Impact Of Biopolymer In The Soil Strength

With the rapid development of economy in China,there are lots of construction projects in progress.In some projects about geotechnical engineering,the most important and difficult problem is about soil stabilization.Soil can often be regarded as important material which has low tensile and shear strength.The procedure called soil reinforcement is often used to improve the properties of soils by utilizing mechanical energy and manmade materials,including cement,gypsum and lime.These procedures have been performed for century.Both of these required substantial energy for material production or installation.Simultaneously,environmental degradation is caused by these methods or materials such as underground water pollution,soil erosion,carbon emission et al.The biogeotechnical engineering is an interdiscipline by utilizing biological technique to solve geotechnical engineering problems.Stabilization of soil using plant is a long-practiced,effective,and environmentally friendly method that results in minimal disturbance to the subsurface soil and environment.Some comprehensive literature reviews show that the presence of plant roots can improve the strength of the soils and the stability of natural slopes.Plants root can influence both the supply and availability of nutrients in the soil.These may lead to the change of biopolymers in the soil which have close relevance with soil mechanical properties.The interactions between the biopolymers and soil have significant effects on geochemical process such as biofilm formation,physical and chemical properties of soil,soil structure.However,there are less quantitative analyses about to what extent biopolymers in the root zone may influence the soil structure.Therefore,it is important to analyze the combined effect of plant roots/biopolymers in biogeotechnical stabilization of soils and geotechnical structures.This research tried to use artificial biopolymer and fiber to mimic the biopolymer/root effect in the soil,by carrying out direct shear test,hydro conductive test,bonding test,and scanning electron microscope,the geotechnical of property of biopolymer and fiber effect in the soil have been measured.The synopsis of the data and implications are briefly summarized below:(1)In geotechnical engineering the influence of biopolymers is rarely if ever considered,as their effects naturally reoccur almost exclusively in the surface regions of the soil.We explore the processes in natural phenomena where biopolymers impact the properties of soils and sediments,as well as the potential for artificial formation of soil/biopolymer composites in ground improvement,and considers the key lessons of value for engineered use of such materials.The natural precedents of soil/biopolymer composites illustrate that there are potential engineering applications of natural and artificial biopolymer in soils for engineering purposes,particularly for shallow failure mechanisms such as erosion or translational slope failure.(2)The ability of plant roots to improve the mechanical properties of soil is generally considered to be as a result of both dewatering and the physical restraint offered by the root system.Fibre reinforcement in soils mimics this restraining effect and has been shown to offer considerable improvements to soil strength.However,the physiological behaviour of roots in terms of their effect on geotechnical performance is not fully understood,in particular,the effect of plant mucilage and microbial biofilms in the rhizosphere.Artificial root/biopolymer systems comprising 3D-printed fibres and xanthan gum biopolymer in sand have been tested under direct shear loading under very low vertical normal stress to understand the impact of realistic levels of biopolymer on root strengthening.The effect of fibre content,fibre shape,xanthan gum gel concentration and impact of wetting and drying cycles are all considered.The behaviour of this idealised system suggests that plant mucilage and other root-associated biopolymers contribute significantly to the stabilisation of shallow vegetated soil by creating bonds between the root and soil grains.Results indicated soil shear strength increased with fibre content increase,fresh biopolymer gel and fibre caused insignificantly effect on soil,but subsequent drying lead to the soil strength increase.Dry cycles increase biopolymer fibre soil strength up to 100% while this strengthening effect lost at wet cycles.(3)The contribution of typical levels of biopolymer in soil to the geotechnical behaviour of the medium has been explored using a highly controlled artificial sand/biopolymer composite to model natural conditions with the outcomes presented below.This enables the isolation of the effect of biopolymers specifically from other confounding factors and allows us to determine the potential for natural biopolymers to be managed to enhance or control soil properties.The purpose of this study was therefore to use artificial biopolymer to mimic natural biopolymers in the soil,and explore its influence on soil strength under different water condition and treatment.A range of moisture conditions including drying,partial wetting,full saturation and drying-wetting cycles were applied to mimic realistic moisture regimes in the soil and to help understand the behaviour of soil/biopolymer composites under natural conditions.Results indicated the importance of drying and wetting effect in the biopolymer treated soil and exposure the behaviour of biopolymer soil under different water condition.Wet cycles caused redistribution of the biopolymer and change its subsequent strengthening effect behaviour from relatively strong.(4)This study explains how curing influences biopolymer treated soil strength,especially for the behaviour of xanthan gum biopolymer and sand interaction during the curing.By curing biopolymer treated soil to different water contents under different curing conditions,the direct shear tests were carried out in measuring biopolymers treated soil strength.Finally,the bonding property of biopolymers after curing was discussed to give a further explanation of how biopolymer performed under different curing conditions.Results indicated biopolymer treated soil increased with water content decrease.The increase of drying temperature lead to the biopolymer gel bonding strength increase thus to increase soil cohesion.Scan electron microscopy(SEM)analysis presented the interparticle behaviour of the biopolymer treated soil mixture.