ASTM D4318 Atterberg Limits: Modern LL, PL, and PI Workflow for Geotechnical and CMT Labs

What Is ASTM D4318?

ASTM D4318 defines the procedures for determining a soil’s Liquid Limit (LL), Plastic Limit (PL), and Plasticity Index (PI). These values are essential for:

• Soil classification
• Shrink swell potential
• Evaluating compressibility
• Determining suitability of material for engineered fill
• Pavement and foundation design

Most geotechnical projects require Atterberg Limits early in design. Because LL and PL directly influence boring logs, laboratory reports, and geotechnical recommendations, accuracy and documentation matter.

Quick Definitions: LL, PL, and PI

Liquid Limit (LL): The moisture content at which a soil transitions from a plastic to a liquid state.

Plastic Limit (PL): The moisture content at which a soil begins to crumble when rolled into threads.

Plasticity Index (PI): PI is one of the most important indicators of soil behavior. High PI soils tend to be expansive, compressible, and moisture sensitive, while low PI soils behave more like non plastic or granular materials.

These values directly influence:

• Site grading decisions
• Foundation recommendations
• Pavement design
• Shrink swell analyses
• Material suitability assessments

Why ASTM D4318 Is Critical for Geotechnical Work

Engineers use LL, PL, and PI to:

• Select fill materials
• Estimate settlement potential
• Predict seasonal shrink and swell
• Input values into USCS or AASHTO classifications
• Populate boring logs and final geotechnical reports

This means errors or inconsistent documentation slow down design, cause confusion in field operations, and create audit risks.

ASTM D4318 Test Procedure (Step by Step)

1. Sample Preparation

• Reduce soil to pass No. 40 sieve
• Adjust moisture and mix thoroughly
• Identify containers for LL and PL trials

2. Liquid Limit Test

Performed using fall cone or Casagrande apparatus.

You record:

• Wet soil weight
• Dry soil weight
• Number of blows (Casagrande method)
• Depth of penetration (fall cone method)

Objective: determine the water content at the LL point.

3. Plastic Limit Test

• Roll soil into 3 mm threads
• If threads crumble, record water content
• Repeat and average values

4. Calculate LL, PL, and PI

• Moisture content calculations
• Plot LL curve (if using Casagrande)
• Compute PI = LL - PL

These values feed into classification and design workflows.

Why Traditional Atterberg Limits Workflows Slow Labs Down

Manual worksheets near ovens

Wet and dry weights are handwritten, then transcribed later.

Spreadsheet inconsistency

Different file versions produce different formulas and PI values.

Lost or incomplete sample information

Photos, sample IDs, and boring log context often arrive separately.

Manual transfer into boring logs

Technicians type LL, PL, PI into logs by hand, causing delays.

Poor traceability

Auditors cannot easily match PI values back to original sample data.

Aldoa fixes all these issues by connecting field and lab workflows inside one platform.

Aldoa’s End to End ASTM D4318 Workflow

Step 1: Field Sample Creation

Field technicians create a sample directly in Aldoa, capturing:

• GPS location
• Depth
• Sample type
• Observations
• Photos

Sample IDs flow directly into project logs, ensuring the lab receives complete context.

Step 2: Lab Receives Sample Data Instantly

Technicians see incoming samples organized by:

• Project
• Required tests
• Priority
• Assigned tech

Supervisors can plan LL and PL testing without guesswork.

Step 3: Digital LL and PL Worksheets

Standardized digital forms ensure every technician uses the same process.

Aldoa automatically computes:

• Moisture contents
• Average LL
• Average PL
• Plasticity Index (PI)

Internal checks flag possible mistakes before approval.

Step 4: Review and Supervisor Approval

Managers can:

• Review moisture calculations
• Validate consistency
• Add notes
• Approve or request edits

Every action is logged for QA and DOT audits.

Step 5: Automatic Reporting and Boring Log Integration

Once approved, Aldoa automatically updates:

• LL, PL, PI values
• Soil classification
• Boring logs
• Geotechnical summaries

There is no manual data entry between systems.

Key Benefits of Using Aldoa for Atterberg Limits Testing

• Standardized documentation across all technicians
• Accurate calculations every time
• Complete traceability from sample creation to report delivery
• Faster turnaround for project managers and clients
• Integrated boring logs that eliminate manual entry
• Cleaner workflows between field and lab teams

FAQ: Common Atterberg Limits Questions

What is the difference between LL and PL?

LL is the moisture at which soil behaves like a liquid.
PL is the moisture at which soil crumbles when rolled.
PI = LL - PL.

What method does ASTM D4318 use for LL?

Casagrande cup or fall cone; both are allowed.

Is PI important for design?

Yes. PI influences shrink swell behavior, compressibility, and material suitability.

Does Aldoa support both LL methods?

Yes. Technicians can record Casagrande or fall cone data in standardized digital worksheets.

See How Aldoa Modernizes Atterberg Limits Workflows

👉 See Atterberg Limits Workflow Demo: Schedule Demo

Conclusion

LL, PL, and PI testing should be accurate, consistent, and fast. Aldoa unifies field sampling, lab calculations, PI generation, and boring log reporting into a single connected workflow. This reduces errors, speeds up turnaround, and improves visibility across geotechnical teams.

Aldoa gives labs and field teams a modern way to run ASTM D4318 without spreadsheets, manual transcription, or outdated legacy systems.