Abstract:
Background Tree roots can inhibit shallow landslides. Quantitative evaluation of the effect of root reinforcement is a key step for assessing the effectiveness of vegetation in slope stabilization. The traditional calculation method of root-soil composites did not consider the influence of roots on the elastic parameters of root-soil composites. Meanwhile, it is difficult to calculate a slope with a large number of roots. In fact, trees are often planted in a spatial layout of regular planting arrangement on slopes to create plantations; thus, this research treats periodically arranged tree roots and the surrounding soil as a periodic composite.
Methods The representative volume element (RVE) method was introduced to directly construct the three-dimensional constitutive relation of root-soil composites. The theoretical results obtained by the RVE method were verified by direct shear tests and repeated shear tests with length-varied roots. The roots and soil used in the test were collected in Jixian, Shanxi. The application feasibility of the equivalent mechanical properties of the root-soil composite obtained by the RVE method to evaluate the slope stability was verified by numerical simulation.
Results The RVE method can be used to accurately evaluate the equivalent elastic properties of root-soil composites, and the improvement rate of the shear elastic modulus is only 0.24% higher than the repeated shear test. The difference for cohesion c and internal friction angle φ is only 2.45 kPa and 3°, respectively. The cohesion calculated by the Wu model is overestimated about 5 times compared to the test results. Compared with the pure soil slope, the safety factor of the vegetated slope with the test data increases by 7.20% and the RVE slope model increases by 9.78%, while the safety factor of the slope with the Wu model increase by 29.33%. The Wu model has the risk of overestimating the slope stability compared with the RVE model.
Conclusions The RVE method can accurately predict the alterations of the elastic parameters and strength parameters c and φ of the root-soil composite. The strengthening effect of roots on the soil not only improves the cohesion, but also changes the internal friction angle and elastic parameters. RVE method combined with numerical simulation provide new method and technical means to realize the stable calculation of the slope with a large number of roots.
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