Experience Study On Granite Residual Soil Improved By Lime-fly Ash

The Granite residual soil is widely distributed in South China,especially in the southeast coastal area.If the granite residual soil is used as the roadbed reclamation directly,it would be easily softened by because of being influenced by the groundwater or surface water,besides,the vibration liquefaction phenomenon of the soil is very serious as well.The disasters such as collapse and landslide usually happen because of the poor non-deformability and water stability,which is potentially destructive to the construction.Therefore,it is necessary to study the improvement of engineering properties of the granite residual soil.This paper mainly studi'es the granite residual soil in a certain area of Fuzhou,three different improvement schemes were proposed:the first one is modified method of fly ash,in which the content of fly ash was 0%,5%,10%,15%and 20%,secondly is modified method of lime,and the content of lime was 0%,2%,4%,6%and 8%;the last one is modified method of lime-fly ash,The ratios were 1:2:7,1:3:6 and 8:32:60.The improved soil with fly ash,modified lime-modified soil and lime-fly ash were obtained respectively,three kinds of improved soil were tested by compaction,direct shearing,infiltration and wetting.Through studying engineering characteristics of the improved soil,we can get and the change rules of shear strength,permeability and water stability of improved granite residual soil under different conditions of dosage,proportion and curing time.The main test results of this paper are as follows:(1)The results show that:within the scope of experimental study,the m'aximum dry density increases with the increase of the component of fly ash in the improved granite residual soil,while the optimal water content decreases.The maximum dry density decrea'ses and the optimum moisture increases due to the increasing ot-component of lime,and the maximum dry density is decreased after mixing with fly ash and lime.The optimum water content is related to the amount of component of lime and fly ash.(2)After adding fly ash and lime into granite residual soil,the shear strength increased,and the increment of the shear strength of the modified soil is relatively prominent when the ratio is 1:2:7 and 8:32:60.The shear strength of lime-fly ash modified soil is the highest,followed by the lime modified soil;and'the fly ash modified soil throughout the experiment.(3)The impermeability of fly ash modified soil is significantly higher than that of lime-modified soil'but the impermeability of'lime-fly ash modified soil with I1:2:7 ratio is obviously higher than that of fly ash modified soil.(4)The water stability of lime modified soil is higher than that of fly ash modified soil,but the water stability of lime-fly ash i:modified soil is the best.(5)It is found that the shear strength and water stability of lime-modified soil and lime-fly ash modified soil are generally higher than fly ash modified soil,but as for impermeability,the forgoing two are poor than fly ash to improve soil,what's more,in the case of lime-fly ash modified soil,the engineering properties are all good when the ratio is 1:2:7.It can be concluded from the test results,a certain amount of lime and fly ash should be added to the foundation or dam when the demands of strength,stability and impermeability of the engineering projects are strict.The research results can provide reference for the research and engineering application of granite residual soil.