Overview of the Driving System
The driving system consists of:
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 lead, also called the set of leads, sometimes including a brace that allows for the adjustment of the lead angle.
- The hammer cushion, which protects both the hammer and the pile from excessive stress.
- The helmet, which aligns the pile head and hammer.
- The pile cushion. This is only needed on concrete piles. It is typically made of several layers of plywood.
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.
Junttan Pile Driving Rig
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 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.
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.
APE 180-2 Impact Pile Driver
BSP - Hydraulic Drop Hammer - SL Type
APE Model 15/60 Hydraulic Impact Hammer
Junttan Hydraulic Impact Hammer HHK S-SERIES
APE D25-32 Diesel Impact Hammer
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.
Most impact hammers have some type of cushion under the end of the ram to protect the hammer’s striking parts from damage.
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.
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.
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).
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.
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.
SPS Cylinder Pile Cushions
Pile Driving Helmet by Geoquip USA
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
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.
These are hammers with a vibratory frequency of 10 to 30 Hz, used for piling such as sheet piles and small pipe piles.
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.
PILE BUCK’S TOP RECOMMENDED IMPACT HAMMERS AND VIBRATORY DRIVERS
The Junttan HHK S-series provides an adjustable stroke of up to 4.9 ft and up to 20% more efficiency than a traditional free-fall hammer of the same weight. The impact hammer is suitable for driving all types of piles: precast concrete, steel tube, sheet, and timber piles. The design of the hammer frame and drive cap makes for low impact noise and less vibration while piling. All impact energy is concentrated in the center of the pile. The construction of the hammer makes it possible to use biodegradable hydraulic oils. The hammer is easy to connect to different hydraulic systems and can be operated either by the hydraulic system of the rig or by a separate power pack. Furthermore, it can be mounted on all kinds of leaders or be freely suspended.
Max energy: 97,646 ft-lb (132 kNm)
Max drop height: 4.92 ft (1,5 m)
Blows per minute: 30-100
Ram weight: 19,842 lb ( 9 000 kg)
Total weight: 30,865 lb ( 14 000 kg)
Oil flow: 87 gpm (328 l/min)
Operating pressure: 3,771 psi (260 bar)
Theoretical power output: 3,771 psi (142 kW)
- Variable Moment type Vibratory Hammer
- Eccentric Moment: 0 – 24 kgm
- Compactly built Vibratory hammer
- Forced lubrication system
- Resonance free stop and start
- Suitable in urban areas and vibration sensitive projects
- Rifle-bored top plate delivers oil to motors without using hoses
- Patented one piece helical gear/eccentric eliminates gearbox failures caused by broken pins, keys, bolts or splines found in all other vibro gearboxes
- Giant double roller spherical bearings for super long life
- Center safety pin shows the line load on pile and cranes
Eccentric moment: 5,080 kg-cm (4400 in-lbs)
Frequency (variable): 0-1800 vpm
Driving force @ 1600 vpm (standard): 145 metric ton (160 US tons)
Driving force @ 1800 vpm (for driving in sand): 183 metric ton (202 US tons)
Amplitude: 30 mm (1.17 in)
Maximum line pull: 1,335 kN (150 US tons)
Suspended Weight (with universal clamp): 6,167 kg (13,600 lbs)
Length: 256 cm (101 in)
Width throat: 35 cm (14 in)
Width at widest point: 43 cm (17 in)
Height (with 223 kN (30 ton) (short suppressor & clamp): 153 cm (60 in)
Height (with 1,335 kN/150 ton)(suppressor & 200 clamp): 238 cm (94 in)
Hydraulic hose length (standard): 46 meters (150 ft)
Hydraulic hose weight: 680 kg (1,500 lbs)
Originally BSP designed and developed the DX hydraulic hammer range to meet the technical and equipment requirements of contractors engaged in installing equipment and maintaining the UK’s rail network. It was specifically developed to drive steel piles to support electrification staunchions, gantries and other railway projects requiring foundation piling. It has been designed as an attachment for mounting on road/rail or tracked excavators with an operating weight of around 32t or greater.
Technical Specs (DX30 model)
Overall length: 4300 mm
Hammer width: 500
Hammer mass: 5500 kg
Crane Suspended Vibro Hammer (SVR) and Excavator Mounted Vibro Hammer (OVR) types of vibratory pile drivers are designed to drive and extract all types of piles including sheet, tube (casing), timber and H-beam, also I-beam, Z-beam and steel plates. SVR type of vibratory pile drivers are recommended in projects requiring a high driving or extracting force. SVR type pile hammers are powered by OMS Hydraulic Power Packs, all of which have remote control and touch screen control panels. These controls are used to adjust the vibrator to suit varying ground conditions.
Technical Specs (SVR 50 NF model)
Eccentric Moment: 50.2 kgm
Centrifugal Force: 1409 kN
Power: 368 kW
Total Weight w/o Clamp: 6150 kg
Length: 3000 mm
Height: 1971 mm
Width: 388 mm
MKT continues to be the leader in lifetime value and total cost performance with each of its Vibratory Pile Driver/Extractor systems. From the lightweight V-1 to the extra heavy-duty V-52 (201 tons of driving force), each MKT System provides outstanding driving and extracting performance for the many foundation construction scenarios that call for nonbearing piling. We offer the best combination of hydraulic horsepower, frequency and total weight.
Driving Force: 53 tons (472kN)
Frequency: 1700 CPM
Eccentric Movement: 1300 in-lbs (1500 kg-cm)
Amplitude: 1 in (25.4 mm)
Clamping Force: 62 tons (550 kN)
Maximum Line Pull: 30 tons (267 kN)
Height: 75 in (1905 mm)
Throat Width: 13 in (330 mm)
Shipping Width: 85 in (2159 mm)
Weight w/ Standard Clamp: 6200 lbs (2813 kg)
Hose Bundle Length: 100 ft (30 m)
Hose Bundle Width: 830 lbs (378 kg)
Berminghammer direct-drive diesel impact hammers represent some of the most rugged and comprehensively field-tested pile driving equipment in the world. Combining the extensive contracting and manufacturing experience of Berminghammer’s world class team of designers, engineers and field personnel has resulted in the most efficient, versatile and reliable pile driving hammers in the world. With innovative features such as on-board energy monitoring, clean combustion, free-standing operation, remote throttle and the ability to use environmentally friendly bio-fuels and oils, Berminghammer hammers continue to redefine industry standards.
Rated Energy: 202,900 ft-lbs
Kinetic (Impact) Energy: 130,000 ft-lbs
Stroke at Rated Energy: 11.5 ft
Stroke Range: 4.5 – 11.5 ft
Blow Per Minute at Rated Energy: 35 min-1
Range of Blow-Rates: 56-35 min-1
Weight of Bare Hammer: 37,000 lbs
Hammer w/ Typical Box Lead Guides: 37,650 lbs
Weight of Typical Direct Drive Housing: 2,600 lbs
Total Typical Operating Weight: 40,250 lbs
Since 1980, HPSI has been designing and manufacturing the highest quality, most dependable, and longest-lasting vibratory hammers and hydraulic systems on the market. The HPSI Model 500 has proven itself to be the gold standard in the industry when it comes to delivering peak-performance at the pile without compromising on quality or reliability. The HPSI Model 500 is adaptable to any type of pile (pipe pile, steel sheet pile, h-pile, king pile, concrete piles, etc.) using a variety of specialized clamp attachments.
Eccentric Moment: 5,000 in. lbs.
Dynamic Force: 182 tons
Frequency: 1600 VPM (maintained under load)
Amplitude: 1.12 in
Pile Clamp Force: 200 tons
Maximum Line Pull: 75 tons
Suspended Weight: 22,500 lbs
Length: 102 in
Width: 14 in
Height: 102 in
Our range of vibrodriver H/HD with standard frequency and fixed eccentric moment. This robust range adapts to applications needing to drive sheet piles and casings with total weights up to 150 tons which makes it the largest range of “Heavy Duty” Vibrodrivers in the world.
Technical Specs (50 HD model):
Eccentric Moment: 50 m.kg
Hydraulic Power: 304 kW / 413 HP
Oil Flow: 507 L/min
Max Frequency: 25 Hz / 1500 rpm
Max Centrifugal Force: 1258 kN
Max Line Pull Capacity: 625 kN
Vibrating Weight Without Clamp: 3060 kg
Total Weight Without Clamp: 5650 kg
Max Amplitude: 32.7 mm
Length: 2.500 m
Max Width: 0.910 m
Centre Width: 0.330 m
Height Without Clamp: 2.197 m