GeoStructPy
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Disclaimer: This tool is intended for use by the APEC Consultancy team for preliminary geotechnical calculations only. The developers assume no liability for design decisions made based on the output of this application. All results must be verified by a qualified geotechnical or structural engineer before use in any project.

SPT & UCS Graph Maker

Generate professional SPT N-value, corrected N60, and UCS vs Depth charts for geotechnical reports. Enter raw SPT N-values per borehole — all three charts are generated automatically.

Correlations used: N60 = N × (Er/60), where Er = 72% (safety hammer)  |  UCS ≈ 12.5 × N60 (kPa)

QA rule: The chart panels show correlated UCS by default. If a measured UCS test result is available for any sample, supply it via the Borehole Log Digitizer (the ucs field) and the stronger measured value will take precedence over the SPT correlation in downstream calculators (bored pile α-method, slope stability cohesion). Rely on correlations only when no laboratory UCS is provided.

Accepts borehole log JSON files (same format as Borehole Log exports). Select multiple files to overlay boreholes.

References & Methodology

  1. Das, B.M. & Sivakugan, N. (2019). Principles of Foundation Engineering, 9th Edition, SI. Cengage Learning. Ch. 3 — Natural Soil Deposits and Subsoil Exploration: §3.13 Exploratory borings; §3.15 Split-spoon sampling and the standard penetration test (energy correction, N60, overburden correction); §3.21 Cone penetration test; §3.27 Preparation of boring logs.
  2. ASTM D1586 / D1586M-18. Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils.
  3. ASTM D2166 / D2166M-16. Standard Test Method for Unconfined Compressive Strength of Cohesive Soil.
  4. Skempton, A.W. (1986). Standard penetration test procedures and the effects in sands of overburden pressure, relative density, particle size, ageing and overconsolidation. Géotechnique, 36(3), 425–447.
  5. Stroud, M.A. (1974). The standard penetration test in insensitive clays and soft rocks. Proc. Eur. Symp. Penetration Testing, Stockholm, 2.2, 367–375.
  6. Terzaghi, K. & Peck, R.B. (1967). Soil Mechanics in Engineering Practice (2nd ed.) — consistency-N table for clays. Wiley.
  7. Schmertmann, J.H. (1970). Static cone to compute static settlement over sand. J. Soil Mech. Found. Div., ASCE, 96(SM3).
  8. Peck, R.B., Hanson, W.E. & Thornburn, T.H. (1974). Foundation Engineering (2nd ed.) — SPT-φ correlation for sands.