Swl

Profile

Varies

Profile

Varies

Poured concrete or sheet-pile diaphragm height varies

Armor stone

Armor stone

Bottom varies

Cross section

Bottom varies

Cross section

Figure 3-10. Groins.

foot deep cavity. These data may be supplemented by the diver's opinion regarding the structural adequacy of the wall if the nature of its condition is obvious. But a final conclusion can only be reached after an analysis of the structure's existing condition has been carried out.

Since divers' observations and measurements are often the only data available for the topside to make an engineering assessment, the reliability of such data is critically important. Therefore, the quality control of the measurements becomes an important issue. At least 10 percent of all measurements and observations must be re-checked by a second diver to ensure accuracy. If there is any discrepancy, all measurements and observations must be re-checked.

An important part of any inspection operation is the recording of the diver's observations. Observations, both qualitative and quantitative, can be recorded underwater on a Plexiglas slate with a grease pencil. However, direct hardwire communication between the diver and topside is much more efficient. In addition, use a video recording system, a photographic camera, and a voice recorder whenever possible. The dive supervisor or detachment leader should debrief the working diver as soon after the dive as possible. This valuable information should be recorded for later reference.

3.3.1 Levels of Inspection

Three basic types or levels of inspection are used for inspecting marine facilities. They are distinguished by the resources and preparation needed to do the work and the type of damage/defect that is detectable, as:

• Level I - General Visual Inspection.

The Level I effort can confirm as-built structural plans and detect obvious major damage or deterioration due to overstress (collisions, ice), severe corrosion, or extensive biological growth and attack.

This type of inspection does not involve cleaning of any structural elements and can therefore be conducted much more rapidly than the other types of inspections. The Level I effort is essentially a general inspection "swim-by" overview. It does not involve cleaning of structural elements, which allows the inspection to be conducted rapidly. The underwater inspector relies primarily on visual and/or tactile observations (depending on water clarity) to make condition assessments. These observations are made over the specified exterior surface area of the underwater structure, whether it is a quay wall, bulkhead, seawall, pile, or mooring. Although this is an overview, close attention should be given to confirming or providing information to update available facility drawings and condition evaluations.

• Level II - Close-Up Visual Inspection.

Level II efforts are complete, detailed investigations of selected components or subcomponents, or critical areas of the structure, directed toward detecting and describing damaged or deteriorated areas that may be hidden by surface biofouling. Limited deterioration measurements are obtained. These data are sufficient for gross estimates of facility load capability. This type of inspection will generally involve prior or concurrent cleaning of part of the structural elements. Since cleaning is time consuming, it is generally restricted to areas that are critical or that may be typical of the entire structure. Simple instruments such as calipers and measuring scales are commonly used to take physical measurements. Subjective judgments of structural integrity are occasionally made by probing wood with ice picks and by pounding concrete with hammers.

• Level HI - Highly Detailed Inspection.

This level of inspection is primarily designed to provide data that can be used to perform a structural assessment and will often require the use of Nondestructive Testing (NDT) techniques. The procedures are conducted to detect hidden or imminent damage. The training, cleaning, and testing requirements will vary depending on the type of damage/defect that is to be investigated and the type of inspection equipment to be used. In some cases, Level III inspections will require the use of partially destructive techniques such as sample coring in wood or concrete, material sampling, and in-situ surface hardness. The use of Level III inspection techniques is usually limited to key structural areas that may be suspect, or to structural areas that may be representative of the overall structure.

On steel H-piles, pipe piles, and sheet piles, metal thickness measurements are made with ultrasonic thickness equipment (Section 3.6.4.3). In addition, electrical potential measurements, using a half cell, are taken to verify the performance of the cathode protection system for steel structures. Concrete surfaces can be evaluated for hardness using the rebound hammer described in Section 3.6.4.2. A magnetic rebar locator (Section 3.6.4.1) can be used to establish the location and depth of rebar. There are few underwater instruments cur-rendy available for assessment of the interior of wood structures. Wood is inspected using calipers, ice picks, and hammers, and in some cases an incremental borer is used to obtain a core sample.

Table 3-1 summarizes the type of damage that is detectable with the three types of inspection. The level of inspection to be used for a particular task is usually decided early in the planning phase. However, depending upon visibility, marine growth, and extent of deterioration, this may be adjusted as the inspection proceeds. Often, die requirements of the local Public Works office Staff Civil Engineer or other authority will dictate the level of inspection.

The time and effort required to carry out the three different levels of inspection are quite different, and the time required for any particular level will depend on a number of factors, including visibility, currents, wave action, water depth, severity of marine growth, and the skill and experience of the diver.

Table 3-2 provides a guide for estimating the time required to conduct Level I and Level II inspections. This information is based on:

(1) a water depth of 30 to 40 feet

(2) visibility of 4 to 6 feet

(3) warm, calm water

(4) moderate marine growth (about 2 inches thick)

(5) an experienced diver of average skill

For the Level II inspection it has been assumed that 3 feet of the structural element in the splash zone, 1 foot at mid-depth, and 1 foot at the bottom will be completely cleaned of marine growth. It has also been assumed that the most efficient method of removing marine growth will be used (refer to Section 2.3).

Level III inspections depend on the extent of existing damage, the type of inspection techniques, the equipment used (ultra-

Table 3-1

Level of Inspection Versus Detectable Damage to Waterfront Structures

Table 3-1

Level of Inspection Versus Detectable Damage to Waterfront Structures

Level

Purpose

Detectable Defects

Steel

Concrete

Wood

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