| In the past,grouted rubble and reinforced concrete were mainly used to protect river bank in river control projects in China.Nevertheless,this revetment method can not only block the organic connection between the aquatic ecosystem and the terrestrial ecosystem,but also reduce the ecological diversity and destroy the various ecological processes of the river,thus lead to a decline of the self-purification of water body and the self-recovery ability of aquatic ecosystem.In recent years,some ecological engineering measures have been applied in restoration of river ecosystem,such as artificial grass slope protection,ecological bag slope protection,grid ecological slope protection and so on.However,these slope protection measures can not apply the control requirements of high velocity rivers because of their lower security performance.Soil bioengineering,an integrated engineering technique which using fresh plant branches as the main body and flexible engineering techniques as the auxiliary technology to build various slopes to prevent slope erosion and improve habitat ecology,can effectively improve the stability of the whole soil bank slope,enhance the self recovery capacity of the water ecosystem and be more economical relative to the "hard" structure,what's more,it also have higher security relative to some ecological engineering measures.Therefore,it is of great significance to research the characteristics of soil bioengineering with the development of time,to make it standardize on the design and to improve the ecological restoration of riverbank in the future under the background of serious degradation of riparian ecosystem in China at present.In this experiment,the living branches of Salix matsudana Koidz are used as experimental materials and set up four kinds of soil bioengineering measures which including cuttings,brushmattress,brush layering and living fascine on artificial slope.In addition,the plant above-ground and roots growth characteristics of different soil bioengineering measures is investigated in 4 months,8 months and 12 months after completion were analyzed.The relationship between the tensile strength and the root diameter of plant roots through the single tensile test were quantitatively analyzed;The root-soilcohesive force and internal friction Angle of different soil layers were measured through the triaxial shear test "RWM model" were used to obtain the additional cohesion of the root system of the four measures and quantify the effect of four different soil bioengineering measures on soil shear strength.The slope safety factors of four different measures were simulated by using finite element method.The soil compactness of bare Slope and four kinds of soil Bioengineering were measures by Digital display soil compactness Meter.According to the results of the study:(1)After 4 months,8 months and 12 months of completion,cuttings were best in height and base diameter.It has a significant difference with the other three measures.The order of growth status soil bioengineering measures from good to bad were cuttings > brushmattress > brush layering > living fascine.The growth rate of the plants from April to August was higher than that from August to December,and it developed rapidly in the early stage of plant growth.(2)After 4 months of completion,the root system of the cuttings and brush layering was less in the depth of 0 to 30 cm,their reinforcing effect on the surface layer soil was small.In the early growth stage of brushmattress and living fascine,the root system was dense in shallow soil,and most of them are fine roots(<1mm).The effect of stabilizing shallow slope was better than that of cuttings and brush layering;After 12 months of completion,the root depth of cuttings and brush layering was 60 cm,and most of them were thick roots(>2mm).In the range of 0~50cm,the dry weight of root system accounts for 94.9% of the total root dry weight,and the coarse root with diameter ? 2 mm accounts for 97.21% of the total root dry weight,which can anchor the deep soil of the slope.And the root system of brushmattress and living fascine was mainly distributed in the soil layer of 0 ~ 30 cm depth.The content of brushmattress with root diameter ? 1 mm accounted for 32.8% of the total root quantity.The fine root of living fascine accounted for 20.4% of the total root amount.Cuttings and brush layering could stabilize the deeper slope,and brushmattress and living fascine could protect the slope from the erosion of water and prevent the erosion of topsoil in the early stage of construction.(3)The average single root tensile strength of the root system with diameter < 2mm is 20.172 Mpa,which is 8.5% of the yield strength of the first grade steel,and can produce significant root reinforcement;The average single root tensile strength of the root system with diameter > 2mm was 15.04 Mpa,which was 6.4% of the yield strength of the first grade steel,and could produce a certain anchoring effect.The maximum tensile strength of root system increases with the increase of root diameter,and the tensile strength decreases with the increase of root diameter.(4)After 8 months of completion,shear strength of root-soil complex with four different soil bioengineering measures were higher than that of the untreated soil.The shear strength of the cuttings was 53.62% higher than that of the untreated soil,the brushmattress increased by 44.19%,the brush layering measures increased by 47.63%,and the living fascine measures increased by 27.35%.So soil bioengineering can effectively improve the shear strength of slope,prevent soil deformation and enhance slope stability.After 12 months,the shear strength of cuttings,brushmattress,brush layering and living fascine were increased by 25.47% and 13.87%,compared with that after 8 months.And the shear strength of cuttings,brushmattress,brush layering and living fascine were increased by 64%,57.6%,60.97% and 37.4%,compared with plain soil.The contribution to slope stability order from large to small were:cuttings > brushmattress > brush layering > fascine.(5)The soil compaction of the slope with the application of soil bioengineering measures is obviously higher than that of the bare slope,especially near the slope bottom,the soil compaction is 2.8 times higher than that of the bare slope.Compared with the other three measures,cutting measures can improve soil compactness obviously,the highest is 280 pa.And compared with bare slope cutting,the soil compactness was increased by 8 times,and the effect of fascine on soil compaction was relatively less improved by 2.8 times.Four measures relative to the bare slope stability has the obvious enhancement,including cutting measures increased by 46.4%,brushmattress measures increased by 67.7%,brush layering measures increased by 41.8%,fascine measures increased by 29.2%,and cutting measures are most prominent contribution to soil compaction.The contribution to soil compaction order from large to small are: cuttings > brushmattress > brush layering > fascine.According to the plant growth characteristics of four different measures and its effect on slope stable,brushmattress and fascine measures are more suitable for reinforcement of shallow soil,cuttings and brush layering measures can anchor in deep soil layer.Four measures applied to river bank slope protection effect are: cuttings > brushmattress > brush layering > fascine.The research results provide quantitative evaluation method and theoretical guidance for the wide application of soil bioengineering technology in riverbank revetment. |
PDF Full Text Request