Civil Engineering Reference
In-Depth Information
(1984)
A 1250 m (410 ft) long, 30 m (100 ft) high zone-filled earth embankment was being
constructed as part of a water storage reservoir for the Severn-Trent Water Authority
to regulate flows in the River Derwent in England. The reservoir was designed so that
water would be diverted through a 10 km (6 mile) long tunnel during the winter and
stored in the reservoir with an estimated capacity of 35 million cu m (46 million cubic
yards). Water would be released from the reservoir when the water level in the river
was low.
The central clay core of the embankment connected to a shallow trench that
was excavated upstream of the centerline into the weathered gray foundation mud
stone. A grout curtain extended below the base of the trench. Fill in the upstream and
downstream shells was classified as Type I and Type II. The Type I fill, used
immediately upstream and downstream of the clay core, was described as a yellow-
brown mottled clay with mud stone peas < 5 mm (0.2
in.) and pebbles. The Type II
soil specified for the outer portions of the shells was to be the same general type of
material as Type I, but without pebbles.
Construction of the embankment began in July, 1982 and reached a height of
about 6 m (20 ft) at the end of the construction in late October. Construction during
the second year between April and October added an additional 15 m (50 ft) to the
embankment. Placement of an additional 4 m (13 ft) of fill took place in the two
months preceding the failure. Tension cracks over an approximate 65 m (213 ft)
length were first observed on the crest of the embankment on June 4, 1984 when
about 1 m (3 ft) of crest remained to be placed. Thirty six hours later, a 400 m (1,300
ft) long section of the upstream slope failed with a maximum horizontal displacement
of 15 m (50
ft).
Lessons Learned
The failure of Carsington Embankment is considered of importance in that it led to
additional attention being given to the role of the construction equipment and
procedures in the subsequent stability of a structure. In this case, the compaction
equipment selected and the rate of fill placement are considered to have been key
factors in the observed failure. In addition, the importance of selecting
instrumentation, which can provide a precursor to a failure, was reinforced.
References
New Civil Engineer (1984). "Weak Ground Cited as Carsington Fails," June 14.
Rowe, P.W. (1991). "A Reassessment of the Causes of the Carsington Embankment
Failure,"
Geotechnique
, 41 (3), 395-421.
Skempton, A.W. (1985). "Geotechnical Aspects of the Carsington Dam Failure,"
Proceedings of 11th International Conference on Soil Mechanics and
Foundation Engineering
, 5, 2581-2591.
