IS 11550 : 1985Code of practice for field instrumentation of swelling pressure in expansive souls code of practice for field instrumentation of swelling pressure in expansive soils
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IS 11550:1985 is the Indian Standard (BIS) for field instrumentation of swelling pressure in expansive souls code of practice for field instrumentation of swelling pressure in expansive soils. This standard specifies the in-situ method for determining the swelling pressure of expansive soils using field instrumentation. It covers the apparatus, installation procedure, and the method for observing and calculating the pressure exerted by the soil upon wetting.
Code of practice for field instrumentation of swelling pressure in expansive souls code of practice for field instrumentation of swelling pressure in expansive soils
! Ensuring complete saturation of the soil surrounding the instrument is critical for obtaining the maximum swelling pressure, which may require a dedicated water supply system at the test location.
! The reaction frame must be sufficiently rigid and anchored well outside the zone of soil influence to provide a stable reference point against the upward soil pressure.
! Installation must be done with minimal disturbance to the natural soil structure to get results representative of in-situ conditions.
ISO 18674-5:2017International Organization for Standardization (ISO), International
HighCurrent
Geotechnical monitoring by field instrumentation — Part 5: Stress-change measurements by total pressure cells (TPC)
Covers the field use of total pressure cells to measure stress changes, which is the exact instrumentation used for swelling pressure.
BS EN ISO 18674-5:2017British Standards Institution (BSI), United Kingdom
HighCurrent
Geotechnical monitoring by field instrumentation. Stress-change measurements by total pressure cells (TPC)
The British and European adoption of ISO 18674-5, covering the same scope of field pressure cell instrumentation.
ASTM D4546-21American Society for Testing and Materials (ASTM), USA
LowCurrent
Standard Test Methods for One-Dimensional Swell or Settlement Potential of Cohesive Soils
Measures the same phenomenon (swelling pressure) but in a controlled laboratory environment, not with field instrumentation.
Key Differences
≠IS 11550 is a specific code of practice for measuring swelling pressure in expansive soils, while ISO 18674-5 is a general standard for using total pressure cells for any type of stress-change measurement in soil or rock.
≠The Indian standard from 1985 describes older technologies like hydraulic and pneumatic cells, whereas the modern ISO 18674-5 (2017) is more aligned with current technologies like vibrating wire sensors and provides detailed guidance on electronic data acquisition.
≠ISO 18674-5 provides more rigorous and quantitative requirements for instrument characteristics, calibration, data processing, and reporting (including uncertainty analysis) compared to the more qualitative guidance in IS 11550.
≠IS 11550 is a standalone document, whereas ISO 18674-5 is part of a comprehensive series (ISO 18674) on geotechnical monitoring, which provides a more integrated framework for planning and execution of monitoring programs.
Key Similarities
≈Both standards are based on the fundamental principle of using a diaphragm-based total pressure cell (earth pressure cell) to measure the normal stress exerted by the surrounding soil.
≈Both IS 11550 and ISO 18674-5 emphasize the critical importance of proper installation, ensuring intimate contact between the pressure cell and the soil to obtain meaningful data.
≈The recommended installation procedures are conceptually similar, with both standards describing methods for placement in boreholes or trenches and the use of a grout or sand backfill to fill voids.
≈Both codes recognize the importance of laboratory calibration of the pressure cells over their intended operational range before field installation.
Parameter Comparison
Parameter
IS Value
International
Source
Cell Aspect Ratio (Diameter/Thickness)
Should generally be more than 5.
Desirable to have an aspect ratio > 5, and preferably > 10.
ISO 18674-5:2017
Guidance on Cell Stiffness
Qualitative: 'The cell should be sufficiently stiff so that its own compression is negligible.'
Quantitative: Provides formulae in Annex B to assess the measurement error related to the relative stiffness of the cell and the ground.
ISO 18674-5:2017
Borehole Clearance During Installation
The diameter of the borehole should be about 25 mm larger than the cell diameter.
Clearance should be as small as possible, typically 10 mm to 25 mm on the diameter.
ISO 18674-5:2017
Backfill Material for Borehole Installation
Grout (cement-bentonite) or sand-bentonite mixture with properties matching the surrounding soil.
Grout or compacted sand with mechanical properties (stiffness) as close as possible to the surrounding ground.
ISO 18674-5:2017
Baseline Reading
Initial readings should be taken as soon as the installation is completed.
A set of base readings shall be taken after installation is complete and the system has stabilized, before expected stress changes occur.
ISO 18674-5:2017
Instrument Range
The range of the cell should be adequate to cover the anticipated maximum swelling pressure.
The measuring range of the total pressure cell shall be selected to cover the range of expected total stresses.
ISO 18674-5:2017
⚠ Verify details from original standards before use
Key Values3
Quick Reference Values
Initial seating pressure on cell5 to 10 kPa
Minimum diameter of bearing plate150 mm
Typical observation periodUntil pressure stabilizes (several days to weeks)
Key Formulas
Swelling Pressure (p_s) = P / A; where P is the maximum force recorded by the load cell and A is the area of the bearing plate.
To provide a standardized field procedure for measuring the maximum upward pressure exerted by expansive soils when they get wet.
What is the main apparatus required for this test?+
A swelling pressure cell (a type of load cell), a reaction frame, and a data recording unit. (Clause 3)
Is this a laboratory test or a field test?+
This is a code of practice for field instrumentation, meaning the test is performed on-site (in-situ) within a borehole or test pit.
How long does the test take?+
Observations are continued until the swelling pressure reading stabilizes, which can take from several days to several weeks depending on the soil's permeability.