Expansive Subgrade Soil Classifier & Stabilization Sizer
Classify AASHTO soil groups ($A-1$ to $A-7-6$), calculate Group Index ($GI$), evaluate subgrade volumetric swelling potential, and determine required undercut depths, non-expansive capping layers, and lime/cement stabilization dosages per ERA standards.
Report Metadata
Laboratory Soil Test Parameters
ERA Subgrade Undercut & Stabilization Recommendations
Critical Black Cotton Soil detected: Minimum 600mm undercut & excavation required. Place a heavy woven geotextile separator fabric, followed by 500mm non-expansive capping layer (CBR ≥ 15%, PI < 12%) or in-situ 4% hydrated lime stabilization.
- Execute excavation during dry weather to prevent heavy machinery bogging.
- Do NOT allow water to pond in excavated subgrade trenches.
- Compact capping layer to 95% Modified AASHTO T-180 dry density.
EXPANSIVE SUBGRADE SOIL & STABILIZATION REPORT
Strictly Formatted per ERA Geotechnical & Pavement Design Manual 2013
| Project Name: | [Insert Project Title] | Date / Time: | 8/10/2026 |
| Station / Borrow Pit: | [Insert Section Details] | Design Standard: | ERA Geotechnical Manual 2013 |
| Materials Engineer: | [Insert Engineer Name] | AASHTO Group: | A-7-6 (34) |
1. Laboratory Soil Classification & Volumetric Swell
| Liquid Limit (LL) | Plastic Limit (PL) | Plasticity Index (PI) | Passing #200 (%) | Free Swell (%) | Swelling Rating |
|---|---|---|---|---|---|
| 65% | 24% | 41% | 78% | 110% | Very High (Expansive Black Cotton Soil) |
2. Specified Subgrade Improvement & Stabilization Schedule
| Undercut Depth | Capping Bed (CBR ≥ 15%) | Lime Dosage (%) | Cement Dosage (%) | Geotextile Fabric |
|---|---|---|---|---|
| 600 mm | 500 mm | 4% | 3% | REQUIRED |
I hereby certify that the expansive subgrade soil evaluation and stabilization recommendations reported herein comply strictly with the Ethiopian Roads Administration (ERA) Geotechnical & Pavement Design Manual 2013.
Geotechnical Guidance (ERA 2013 Manual)
1. Black Cotton Soil Characteristics
Black cotton soils contain active montmorillonite clay minerals. They exhibit extreme volume change (high swelling when wet, deep shrinkage cracking when dry). Never place subbase directly on untreated A-7-6 subgrade.
2. Lime Stabilization Chemistry
Hydrated lime Ca(OH)₂ reacts with active clay minerals via cation exchange and pozzolanic reactions, permanently lowering PI and raising CBR from 2% to > 15%.
3. Moisture Ingress Prevention
Extend non-expansive capping layers across the full embankment width into the side slopes to prevent edge moisture infiltration.
Expansive Soil & Stabilization Sizer Documentation
Technical specifications, mathematical formulas, and civil guidelines
1. Functional Purpose
The Expansive Soil & Stabilization Sizer classifies subgrade soils per AASHTO M-145 (A-1 to A-7-6) and Group Index (GI), evaluates volumetric swelling threat (Low to Very High Black Cotton Soil), and calculates required undercut excavation depth, non-expansive capping thickness (CBR ≥ 15%), and lime/cement stabilization dosages according to the ERA Geotechnical Design Manual Final 2013 and ERA Pavement Design Manual 2013.
It mitigates pavement heave, longitudinal cracking, and subgrade shear failure by outputting clear engineering recommendations and generating a dark bold-lined printable submittal report.
2. Practical Workflow Instructions
- Input Soil Test Results: Enter Liquid Limit (LL%), Plastic Limit (PL%), Percent Passing #200 Sieve (F200%), and 4-Day Soaked Free Swell Index (%).
- Review AASHTO Classification & GI: Inspect the calculated Plasticity Index (PI = LL - PL), Group Index (GI), and AASHTO Soil Group (e.g. A-7-6).
- Analyze Stabilization Recommendations: Review required undercut depth, capping layer thickness, geotextile requirements, and hydrated lime dosage (3% - 5%).
- Export Print Report: Click Print Clean Report to export a black-bordered professional geotechnical submittal report.
3. Mathematical & ERA Standard Basis
Group Index (GI) is calculated using the standard AASHTO formula:
Soils with PI > 35%, LL > 70%, or Free Swell > 120% are rated Very High (Expansive Black Cotton Soil) and require minimum 600mm undercut and 500mm non-expansive capping layer.