Experimental Studied On Expansive Soil With Polypropylene Fiber In Wetting-drying Cycles

This paper aims at studying the expansive soil improved by polypropylene fiber which is located at a mining area in Nanning.In order to investigate the effect of drying and wetting circle on the engineering properties of fiber expansive soil,a large number of indoor tests were carried out for the soil samples,including trails on the basic physical properties of expansive soil samples,the compaction test of fiber expansive soil,direct shear test,consolidation test,the expansion ratio without loading with the action of drying and wetting circles.And after exploring the development and changes of fractures of fiber expansive soil due to cyclic wetting-drying,the author has obtained the following conclusions:(1)Liquid-plastic limit and plasticity index vary according to soils with different particle sizes.(2)rease of fiber weight,the peak value of dry density of fiber expansive soil decreases unceasingly,which is means that the maximum dry density is decreasing.In contrast,the rangeability of optimum water content is not very large with the increase of fiber weight,but the optimal water content begins to grow when it comes to increasing the fiber weight to a certain value.(3)The action of drying and wetting circle has a significant impact on the consolidation characteristics of expansive soil.Under normal circumstances,with the increase of the number of wet and dry cycles,the compressibility of expansive soil increases gradually,which its increasing trend can be approximately described by a linear regression equation.Adding the fiber into the expansive soil can apparently improve compressor characteristics of the soil.The relationship between them is that the higher the fiber weight,the lower the compression coefficient.Therefore,adding the right amount of fiber into expansive soil can effectively refrain from the base settlement deformation in the construction of the project.(4)hen the author did the direct shear test on fiber expansive soil,the tensile stress,which generated from fiber,prevented the the shear failure of soil mass,and the cohesion enhanced accordingly.At the same time,the associative architecture between soil particles was destroyed,and the friction between fiber and soil particles became weaker than the friction between soil particles,these all made the internal friction angle decreases slightly.(5)After water swelling,the expansion rate of expansive soil was divided into three processes: acceleration,deceleration and smooth.When fibers were added to the soil,they were intertwined to form a lattice structure,which limited the expansion of expansive soils.Dry-wet cycle also reduced the expansion of expansive soil.With the increase of fiber content,the no-load expansion rate of expansive soil would decrease.When the amount of fiber was increased to a certain extent,the expansion rate would be stable.With the increase of dry-wet cycles,the no-load expansion rate of expansive soil would reduce,and the expansion rate would be stable after dropping to a certain value.(6)With the increase of dry-wet cycles,the number,length and width of pattern cracks would gradually increase after dehumidification;while the increase of fiber content would significantly inhibit the number,length and width of pattern cracks.However,when the number of dry-wet cycles and fiber content increased to a certain extent,the changes of cracks became stable.