HPSI 500	Model 300-4	OMS 50 NF
GeoQuip Power Systems	American Piledriving Equipment	OMS Pile Driving Equipment
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D280-22	36-3000 Air Hammer	V5Esc
Pileco	Pile Master	MKT Manufacturing
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TABLE OF CONTENTS

Overview of the Driving System
Types of Hammers
Driving Accessories
Vibratory Drivers
Pile Buck’s top recommended rigs

Overview of the Driving System 

All components of the driving system have some effect on the performance of a hammer and/or how the hammer transfers its energy to a pile.

The driving system consists of:

1. The lead, also called the set of leads, sometimes including a brace that allows for the adjustment of the lead angle.
2. The hammer cushion, which protects both the hammer and the pile from excessive stress.
3. The helmet, which aligns the pile head and hammer.
4. The pile cushion. This is only needed on concrete piles. It is typically made of several layers of plywood.

Equipment Selection 

Hammer selection is the most important aspect of pile installation. Identify the broadest possible selection of hammers for the job. In some installations only one hammer type may be applicable for the pile-soil combination, while for others several types may be suitable. When it comes to pile driving, a hammer isn’t just a hammer. It’s also a piece of testing equipment. The vertical advance of a pile under a given hammer blow is used as a measure of the pile’s bearing capacity. The hammer’s interaction with the pile-soil system is both modeled before driving (wave equation analysis) and monitored during pile installation (pile driving analyzer).

Evaluation must consider:

• The need to use pile penetration rate as the means to end driving.
• The ability to drive the pile without structural damage or reducing soil capacity.
• The ability to obtain penetration rates within the desired band.
• The realization that some hammer types may cause reduced capacities for identical pile lengths.

Selection of a hammer should consider the anticipated driving resistance, ultimate capacity, pile stresses expected during driving, and soil set-up.

Types of Hammers 

Over the years, technology has advanced toward the development of larger and faster hammers. These developments included rams that were raised by ropes through human or horse muscle, those hoisted by steam winches or powered by steam, air, or hydraulic pressure, and finally the diesel hammer. Double acting hammers were developed in order to speed up operations.

Impact Hammers 

Impact pile driving hammers consist of a ram and an apparatus that allows the ram to move quickly upwards and then fall onto the driving system and pile. The ram must have a mass and impact velocity that is sufficiently large to move the pile.

A properly functioning hammer strikes the pile in quick succession. It transfers a large portion of the kinetic energy of the ram into the pile. The stroke of a pile- driving hammer is usually between three and ten feet (900 to 3000 mm).

External Combustion Hammers 

External combustion hammers burn the fuel that provides the energy for the operation outside of the hammer itself. These hammers have external power sources such as the crane, steam boilers, air compressors, and/or hydraulic power packs. The energy moves the ram upward, and in some hammers, downward as well.

Drop Hammers 

The drop hammer is the oldest type of pile driving hammer in existence. The hammer is connected to a cable that is attached to a winch on the crane. The hammer is raised to the desired stroke. The winch has a clutch on it that allows the operator to release the hammer, which falls by its own weight and strikes a pile cap and the pile.

The available energy per blow of a drop hammer is the product of the ram weight times the drop height. Standard ram weights range from 500 to 10,000 lbs (2.5 to 50 kN). Typical drop heights are approximately 4’ (1.2 m). For a given hammer, varying the drop height can vary the energy per blow. Drop hammers are typically used on very small projects and for small piling.

Advantages of Drop Hammers 

• Simplicity of operation.
• Ease of mobilization and demobilization.
• Low investment and maintenance costs.
• Drop height can easily be changed.

Single Acting Air/Steam Hammers 

Single acting air/steam hammers are essentially drop hammers, except that the hoisting cable is replaced by pressurized air or steam (motive fluid). The ram is usually a short, stocky block of steel that is connected at its top to a piston. It is guided by columns or inside guiding enclosure.

Single acting air/steam units from Vulcan and Menck are commonly used to drive piles offshore.

The operating rate of single acting air/steam hammers range between 35 and 60 blows per minute. This rate is comparable to most other hammer types that lack downward assist.

Advantages of Single Acting Air/Steam Hammers 

• Higher rate of blows per minute than drop hammers.
• Relatively consistent operation.

Disadvantages of Single Acting Air/Steam Hammers 

• Additional equipment needed (e.g., boiler, compressor, hoses, etc.)
• Relatively heavy hammer that requires higher crane and handling equipment capacities.

Double, Differential and Compound Acting Air/Steam Hammers 

The desire to create a hammer that applies blows in rather quick succession for increased productivity led to the development of double acting air/steam hammers. For an increase in blow rate, the stroke was shortened. In order to maintain a comparable energy rating, the ram was accelerated during its down stroke using active pressure.

Advantages of Double, Differential and Compound Acting Air/Steam Hammers 

• The speed of operation is twice as fast.

Disadvantages Double, Differential and Compound Acting Air/Steam Hammers 

• Energy output is very sensitive to proper valve timing, and to pressure and volume of the motive fluid.
• Each blow is more difficult to inspect and verify.
• The applied hammer energy output is sensitive to soil resistance.

Hydraulic Impact Hammers 

A hydraulic hammer incorporates the use of an external energy source to lift the hammer to the top of its stroke. For the single acting hydraulic hammer, the free-falling piston develops the actual energy induced into the pile, much the same power stroke as a drop hammer or a single acting air/steam hammer.

These hammers substitute hydraulic fluid for air or steam, and it is applied to the piston to move the ram. A hydraulic power pack provides the pressurized fluid to operate the hammer. Hydraulic impact hammers can be single acting, double acting, differential acting, or other variations. Most but not all hydraulic hammers employ the use of an electric valve operated with a variable timer. The timer allows for flexible control of the output energy. Others use a purely hydraulic system to control the valve and thus the cycling of the ram. Some are powered using the hydraulic power units on the crane or excavator.

Most hydraulic hammer manufacturers claim high efficiencies for their hammers. Although there are many improvements in hydraulic hammers that enable a more efficient drop, the main reason for the higher efficiencies is that they have some kind of downward assist to equalize the hydraulic flow during the hammer cycle.

Internal Combustion Hammers 

These hammers burn the fuel that powers them inside of the hammer itself. The diesel hammers are the only constituent of this class, although other types of fuel are being used.

Single Acting (Open End) Diesel Hammers 

An open-end diesel hammer consists of a long slender piston (the ram), which moves inside a cylinder. The cylinder is open at its upper end, thus allowing the ram to partially emerge from the cylinder. Since the ram falls only under gravity, the OED is also called single acting.

There are many manufacturers of open-end diesel hammers throughout the world. The hammer ratings vary from 5 to more than 300 kip-ft with ram sizes between 1 and 35 kips.

Advantages of Single Acting (Open End) Diesel Hammers 

• Self-contained unit does not require additional equipment.
• Increasing strokes in hard driving provide increasing energies.
• Low strokes in easy driving protect concrete piles.
• Relatively low ram weight compared to energy (high strokes.)

Disadvantages of Single Acting (Open End) Diesel Hammers 

• Stroke dependent on hammer-pile-soil system.
• Relatively low blow rates with high strokes.
• Potential for environmental problems (very dependent upon how hammer is outfitted with fuel and lubricants).

Upon impact, the ram pushes the impact block, hammer cushion, helmet, and pile head rapidly downward, allowing the cylinder to fall under gravity. The impact block separates from the ram within a very short time and the pressure of the combusting air-fuel mixture will cause further separation as the ram is forced upward.

Double Acting (Closed End) Diesel Hammers 

A closed end diesel hammer consists of a long slender piston (the ram), which moves inside a cylinder. The cylinder is closed at its upper end, thus causing the ram to compress the air trapped between ram and cylinder top. When the ram falls, it is subject to both gravity and the pressure in the bounce chamber. For this reason, the CED is also called double acting.

There are two prominent manufacturers of closed end diesel hammers distributing their products in North America: Bermingham and MKT Geotechnical systems. The hammer ratings vary from 5 to not more than 80-kip-ft, with ram sizes between 1 and 10 kips. The MKT hammers are built using liquid fuel injection. Bermingham’s closed end models use atomized fuel injection.

Advantages of Double Acting Diesel Hammers 

• Self-contained unit does not require additional equipment.
• High blow rate compared to open-end diesels.

Disadvantages of Double Acting Diesel Hammers 

• Uplift in hard driving.
• Uncertain energy when combustion prevents ram-anvil impact.
• Stroke is not easily determined.
• Complex maintenance.

Driving Accessories 

It is not possible for the striking end of the ram of an impact hammer to directly adapt itself to all shapes of piles. It is necessary to have driving accessories of various types and sizes inserted between the bottom of the hammer and the pile to both mate the two geometrically and transmit the impact hammer force to the pile.

Hammer Cushion 

Most impact hammers have some type of cushion under the end of the ram to protect the hammer’s striking parts from damage.

Anvil

The rams of most external combustion hammers strike the hammer cushion or top plate directly. With internal combustion hammers, an anvil is necessary to trap the combustible mixture and allow it to build pressure.

Helmet 

The helmet is the heavy and rigid steel block between hammer and pile. Often the hammer manufacturer supplies helmet inserts or adapters. The helmet distributes the blow from the hammer more uniformly to the head of the pile to minimize pile damage. It is important that the helmet’s striking surface is smooth and contacts the pile top evenly. It should not allow more than approximately 2 inches (50 mm) of lateral movement. The helmet weight (more properly mass) must be known to evaluate the drivability of a pile using the wave equation.

Pile Cushion 

If the pile is in danger of being cracked in tension during driving, then pile cushions may be very thick (up to 18” (457 mm)). For the protection of the pile top against a compressive damage, thinner cushions are usually sufficient. The depth of these cushions can vary from 6” (152 mm) to 18” (457 mm).

Mandrel 

A mandrel is used to install thin-wall shell piles, which are subsequently filled with concrete. The mandrel is necessary because the pile wall is too thin to withstand the stresses of driving.

Followers 

A follower is a steel member placed between the pile hammer and pile that allows the pile to be driven below the reach of the leads. The most common uses are to drive a pile below the top of an existing structure or for driving piles over water.

Vibratory Drivers 

A vibratory pile driver is a machine that installs piling into the ground by applying a rapidly alternating force to the pile. This is generally accomplished by rotating eccentric weights about shafts. Each rotating eccentric produces forces acting in a single plane and directed toward the centerline of the shaft.

Types of Vibratory Hammers 

Low-Frequency Hammers 

These are vibratory hammers with a vibratory frequency of 5 to 10 Hz, used primarily with piles which have high mass and toe resistance such as concrete and large steel pipe piles.

Medium-Frequency Hammers 

These are hammers with a vibratory frequency of 10 to 30 Hz, used for piling such as sheet piles and small pipe piles.

High-Frequency Hammers 

These consist of all vibratory hammers that vibrate at frequencies greater than 30 Hz.  There are of two basic types. The first machines are in the 30 to 40 Hz range that are designed primarily to minimize vibration of neighboring structures. The primary advantage of these machines is their lowered transmission of ground excitation to neighboring structures.

Sonic or Resonant Hammers 

In a class by itself is the resonant pile driver, first introduced in the early 1960’s. The central principle of the resonant driver is to induce resonant response in the pile. This facilitates driving and extracting. The resonant driver operates at frequencies in the range of 90 to 120 Hz.