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The Mesopotamian
Engineering Geology researches..
The Effect of Physical
and Mechanical Soil Properties
And Water Movement on bank Stability of Shatt AL- Arab (Maqaal
- Umm-Alrissass)
Naji Kheralla Mustaffa Albahili
Abstract
The sigment of Shatt Al- Arab river, which lies between
the Sundibad and Umm- Alrissass islands has been
selected as a study area. Four sites for the banks are
selected as a main stations to study the stability. The
geometric properties of the banks are measured. Besides
the physical and mechanical properties of the bank soil
at two meter depth are tested, and each profile of the
bank is divided into four depths depending on the
morphological variations. Nine river cross sections are
selected in order to determine the annual linear erosion
rates of the banks as well as the hydrological
properties of Shatt Al- Arab river, wave character
generated by river traffic, block failure and
vegetation.
The results have appeared that there are variations in
the soil properties between the main stations at
different depths of each station, which the soil texture
ranges between clay and silty clay, also It has been
found out that there are variations in values of the
porosity, natural moisture content, wet bulk density,
plasticity index and the shrinkage properties. While the
compaction percentage did not exceed to the maximum
level, whereas the natural moisture content has exceeded
to the optimum moisture content for the compaction in
all stations. At the same time, the over consolidation
ratio values approached to one unit in those had been
found to have medium compressibility. Also the results
have stations, and the consolidation of the soil banks
is normal. The bank soil proved that the density, genus
and parts of vegetation have a clear effect on the
cohesion of the bank soil and consequently on its
erodibility.
This study has shown that the flow level of Shatt
Al-Arab river has fluctuated during the year. While the
type of this flow is semidiurnal. There is a variance in
the values of the flow shear stress, the maximum value
has been remarked at Hamdan region, while the minimum
value has been recorded at Abu Flus region. Some
fluctuation in the ground water level of the banks
depending on the hydrological system of Shatt Al- Arab
river and other interference factors which have been
remarked. Also this study has been proved that there are
many factors affecting wave character generated by the
river traffic, such as the boat geometry, boat speed,
the distance between the sailing line and the river bank
as well as the boat direction relative to the flow
direction.
The two sides of all cross sections of the stations
except the west side at maqaal region have been exposed
to sedimentation process. The highest degree of the bed
erosion has occurred at Hamdan region, while the lowest
degree has been shown at Abu Flus region, which has been
affected by the sediments of Karun river. Also there may
be some fluctuation in the bed level along the
longitudinal section of the river under investigation.
The lateral linear erosion rates of the banks varied,
the highest value of these rates is at the period
between May and June, while the lowest value at the
period between December and February, the annual total
rate which was calculated by the pin method is 0.26
m.year¹ and 0.24 m.year¹ by the field reference
method. The bank failure of the block failure type is
common, and the cantilever failures are widspeard at
some regions of Shatt Al- Arab river, whereas the rate
of the soil volume removed from the banks in the form of
blocks has been 0.38 m³.year¹ for each one meter of
bank, this value has exceeded the rate of erosion
calculated by the pin method. All of the bank slopes
which are selected for this study are in the stable
state, but they vary in the degree of stability, the
west bank of the third station at Hamadan region has
been classified as of questionable safety, while the
other banks have been classified as of satisfactory
safety.
The cohesion property is more effecting than other physical
and mechanical properties of soil it has played the main
role in participation with the hight of the bank slope
to specificate the degree of Shatt Al-Arab bank
stability. This property has been effected by the flow
stages of the river and the ground water level of the
banks. In the future, this stable state of some banks
may change into unstable state when the conditions
become worse. Therefore, some prediction equations have
been found in this study in order to know the stability
stat under different conditions which affect the bank
slope stability, especially the change which affects on
the cohesion which is considered the most affective
factor on the stability stations under investigation
Unpublished Ph.D. Thesis, University of Basra , 2006
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