Frost Jacking Characteristics And Bearing Capacity Of Tower Foundation In Seasonally Frozen Soil

In China's seasonally frozen soil area,the shallow foundation of the high-voltage transmission line suffers from frost jacking frequently.To solve the problem of frost jacking of tower foundations in seasonally frozen soil regions,a new type of conical foundation is proposed in this paper.The model tests and numerical simulations were employed to evaluate the anti-frost jacking and the load-bearing performance.The main research results are as follows:(1)Based on the indoor freezing test considering the negative temperature of the earth's surface,the influence of the foundation on the freezing characteristics of the ground is studied.The shallower the buried depth is,the greater the reduction range of the temperature around the foundation is.When the ground surface temperature decreases from-5? to-10? and-15?,the maximum freezing depth of foundation soil increases from 43.32 cm to 78.76 cm and 100.00 cm.In the process of soil freezing,the ground freezing rate decreases exponentially with time,but the maximum freezing rate increases with the decrease of ground surface temperature.(2)Through the indoor freezing tests,the anti-freezing ability of the new type of foundation was studied.The results show that frost jacking displacement of the new foundation and the frost heaving displacement of the soil ground have the same change trend,and the displacement of foundation is about 1/2 of the displacement of soil ground.In addition,the frost jacking displacement of the novel foundation increases with the decrease of temperature.Under the condition of-15?,the frost jacking displacement is about 12 mm,and the average frost jacking rate is 1.174%,which shows good anti-frost capacity.(3)Through the indoor loading test,the load-bearing performance of the new foundation was studied under three different conditions,which include vertical pulling loading,horizontal loading,and the composite loading style of above two loading types.The results show that the lower the ambient temperature,the higher the mechanical strength of the soil,the better the anti-frost jacking and anti-overturning capacity of the foundation;the pull-up failure is divided into four stages: linear elastic deformation,elastoplastic deformation,sliding surface and overall failure;Horizontal failure is divided into three stages of elastic deformation,plastic development and foundation instability;the uplift load in composite loading plays a leading role in the deformation and failure of the foundation.(4)The bearing capacity of the new foundation is analyzed by numerical simulation considering uplift and horizontal loading.The ultimate bearing capacity of the new foundation increases in the form of quadratic function with the decrease of test temperature.Under the combined action of uplift and horizontal loading,the horizontal bearing capacity and the uplift bearing capacity are reduced.Under the condition of alternating uplift load and horizontal load,when the horizontal load is about 40% of the bearing capacity and the uplift load is about 80% of the uplift bearing capacity,the uplift failure of the new foundation will occur.