What is this code's primary purpose?

To design hydraulic structures (weirs, barrages) on sandy foundations to be safe against failure from subsurface water flow (seepage).

What is the most critical check in this code?

Ensuring the exit gradient at the downstream end is less than the safe exit gradient for the foundation soil to prevent piping failure (Clause 5.2).

What theory is this code based on?

It is primarily based on Khosla's theory of subsurface flow, which calculates uplift pressures under the structure (Annex A).

What is a safe exit gradient for fine sand?

Between 1/7 and 1/6, as per Table 1.

Does this code cover dam design?

No, this code is for weirs and barrages on permeable foundations. For dam design, refer to codes like IS 6512 (Gravity Dams) or IS 1893 Part 5 (Seismic Design of Dams).

IS 15632

: 2015

Criteria for Seismic Design of Hydraulic Structures

CurrentSpecializedCode of PracticeBIMWater Resources · Irrigation and Canal Structures

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This code provides design criteria for hydraulic structures like weirs and barrages founded on permeable soil. It focuses on analyzing and controlling subsurface seepage to ensure safety against uplift pressure and piping failure, primarily using Khosla's theory of seepage flow. Note: This code does NOT cover seismic design.

Lays down criteria for the seismic analysis and design of various hydraulic structures.

Quick Reference Values

Safe exit gradient for fine sand/silt1/7 to 1/6

Safe exit gradient for coarse sand1/6 to 1/5

Safe exit gradient for shingle1/5 to 1/4

Recommended factor of safety for floor thickness against uplift1.33 (or 4/3)

Key Formulas

Exit Gradient GE = (H/d) * (1 / (π * sqrt(λ))) — Khosla's formula for exit gradient at the downstream end of a simple floor.

Floor Thickness t = h / (G-1) — Basic formula to calculate floor thickness required to balance uplift pressure 'h' by its submerged weight (G=sp. gravity of material).

Practical Notes

The user's provided title 'Criteria for Seismic Design of Hydraulic Structures' is incorrect for this code. IS 15632 deals with seepage below hydraulic structures, not seismic design. For seismic design, refer to IS 1893 (Part 5).

Khosla's theory (Annex A) is the cornerstone of this standard and requires careful application of correction factors for mutual interference of piles, floor thickness, and slope.

Determining the safe exit gradient (Table 1) is critical, but it relies on accurate soil classification, which is often a major source of uncertainty in design.