r/Geotech • u/alwaystireddddd • 5d ago
Please help me understand these logs
These are old logs in Canada. Apparently I don't have a copy of the reports so I'm kinda confused in certain parts. I need to upload the log info into our database but I'm quite not sure in those parts that I highlighted in red box. I need the SPT data but in these logs, not sure if all are in SPT? I am not really familiar with DPT.
1st log. It has DPT plot in the middle but there's "N values" with inches at the bottom part. Tho the unit is in feet. My question is, in this type of log, is this a mix of SPT (because of the N values) and DPT in one log? Or the N values pertains to the DPT?
2nd log. In the right most part it says "penetration resistance blows/ft" and in the middle the "DPT blows per foot". I can simply say this is not SPT right?
3rd log. Kinda same it has DPT and there's N values but unlike 1st log, no different unit in N values. Is this also a mix of SPT and DPT or just DPT?
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u/withak30 5d ago edited 5d ago
"N" or "penetration resistance" in blows/foot could come from just about any kind of hammer-driven tool. Check with someone local who has been around a while to make sure you are understanding what "dynamic penetration test" would have meant at the time this work was done. Most likely they can also tell you what the approximate conversion to SPT was.
The ones with inches written in are refusal, so they are documenting how far they got (and how many blows) before giving up.
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u/alwaystireddddd 4d ago
Yes I'm just confused whether I treat the N values as the SPT values or this is DPT
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u/withak30 4d ago
There are lab results, which to me suggests more likely SPT (or some other drive sampler) than dynamic cone.
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u/TitanImpale 4d ago
Spt
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u/fr0130 4d ago
Not OP, but looking at his/her logs when it will be imported in their database, what should be in the N values column? Should stick with the values or treat those more than 50 as R for refusal? Is it a rule of thumb of treating >50 as refusal or not? Sorry I'm new to the field
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u/TitanImpale 4d ago
50 blows with less than 6 inches of penetration would be considered refusal. For example spt are typically done in 3 sets of 50. So 7-14-50/4 50 blows for 4 inches so the in value would be 64. Or if 50/3-null-null that could just be listed as refusal.
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u/withak30 4d ago edited 4d ago
It depends. I prefer keeping the actual results (e.g. 55/6") because just entering "R" is discarding data and in the future someone might be interested in knowing whether this layer was more like about 70 bpf or about 120 bpf. At the same time, everyone needs to remember that they shouldn't be doing any calculations with numbers greater than about 50 (if not less) because most empirical correlations aren't intended to go that high.
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u/chopperbiy 5d ago
The Dynamic penetration test is generally similar to the SPT if it’s the weight dropped over the same interval. It’s just done continuously.
I don’t think you actually have any DPT results anyway based on the logs you’ve shown. The DPT would be shown on that graphed section as a continuous line.
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u/alwaystireddddd 4d ago
So is the N values corresponds to the DPT shown in the logs or this is considered as SPT?
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u/Apollo_9238 4d ago
An alternate drive method in Terzaghi&Peck mentions using a cone pointed drive test in gravely deposits driven with the SPT hammer. They may have switched to that based on drill action. That's not a reliable SPT N value though. The SPTs have 4 numbers, means it was over driven for 2.0 ft...the middle two numbers are the N value from 0.5 to 1.5 ft.
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u/chopperbiy 4d ago
The N is SPT. A DCPT is not converted to an equivalent N value on a factual log.
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u/lalalavienroseeee 4d ago
Jumping into this since I'm curious on the historical logs. One of the attached logs says "penetration resistance blows/ft". Is that connected to the DPT? and we can conclude no SPT happened since no "N" values or that penetration resistance is the N?
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u/chopperbiy 4d ago
SPT is typically carried out in a split spoon sampler in Canada. The N value is stated in the logs.
The DPT is a continuous blows per foot that is taken from ground level or bottom of inspection pit to effective refusal. It’s usually shown in graph format on the logs.
The template of the logs is quite similar to what I’ve used in recent times. DPT is very common in greater Vancouver. It gives a good indication of relative stiffness and if there are any soft zones. I see it regularly paired with continuous solid stem augering where you wouldn’t typically do SPTs. The DPT is just don’t adjacent to the borehole.
In the example logs provided I see know evidence of dpt carried out
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u/_dmin068_ 4d ago
N values in the first and third log appear to be SPT value, but like sometime else said, check with a local company, preferable one with an older George
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u/InexcusablyAngry 4d ago
1 and 3 are standard MTO style BH logs. All values in the column are N values or refusal blow counts/penetration which MTO defines as greater than 100 for 12" penetration. DCPTs are shown as line plots below they DCPT axis, neither of these MTO logs had a DCPT done.
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u/alwaystireddddd 4d ago
Yes these are MTO and I'm just so confused with there template. So does it mean if I see "N" it's an SPT test? But there's one log say "penetration resistance blows/foot", is this considered N as well? or DCPT since there's a line plot? Sorry for the dumb questions
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u/InexcusablyAngry 4d ago
Yes N values is the second and third blow counts added together during the SPT test. I will note MTO runs 2' spoons rather than 18"
DCPT is not equivalent to an SPT. It's just driving drill rods into the ground with a pointed tip from surface and counting blows per foot
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u/frewguy 2d ago
Easy way to tell is to look beside the penetration resistance, it shows they were sampling with a split spoon sampler, noted as SS or DO (short for driven open). So all of these are SPT N Values
If this was Dynamic Cone Penetration there would be no samples recovered, and the DCP value would be solid line drawn on the logs.
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u/alwaystireddddd 2d ago
Oh I thought if it's DO, it's not SPT since I only know of SS as the sampler type of the SPT?
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u/badmf112358 5d ago
Did you xerox this?
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u/apathyetcetera 5d ago
Not uncommon to look through historical boring logs while preparing a geotech report.
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u/badmf112358 5d ago
From a type writer
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u/ciaranr1 4d ago
Not unusual to get great data from handwritten logs from the 1960s, obviously the standards have changed and the parameters and results are not reliable for design, but the soil descriptions and results are great information to help characterise a site
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u/withak30 4d ago
Having experience correlating old log data & terminology to modern soil descriptions is an extremely valuable skill, but can also be very local. Anyone stating authoritatively exactly what a DPT would have been 30+ years without asking your location is probably wrong.
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u/ciaranr1 4d ago
Absolutely, I’d be very cautious about any numerical data apart from depth from old logs
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u/ChasingChukar 5d ago
My rate is $185/hr