Study On The Uplift Bearing Capacity Of Belled Pier Foundation In Coarse-Grained Saline Soil

The load characteristics of the transmission line foundation are complex,and the uplift and overturning stability are the control conditions of the transmission line foundation design.The coarse grained saline soil has good cementation and high bearing capacity under the crystalline state,while the salt cementation is lost and the strength is reduced under the dissolution state.This paper take the belled pier foundation in coarse grained saline soil as the research object.Study on its uplift bearing characteristics with consideration of the occurrence of coarse particles in saline soil layer.Based on the lab scale model test of the undercut foundation of coarse saline soil,the uplift bearing characteristics of the belled pier foundation were analyzed.Results indicate that the range where land uplift in foundations show circular expansion at higher uplifting loads and the overall shear failure finally occurred.The load-displacement curves are primarily softening.The uplift bearing capacity for cases when coarse-grain saline soils in crystalline state increases at larger thickness,higher than that in dissolved state.The failure plane all exhibits approximately linear change from bottom up.The angles of uplift for coarse-grained saline soils in crystalline and dissolved states are 34o and 18o,while 32o for conventional coarse soils.A numerical analysis model was established based on laboratory test,the influence of depth/diameter ratio,thickness of saline soil and horizontal load on the uplift capacity and failure surface of excavated foundation in coarse saline soil foundation is studied.The results show that the uplift load capacity increases with the increase of depth/diameter ratio,and the increment of uplift capacity decreases significantly after the depth/diameter ratio ? exceeds 3.5.With the increase of depth/diameter ratio,the angle of uplift fracture surface of foundation soil decreases.The shape of the fracture surface of the underlying foundation transforms from the bell mouth to the cylindrical shape.When the aspect ratio of foundation is more than 3.5,the rupture surface is approximately cylindrical below 3.5D depth.The failure modes of belled pier foundation are divided into two types.When the aspect ratio ? is not greater than 3.5,the contour of the fracture surface is approximately two straight lines.When the aspect ratio ? is greater than 3.5,the contour line of the fracture surface is three straight lines.Under the crystalline state of the coarsegrained soil layer,the uplift bearing capacity increases with the increase of the thickness of the saline soil layer.In the initial stage,the uplift bearing capacity of the soil increases with the increase of the thickness of the saline soil layer,but then tends to be stable.The influence coefficient of the horizontal load gradually decreases with the increase of the load ratio,and the attenuation amplitude increases,and the influence coefficient of the horizontal load is higher than the corrosion state because of the higher strength and bearing capacity of the upper saline soil layer under the crystallization state.