JNTU B.Tech III EARTH AND ROCKFILL DAMS AND SLOPE STABILITY Previous Question Paper (August - 2022 - R16)

An earthen dam is a structure constructed primarily of compacted soil, sand, gravel, or rock fragments. It relies on its own weight to resist the forces exerted by the reservoir water and is designed with an impermeable core or upstream facing to prevent excessive seepage.

Earthen dams are preferred under the following circumstances:

• When the foundation material is relatively weak or compressible, as the dam can accommodate minor settlements better than rigid concrete structures.
• When suitable construction materials like soil, sand, and gravel are locally available in abundance, significantly reducing transportation costs.
• In regions where the seismic activity is high, as earthen dams possess inherent flexibility and can withstand ground vibrations more effectively.
• When the site topography is broad and the valley is wide, making the construction of a gravity dam economically unfeasible.

Earthen dams are classified based on their cross-sectional composition and the method of construction:

1. Homogeneous Embankment Dam: Constructed entirely of a single type of soil material. It is suitable for low-height dams where the soil is sufficiently impervious.
2. Zoned Embankment Dam: Composed of a central impervious core (clay) to prevent seepage, flanked by shells of more pervious material (sand/gravel) to provide structural stability and drainage.
3. Diaphragm Type Dam: Features a thin central core or diaphragm made of concrete, steel, or timber, supported by an embankment of pervious soil or rockfill.

Sketch descriptions:

• Homogeneous: A simple trapezoidal section with a uniform material composition throughout.
• Zoned: A trapezoidal section with a distinct vertical or inclined central clay core, surrounded by filter zones and outer shells of rock or gravel.
• Diaphragm: A trapezoidal embankment with a thin, vertical, impermeable membrane (the diaphragm) extending from the crest to the foundation.