Analysis Of The Bearing Capacity And Research Of Design Method Of Composite Foundation

Ground improvement is a very vivid research field in civil engineering at present .The theory of composite foundation is greatly developed in recent more than ten years . Because the material , strength and effect are not same for the different reinforced pile body installed in composite foundation , the work mechanism of all kinds of composite foundation are different . It leads to that the computation methods of bearing capacity and settlement of all kinds of composite foundation are different.The bearing capacity characteristics and design methods of composite foundation are systematically studied in this dissertation .At first , the computation formulas of the ultimate bearing capacity of the granular material pile are discussed .The modified passive earth pressure method is put forward , it make the results more reasonable . Based on engineering practice and experiment , considering the lateral interaction of the pile and soil between piles , the computation formula of bearing capacity of granular material pile is proposed .The computation method of settlement of granular material pile is discussed ,the determining method of pile body modulus of deformation of granular material pile is given .By the parametric potential energy variational principle ,the analytic solution of expansion problem of granular material pile is obtained .The common design methods of granular material pile composite foundation are discussed .Secondly , after analyzing the load transmission mechanism of flexible pile , by the theory of elasticity , the stress of pile body of flexible pile composite foundation is solved , it provides a new path for determining the pile-soil stress ratio of flexible composite foundation . After the lime-flyash pile is simplified as sand drain, according to the drainage theory of non-ideal vertical drain , the consolidation characteristics of lime-flyash pile composite foundation is analyzed. Based on the static load test of lime-flyash pile composite foundation , the load bearing ratio of pile and soil , pile-soil stress ratio , proportional limit of pile body and relative deformation value select of static load test are obtained . After the work mechanism of lime-flyash pile composite foundation is stated , the design methods of lime-flyash pile in new fill soil and non-homogeneous subsoil are put forward , the reduced coefficient of improving fill soil and non-homogeneous influence coefficient of improving non-homogeneous subsoil aregiven .The computation method of settlement for lime-flyash pile composite foundation is also proposed . When the strength of lime-flyash pile body and soil between piles are tested by static cone penetration test ,the computation formula of pile-soil stress ratio is proposed , so the improvement effect can be evaluated without static load test of composite foundation . Some existing problems in design and construction of deep mixed-in-place cement pile are also discussed .Thirdly , the design thought of rigid pile composite foundation is discussed . Based on the static load test of flyash concrete pile composite foundation with bearing plates of different dimension in soft soil region , the mobilization coefficient of the bearing capacity of soils, between piles is determined. By the experiments of sand or gravel cushion with different thickness , along with engineering practice, the proper thickness of sand or gravel cushion is proposed in rigid pile composite foundation . The computation methods of bearing capacity , settlement and select of parameter in rigid pile composite foundation design are discussed .The compound proportion tests of pile body material of flyash concrete pile are carried out .The construction technology of flyash concrete pile in soft soil region is studied .The probability characteristics of bearing capacity of rigid pile composite foundation is analyzed . The earthquake resistant mechanism of rigid pile composite foundation with sand or gravel cushion is discussed .At last, the new concept of multi-element composite foun...