--- title: "Seepage control measures in embankment dam" subject: "Hydropower Engineering" chapter: 4 key: "semester_7/hydropower_engineering:embankment-seepage-control-measures" source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/embankment-seepage-control-measures site: BCT Engineering --- # Seepage control measures in embankment dam Hydropower Engineering · Chapter 4: Headworks of Storage Plants - Asked in: 2071 Chaitra, 6 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/embankment-seepage-control-measures - Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-4 ## Question Show with neat sketches various seepage control measures in an embankment dam. ## Short answer Seepage through the dam body is controlled by a central or inclined impervious core, chimney filter, blanket drain and toe drain. Foundation seepage is reduced by a cut-off trench, sheet piles or grout curtain, upstream impervious blanket, relief wells and a downstream loaded filter berm. ## Answer Seepage through and under an embankment dam is controlled to reduce water loss, keep the phreatic line inside the section, and keep the exit gradient below the critical value. The usual measures are shown below. #### 1. Control of seepage through the embankment body ```text (a) Central impervious core (b) Inclined core | core | \ core ___|_______|___ ____\____________ / | clay | \ / \ \ / shell| |shell\ / shell \ shell \ ``` The core of clay (or an asphalt/concrete membrane on the u/s face) reduces the flow, while the pervious shells give stability. ```text (c) Toe drain (d) Horizontal blanket drain ___________ __________________ / \ / \ / phreatic \__ /____________________\ /_____________ ▒▒| ==== sand-gravel blanket ==== toe drain (rock toe) ``` ```text (e) Chimney drain + blanket ____ / | \ vertical (chimney) filter / |▒ \ connected to a horizontal blanket /____|▒▒▒\_____ drain ``` Toe, blanket and chimney drains collect seepage and carry it safely out, lowering the phreatic line; they are protected by graded filters. #### 2. Control of seepage under the foundation ```text (f) Cut-off trench (g) Sheet pile / grout curtain _______________ _______________ / \ / \ /_________________\ /_________________\ ==pervious===|||== ==pervious== | | | == =====clay====|||======= ======= grout holes == (to impervious layer) (rock / alluvium) ``` ```text (h) Upstream impervious blanket (i) Relief wells at toe ____blanket_____/\_______________ ______________ clay laid on bed, / dam \ / dam \ lengthens seepage path /______ O O O __\ ====== pervious foundation ==== wells relieve uplift ``` - **Cut-off trench** filled with compacted clay: the best if it reaches the impervious layer (positive cut-off). - **Sheet piles / grout curtain / diaphragm wall** when the pervious layer is deep (partial cut-off). - **Upstream blanket** increases the length of the seepage path (as in Bligh's creep theory) and so reduces the exit gradient. - **Relief wells** and a **d/s berm** (weighted filter) release the uplift pressure at the toe and prevent boiling. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does the impervious core do? A. Reduces flow through the dam while the pervious shells give stability B. Increases seepage C. Acts only as slope protection D. Relieves uplift at the toe Answer: A. The clay core cuts the flow, and the shells provide stability. (Key point: Core function) 2. Toe, blanket and chimney drains serve to A. Lengthen the seepage path B. Collect seepage and carry it out safely, lowering the phreatic line C. Increase pore pressure D. Protect the u/s face from waves Answer: B. They drain seepage, protected by graded filters. (Key point: Toe/chimney drains) 3. An upstream impervious blanket reduces exit gradient by A. Increasing weight at the toe B. Cutting through the foundation C. Lengthening the seepage path D. Draining the reservoir Answer: C. A longer creep path means less head loss gradient at exit. (Key point: Upstream blanket) 4. A positive cut-off trench is the best when A. The pervious layer is very deep B. It reaches the impervious layer C. It is made of sand D. It is placed at the toe only Answer: B. A trench reaching the impervious layer stops foundation seepage; deeper layers need partial cut-offs. (Key point: Positive cut-off) ## Related in Hydropower Engineering - [Seepage under embankment dam on pervious foundation](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aseepage-pervious-foundation-consequences) — Hydropower Engineering, chapter 4 - [Seepage through dam with central core (45 m dam)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aearthen-dam-impervious-core-seepage-2075c) — Hydropower Engineering, chapter 4 - [Design criteria of earthen embankment dam](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aearthen-dam-design-criteria) — Hydropower Engineering, chapter 4 - [Seepage line for 22 m high earthen dam](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aearthen-dam-seepage-line-22m-45deg) — Hydropower Engineering, chapter 4 - [Seepage discharge through dam body (k = 1×10⁻⁶ m/s)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aearthen-dam-seepage-gradient-figure-2072k) — Hydropower Engineering, chapter 4 - [Seepage through dam with central core (33 m dam)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aearthen-dam-impervious-core-seepage-2070c) — Hydropower Engineering, chapter 4 ## Related in other subjects - [Control of sub-surface water and seepage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Asubsurface-drainage-measures) — Transportation Engineering I, chapter 4, asked 15× - [Steady 2D model: seepage under a dam](https://www.bctengineer.com/question.md?key=semester_8%2Fcomputational_techniques_in_civil_engineering%3Aseepage-under-dam-2d-model) — Computational Techniques in Civil Engineering, chapter 7, asked 3× - [Earth dam with filter, seepage quantity](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aearth-dam-horizontal-filter-seepage) — Soil Mechanics, chapter 7 - [Impervious dam seepage discharge](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aimpervious-dam-seepage-discharge-numerical) — Soil Mechanics, chapter 7