الفهرس 
1INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The use of geotextile tubes in temporary and permanent structures for flood control, retaining and protection works, and storage applications is gaining much considerationduring the past decades. Although, theyweresuccessfully applied in many storage and protection applications, further worksarerequired in order toextrapolate their performance when using in marine causeways exposed to flood and water pressure.
The current research focuses on (coastal/ marine) causeway,which are very close to the coasts and shorelines.
The coastal causeways may be subjected to several disorders, which are destroyed by floods as a result of the progression and height of the sea water surface during storms. These may cause several problems in the stability of coastal causeways, as well as, the possibility of exposure to erosion.
Therefore, the current research work studies the stability of marine causeways close to the coasts when constructingby using the new technique of geotubes.
In the present study, computer software (ABAQUS)was used to investigate the stability of geotubes as soil retaining structure for marine causeway.Flexible shells contain elasto-plastic soil materials were used to model the geotubes.
Severalpatternscomprised of two geotubes lining the side of a marine causeway, were modeled to explore their effect on the causeway displacementunder gravity and surcharge loads in the presence of the effect of water. The stability of the system was investigated for a 1:1 slope considering the deformed shape of the geotubes resulting fromapplying different pumping pressures(0.0, 5.0, 20.0 and 50.0 kPa) on them. Also, the effect of water level fluctuation due to tidal effect was also taken into account by considering water depths of 0.5,1.5 and 2.0m measured from the toe.
Twenty four different designs of the stacked tube retaining structures in the flood conditionswere modelled using finite elements model (FEM). It can be concluded thatacceptable results have been got when using geotubes formed from pumping pressure =5.0kPa under water depth = 0.5 and 1.5 m as compared to the other tested pumping pressures.However,at water depth = 2.5 m, the deformation of the marine causeway was higher in case of using tubes in place than without being in place.Additionally, the lateral displacement values of the causeway reinforced by geotubes subjected to specific pumping pressure were affected by the fluctuation of water level (tidal range).
Finally, values of pumping pressure from 20.0 to 50.0 kPa cannot be solved at lower water levels (0.5 and 1.5m).This may be occurred due to failure of upper tube as the contact area between the tubes and the slope was reduced. In addition, lower water depth did not provide the restriction needed for the upper tube. High water depth increases the stability of upper geotubes.
Generally,the plastic strain and stressesimproved inmost areasin slope region and increased in the area near the toe.
Two additional scenarios were only modelled in dry case for pumping pressure equal to 0.0 kPa with gravity and surcharge loads. The reason for that was the instability of the numerical solution when using higher pumping pressures. At higher pumping pressures, the geometry of geotubes was greatly influenced which lead to failure of the upper tube. However, causeway reinforced by geotube subjected to pumping pressure equal to 0.0 kPa remarkably reduced the lateral displacement.
Due to the numerical instability with higher pumping pressures in the dry case, two alternative scenarios were suggested. These two scenarios were: (1) using individual tubes with different diameter and (2) changing the inclination angle of the causeway slope. By changing the causeway slope angle from 45o to 30o in case of pumping pressure = 5.0 kPa, the numerical solution stability was achieved, as some of the tube weight was transported to the causeway slope. On the other hand, a reduction in lateral displacement were achieved when applying individual geotubes with bigger diameters subjected to pumping pressure = 20 kPa.