Technical Analysis And Engineering Application Of Rectifying And Strengthening For High-rise Building In Deep Filling Loess

With the rapid development of economic construction and the acceleration of urban construction,more and more buildings begin to appear uneven settlement and tilting disease.Existing buildings are the wealth of human society.If the existing buildings can be restored to the use function and the waste discharge can be reduced through building reconstruction and disease management,it will have important engineering significance and economic value for the sustainable development of construction industry.In this paper,based on the tilting problem of a existing high-rise building in deep filling loess,a rectifying and strengthening method is put forward.The specific research contents are as follows:(1)Through the investigation of more than 20 buildings in three filling loess fields,the causes of building diseases were analyzed from the aspects of site investigation,architectural design,construction,management and maintenance.Most of the building diseases on the fill foundation are caused by the geological conditions of the site.The consolidation settlement,the collapsing settlement and the rise of the groundwater level are the main reasons for the uneven settlement and inclination of buildings in the fill area.(2)The field of stress,displacement and plastic zone in elastic and elastic-plastic stages were derived by using Tresca yield criterion and Mohr-coulomb yield criterion,based on the basic assumptions of elasto-plastic mechanics.The variation of stress field and displacement field in each stage was analyzed.And the finite element software was used to simulate the influence of the hole diameter and the hole wall support on the soil displacement around the hole.The analysis show that the stress field in elastic region is related to horizontal distribution force,and stress field in plastic zone is related to the strength parameter of material.The plastic zone radius of the stress relief hole is related to the pore diameter,the depth and the strength parameters of the soil.The maximum soil displacement around the hole appears in the middle of the excavation section,and the support of the hole wall has little effect on the displacement of the soil around the hole of the excavation section,so the stability of the upper soil can be ensured by using the support.(3)The stress-strain relationship of the micro-steel-pipe pile,the axial force of pile body and the displacement of pile top under various loads were measured by laboratory test and field test.The elastic modulus of composite section,the load ratio of steel pipe to cement paste,the transfer law of the pile's axial force and lateral resistance were analyzed.And the influence of different pile length and diameter on the bearing capacity of pile was simulated by using finite element software.The results show that the steel tube collar effects on the elastic modulus of composite section is small,the measured value is only 1.2 times of the calculated value without considering the collar effect,and the steel-pipe's internal force in the micro-steel-pipe pile is relatively large,accounting for about 2/3 of the total internal force.The Q-s curve of micro-steel pipe pile is slowly deformed in filling area,and the load shared by end resistance tends to zero,which shows the characteristic of friction pile.Because of the influence of construction technology and geological conditions,the pile body appears negative friction resistance phenomenon.Proper increasing the pile's length and diameter can improve the pile's bearing capacity and reduce the settlement and deformation of the pile top.(4)Taking the actual engineering for example,through theoretical analysis and experimental research results,the existing building was designed for rectifying and strengthening on the basis of correct analysis tilting reasons.After reasonable construction and on-site monitoring,the inclined building has been tilted back from 13.75 ‰ to 2.8 ‰,which meets the requirements of the code and verifies the feasibility of the rectifying and strengthening method of stress-releasing around pile & forced drop through truncated pile & micro-steel-pipe pile.It provides the engineering experience for the engineering of rectifying and strengthening in the deep filling loess.