that all inspection personnel be adequately trained in the key aspects of proper culvert inspection and that they become familiar with the nuances and unique design features of the various culvert materials and types used in their area of responsibility. Such inspections can be, and often are, undertaken by agency personnel, but the need for proper knowledge in the functional hydraulic and structural design aspects of the particular culvert product type, along with familiarity of the site-specific installation conditions, can not be overemphasized.
There are also firms that specialize in such inspection services and that are capable of evaluating culverts based on the proper set of criteria applicable to that particular type of culvert. These firms should be familiar with the proper design procedures, standard installation practices, and relevant factors influencing evaluation and assessment of existing culverts for the type of culvert being investigated.
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