SPT Result Interpretation 4

[Llessur]

Hi,

I have been given the task of writing an interpretive report on some borehole data from a potential (large) site but being fairly new at this I am not sure of the correct procedure to undertake.

The borehole logs show the SPT results for every few meters through various strata down the borehole and the corresponding N values.

However I have approx 20 boreholes, each through 5 different lithologies with up to 15 SPTs done throughout each lithology and I am a little confused as to how to start working through this large amount of data in order to produce a good report.

Do I need to produce a graph of N value/depth for each bed encountered in each borehole? If so, can I somehow then 'merge' all of these graphs for each borehole to give an idea of the general strength of each lithology over the entire area?

Any help you could give me which would enable me to interpret these data would be much appreciated.

 

[coneboy]

To Llessure

I agree that a good starting point would be to put some cross sections togeather to see if you have horizontal continuity. If the same soil zones have a similar SPT value across the site then your job will be easier, other wise it might be wise to break the site down into sections.
I think a spread sheet would work nicely for looking at SPT values in this type of situation.

As you can see from the wide variety of topics in this site there are numerous geotechnical parameters which you will need to consider when you give your final design recommendations.

Coneboy

 

[Ron]

I agree with coneboy...do a subsurface profile to gain and present info on vertical stratigraphy in horizontal reference. For large amounts of data, do this in a couple of different directions. With computer spreadsheet graphing capability, this can be conveniently shown, but most Geotech. Engrs. prefer to do this step manually for a "feel" of the the profile.

Yes, you need to present a graph of "N" vs. depth as well as other info. This is called a boring log.

Based on your question and admission of lack of experience, this seems like quite a large job for you to be starting on. While you appear to be diligent in your pursuit, there is more to this than just graphing and presenting data. Your experience level does not allow appropriate interpretation of these data and the result can be disastrous. Interpretation of data to the extent you require is beyond the scope and intent of these forums.

I suggest for this task you enlist the help and mentoring of an experienced Geotechnical Engineer on a local basis.

 

[Llessur]

Thanks Ron & Coneboy,

Sorry, didn't want to scare anyone - luckily it's not real data (well, actually it's from a project that was completed years ago) it's something that I took on as part of my training to keep me busy over the weekend!

The interpretation of the data is not so much of a problem - as I have to reseach this as part of my training.

However, I cannot find any reference material (except for BS5930) which gives any instruction as to the proper format and layout which should be applied to an interpretive report.

I am a little confused as to exactly how much data should be graphically presented in the report (i.e. results from each borehole or can I just present data for the site as a whole, or both?).

I do not want to include too many graphs etc but also do not want to include too few.

Are there any rules which I should follow regarding the presentation of the report?

Cheers.

 

[TAC]

In geotechnical reports its important to include a boring log for each boring. As the report gets passed along to whomever is relying on it for various portions of the design (or future designs), a good record of the soil profile (i.e. the complete logs) is passed along with it. If I were using your report, I'd want to see the logs so that I can relate the specific soil data to your summary and recommendations.

You'll also definitely want to summarize the soil profile over the entire site or over portions of the site, as appropriate. The amount of additional graphs, charts, and tables you include in addition to individual borings logs will vary depending on the complexity of the site, the size of the project and the needs of the client. Generally, only include what is essential to make your points clear. Don't "stuff" a report just to make it look more impressive. Since you are just learning. I would recommend reading a few reports. Most companies tend to follow thier own general format for reports and then customize them for specific projects. As you read through them, you'll get a better feel for what your report should contain.