Construction stakes for a perimeter dike center lines are set at every 20-m stations by the engineer. Reference as to alignment, grade, stationing, etc. is made according to a construction layout plan.
The limits of the work (Fig. 30) as marked on the map are staked on the ground for clearing and grubbing (destumping). Clearing and destumping operations include the cutting and felling of trees within the limits of work, done manually using the chain saw and followed by destumping operations done manually or a combination of both manual and mechanized methods using a low ground pressure (LGP) crawler tractor or a crane plucket for uprooting the tree stumps. Uprooting may also be done manually using a combination of pulley and chain blocks (Fig. 28). All materials are removed and disposed of from the limits of work as follows:
Tree stumps are removed inside the work limits and are deposited on the river side near the toe of the perimeter dike in the buffer zone.
Tree trunks may be used as matting for the crane or crawler tractor; otherwise are cut to equal or uniform lengths for sale or used as firewood.
Since pile foundations will be required for the buildings and for the concrete main and secondary gates, some quantity of these trunks of 4–6 inches (0.10–0.15m) in diameter will be cut to appropriate lengths and set aside for future use.
Twigs and branches are piled outside the work limits and are disposed of by burning.
Stripping excavation consists of the removal of the top soil within the limits of work, soil that is unsuitable for use as dike foundation but which may later be used as pond top soil. The operation consists of removing the surface soil which contain unsuitable soil material for foundation. The depth of the stripped soil shall be to the discretion of the engineer. Stripped soil shall be deposited within the pond area, outside the work limits.
Although this is not applicable, rocks larger than 6 inches brought to the surface shall be removed.
Excavation for the cut-off trench if needed is done along the dike centre line, the depth as specified and shown on drawings and the bottom width adjusted to the type of excavating equipment used. The trench sides, whenever possible, should be sloped 1:1 or flatter.
As shown on drawings, the limit of borrow areas are staked in the field.
The cut-off trench shall be backfilled with suitable material and compacted. Fill material should not be placed until foundation preparation has been approved by the engineer.
It was suggested in the Operation Plan of the Rancangan Ban Merbok1 that the project will be implemented initially as a Government project and when the farms are successful and production has stabilized, these farms shall be handed over to the participant farmers.
During construction and initial pond operation, pond levelling and the construction of the tertiary dikes shall preferably be done manually by the prospective and participant-farmers using the basic methods, tools and implements used for excavation and dike construction similar to that practised and used in the Philippines and Indonesia. (Jamandre and Rabanal, 1975)
Tertiary dike construction commences when the clearing and destumping operations will have been completed by the contractor. The limits of the dikes, height, width and side slopes are marked with stakes and strings (Fig. 33).
During excavation, the digging blade is driven vertically along the sides of the rectangular block of earth measuring approximately 50 × 20 × 20 cm. The blade is rocked back and forth along each side of the block and the whole block is removed. During the initial stages, the blocks of earth are carried only a short distance to the dike, either singly or by transfer from one man to another. Walking on wooden planks facilitates the transfer of the earth as it also cuts down on time.
To save on labour and time when the distance of the transfer involved is far, a flatboat is used (Fig. 34). In diking using flatboats, one man works alone with one flatboat - as he cuts the soil, loads on the flatboat, pushes the flatboat and unloads the soil blocks. It has been observed that a labourer can do about 6 m3 or earthwork in one working day of 8 hours for distances; in the Ban Merbok set-up, from the centre of the rearing pond to the tertiary dike. For less skilled workers, two men may be assigned to one flatboat.
The earth blocks have roots in them - they are so arranged that blocks within the dike cross-section have the roots lying parallel to the dike and the blocks at the dike side slopes which have roots within them run perpendicular to the longitudinal axis of the dike. This arrangement gives the minimum of erosion of the dikes side slopes and seepage of water.
Before the next layer is added, the previous layer is tamped and allowed to harden before the next top layer is added. The tertiary dike is finally shaped manually at the sides using a spade or shovel.
Excavation of the pond soil for diking is followed by the levelling of the pond bottom (for the central portion of the pond) and when the secondary and tertiary gates have been constructed.
Water is let into the pond during high tide to a depth of not more than a foot and the water surface is referred to a bench mark of known elevation placed at or near the gate. The gates are closed and sealed with earth. Initial water surface elevation is then marked on poles scattered all over the work area. By means of a depth gauge (Fig. 35), the extent to which the excavation is carried to the desired pond bottom elevation is metered and controlled. The worker adjusts his water level from time to time as soil is removed from the ponds, and also sees to it that there is no loss of water in the pond by seepage during the excavation work (Denila, 1975).
The pond is drained for final levelling. This work is done with a hoe. The pond bottom is maintained level in order that growth of algae will be uniform.
For this project,a crawler-mounted dragline will be used to excavate from borrow pits along the dike and deposit the material to build the dike as the excavating equipment backs up along and parallel to the dike centre line. The limits of work for the construction of the peripheral (main) dike are indicated on a construction plan.
A medium duty, 60 cubic feet struck capacity perforated bucket to a 70-foot boom may be used for the earthwork.
The choice of the equipment are based on the varied advantages as:
Readily available equipment and experienced operators
Works best under conditions existing as it can operate on natural ground while excavating.
Can be used for destumping operations.
In general, a power shovel up to a capacity of 2-1/2 yd3 (0.76m3) can be converted into a dragline by replacing the boom of the shovel with a crane boom and substituting a dragline bucket for the shovel dipper.
For the construction of the drainage and supply canals a power shovel may be used to excavate the materials, although the dragline had the distinct advantage compared with the shovel.
Various tools and implements for manual pond construction in earthwork as for diking and pond levelling will be made available to the workers (Figs. 31 and 32). The use of these tools have already been mentioned in previous paragraphs.
Flatboat - This is a rectangular loading platform made of marine plywood at the top and bottom and measuring 4 ft (1.22m) wide x 8 ft (2.44m) long x 1 ft (0.30) deep. The sides and the inside lateral boards are all of 1-inch (0.025m) x 10-inch (0.255m) stock, thus forming the flatboat frame. One by 2-inch (0.050m) wood are equally spaced and lapped into the lateral boards to serve as furring strips. V-cut holes for the passage and easy removal of water inside the flatboat are provided. At the lateral board edges, 2-inch (0.050m) diameter holes and stoppers are provided at both ends, and a stud for a mooring rope is attached at one corner (Fig. 34).
Digging blades - Figs. 31 and 32 show the different types of pond digging implements used in manual construction of ponds.
One commonly used digging tool in the Philippines is a flat steel blade, about 60 cm long, 10–15 cm wide at the tip, and narrowing to about 5 cm towards the wooden handle which is fixed in line with the blade. These are made out of discarded leaf springs. The edges of the blade at both sides are sharp-edged; used for hacking through the mangrove roots.
Carpenter's level and side slope gimmick - A cheap wooden carpenter's level is used for staking the dike side slopes. Fig. 33 shows 1" × 2" pieces specially made for a dike side slope of 1-1/2:1.
The top of the dike is marked by stick A (horizontal) held by poles B planted vertically at point M measured perpendicular to the dike centre line at a distance one-half of the width of the top. Side slope gimmick determines the base of the slope and the location of the ground slope stake (n) when the bubble of the carpenter's level is centred.
Abney level - This is a very handy piece of equipment for use of a layman. The hand level is held rigid by the use of a forked stick out to a length equal to the height of the operator's eye above the ground.
For use in levelling, the index of the clinometer (protractor) is set at zero. The operator adjusts the level as he sights at the rod man so that the bubble and the horizontal hair are on the same line. The operator makes a reading of the rod or if this is not done, he directs the rod man to slide up or down a piece of paper on the rod as he sights the edge of the paper to coincide with the hairline and bubble. The rod man makes the reading.
The difference in elevation between the two points (operator and rod man) is determined with this instrument.
Water depth gauge - This is a very cheap and simple piece of metering device for measuring the depth of water in the pond as pond levelling is being done (Fig. 35). The length should be such that the operator does not necessarily bend while holding the stick.
A piece of wood about 18" × 18" × 1 inch thick is nailed to the end of a 1-1/2" × 1-1/2" × 4' handle. This prevents the gauge from sinking into the soft mud as it stands by itself when not held by the operator. Graduations in meters are painted red on white background.
Refer to construction methods which describe the use of the water depth gauge.
