Calculation Formula for the Pullout Force of Uniaxial Geogrid-Reinforced Expansive Soil

To obtain the action force between the reinforcing material and filler in reinforced soil, many scholars at home and abroad have conducted pullout tests, which are limited by the testing apparatus. Most of them have studied the pullout force between a biaxial geogrid and sand. The pullout force formula is generally believed to be composed of the surface friction and lateral resistance of transverse ribs, and uniaxial geogrids have rarely been researched experimentally on the basis of the pullout force between them and the expansive soil filler due to the large distance among transverse ribs. This study draws on existing methods to determine the pullout force, conducts a preliminary analysis, proposes a formula for calculating the maximum pullout force, uses a self-developed large-scale CNC pullout test system, and utilizes its large size, bidirectional airbag loading, and ability to eliminate side wall friction. The design of the test scheme is optimized to obtain two important calculation parameters in the formula: one is to cut grids of different lengths to provide lateral resistance and then implement them to obtain the coefficient of sliding friction between grid and fill; the other is to develop different numbers of horizontal ribs in the pullout test of a grille, and the lateral resistance of the end bearing of a single transverse rib is measured. The results of the lateral resistance of the end bearing based on the analysis of the three mechanisms of shear, punching, and Prandtl failures are compared. The lateral resistance of the lateral rib end bearing measured from the test is proven reasonable. Two types of expansive soils reinforced by different types and sizes of grids are analyzed with the calculation formula of the maximum pullout force, and the coefficient of pullout friction is determined to be rational. The research results can be used to guide the design and construction of uniaxial geogrid-reinforced expansive soil and the modification and upgrading of products by grid manufacturers.