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Western Dam Engineering 19 measuring tape and in concrete conduits, locations of cracks along the conduit should be documented using a crack map, or similar reporting method, to track the development of new cracks during future inspections. The continuity of cracks can be investigated using a geologist’s pick to tap on the concrete and listen for variations in pitch that give clues as to the condition of the concrete. In pre-cast conduits, the joints in the conduit should be checked for separation due to settlement along the conduit alignment or issues with construction during assembly of the conduit sections. In conduits accessible for man-entry, joint meters can be installed to monitor the opening and closing of the joints that might be of concern. Other common defects observed during interior conduit inspections include deterioration or corrosion, obstructions, joint offsets and separations, defective joints, voided encasements, heaving, and cavitation damage. Sediment accumulation within the pipe, especially a concentrated build-up, is usually a sign of a defect along the pipe. Cavitation damage generally occurs immediately downstream of mechanical control equipment, such as gates or valves in the outlet works, where pressure flow changes to free flow. Cavitation damage is usually characterized as an erosion issue that begins with pitting and progresses into large cavities. Proper venting is the best method for preventing cavitation damage. The July 2013 issue of the Western Dam Engineering Technical Note can be referenced for information on proper ventilation for outlet works and common indications of cavitation during inspections. Repair methods for some of the defects listed will be covered in more detail in the following sections. Different Types of Conduits and Common Issues Associated with Them A variety of materials has been used to construct conduits through embankment dams during the past 100 years. For the purposes of this article, conduits constructed of concrete, plastic, and metal will be reviewed, as they are the most common conduit materials used in small to medium sized dams. This section presents some common defects with each of these materials and a few potential repair alternatives. All repairs presented below require complete unwatering and isolation of the conduit from the reservoir. Precast Concrete Conduits Reinforced concrete pressure pipe (RCPP) and reinforced concrete pipe (RCP) are two types of conduits that have historically been used in many small to intermediate sized embankment dams. One of the primary advantages of precast concrete conduits is that they are relatively inexpensive and can be purchased in standard lengths. RCP/RCPP conduits are connected using a bell and spigot type of connection and can be constructed to accommodate some expected settlement along the conduit alignment due to the flexibility provided at each joint location. However, leaks are prone to develop at RCP/RCPP joint locations because the reinforcement is not continuous at the joints and there is potential for exceeding the joint extensibility through poor construction techniques or settlement along the conduit alignment. Other common issues to look for during inspections of RCP/RCPP conduits are cracks in the conduit and spalled concrete. Cracks in the conduit typically occur at the transition immediately downstream of the control structure due to differential settlement. Spalling often occurs in precast concrete pipe at the joint locations where there is unequal displacement of the joint in the crown and invert or spring line. It should be noted that a well prepared subgrade, continuously positive slope, and good quality control during construction can go a long way toward preventing these joint offsets and other associated issues. Whenever possible, a concrete cradle should be used beneath pre-cast conduits to ensure support underneath the conduit haunches. Unfortunately, however, these more modern practices have not always been followed in the past, leading to long-term degradation of existing precast concrete conduits. Spalled Concrete Methods to repair spalled concrete within concrete conduits are similar to that of typical concrete structures. The surface must first be prepared by removing the deteriorated concrete down to sound material. Reinforcing steel exposed for more than one-third of its circumference should be completely exposed to provide clearance around the reinforcement for the repair material. The final prepared surface should be free of all loose aggregate, spalled concrete, and dirt, leaving the aggregate of the remaining concrete partially exposed