An Experimental Study on Geogrid with Geotextile Effects Aimed to Improve Clayey Soil

The increase of shear strength in soil, reinforced with the geogrid (alternate reinforcer), is resulted from an increase of modulus of soil hardness, and also from the tensile strength of reinnforcer. The shear strength of contact surface in soil appears due to both the friction strength against the contact surface, and the passive strength formed in front of the elements of the geogrid system. In the clay reinforced with a geogrid, the resistance of the contact surface is low; therefore, contact surface rupture occurs before the tensile strength reaches the ultimate limit. Also, the geogrid is almost ineffective in limiting particles movement and creating passive resistance in clay, due to a big difference in the sizes of geogrid opening (a perture) comparing to clay grains. In this research, we tried to examine the effect of geotextile layers around the geogrid aimed to improve the soil-geogrid interaction in different drainage conditions by means of triaxle (UU) and (CD) trials on a large scale. Experiments were carried out, based on non-reinforced samples, geogrid-reinforced samples and geocomposite reinforced samples. The results of the experiments showed that the geotextile layers around the geogrid in the clay reinforcements not only effectively improved the interaction of contact surface, where the stresses are concentrated on the geogrid, but enhanced the shear strength parameters, the consolidation and drainage processes, as well. Radiographic results taken from fractal samples indicated that the rupture plate gets a reflection state in the reinforcing elements at the location of geocomposite configurations only, relative to the reinforcing elements. Meanwhile, the geogrid layers did not have any impact on the changes of rupture surface situation.