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name: geotechnical-engineering version: "1.0.0" updated: 2026-02-26 category: engineering/marine-offshore description: | Domain expertise for offshore geotechnical analysis planning — soil classification, foundation design method selection, pile/anchor capacity, on-bottom stability, and scour prediction. tags: [geotechnical, soil, foundation, pile, anchor, scour, offshore] platforms: [linux, macos, windows] invocation: geotechnical-engineering depends_on: [] requires: [] see_also:

• mooring-analysis
• structural-analysis
• marine-offshore-engineering

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Geotechnical Engineering Skill

Offshore geotechnical analysis domain expertise for planning soil investigations, selecting foundation design methods, and sizing geotechnical elements (piles, anchors, mudmats, scour protection).

When to Use This Skill

• Planning a geotechnical analysis campaign
• Selecting bearing capacity or pile capacity methods
• Choosing anchor type for given soil and loading conditions
• Reviewing soil parameter derivation from CPT or borehole data
• Mapping standards coverage for geotechnical calculations

Soil Classification Systems

USCS (Unified Soil Classification System)

| Symbol | Description | Typical su (kPa) | Typical φ' (°) | |--------|-------------|-------------------|-----------------| | CH | Fat clay | 20–200 | — | | CL | Lean clay | 10–100 | — | | ML | Silt | 5–50 | 25–30 | | SM | Silty sand | — | 28–34 | | SP | Poorly graded sand | — | 30–36 | | SW | Well graded sand | — | 33–40 | | GP | Poorly graded gravel | — | 35–42 |

Robertson CPT Classification (1990/2009)

| Zone | Ic Range | Soil Behaviour Type | |------|----------|---------------------| | 1 | — | Sensitive fine grained | | 2 | > 3.60 | Organic soils / peat | | 3 | 2.95–3.60 | Clays (clay to silty clay) | | 4 | 2.60–2.95 | Silt mixtures | | 5 | 2.05–2.60 | Sand mixtures | | 6 | 1.31–2.05 | Sands (clean to silty) | | 7 | < 1.31 | Gravelly sand to dense sand |

Method Selection Decision Tree

Bearing Capacity

Undrained (clay)?
  ├── Yes → Brinch Hansen general formula (DNV-RP-C212 Sec 5)
  │         Nc = 5.14 for strip, shape/depth/inclination factors
  └── No (sand) → Terzaghi/Meyerhof drained bearing capacity
                   Nq, Nγ from friction angle

Pile Capacity

Soil type?
  ├── Clay → Alpha method (API RP 2GEO Sec 6.4)
  │          f = α × su; α from su/σ'v ratio
  ├── Sand → Beta method (API RP 2GEO Sec 6.5)
  │          f = K × σ'v × tan(δ); K from Table 6.5.3-1
  └── Layered → Sum unit shaft resistance per layer

Anchor Type Selection

| Soil Type | Load Direction | Recommended Anchor | Standard | |-----------|---------------|-------------------|----------| | Soft clay | Catenary | Drag (Stevpris/Vryhof) | DNVGL-RP-E301 | | Soft clay | Vertical/taut | Suction caisson | DNV-RP-E303 | | Stiff clay | Catenary | Drag (high capacity) | DNVGL-RP-E301 | | Sand | Catenary | Drag anchor | DNVGL-RP-E301 | | Any | Vertical (TLP) | Suction/driven pile | API RP 2GEO | | Deep water | Taut leg | Torpedo/SEPLA | project-specific |

Typical Parameter Ranges

| Parameter | Symbol | Soft Clay | Stiff Clay | Sand | |-----------|--------|-----------|------------|------| | Undrained shear strength | su | 5–25 kPa | 50–250 kPa | — | | Friction angle | φ' | — | — | 28–40° | | Submerged unit weight | γ' | 4–7 kN/m³ | 7–10 kN/m³ | 8–11 kN/m³ | | OCR | OCR | 1–3 | 3–20 | 1–5 | | CPT cone factor | Nkt | 10–18 | 15–25 | — | | su/σ'v (NC clay) | — | 0.20–0.30 | — | — |

Standard Reference Map

| Standard | Key Sections | Topic | |----------|-------------|-------| | API RP 2GEO | Sec 6 (piles), Sec 8 (foundations) | Pile + foundation design | | DNV-RP-C212 | Sec 5 (bearing), Sec 6 (piles) | Soil mechanics | | DNV-RP-E303 | Sec 4–7 | Suction anchor capacity | | DNVGL-RP-E301 | Sec 3–5 | Drag/fluke anchor design | | DNV-RP-F109 | Sec 3 | Pipeline on-bottom stability | | DNV-RP-F107 | Sec 5 | Scour assessment | | ISO 19901-4 | Sec 7–10 | Foundation design | | API RP 2SK | Sec 6 | Mooring anchor requirements |

Module Import Paths

from digitalmodel.geotechnical.soil_models import SoilProfile, SoilLayer
from digitalmodel.geotechnical.piles import PileCapacityAnalysis
from digitalmodel.geotechnical.foundations import ShallowFoundation
from digitalmodel.geotechnical.anchors import AnchorCapacity
from digitalmodel.geotechnical.on_bottom_stability import OnBottomStability
from digitalmodel.geotechnical.scour import ScourPrediction

Related Skills

• mooring-analysis — mooring system design consuming anchor capacity
• structural-analysis — structural loads feeding foundation design
• marine-offshore-engineering — general offshore engineering context

Version History

| Version | Date | Changes | |---------|------|---------| | 1.0.0 | 2026-02-26 | Initial skill — method selection, parameter ranges, standards map |