Method of load test on soils

IS 1888 Scope & Key Specifications Summary

• Scope:
  IS 1888 covers methods for plate load tests to determine bearing capacity of soil under shallow foundations.

• Rounding Off (Clause 0.6):
  Final test/analysis values must be rounded per IS 2-1960, retaining the same significant figures as specified values.

• Definitions (Clause 2.1):
  Use definitions from IS 2809-1972 (soil engineering terms) and IS 6403-1981 (allowable bearing pressure).

• Bearing Plates (Clause 3.3):

  • Material: Mild steel
  • Thickness: ≥ 25 mm
  • Size: Circular or square, 300 mm to 750 mm

• Typical Setup Includes:

  • Wooden joists @ 300 mm c/c for loading platform
  • Dial gauge with plumb bob arrangement for settlement measurement
  • Ball and socket arrangement for load transfer
  • Reaction loading platform with cross bar channel and loading truss
  • Chequered/grooved test plates with handles for easy placement (depth ≥ 2/3 width)

Typical Plate Sizes for Different Soils

Rounding Off Rule (IS 2-1960)

• Round off to the same decimal place as the specified value.
• For example, if specified value = 2.50, round 2.496 to 2.50.

flowchart TD
    A[Loading Platform] --> B[Plate Load Test]
    B --> C[Dial Gauge Measures Settlement]
    B --> D[Load Applied via Ball & Socket]
    B --> E[Reaction Platform with Loading Truss]
    E --> F[Supports Load Reaction]

This summary encapsulates the scope, key plate specifications, and test setup essentials from IS 1888.

IS 1888 Key References, Formulas & Specifications

• Bearing Plates (Clause 3.3):

  • Material: Mild steel
  • Thickness: ≥ 25 mm
  • Size: 300 mm to 750 mm (circular or square)

• Rounding Off (Clause 0.6):

  • Follow IS 2-1960 for rounding numerical values
  • Retain significant figures equal to those in specified values

• Glossary & Definitions:

  • Use IS 2809-1972 and IS 6403-1981 for soil engineering terms and allowable bearing pressure determination.

• Typical Setup Details:

  • Loading platforms use wooden joists @ 300 mm c/c
  • Use ball-and-socket arrangements for load transfer
  • Test plates/blocks: minimum depth ≥ 2/3 width, with chequered/grooved base for grip

• Figures:

  • Fig. 1: Gravity loading platform setup
  • Fig. 2: Reaction loading platform setup
  • Fig. 3: Loading truss setup
  • Fig. 4: Chequers/grooves detail

Summary Table: Bearing Plate Sizes

Rounding Off Rule (IS 2-1960)

• Round final test/analysis results to the same significant figures as the standard's specified values.

flowchart TD
    A[Loading Platform] --> B[Wooden Joists @ 300 mm c/c]
    B --> C[Steel Bearing Plate (≥25 mm thick)]
    C --> D[Test Plate/Block (≥ 2/3 width depth)]
    D --> E[Load Applied via Ball & Socket]
    E --> F[Dial Gauge Measurement]

For detailed soil engineering terms and allowable bearing pressure, refer to IS 2809 and IS 6403 respectively.

IS 1888: Apparatus and Equipment Key Points

• Ball and Socket Arrangement: Used for flexible load application (Clause 3.6).
• Loading Columns, Steel Shims, Wooden Blocks, Collars: For precise load transfer and alignment (Clause 3.6).
• Reaction Girder with Cradles: Adjustable fitting to reaction platform to suit test setup (Clause 3.6).
• Hydraulic Jack: Must have calibrated load measuring device (pressure gauge, electronic load cell, or proving ring) (Clause 3.2).
• Plate Sizes: Specific sizes are prescribed depending on soil type (cohesive, cohesionless, partially cohesive) - refer to IS 1888 tables (Clause 0.5).
• Rounding Off Results: Final test values must be rounded per IS 2-1960 rules, matching significant figures of specified values (Clause 0.6).

Typical Load Measurement Setup

graph LR
A[Hydraulic Jack] --> B[Load Measuring Device]
B --> C[Loading Column]
C --> D[Ball & Socket Arrangement]
D --> E[Soil Sample]
F[Reaction Girder with Cradles] --- E

For detailed plate sizes and zero correction charts, refer to IS 1888 tables for soil type-specific values.

IS 1888: Test Procedure Key Points

1. Test Arrangement (Clause 4.5)

• Follow specified setup for plate bearing tests.
• Record test elevation, natural water table, and test pit profile.
• Use appropriate bearing plate size based on soil type:
  • Smaller plates for cohesive soils
  • Larger plates for cohesionless soils

2. Data Recording (Clause 6.1)

• Continuously log time, load, and settlement data.
• Note any irregularities in the test setup.

3. Rounding Off Results (Clause 0.6)

• Round final test values per IS 2-1960.
• Maintain the same number of significant digits as the standard's specified values.

4. Plate Sizes (from revision notes)

5. Additional Notes

• Zero correction must be applied to settlement readings.
• Use log-log scale plots for cohesionless and partially cohesive soils to interpret results.

flowchart TD
    A[Test Setup] --> B[Select Plate Size]
    B --> C[Conduct Test]
    C --> D[Record Data: Time, Load, Settlement]
    D --> E[Apply Zero Correction]
    E --> F[Plot Log-Log Scale (if cohesionless soil)]
    F --> G[Round Off Results per IS 2-1960]
    G --> H[Interpret Bearing Capacity]

This summarizes the test procedure essentials from IS 1888 for plate bearing tests.

IS 1888: Interpretation of Results – Key Formulas & Specifications

1. Rounding Off Results (Clause 0.6)

• Final test/analysis values must be rounded per IS 2-1960.
• Retain the same number of significant figures as specified in the standard.

2. Bearing Plates (Clause 3.3)

• Mild steel circular/square plates
• Thickness: ≥ 25 mm
• Size range: 300 to 750 mm

3. Settlement Relation (Clause 5.3)

To estimate footing settlement (St) from plate settlement (Sp):

[ St = Sp \times \frac{B \times (B_p + 0.3)}{B_p \times (B + 0.3)} ]

Where:

• ( B ) = footing size (m)
• ( B_p ) = test plate size (m)
• ( Sp ) = observed plate settlement (m)
• ( St ) = estimated footing settlement (m)

4. Data Recording (Clause 6.1)

Record continuously:

• Time, load, settlement
• Test elevation, water table level
• Test pit profile
• Bearing plate size & irregularities

5. Load-Settlement Curves (Fig. 5)

• Used to determine safe bearing pressure for various soils:
  • Loose to medium cohesionless
  • Dense cohesionless
  • Cohesive
  • Partially cohesive

graph LR
A[Plate Settlement (Sp)] --> B[Calculate Footing Settlement (St)]
B --> C{Use Formula}
C --> D[St = Sp × (B(Bp+0.3)) / (Bp(B+0.3))]

Summary: Use the above formula to interpret plate test results for footing settlement, maintain proper rounding, and record detailed test data for compliance.

IS 1888: Key Points on Recording and Reporting

1. Recording Requirements (Clause 6.1)

• Continuous recording of time, load, and settlement data during each test.
• Include details:
  • Test elevation
  • Natural water table level
  • Profile of test pit
  • Size and irregularities of bearing plate

2. Rounding Off (Clause 0.6)

• Final test values must be rounded per IS 2:1960.
• Retain the same number of significant figures as specified in the standard.

3. Bearing Plates (Clause 3.3)

• Plates must be mild steel, ≥ 25 mm thick.
• Size range: 300 mm to 750 mm (circular or square).
• Plates have chequered/grooved bottom for grip (see Fig. 4).

4. Settlement Measurement (Clause 3.4)

• Use dial gauges with:
  • 25 mm travel
  • Accuracy of 0.01 mm

Typical Setup Summary (Fig. 1-4)

• Loading platforms with wooden joists spaced at 300 mm c/c.
• Use of ball & socket, dial gauge fixtures, and reaction loading platforms.
• Test plates or blocks should be at least two-thirds the width in depth.

Example: Rounding Off Rule (IS 2:1960)

flowchart LR
    A[Start Test] --> B[Record Time, Load, Settlement]
    B --> C[Note Test Elevation & Water Table]
    C --> D[Check Bearing Plate Size & Irregularities]
    D --> E[Measure Settlement with Dial Gauge (0.01 mm)]
    E --> F[Round off values per IS 2:1960]
    F --> G[Report Test Results]

This ensures comprehensive, standardized, and accurate reporting of plate load test data as per IS 1888.

Limitations of Plate Load Test (IS 1888)

• Test Depth Influence: Results reflect soil behavior only to a depth < 2× plate width. Foundations are usually larger, involving deeper soil strata affecting settlement and shear resistance.
• Soil Variability: If soil properties vary at shallow depths, test results may be misleading.
• Ultimate Settlement: Test does not reliably predict ultimate settlements, especially in cohesive soils.
• Size Effect: For clayey soils, bearing capacity from shear is nearly the same for small plates and larger foundations, but settlement behavior may differ.
• Loading Platform Setup (Clause 4.5.1):
  • Platform height ≥ 1 m above pit bottom
  • Supported ≥ 2.5 m away from test area
  • No supports within 3.5× plate size radius from plate center

Recommendation: Combine plate load test with thorough soil exploration (IS 1892) to account for deeper weaker strata.

Summary Table

Reference: IS 1888, IS 1892, IS 2 (rounding rules)

IS 1888: Safety and Accuracy Considerations – Key Points

1. Rounding Off (Clause 0.6)

• Final test or analysis values must be rounded according to IS 2-1960.
• Retain the same number of significant figures as the specified value in the standard.

2. Test Arrangement (Clause 4.5)

• Use calibrated hydraulic jacks with load measurement devices (pressure gauge, load cell, proving ring).
• Loading platform setups include:
  • Gravity loading platform with wooden joists @ 300 mm c/c.
  • Reaction loading platform with dial gauge fixtures.
  • Loading truss with cross bar channels.
• Use bearing plates (Clause 3.3) of mild steel:
  • Thickness ≥ 25 mm.
  • Size: 300 to 750 mm (circular or square).

3. Accuracy Enhancements

• Use dial gauges with fixtures and plumb bob arrangements for precise displacement measurement.
• Clamp dial gauge fixtures securely to avoid movement errors.
• Use ball and socket arrangements for load transfer to ensure even distribution.

Typical Setup Summary:

flowchart TD
    A[Test Setup] --> B[Hydraulic Jack]
    A --> C[Loading Platform]
    C --> D[Wooden Joists @ 300 mm c/c]
    C --> E[Bearing Plate (≥25 mm thick)]
    A --> F[Dial Gauge Fixture]
    F --> G[Plumb Bob Arrangement]
    F --> H[Ball & Socket Joint]

Summary: Ensure calibrated instruments, proper load distribution via bearing plates, and precise displacement measurement using dial gauges and plumb bobs for safety and accuracy in load tests per IS 1888.

IS 1888: Key Annexures, Figures, and Specifications Summary

• Bearing Plates (Clause 3.3):

  • Material: Mild steel
  • Thickness: ≥ 25 mm
  • Size range: 300 mm to 750 mm (circular or square)

• Excavation Depth for Plate Load Test (Clause 6.2):

  • Excavate soil below test plate to depth = 2 × plate dimension

• Rounding Off (IS 2-1960):

  • Final test/analysis values rounded off to same significant figures as specified values

• Typical Setup Figures:

  • Fig. 1: Gravity Loading Platform (wooden joists @ 300 mm c/c, dial gauge setup)
  • Fig. 2: Reaction Loading Platform (ball and socket, cross bar channel)
  • Fig. 3: Loading Truss
  • Fig. 4: Chequered/Grooved Test Plates (depth ≥ 2/3 width, handles, center marked)
  • Fig. 6: Load-Settlement Curve (log-log scale for elastic/plastic settlement)

Typical Plate Load Test Setup (Simplified Mermaid Diagram)

graph TD
    A[Loading Platform] --> B[Wooden Joists @ 300 mm c/c]
    B --> C[Dial Gauge Fixture]
    C --> D[Test Plate (Mild Steel, ≥25mm thick)]
    D --> E[Soil Surface]
    E --> F[Excavation Depth = 2 × Plate Dimension]

Important Notes:

• Use chequered or grooved plates for better soil-plate interaction.
• Plates can be cast-in-situ or precast concrete blocks if ≥ 2/3 width in depth.
• Settlement readings taken via dial gauge with plumb bob arrangement.

This concise summary integrates IS 1888 specifications and typical test arrangements for foundation bearing capacity evaluation.