Seismic response law and supporting mechanism of slope living stumps

A tree stump can remain biologically alive, called a living stump, after the tree above ground has been cut down. The slope stability often depended on the mechanical behavior of the living stumps during earthquake action. But it is still lacking in the mechanical response and slope support mechanism. This study aims to reveal the mechanical response of the living stumps slope under earthquake action. A large-scale shaking table test was conducted to explore the influence of the wave excitation intensity and direction on the main root bending moment and lateral root axial force of the slope’s living stumps in the Wenchuan earthquake. A finite element three-dimensional simulation was also implemented to investigate the influence of the living stumps on the slope shear strain and safety factor. The support mechanism of the living stumps on the slopes was obtained after simulation. The results show that: (1) The main root of the living stumps was subjected to the action of the bending moment, the absolute value of which gradually decreased from the top to the bottom along the depth of the main root. The bending moment increased by 4% to 40% with every level of the increase in the excitation intensity. The direction of the bending moment and the position of the inflection point were significantly dependent on the lateral roots, but there were no effects of the excitation direction and intensity. The direction of the excitation had a significant impact on the magnitude of the bending moment, with a 12% to 18% increase in the XZ bidirectional excitation, compared with the X unidirectional excitation. While there was the 30% to 42% increase compared with the Z unidirectional excitation. (2) The lateral roots were born under the axial force, and the axial forces on both sides of the lateral roots presented a tension-compression state in pairs. The absolute value of the axial force increased with the increase in the excitation intensity. The larger axial force was observed as it approached the root tip. The excitation direction failed to change the tensile and compressive properties of the lateral root. But there was a significant impact on the magnitude of the axial force. The axial force during XZ bidirectional excitation was 8%-10% higher than that during X unidirectional excitation, and 39%-47% higher than that during Z unidirectional excitation. (3) The presence of the living stumps caused the redistribution of the slope stress and its migration towards the deeper soil layers. Living stumps assisted the main root to exert the "anti-sliding pile" effect through the "anchor support" effect of the lateral roots, thereby enhancing the seismic stability of the slope. The anti-sliding degree of the living stumps was related to their position, indicating the strongest at the top of the slope, followed by the middle of the slope, and the weakest at the bottom of the slope. Seismic design was verified on the living stump slopes. The finding can provide a strong reference to select the root system types and arrangement positions of the living stumps. Seismic response of the living stump roots and seismic support mechanisms can also be achieved in the seismic research of the living stump slopes.