Code of practice for site investigations for the foundation in gravel-boulder deposit

IS 10042: Scope - Key Formulas, Tables & Specifications

Scope:
IS 10042 provides guidelines for subsurface investigations for foundations, including soil sampling, grain size analysis, and allowable soil parameters.

Key Symbols (Clause 3.1)

Important Formula (Clause 2.54)

[ L = N" \times Sa \times D \times B ]

• (Sa) = allowable deformation (cm), depends on structure type
• (B) = footing width (m)
• (N"), (D) values from Fig. 6 (not provided here)

Laboratory Test (Clause 7.2.1)

• From grain size analysis, determine proportion of boulder/gravel in sample.
• Used to decide if boulder/gravel is matrix or inclusion.

Units (SI Units)

flowchart LR
    A[Soil Sampling] --> B[Grain Size Analysis]
    B --> C{Proportion of Boulder/Gravel}
    C -->|Matrix| D[Classify Soil Matrix]
    C -->|Inclusion| E[Classify Boulder/Gravel]
    D & E --> F[Decide Foundation Design Parameters]

IS 10042: Definitions and Symbols - Key Points

1. Symbols (Clause 3.1)

• B = Width of strip foundation / side of square foundation / diameter of circular foundation (m)
• qa = Allowable soil pressure for 12 mm or 25 mm settlement (tonnes/m²)
• To = Residual soil strength (tonnes/m²)
• Sa = Allowable settlement for structure (cm)
• N" = Cumulative number of blows at penetration depth De (m)
• Dc = Depth of penetration (cm)
• Bc = Diameter of cone (cm)
• Yc = Natural unit weight of soil (tonnes/m³)

2. Key Formula (Clause 2.54)

[ L = N'' \times S_a \times D \times B ] Where:

• (S_a) = allowable deformation (cm),
• (B) = footing width (m),
• (N''), (D) from Fig. 6 (not provided here).

3. SI Units (International System)

4. Notes

• Use qa for allowable soil pressure limits based on settlement.
• Refer to Fig. 6 for values of (N'') and (D) when calculating footing parameters.
• Settlement limits and soil strength are critical for foundation design.

graph LR
A[Foundation Width (B)] --> C[Allowable Settlement (Sa)]
C --> D[Number of Blows (N'')]
D --> E[Depth of Penetration (D)]
E --> F[Calculate Load (L = N'' × Sa × D × B)]

This concise overview aids in interpreting symbols and formulas essential for foundation design per IS 10042.

Nature of Gravel-Boulder Deposits (IS 10042)

1. Nature of Deposit (Clause 4.2)

• Boulder deposits are either fluvial or glacial origin.
• Contain boulders/gravel with filler material: sand, silt, or clay.
• Two configurations:
  • Filler in interstices of boulders (Fig. 1A)
  • Boulders in matrix of filler (Fig. 1B)

2. Behaviour Under Load (Clause 4.3)

• Load behavior depends on:
  • Size, quantity, and packing of boulders.
  • Nature and amount of filler.
• When filler absent: high load capacity, low compressibility.
• With filler: initial compression followed by low compressibility.
• If boulders > 30%, initial rapid compression then load carried mainly by boulders.
• If boulders < 30%, use normal soil load test methods (IS 1888-1982).

3. Influence of Filler (Clause 4.4)

• If boulders in filler matrix, matrix properties dominate.
• If filler in boulder interstices, boulders dominate behavior.

Key Specifications & Guidelines

Summary Diagram: Gravel-Boulder Soil Stratum

graph LR
    A[Filler in Interstices of Boulders] --> Behaviour1[Load carried mainly by boulders]
    B[Boulders in Matrix of Filler] --> Behaviour2[Load governed by filler matrix]
    A & B --> LoadBehavior[Load Behavior Depends on Composition]

Practical Note:

• Determine boulder/gravel proportion by grain size analysis (Clause 7.2.1).
• Use conservative design load to reduce deformation.

For detailed design, refer to IS 10042 clauses 4.2

Behavior & Properties of Boulder-Gravel Soils (IS 10042)

Key Points from Clause 4.3 & 4.4:

• Boulder-Gravel Proportion > 30%:

  • Initial rapid compression followed by low compression as boulders carry the load.
  • Load capacity is high, compressibility low when filler absent.
  • Advantageous to design allowable load beyond initial compression load to reduce deformation.

• Boulder-Gravel Proportion < 30%:

  • Use normal soil load interpretation methods (IS 1888-1982).
  • Behavior governed mainly by filler material if boulders exist in matrix (Fig. 1B).

• Filler Material Influence:

  • If filler exists in interstices (Fig. 1A), behavior governed by boulders.
  • If boulders in filler matrix, filler properties dominate but compressibility reduces.

Laboratory & Investigation (Clause 7.2, 7.2.1)

• Grain Size Analysis separates:
  • Boulder/Cobbles/Gravel: > 4.75 mm
  • Matrix (filler): < 4.75 mm
• Proportion of boulder/gravel used to decide soil behavior type.

Simplified Behavior Summary Table:

Conceptual Diagram (Mermaid.js)

graph LR
A[Boulder-Gravel Soil] --> B{Boulder-Gravel %}
B -->|>30%| C[High Load Capacity, Low Compressibility]
B -->|<30%| D[Normal Soil Behavior]
C --> E{Filler Location}
E -->|Interstices| F[Boulder governs behavior]
E -->|Matrix| G[Filler governs behavior]
D --> H[Use IS 1888-1982 Methods]

Units & Symbols (SI Units):

• Length = **

IS 10042: Methods of Investigation - Key Points

1. In Situ Density Measurement (Clause 5.3)

• Use Water Replacement or Sand Replacement method.
• Excavate a pit of 1 m × 1 m × 0.5 m.
• Weigh excavated soil using a spring balance (100 kg capacity).
• Cover pit with polyethylene sheet.
• Fill pit with water; volume of water = volume of soil.
• Calculate density:
  [ \text{Density} = \frac{\text{Mass of soil}}{\text{Volume of pit (water replaced)}} ]
• Reference: IS 2720 (Part XXXIII) - 1971.

2. Grain Size Analysis & Boulder/Gravel Proportion (Clause 7.2.1)

• From sample grain size analysis, determine the proportion of boulder/gravel.
• Helps decide if boulder/gravel is matrix or vice versa.

3. Units and Symbols

• Length: m, Mass: kg, Time: s
• Force: N = kg·m/s², Pressure: Pa = N/m²
• Energy: J = N·m, Power: W = J/s

4. Additional Notes

• Interstitial material (<5 cm) affects load capacity (see Table and Fig. 4 in IS).
• Soil samples from pit can be used for classification and grain size tests.

flowchart TD
    A[Excavate Pit (1m x 1m x 0.5m)] --> B[Weigh Excavated Soil]
    B --> C[Cover Pit with Polyethylene Sheet]
    C --> D[Fill Pit with Water]
    D --> E[Calculate Volume of Water = Volume of Soil]
    E --> F[Density = Mass of Soil / Volume of Water]

This concise summary covers the key investigation methods and specifications from IS 10042.

Allowable Soil Pressure (qa) — IS 10042 Key Points

Definitions (Clause 3.1)

• B = Width of strip foundation / side of square foundation / diameter of circular foundation (m)
• qa = Allowable soil pressure for 12 mm or 25 mm settlement (tonnes/m²)
• To = Residual soil strength (tonnes/m²)
• Sa = Allowable settlement (cm)

Formula from In-Situ Shear Tests (Clause 6.3)

[ \boxed{ q_a = X \times T_o \times B_r } ]

• X = Constant
  • 6 to 25 for 12 mm settlement
  • 8 for 25 mm settlement
• Br = Width of footing (m)
• To = Residual shear strength from BBT or CBT (tonnes/m²)

Testing & Application Notes

• Load tests (Clause 6.1) validate results from BBT, CBT, and DCPT.
• Normal load on samples in BBT/CBT should equal overburden or expected load but not exceed twice the soil shear strength (Clause 5.10).
• Follow IS 7746-1975+ and IS 2720 (Part 39/Sec 2)-1979 for high normal load shear strength tests.

Summary Table: Constants for X

This approach ensures safe bearing capacity considering soil strength and allowable settlement limits.

IS 10042 - Laboratory Testing Procedures (Clause 7.2.1 & related)

• Grain Size Analysis:
  From the known sample quantity, determine the proportion of boulder/gravel. This helps decide if boulder/gravel is matrix or vice versa.

• Key Test Setups:

  • Boulder-Boulder Test (BBT)
  • Concrete Boulder Test (CBT)
  • Use hydraulic jack (20 T capacity), proving rings, steel plates, and supports as per Figs. 8 & 9 for sample shear tests.

• Allowable Pressure (qa) Calculation (Clause 6.3):
  [ q_a = X \times T_o \times B_r ] where:

  • (X = 6 \text{ (for 12 mm deformation)}) or (8 \text{ (for 25 mm deformation)})
  • (T_o =) residual shear stress from BBT/CBT tests (kg/cm²)
  • (B_r =) width of footing (m)

• Units:

  • Shear stress in kg/cm²
  • Displacement in mm
  • Force in Newton (N), Pressure in Pascal (Pa)

Summary Table: Allowable Pressure Calculation

flowchart LR
    A[Sample Collection] --> B[Grain Size Analysis]
    B --> C[Determine Boulder/Gravel Proportion]
    C --> D[Laboratory Shear Tests (BBT/CBT)]
    D --> E[Measure Residual Shear Stress \(T_o\)]
    E --> F[Calculate \(q_a = X \times T_o \times B_r\)]
    F --> G[Design Foundation Parameters

IS 10042: Field Testing Equipment & Setup – Key Points

1. Equipment for Boulder/Gravel Testing (Clause 7.2.1 & Figures 8 & 9)

• Hydraulic Jack: 20 T capacity for applying load.
• Proving Ring: 20 T capacity to measure load.
• Steel Shear Box & Steel Plates: To hold samples.
• Wooden Sleepers & Supports: For stable setup.
• Flexible Pipes & Pump: For jack operation.
• Weights (Steel/Concrete/Sandbags): To apply static load.
• Dial Gauge & Magnetic Holder: For displacement measurement.

2. Setup Details

• Samples placed inside rigid formers.
• Use of angle iron stiffeners for frame rigidity.
• Setup dimensions in cm (refer IS fig. 8 & 9 for exact layout).

3. Key Symbols & Units (SI Units)

4. Important Formula (Clause 3.1)

• Allowable soil pressure (qa) related to settlement:

  [ q_a = \text{Allowable soil pressure corresponding to 12 mm or 25 mm settlement (tonnes/m}^2) ]

• Dynamic Cone Penetration test relation (Clause 6.2):

  [ q_a = f(N", D, B_c) ]

  where (N") = cumulative blows, (D) = depth, (B_c) = cone diameter.

5. Testing Notes

• Collect known quantity samples for grain size analysis.
• Determine proportion of boulder/gravel in matrix.
• Avoid equipment damage by limiting blows (e.g., stop if blows > 100 for last 30 cm penetration).

Visual Summary: Test Setup Components

graph LR
A[Hydraulic Jack 20T] --> B[Proving Ring 20T]
B --> C[Steel Shear Box]
C --> D[Boulder/Gravel Sample]
D --> E[Steel Plates & Supports]
E --> F[Dial Gauge & Magnetic Holder]
A --> G[Pump & Flexible Pipe]
E --> H[Weights (Steel/

IS 10042: Load Testing of Foundations - Key Points & Formulas

1. Load Test Setup

• Use cast in-situ concrete footing or precast blocks with fresh mortar for perfect soil-block bond.
• Minimum footing size:
  [ \text{Footing size} \geq \max(10 \times \text{average grain size}, 150 \text{ cm}) ]
• Load applied via hydraulic jack (100 tonnes capacity) and dead load platform.

2. Load Application & Measurement

• Deformation measured with 4 dial gauges (0.001 mm accuracy) as per IS 1888-1982.
• Load increments held for minimum 1 hour or until deformation rate ≤ 0.02 mm/min.
• Record deformation at 1, 4, 10, 20, 40, 60 min, then hourly.
• Minimum 8 load increments until 50 mm settlement or failure.

3. Allowable Soil Pressure (Clause 3.1)

• ( q_a ) = allowable soil pressure (tonnes/m²) corresponding to 12 mm or 25 mm settlement.
• ( S_a ) = allowable settlement (cm).
• Use load-settlement curve to determine ( q_a ).

4. Residual Shear Strength (CBT & BBT Tests)

• Residual shear stress ( T_0 ) (tonnes/m²) from Concrete-Boulder Test (CBT) or Boulder Block Test (BBT) are equal.
• Plot shear stress vs displacement to obtain soil strength parameters.

Summary Table: Load Test Parameters

Load-Settlement Curve Illustration

graph LR
A

Interpretation of Test Results (IS 10042 - Clause 7.2.1)

• Proportion Calculation:
  From the known quantity of collected samples and grain size analysis, calculate the overall proportion of boulder/gravel.
  This helps determine if boulder/gravel is part of the matrix or vice versa.

• Key Symbols (Clause 3.1):

  Symbol	Meaning	Unit
  B	Width/side/diameter of foundation	m
  qa	Allowable soil pressure (at 12 or 25 mm settlement)	tonnes/m²
  To	Residual soil strength	tonnes/m²
  Sa	Allowable settlement	cm
  N"	Cumulative blows at depth De	-
  Dc	Depth of penetration	cm
  Bc	Diameter of cone	cm
  Yc	Natural unit weight of soil	tonnes/m³

• Allowable Soil Pressure (qa) Estimation:
  For max grain size ≤ 100 mm, use dynamic cone penetration test results per IS 4968 (Part I) to compute qa.

• Rounding Off Results:
  Final test values should be rounded as per IS 2-1960, matching significant figures of specified values.

Summary Table for Boulder/Gravel Interpretation

Visual Concept: Boulder/Gravel Proportion Decision Flow

flowchart TD
    A[Collect Soil Sample] --> B[Grain Size Analysis]
    B --> C{Calculate Boulder/Gravel Proportion}
    C -->|High Boulder Content| D[Classify as Boulder Matrix]
    C -->|Low Boulder Content| E[Classify as Gravel Matrix]

Note: For detailed test setups and shear stress comparisons, refer to Figures 8, 9, and 10 in IS 10042.

IS 10042: Safety and Excavation Guidelines - Key Points

While IS 10042 primarily focuses on subsurface investigations, key safety and excavation guidelines can be summarized as:

1. Safety in Excavation

• Slope Stability: Ensure excavation slopes are stable based on soil type and depth.
• Shoring/Bracing: Use appropriate shoring to prevent collapse in deep excavations.
• Access: Provide safe means of entry/exit (ladders, ramps).
• Hazard Identification: Check for underground utilities and water ingress.
• Personal Protective Equipment (PPE): Helmets, boots, gloves mandatory.

2. Excavation Specifications

• Excavation Depth: Limited by soil type and groundwater conditions.
• Boulder/Gravel Identification: From Clause 7.2.1, grain size analysis determines boulder/gravel proportions, critical for deciding excavation methods.
• Allowable Soil Pressure (qa): Used for foundation design, linked to settlement criteria (12 mm or 25 mm settlement).

3. Relevant Formula (from Clause 3.1)

[ Sa = \text{allowable settlement (cm)}; \quad B = \text{foundation width (m)} ]

Use cumulative blow counts (N'') and depth (D) from standard charts (Fig. 6 in IS 10042) to assess soil bearing capacity and excavation safety.

Units & Symbols (SI Units)

Summary Diagram: Excavation Safety Workflow

graph TD
  A[Site Assessment] --> B[Soil Sampling & Grain Size Analysis]
  B --> C[Determine Boulder/Gravel Proportion]
  C --> D[Decide Excavation Method & Slope]
  D --> E[Implement Safety Measures]
  E --> F[Excavate with Monitoring]
  F --> G[Foundation Preparation]

Note: For detailed excavation slopes, shoring types, and safety distances, refer to IS 3764 (Safety Code for Excavation Work) and IS 1893 (for seismic considerations).

IS 10042: References and Related Standards - Key Points

1. Related Standards

• IS 2809-1972: Definitions for subsurface investigations for foundations.
• IS 2-1960: Guidelines for rounding off numerical values.
• Central Building Research Institute, Roorkee, contributed to the formulation.

2. Units and Symbols (SI Units)

3. Grain Size Analysis (Clause 7.2.1)

• Determine proportion of boulder/gravel from sample quantity and grain size.
• Use this to decide if boulder/gravel is embedded in matrix or vice versa.

4. Rounding Off (Clause 0.4)

• Follow IS 2-1960 for rounding test/analysis results.
• Maintain the same number of significant digits as specified values.

flowchart TD
    A[Sample Collection] --> B[Grain Size Analysis]
    B --> C{Proportion of Boulder/Gravel}
    C -->|High| D[Boulder in Matrix]
    C -->|Low| E[Matrix in Boulder]

This summary helps ensure compliance with IS 10042 by referencing related standards, units, testing methods, and rounding rules.