Effects of plant root lengths on stability of ecological bag reinforced retaining wall

In the flexible ecological reinforced retaining wall, the vegetation can not only play a greening and environmental protection role, but also the growing plant roots have a three-dimensional reinforcement effect. In order to explore the effect of plant roots on stability of the ecological bag reinforced retaining wall, In this study, three round-trips vertical load tests were carried out on four groups of ecological bag reinforced retaining wall models with different root lengths. That were, no root in the ecological bag, and the roots extended out ecological bag of 10, 20 and 30 cm respectively. Palm leaves were selected to replace plant roots in the tests due to plant roots are easy to wilt and lose strength, while palm leaves are not easy to wilt and still have large tensile strength after wilting. The variations of four parameters, horizontal displacement of ecological bag reinforced retaining wall, horizontal earth pressure behind the ecological bag wall-plate and near reinforced body end, the tensile strain of geogrid, were studied with root length and load. The results showed that the variation rules of the four parameters with the increase of load in the four sets of model tests were similar. Through the comparative analysis of the test data, it was found that the presence of roots increased the overall rigidity of the ecological bag wall-plate, under the same load, compared with no root, the horizontal displacement in the three types of retaining walls with different root lengths all decreased, and the more root length increased, the more the values decreased. The horizontal displacement had slightly decrease in load less than 80 kPa, while obviously decrease in load more than 100 kPa. The horizontal earth pressures behind the ecological bag wall-plate without roots in different wall heights were all greater than that of the rooted reinforced retaining wall under the same load, especially the roots extended out the ecological bag of 30 cm. The horizontal earth pressures near reinforced body end and tensile strain of the geogrid had similar trends with the horizontal earth pressures behind the ecological bag wall-plate,and they were gradually decreased under the same load with the root length increased. Then the sensitivities of the four parameters affected by the root length were analyzed, and the sensitivities of the four parameters were in order from high to low as follows: horizontal earth pressure behind the ecological bag wall-plate, horizontal displacement of retaining wall, horizontal earth pressure near reinforced body end, tensile strain of geogrid. The two parameters, horizontal earth pressure behind the ecological bag wall-plate and horizontal displacement of ecological bag reinforced retaining wall, were more sensitive to the change of root length. The results showed that the plant roots could improve the integrity and stiffness of the ecological bag wall-plate, and increased the internal and external stability of flexible ecological reinforced retaining wall. With root length increased, the strengthening effect became more obvious. The successful implement of this research can provide important experimental basis for understanding the nature of the role of plant roots on flexible ecological reinforced retaining walls. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.