15 August 2002
with relieved floors, grade the foundation course material to function as a filter. Where
drainage pipes are used in conjunction with the filter course, the material around the
pipes must be carefully placed and carefully compacted, to preclude damage to the
Foundation Slabs. Foundation slabs may be poured either by the tremie
method or in the dry.
Tremie Method. For the tremie method, divide the floor slab into
reasonable size pours by forms placed underwater, refer to American Civil Engineering
Practice, Volume II, for illustrations of methods of tremie concrete. Pour as follows:
Each pour must be placed through multiple pipes to minimize the distance
of concrete flow after emerging from the tremie pipe end. Pipes should be
no more than 3.66 m (12 ft) apart.
Water must be excluded from tremie pipes before they are filled with
concrete. Water may be kept out by special foot valves, or expelled by
various go-devil devices that separate water from the concrete columns in
the pipes as the columns build up with introduced concrete.
Tremie concrete must be brought to within 1.46 or 0.61 m (1-1/2 or 2 ft)
(nominally) of the top of the finished slab. Pour the remainder of the
finished slab in the dry. This procedure allows cleaning the top of the
tremie concrete after dewatering, embedment of various floor fixtures, and
a final accurate floor finish and elevation.
In the Dry Method. When docks are constructed in the dry, the floor is
poured to full thickness in one operation, and contains the embedded items.
Field Verification of Weight. For full hydrostatic docks, verify the actual
weight of concrete and reinforcing steel being placed during construction, in order to
ascertain the possible necessity for additional weight for conformity with design
dry. For drydocks constructed entirely in the dry, this is no special problem. For walls
constructed on tremie placed slabs, the walls must be built within unwatered cofferdams
placed on top of the tremie slabs. See Figure 5-3 for examples of cofferdams on tremie
Miscellaneous Items. Other structures built in connection with a graving
dock (such as capstan, bollard, and crane rail foundations) present no unusual
problems and may be constructed in accordance with accepted practice. Care must be
taken to ensure accurate positioning of items to be embedded in concrete, and
watertightness of such structures as capstan pits, pumpwells, and service galleries. All
holes left by removal of items (such as from ties) should be patched, because such
unevenness in concrete surfaces accelerates deterioration and may cause leakage.