IS 3955 : 1967Code of Practice for Design and Construction of Well Foundations

IS 3955:1967 is the code of practice for design and construction of well foundations — the large-diameter sunk caisson ('well') foundations used for major bridge piers and abutments, jetties and heavy structures, especially in rivers with deep scour. It is the foundational code for the dominant Indian bridge-pier foundation type.

It is read with the bridge-foundation stack:

• IRC 78 — road-bridge foundations & substructures (well foundations — the primary bridge code) · IRC 45 — soil resistance below scour
• IRC 5 / IRC 6 — bridge general features / loads · IS 456 — RCC steining/curb/plug
• IS 2911 — pile foundations (the alternative deep foundation) · IS 6403 / IS 1888 — bearing capacity / plate-load

A well is a hollow RCC/masonry shaft (the steining) with a cutting curb at the bottom; it is sunk by excavating (dredging) inside it until it founds on firm strata well below the maximum scour level, then sealed with a bottom plug and filled. IS 3955 governs:

• Founding depth / grip length: the well must go deep enough below max scour that the soil below provides the required vertical capacity *and* lateral (transverse) resistance against the worst horizontal loads (water current, braking, wind, seismic) — the lateral check (read with IRC 45) often governs the depth
• Steining design: thickness for sinking stresses + service loads; curb & cutting edge designed to take sinking and bottom-plugging
• Sinking: controlled, plumb, with provision for tilt and shift correction (the dominant construction problem) and for sand-blowing/kentledge/jetting
• Bottom plug, top plug, well cap transferring pier load into the steining
• Stability checks: against the worst load combination — bearing, sliding, overturning, and the elastic/ultimate lateral-resistance method

The key point: a well is **designed for the *scoured* condition** (river bed at max scour, full lateral load), not the as-built bed level.

Scenario: a well foundation for a river-bridge pier.

Step 1 — max scour: compute the design maximum scour level (per IRC 78/IRC 5 hydraulics) — the well is designed as if the bed is at this level.

Step 2 — grip: set the founding level so there is adequate grip length below max scour in firm strata for both vertical bearing and lateral resistance.

Step 3 — lateral resistance (IRC 45): check the soil resistance below scour against the worst transverse load (current + braking + wind/seismic) — this lateral/stability check frequently dictates the depth, not bearing.

Step 4 — steining: thickness for sinking stresses + service; curb designed for sinking & plugging; check the well as a deep elastic member.

Step 5 — sinking provision: plumbness control with tilt/shift limits & correction methods designed in; bottom plug, top plug and well cap detailed.

Result: a foundation safe in the *scoured, fully-laterally-loaded* state — the condition that actually governs bridge-foundation safety, not the placid as-built river.

1. Designing for the as-built bed, not max scour. The governing condition is the *scoured* river with full lateral load — under-gripping below max scour is the classic, dangerous error.

2. Bearing-only design, ignoring lateral resistance. Well depth is often governed by lateral stability below scour (IRC 45), not vertical bearing — checking bearing alone under-designs the grip.

3. No tilt-and-shift provision. Tilt/shift during sinking is the dominant construction problem; not designing limits and correction methods leads to out-of-tolerance, hard-to-rectify wells.

4. Under-designed curb/steining for sinking stresses. The well must survive *sinking* (and dredging/blowing) stresses, not just service loads.

5. Ignoring the IRC framework. Road-bridge wells are governed by IRC 78/IRC 5/IRC 6 + IRC 45 (loads, scour, soil resistance); IS 3955 is the construction-practice companion, not a standalone.

• IRC 78 — foundations & substructure of road bridges (primary) · IRC 45 — soil resistance below max scour
• IRC 5 / IRC 6 — bridge general features / loads · IRC 6 — loads & stresses
• IS 456 — RCC steining / curb / plug / well cap
• IS 2911 — pile foundations (alternative) · IS 6403 / IS 1888 — bearing capacity / plate-load
• [IS 3955]/(IS 9527) — caisson / cofferdam references

IS 3955 is old (1967) and reaffirmed; in current bridge practice the governing codes are the IRC series (IRC 78 for foundations, IRC 5/6 for hydraulics & loads, IRC 45 for soil resistance below scour), with IS 3955 used as the construction-practice reference for sinking. Well foundations remain the workhorse for major Indian river bridges precisely because they perform well under deep scour where piles are vulnerable.

The practitioner essentials never change: design for the maximum-scour, fully-laterally-loaded condition, let the lateral-resistance/grip check (IRC 45) drive the depth, design the steining and curb for sinking stresses, and build tilt-and-shift limits and correction methods into the construction plan — sinking control, not the static calculation, is where well foundations succeed or fail in practice. Read it inside the IRC framework, not as a standalone IS document.