Wave equation analysis

[rainandcm]

I struggled a lot on performing wave equation analysis. I read lots of material but still remain in confusion. I want to post some of my understanding and questions here and hope somebody can enlighten me. I'd really appreciate your help.

There are three types of analysis to be performed, and they all require different input and give different out put. They are Bearing Graph, Drivability, and Inspector's chart.

1. Bearing Graph: I think the actual insitu soil was not an input of the analysis (am I right?). The output gives a plot of capacity and blows/ft. However, it didn't include stroke. Stroke may change during driving. Shouldn't the capacity should be a function of both "stroke" and "blow counts"?

2. Drivability analysis: In-situ soil is needed in the input.The output will give "Stroke", "Blows", and "stress" as the output. If the stress is reaching the yielding stress, this means the hammer is too large. If I change to a smaller hammer, the stress might be okay, but blow counts may go 9999/ft, which doesn't work either. If an intermediate hammer can be found to output appropriate stress and blow counts, this means I need to use stronger pile? Is this understanding right?

3. Inspector's chart: This one seems making sense to me. An in-situ soil parameters were defined in the program. Seems like the "inspector's chart" basically does what "bearing graph" does -- for field engineer to quickly identify reached capacity based on observations. Then why need "Bearing Graph"?

I've been struggling on this subject for a long time now and finally decided to write them down. Can you help to explaine some?

Thank you.

 

[Retrograde]

If the stress is reaching the yielding stress, this means the hammer is too large.

Not necessarily. Using a larger hammer with a smaller drop should decrease the driving stresses.

 

[rainandcm]

There might be a situation where you have to have enough energy to get the pile in. If set the stroke too low, the blow counts may go very high. Can this situation happen?

 

[Retrograde]

Certainly for the same weight hammer decreasing the stroke will increase the blow count.

 

[Panars]

1. Bearing Graph: I think the actual insitu soil was not an input of the analysis (am I right?). The output gives a plot of capacity and blows/ft. However, it didn't include stroke. Stroke may change during driving. Shouldn't the capacity should be a function of both "stroke" and "blow counts"?

The bearing graph requires a pile resistance distribution, which can be developed from a soil profile. So in that sense the insitu soil is an input. For the bearing graph, you need to specify what percentage of the resistance comes from the tip and from side friction. You also need to specify how the distribution of side friction changes along the length of the pile. You can specify this directly, or determine from a static pile capacity analysis based on your soil profile. Some programs (GRLWEAP) can do this for you if you input the soil profile.
The output should include the stroke for a diesel hammer, as the stroke is dependent on the dynamic resistance. Maybe you didn't check the box to show stroke in the output. For a hydraulic hammer, the stroke is one of the inputs that the pile hammer operator can set.

2. Drivability analysis: In-situ soil is needed in the input.The output will give "Stroke", "Blows", and "stress" as the output. If the stress is reaching the yielding stress, this means the hammer is too large. If I change to a smaller hammer, the stress might be okay, but blow counts may go 9999/ft, which doesn't work either. If an intermediate hammer can be found to output appropriate stress and blow counts, this means I need to use stronger pile? Is this understanding right?

Correct.

3. Inspector's chart: This one seems making sense to me. An in-situ soil parameters were defined in the program. Seems like the "inspector's chart" basically does what "bearing graph" does -- for field engineer to quickly identify reached capacity based on observations. Then why need "Bearing Graph"?

The inspector's chart presents the blow count and stroke for a specified pile resistance (capacity). The bearing graph shows how the stroke and blow count vary with different pile resistances.