The Application And Experiment Research Of Cement Power-sprayed Piles To Improve Soft-soil Roadbed

Distributed widely in our country ,soft soil has low shear strength and large deformation .If soft soil was treated in mistake way,foundation would come into being local shear failure or general-shear failure. In railway and road engineering ,the line often crosses soft soil section .For ensuring the safety of superstructure ,it is important to improve soft soil roadbed. The technique of cement power-sprayed piles is one of improving soft-soil roadbed technology presently.Combining with the construction and field tests of Nanjing-qidong railway, some research of using cement power-sprayed piles to improve soft- soil roadbed was conducted and the research includes several aspects below:1.The authour first introduces the formation.distribution,physical mechancial behaviour and engineering characteristic of soft soil, and clarifies the necessity of improving soft-soil roadbed. Afterwards,the authour studies the mechanism of cement power-sprayed piles composite foundation from the chemical reaction between cement particle and soil grain.2.The design of cement power-sprayed is introduced in the thesis including composite foundation bearing capacity design,the checking computations of underlayer strength and composite foundation deformation.3.Combining with field constuction, the factors influencing the construction quality of cement power-sprayed piles are analyzed,and the often- occured quality defects are discussed.Then the author puts forward the constructive measure for coping with the quality defects.4. By field loading tests and small strain measurement,the result of improving soft soil with cement power-sprayed piles is alalyzed.The author believes that the result is good and composite foundation is able to meet the superstructure's requirement for foundation strength and formation.5. Combining with field test,the author disputes load transfering mechanism and mode of failue about cement power-sprayed,and studies the relationship of n (the stress ratio of piles to soil) to load P .At last,the author summizes the factors to effect n.6.Using present theoretics, the author puts forward the theory of calculating the value of n by the modified value of modulus of compressibility A:.The value ofk is 1.1-1.2 in the engineering of nanjing-qidong railway.