Mechanism Research Of Biological Earth-bank Reinforcement In Polypropylene Geotextile Bags

Polypropylene geotextile bags（PP geotextile bags for short）provide much help to tobuild bank of terrace as a new martial. Planting suitable plants in the terrace bank built by PPgeotextile bags not only can make full use of ridge and bank space, but also can produceeconomic benefits and play an important role in stabilizing the terrace bank. Experimentalmaterials: Lolium perenne, Festuca arundinacea, Trrifolium repens, Medicago sativa, Liriopespicata, Salix matsudana, Lonicera japonica, Hemerocallis citrina, Amorpha fruticosa. The9plant species were planted in different ways on the terraced bank which built by thepolypropylene geotextile bags. The growth index in different growing stages of9plantspecies was studied by observation and statistic analysis. After the plants grown1.25years,the anti-shearing strength, soil anti-scouribility and soil anti-erodibility of nine root-soilcomposite system were researched by the ways of field sampling on similar position andchamber experiment. Through the tests of above indicators to analysis the mechanism ofbiological earth-bank reinforcement in the new type of bank construction, Syntheticallyconsidering the the economic and environmental benefit, to select the best plants to protectthe terrace bank. The result of this experiment are as follows：(1) Vegetation coverage of9plant species were changed with the grown time. Vegetationfraction of these plants which growed for1.25year was Festuca arundinacea> Loliumperenne> Medicago sativa> Trrifolium repens> Amorpha fruticosa> Salix matsudana>Liriope spicata> Hemerocallis citrine> Lonicera japonica; the vegetation coverageincreasing rate in the second year is Medicago sativa> Festuca arundinacea> Loliumperenne> Trrifolium repens> Amorpha fruticosa> Salix matsudana> Hemerocalliscitrine> Lonicera japonica> Liriope spicata.(2) The per unit above-ground biomass of9plant species was Salix matsudana> Amorphafruticosa> Medicago sativa> Festuca arundinacea> Lolium perenne> Hemerocallis citrine> Trrifolium repens> Lonicera japonica> Liriope spicata..The direct economicbenefit of9plant species was Lonicera japonica> Hemerocallis citrine> Medicago sativa>Festuca arundinacea> Lolium perenne> Salix matsudana> Amorpha fruticosa> Liriopespicata..(3) The results showed that the relationship between the shear strength of the nine root-soilcomposite systems and vertical pressure could be described by Coulomb equation. When thewater content of six Samples was14.68±0.21%and roots content of five root-soil compositesystem was0.15±0.02mg/cm3, compared with the soil without roots, the soil cohesion addedvalues caused by root-soil composite were big as the influence over soil internal friction angleof roots was small. The growth rate of soil cohesion caused by the9plant species couldincrease by: Amorpha fruticosa62.3%, Trrifolium repens56.3%, Salix matsudana54.9%,Lonicera japonica51.2%, Lolium perenne51.1%, Medicago sativa50.7%, Hemerocalliscitrine47.6%, Festuca arundinacea30.9%, Liriope spicata15.2%.However, the changerange of soil internal friction angle about9plant species only from-1.5to0.8, which showedthat the roots enhance the soil shear strength of soil mainly instead of soil internal frictionangle through the enhancement of soil cohesion．The9plant species all could enhance the soilshear strength of soil in the PP geotextile bags, and the best enhance effect of plant specieswere Amorpha fruticosa and Trrifolium repens, the better ones were Salix matsudana,Lonicera japonica, Lolium perenne, Medicago sativa and Hemerocallis citrine.(4) Compared with the soil without roots, the6herb plants have enhancement effects onsoil anti-scouribility and soil anti-erodibility. Enhancement effects on soil anti-scouribility ofsame plant is slightly different as the erosion slope different. Under the same erosion slope,enhancement effects on soil anti-scouribility increasing with the amount increasing of theroots. Roots of Trrifolium repens have the best enhancement effects on soil anti-scouribility,which higher than other herb plants. The better ones were Festuca arundinacea, Medicagosativa and Liriope spicata. Enhancement effects on soil anti-erodibility increasing with theamount increasing of the roots. Roots of Festuca arundinacea have the best enhancementeffects on soil anti-erodibility. The better ones were Hemerocallis citrine, Lolium perenne and Liriope spicata.(5) Compared with the soil without roots, the Lonicera japonica, Amorpha fruticosa, Salixmatsudana have enhancement effects on soil anti-scouribility and soil anti-erodibility.Enhancement effects on soil anti-scouribility of same plant is slightly different as the erosionslope different. Under the same erosion slope, enhancement effects on soil anti-scouribilityincreasing with the amount increasing of the roots. Enhancement effects on soilanti-erodibility increasing with the amount increasing of the roots.Roots of Amorpha fruticosahave the best enhancement effects on soil anti-scouribility and soil anti-erodibility. The betterones were Salix matsudana.Synthesize the multiple factors of the enhancement effect of plants’ stabilizing the terracebank, we can chose river Amorpha fruticosa, Salix matsudana, Hemerocallis citrine,Trrifolium repens, Medicago sativa and Festuca arundinacea to plant in the terrace bankcovered by PP geotextile bags.