Hydraulic Structures: Fourth Edition

Table 2.4 Embankment dam defect mechanisms and preventive measuresDefect

Characteristics

Causes

Preventive–corrective measures

ExternalOvertopping

Flow over dam and

Inadequate spillway

Adequate spillway capacity and

possible washout;

and/or freeboard

initial freeboard, and/or

less cohesive soils

reinforced grass surface to slope

most at risk; mostserious if localized

Settlement reducing

Restoration of settlement; crest

freeboard; spillway

protection; good maintenance

obstructed

Wave erosion

Damage to

Face protection

Proper design and maintenance

upstream face

disturbed or

and shoulder

damaged

Toe erosion

Flood discharge

Spillway channel badly

Good hydraulic design; training

damaging toe

designed and/or located

walls

Gullying

Local concentrated

Poor surface drainage

Vegetation, surface

erosion of downstream

reinforcement

face by precipitation

and/or drainage

Internal seepageLoss of water

Increased seepage

Pervious dam and/or

Cut-off and core grouting

loss and/or irregularities

foundation;

in phreatic surface;

cut-off inadequate

soft spots on slopes or

Internal cracking

Careful design; grouting

downstream

Seepage erosion

Turbid seepage through

Internal cracking

Internal drainage; filters; careful

(concealed

drainage system

zoning of fill

internal erosion)

Leakage along

Detail design; use of collars;

perimeter of

grouting

culverts, tunnels,pipework etc.

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