| The foundation pressure of high-rise buildings is high and the deformation control requirements are high.When the foundation bearing capacity is insufficient,it will cause large deformation of the foundation and tilt the building.Therefore,it is necessary to strengthen the foundation;If the tilting of the building affects its safety or normal use,it is necessary to correct the tilt of the building.Commonly used underpinning techniques for settlement prevention and reinforcement of inclined buildings include anchor static pressure piles and micro piles;However,for high-rise buildings,due to the large overall load,if small diameter piles are used for underpinning,there will be adverse effects such as a large number of underpinning piles and large disturbance to the foundation.When the high-rise building is tilted and the foundation is more sensitive,large-diameter piles can be used for anti-settling and underpinning on the side of the building where the settlement is large.At present,when large-diameter piles are used for underpinning of inclined high-rise buildings,the interaction between the pile and the foundation,the internal force change of the foundation and the superstructure,etc.are less researched.To further study the role of large-diameter piles in the process of foundation underpinning and anti-settling of buildings,In this title,based on an example of a high-rise building in a karst area,the deformation and failure mechanism of the CFG pile composite foundation in the karst site is analyzed through the finite element analysis software;Analyzed the influence of the force change of the large diameter pile and the force of the large diameter pile on the force distribution of the CFG pile composite foundation in the process of adopting the large diameter rock-socketed pile to stop the settlement;Analyzed the internal force changes of the external cap and the original structure when the large-diameter rock-socketed pile stopped sinking;Analyzed the law of force changes of large diameter piles and CFG piles under different inclination rates during the tilt correction process.The main conclusions are as follows:(1)The reason for the inclination of the building is that the CFG pile composite foundation in the karst cave area has a large plastic zone,and the foundation has plastic deformation,which results in larger settlement;The CFG pile in the karst cave area could not bear the force due to the complete destabilization of the foundation,and the CFG at the settlement boundary The pile composite foundation has potential dangerous points where the force is concentrated.(2)In the process of anti-settling underpinning,the large-diameter rock-socketed pile plays the role of underpinning to effectively share the force of the composite foundation of the CFG pile in the cave area.After the single-sided large-diameter pile is underpinned,the CFG pile composite foundation is redistributed.The force of the CFG pile composite foundation in the karst cave area is shared by the large-diameter pile and the CFG pile composite foundation in the non-karst cave area.The force of the CFG pile closer to the large diameter pile is greatly reduced,and the force is almost no longer applied;The amount of force reduction of the CFG pile gradually decreases with the increase of the distance from the large-diameter pile,and the force of the CFG pile farther from the large-diameter pile shows a slight increase trend.The design of the bearing capacity of large-diameter piles should be comprehensively determined according to the engineering geological conditions,the upper load and the slope of the building.In this thesis,the large-diameter piles share the load of 57828 k N,which accounts for33% of the total force of the CFG pile.The force of a single CFG pile is reduced by 80%.(3)In the process of anti-settling,the different external structure forms affect the bearing capacity of large-diameter rock-socketed piles.When only the external raft is expanded,the load of the main structure cannot be effectively transmitted to the large-diameter rock-socketed pile through the external raft due to the limitation of the external raft's own structural bearing capacity,resulting in less force on the large-diameter pile;When the box-shaped structure is connected,the box-shaped structure and the main structure bear uniform force and small deformation.The main structure load is effectively transmitted to the large-diameter rock-socketed pile through the box-shaped structure,so the large-diameter pile bears greater force and exerts a high degree of bearing capacity.In this thesis,only the externally expanded raft and the external box-shaped structure large-diameter piles differ in force by about 67%.(4)During the tilt correction process,the force of the large-diameter pile decreases with the decrease of the inclination rate.The force of the composite foundation of CFG pile is relatively stable as a whole,because most of the force of the composite foundation of CFG pile is suppressed in the anti-settling stage.The large-diameter piles share the force,although the force changes during tilt correction,but the change is small.The main change is that the force on the composite foundation of the CFG piles closer to the large-diameter piles is slightly reduced,and the larger-diameter piles are farther away.The force on the composite foundation of the CFG pile on the leaning back side is slightly increased.In this thesis,the force of the CFG pile in the tilt correction stage is only reduced by 28 k N at the maximum,and only increased by 47 k N at the maximum.(5)In the process of tilt correction,because the soil is taken from the cushion layer to correct tilt,the development of the plastic zone only appears on the edge of the foundation on the leaning back side and the range is small,indicating that the damage range of the foundation on the leaning back side is smaller,compared with the general anti-settling method,the range of foundation reinforcement required for tilt correction is small,and the disturbance to the foundation is also small. |
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