Research On Static And Dynamic Property Of Composite Foundation

It can yield good economic benefits and social benefits to adopt composite ground improving technology because the bearing capacity of weak soil can be improved and the settlement can be reduced. As to building on thick soft soil layer, engineers will pay more attention to settlement controlling than to bearing capacity. For many problems about this kind of building are caused by settlement, especially the differential settlement. The foundation's rigidity can affect ground settlement and cannot be ignored, but present methods of ground settlement cannot consider the effect. Furthermore with the wide use of composite ground technology in earthquake region and foundation design of dynamic machine, so it is urgent to study the dynamic interaction of composite ground and foundation. According to present study, the followings are studied in this thesis:1 The concept, classification and present study state about composite ground are illustrated in system. Present calculation methods of settlements of composite ground have summarized, as well as analyze their merits and demerits. In addition, the present study state about static and dynamic interaction has been summarized.2 This paper has presented transversely isotropic model of composite ground firstly. When the soft soil (called base body within composite ground) was improved by piles (called strengthened body) such as cement piles, the property of soil would be changed, especially the vertical displacement decrease dramatically. According to this character, assuming the strengthened pile as vertical disperse fiber in soil and regarding the composite ground as transversely isotropic material, the formula of material parameters have been deduced, and also study the way to determinate parameters of strengthened body and base body. Transversely isotropic model meet the actual situation more than other methods as long as adopting appropriate material parameters.3 Taking advantage of simulating infinite field and quick convergence of semi-analytical theory, the methods to calculate composite ground's settlement and analyzethe foundation and composite ground's static and dynamic interactions have been deduced. Rectangular free plate element is used to simulate foundation, and layer element for composite ground and soil mass. Layer element is analyzed along two horizontal directions, and interpolated along the vertical direction by polynomial expression. To simulate infinite field, infinite extending horizontal layer element is used beside and under composite ground, and construct different functions in different zone to simulate the settlement fading down along horizontal direction.4 The effect of parameters on displacement of composite ground has been studied roundly. Though changing substitution ratio, improved depth and modulus ratio of pile to soil of composite foundation, the reinforcement effects have been investigated. The results indicate that the deformation can be ignored when the modulus ratio of pile to soil is more than 500.From the effect of substitution ration and strengthened pile length on foundation's settlement, as to reducing the settlement of composite ground, it can obtain good effect to increase the depth of strengthened pile. So in order to control the settlement during the optimum design of composite ground, it is economic to increase reinforcement depth. Furthermore it can be found that increasing horizontal zone has little effect on foundation's settlement.5 The effects of foundation's rigidity and composite ground's parameters on deformation character have been investigated. It is found that foundation rigidity has great influence on the composite ground's settlement. With the increment of substitution ratio, the settlement decreases, so for the regular trigonal layout, piles spacing Se= (3-4) d is more appropriate to reduce settlement. When the modulus ratio of pile to soil is less than 20, then with the increment of strengthened pile length, the foundation's displacement changes little. But when the modulus ratio of pile to soil is greater than 50, the foundation's displacement decrease greatly with the increment of strengthened pile length. With the increment of modulus ratio of pile to soil, the displacement of foundation decrease at some extends and the deformation of underlying stratum increases, however while the ratio is greater than 500,foundation's displacement change little and compression deformation of composite ground mass can be ignored.6 The dynamic interaction of soil and foundation has great influence on building's dynamic response. Because of vertical (or horizontal) strengthened body implanted in weak soil, the dynamic property of the construction site should be changed. So this paper adopt semi-analytical method firstly to study the natural vibration property of foundation slab-composite ground system, and also investigate the influence factors such as substitutionratio, reinforced depth and the modulus ratio of pile to soil. The results indicate that increment of these factors can affect the amplitude of vibration and increase the system's frequency. So when designing the foundation of power machine, some attention should be paid to the influence of composite ground on the alteration of dynamic property of ground.7 Taking advantages of Matlab's functions of numerical calculation, numerical analysis, system analysis, graph display and symbolic operation, the computer program of foundation's settlement and static and dynamic interaction between composite ground and foundation have been programmed. In addition, software of interface of Matlab and VB has developed and realized visual display.