Laboratory Experimental Study On Modification Of Organic Disseminated Sand

The current economy of China is developing rapidly,to be specific,the faster and better development of the economy in coastal areas is the guarantee of China's economy in the long-term sustainable development.Hainan province has 68 islands,we find organic disseminated sand existed in 8 bays out of 12 bays investigated,account for the number of 2/3 bays researched.Through plenty of survey,the presence of organic disseminated sand causes a series of problems in practical engineering:the difficulty of cement soil mixing,composite foundation failure and reducing the sealing effect etc.This kind of sand not only delays the progress of the project,but also increases the cost of engineering and hinders the overall economic development.On the contrary,if we make the laboratory experimental study with respect to the modification of organic disseminated sand,the results will be used in foundation treatment,reinforcement engineering,embankment reinforcement engineering,reclamation and road engineering widely,that is,changing harm into benefit,which has great practical significance.Based on the program of the National Natural Science Foundation of China,this paper studies on laboratory modification experiment of organic disseminated sand.The specific contents as follows:Firstly,we can understand the basic characteristics of organic disseminated sand through the geotechnical test and analyze the modify mechanism of organic disseminated sand.Secondly,orthogonal test was performed to analysis the influencing factors and rules of organic disseminated sand cement soil compressive strength.Thirdly,it was found that the organic disseminated sand cement mixture ratio and analyzed the specimen uniaxial stress strain of organic disseminated sand cement through organic disseminated sand laboratory modification experiment and plenty of unconfined compressive strength test.Finally,a strength prediction formula based on interior modified test results was founded,which can be used for practical engineering.(1)We can understand the basic characteristics of organic disseminated sand through geotechnical test which conclude the engineering properties of the minimum and maximum dry density,optimum moisture content,grain size,the mechanism of modified and analyze the effect of the presence of organic matter in sand to hydration reaction besides cement and sand,the action besides particles of organic disseminated sand and cement.(2)The strength of P·O42.5 group cement soil is obviously higher than the P·C32.5 group test by orthogonal experiment;in the comparison of the two group test with the strength of cement soil,admixture type is the main influencing factors,the latter is cement mixing ratio,the water cement ratio has a minimal influence.The optimum level of admixture is slaked lime,cement mixing ratio is 20%and water cement ratio is 0.45.(3)The result of laboratory modification experiment is consistent with the orthogonal test:the strength of P-042.5 group test is significantly higher than that in the group of P·C32.5;admixture type is the most obvious effection,the hydrated lime is best,limestone powder is second and fly ash is the worst;the compressive strength is higher with the increase of cement mixing ratio,but the growth rate decreased;water cement ratio effect is not obvious,the optimal water cement ratio is 0.45?0.60;hydrated lime as admixture of the optimal doping amount is 7.5%.The uniaxial stress-strain curve analysis shows:the form of failure is generally brittle shear specimen,which has obviously inclined failure surface and less strain with the sample of high strength.On the contrary,the failure mode is generally plastic shear,specimens is drum shaped,no obvious failure surface,large strain with the sample of low strength.(4)We can predict the compressive strength of cement soil in 28 days by cement ratio and water cement ratio two factors in strength prediction formula,debug the reasonable cement ratio and water cement ratio for the engineering which need to reach the strength,to reduce the test cycle and the number of projects,accelerate the project progress and cost saving.