Axial Bearing Capacity And Reliability Analysis Of Helical Anchor Foundationin In Serviceability Limit State Design

In the rapid development of the national economy today,wind power generation,transmission lines,submarine pipelines,offshore oil platform and high-speed railway to a wide range of engineering construction,more and more large special engineering structure based on safety considerations are using anchor foundation,especially large diameter screw anchor or there are more and more application of screw pile foundation.So the stability of anchor foundation becomes more and more important.With the emergence of large structures,higher requirements are put forward for the axial bearing capacity of foundations.Due to the complexity of engineering structures,the uncertain factors of loads are gradually increasing.These reasons make the research work of reliability and safety of screw anchor foundation become more and more important.Screw anchor or pile foundation has been widely used in all kinds of geotechnical engineering problems due to its advantages of convenient installation,small environmental disturbance,low noise and high resistance and bearing capacity of deep soil.It has also been widely used in the power transmission industry in China.However,the research on reliability analysis of axial bearing capacity of spiral anchor foundation is relatively limited.At present,reliability design methods in the field of structural engineering are increasingly unified and standardized,and the design tends to be more scientific and reasonable.Reliability design in geotechnical engineering is the development trend in the future.Considering that screw anchor foundation is widely used in engineering at present,this paper will study the reliability level of axial bearing capacity of screw anchor foundation under normal service limit state based on the existing literature research.The main contents of this paper include the following sections:(1)Based on the research literature and industry specifications of screw anchor foundation,the engineering applicability of using torque correlation coefficient to predict the uplift bearing capacity is discussed,and the influencing factors of theoretical torque correlation coefficient of screw anchor under the condition of deep burial in sand are analyzed.(2)By analyzing the characteristics of the curve of load ratio Q/Q_um-displacement y of screw anchor foundation,the hyperbolic model is adopted to predict it,and the physical significance of the parameters is described.The hyperbolic parameters were determined by fitting and the correlation analysis was carried out between the hyperbolic parameters and the variables.The ultimate bearing capacity determined by the theoretical torque correlation coefficient above was replaced by the measured value Q_um in the hyperbolic formula,and the correction coefficient?was introduced to correct the prediction error of the load-displacement relation curve caused by it.The application of the calculation model was illustrated by an example.(3)The concept of geotechnical engineering reliability is briefly introduced,and the first-order second-moment method is selected to evaluate the uncertainty of the above model.Monte Carlo simulations are used to calculate the resistance coefficient?values of small diameter(d<168mm)and large diameter(d?168mm)screw anchor foundations under different ratios?of permanent load(dead load)and variable load(live load)and different target reliability index?_T under ULS and SLS conditions.Thus,the resistance coefficient can be determined according to the reliability index and failure probability of screw anchor foundation under ULS and SLS conditions,which can provide reference for engineering design.