Research On The Bearing Characteristics Of The Saturated Loess Foundation Reinforced By The Cement-Soil Mixing Pile

As saturated loess is a kind of high water content, high compressibility, low bearing capacity soil and its natural foundation can not meet the requirements of the project, theundisturbed foundation should be treated. Saturated loess foundation is often treated sweak foundation. Cement-soil mixing pile is a common method which is usually useodeal with soft soil foundation. In the reinforcement of saturated loess foundation of railway subgrade, the use of cement soil mixing pile method is less and the regional accumulationExperience is lack. Through field test, research on the bearing characteristics of thesaturated loess foundation under the embankment reinforced by the cement-soil mixingpile, which accumulate experience for the Lanzhou area. The models of single pile composite foundationand group pile composite foundation are established by FLAC3 D software, studied on the bearing characteristics.The main conclusions have been reached as follow:(1) As time increasing, the stress shared pile and soil around the pile is increased,but the stress shared pile is much more than soil in cement-soil mixing pile composite foundation of the same cement and fly ash under the embankment.(2) Because the strength of piles containing different amounts of cement and fly ash is different,the stress shared by cement-soil mixing piles containing different amounts of cement and fly ash are different. The stress of piles containing cement and fly ash 20% is the biggest, the second is 16%, the least is 12%.(3) With the increase of time of embankment filled,the pile-soil stress ratio of cement-soil mixing pile composite foundation of the same cement and fly ash is increased.During the period of embankment filled, the pile share most of the pressure of embankment, the pile-soil stress ratio increases rapidly.In the stage of consolidation settlement of embankment, the pile-soil stress ratio increases slowly, tends to stable value finally.(4) With the increase of time of embankment filled,the pile-soil stress ratio of cement soil mixing pile composite foundation of the different quantity of cement and fly ash is increased. With the increasing of incorporation of cement and fly ash, the modulus of cement-soil mixing pile become bigger, as a result, the load of the pile can withstand increase and the load soil bear decrease, which lead to the increase of pile-soil stress ratio.(5) The stress concentration coefficient of pile increases with the increasing of load.the change experience homo-linear stage, plastic change stage and stable change stage. The stress decrescencing coefficient of soil reduces with the increasing of load.(6) The models of group pile composite foundation are established by FLAC3 Dsoftware, it is found that the stress of pile increases and the settlement increases with the increasing of the load.The piles in different positions have different variation law, the stress and settlement of middlepile is biggest, sidepile is second,corner-pile is least. The pile-soil stress ratio of middle-pile, side-pile and side-pile is different.