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IS 3955:1967 is the Indian Standard (BIS) for design and construction of well foundations. Provides comprehensive guidelines for the design and construction of well foundations, primarily used for bridges and heavy structures across riverbeds. It covers the estimation of scour depth, design of well components like steining and bottom plug, and safe sinking practices including pneumatic methods and tilt/shift limits.
Lays down provisions for the design and construction of well foundations, commonly used for major bridges, covering sinking, and founding levels.
! Continuous monitoring of tilts and shifts is critical during the open dredging/sinking process to ensure they do not exceed the 1-in-80 and 150mm limits.
! Kentledge loading must be applied symmetrically to prevent eccentric stresses and unwanted tilting during well sinking.
! The bottom plug must be designed and cast underwater carefully to resist upward hydrostatic pressure before the well can be safely dewatered.
Section 10 (Foundations) provides detailed LRFD-based design guidance for caissons.
EN 1997-1:2004+A1:2013European Committee for Standardization (CEN), Europe
MediumCurrent
Eurocode 7: Geotechnical design - Part 1: General rules
Covers Limit State Design principles for deep foundations, including piers and caissons.
JRA S-HB-V4 (2017)Japan Road Association (JRA), Japan
HighCurrent
Specifications for Highway Bridges, Part IV: Substructures
Provides comprehensive and specific design and construction rules for caisson foundations.
BS 8004:2015+A1:2020British Standards Institution (BSI), UK
MediumCurrent
Code of practice for foundations
Offers practical guidance on the design and construction of caissons, as a supplement to Eurocode 7.
Key Differences
≠IS 3955 is based on the Working Stress Method (WSM) using a single global factor of safety, while modern standards like AASHTO LRFD and Eurocode 7 use Limit State Design (LSD) with partial safety factors on loads (actions) and material/geotechnical resistances.
≠The seismic design provisions in the 1967 IS code are rudimentary (static coefficient method). Modern codes (AASHTO, JRA) require sophisticated dynamic analysis, capacity design principles, and ductility detailing for seismic performance.
≠IS 3955 provides general guidance for scour depth. In contrast, AASHTO LRFD mandates a detailed hydraulic analysis based on FHWA HEC-18 to determine total scour (local, contraction, and long-term degradation) for various flood return periods.
≠Material and durability specifications are less stringent in IS 3955. Modern codes specify higher-performance concrete, detailed requirements for concrete cover based on environmental exposure, and strict crack width control for enhanced durability and service life.
Key Similarities
≈All standards address the same fundamental load combinations, including vertical loads (dead/live), lateral loads (earth pressure, water current, wind, seismic), and their resulting moments on the foundation.
≈The fundamental geotechnical stability checks against bearing capacity failure, sliding, and overturning are a common basis for design in both IS 3955 and its international counterparts.
≈The contribution of skin friction along the vertical sides of the well to its overall capacity and stability is a recognized and integral component of design in all relevant standards.
≈All codes recognize the critical importance of controlling the well's position during sinking and provide prescriptive or performance-based limits on permissible tilt and horizontal shift.
Parameter Comparison
Parameter
IS Value
International
Source
Design Philosophy
Working Stress Method (WSM)
Limit State Design (LSD) / Load and Resistance Factor Design (LRFD)
AASHTO LRFD / EN 1997-1
Geotechnical Bearing Resistance Factor
A global Factor of Safety of ~2.5 is used on ultimate capacity.
A resistance factor (φ) of 0.50-0.65 is applied to nominal bearing resistance.
AASHTO LRFD BDS-9
Allowable Construction Tilt
Prescribed as 1 in 100.
No single value; effects of tilt must be included in structural analysis. Often limited to 1% to 1.5% by state agencies.
AASHTO LRFD (General Practice)
Minimum Concrete Grade (Steining)
M15 (15 MPa cube strength); M20/M25 in modern practice.
Min. f'c = 4000 psi (approx. 28 MPa cylinder strength) for caissons in aggressive environments.
AASHTO LRFD BDS-9
Bottom Plug Thickness
Minimum thickness not less than half the dredge hole diameter.
Designed to resist hydrostatic uplift and arching soil/rock pressures; typically 3-5 ft (0.9-1.5m) or as per analysis.
FHWA-NHI-10-016 (Drilled Shafts)
Grip Length below Scour Level
Minimum of 1.2m to 2.0m below calculated max scour level (as per related IRC:78 code).
No prescriptive value; foundation base must be below total scour elevation and have adequate capacity for the scoured condition.
AASHTO LRFD
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Permissible tilt during sinking1 in 80
Permissible shift during sinking150 mm
Minimum vertical reinforcement in steining0.12% of gross cross-sectional area
Minimum hoop reinforcement in steining0.04% of gross volume
Key Formulas
d = 0.473 * (Q/f)^(1/3) — Normal depth of scour using Lacey's formula
What are the acceptable limits for tilt and shift in a well foundation?+
Generally, tilt is restricted to 1 in 80 and shift to 150 mm, as specified in Clause 5.5.
How is the thickness of the steining determined?+
It must provide sufficient self-weight for sinking by overcoming skin friction, and withstand structural stresses during the sinking process and service life (Clause 4.5).
What is the purpose of the bottom plug?+
It acts as an inverted dome to transfer the foundation load to the soil and resists the upward hydrostatic pressure, allowing the well to be dewatered safely (Clause 4.8).