Methods of test for stabilized soils, Part 5: Determination of unconfined compressive strength of stabilized soils
1970 Edition

Scope Overview

This section defines the scope, covering preparation, curing, and testing of stabilized soil specimens primarily for unconfined compressive strength evaluation.

Key Requirements

• Report specimen size and shape, stabilized soil composition, dry density, moisture content, compaction and curing methods, curing duration, and temperature.
• Maintain curing temperature within ±2°C for laboratory tests and ±5°C for on-site quality control, with maximum and minimum temperatures documented.
• Store specimens in sealed containers to preserve moisture, suitable for cement or lime stabilization; follow manufacturer instructions for other stabilizers.
• Strength testing periods typically include 3, 7, 14, and 28 days for cement stabilization, with 7 days often used for rapid assessments.

Specimen Mold Dimensions

Specimen Preparation & Curing Workflow

flowchart TD
    A[Mix Soil and Stabilizer] --> B[Compact in Mold]
    B --> C[Place Specimen in Sealed Tin]
    C --> D[Cure at Constant Moisture]
    D --> E[Conduct Strength Tests at Various Ages]
    E --> F[Compile Report with Details]

Maintain curing conditions strictly to assure reliable strength outcomes.

Soil Grouping Criteria

Explanation

• Fine-grained soils mainly comprise silts and clays with over 90% passing the 2.36 mm sieve.
• Medium-grained soils include sands and fine gravels passing the 20 mm sieve.
• Coarse-grained soils consist of gravels and larger particles passing the 40 mm sieve.

Application

This classification aids in selecting appropriate specimens for unconfined compressive strength testing. Specimens are prepared at predetermined dry densities or with constant compactive effort to ensure consistent evaluation.

Soil Classification Diagram

flowchart TD
    A[Received Soil Sample] --> B{Particle Size Distribution}
    B -->|≥ 90% pass 2.36 mm| C[Fine-Grained Soil]
    B -->|≥ 90% pass 20 mm| D[Medium-Grained Soil]
    B -->|≥ 90% pass 40 mm| E[Coarse-Grained Soil]

This classification supports precise specimen preparation and dependable strength analysis.

General Equipment

• IS sieves: 20 mm for medium-grained soils; 40 mm for coarse-grained soils.
• Precision balance with ±1 g accuracy.
• Steel or cast iron molds for 150 mm cubic specimens:
  • Height and face dimensions: 150 ± 0.2 mm
  • Interior angles: 90° ± 0.5°
  • Flatness tolerance: 0.03 mm
  • Equipped with baseplate and clamps.
• Plasterer's steel trowel.
• Curing containers: sealed tins sized 160×160×155 mm.
• Compression testing machine capable of uniform load increase of approximately 35 kgf/cm²/min.
• Palette knife (approximate blade size: 200×30 mm).
• Flat metal plates (approx. 200×200×3 mm) to prevent moisture loss.
• Moisture content apparatus complying with IS 4332 Part II.

Additional Equipment for Pre-determined Dry Density Specimens

• Electric or pneumatic vibrating hammer.
• Square or rectangular tamper with an area near 8,000 mm² (preferably square).
• Tamper collars to restrict penetration depths to 50 mm, 100 mm, or 150 mm.

Equipment for Constant Compactive Effort

• Same as above, with apparatus specified for this compaction method.

Equipment for Compaction to Refusal

• Vibrating hammer.
• Square tamper (~8,000 mm²).
• Steel straightedge (approx. 300×25×3 mm) with one beveled edge.

Tamper Collar Sizes

flowchart TD
    A[Specimen Preparation] --> B[General Equipment]
    A --> C[Pre-determined Dry Density Setup]
    A --> D[Constant Compactive Effort Setup]
    A --> E[Refusal Compaction Setup]

Specimen and Mold Dimensions

• Cubic specimens measuring 150 mm × 150 mm × 150 mm with ±0.2 mm tolerance.
• Mold interior angles maintained at 90° ± 0.5°.
• Surface flatness within 0.03 mm.
• Molds made from steel or cast iron, robust with baseplate and clamps.
• Curing containers of 160×160×155 mm dimensions, sealed with lids and tape.

Testing Apparatus

• IS sieves of 20 mm and 40 mm for classification.
• Balance accurate to ±1 g.
• Compression testing machine (lever or proving ring type) with a loading rate of approximately 35 kgf/cm²/min.
• Palette knife blade size about 200×30 mm.
• Flat metal plates of 200×200×3 mm to prevent moisture loss.

Moisture Content Measurement

• Conducted as per IS 4332 Part II (1967), sampling interior specimen fragments.

Curing Requirements

• Temperature controlled within ±2°C in laboratories and ±5°C for field quality control.
• Storage in sealed tins to preserve moisture.
• Typical curing durations: 3, 7, 14, and 28 days for cement stabilization; 7 days for rapid assessments.

Summary Table

Wax Coating

• Apply paraffin or suitable wax to specimens to maintain constant moisture.
• Cool wax before application for ease of removal.

Apparatus for Compaction to Refusal

• Electric or pneumatic vibrating hammer.
• Square tamper (~8,000 mm² area).
• Steel straightedge (approx. 300×25×3 mm) with a beveled edge.

Mold and Specimen Dimensions

• Cubic molds with 150 mm sides, ±0.2 mm tolerance.
• Interior faces flat within 0.03 mm; angles at 90° ± 0.5°.
• Use 20 mm or 40 mm IS sieves for medium and coarse-grained soils respectively.

Compaction and Curing

• Use tampers with collars to control compaction depth.
• Cure specimens in sealed tins measuring 160×160×155 mm.
• Maintain curing temperature within ±2°C (laboratory) or ±5°C (site QC).
• Typical curing durations for cement-stabilized specimens are 3, 7, 14, and 28 days.

Reporting

• Document specimen size and shape, stabilized soil composition, dry density, moisture content, compaction and curing methods, curing duration, and temperature.

Additional Notes

• Cohesive mixtures may be removed immediately from molds; non-cohesive soils may remain for 24 hours.
• Strength increases with curing time; test at multiple intervals.
• Compression machine loading rate approximately 35 kgf/cm²/min.

Specimen Mold Dimensions Summary

Initial Curing

• After removing the upper mold, level off the specimen using a straight edge flush with the lower mold.
• Fill surface irregularities with material from the same batch.
• Cover the mold with a metal plate and store at 27 ± 2°C for approximately 24 hours.
• Remove the specimen and weigh it to the nearest gram.

Further Curing

• Place the specimen inverted inside a sealed curing tin.
• Seal the tin with tape and weigh it.
• Store the sealed tin at 27 ± 2°C for the required curing duration depending on the stabilizer used.

Curing Duration Recommendations

• Cement-stabilized specimens: 3, 7, 14, and 28 days.
• Rapid assessment: typically 7 days.
• Wax coating is recommended to maintain moisture during curing.

Temperature Controls

• Laboratory: ±2°C tolerance.
• Site quality control: ±5°C tolerance with max and min temperatures recorded.

Curing Summary Table

Important Remarks

• Wax coating aids in moisture retention.
• Timing of specimen removal depends on soil cohesiveness.
• Report curing parameters and specimen details as required.

Specimen Preparation and Compaction

• Two compaction approaches:
  • To constant compactive effort requiring tampers and specialized equipment.
  • To refusal employing vibrating hammer, square tamper (~8,000 mm²), and steel straightedge.

Specimen Handling

• Cohesive stabilized soils may be extracted immediately from molds.
• Non-cohesive stabilized soils may remain in molds for about 24 hours to gain strength.
• Specimens are coated with cooled wax to preserve moisture and facilitate removal.

Curing and Storage

• Cement-stabilized specimens are cured typically for 3, 7, 14, and 28 days.
• For rapid quality checks, a 7-day curing period is standard.
• Curing temperature tolerances: ±2°C in laboratory settings and ±5°C on-site with recorded temperature extremes.

Reporting

• Include specimen dimensions, stabilized soil makeup, dry density, moisture content, compaction and curing methods, curing duration, and temperature.

Curing Periods Summary

Workflow Diagram

flowchart TD
    A[Mix Soil & Stabilizer] --> B[Prepare Specimen]
    B --> C{Choose Compaction Method}
    C -->|Constant Effort| D[Use Tamping Equipment]
    C -->|Refusal| E[Vibrating Hammer + Tamper]
    D & E --> F[Apply Wax Coating]
    F --> G[Cure Specimen]
    G --> H{Select Curing Duration}
    H --> I[3, 7, 14, or 28 Days]
    H --> J[7 Days for Rapid QC]
    G --> K[Maintain Temperature Tolerance]

Moisture Content Measurement

• Performed as stipulated in IS 4332 Part II (1967) using representative interior samples.

Specimen Preparation

• When compacting to a constant dry density, additional apparatus as specified is employed.

Reporting Details

• Reports should detail specimen dimensions and shape, stabilized soil composition, dry density, moisture content, compaction and curing methods, curing period, and temperature.
• Curing temperature tolerances: ±2°C for lab tests, ±5°C for site QC with recorded max/min values.

Specimen Storage and Testing

• Specimens are stored in sealed tins to retain moisture.
• Cement or lime stabilization is standard; other stabilizers require manufacturers’ guidance.
• Strength is tested at intervals of 3, 7, 14, and 28 days, with 7 days often used for rapid quality control.

Dry Density Formula

[ \rho_d = \frac{W_d}{V} ] Where:

• (W_d) = dry mass of specimen
• (V) = volume of specimen

Curing Periods and Purposes

Process Flow

flowchart LR
    A[Soil + Stabilizer] --> B[Compact to Required Density]
    B --> C[Prepare Specimen]
    C --> D[Determine Moisture Content]
    D --> E[Cure in Sealed Tins at Controlled Temperature]
    E --> F[Test Strength at Specified Intervals]
    F --> G[Document Results]

Reporting Requirements

• Specify specimen size and geometry.
• Detail the composition of stabilized soil mixture.
• Include dry density of the combined soil and stabilizer.
• Record moisture content as per relevant clauses.
• Describe compaction and curing methods used.
• State curing duration and temperature with tolerances (±2°C lab, ±5°C site QC).
• Report maximum and minimum temperatures if tolerances are exceeded.

Additional Notes

• Specimens should be stored in sealed containers or wax-coated to preserve moisture.
• Strength testing typically conducted at 3, 7, 14, and 28 days; 7 days for rapid evaluation.
• Non-cohesive soils may remain in molds up to 24 hours before removal.

Formula for Apparent Density (\gamma_a)

[ \gamma_a = \frac{100 \times W_2}{A_m \times L \times (100 + m)} \quad (g/cm^3) ] Where:

• (W_2) = weight before wax coating (g)
• (A_m) = cross-sectional area for medium-grained soil (cm²)
• (L) = length of specimen (cm)
• (m) = moisture content (%) after curing

Reporting Summary Table

Process Diagram

flowchart LR
    A[Prepare Specimen] --> B{Determine Soil Type}
    B -->|Fine-Grained| C[Report Fine-Grained Parameters]
    B -->|Medium-Grained| D[Report Medium-Grained Parameters]

Instrumentation Accuracy

• Balance must provide readings accurate to within 1 gram for soil measurement.
• Calipers should have accuracy up to 0.25 mm.
  • Minimum opening: ≥100 mm for fine-grained soils.
  • Minimum opening: ≥200 mm for medium-grained soils.

Rounding Protocol

• Follow IS 2-1960 for rounding numerical test results to maintain consistency.
• Rounding rules:
  • Digits 0,1,2: round down.
  • Digits 3,4: round up if preceding digit is odd, down if even.
  • Digit 5: always round up.
  • Digits 6-9: round up.

Practical Guidance

• Use calibrated devices meeting specified accuracy to ensure reliable results.
• Record measurements precisely before rounding.
• Avoid introducing errors beyond instrument precision during rounding.

Accuracy Workflow

flowchart LR
    A[Measurement Taken] --> B[Check Instrument Type]
    B -->|Balance| C[Accuracy ± 1 g]
    B -->|Caliper| D[Accuracy ± 0.25 mm]
    C & D --> E[Apply IS 2-1960 Rounding]
    E --> F[Final Reported Value]

Classification Criteria

• Fine-grained soils: ≥ 90% passing 2.36 mm IS sieve.
• Medium-grained soils: ≥ 90% passing 20 mm IS sieve.
• Coarse-grained soils: ≥ 90% passing 40 mm IS sieve.

Sample Preparation

• Use material passing the 20 mm sieve for medium-grained soils.
• Use material passing the 40 mm sieve for coarse-grained soils.
• Follow IS 4332 (Part I)-1967 for compaction methods.

Specimen Handling

• Wax coating is recommended to preserve moisture.
• Curing temperature tolerance: ±2°C in laboratories and ±5°C on-site.
• Common curing durations: 3, 7, 14, and 28 days; 7 days for rapid tests.

Soil Grouping Summary

Classification Diagram

flowchart TD
    A[Collected Soil Sample] --> B{Percent Passing IS Sieve}
    B -->|≥ 90% pass 2.36 mm| C[Fine-Grained]
    B -->|≥ 90% pass 20 mm| D[Medium-Grained]
    B -->|≥ 90% pass 40 mm| E[Coarse-Grained]

Required Tools

• Electric or pneumatic vibrating hammer to provide controlled compactive energy.
• Square or rectangular tamper with an approximate area of 8,000 mm².
• Tamper collars rigidly fixed to the tamper shaft to limit penetration depth:
  • 50 mm
  • 100 mm
  • 150 mm

Function

These devices ensure consistent and uniform compaction depth and energy application, critical for achieving the target dry density.

Tamper Collar Specifications

Equipment Use Flow

flowchart LR
    A[Vibrating Hammer] --> B[Square Tamper (8,000 mm²)]
    B --> C{Set Penetration Limit}
    C --> D[50 mm]
    C --> E[100 mm]
    C --> F[150 mm]

Specifications

• Medium-grained soils prepared with material passing the 20 mm IS sieve.
• Coarse-grained soils prepared with material passing the 40 mm IS sieve.
• Follow guidelines in IS 4332 (Part I)-1967 for specimen preparation.

Apparatus

• Electric or pneumatic vibrating hammer.
• Square or rectangular tamper (~8,000 mm²), preferably square.
• Steel straightedge measuring 300×25×3 mm with one beveled edge.

Procedure

• Compact the specimen until refusal, i.e., no further densification occurs despite additional compactive effort.
• Use vibrating hammer and tamper for compaction.
• Level the surface with the straightedge.

Dry Density Calculation

[ \rho_d = \frac{W_s}{V} ] Where:

• (W_s) = dry weight of soil (g)
• (V) = specimen volume (cm³)

Sieve Sizes for Compaction to Refusal

Procedure Diagram

flowchart TD
    A[Soil Sample Preparation] --> B[Pass Through IS Sieve]
    B -->|Medium-Grained| C[20 mm Sieve]
    B -->|Coarse-Grained| D[40 mm Sieve]
    C & D --> E[Compact Using Vibrating Hammer + Tamper]
    E --> F[Compact to Refusal]
    F --> G[Measure Dry Density and Volume]