Comparison of Diesel and Hydraulics Hammer PDF
Comparison of Diesel and Hydraulics Hammer PDF
Comparison of Diesel and Hydraulics Hammer PDF
1. Operational Criteria
A. Safety
Equipment manufacturers of all types of hammers have
addressed the issue of safety. It is difficult to give an advantage
to either diesel hammers or hydraulic hammers in the area of
B. Reliability
The simplicity of operation of a diesel hammer gives it an
advantage over hydraulic hammers in the area of reliability.
During operation, a single-acting diesel pile hammer can have as
few as five (5) moving parts, most of which can be serviced or
replaced in a matter of minutes. As a self-contained, selfpowered unit, a diesel hammer requires no external power
source, and thus avoids potential problems related to a hydraulic
power unit engine, pump, and hoses. While problems with
hydraulic hammers generally necessitate repairs by a qualified
service technician or manufacturer representative, problems with
diesel hammers can most often be diagnosed and solved by the
contractors own site personnel.
C. Familiarity
It would be very difficult to find a piling contractor in the
world that does not have experience with diesel pile hammers.
This evaluation criterion, while it may seem trivial, can be a
major factor in a contractors selection of pile driving
equipment. Contractors in the United States seem particularly
loyal to diesel hammers.
D. Operating weight
The operating weight of a pile hammer can influence the
selection of the crane or piling-rig, which can be the single
largest equipment cost for a contractor. Typically, a diesel
hammer will deliver higher impact energy than a hydraulic
hammer at an equivalent or lesser operating weight. A more
thorough comparison of two competing technologies is shown
later in this paper.
It should be noted that the weight of the hydraulic power
unit associated with the operation of a hydraulic hammer is often
forgotten. Hydraulic power units are generally large, and while
these units can sometimes be mounted on the back of the piling
rig, many times they cannot, creating an added complication to
the mobility of the piling operation. Dedicated hydraulic piling
rigs can overcome this problem by incorporating the necessary
hydraulic flow to run the hammer into the design of the base-unit
itself. However, these dedicated rigs are expensive and as such
have very little penetration into the North America.
In the area of operating weight diesels have the advantage.
2. Controllability
One of the main misconceptions about diesel hammers is
that they are not controllable. This is partly due to the fact that
the performance (impact energy) of a diesel hammer depends on
the soil resistance, and the mass and stiffness of the pile
foundation being driven. Because the capacity of a pile
foundation depends on the performance of the pile-driving
hammer, governments and consulting engineers have shown a
recent preference for hydraulic hammers, since the impact
energy or stroke of a hydraulic hammer is relatively
independent of the pile resistance. The interdependency of the
pile capacity and the hammer performance can add an extra level
of complexity and uncertainty to the pile installation process.
Traditional diesel hammers are equipped with discrete
energy settings. These settings control the amount of fuel
delivered to the hammer, and thus the resulting stroke and
impact energy. More modern diesel hammers are equipped with
an infinitely adjustable fuel delivery or throttle mechanism,
which allows the operator better control over the hammer
performance, up to the maximum performance permitted by
the pile resistance. Many governments and consultants are not
yet familiar with these features.
While these newer
developments have increased the controllability of diesel
hammers, the advantage of controllability must still be given to a
properly functioning hydraulic hammer.
3. Verifiability
In pile driving, QA and QC typically consist of pile
installation records that log the number of blows per unit of
penetration, and the final tip elevation for each pile. Very often,
however, the performance of the pile hammer is not logged on
the pile installation record, or more disturbing, the pile hammer
may appear to be operating at the desired impact energy, while
in fact it is not. This can lead to a potentially dangerous
situation, whereby piles are believed to have more capacity than
they actually do.
Historically, the most common problem with diesel
hammers has been the phenomenon of pre-combustion or preignition. This problem still exists for diesel hammers that
operate using a fuel delivery system known as impactatomization.
Unfortunately, a diesel hammer that is
experiencing pre-combustion may not show any visible signs of
a problem. The hammer may still run with the desired stroke,
yet the impact velocity may be reduced, causing the blow-count
to increase and creating the artificial impression of pile capacity.
A similar problem can occur with an improperly adjusted
hydraulic hammer. If the hydraulic cylinders that lift the ram are
activated prematurely, then the actual impact velocity of the ram
can be reduced. Again, a dangerous over-estimation of pile
capacity will result.
Diesel hammers that operate using a more modernized fuel
injection system do not experience pre-ignition. Verification of
the performance of a diesel pile hammer is possible through the
use of an instrumentation port that allows for monitoring of the
impact velocity of the ram using magnetic proximity switches.
Testing has shown that fuel injected hammers do not experience
a loss in impact velocity as the hammer temperature increases.
This innovation has lead to further development of the velocity
A. Efficiency
B. Effectiveness
Hydraulic
Hammer
26,000
Diesel
Hammer
53,000
25,000
25,000
6,600
15.6
4,630
18.6
25,000
34,000
15.6
21.7
14,000
11,000
1.8
3.1
C. COST
Cost is probably the single most important variable in a
contractors evaluation of pile-driving hammers. In this respect,
the American Contractors loyalty to the diesel hammer is
explained. For a given impact energy, efficiency, effectiveness,
etc., the cost of a diesel hammer can be estimated at 50-75% of
an equivalent hydraulic hammer or even less in the case of
Chinese made diesel hammers. Capital cost of the equipment
combined with much lower fuel costs make diesel hammers the
clear-cut winner on the basis of economy.
As diesel hammers continue to catch-up to hydraulic
hammers in the areas of controllability and verifiability, their
lower cost will ensure their continued presence in the world piledriving market.
5. Environmental Concerns
Recently, diesel hammers have fallen out of favor in some
countries and some urban areas due to their environmental
impact mostly, noise, vibration, and black smoke. In the
United Kingdom, for instance, it has been nearly 10-years since
diesel hammers have been used. While no formal legislation
prohibits the use of diesel hammers in the UK, contractors have
avoided their use in an effort to avoid complaints, and likely to
appear more modernized. Many observers of the global
foundation equipment market would classify the diesel pile
hammer as nearing the end of its product life-cycle.
6. Optimal Pile-Driving
This is an area of pile driving that is currently under
development. By combining the data from an on-board hammer
energy monitor and the data from a conventional PDA testing
system, together with a system for controlling the energy of a
hammer (such as the remote throttle), it is theoretically possible
to construct a control-system that is designed to operate a
hammer at the most effective energy setting, or perhaps a target
energy. The potential for an intelligent pile-driving control
system is very real. So far the only hindrance has been the
general lack of sophistication among hammer manufacturers,
combined with a separation between the manufacturers and
design engineers and owners. The recent increased demand for
QA and QC for pile driving, has paved the way for these types
of intelligent systems. These systems are coming, and with
them the resurgence of the diesel hammer; even in European and
other markets where they have fallen out of favor.