Experimental Study On Redesign Of Pile Foundation For Increasing Storey On Built Building

As our country has a large population and finitude land resource, we can prolong the life length of building to realize the sustained development by increasing storey and rebuilding the built building. When we decide to rebuild the built building, the first problem is how to evaluate the characteristics of foundation soil correctly and how to rebuild it. So far people have researched the compression effect of natural foundation so much under long-term sustained loading, but have little focused on the time effectt of pile and compression effect of pile foudation. By a volume of single pile and a volume of four piles foundation which under long-term sustained loading test or not to simulate the alternation of subsoil'property under long-term sustained loading test. We simulate the pile foundation completely which is not satisfied with load fluctuation after increasing storey, by enlarging pile group area period or not.As micropile is used widely in construction, we adopt the micropile to reinforce the isolated footing and simulate the micropile composite foundation. By analyzing the p-s curve, subgrade reaction settlement of foundation and pile stress, we get some significant conclusions:(1)The characteristics of soil around, the bottom of pile and pile group have changed greatly under the long-term sustained loading test. The soil has occurred compaction effects and the p-s curve becomes gentle when additional load is added.(2)Increasing the side friction resistance of friction-type pile is the important factor of enhancing the pile's bearing capacity.(3) For storey of existence pile foundation increasing rehabilitation directly design, if the soil is uniform and the superstructure rigidity is adaptable, the bearing capacity of the building can increase by 10-20 percents.(4)To ascertain the bearing capacity of the pile for directly increasing storey design, we can do the suite test of the pile nearby the pile foundation under long-term sustained loading.(5) Under long-term sustained load, if the pile-group foundation area is enlarged to be two times of the original one, the p-s curve is still similar with that of the original foundation. In other words, when the pile-group foundation of the built building is enlarged, the original building's investigation data can be directly applied to the measurement of the bearing capacity and settlement of the subsoil.(6)The foundation soil occurs compression effect under long-term sustained loading test,when we use the micropile to reinforce the foundation,the subgrade reaction will be larger than the same size of pile-group foundation under the same additional load.(7)When we embed micropile inner, exterior or inner and exterior simultaneous the isolated foundation, the micropile don't display synchronism with subgrade reaction under cushion cap,the micropile in the different position don't display synchronism too, we should definite the sharing load tation of micropile and original foundation to optimat the design of the foundation.(8) Micropile rigid foundation has the ability to transfer the load to the top of the micropile, the stress ratio of pile-soil is increasing as the load is increasing.