Environmental Engineering Reference
In-Depth Information
Figure 15.39.
Localization of the cracks in the concrete face of Aguamilpa dam (Gomez 1999).
reductions in embankment deformations. Marulanda and Pinto (2000) report that “mon-
itoring of the performance of compacted CFRD dams has indicated that most of the face
is under biaxial compression”, with small tensile stresses observed near the toe and crest
of the dam and around the perimeter. However, recent performance of face slabs on some
new CFRD dams may suggest that tensile stresses can develop within the face slab under
particular conditions.
At Khao Laem in Thailand (130 m high) vertical cracking of the face slab occurred
above a foundation ridge. In this dam, apart from a few contraction joints the face slab is
a continuously reinforced membrane with steel extending across the vertical construction
joints. The cracks appear to have resulted from differential embankment deformation
across the foundation ridge. Watakeekul et al. (1985) note that cracking may have
occurred due to an inadequate number of contraction joints within the face slab. The
authors understand that after some attempts to repair these cracks with grouting, J.B.
Cooke suggested sand be dropped in the crack, which resulted in a rapid drop in seepage.
At Aquamilpa Dam in Mexico (187 m high) several cracks have occurred in the upper
section of the face slab, as illustrated in Figure 15.39. Marulanda and Pinto (2000) report
that a 165 m long crack was found 55 m below the crest, approximately three years after
completion of first filling. The cause of this cracking has been attributed to the large dif-
ference in modulus between the compacted gravel alluvium in the upstream half of the
zoned embankment and the rockfill in the downstream half of the embankment (Gomez
et al., 2000). Modulus values for the gravel and rockfill were estimated to be
200-300 MPa and 40-60 MPa respectively (Marulanda and Pinto, 2000). Similarly large
differences in modulus between zones were reported for Salvajina (ICOLD, 1989), yet no
cracking has been observed. Marulanda and Pinto (2000) suggest that this difference in
behaviour is related to the gradient between zones. The contact between upstream and
downstream zones at Salvajina had a slope of 0.5 V:1 H, while at Aguimilpa the contact
between the upstream gravel fill and the transition zone is vertical. Differential settlements
in the upper half of the embankment resulted in development of tensile stresses in the face
slab and consequent cracking.
Cracking was observed at Scotts Peak dam, a dam with an asphaltic concrete face, again
due to the use of rockfill zones with marked contrast in modulus. Well compacted gravels
were placed at the upstream toe (to a height of approximately one-third the total embank-
ment height), while the main embankment comprised compacted argillite rockfill. On first
filling, large differential deflections caused tensile cracking of the upstream face near to
the contact between the gravel and argillite rockfill zones, as illustrated in
Figure 15.40
.
