Study On The Bearing Capacity Of Anti-floating Underreamed Anchor In Sandy Soil Site

After more than 50 years of development,underreamed anchor has been widely used in deep pit engineering,slope engineering,anti-floating engineering,supporting engineering and so on.The advantages of anchorage technology are that it can fully mobilize the strength and self-stability of soil,reduce the volume and weight of support structure,and save construction materials.Anchorage technology has become one of the most reliable and economical methods to improve the stability of soil and to solve complex engineering problems,but the bearing characteristics of the underreamed anchor under different geological conditions have great uncertainty,especially the influence of the buried depth and size of the underreamed anchor on the ultimate bearing capacity is particularly significant,which is also one of the most concerned problems in the project.At present,the commonly used bearing capacity calculation formula in the project cannot accurately estimate its actual bearing capacity.Based on the latest indoor and outdoor test results,this paper uses the particle flow software PFC3 D to simulate the failure mode under the pull-out load of the anti-floating underreamed anchor in the sand,analyzes the pull-out failure bearing capacity of the underreamed anchor under different buried depth conditions,studies the influence of the buried depth and the diameter of the expansion section on the load-displacement relationship,and presents a new calculation method of the ultimate bearing capacity of the underreamed anchor in the sand.The main contents of this paper are as follows:1.Based on the test results of indoor and outdoor anti-floating underreamed anchor,the failure rules of the underreamed anchor under different working conditions are systematically analyzed.On this basis,a three-dimensional numerical model of anti-floating underreamed anchor based on PFC software platform is established.Aiming at the shallow and deep buried vertical tensile underreamed anchor,the failure mode and influencing factors of pull-out failure of underreamed anchor in sand are analyzed systematically.According to the characteristics of the bearing capacity of the underreamed anchor,the development law of the side resistance and the end bearing capacity of the anti-floating underreamed anchor is deeply revealed,and the evaluation model of the formation mechanism of the side friction resistance,the end bearing capacity and the side friction resistance of the free section is established.2.According to the load-displacement relationship of anti-floating underreamed anchor obtained from the test and numerical simulation results,the hyperbolic mathematical model of load-displacement under different working conditions of anti-floating underreamed anchor tensile load in sand is established,the determination method of model parameters is systematically analyzed,the characteristics and rules of model parameters under different engineering geological environment are studied,the influence of the buried depth,the geometry of the underreamed anchor and the groundwater on the model parameters is clarified,and a new model for estimating the bearing capacity of the underreamed anchor in sand is proposed.The rationality and reliability of the model are demonstrated by comparing with the actual project.3.In order to further reveal the mechanism of the large increase of the bearing capacity of the anti-floating underreamed anchor,the law of the change of the displacement field and stress field of the soil in the construction of the underreamed anchor is numerically simulated,the mechanism of the squeezing-soil effect of the underreamed anchor in the construction process is systematically analyzed,and the law of the influence on the surrounding soil in the construction process of the shallow and deep buried underreamed anchor is revealed.The paper provides a theoretical reference for the design and construction technology selection of anti-floating underreamed anchor.With the rapid development of China's high-rise,super high-rise buildings,sea crossing and river crossing large-scale buildings and structures,the application of underreamed anchor,which has good economy and can greatly improve the bearing capacity of the foundation,will usher in a larger development space.The research results of this paper provide a good reference for the engineering design,bearing capacity evaluation and construction process of anti-floating underreamed anchor.