Before you Begin! – Crane Operator meeting
Before driving the first pile it is very important for the hammer operator and the crane operator to have a meeting. During this meeting the hammer operator will inform the crane operator of the operating procedure of how to drive the pile. This meeting is absolutely essential for a successful pile driving operation. Below are the steps the crane operator needs to know:
Pile driving Process
Step 1:
Lift pile into position
Step 2:
Pick up hammer and close clamps onto the pile
Step 3:
Crane operator should hold about 80% of the weight of the hammer and pile while less than 20% of the pile and hammer weight is on the soil. Only allow the pile to enter the soil about 10cm max.
Step 3:
"Bump" the machine. Turn the Power Unit up to at least 1500 RPM, then turn the vibro on for about 1 second. Basically turn it on and off. The pile should sink into the ground quickly.
Step 4: Crane operator slowly lets off some of the weight of the pile while the vibratory hammer operator continues to "bump" the vibro for 1-2 second blasts. It's important that the Crane operator understand he is not to let more than 80% of the weight of the hammer and pile onto the soil during this time.
Step 5: Continue bumping for longer periods of time, 2-3 seconds, 4-5 seconds. Make sure the hammer is relatively straight but do not worry about it being perfectly accurate at this time. The Crane operator at this time should know that his goal is to keep the hammer as straight as he can but not perfect.
Step 6: Continue "bumping" for longer period of time until the pile is about 1/3 into the ground.
Step 7: Once the pile is about 1/3 into the ground for best results the vibratory hammer should not be shut off again until the pile is to grade. Now that the pile is 1/3rd down the soil around the pile will act like a template to hold the pile, however the pile at this point is likely not going straight down into the ground. Now it is time for the Crane operator to pull up on the pile and extract the pile 3cm to max 10cm while the hammer is under vibration.
Step 8: Once the pile has come up out of the ground about 3-10cm, because of gravity, the pile will want to start going down straight, this is the time the Crane operator can make some final adjustments. The crane operator should know that as he lets off the weight of the hammer and pile into the soil his boom could "unflex" and he may need to "boom back" to compensate for this.
Step 9: The crane operator can slowly start releasing more and more weight off of the hammer and pile. A ground man can measure the accuracy of the pile when it's still under vibration. If the soil is very soft then the Crane operator will need to "steer" the pile into the ground slowly. if the soil is very hard he can let off on the crane and allow the hammer to freely drop.
Step 10: As the pile goes into the ground the vibratory hammer may need to increase speed, however it should be known that increasing speed isn't always the best answer. A good vibratory hammer operator can feel the ground shake and find the "resonance" frequency of the pile and stay within that frequency.
Electric vs Hydraulic
Electric vibratory hammers can only cancel out at best 80% of the vibration of the hammer into the Crane. So with an electric hammer the crane operator will not want to pull back up on the pile after 1/3rd driven into the ground. If a crane operator has used an electric hammer before and never used a hydraulic hammer he will be scared and reluctant to go by the above steps. Only after he is convinced to do it one time will he see that his crane is in no danger at all.
Electric hammers cannot "free hang" vibrate very well because they will shake the crane violently. In some cases they can break the top of the crane boom completely off which is very dangerous. Hydraulic APE hammers are very gentle on the crane. One way to show the operator that the hammer is safe use is to do a free hang test. The crane operator will likely be concerned but after the hammer is turned on he will quickly be surprised and in shock of how little vibration he feels in the crane. Just make sure the turn the hammer up to over 1,000 VPM and do not do a lot of starting and stopping if you do this type of test.