Performance Evaluation of the Screw Nailed Walls in Tabriz Marl

Abstract

Urban development and rapid extension of cities have been accompanied by considerable growth in excavation projects. Soil nail walls have been found to be an economical solution to many soil reinforcement and excavation support problems. To overcome some of the intrinsic problems with the conventional grout soil nails, screw soil nails were developed in recent years that provide several advantages over grouted soil nails. Tabriz marl outcrops at considerable parts of this city. Considering the rapid development of the Tabriz (as one of the biggest industrial cities of Iran), a large part of new urban areas and industrial zones will be located on marl soils. Therefore, it is necessary to evaluate the efficiency of the screw nailing method in Tabriz marl soils. In the present study, the performance of the walls reinforced by screw and grouted nails in different types of Tabriz marls was studied. For this purpose, a three-dimensional (3D) modeling is performed using the ABAQUS software. The results of the numerical analyses revealed that the failure zone of the screw and grout nailed walls is similar and consisting of parts entitled A and B. There is no significant difference between the characteristics of part B at both of the screw nailing and grout nailing methods. While, the A part of the failure zone and the maximum soil displacements in this part at the screw nailing method are smaller than those of the grout nailing method. At all types of the Tabriz marl, the lateral and vertical displacements of the reinforced walls by screw nails are smaller than those of grout nails, and in the case of yellow marl, the difference is considerable, while, at brown marl, it is negligible. The results of analyses show that the screw nail performs better than the pressurized cement grouted nail in terms of wall displacement. The efficiency of the screw nails increases in comparison to grouted nails by proceeding with the excavation process. At yellow marl because of lower elastic modulus value, the performance of the screw and grouted nails is more obvious than the other types of marl. The rate of increase in settlement values and maximum settlement of the soil for screw nailed walls are smaller than those of grout nailed walls. Also, the settlement profile of ground surface behind the wall is consisting of two parts, including critical and non-critical parts. The difference in the behavior of the screw and grouted nailed walls is obvious in the critical part of the soil behind the wall.