Changing Times — The Challenges and
Risks of Managing Aging Infrastructure
Under a New Financial Reality
33rd Annual USSD Conference
Phoenix, Arizona, February 11-15, 2013
Co-Hosted by
Bureau of Reclamation and Salt River Project
On the Cover
The original Theodore Roosevelt Dam was completed in 1911, the first major structure built by the Bureau of
Reclamation on the Salt River Project. The dam, located about 75 miles northeast of Phoenix, had an original height
of 280 feet, and was highest masonry dam in the world. In 1996, a project to expand and renovate the dam was
completed. This project raised the dam by 77 feet for a total height of 357 feet and resulting in a 20 percent increase
in reservoir capacity. The expansion of the dam was accomplished using a concrete overlay. The cost of the
expansion totaled $430 million and included the realignment of a highway over a new bridge, improvements to the
power plant and a tunneled lake tap.
U.S. Society on Dams
Vision
To be the nation's leading organization of professionals dedicated to advancing the role of dams
for the benefit of society.
Mission — USSD is dedicated to:
• Advancing the knowledge of dam engineering, construction, planning, operation,
performance, rehabilitation, decommissioning, maintenance, security and safety;
• Fostering dam technology for socially, environmentally and financially sustainable water
resources systems;
• Providing public awareness of the role of dams in the management of the nation's water
resources;
• Enhancing practices to meet current and future challenges on dams; and
• Representing the United States as an active member of the International Commission on
Large Dams (ICOLD).
The information contained in this publication regarding commercial projects or firms may not be used for
advertising or promotional purposes and may not be construed as an endorsement of any product or
from by the United States Society on Dams. USSD accepts no responsibility for the statements made
or the opinions expressed in this publication.
Copyright © 2013 U.S. Society on Dams
Printed in the United States of America
Library of Congress Control Number: 2013930528
ISBN 978-1-884575-58-7
U.S. Society on Dams
1616 Seventeenth Street, #483
Denver, CO 80202
Telephone: 303-628-5430
Fax: 303-628-5431
E-mail: stephens@ussdams.org
Internet: www.ussdams.org
REHABILITATION OF TEMPORARY COMPOSITE DAMS —
CASE STUDY: MARED SOIL-SHEET PILE DAM
Saber Alidadi1
Masoud Hakami2
ABSTRACT
Flow rate of Karun river, which is the longest and largest river in Iran, decreased from
600 m3/s to 100 m3/s in average, due to the drought in early 2008. This reduction caused
water from Persian Gulf to advance farup-river and reach araw water supply basin and
increase water electrical conductivity (EC) to 5,000 μmoh/cm. A temporary dam
constructed from soil-sheet pile was installed to prevent salty water progress to the water
supply location. Heavy rain fall and flooding with a flow rate of 1000 m3/s destroyed
one-third of the dam in November 2008 and therefore, the lives of nearly 300,000 people
were in danger due to water shortcoming. In this paper a new and innovative method for
repairing the aforementioned dam is presented considering constraints such as type of
dam destruction, limited time and cost, and other operating limitations. In this method,
the damaged section of the dam was restored by composite geo-box piles. The piles were
installed in two rows against the water to create a corridor and then the corridor was filled
with soil geo-boxes. Based on the seepage and overturning analysis, and considering
implementation conditions, the geometry of proposed method was selected. After
successful implementation of the plan, the dam was restored and consequently the EC of
the water was reduced to 1,800 μmoh/cm and raw water quality improved significantly in
less than 2 months with minimum cost. It was finally realized that the soil erosion inside
the cells was reduced; the bed was stabilized and its integrity over the dynamic loads was
sustained. Therefore, it can be said that there is a significant uniformity between the fixed
part and the existing structure of the dam. It can be concluded that this method of
rehabilitation is an innovative and fast method to fix the damaged dams with minimum
cost.
INTRODUCTION
Drought and advance of seawater has caused the confluence of saline water with Karoon
River in the Mared region, near the town of Abadan and has even disturbed the ordinary
life of Local residents. According to studies conducted by Mahab Qods and Seoko
Consulting Engineering Companies, construction of a permanent dam at the current site
of Mared could solve the problem of salty water interference. Since the plan was never
executed, the decision was made to construct a temporary dam with the priority of
meeting local drinking and agricultural water demands and controlling floods.
Considering the geotechnical characteristics of the region and various parameters by
Mahab Qods Consultant Engineers, a soil-sheet pile dam was constructed based on cost
1
MSc. Geotechnical Engineering, Khuzestan Water & Power Authority, Department of Dam and
Powerplant Development, Ahwaz, Iran. Phone:00989166141235, email:alidadis@yahoo.com
2
Khuzestan Water & Power Authority, Department of Dam and Powerplant Development, Ahwaz, Iran.
Phone:00989166177933, email:hakami@kwpa.ir
Rehabilitation of Temporary Composite Dams
1125
analysis, executive conditions and design parameters. The Mared earth-fill sheet pile
dam was constructed by a combination of AU sheet piles and circular cells made of sheet
piles as supports and an embankment around the sheet piles (Fig. 1). Many different cell
dams have been constructed around the world. A number of such dams have been also
established in Abadan, in southwestern Iran. In an earth-fill sheet pile dam, sheet piles are
integrated to each other to create a large cell. However, due to it being a temporary
structure, circular cells made of sheet piles are used as supports along with an inner core
made of a row of sheets to connect the cells.
A year after Mared Soil Sheet Pile Dam was constructed, a flood of 1,000 m3/s flow (a
200 years of return period) occurred in the Mared region in late September 2008. Since a
flood of such volume would not be considered in the dam design parameters, 90m long
segments of the sheet pile dam were destroyed (Fig. 3) where they interlock and were
buried in the river bed. By breaking of the dam, saline seawater advanced into river,
leading to insufficient water supplies available to local residents of the region. Water EC
also reached 5,000 μmoh/cm. After this structure was completely destroyed, the sheet
piles in the river bed were turned up due to extreme horizontal force of the water. Only a
few sheet piles near main dam cells (no.1 and 2) remained undamaged due to their direct
attachment to cells structure.
Figure 1. Plan and Section of Mared Soil-Sheetpile Dam
1126
Karun River, the longest and largest river in Iran, has flows of 500 m3/s with a 300m×10
m rectangular section in the Mared region. A pumping station with 100 m3/s flow has
been constructed upstream to supply drinking water (Fig. 2).
Figure 2. Plan Location of Project
The advance of sea tides with saline water continues to 20 km, then it enters the pumping
station reservoir. The temporary dam prevents water from advancing into the section.
About 90 m of the distance between cells 1 and 2 of sheet pile core was destroyed up to
95%, so that after water overtopped the dam, upstream and downstream embankments
were washed away and the sheet pile core could operated as a free spillway for as long as
7 hours (Figures 3 & 4). The water height on the sheet piles reached to 1/6 m leading to
sheet pile damage. The destruction continued rapidly in the section.
By studying the conditions of river at this point one would notice that a permanent
concrete spillway needs to be constructed in this area to maintain river water level to its
maximum capacity, and after water rise, water would overflow permanently from the
dam crest. Also, it would prevent tidal water from proceeding to the section to stop saline
water advance into river. However, the construction of such dam with the intended
specifications would require significant funding and sufficient time for water diversion
and supplying raw water to meet local demands during construction phase. This led to
the decision to restore the temporary dam.
Rehabilitation of Temporary Composite Dams
1127
Figure 3. Mared Composite Dam after Failure
Figure 4. The Failed Section 10 days after Flood
MATERIALS AND METHODS
Some of the main reasons of failure in Mared dam are as follows: neglecting a flood of
the volume above in designing of the dam section, insufficient depth of sheet piles in soil
and high leakage from bottom of the sheet piles that ended in instability and sheet pile
failure during a flood event. The only resisting force to keep the core sheet constantly
against water force was the sheet piles interlocking and their bending resistance at the
sections, which was not sufficient because of soil erosion at the bottom of sheet piles and
their loose connection to bed soil.
After a careful visit to the destroyed sheet piles by professional divers, it was found that
due to high integrity between existing sheets in the dam body, all the sheet piles had
withstood the conditions in the past; however, they were twisted in each other’s locks and
because of high flow forces of the river and weakness of the bed soil, they were buried in
the riverbed. Although because of sheet piles pounding with more lengths, lower depth of
the river in the section, and different geotechnical characteristics of riverbed, the seepage
flow was still negligible and did not damage these sections.
Considering the destructed river section, two plans were proposed. According to the first
plan, the dam would be reconstructed by restoring sheet piles buried in the riverbed.
Second, a new system would be designed which could operate continuously with the
existing structure having a high safety factor against the loads. After studying
1128
circumstances and doing necessary computations, it became clear that a direct force of
120 tons would be required to raise and restore 30 m of the total length of existing sheet
piles. However, since water diversion was not feasible in the region due to extensive
farmlands along river banks, the reconstruction works would be performed along the
continuous flow of the river. The position of farmlands along river and using barges to
mobilize work on water flow did not allow force to be applied directly or by pulley to the
destroyed sheet piles. Using vehicles like a bulldozer and by the help of a crane, piles
were pulled by pulley to the left bank (adjacent to 1 cell). Due to the water force, soil and
sheet pile weights, locks and sheet piles complexity in their section, the sheet piles could
not fit into their actual sections more than a few inches. Since according to geotechnical
data, characteristics of erosion in bed section were favorable as such that during high
flows an erosion of 10m was expected in bed, measures needed to be taken to not only
narrow the section to block it, but also bed erosion would be taken into account. Strong
tidal water occurred at the project site as the tidal difference was almost 1.2 m.
Considering the project duration of 2 months, the second plan was chosen as:
1. The system could withstand flood water force without using embankment, so
that if overtopping should occur because of the reasons above and the
embankment be destroyed, the dam core could resist.
2. In addition to having an effective safety factor against drive forces, the system
should be able to resist excessive seepage from the dam body riverbed erosion in
this section. Actually, this system should help to reinforce the riverbed in the
intended section.
3. The proposed system should maintain stability between two cells to act together
against driving forces.
The sheet piles adjacent to the second cell remained in their desired shape because of
being close to the support. Of course, due to insufficient depth and weak sections against
strong tidal forces, the sheet piles began to move with respect to their initial location,
although they were connected to the buried sheet piles in riverbed soil. Also, the soil
inside the 2nd cell was being removed due to the reciprocating movements of sheet piles
and high seepage flow from the connections of sheet piles to cells. According to the
calculations and also considering the prevailing situation at site, the restoration of dam
would be achieved by applying different practices including expanding geo-tube on the
river bed, remaking sheet piles with a stronger section and even constructing an
additional cell. Nonetheless, since metal sheet piles with suitable depth are not available
in Iran and also to integrate dam sections, a decision was made to design a new,
combined method for the dam restoration. Considering the prevailing conditions, cost,
time restriction and practical difficulties it was found that the use of a geo-box pile
composite structure was the best method. A computer model was developed by Plaxis
code, and considering water dynamic and static forces, seepage analysis results, structure
settlement and diversion control in structure design, the piles arrangements, section and
length were obtained. However, the application of the method was executed stepwise
considering complexities of damages and changing river flow regime.
Rehabilitation of Temporary Composite Dams
1129
Methods Application
Because of soil erosion inside the 2nd cell, the restoration of driving sheet piles ending to
the 2nd cell, moving in flabellate form in the tidal direction was the first priority. This
was performed by pounding 24 m fender piles first, in rising tide and then in ebb tide, on
both sides of the sheet pile such that the sheet piles movement was reduced to a few
centimeters. After the restoration of 20 sheet piles in 14 m length was completed, the
river section became narrower and the flow rate increased through the still-breached
section. Also, due to the decrease of seepage flow from connection points of sheet piles to
the cell, and water stillness in that section, soil fracture was reduced inside the 2nd cell.
Because of suitable depth, free pounding in severe tidal conditions and resistance against
lateral and vertical loads, the use of piles in the section with 24 m of length (Fig. 4)
seemed to be suitable .
Figure 4. Plan of Combination Pile-Geobox
The 50 cm distance between piles would be used for easy pounding and using geo-boxes
as fillers. It is of note that the load resistance mechanism by pounded piles is such that
due to geotechnical characteristics of the region and an average 14m infiltration depth,
the piles resisted frictionally against vertical loads including their own weight and the
upper embankment. Also they resisted by bending resistance against lateral loads. The
piles also stabilized the river bed. The 2 m distance between two piles, was used for a
safety factor against diversion. Additionally, the volume of filling materials should be
cost effective. The geo-boxes of 2 m x2 m x 0.5 m size were filled, loaded and settled
with the region soil.
Steel pile pounding was faced with difficulties caused by tidal conditions, The piles could
not be placed vertically by using a dynamic impact hammer, so a structure was used to
perform balanced, orderly pounding of piles.
Pounding two opposite rows of piles began with the first cell making a 30 m length
corridor. Then the geo-boxes were filled and settled, and then earth filling was performed
simply in a 20 m distance. At this stage, in order to block the second cell, the section
length was reduced from 90 m to 45 m and the flow rate became 2 m/s. Also, the flow
rate was too much to allow settling geo-boxes, since it carried them out of the corridor. It
1130
was decided to close the corridor by pounding some piles against the flow direction. In
fact, the remaining 45 m was divided into 3 corridors, each of 15 m to stop flow by
settling and earth-filling geo-boxes.
It is notable that settling geo-boxes was performed by crane installed on the barge. The
destroyed portions were blocked in less than 30 days. Since the seepage from dam body
and bottom was negligible, provided that no piping phenomenon would occur, the
possibility of water passage through dam section was provided due to the use of proper
structure, and no soil erosion because of pile pounding occurred.
Now that the problem of salty drinking water of the residents is solved, it is possible to
either construct canals on the left and right banks to prevent flow overtopping during
flood events or install a spillway on the crest so it can take out the water during ebb time
and in high tide and the water is prevented from reaching the top. In fact, the pounded
piles in the dam core could act as a foundation pile for this metal spillway.
CONCLUSION
1. When conditions do not allow water diversion and timing is seriously restricted,
pile pounding and filling them by soil fillers can be used to establish temporary
earth dams.
2. The application of this method with due regard to the materials used leads to
integrity between the new and old structures, and the restored dam section works
effectively against driving forces.
3. In the case of constructing a permanent dam and removing the temporary
structure, the main dam structure, including piles and geoboxes can be taken out
completely from the river to prevent any probable environmental damages.
4. Water quality was significantly improved and water EC decreased from 3,500 to
500moh/cm; also, the problem of saline water entering the drinking water at the
pumping station reservoir was resolved.
5. By the use of piles, the structure can resist against vertical loads, and one can
construct a metal spillway on a section of the dam body.
ACKNOWLEDGEMENTS
Mr. Kamran Ajdari, Mechanics Engineer, Khuzestan Water & Power Authority
Mr. Ali Abuhamidi, Mechanics Engineer ,Khuzestan Water & Power Authority
Mr. Amin Jasayeri, Civil Engineer ,Khuzestan Water & Power Authority
Rehabilitation of Temporary Composite Dams
1131
REFERENCES
1. Ashraf A Ahmed Design of hydraulic structures considering different sheetpile
configurations and flow through canal banks Original Research Article,Computers and
Geotechnics, Volume 38, Issue 4, June 2011, Pages 559-565
2. Emilios M. Comodromos, Mello C. Papadopoulou, Ioannis K. Rentzeperis, Pile
foundation analysis and design using experimental data and 3-D numerical analysis
Original Research Article, Computers and Geotechnics, Volume 36, Issue 5, June 2009,
Pages 819-836
3. Professor Kamran M. Nemati, University of Washington Department of Construction
Management Cm 420 Temporary Structures, Winter Quarter 2007
4. U.S. Army Corps of Engineers, Design of Sheet Pile Walls ,EM 1110-2-2504, 31
March 1994
5. U.S. Army Corps of Engineers, Design of Sheet Pile Cellular Structures Coffedams
And Retaining Structures, 29 September 1989
6. USBR, (1987), Design of Small Dams, U. S. Bureau of Reclamation, Department of
Interior, Col., USA
7. Sherard, J. L. et al., (1963), Earth and Rockfill Dams, John Wiley and Sons Inc., New
York
8. Sarma S. K., Seismic Stability of Earth Dams and Embankment, Geotechnique, Vol.
25, NO 4, 1975, 743-761.
9. Stability of Earth-Rockfill Dams: Influence of Geometry on the Three-Dimensional
Effect .Computers and Geotechnics, Volume 32, Issue 5.
10. Fundamentals of Geotechnical Engineering by Braja M. Das (Nov 29, 2007)
1132