Type: INT 97-32 **NSF/Tokyo Report: Measurement of Lateral Forces on a
Sheet-Pile Wall During Seismic Loading**

Org: INT

Date: 9/19/97

Replaces: None

The National Science Foundation\'s offices in Tokyo and in Paris
periodically report on developments abroad that are related to the
Foundation\'s mission. These documents present facts for the use of NSF
program managers and policy makers; they are not statements of NSF
policy.

Special Scientific Report #97-28 (September 5, 1997)

MEASUREMENT OF LATERAL FORCES ON A SHEET-PILE

WALL DURING SEISMIC LOADING

Mr. Eric Liedtke, a graduate student in the Department of Civil
Engineering at the University of Texas at Austin, prepared the following
report. Mr. Liedtke was a participant in the 1997 Summer Institute
sponsored by NSF and the Science and Technology Agency of Japan.
Professor Ikuo Tohata of the Geotechnical Engineering Laboratory in the
Department of Civil Engineering at the University of Tokyo hosted Mr.
Liedtke. Mr. Liedtke can be reached via email at:
eliedtke@mail.utexas.edu

INTRODUCTION

The failure of a man-made river embankment can be a problem for areas
lying below the elevation of the river. Seismic activity is one possible
source of embankment failure. A method to retrofit embankments to
minimize the potential of failure is proposed. The effectiveness of this
proposed method is being investigated by experiments performed on soil
models. A large shake table is used to simulate seismic events on the
models.

During an earthquake embankments may fail. In particular if the
embankment was constructed on top of a loose deposit of aturated sand,
failure may occur due to the decrease in the effective stress of the
sand deposit that can occur during an earthquake.

The sudden loss in the effective stress of the loose, saturated sand is
called liquefaction. The mechanism of this phenomenon is the sudden
increase in pore water pressure caused by the rearrangement of the loose
sand particles during a seismic event. Thus, in simple terms, during a
seismic event the sand and water essentially become a fluid that is
incapable of supporting the weight of the embankment. This in turn will
cause the embankment to sink into the sand, displacing the sand-water
mixture to the sides.

A method proposed to reduce the risk of failure of embankments
constructed on loose deposits of saturated sand is to construct two
sheet-pile walls at the toes of the embankment and parallel to the
length of the embankment. The sheet-pile walls will not

prevent liquefaction from occurring but might minimize the lateral
movement of the soil-water mixture that may keep the bulk of the
embankment in place. To study the effectiveness of using sheet-pile
walls to minimize the risk of failure of an embankment during a seismic
event, several model tests were performed. One such test is described
below.

MODEL

The model consists of a tank constructed of clear plastic 20 mm thick.
The dimensions of the tank are: length equal to 100 cm, width equal to
20 cm and a height equal to 40 cm. Toyoura sand was used in the
experiment. A dense layer (Dr = 63%) of sand was compacted on the bottom
of the tank with a thickness of 12.5 cm. Next, a loose layer of sand (Dr
= -7%), 15 cm thick, was placed on top of the dense sand. The sand
layers were then flooded and allowed to become saturated. Finally the
embankment was placed on top of a thin layer of gravel placed over the
loose sand. The gravel was used to minimize capillary pressures in the
embankment. The embankment was 20 cm long (the width of

the tank), 5 cm high and 5 cm wide at the crest with 2:1 (H:V) slopes.
The sheet-pile walls were placed at the toes of the slopes. The
dimensions of the sheet-piles were 25 cm tall (placed flush with the
surface of the loose sand layer) and 20 cm wide. A different thickness
sheet-pile was used for each toe: 1.0 mm and 0.8 mm.

INSTRUMENTATION

Six pore water pressure transducers were placed in the tank to measure
the excess pore water pressures within the loose and dense sand layers
during the test. Three accelerometers were placed inside the tank to
record accelerations in the loose sand layer. An additional
accelerometer was placed outside the tank on the shake table to measure
the input accelerations. Ten pairs of strain gauges were placed on each
of the sheet-pile walls to measure the strains in the walls caused by
the outward force of the loose sand under the embankment during testing.

SHAKE TABLE

The shake table was 2 m by 3 m and was capable of generation
accelerations up to 0.8 g and frequencies ranging from 0.1 Hz to 150 Hz
in two dimensions. The accelerations, frequencies and event time were
controlled by a personal computer. During testing the table was
supported by pressure from oil and two actuators acting in perpendicular
directions on the table generated movement.

For the test of the model described above the following values were used
as input for the shaking table: 10 Hz and 0.34 g for 10 seconds. The
pore water pressure transducers, accelerometers and strain gauges were
read and recorded digitally at a sampling rate of 200 times per second.

ANALYSES

The data were collected and are currently being analyzed. Tests on a
larger model (2 m x 2 m) will be performed in the near future.