Fatigue cracks are amongst the most important factors for destruction of asphalt pavements, caused by excess loads and traffic in roads and airports. Geosynthetics, as strengthening materials, are able to increase fatigue life and prevent early cracks in asphalt pavements, to a large extent. Efficiency of geosynthetics in asphalt pavements depends on many factors including asphalt mix, temperature, location, etc ... This paper studies the performance of two types of geosynthetics (Geogrid and Geotextile)on the fatigue life of asphalt blocks with dimensions of 381x63x50 mm. Samples were provided of non reinforced, reinforced by geotextiles and geogrids, from asphalt slabs for the purpose of testing. Fatigue tests were conducted by four point beam test, and fatigue load by half-sin wave at a frequency of 10 cycle/sec (no rest period) has been used. The end of fatigue life is defined as decrease stiffness to 50% of its primary stiffness. Results indicated that the fatigue life of reinforcement beam with geogrid and geotextile increase 56% and 50% respectively. Furthermore reinforcing layer increases primary stiffness and reduces rate of cracks propagation in reinforcement specimens compared to non- reinforcement specimens.

This paper presents a recently developed automated pullout apparatus for soil-geogrid strength and deformation behavior investigation. The new apparatus is capable of applying load/displacement controlled monotonic/cyclic loads at different rates/frequencies, different wave shapes and loading patterns, through a computer closed-loop system. An extruded uniaxial geogrid and silica sand are used throughout the experiments. The effects of normal pressure (surcharge) and relative density are investigated on displacement distributions and pullout capacity of the geogrid in both monotonic and cyclic tests.In monotonic tests, it is observed that with increase in relative density and surcharge, pullout resistance has increased. In cyclic tests, despite some minor observations of post-cyclic strength increased, no specific comment can be made at this stage on the post-cyclic strength.

Large size direct shear tests (i.e.300´300mm) were conducted to investigate the interaction characteristics between clay-geogrid, sand-geogrid and clay-sand-geogrid. The lack of adequate frictional resistance between clay and reinforcing elements was compensated by using thin sand layers to encapsulate the geogrid. Results indicate that encapsulating geogrids in thin layers of sand is very effective in enhancing the strength and deformation behaviour of reinforced clay. Variations of bond coefficient indicate that the shear resistance between the geogrid and the soil can be larger than the shear resistance of the soil itself. The increase in the shear resistance is mainly due to the influence of the geogrid apertures providing some bearing resistance during shear. In order to investigate the effects of passive resistance provided by the transverse members of the geogrid, several tests were conducted with these members removed. Total shear resistance provided by the geogrids with transverse members removed was approximately 10% lower than shear resistance of geogrids with transverse members.

It is widely known that the bearing capacity of a shallow foundation is reduced when the foundation is subjected to rocking moment and horizontal loads during an earthquake event. This paper discusses a series of numerical solution carried out in FLAC that calibrate with results of experimental testing on small scale reinforced foundation in order to measure the bearing capacity of a reinforced shallow foundation due to horizontal cyclic loading. In this study, the horizontal bearing capacity ratio (HBCR) was compared with vertical bearing capacity ratio (BCR) and the effect of such parameters as number of cycles and loading magnitude on the dynamic bearing capacity of reinforced soil was discussed.

The reinforced soil walls have shown an acceptable seismic behavior in most earthquakes. However, they can show a considerable deformation which has been studied by many researchers. The presented research aims to study different parameters which affect the seismic deformation of reinforced soil walls. In the research, five different series of tests conducted on reinforced soil wall models on a shaking table and the effects of soil density, embedded depth, length of geogrids, stiffness of geogrids and friction angle between soil and geogrids were investigated. The behavior of the models was monitored using four accelerometers and four LVDTs in each test.The methodology of the presented research could be summarized as follows: 1. The increase of geogrids length from 0.7 H to 0.9 H could decrease horizontal deformations up to 50%. It also significantly reduces the amplification of the acceleration. 2. Embedded depth has an important effect on reducing the vertical deformation around the developed failure zone.3. When stiff reinforcements with relatively high tensile strength are used, the pullout mode of failure happens rather than yielding of reinforcements. The stiffness of geogrids, in this case, does not have any effect on seismic deformation.4. The friction angle between the soil and the geogrids had a significant effect on seismic deformations.5. Two modes of deformation, named bulging and tilting, have been investigated in the study. These modes are related to the overall stiffness of the system and the dynamic wave characteristics. The overall stiffness of the reinforced soil walls is mainly related to the soil density, geometrical properties of the wall; and also the number of reinforcement layers, length and mechanical properties of geogrids.The paper concludes that it is possible to design the reinforced soil walls in a way which decreases the horizontal and the vertical deformations up to a requested performance design level for seismic loads; however it needs more research. In this research it is found that the most considerable parameters which have effect on seismic deformations are soil density, physical and mechanical characteristics of geogrids (length, tensile strength, friction angle between soil and geogrids) and embedded depth. On the other hand, the characteristics of the dynamic waves, such as the amplitude, duration and the seismic wave frequency content, may have also effect on seismic deformations which also needs more research.

In this research, failure mechanism, soil deformation and effect of reinforcement below a strip foundation were studied using physical modeling and PIV method. For this purpose, a comprehensive set of tests were undertaken on dense and loose sands and different geosynthetic materials such as geotextile and geogrid for soil reinforcing. In each step of loading, digital image of deformed soil was captured and image processing was applied with GeoPIV software. The experimental results showed that using of geogrid and geotextile leading to increase bearing capacity considerably, reduce settlement and change the failure mechanism of sand. The test results showed also that geogrid has an effective performance in comparison with geotextile in sand at the range of small strains.