Geotechnical Engineering Expert

---
name: geotechnical-engineering-expert
version: 1.0.0
description: Expert-level geotechnical engineering covering soil classification, shear strength, consolidation, foundation design, slope stability, and retaining structures.
author: luo-kai
tags: [geotechnical, soil mechanics, foundations, slope stability, consolidation, retaining walls]
---

# Geotechnical Engineering Expert

## Before Starting
1. Foundation design or slope stability?
2. Shallow or deep foundation?
3. Sand or clay soil behavior?

## Core Expertise Areas

### Soil Classification
USCS: unified soil classification system, grain size and plasticity-based.
Grain size: gravel, sand, silt, clay based on particle size distribution.
Atterberg limits: liquid limit, plastic limit, plasticity index for fine soils.
Relative density: measure of sand compactness, Dr = e_max minus e over e_max minus e_min.
Compaction: Proctor test determines optimal moisture content for maximum dry density.

### Shear Strength
Mohr-Coulomb: tau_f = c plus sigma prime tan phi, cohesion plus friction.
Drained vs undrained: sand drains fast, clay drains slow under load.
Effective stress: sigma prime = sigma minus u, pore pressure reduces effective stress.
Triaxial test: measure shear strength at different confining pressures.
SPT and CPT: in-situ tests correlate to strength and stiffness parameters.

### Consolidation
Primary consolidation: volume change from pore pressure dissipation in clay.
Terzaghi theory: cv dU over dz2 = dU over dt, diffusion of excess pore pressure.
Settlement calculation: delta = Cc times H over 1 plus e0 times log sigma_f over sigma_0.
Time rate: T_v = cv times t over H2, use time factor chart.
Secondary compression: creep settlement after primary consolidation complete.

### Foundation Design
Bearing capacity: Terzaghi and Meyerhof equations for shallow foundations.
Net bearing pressure: gross minus overburden pressure.
Pile capacity: end bearing plus skin friction, static and dynamic methods.
Group effects: pile group efficiency, settlement of pile groups.
Mat foundation: uniform pressure distribution, used on weak or variable soils.

## Best Practices
- Always conduct adequate site investigation before foundation design
- Use conservative soil parameters given natural variability
- Check both bearing capacity and settlement for shallow foundations
- Consider groundwater effects on effective stress and stability

## Common Pitfalls
| Pitfall | Fix |
|---|---|
| Ignoring differential settlement | Check settlement variation across structure footprint |
| Wrong drainage condition for clay | Use undrained strength for short term, drained for long term |
| Underestimating secondary compression | Account for creep in organic soils and soft clays |
| Missing groundwater in slope stability | Pore pressure dramatically reduces factor of safety |

## Related Skills
- structural-engineering-expert
- hydraulics-expert
- geology-expert