Introduction to Hydraulic Structures
Lecture-1
Hydraulic structure
A hydraulic structure is
a structure submerged or partially submerged in any body of water, which
disrupts the natural flow of water. They can be used to divert, disrupt or
completely stop the flow. An example of a hydraulic structure would be a dam,
which slows the normal flow rate of river in order to power turbines. A
hydraulic structure can be built in rivers, a sea, or any body of water where
there is a need for a change in the natural flow of water.
Definition of Seepage
Seepage
refers to the slow movement of water through soil or other porous media under
the influence of gravity or pressure differences. It commonly occurs in dams,
embankments, and foundations, where water infiltrates soil layers. Seepage
plays a critical role in geotechnical engineering as it affects soil stability,
strength, and permeability.
Figure: Seepage
Why Seepage Analysis is Important
·
Ensuring Structural Stability
·
Preventing Erosion and Piping
·
Controlling Groundwater Levels
·
Optimizing Drainage Design
· Understanding Uplift Pressure
Failure of Hydraulic Structures on Pervious
Foundations
Dams, weirs, barrages,
head regulators, cross-drainage works, and other hydraulic structures can be
built on either a pervious or an impervious solid rock base. Such a structure
is susceptible to water seepage beneath it whenever it is built on a pervious
base.
The water flowing beneath
the hydraulic structure threatens its stability and may lead to its failure by-
(i)
Piping
(ii) Direct uplift
Piping
When seepage water keeps
adequate continuing pressure at the downstream end of the structure, it can
elevate soil particles. This results in increased permeability of the soil due
to the gradual erosion of soil beneath the foundation. The structure may
eventually collapse into the void developed, leading to its failure.
Figure: Piping
Direct uplift
The water seeping below
the structure, exerts an uplift pressure on the floor of the structure. If this
pressure is not counterbalanced by the weight of the concrete or masonry floor,
the structure will fail by a rupture of a part of the floor.
Figure: Uplift Force
Seepage Theories
Generally, Three Seepage Theories
1.
Bligh's Creep Theory
2.
Lane’s Weighted Creep theory
3.
Khosla’s Theory