Control of seepage, internal erosion and piping for embankment dams - Geotechnical Engineering of Dams - page 426

Table 10.6. Influence of factors on the likelihood of a concentrated leak - high permeability zone (Foster

and Fell, 2000).

Influence on likelihood of a high permeability zone

Factor More likely Neutral Less likely

Compaction Poorly compacted, 95% standard 95-98% standard Well compacted, 98%

compaction density ratio (1) density ratio compaction standard compaction

density ratio density ratio

Compaction Dry of standard optimum water Approx Optimum or wet of

water content content (approx. OWC-3%) OWC-1% to standard optimum

OWC-2% water content

General quality Poor clean up after wet, dry or Removal of dried, wet or

of construction frozen periods during construction frozen layers before

No engineering supervision of resuming construction

construction Good engineering

supervision

Instrumentation Poor compaction around No instrumentation in

details instrumentation, particularly if the core

pass through the core

Characteristics Large variability of materials in Low variability of

of core borrow area, moisture content, materials in borrow areas

materials conditioning and grain size Low shrinkage potential

Core materials susceptible to Narrow grading

shrinkage cracks due to drying.
Widely graded core materials
susceptible to segregation

Notes: (1)

93% Standard, dry of OWC, much more likely.

Table 10.7. Influence of factors on the likelihood of a concentrated leak associated with a conduit (Foster

and Fell, 2000).

Influence on likelihood of concentrated leak

Factor Much more likely More likely Neutral Less likely

Conduit Masonry, brick Steel, cast iron, Cast iron, concrete Concrete encased

type (1)

Corrugated steel not encased encased steel

Concrete precast Concrete cast in-situ

Conduit Open joints, or Open joints High quality joints, High quality

joints (1) cracks signs of “open” up to 5 mm joints, no openings,

erosion but with waterstops waterstops

Pipe Old, corroded cast Old cast iron, New steel with

corrosion (1) iron or steel steel corrosion protection

Conduit Significant settlement Some settlement, Little or no

details (1) or deep compressible shallow settlement or rock

foundation soils compressible foundation

Junction with shaft foundation soils

in embankment

Conduit trench Narrow, deep, near Medium depth, Wide, side slopes Trench totally in

details (2) vertical sides. Vertical width, slope. flatter than 1 H:1 V rock, backfilled

sides, trench in soil Excavated with concrete

(backfilled with through dam

concrete)

Notes:

(1) Conduit type, joints, corrosion and details mostly affect piping into the conduit.
(2) Conduit trench details mostly affect piping along the conduit.