Study On Bearing Capacity Of Excavated Foundation With Wing Slab Of Transmission Line In Loess Area

In the process of transmission project construction,due to the difference of engineering properties and the particularity of power engineering,many key problems need to be solved,among which the basic bearing capacity of transmission line is one of the most critical problems.Transmission line tower foundation is an important part of overhead transmission line,its construction period,labor consumption and cost account for a large proportion in the whole project.In this paper,based on in-situ test,m-method theoretical calculation and finite element numerical simulation,the bearing characteristics,foundation soil interaction,and the influence of soil around the foundation under bearing conditions are analyzed and studied,which provides a theoretical basis for the engineering application and design of the foundation in loess area.(1)Based on the in-situ test,the load displacement curves of foundation deformation and bearing capacity are drawn,and the relationship between uplift load and uplift displacement under various working conditions is "slowly changing".The position of the rotation center of foundation is at,and in the process of loading from the same working condition,with the change of load,the position of the rotation center slightly changes,especially under uplift horizontal load With the increase of load,the position of rotation center tends to move down.Under the action of vertical uplift horizontal failure load,the maximum influence range of soil around the foundation is(the foundation buried depth),while under the action of vertical downforce horizontal load,the influence range of uplift load is wider than that of downforce load.(2)The ABAQUS finite element numerical model is established.Based on the test data of the static load test in the field,the parameters of the finite element model are adjusted through analysis,so that the results of the finite element simulation are consistent with the results of the static load test in the field.Combined with the actual engineering situation,12 groups of 48 numerical simulation conditions are designed,and on this basis,the finite element simulation analysis is carried out.It is concluded that the vertical direction of the wing under horizontal load is more favorable to the anti overturning stability of the cut foundation with wing.(3)In this paper,the bearing capacity of pile with wing plate under the combined load of one-way and uplift horizontal is studied.Compared with the common digging foundation,the bearing capacity of wing sheet pile under combined load is greatly improved.The numerical simulation model of horizontal load and vertical load with different proportion is carried out.When the ratio of horizontal force and uplift force is 0.1:1,the limit displacement state is controlled by vertical displacement(uplift 25 mm).When the ratio of horizontal force and uplift force is 0.2:1 and 0.3:1,the uplift displacement first reaches the allowable value,i.e.the horizontal control displacement(10 mm),and the limit displacement state The state is controlled by horizontal displacement.When the design parameters are the same,the horizontal displacement at the top of the foundation with wing varies nonlinearly with the setting depth of the wing plate,with different ranges and varying rules.The optimal depth of the flange is about20%-25% of the buried depth.(4)Based on the definition of the scale coefficient m value of the horizontal resistance coefficient of the foundation soil,the p-x curve of the change relationship between the earth pressure and the horizontal displacement in front of the pile and the k-y curve of the relationship between the horizontal resistance coefficient of the foundation and the depth under the combined load and at different depths are drawn.The analysis shows that the horizontal resistance coefficient k value of the foundation basically increases linearly with the depth,which is mainly reflected in the depth range Is the depth below the ground.The m value obtained from the solution is 9.4-14.5,which is smaller than the m value obtained from the industry standard methods such as technical code for design of overhead transmission line foundation(DL / T5219-2014).The definition formula does not consider the structure and external load of the soil,but only the distribution of the soil resistance mode.The m value obtained is only related to the physical and mechanical properties of the soil,such as the density,deformation modulus,Poisson’s ratio,shear strength,etc.,while the m value obtained from the empirical formula of the code is the parameter reflecting the resistance performance of the pile soil interaction system.