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# Equations for soil properties using STP N-values3

## Equations for soil properties using STP N-values

(OP)
I am trying to find equations for soil strength, soil compressibility, foundation bearing capacity, foundation settlement, and liquefaction potential using STP N-values.  I would be grateful for any information you have - even if you just have a reference to a good website or book containing these.

Thank You,

pmhawkes

### RE: Equations for soil properties using STP N-values

2
Hi,
There are some equations that have the relationship between SPT-N values and settlement.
(Meyerhof)
Se=4*q/N for B<=4 ft
Se=6*q/N*((B/(B+1))^2 for B>4 ft
q: intensity of applied load, kip/ft^2
B: width of footing, ft
Se: settlement, in

(Bowles)
Se=2.5*q/N for B<=4 ft
Se=4*q/N*((B/(B+1))^2 for B>4 ft

(Meyerhof) for shallow foundations
for sand and gravel
Se=q*(B)^0.5/(2*N)
for silty sand
Se=q*(B)^0.5/(N)
Se: settlement,in
q:intensity of the applied load (tons/ft^2)
B: width of foundation, in

I also have some relations about stress-strain modulus by SPT. I may send them if it is necessary for you.

### RE: Equations for soil properties using STP N-values

you can looking for information about correlations with SPT in the books:

-Virginia Polytechnich Institute and State University
The Charles E. Via, Jr.
Depatment of Civil and Environmental Engineering
Center for Geotechnical Practice and Research

1)Performance and Use of the Standard Penetration Test in Geotechnical Engineering Practice by
J. McGregor and J.M.Duncan

2)Shear Strength Correlations for Geotechnical Engineering by J.M. Duncan, R.C. Horz, T.L. Yang

-Manual of Estimating Soil Properties for Foundation Design
by Kulhawy and Mayne
Electric Power Research Institute, Palo Alto California

-Foundation Analysis and Design by J. Bowles
fifth edition

-Principles of Foundation Engineering by B. Das

### RE: Equations for soil properties using STP N-values

I would be certain that the fundamentals of soil mechanics are well understood before applying these equations.

The equations do not address soil expansion and hydrconsolidation, and zonal soil variations which are factors that cause most foundation distress.

### RE: Equations for soil properties using STP N-values

SPT N values can also be used to calculate the shaft friction on bored cast in-situ piles. General pracice is fs = 2-3N (kPa)

### RE: Equations for soil properties using STP N-values

Stroud and Butler (1975) in The Engineering Beahaviour of Glacial Materials - -The Midlands Soil Mechanics and Foundation Engineering Society - give correlations between SPT N and Cu and Mv for glacial tills, which are commonly used in the UK.

### RE: Equations for soil properties using STP N-values

For glacial deposits, we've found a reasonable approximation of allowable bearing capacity to be qa=N/3.

For all of the noted correlations, I would caution that most are very coarse.  Also, be aware of the difference between N-values using the older type manual hammers (safety hammer with cathead) and the newer autohammers.  Expect higher blow counts for a given soil strength with a manual hammer because those hammers are generally less efficient.  Most correlations were developed using manual hammer data.

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