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Lessons learned from Mohale

13 July 2007
13

Palmi Johannesson and Sixtus L. Tohlang address the behaviour during and after reservoir
filling of the 145m high Mohale CFRD in Lesotho, with emphasis on cracking of the concrete
slab

The 145m high Mohale CFRD was completed in 2000 in Lesotho. A

background of the dam, including behaviour during construction, is addressed
in References 1-4. In February 2006 heavy rains hit the Mohale region,
resulting in a rapid rise of the reservoir to spilling conditions (Figure 1). This
resulted in significant dam settlements downstream and cross valley
movements of the crest, which in turn increased the already high compressive
stresses within the center portion of the concrete slab, resulting in spalling
failure of the slab.
The dam was visited on 13 February 2006, with no anomalies detected. The
following day a crack in the concrete slab was reported. The slab cracking
resulted in a significant jolt, which likely broke the bond between the concrete
slab and the underlying extruded curb concrete. On 14 February 2006 at
02:24:58 hour the jolt was recorded on a micro-seismic station located on the
left abutment, of seismic moment magnitude 1.2E+11 MNm. Freeing the slab
from the curb concrete significantly reduced horizontal slab strain and increased
the joint opening both for vertical as well as for perimeter joints at flank
sections.
Figure 2 shows the maximum dam cross section with crest detail as well as
zoning details close to the plinth perimeter joint. The dotted line indicates
suggested modification of the outline of Zone 6, addressed in detail in Ref. 5.
Figure 3 shows Mohale concrete slab, indicating the location of the main slab
instrumentation. The location of the 14 February slab crack is indicated by a
thick dotted line.
Assessment of instrumented behaviour indicates that the primary slab spalling
that took place on 14 February was due to high horizontal strain between slabs
17 and 18 (Figures 4 and 5). Subsequently seepage increased significantly,
peaking at some 600l/sec (Figure 6). As IWP&DC goes to press, an attempt is
being made to determine the extent of slab cracking and the location of slab-
leakage, by means of underwater cameras and divers.
Seepage assessment
If one assumes laminar flow through Zone 3, and that the zone of infiltration is
sited at 100m depth one gets:
Q = 0.6m3/sec =A*(k*100/3.5); k =10-2 m/s: Inflow zone A=2.1m2.
If one assumes turbulent flow using Wilkins formula, with C=0.05 (Table 4-1 in
Marulanda and Pinto, 2000) one gets:
Q=0.6m3/s=A*C*(100/3.5)0.54: A=1.96m2.
A relatively narrow crack in the slab may thus be feeding into Zone 3 area; at
depth of ~100m, over an area of some 2m2.
Typical hydraulic settlement data vs head are plotted on Figure 7, showing
rebound as the reservoir dropped. Based on measurements of the bent rebar
shape taken on 5 March 2006 (see Figure 8) the horizontal overlapping
amounted to 78mm. The apparent overlapping of the concrete joints may be as
much as 120mm, while the right slab (#18) lifted up ~75mm above slab 17. The
combined opening of vertical abutment joints amounts to some 340mm.

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End of construction (EOC) deformations and modulus

Settlements during construction were measured at three dam cross sections.
Details are provided in; a) the Mohale Dam Impoundment Manual, September
2002 and in; b) Appendix I to the Mohale Dam Design Report, Design
Parameters, Stability Analyses and Static and Dynamic Deformation Analyses,
March 2003; both prepared by the principal author of this paper as well as in
References 5 and 6.
EOC iso-settlement lines for the maximum dam section are shown on Figure 9.
EOC settlements for the three instrumented dam sections are listed in Table 1,
yielding Mv (1D- modulus) for the u/s shell ~ 40 MPa and 30 MPa for the d/s
shell, back-calculated from centerline settlement values (Poisson's ratio
correction has not been done).
Within the dam cross section, the embankment settlement values used to
assess Mv are affected by (internal) arching, i.e. d/s shell should settle more
and u/s shell less if this arching (dragging down) was not in effect. The 2D
modulus (considering the triangular dam shape) is probably closer to ~40* 0.8 =
32 MPa and that of the d/s shell around 30*0.8 = 24 MPa (detailed later in this
paper). Shortcomings in empirical assessment may largely be overcome by
careful 3D modelling.
The basalt is strong, however, very angular, with poor gradation and high void
ratio. After initial compaction this fill takes on an interlocked - apparent modulus
in the range of 100 MPa (Figure 10). However, once the load on top increases,
grain breakage sets in, which may start at a vertical stress (Figure 10) of only
0.2 MPa.
With a better gradation, a modulus envelope as shown on Figure 10 may
evolve, with grain breakage setting in first around 0.6-0.8 MPa, however, after
collapsing of the initial grain structure, ending in a very low modulus. Similar
experience has been gained from the Kárahnjúkar project, although constructed
of fine graded basalt [5/6]. Analysis of published data on ita give a similar drop
in modulus with increased vertical stress.
Measurements of surface movements and modulus during reservoir filling
The Mr (during impoundment) modulus is estimated by conventional method to
~70 MPa. Considering the rapid reduction in stress within the fill (see i.a.
discussion on load cells), the Mr is probably closer to 60 MPa. This yields a
ratio of Mr/Mv of 60/32 = 1.9. In view of 3D effects, one should expect the
FLAC-2D analysis to over-estimate the horizontal deflection, which it does, but
on Mohale not by much.
Figure 11-left shows the orientation of the principal stresses during construction,
while Figure 11-right shows the rotated stresses once water load comes on.
For reservoir loading conditions close to the slab surface Penman and Charles
(1985) suggested Poisson's ratio of zero. Saboya (1999) points out that Mr/Mv=
(1-µr)/(1- µv); where µr and µv is the Poisson's ratio during reservoir filling and
during construction, respectively. Inserting µr= 0 and µv= 0.3 and 0.25 yields
Mr/Mv = 2.9 and 2.0 respectively. Giudici (2000) used µ of 0.26 in his 3D
analyses of Tasmanian dams. For Tasmanian dams, Fitzpatrick (1885) reports
on Mr/Mv in the range of 2, while this ratio for Mohale dam was 1.9 [5].
Stiffening of the Mohale dam crest was proposed during construction, in view of
the significant grain breakage which took place as the dam embankment was
raised (Figure 10). This suggestion was not followed with reference to
precedent of other dams where such precautions had not been considered
necessary as well as considering impact on schedule and cost. The experience
with Mohale dam has demonstrated that site specific assessment, based on
sound engineering principles, shall precede over robotic empirical design.
Under this concept a vertical joint was provided in the Kárahnjúkar slab at El
498, much in line with the joint details of the New Exchequer and the Sigalda
Intake dams [5], in addition to a bond breaker and 'space' between compression
slabs.

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Figure 12 plots and Table 2 lists FLAC estimated as well as measured

settlements of the embankment from EOC to September 2006. The FLAC
contour lines (dotted) assume elastic behaviour while the measured contours
include creep. Primarily for this reason, the settlements for measured values go
deeper into the fill.
Figure 13 shows the measured settlement of the u/s slope, dam crest and the
d/s slope of the Mohale dam. Previous experience shows that horizontal
displacements are ~ 0.6* settlement of the crest, however, at Mohale the ratio is
140/400 = 0.35.
Figure 14 plots the FLAC slab deflection estimate for E 60 and 80 MPa,
respectively, vs measured as of September 2006. The deflection of the concrete
slab can be seen on Figure 15, taken for RWL 10m below the spillway crest,
during natural lowering from spilling conditions.
Figures 16-18 plot cross valley and d/s movements as well as settlements of
the dam surface due to water load, after cracking of the slab, with data up to
September 2006.
Load cells within dam embankment
The Mohale load cells, as the instrumentation in general, have yielded excellent
information. Data from the construction phase gave load in the outer shells
about 15-20% above vertical gravity load measured from the sloped surface
above, while the load in the center portion was around 0.8-0.9 times the gravity
load, measured from the dam crest. This complies with FLAC simulation (Figure
11), comparing infinitely wide fill vs triangle dam shape fill. This is why Mv
measured from dam center settlement data must be multiplied by 0.8-0.85 to
get a true end-of-construction modulus (after correction; considered a 2D
modulus). Once arching effect of steep valleys is considered this will further
reduce the modulus, for Mohale probably to 50% of Mv.
Load cell reaction to the water pressure is plotted on Figure 19 vs time and on
Figure 20 vs reservoir pressure in kPa; showing that the water load is not
transferred onto the inner dam shell until substantial load has accrued (due to
material strength and arching). However, at a certain point the load kicks in with
almost the same gradient as the water load, see parallel lines on Figure 20.
Figure 21 shows the loads in kPa over the dam cross section as measured by
the load cells. Taking a section parallel to the dam surface at middle height, the
pressure varies from 0.7 MPa at the surface to 0.385 MPa at the rock line. This
results in Mr-modulus of 60 MPa.
Load cells on plinth back head
On Mohale a few load cells were placed on the back slope of the plinth where it
became high (Figure 22). Readings from those cells are plotted on Figures 23-
24. It is very interesting to note how the load on the heel of the plinth mobilises.
Load does not follow conventional theory.
Limited load is transferred until plastic failure within the fill occurs at which time
high load is transferred. This complies with the parallel lines of the internal load
cells addressed above. This in turn means that stability of such retaining
structures must be checked both for low load, with ko ~ 0.3 or less, but then
also for ko approaching 1, in case of 'plastic failure' within the fill (small amount
of sliding) as demonstrated on Figure 24.
Perimeter Joint Meters (PJM)
Locations of PJMs is shown on Figure 3. Max permanent joint openings of
Mohale slab are listed in Table 3 and plotted on Figure 25 for PJM #4 and #9.
Except for PJM 3 and 4, all movements have been plastic (permanent). Note
the significant sudden jolt-movement of up to 30mm, occurring as the slab
cracked on 14 February 2006. Combined JM-vertical joint opening and PJM
movement in excess of 7cm, with shear as high as 4.6cm, is significant. This
may have sheared some waterstops, in particular copper waterstops which are
less flexible to shear movements than the rubber waterstops. Furthermore, the

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jolt, which went through the slab, probably caused instantaneous (cracking
caused dynamic shock) movements in excess of permanent/recorded values.
Joint meter movements (JM)
Max openings of left abutment vertical joints located close to the crest are
plotted on Figure 26 and listed in Table 4 with max value of 26mm.
JM openings on the left bank close to the plinth are listed in Table 5 and plotted
vs time on Figure 27, while their location is shown schematically on Figure 28.
Note that vertical joint openings are generally much larger close to the plinth
than close to the crest.
Openings of the right bank JMs located close to the plinth are plotted vs time on
Figure 30, with location shown schematically. Figure 31 plots the movement of
those JMs, with X axis going parallel to the dam axis. Note the sudden joint
opening as a result of the slab cracking. The sum of these vertical joint
movements amounts to 169mm, while the sum of the left bank JMs opening
amounts to 133mm, in total probably around 170mm, i.e. 340mm combined for
both abutments.
Surface movements

Figures 32 to 34 plot Y (cross valley), X (d/s) movements and Z (settlement)

movements vs time as surveyed from the Parapet wall and the d/s dam crest
beacons. At lower elevations within the dam body, the collapsing effect seen by
the settlement cell data during construction has already occurred to a significant
degree, and the fill has come close to achieving elastic deformation modulus
within the existing load range. For the u/s 30-40m and the dam crest this had
not occurred, and accordingly, more significant plastic deformation occurred
upon filling the reservoir for the fist time. Slab crushing induced movements
amount to:
* Y: ~ 60mm in cross valley direction at middle flank sections, with total of
100mm
* X: ~ 130mm d/s movement of the max dam section at the crest, with total of
140mm
* Z: ~ 230mm settlement of the max dam section at the crest, with total of
400mm.
Figures35-37 plot the Y - cross valley movements, from left to the right
abutment, the d/s (X) movements and settlements (Z), respectively. The dotted
symmetry line on Figure 36 is drawn to underline the higher movement of the
right flank. Mohale dam valley shape represents the left bank slope of 1: 2.3
and right bank slope of 1: 1.72. One would expect the steep right embankment
fill constructed ahead of the left bank fill to deform less, due to a) higher portion
of pre-impoundment settlement and b) greater 3D arching. Furthermore, the
lack of symmetry noted from Figure 35 and Figure 36 is not seen in Figure 37.
An explanation for this is not at hand.
Strains and stresses in slab
Strain variation vs time
Location of the strain cells placed in the Mohale dam is shown on Figure 3.
These strain cells, having provided excellent data for back analysis, including
where and when the failure(s) took place, if promptly interpreted, could have
given warning of what was about to happen. Horizontal strains vs time in slabs
18 and 21 up-to and shortly after failure are plotted on Figure 38 and Figure 39,
while the plot on Figure 40 shows vertical strain in slab 21.
Location and timing of slab cracking
Based on strain data from slab 18/21, slab cracking occurred first on 14
February at 2:24:58 hours, as also recorded by the local micro-seismic station,
with cracking starting at the top at horizontal strain level of 590 micron,
corresponding to compression of ~21 MPa (includes Poisson's correction). The
water load at the top was inadequate to avoid lifting up and buckling of the
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slabs. A significant drop in horizontal strain was recorded at all strain-cells, in

particular at cell 7B, Figure 41-left. This in turn increased vertical strain at depth
(at El ~1976 masl), see plot on the right side on Figure 41. Vertical strain
release (cracking) occurred at this level on 15 March at peak value of ~650
micron (´v = 0.00065), corresponding to compression of 19.5 MPa, without
Poisson's ratio application, and ~24 MPa with Poisson's-ratio effect. A third
stage cracking appears to have occurred on March 16. No significant vertical
seepage increase was seen as result of this.
The strain data from slab 21, located four slabs to the right of the cracked slabs
supports the above (Figure 42); with initial cracking at the top due to horizontal
strain exceeding 600 micron around 14 February, with apparent later cracking
at depth around 16 March due to vertical strain. This occurred one day after
slab 17/18 cracked at depth i.e. the slab appears to have cracked in three
phases, with possible 30-45° shear failure at El ~ 1976 left of slab 18 on 15
March and then a third phase shear cracking on 16 March at a higher level (say
around 2020) right of slab 21.
Strain in slab vs elevation
Figure 43 plots the horizontal and vertical stresses in slab 21; a) at EOC; b) at
the time of slab cracking and c) afterwards (by September 2006), at which time
stresses had been greatly relieved as the bond broke between the slab and the
extruded curb. The stresses are calculated by the following formula, applying
Poisson's ratio of 0.25:
EQUATION HERE
Figure 44 plots adjusted horizontal, inclined and vertical stresses vs elevation in
the concrete slab 18 and 21 at the time of failure. Means to avoid high
horizontal strain in the slab are addressed later in this paper.
Relevant construction aspects of Mohale dam
Figure 45 shows the concrete beam at El 2040 carrying the paving equipment,
which resulted in intensified compaction of the rockfill in this region. As the
concrete beam and rails present a stiff foreign object just under the slab, in the
authors view the reinforced concrete slab and steel rails should have been
removed.
Figure 46 shows the u/s slope of the Mohale dam during initial reservoir filling.
Note numerous cracks in the slab above joint 2040, with concentration in the
region of the side ramp/later constructed fill, causing differential settlement after
paving of the slab. Although surface reinforcement was added over the 2040
joint, its length above the vertical joint was inadequate. For this reason such
reinforcement on Kárahnjúkar was made longer [6].
Figure 47 shows spalling at the slab/ plinth contact already occurring during
construction, as the result of dam settlement, pushing the slab onto the plinth.
While providing 'space' at this joint, e.g. by soft impregnated wood or similar, is
helpful, reducing the downward movement of the slab by stiffer fill and other
means addressed herein is most important.
Figure 48 shows tension/cross valley induced cracks which formed during
construction in the curb concrete on the right bank. Note the already paved slab
on the right side. Tension joints in the abutment are provided to cope with such
movements, which cause compression in the center section of the slab. First at
the Kárahnjúkar dam were lines of defense provided to handle such cross
valley movements.
Figure 49 gives a view of the right bank of the Mohale dam during stage 1
construction, showing how badly the 1” shotcrete surface protection buckled
due to massive settlement of the rockfill, while the extruded curb above did
much better. For unknown reasons this shotcrete was not removed; see Figure
50.
Conclusions
Selection of rock for embankment fill, including rip-rap
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Prior to involvement of the authora in the design of Mohale dam, it was planned
to use only doleretic basalt for the embankment. This rock was found on the
right reservoir flank under a thick cover of amygdaloidal basalt. Due to its
hardness/ brittleness, doleretic basalt yields rockfill of high void ratio and high
apparent modulus (after compaction). However, under increased vertical stress
it undergoes massive grain breakage, resulting in an overall low modulus at 0.5-
1 MPa vertical stress of only some 30-40 MPa (without 2D or 3D correction). It
is believed that favouring doleretic basalt as embankment fill, or any such
strong and brittle clean rock, is a 'left-over' from the outdated era specifying
'clean' rockfill. The weaker basalts tend to break up to a lesser skip gradation,
with lower void ratio after compaction, thus providing fill with higher modulus.
Due to its brittle nature and high thermal conductivity doleretic basalt is not an
ideal rock for rip-rap. Thermally induced tension from day-to-night cycles
combined with very high modulus slices (tension cracking) the doleretic
boulders to small fragments (Figure 51).
The authors feel that inadequate attention is placed on collecting in-situ
performance data, which should be published in a CFRD-Performance-
Catalogue, accessible to the profession at large. Laboratory tests are of value
when correlated to such field performances. On Mohale, the pre-construction
tests on different basalt rock types may have failed identifying resistance of
'dolerite' to cyclic weather exposure. Possibly other varieties of basalt may be
equally or more durable under field exposure. The author is not aware of any
field data or calibrated laboratory evidence indicating that amygdaloidal basalt
is inferior to e.g. doleretic basalt for use in rip-rap or as concrete aggregate. We
need to improve the testing methods, supported by field performance
precedent, to arrive at a suitable characterization of rock for rip-rap and
concrete aggregate. Some laboratory tests in use classify rock with 30-50 years
excellent field performance as not suitable in concrete. In this field our
knowledge needs to be advanced.
A somewhat different view on the durability of Lesotho basalts is presented in
an excellent paper by Riemer (2003). There is probably need for a more in-
depth assessment of the performance of rock, including amygdaloidal and
doleritic Lesotho basalts, in the various zones of high CFRDs.
It is noted that quartzite, believed to have somewhat similar properties as
doleritic basalt, was successfully used in the Cethana dam, yielding a very high
modulus (Mv of 145 MPa). This simply demonstrates that if well executed,
including carrying out proper quarry blasting tests, with the aim of producing
uniform, low void ratio fill (~ 0.25), most rock can be used. Emphasis shall be
placed on the u/s 30m zone and the crest section (H/4). A void ratio of 0.3-0.32
for the d/s shell is probably adequate in most cases. Except for the slab
supporting zone (Zone 3), it appears more meaningful to specify void ratio and
density rather than gradation.
Importance of watering the embankment
It is recommended that the u/s 30-40 m zone will be compacted at optimum
moisture (Zone 3) or applying =200 l/m3 of water to the fill (Zone 4/5). Water
shall also be used for the coarser rock, by keeping the rock wet at depth,
helping grain breakage during construction. For budgetary purposes 100l/m3 is
probably adequate.
Sequence of slab pouring
In the high portion of the dam the concrete slab should not be placed until the
dam embankment has reached a level at least 0.75H.
Joints and strain in slab
Accumulated horizontal joint openings at Mohale from both abutments
amounted to ~2*170mm=340mm, while overlapping of slabs 17/18 probably
amounted to 120mm. This suggests that space between slabs in the
compression zone should exceed say 220mm. Here 'space' means distance
between concrete slabs, formed by impervious material, compressible to > 50%

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of its thickness at < 8 MPa. For dams of configuration similar to Mohale,

constructed of low modulus embankment, the space between slabs at vertical
joints should amount to four joints with 50mm gap at dam center, with some
seven joints on either side of width 25mm. However, providing a stiffer
embankment shall be given top priority.
In practice it is much more difficult to reduce the high vertical strain than the
cross-valley induced horizontal strain. Remedial measures include a-c) high
rockfill modulus, with emphasis on the u/s 30-40m section of the dam; d)
providing space at the perimeter joint (~50mm, by soft wood or a similar low
modulus sheet) and at all planned horizontal construction joints; e) placing the
slab in the dam center portion as late as possible; f) providing viscous asphalt
emulsion bond breaker between curb concrete and the slab in the compression
zone (except at starter slabs), of thickness min 3-4mm; g) providing shear
reinforcement at all planned joints; h) avoid thinning in the slab at all joints; i)
place the main reinforcement 150mm from the surface; j) for slabs thicker than
0.6m, provide a second layer of reinforcement placed 100-150mm from the
lower surface, of quantity 1/2 that of the surface layer [5/6].
For a slab paved in three phases, providing space at planned horizontal joints
(including at the plinth perimeter joint) amounting to 3*50mm will for a 200m
high dam with slope 1:1.3 reduce vertical strain in the slab approaching
3*0.050/(200x1.64) * 30000 = 13.7 MPa, say by 10 MPa. In most cases this
would be adequate to avoid spalling at plinth and shear slab failure.
Parapet wall
Limit wall height to 6-6.5m and the length of each element to 7.5m (for flat
abutments 15m may be used), with 'space' between elements of 25mm. When
reservoir level rises frequently above the crest/slab joint level, at the
slab/Parapet wall perimeter joint and at vertical Parapet wall joints, specify both
copper and rubber waterstops.
Waterstops
At vertical abutment joints, provide both bottom copper waterstop as well as
embedded rubber waterstop. At compression center slab vertical joints and at
planned horizontal construction joints falling within 0.3H and 0.7H (measured
from the river bed), provide bottom copper waterstop as well as either a short
embedded rubber waterstop of a width of only 200mm, or provide a surface
waterstop (copper, stainless steel or hypalon/PVC/HDPE) as a second line of
defense (Reference 6, Figure 32). Along steep abutments and at high plinth
sections, increase the height of the copper waterstop U to 100mm and provide
a 150 mm wide stretching zone for the rubber waterstop [5/6]. As a 3rd line of
defense along the perimeter joint, provide a hypalon waterstop (Reference 6,
Figure 39).

List of symbols and abbreviations:

Abbreviations:
* CFRD and CFED: Concrete Faced Rockfill Dam and Concrete Faced
Embankment Dam
* RWL: Retention water level, same as Full Supply Level
* RTE: Reservoir triggered earthquake, rather than reservoir induced
earthquake
Symbols:
* E: Young's modulus, MPa
* Mv: One dimensional modulus of rockfill, in MPa
* Mr: Modulus used to estimate slab deflection during impoundment
* Poisons ratio; m = ´1/´2 = lateral expansion strain/axial compression strain.
Table 1 Table 2 Table 3 Table 4 Table 5 Figure 1a: Mohale dam during initial
impoundment, 24/2/2001 Figure 1a Figure 1b: Mohale dam seen from d/s on 13
February 2006 Figure 1b Figure 2: Mohale dam cross section with plinth and crest
details Figure 2 Figure 3: Mohale concrete slab with main instrumentation, also showing
cracks in slab Figure 3 Figure 4: Joint 17/18 crack seen from above Figure 4 Figure 5:
Slabs 17/18, after removing sheared concrete Figure 5 Figure 6: Reservoir leve; and
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seepage vs time Figure 6 Figure 7: Typical hydraulic cell settlement vs reservoir level
Figure 7 Figure 8: Failure mode of Mohale slab Figure 8 Figure 9: EOC iso-settlement
contours for max dam section Figure 9 Figure 10a: Settlement/load data and moduli, for
poorly graded basalt Figure 10a Figure 10b: Settlement/load data and moduli for well
graded basalt Figure 10b Figure 11: Principal stress plot EOC and for full reservoir
Figure 11 Figure 11b: Principal stress plot EOC and for full reservoir level Figure 11b
Figure 11c: Principal stress plot EOC and for full reservoir level Figure 11c Figure 12:
FLAC 80MPa water load settlements contours vs measured from EOC to Sept 2006,
including creep Figure 12 Figure 13: Settlement of u/s and d/s slope and dam crest,
June 2006 Figure 13 Figure 14: FLAC E 60 and 80 MPa water load slab deflection vs
measured, latter including creep Figure 14 Figure 15: Mohale slab deflection,
September 2006 Figure 15 Figure 16: Cross valley movements for full reservoir Figure
16 Figure 17: D/S slope deflection for full reservoir Figure 17 Figure 19: Load-cells
pressures and reservoir load above cells in kPa vs time Figure 19 Figure 20: Measured
pressure (Y); cells El 2010 vs reservoir pressure (X); all in KPA Figure 20 Figure 21:
Measured stress contour lines due to water load Figure 21 Figure 22: Load cell
arrangement on back slope of plinth Figure 22 Figure 23: Load cells at plinth heel, left
abutment Figure 23 Figure 24: Load cells at plinth, right abutment Figure 24 Figure 25:
PJM 4 and PJM 9 movements Figure 25 Figure 26: Left bank top slab JM movements
Figure 26 Figure 27: Left bank JMs close to plinth Figure 27 Figure 28: Left bank JMs,
close to plinth, location and operation Figure 28 Figure 29: Right bank JMs close to
plinth Figure 29 Figure 30: Right bank JM joint opening Figure 30 Figure 31: Right bank
joint meter opening Figure 31 Figure 32: Y (cross valley) movements of Parapet vs time
Figure 32 Figure 33: X (d/s) movements of parapet wall vs time Figure 33 Figure 34: Z -
settlements of parapet wall vs time Figure 34 Figure 35: Crest movements Figure 35
Figure 36: X movements across dam crest Figure 36 Figure 37: Settlement of dam crest
from left to right abutment Figure 37 Figure 38: Horizontal strain in slab 18 Figure 38
Figure 39: Horizontal strain in slab 21 Figure 39 Figure 40: Vertical strain in slab 21
Figure 40 Figure 41: Strain in slab 18 around the timing of slab cracking Figure 41
Figure 42: Strain in slab 21 around time of cracking Figure 42 Figure 43: Horizontal and
vertical stress in slab 21, EOC, at time of cracking and Sep 2006 Figure 43 Figure 44:
Adjusted horizontal, inclined and vertical stresses in slab 18 and 21 at time of failure
Figure 44 Figure 45: Beam at El 2040, carrying paving equipment, causing extreme
local stiffness Figure 45 Figure 46: U/s slope of Mohale dam during initial reservoir
impoundment, revealing numerous shear cracks Figure 46 Figure 48: Tension crack in
extruded curb, right bank Figure 48 Figure 49: Right bank of the dam, with shotcrete
surface protection below and extruded curb above Figure 49 Figure 50: Close-up view
of broken shotcrete left in place Figure 50 Author Info:
P. Johannesson, President of Palmi Associates, USA: Email:
palmi@palmiassociates.com; S. Tohlang, Chief Delegate, LHWC, Lesotho:
Email tohlas@lhwc.org.ls
The authors are grateful to Landsvirkjun and the Kárahnjúkar Joint Venture,
which includes Montgomery-Watson-Harza, in charge of the Kárahnjúkar dam
design; and to Lesotho Highland Water Commission/ Lesotho Highland Water
Authority; for the permission to use information from performance of
Kárahnjúkar and Mohale CFRDs, respectively. Particular appreciation is
expressed to Professor Dr. Kaare Hoeg and Dr. Wynfrith Riemer for valuable
observations and editing comments, greatly enhancing this paper. Further
appreciation is expressed to Bayardo Materon for his support and
encouragement.
Tables

Table 5
Table 1
Table 2
Table 3
Table 4

Figure 1a

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Figure 1b

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

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Figure 9

Figure 10a

Figure 10b

Figure 11

Figure 11b

Figure 11c

Figure 12

Figure 13

Figure 14

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Figure 15

Figure 16

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Figure 19

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Figure 23

Figure 24

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Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

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Figure 31

Figure 32

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Figure 33

Figure 34

Figure 35

Figure 36

Figure 37

Figure 38

Figure 39

Figure 40

Figure 41

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Figure 46

Figure 48

Figure 49

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Figure 50

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