1. CONSTRUCTION METHODS & TECHNOLOGY
CIVL462

3. There was a world-wide increase in the construction of heavy foundations in the period from 1950 to the 1970s as a result of developments in high office buildings, heavy industrial plants and shipyard facilities. The same period also brought the major developments of offshore oilfields.
A high proportion of the heavy structures required for all such developments involved piled foundations, which brought about a great acceleration in the evolution of piling equipment.
There were increases in the size and height of piling frames, in the weight and efficiency of hammers, and in the capacity of drilling machines to install piles of ever-increasing diameter and length.
The development of higher-capacity machines of all types was accompanied by improvements in their mobility and speed of operation.

4. The development of piling equipment proceeded on different lines in various parts of the
world, depending mainly on the influence of the local ground conditions.
Examples
In Northern Europe the precast concrete pile continued to dominate the market and this led to the development of light and easily handled piling frames. These were used in conjunction with self-contained diesel hammers and winches, with the minimum of labor and without the need for auxiliary craneage, steam boilers, or air compressors.
The stiff clays of the Midwestern states of America and the Great Lakes area of Canada favored large-diameter bored piles, and mobile rotary drilling machines were developed for their installation.

5. Equipment Standards
All piling equipment should comply with the requirements in BS EN 996: 1996 Piling equipment – Safety requirements and BS EN 791: 1996 Drill rigs – Safety.

6. Piling frames
The piling frame has the function of guiding the pile at its correct alignment from the stage of first pitching in position to its final penetration. It also carries the hammer and maintains it in position co-axially with the pile.
The essential parts of a piling frame are the leaders or leads, which are stiff members of solid, channel, box, or tubular section held by a lattice or tubular mast that is in turn supported at the base by a moveable carriage and at the upper level by backstays.
The latter can be adjusted in length by a telescopic screw device, or by hydraulic rams, to permit the leaders to be adjusted to a truly vertical position or to be raked forwards, backwards, or sideways.

8. Piling hammers
The simplest form of piling hammer is the drop hammer, which is guided by lugs or jaws
sliding in the leaders and actuated by the lifting rope.
The leads acts as guides for the drop weight and the pile.
The drop hammer consists of a solid mass or assemblies of forged steel, the total mass ranging from 1 to 5 tonne.
The height of drop or fall most frequently used varies from about 5 to 20 ft.
The maximum recommended drop height varies with the pile type, 15 ft for timber piles and 8 ft for concrete piles.
When a large energy per blow is required to drive a pile, it is better to use a heavy hammer with a small drop than light hammer with a large drop.

9. FIGURE 10-5. Drop hammer pile driver.

11. Advantages of drop Hammers
Small investment in equipment
Simplicity of operation
Ability to vary energy per blow by varying the height of fall
Disadvantages of drop hammers
Slow rate of driving piles
Danger of damaging piles by lifting a hammer too high
Danger of damaging adjacent buildings as a result of the heavy vibration caused by a hammer
Unable to use directly for underwater driving

12. The Single-acting hammer is operated by steam or compressed air, which lifts the ram and then allows it to fall by gravity.
BSP single-acting hammers of the type range in mass from 2.5 to 6 tonne with a maximum height of fall of 1.37 m.
The single-acting hammer is best suited to driving timber or precast concrete piles, since the drop of each blow of the hammer is limited in height and is individually controlled by the operator.
The single-acting hammer is suitable for driving all types of pile in stiff to hard clays, where a heavy blow with a small drop is more efficient and less damaging to the pile than a large number of lighter blows.

16. The ram of hydraulic hammers is raised by hydraulic fluid under high pressure to a predetermined height, and then allowed to fall under gravity or is forced down onto the pile head.
The hammer then falls freely under gravity and repositions the piston rod for the next stroke. Using a remote control panel these hammers can deliver an infinitely variable stroke and blow rate within the limits stated.

18. Advantages of Single acting drop hammer
The greater number of blows per minute permits faster driving
The heavier ram falling at lower velocity transmits a greater portion of the energy to driving piles.
The reduction in the velocity of the ram decreases the danger of damage to piles during driving
The enclosed types may be used for underwater driving
Disadvantages
They require more investment in equipment such as a steam boiler or air compressor
They are more complicated , with higher maintenance cost
They require more time to set up and take down
They require a large operating crew
They require a crane having a greater lifting capacity

20. Double-acting (or differential-acting) hammers are steam- or air-operated both on the upstroke and down stroke, and are designed to impart a rapid succession (up to 300 blows per minute) blows to the pile.
Double acting hammers are lighter than single acting hammers of same capacity.
Double-acting hammers have their main use in driving sheet piles and are not used for bearing piles in preference to diesel hammers.
However, unlike the diesel hammer they can operate underwater, provided that the ram is fully enclosed.

22. Advantages of double acting hammer compared with single- acting hammers
The greater number of blows per minute reduces the time required to drive piles
Piles can be driven more easily without leads
Disadvantages of double acting hammer compared with single- acting hammers
The relative light weight and high velocity of the ram make this type of hammer less suitable for use in driving heavy piles in to soils having high frictional resistance.
This hammer is more complicated

23. Diesel hammers
Diesel hammers are suitable for all types of ground except soft clays.
They have the advantage of being self-contained without the need for separate power packs, air compressors or steam-generators.
They work most efficiently when driving into stiff to hard clays.

24. Principle of Operation
The hammer is started by lifting the ram(B) with the crane hoist line (A).
The trip mechanism (C) automatically releases the ram at the top of the cylinder.
As the ram falls , it actuates the fuel pump cam (D), causing fuel to be injected in to the fuel cup in the anvil (E) at the bottom of the cylinder
As the ram continues to fall , it blocks the exhaust ports (F), compressing the fuel-air mixture.
When the ram strikes the anvil, it imparts an impact blow to the pile top and also fires the fuel-air mixture.
As the cylinder fires , it forces the body of the hammer down against the pile top and drives the ram upwards to start a new cycle.
Operation of the hammer is stopped by pulling the rope (G), which disengages the fuel pump cam (D).

28. Advantages and Disadvantages of Diesel Hammer
Diesel hammers are compact, light, and economical and can operate in freezing weather.
However, they may fail to operate in soft soil, where hammer impact may be too weak to fire the fuel-air mixture

29. Piling vibrators
Vibratory hammers drive piles by a combination of vibration and static weight.
Vibrators consisting of pairs of exciters rotating in opposite directions can be mounted on piles when their combined weight and vibrating energy cause the pile to sink down into the soil .
The two types of vibratory hammers, either mounted on leaders or as free hanging units, operate most effectively when driving small displacement piles (H-sections or open-ended steel tubes) into loose to medium-dense granular soils.

30. FIGURE 10-7. Hydraulically powered vibratory driver/extractor
FIGURE Hydraulically powered vibratory driver/extractor. (Courtesy of MKT Manufacturing, Inc.)

33. Selection of type of piling hammer
The selection of the most suitable type of hammer for a given task involves a consideration of the type and weight of the pile, and the characteristics of the ground into which the pile is to be driven.
Single and double-acting hammers, hydraulic and diesel hammers are effective in all soil types and the selection of a particular hammer for the given duty is based on a consideration of the value of energy per blow, the striking rate and the fuel consumption. The noise of the pile-driving operation will also be an important consideration in the selection of a hammer.

34. A knowledge of the value of energy per blow is required to assess whether or not a hammer of a given weight can drive the pile to the required penetration or ultimate resistance without the need for sustained hard driving or risk of damage to the pile or hammer.
Present-day practice is to base the selection of the hammer on a derivability analysis using the Smith wave equation to produce curves of the type shown in Figure 3.17.

38. Example:
The falling ram of a drop hammer used to drive a timber pile is 5000 lb. The free height during driving was 19 in., and the average penetration for the last eight blows was 0.5 inch per blow. What is the safe rated load using the Engineering News equation?
If the hammer in the above problem had been a single acting steam type what will be the safe rated load using the Engineering News equation?

39. Procedure in pile installation
Each class of pile employs its own basic type of equipment and hence the installation methods for the various types of pile in each class are the same.
Driving timber piles
Timber piles are driven by drop hammer or single-acting hammer after pitching them in a
piling frame, in crane-suspended leaders or in trestle guides.
The Swedish piling code requires the hammer to weigh at least 1.5 times the weight of the pile and helmet with a minimum of 1 tonne.
Diesel hammers, unless they are of the light type used for driving trench sheeting, are too powerful and are liable to cause splitting at the toe of the pile.
The heads of squared piles are protected by a helmet of the type shown in Figure 3.20.