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.

Slope Stability Parameters (Midas GTS NX Input)

Enter soil layer properties from borehole data. Computes derived parameters for Midas GTS NX Mohr-Coulomb material model: General, Porous, and Non-Linear tabs. Variable definitions and parameter ranges are aligned with Bowles (1996, 5e) Ch. 2 (§2-2/2-3 weight–volume, §2-8 K0 p. 39, §2-10 consolidation p. 56, §2-11 shear strength p. 90, §2-14 elastic properties p. 121), Das & Sivakugan (2019, 9th SI) Ch. 2, Mohr (1900), Coulomb (1776), and the Midas IT (2023) GTS NX User Manual.

QA notes on the column inputs (hover the i icons in the table headers below):
• c (cohesion, kPa): Provide a value only if a UCS / unconsolidated-undrained triaxial result is available. Otherwise leave 0 and let the SPT correlation drive c (Polish PN-59/B-03020). Bowles (1996, 5e) §2-11 (p. 90) classifies cohesion as the interparticle attraction component of shear strength, s = c + σtanφ.
• φ (friction angle, deg): Bowles (1996, 5e) §2-11.3 — depends on density / relative density and confining pressure for cohesionless soils. Use φ\' (effective) for drained CD tests; for cohesionless soils Bowles notes "saturated CU/U conditions are meaningless" because the sample drains during loading.
• E (stress–strain modulus, kPa): Bowles (1996, 5e) Table 2-8 (p. 148) gives ranges — very soft clay 2–15 MPa, soft 5–25, medium 15–50, hard 50–100, sandy clay 25–250; loose sand 10–25, dense 50–81; loose sand+gravel 50–150, dense 100–200; loess 15–60; shale 150–5000. Field values "depend on stress history, water content, density, and age of deposit."
• ν (Poisson's ratio): Bowles (1996, 5e) Table 2-7 (p. 145) — saturated clay 0.4–0.5, unsaturated clay 0.1–0.3, sandy clay 0.2–0.3, silt 0.3–0.35, sand/gravelly sand 0.1–1.0 (commonly used 0.3–0.4).
• γsat (saturated unit weight): Derived as (Gs + e)/(1 + e) · γw with e = Gs·w. Bowles (1996, 5e) §2-3 Eq. 2-11 derives the same expression from Ws = VsγwGs. If your moisture content is field-not-saturated, γsat in the report is theoretical, not measured.
• K0 (at-rest earth pressure): Bowles (1996, 5e) §2-8 Eq. 2-18a (p. 39): K0 = 1 − sinφ\' (simplified Jaky 1948). For sloping ground use Eq. 2-19, for OCR > 1 use Eq. 2-23: K0,OCR = K0,nc·OCRn.
• Porous tab (kx, ky, kz): Currently set to a constant 1×10−5 m/s default. Replace with project-specific permeability from falling-head / pumping tests when available.
• Dilatancy ψ = max(φ − 30°, 0): Bolton (1986) empirical relation — valid only for medium-dense to dense sands. For clays / loose sands set ψ = 0. Bowles (1996, 5e) §2-11 treats clays as non-dilative under undrained loading.
• Tensile strength: Set to 0 (soil cannot sustain tension; tension cut-off in Mohr-Coulomb).
• Interface reduction Rinter: Not auto-computed — for soil-structure interaction in Midas GTS NX use Rinter = 0.6–0.8 for sand/concrete, 0.5 for clay/concrete (Plaxis Material Models Manual).

Import from Borehole Log JSON

Paste JSON from Borehole Log Digitizer — soil parameters (φ, c, γ, E) are auto-derived from SPT N-values using Polish Code PN-59/B-03020 correlation tables.

References & Methodology

  1. Bowles, J.E. (1996). Foundation Analysis and Design, 5th Edition. McGraw-Hill. Ch. 2 — Geotechnical and Index Properties: §2-2 Basic relationships and definitions, §2-3 Major factors that affect the engineering properties of soils (Eq. 2-1 to Eq. 2-11 weight–volume); §2-8 In Situ Stresses and K0 Conditions, p. 39 (Eq. 2-17 K0 = σh/σv; Eq. 2-18a Jaky simplified K0 = 1 − sinφ\'; Eq. 2-19 sloping ground; Eq. 2-22 K0 from ν; Eq. 2-23 OCR adjustment); §2-10 Consolidation Principles, p. 56; §2-11 Shear Strength, p. 90 (Eq. 2-52 s = c + σtanφ; UU/CU/CD test conditions; §2-11.3 cohesionless soils); §2-14 Elastic Properties of Soil, p. 121 (Hooke's law; Table 2-7 Poisson's ratio ranges; Table 2-8 stress–strain modulus Es ranges).
  2. Das, B.M. & Sivakugan, N. (2019). Principles of Foundation Engineering, 9th Edition, SI. Cengage Learning. Ch. 2 — Geotechnical Properties of Soil: weight–volume relationships, shear strength parameters; Ch. 3 — Subsoil Exploration: §3.15 Split-spoon and SPT, §3.21 CPT, §3.27 Boring logs.
  3. Coulomb, C.A. (1776). Essai sur une application des règles de maximis et minimis à quelques problèmes de statique. Mém. Acad. Roy. Sci.
  4. Mohr, O. (1900). Welche Umstände bedingen die Elastizitätsgrenze und den Bruch eines Materials? Zeitschrift VDI, 44.
  5. PN-59/B-03020 (1959). Posadowienie bezpośrednie budowli — Obliczenia statyczne i projektowe (Polish Code — soil parameters from SPT-N tables).
  6. Bolton, M.D. (1986). The strength and dilatancy of sands. Géotechnique, 36(1), 65–78. (Source of ψ ≈ φ − 30° for dense sands.)
  7. Jaky, J. (1944). The coefficient of earth pressure at rest. J. Soc. Hungarian Architects and Engineers, 78(22), 355–358. (K0 = 1 − sinφ.)
  8. Schmertmann, J.H. (1970). Static cone to compute static settlement over sand. J. Soil Mech. Found. Div., ASCE, 96(SM3). (Es ≈ 500(N60+15) kPa.)
  9. Midas IT (2023). Midas GTS NX User Manual — Material Models: General, Porous, Non-Linear (Mohr-Coulomb).
  10. Plaxis (Bentley Systems, 2023). PLAXIS Material Models Manual — Interface Reduction Factor Rinter.
  11. ASTM D2166 / D2166M-16. Standard Test Method for Unconfined Compressive Strength of Cohesive Soil.
  12. ASTM D1586 / D1586M-18. Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils.