Geotechnical Engineering Toolkit

Professional Notice

This tool is for educational and preliminary analysis purposes only. All calculations are based on first principles engineering mechanics. Standards and regulations referenced may be subject to change. Final engineering designs must be verified by qualified professional engineers and comply with current local regulations and site-specific conditions.

Cation Exchange Capacity (CEC) from Lab Results

Enter exchangeable cations from lab report (AS 1289).

Calcium (Ca²⁺)

1850 mg/kg (ppm)

Magnesium (Mg²⁺)

620 mg/kg (ppm)

Potassium (K⁺)

210 mg/kg (ppm)

Sodium (Na⁺)

95 mg/kg (ppm)

Calculation Breakdown

Ca (meq/100g) 9.23

Mg (meq/100g) 5.10

K (meq/100g) 0.54

Na (meq/100g) 0.41

Total CEC (meq/100g) 15.28

Formula: CEC (meq/100g) = ppm / (Equivalent Weight * 10)
Equivalent Weights (g/eq): Ca=20.04, Mg=12.15, K=39.10, Na=22.99

Exchangeable Sodium Percentage (ESP)

Calculates soil dispersivity risk based on the ratio of Sodium to total CEC.

Exchangeable Na⁺ (meq/100g)

0.41 meq/100g

Value linked from CEC Calculation tab.

Total CEC (meq/100g)

15.28 meq/100g

Value linked from CEC Calculation tab.

ESP Result

Calculated ESP 2.68 %

Risk Classification Non-Dispersive

ESP > 15%: Highly Dispersive
ESP 6% - 15%: Potentially Dispersive
ESP < 6%: Non-Dispersive

Sodium Adsorption Ratio (SAR)

Calculates the dispersivity risk from pore water or leachate (from 1:5 extract).

Na⁺ Concentration

150 ppm (mg/L)

Ca²⁺ Concentration

20 ppm (mg/L)

Mg²⁺ Concentration

12 ppm (mg/L)

SAR Result

Calculated SAR 9.24

Note: SAR is unitless. Result must be plotted against Total Cation Concentration (TCC) to determine risk.

Soil Amelioration Rate

Select Amelioration Type:

Gypsum (for Dispersivity / Sodicity) Lime (for Acidity / pH)

Gypsum Requirement Inputs

Total CEC (meq/100g) 15.0

Initial ESP (%) 18.0

Target ESP (%) 5.0

Dry Bulk Density (t/m³) 1.6

Treatment Depth (m) 0.3

Gypsum Purity (%) 95

Calculation Result

Target Na⁺ Removal 1.95 meq/100g

Soil Mass to Treat 4800 t/ha

Calculated GR (pure) 8.04 t/ha

Adjusted Gypsum Rate 8.47 t/ha

Primary Consolidation Settlement (S_c)

Calculates 1D Primary Consolidation (Terzaghi) based on oedometer test data (AS 1289.6.6.1).

Layer Thickness (H₀) 5.0 m

Initial Void Ratio (e₀) 1.1

Compression Index (C_c) 0.45

Recompression Index (C_r) 0.08

Stress Conditions

Initial Stress (σ'₀) 70 kPa

Preconsolidation Stress (σ'_p) 100 kPa

Applied Load (Δσ) 150 kPa

Settlement Calculation

Initial Stress (σ'₀) 70.00 kPa

Final Stress (σ'_f) 220.00 kPa

Preconsolidation (σ'_p) 100.00 kPa

Soil State Overconsolidated (Case B)

Total Settlement (S_c) 0.3807 m

Case NC: σ'₀ ≈ σ'_p
Case OC-A: σ'_f ≤ σ'_p
Case OC-B: σ'₀ < σ'_p < σ'_f

Erosion Factor of Safety (FOS)

Compares hydraulic applied shear (Tractive Force) against the soil's critical shear resistance.

1. Hydraulic Applied Shear (τ_a)

Design Flow Depth (d) 0.30 m

Channel Slope (S) 0.005 m/m

2. Geotech Critical Shear (τ_c)

Emerson Class (AS 1289.3.8.3) 5 Class

Exchangeable Sodium (ESP) 2.7 %

ESP value linked from Soil Stability tab.

Factor of Safety Analysis

Applied Shear (τ_a) 14.72 Pa

Soil Classification Non-Dispersive

Critical Shear (τ_c) 2.00 Pa

Factor of Safety

0.14

CATASTROPHIC FAILURE. Channel will erode.

FOS = τ_c / τ_a
< 1.0: Fail | < 1.5: Marginal | ≥ 1.5: Pass