Stress Distributions and Pullout Responses of Extensible and Inextensible Reinforcement in Soil Using Different Normal Loading Methods

In design of reinforced soil structures, pullout capacity of reinforcement in an anchorage zone is an important parameter for stability analysis. This parameter is generally quantified by conducting laboratory or field pullout tests. In the laboratory pullout test, the reinforcement is embedded in the soil mass at a normal stress, which is commonly applied by a pressurized airbag or a hydraulic jack through a rigid plate, and then a horizontal tensile force is applied to the reinforcement. This article reports an experimental study conducted to evaluate the effect of the load application method using an airbag with and without stiff wooden plates on the vertical stress distribution and the pullout capacities and deformations of extensible (geogrid) and inextensible reinforcement (steel strip) in the soil in a large pullout box. This study monitored the distributions of the vertical earth pressures at the top and bottom of the soil mass in the pullout box, and at the level of reinforcement using earth pressure cells. The measured earth pressures show that the airbag with stiff plates resulted in a nonuniform pressure distribution, whereas the tests with an airbag directly on the soil had an approximately uniform pressure distribution. The nonuniform pressure distribution resulting from the airbag with stiff plates reduced the pullout resistance of the reinforcement as compared with that using the same airbag without stiff plates. The nonuniform pressure distribution effect was more significant for narrow inextensible reinforcements than wide extensile reinforcements. The test results also show that the displacements in the cross section of the same transverse bar were not equal when the normal load was applied through stiff plates.