No. of Blows per sq. ft 1

• Feb 4, 2011

• #2

cvg

Civil/Environmental

Dec 16, 1999

6,868

US

you can find all of them when you call the geotech

 

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• Feb 4, 2011

• #3

Ron

Structural

Sep 24, 1999

16,336

US

The number of "blows" is typically related to the Standard Penetration Test (SPT). The parameter is not "blows per square foot", but just "blows". It refers to the number of blows required to drive a split barrel sampler a total of 12 inches, in 2-six-inch increments.

 

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• Feb 4, 2011

• #4

HSIII

Structural

Nov 23, 2010

86

US

I've never heard of "blows per sq. ft." I've heard of number of "blows" when it comes to borings for SPT, and also for deep dynamic compaction requirements.

Maybe a geotech would know better.

 

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• Feb 9, 2011

• #5

csd72

Structural

May 4, 2006

4,574

GB

sach4u1,

You need to get someone involved who knows what they are doing.

There is much more involved than just a simple conversion.

 

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• Mar 23, 2011

• #6

kieran1

Structural

Feb 27, 2002

178

GB

Is this a plate test you are refering to? You would normally use plate tests to determine CBR

Kieran

 

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• Apr 14, 2011

• #7

LiloSA

Structural

Feb 21, 2011

13

ZA

Also sounds to me like a plate load test - used to determine the compressibility and sometimes the bearing capacity of soil.

I stand to be corrected but to find undrained shear strength of cohesive soils you can use the triaxial compression test.

 

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• Apr 26, 2011

• #8

Deacy

Civil/Environmental

Jan 27, 2005

8

IE

If sach4u1 is getting the number of blows from a drilling log they could be blows recorded from a number of different methods (bs1377 part 9 gives details of CPT, SPT and DP tests). There are significant limitations on the intrepretation as outlined in Clayton, CRI, The standard penetration test: Methods and use CIRIA 143 LONDON 1995.Correlation between dynamic probing results and soil properties are being developedby Butcher et et al and Tonks et al in the UK.

 

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• Apr 26, 2011

1
• #9

BigH

Geotechnical

Dec 1, 2002

6,012

TJ

There are significant limitations in almost everything we do - which is why we keep trying to plug first order data into 5th order theoretical equations and keep wondering why it doesn't fit that well . . . it is obvious that the original poster (who, by the way, doesn't seem that interested in the responses) it talking about the SPT test. And yes, there are correlations - very rough unless a specific firm has correlated the N value to a particular location's soil types - that can estimate the undrained shear strength. Always with a grain or two of salt. While the rough correlations do depend to a degree on the degree of plasticity of the clayey material - this is found in most text books 0-2 (up to 12.5 kPa); 2-4 (12.5 to 25 kPa); 4-8 (25 to 50 kPa); 8-15 (50 to 100 kPa); 15-30 (100 to 200 kPa); > 30 (> 200 kPa). Approximate but perhaps that is all that's required for a green light / red light situation.

 

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