| With the development of economy and the further maturity of composite foundation construction technology,the type of composite foundation has also evolved from the early composite foundation improved by single pile type to one by combination pile types.The combined composite foundation can speed up the consolidation of foundation drainage,improve the complex modulus of soft soil foundation significantly,and provide a safe and stable foundation for construction.It has been effectively used in the treatment of soft soil foundation along the southeast coast of our country.However,the research of consolidation theory for a composite foundation is still in the development stage since its consolidation model is complex and its consolidation characteristics are very difficult to study.Hence,it is of great vitalness to build the consolidation calculation model of composite foundation in theory and study the influences of various parameter changes on the consolidation characteristics,which are of great importance for enhancing the guiding role of engineering practice and improving the consolidation theory of composite foundation.In this paper,a new consolidation model of composite foundation reinforced by stone columns and impervious piles is proposed.The consolidation problems of composite foundation affected by multi-stage loading,variation of additional stress with time and depth,vertical volume compression of stone columns and disturbance impact of piles building are researched.The main research work and contents are below:(1)The expression of consolidation degree for the velocity of composite foundation is given considering the influences of factors such as multi-stage loading,the vertical volume compression of stone columns and the linear change for the radical permeability coefficient of perturbed soil in the zone of piles side.Furthermore,the solution in this paper is reduced to a consolidation solution under single-stage loading and compared with the existing solutions and the finite element solution,which verified its correctness.Finally,the consolidation characteristics of the composite foundation reinforced by stone columns and impervious piles are studied by a series of parametric analysis.The consequences indicate that the velocity of composite foundation consolidation can be accelerated by shortening the loading duration of upper load,decreasing the effects of well resistance and the disturbance effect of stone columns or increasing the compression modulus of impervious piles.The change of the disturbance effect of impervious piles construction have little influence on the velocity of composite foundation consolidation compared with stone columns.The change of the compression modulus of stone columns have little influence on the velocity of composite foundation consolidation compared with impervious piles.(2)The influence of radial and vertical flows within stone columns and the stress varied with time and depth on the velocity of composite foundation consolidation were considered,the consolidation count model of composite foundation was established,the analytical solution of composite foundation under time and depth dependent stresses was derived by using analytical method.The curve of consolidation degree of composite foundation under the impact of different factors was drawn by example analysis.The consequences shows that the increase in the ratio of additional stress between top and bottom of foundation and the ratio of radial permeability coefficient between stone columns and soil accelerates the velocity of composite foundation consolidation;Ignoring the radial flow in the stone columns will overestimate the velocity of composite foundation consolidation;The velocity of composite foundation consolidation can be significantly increased by decreasing the radius ratio of unit model to stone columns;Increasing the displacement rate of impervious piles in the exterior has no obvious effect on the accelerating the velocity of composite foundation consolidation.(3)An axisymmetric consolidation calculation model with bidirectional flowing is established.Based on the assumption that the difference between the water outward seepage the center and the peripheral stone columns along the radial direction and the water inward seepag along the vertical direction is the volume compression of the center and the peripheral stone columns,and considering the effects of the disturbance of stone columns and impervious piles construction.The consolidation degree expression of the combined composite foundation under four different loading methods are deduced,including the expression excess pore water pressures within the stone columns and the surrounding,and the expression of overall average degree of the composite foundation consolidation.Finally,the consolidation characteristics of the composite foundation is studied.The consequences show that a greater permeability coefficient of the stone columns,a denser distribution of the stone columns and the impervious piles,and a higher compression modulus of the impervious piles,will result in accelerated the composite foundation consolidation.The smearing effect of stone columns on the composite foundation consolidation is greater than that of impervious piles.Ignoring the volume compression of stone columns will overestimate the consolidation rate of composite foundation,and the error increases with the decrease of radius ratio.Good anastomosing can be observed between the predicted settlement by the analytical solution and the monitored settlement.(4)Based on the calculation model of axisymmetric consolidation with bidirectional seepage,the consolidation differential equation of composite foundation reinforced by stone columns and impervious piles is established considering the volume compression of central and peripheral stone columns,well resistance effect of piles itself and the disturbance impact of piles construction.The expressions of consolidation degree of stone columns,soil between piles and composite foundation reinforced by stone columns and impervious piles are derived under the variation of time and depth dependent additional stresses. |
PDF Full Text Request