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IS 11568:1986 is the Indian Standard (BIS) for criteria for design of protective filters for hydraulic structures. This standard provides design criteria for protective granular filters in hydraulic structures like dams and weirs. Its primary purpose is to prevent internal erosion (piping) of fine soil particles due to seepage, while simultaneously allowing water to drain freely to relieve pore pressure. The design is based on specific ratios between the particle sizes of the filter material and the base soil being protected.
Lays down criteria for the design of granular filters to protect hydraulic structures from piping and erosion.
! The criteria are primarily for cohesionless base soils. Dispersive clay soils require special investigation and cannot be designed for using these criteria alone.
! Ensure filter materials are clean, hard, durable, and free from organic matter. The particles should be rounded rather than angular.
! For critical structures or non-uniform base soils, constructing a graded filter with multiple layers may be necessary to satisfy the criteria between each layer.
Dedicated chapter covering granular filter design for embankment dams, very closely related.
CIRIA C750CIRIA (Construction Industry Research and Information Association), UK
MediumCurrent
Groundwater control: design and practice (2nd edition)
Provides guidance on filter design for dewatering systems, including granular and geotextile filters.
ICOLD Bulletin 95International Commission on Large Dams (ICOLD)
HighCurrent
Embankment Dams, Granular Filters and Drains
International bulletin focused specifically on the design and performance of filters and drains in dams.
Key Differences
≠IS 11568:1986 primarily covers granular filters, whereas modern international standards like USACE EM 1110-2-1901 and CIRIA C750 provide extensive, specific design criteria for geotextile filters, including requirements for apparent opening size (AOS) and permeability.
≠International standards offer more detailed and separate criteria for base soils that are broadly-graded, gap-graded, or cohesive. For example, USACE requires designing the filter based on the finer fraction of broadly-graded base materials.
≠Modern international standards place a stronger emphasis on ensuring the internal stability of the filter material itself to prevent segregation and internal erosion. They often specify limits on the filter's coefficient of uniformity (Cu) or require gradation curves to be smooth and without gaps.
≠The Indian standard provides a single upper limit on the permeability ratio (D15F/D15B ≤ 20), whereas international practice often controls this indirectly through requirements for gradation curve parallelism and internal stability, rather than a fixed ratio.
Key Similarities
≈All standards are fundamentally based on the Terzaghi retention criteria, using a ratio of the filter's D15 size to the base's D85 size (D15F/D85B) to prevent the migration of base soil particles.
≈A core principle across all standards is that the filter must be significantly more permeable than the base soil, which is universally assessed using a minimum ratio of the D15 particle sizes of the filter and base (D15F/D15B).
≈There is a common requirement to strictly limit the percentage of fines (material passing the 0.075 mm / No. 200 sieve) in the filter material, typically to less than 5%, to ensure long-term permeability.
≈Both IS 11568 and its international counterparts mandate that any fines present in the filter material must be non-cohesive and non-plastic to prevent clogging and ensure drainage performance.
Parameter Comparison
Parameter
IS Value
International
Source
Filter Retention (Piping Prevention)
D15(Filter) / D85(Base) ≤ 5
D15(Filter) / D85(Base) < 5
USACE EM 1110-2-1901
Permeability Requirement
4 ≤ D15(Filter) / D15(Base) ≤ 20
D15(Filter) / D15(Base) ≥ 5
USACE EM 1110-2-1901
Fines Content in Filter Material
Material passing 75 micron sieve should be less than 5%
Material passing No. 200 sieve (0.075 mm) must be < 5%, and be non-plastic (PI=0)
USACE EM 1110-2-1901
Secondary Uniformity Ratio
D50(Filter) / D50(Base) ≤ 25
5 ≤ D50(Filter) / D50(Base) ≤ 40
USBR DS-13(5)
Maximum Particle Size in Filter
Generally less than 75 mm
Typically less than 3 inches (76 mm) and must be less than 1/3 of the filter layer thickness
USBR DS-13(5)
Internal Stability of Filter
Not explicitly defined with a separate criterion.
Coefficient of Uniformity (Cu = D60/D10) of the filter should be less than 20.
USBR DS-13(5)
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Piping (retention) ratio D15(filter)/D85(base)<= 5
Permeability ratio D15(filter)/D15(base)4 to 20
Uniformity ratio D50(filter)/D50(base)<= 25
Max fines (<75 micron) in filter material5%
Maximum particle size in filter75 mm
Filter opening size to prevent movement of uniform grain size base materialD85 (base)
Key Formulas
D15(F) / D85(B) ≤ 5 — Retention (Piping) Criterion: Prevents base material from entering the filter.
4 ≤ D15(F) / D15(B) ≤ 20 — Permeability Criterion: Ensures filter is permeable enough to allow drainage.
D50(F) / D50(B) ≤ 25 — Uniformity Criterion: Ensures filter and base gradations are not excessively different.
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 3 - Functions of a Filter
Clause 4 - Requirements of Filter Material
Clause 4.1 - Piping Requirement
Clause 4.2 - Permeability Requirement
Clause 6 - Filter Design for Cohesionless Base Material
Clause 7 - Graded Filter
Frequently Asked Questions4
What is the main function of a filter in a hydraulic structure?+
To allow water to pass freely while preventing the movement of soil particles from the base material, thus preventing internal erosion (piping) and ensuring structural stability.
What is the piping or retention criterion for a filter?+
The ratio D15 of the filter to D85 of the base material should be less than or equal to 5. This ensures the filter pores are small enough to retain the particles of the base soil.
What is the permeability criterion for a filter?+
The ratio D15 of the filter to D15 of the base material should be between 4 and 20. This ensures the filter is sufficiently more permeable than the base soil for effective drainage.
Can these criteria be used for designing geotextile filters?+
No, this standard is for granular filters. Geotextile filter design follows different principles based on Apparent Opening Size (AOS) and permeability, often covered in codes like IS 11057.