Research On Root Reinforcement Mechanisms And Evaluation Of Vegetation Slope Stability In Beijing

As a mountainous country,mountain area covers about 66.7%of land area in China.Due to the unreasonable use of resource and environmental transformation,many mountain hazards happened,leading to great property losses and have becoming serious threat to life safety.As one of the main types of mountain hazards,landslides are widely distributed in mountainous area.Fragile ecological environment and complex geological structure in mountainous area make it difficult to control landslides.As a natural barrier,the existence of plant roots have reinforced the soil cohesion,absorbed water from soil and reduced pore water pressure then enhanced soil shear strength.Vegetation slope protection technology is an effective method to stabilize slope.In the construction of slope protection engineering,it is necessary to concern about tree species selection and spatial allocation.However,this few studies were performed to determine the root reinforcement mechanisms of the vegetation slope protection technology.Therefore,14 common plant species in Beijing were used to configure planting collocation.Meanwhile,numerical simulations were conducted to simulate and evaluate factor of safety of different vegetation slopes.The results are as follows:(1)There were a lot of lateral roots existed in tree plants.Tap root was founded in shrubs with a deep depth and few vertical and lateral roots existed in root structure.Herbs were mainly loose rooting type.Due to the widely distributed of roots in all directions,tree plants had a good performance on soil resistance especially those with large root diameter and deep vertical roots.Roots of shrubs had great tillering capacity,which caused large friction between root and soil.Herbs had different maximum root depth,such that most of these roots were distributed in shallow soil layer.(2)There was no relationship between root tensile strength within 14 plant species.Influence of root diameter on tensile strength was few in herb roots,followed by tree roots and shrub roots.For the pull out strength,the biggest impact factor was diameter in the pull out position,followed by the branching points.Those plant species with more root quantity and longer roots seemed to have larger strength.Anchorage force was influenced by root architecture.Associated with numerical simulations on root architecture,the best behavior of anchorage plant species were Ulmus pumila,Platycladus orientalis,Robinia pseudoacacia and Vitex negundo.(3)For homogeneous slope,when there had one plant species on it,Platycladus orientalis showed the best performance on factor of safety at early years.When considered wind force,it was recommended to construct in less windy area.For shrubs,Vitex negundo contributed the best slope stability regardless of wind force.Nerium indicum had showed the worst performance on slope stability.when there had two plant species,collocation mixed with tree and herb had showed the best behavior on slope stability.Collocation mixed with tree and shrub seemed to be unstable when there had wind force on slope.Recommended colloctions were Robinia pseudoacacia mixed with Setaria glauca,Vitex negundo mixed Setaria glauca or Astragalus adsurgens.(4)For shallow soil layer slope,when there had one plant species on it,great factor of safety was founded with Robinia pseudoacacia in steep slope and Koelreuteria paniculata and Ulmus pumila in moderate slope.When considered wind force,Vitex negundo was recommended to plant on slope to prevent slope instability.When there had two plant species,collocation mixed with tree and herb had showed the best behavior on slope stability.For moderate slope,colloctions mixed with Ulmus pumila and Setaria glauca and Astragalus adsurgens could provide better slope stability.For steep slope,colloctions mixed with Robinia pseudoacacia and Setaria glauca and Astragalus adsurgens could provide better slope stability.(5)For convex slope,it was better to plant herbs to improve the stability if there had many shrubs.Tree species could increase slope stability to a large extent,however,when considered wind force,factor of safety of slope covered with tree species might decrease sharply due to the large the crown area.For concave slope,when there was wind force existed,stability of slope with collocation mixed with shrub and herb was much larger than collocation mixed with tree,shrub and herb.