nt.
W A T E R O P E R A T I O N A N D M A I N T E N A N C E B U L L E T I N W A T E R O P E R A T I O N
A N D M A I N T E N A N C E
B U L L E T I N

No. 186
December 1998
I N T H I S I S S U E . . . Liquefaction Mitigation of a Silty Dam Foundation Using Vibro-Stone
Columns and Drainage WicksA Test Section Case History at
Salmon Lake Dam Environmentally Safe "Green" Lubricants for Wicket Gates Reach 11 Dikes ModificationA Vertical Barrier Wall of HDPE
Geomembrane
UNITED STATES DEPARTMENT OF THE INTERIOR
Bureau of Reclamation For further information about the Water Operation and
Maintenance Bulletin or to receive a copy of the index, contact:
Jerry Fischer, Managing Editor
Bureau of Reclamation
Inspections and Emergency Management Group,
Code D-8470
PO Box 25007, Denver CO 80225
Telephone: (303) 445-2748
FAX: (303) 445-6381
Email: jfischer@do.usbr.gov
This Water Operation and Maintenance Bulletin is published quarterly for the benefit
of water supply system operators. Its principal purpose is to serve as a medium to
exchange information for use by Reclamation personnel and water user groups in
operating and maintaining project facilities.
Although every attempt is made to ensure high quality and accurate information,
Reclamation cannot warrant nor be responsible for the use or misuse of information
that is furnished in this bulletin.
Cover photograph: Placement of sealant in interlocked joint.
Any information contained in this bulletin regarding commercial products may not be
used for advertisement or promotional purposes and is not to be construed as an
endorsement of any product or firm by the Bureau of Reclamation.
UNITED STATES DEPARTMENT OF THE INTERIOR Bureau of Reclamation WATER OPERATION AND MAINTENANCE BULLETIN
No. 186December 1998
CONTENTS
Page
Liquefaction Mitigation of a Silty Dam Foundation Using Vibro-Stone Columns
and Drainage WicksA Test Section Case History at Salmon Lake Dam . . . . . . . . . . . . 1
Environmentally Safe "Green" Lubricants for Wicket Gates . . . . . . . . . . . . . . . . . . . . . . . . 13
Reach 11 Dikes ModificationA Vertical Barrier Wall of HDPE Geomembrane . . . . . . . . 25
1
Geotechnical Engineers, Bureau of Reclamation, Denver, Colorado.

2
Principal, Woodward-Clyde Consultants, Oakland, California.

3
Project Manager, Hayward Baker, Santa Paula, California.

4
Regional Manager - Ground Improvement, Hayward Baker, Santa Paula, California.
LIQUEFACTION MITIGATION OF A SILTY DAM FOUNDATION
USING VIBRO-STONE COLUMNS AND DRAINAGE WICKS
A TEST SECTION CASE HISTORY AT SALMON LAKE DAM
by Ron Luehring
1
, Bob Dewey
1
, Lelio Mejia
2
, Mike Stevens
3
, and Juan Baez
4
Abstract
The use of stone columns in combination with drainage wicks is shown to effectively mitigate
the potential for liquefaction of non-plastic silty soils. To achieve acceptable foundation
treatment, proper implementation of stone column construction methods, equipment, and
sequencing are essential. This paper presents the results of a test section using dry, bottom-
feed vibro-stone column construction in up to 70 feet of silt-interbedded fluvial-lacustrine
sandy foundation materials beneath Salmon Lake Dam. Standard Penetration Tests (SPTs)
and Cone Penetrometer Tests (CPTs) were used for site characterization before and after
stone column construction. Liquefaction potential was determined by comparing measured
values of penetration resistance to values required to resist liquefaction under the maximum
credible earthquake. State-of-the-practice data conversions were used to perform the
liquefaction analysis on the basis of clean sand equivalent blowcounts. The test section results
show that: (1) drainage (air and pore pressure relief) is provided by stone columns and
drainage wicks during construction, (2) foundation treatment meeting Bureau of Reclamation
(Reclamation) design objectives is achieved by soil densification between the columns, and
(3) liquefaction can be mitigated by stone column treatment by measurable density increases
even in fine-grained silty soils. Key discussion is provided based on observations related to
column spacings, diameters, and sequencing of construction. Test section results presented
in this paper form the design basis for liquefaction mitigation of the entire downstream
foundation.
Background
Salmon Lake Dam is situated on a tributary of Salmon Creek about 15 miles northwest of
Okanogan in north-central Washington. Completed in 1921, it consists of a 30-foot-high
zoned earthfill embankment with a crest length of 1,260 feet and a combined spillway/outlet
works structure. A cross section of the existing embankment and planned dam safety
modifications is provided on Figure 1. 2
Water Operation and Maintenance Bulletin
Figure 1
The dam foundation consists of Quaternary fluvio-lacustrine sediments under most of the
embankment. These sediments are generally cohesionless, interbedded to laminated silty sand,
with interbeds and lenses of silt with sand, sandy silt, poorly graded sand, and silty sand with
gravel. Minor deposits of silt, and silty gravel, organics, and volcanic ash were encountered
during geotechnical explorations.
Analysis of the earthquake catalog led to the determination of a maximum credible earth-quake
(MCE) of M
L
6.5 for a random event at a distance of 29 kilometers [1]. The maximum peak
horizontal acceleration for this source was estimated to be 0.26 g [2]. This MCE has sufficient
energy to produce significant shear strength loss in foundation layers susceptible to
liquefaction.
Vibro-stone column technology had proven successful for Reclamation and the U.S. Army
Corps of Engineers dam safety modifications to Mormon Island Auxiliary Dam [3, 4].
Although estimates indicated this technique to be the most cost-effective structural mitigation
at Salmon Lake, it was unknown if the presence of a high percentage of low-plasticity fines
and/or apparently dense gravels would hamper the construction and/or the effectiveness of the
stone columns. Reclamation experience for dam safety modifications to Jackson Lake and
Steinaker Dams [5], where wick drains were used in combination with dynamic compaction,
indicated ground improvements in fine-grained silty soils could be enhanced by installation of
drainage wicks prior to performing dynamic compaction. However, it was unknown whether
the vibro-stone column process could also be enhanced by installation of drainage wicks. A
test section was therefore constructed to investigate whether stone columns and drainage
wicks could effectively mitigate liquefaction potential. Data were collected as necessary to
compare foundation strengths before and after ground improvement to optimize final dam
safety designs.
Test Section Design
Testing Locations
Test site locations were determined based on existing site explorations (SPT, Becker Hammer
Penetration Tests, and cross-hole geophysics). Two test sites were investigated at the down-
stream toe representing a range of foundation conditions. Site C, located at about dam Water Operation and Maintenance Bulletin
3
Figure 2
Figure 3
station 10+50, was selected due to the
generally higher fines content of the founda-
tion materials. Site D, located at about dam
station 4+95, was selected because it
appeared to contain the greatest concentra-
tion of materials considered most likely to
liquefy.
Drainage Wicks
Thirty-two wick drains were installed at each
test site prior to the construction of any stone
columns to allow dissipation of air and pore
pressures that are inherent with the dry,
bottom feed method of installing stone
columns. The wick drains were located
equidistant between the planned locations of
the stone columns extending to the full design
column depths (Figures 2 and 3). The
number of wick drains surrounding any stone
column varied as shown.
Stone Column Layout and Depths
Combinations of column diameters (3.0, 3.5,
3.75 feet) and spacings (6.0 and 7.5 feet)
were constructed and investigated to
optimize final designs. Figures 2 and 3
illustrate various combinations of spacing,
diameter, and sequencing. Note that Site C
used predominantly 3.0-foot-diameter
columns, while Site D used larger diameter
columns. The upstream three rows were
advanced to depths of 55 feet, and the
downstream two rows were advanced to
depths of 68 to 70 feet.
Methodology for Evaluation of Liquefaction Potential
Over the past five years, the foundation/embankment explorations of Salmon Lake Dam has
progressed from a general geologic and materials investigation to a specific site characteri-
zation geared towards qualitatively evaluating liquefaction triggering. 4
Water Operation and Maintenance Bulletin
According to Seed [6], there appears to be a strong consensus that in situ testing methods
currently considered sufficiently mature (well-documented, well-calibrated, and verified) to
serve as a useful engineering basis for evaluation of resistance to triggering of liquefaction
are: (1) the Standard Penetration Test (SPT), (2) the Cone Penetrometer Test (CPT), (3) the
Becker Penetration Test (BPT), and (4) shear wave velocity measurements (v
s
). Since the
SPT and CPT are considered reliable for most sandy and low-plasticity silty soils, both were
select