EM 1110-2-1100 (Part V)
31 Jul 2003
(a) Office study. The first phase of the exploration program is an office study of maps, charts, aerial
photographs, and literature sources concerning the survey area (Morang, Mossa, and Larson 1993). A study
of these materials provides general information on the geomorphology and geology of the area, and helps to
identify features that might contain potential fill material. The office study also involves laying out a plan
for the next phase, general field exploration of potential sources. Such a plan would include specification of
an exploratory field data collection program and definition of the equipment needed to execute the program.
The most important equipment used for general field exploration and detailed site surveys are:
seismic reflection equipment, vibracore apparatus, navigation positioning system, and vessels. Grab
samples of surface sediments and side-scan sonar records are also valuable components of the general
exploration phase, and can usually be conducted for a relatively small additional cost. Prins (1980)
provides a detailed list of equipment and equipment capabilities recommended for use in general field
exploration operations. Seismic reflection equipment should provide the highest resolution possible,
consistent with achieving a subbottom penetration of at least 15 m (50 ft). High powered seismic
reflection systems used for many deep penetration studies are not suitable because of their relatively
poor resolution of closely spaced reflectors. Obtaining sediment cores using vibratory coring
equipment is more economical than standard soil boring methods, which require more expensive
support equipment. Vibratory coring equipment having 3-, 6-, and 12-m (10-, 20-, and 40-ft)
penetration capability is available. A 6-m coring device is necessary; a 12-m capability is desirable.
Navigation control should be established using an electronic navigation positioning system having
an accuracy of about 3 m (10 ft) at the maximum range anticipated for survey and coring operations.
Global Positioning Satellites (GPS) technology provides this type of accurate positioning.
An important task of an office study is to lay out trackline plots, similar to those shown in
Figure V-4-5, that are to be followed by the survey vessel in collecting seismic reflection data during
the general reconnaissance phase. A grid pattern as illustrated in Figure V-4-6, having lines approxi-
mately (0.8 km (0.5 miles) apart, should be employed for areas that are judged to be the most viable
either because they are located near the project site or give promise of containing deposits of usable
fill material (Meisburger 1990). Zigzag lines are used to cover areas between grids. The detail of
coverage is determined by trackline spacing. More complex or promising areas may call for closer
spacing.
Core sites can be tentatively selected during the office study. However, final locations should be
determined based on analysis of the seismic reflection records.
(b) General field exploration. During the general field exploration program, data are collected
throughout the survey area to locate and obtain information on potential borrow sources and shallow
subbottom stratigraphy. This phase involves collection of a comprehensive set of seismic reflection profiles
to identify sediment bodies, and a small number of cores to identify and test potential borrow sources.
The initial part of the general exploration phase is the collection of echosounder and seismic
reflection records along predetermined tracklines. The basic survey procedure is for the survey
vessel to proceed along each trackline, collecting data while its position is being monitored by an
electronic positioning system with fixes recorded at a minimum of 2-min intervals. Fixes are keyed
to the records by means of an event marker and identified by a serial fix number. Because seismic
reflection records tend to deteriorate in quality with increasing boat speed, the survey vessel's speed
should be slow enough to avoid significant reduction in record quality. In general, a suitable boat
speed is likely to be less than 4 or 5 knots. The records should be continuously monitored as they
become available. Changes in trackline patterns, if considered desirable, can be made as work
progresses.
V-4-16
Beach Fill Design
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