This article will be limited to dam failures attributable to foundation erosion which is often
first obvious at the downstream of the dam. An earth dam is a retaining structure that
allows inflow but conditionally prevents outflow of water current. It gathers water from
water tributaries or rainfall, that creates a water reservoir which increases in depth as the
inflow continues. The lateral and static pressures exerted by the reservoir could cause
dam failures due to some probable reasons.
The failure is mainly because the induced pore pressure and stresses are not adequately
taken care of, probably due to faulty design or improper construction where the design is
responsive. A faulty design cannot be remedied even by quality construction unless the
design deficits are corrected. Therefore, an investigation of a failed earth damn must start
with critiquing the design before probing the adopted construction methods and
materials’ quality.
The article focuses on the design aspect of a failed earth dam caused by internal erosion
within the dam especially at the foundation. The volume of the water flow at the
foundation is dependent on the height of the water reservoir retained by the earth dam.
The flow does not adversely affect the dam’s structural stability if the induced upward
pore pressure cannot lift up the soil layers above it. Therefore, the design should be such
that the upward pore pressure is limited within safe limits even when the reservoir is at
the highest level.
The safety measures may include using a water proofing geomembrane at the foundation
of the dam that spans upstream away from the earth embankment. This could be a HDPE
geomembrane sandwiched between two layers of geotextiles that provide protection to
the geomembrane.
The geotextile underlay may be the woven type for additional foundation reinforcement
to limit the foundation settlements, while the geotextile above the geomembrane could
be a carefully selected nonwoven geotextile to relieve the geomembrane of damages
from tensile stresses.
The hybrid-geomembrane elongates the flow-nets underneath the earth dam, thereby,
decreasing the upward pore pressures at the downstream of the dam. Depending on the
heights of the earth dam and the retained water reservoir, and the nature of the
foundation soil, it might be necessary to provide a toe-drain at the downstream.
An appropriate nonwoven geotextile may be used to line a trench containing well
arranged stones of suitable sizes to form the toe-drain that traps the underground water
flow from the reservoir, to prevent possible foundation piping. The geotextile’s primary
function is to prevent the migration of the foundation soil particles into the trench to
prevent the undesirable erosion that could lead to the dam failure.
Gabions Geomembrane & Geotextile Limited is a professional company based at
Kaduna-Nigeria that imports and sells geosynthetics within Nigeria and West African
Subregion. The materials include, both woven and nowoven geotextiles, HDPE
geomembranes, hybrid waterproofing geomembranes, geogrids, geomats, erosion
control blankets, geo-drains, geocells, in addition to gabions and reno-mattresses.
We recognise and pursue ours’ customers’ interests by offering high quality materials
made with virgin materials at highly competitive prices and giving free professional advice
to our clients and customers. Contact us at Gabions Geomembrane & Geotextile Ltd
at Kaduna – Nigeria. +234 703 784 5174 & 08020657472
[email protected]
