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NSPT Correction

Use this tool to calculate and visualize NSPT correction.

About NSPT Correction

N-SPT values observed during testing are not utilized directly in the assessment of soil properties. These values need to be corrected to account for hammer efficiency,borehole diameter, sampling method, rod length and the overburden pressure. Current tool sets the rules to allow the calculations for the correct SPT numbers, \([N]_{60}\)and \([N_1]_{60}\). You can activate the tool and then go back to project page to plot corrected SPT numbers with depth.

The corrected number N60is calculated as follows:

Figure: Equipment used to perform the SPT

\(N_{60} = \text{CER} \cdot \text{CRL} \cdot \text{CS} \cdot \text{CB} \cdot \)measured N

The corrected number\([N_1]_{60}\)is calculated as follows:

\([N_1]_{60} = C_N - N_{60}\)

Where:

\(C_{ER}\)= actual energy ration (compared to 60%) = ER/60

\(C_{RL}\)= correction to account for length of rod

\(C_S\) = correction due to liner used

\(C_B\) = correction due to borehole diameter

\(C_N\) = overburden pressure correction factor

Overburden pressure correction factor, CNmethods are defined below:

1. Peck, Hanson and Thornburn [1974]

\(C_{N} = 0.77 \cdot \log \left( \frac{20}{\sigma''_{v0} (\text{TSF})} \right)\)

2. Seed [1976]

\(C_{N} = 1 - 0.25 \cdot \log \sigma''_{v0} (\text{TSF})\)

3.Liao & Whitman (1986)

\(C_{N} = \sqrt {\frac{1}{\sigma''_{v0}(TSF \text{ or } kg/\text{cm}^3)}} \)

4. Skempton [1986]

\(C_{N} = \frac{2}{1+\sigma''_{v0}(TSF)} \)

 

 

Table 1: Summary of typical rod energy ratios

 

CountryHammer TypeHammer ReleaseEm(%)CER
JapanDonutFree fall781.30
DonutRope and pulley671.12
United StatesSafetyRope and pulley601.00
DonutRope and pulley450.75
ArgentinaDonutRope and pulley450.75
DonutFree fall601.00
ChinaDonutRope and pulley500.83
UAEAutomaticFree fall751.25

Table 2: Rod Length Correction, CRL

 

Rod LengthCR
(m)(ft)
3 - 410 - 130.75
4 - 613 - 200.85
6 - 1020 - 300.95
> 10> 301.00

 

Table 3: Sampling Method Correction, Cs

MethodCs
Sampler without liner(most common)1.2
Standard Sampler1.0
With liner for loose sand0.9
With liner for dense sand and clay0.8

Table 4: Correction for Borehole Diameter, CB

DiameterCB
(mm)(in)
65 - 1152.4 - 4.71
15061.05
20081.15

 

References

  1. Geotechnical investigation and testing – Field testing – Part 3: Standard penetration test (ISO 22476-3:2005).
  2. ASTM D 1586-99 Standard Test Method for Penetration Test and Split-Barrel Sampling of Soils.
  3. Kovacs, W. D. Salomone, L. A., and Yokal, F. Y., “Comparison of Energy Measurements in the Standard Penetration Test Using the Cathead and Rope Method,” National Bureau of Standards Report to the US Nuclear Regulatory Commision, 1983.
  4. Schmertman, J. H., “Use the SPT to Measure Dynamic Soil Properties ?-Yes, But..!”, Dynamic Geotechnical Testing, ASTM STP 654, American Society for Testing and Materials, 1978.
  5. Seed, H. B., Tokimastu, K., Harder, L. F. and Chung, R. F., “Influence of SPT Procedures in Soil Liquefaction Resistance Evaluations,” Journal of Geotechnical Engineering, Vol. 111, No. 12, December 1985.
  6. Skempton, A. W., “Standard Penetration Test Procedures and the Effects in Sands of Overburden Pressure, Relative Density, Particle Size, Ageing and Over Consolidation”, Geotechnique 36: 3, September, 1986.
Activated ags files
# Project Ags Name Efficiency Input CS Method CN Method Correct NSPT Maximum N Actions
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Enter Data manually

Drag and drop Excel file here or click to upload
SN Depth N SPTfield Bulk Density Total Normal Stress Pore Water Pressure Effective Normal Stress CER CR CS CB CN N60 (N1)60
m - kN/m3 kN/m2 kN/m2 kN/m2 - - - - - - -