淤积土桥梁桩基承载能力影响参数敏感性分析

Analysis on Sensitivity of Parameters Affecting Bearing Capacity of Pile Foundation of Bridge with Silted Soil

随着高层建筑和大型桥梁的不断建设,普通的中短桩已无法满足其承载力要求,大直径超长钻孔灌注桩因为其良好的承载性能而广泛应用于此类大型基础工程中。大直径超长灌注桩是高规格建(构)筑物桩基工程的发展趋势,但有关桩基的承载力影响因素的研究还较少。为了研究河流入海口淤积土桥梁桩基的承载能力,以海南省南港河大桥的桩基为研究对象,利用ABAQUS有限元软件建立桥梁桩-土接触模型,分析了不同桩长、桩径对桩基轴向力、侧摩阻力和极限承载力的影响,并分析了淤积土层对桥梁桩基的承载力产生的影响。结果表明:在桩径一定的情况下,当桩长由30 m增加到60 m时,桩基的承载能力提高了10200 kN,但当桩长增大到60 m以后,桩基的承载力仅提高了3400 kN;在桩长一定的情况下,桩径由0.6 m增加到1.5 m时,桩基的承载力提升了10200 kN,但是桩径超过1.5 m后,承载力仅提升了3400 kN;当桩径和桩长之比为1/40时,使得该桩径和桩长能够发挥最大承载力;随着淤积土深度的增加,桩基的承载能力逐渐变小,原因是相比较其他土体而言,淤积土的侧摩阻力非常小,淤积土段占整个桩长的比例越大,桩基的承载能力越小。因此,扩大桩径、增加桩长、提高桩周土体黏聚力和改变荷载箱的位置是提高桩基的承载力有效措施。

With the continuous construction of high-rise buildings and large bridges,ordinary short and medium piles cannot longer meet their bearing capacity requirements.Large-diameter and super-long bored piles are widely used in these large-scale foundation projects because of their good bearing performance.Large-diameter and super-long cast-in-place piles are the development trend of high-specified building pile foundation engineering,but there are few studies on the factors affecting the bearing capacity of pile foundations.In order to study the bearing capacity of the bridge pile foundation with silted soil at the estuary of the river,taking the pile foundation of the Nangang River Bridge in Hainan Province as the research object,the bridge pile-soil contact model is established by using ABAQUS finite element software.The influences of different pile lengths and diameters on the axial force,lateral friction resistance and ultimate bearing capacity of the pile foundation are analyzed,and the influence of the silted soil layer on the bearing capacity of the bridge pile foundation is analyzed.The result shows that(1)when the pile diameter is constant and the pile length is increased from 30 m to 60 m,the bearing capacity of the pile foundation increased by 10200 kN,but when the pile length is increased to 60 m,the bearing capacity of the pile foundation is only increased by 3400 kN;(2)under the condition of constant pile length,when the pile diameter is increased from 0.6 m to 1.5 m,the bearing capacity of the pile foundation is increased by 10200 kN,but when the pile diameter exceeded 1.5 m,the bearing capacity is only increased by 3400 kN;(3)when the ratio of pile diameter to pile length is 1/40,the pile diameter and pile length can exert the maximum bearing capacity;(4)as the depth of the silted soil is increased,the bearing capacity of the pile foundation gradually is decreased,because the lateral friction resistance of the silted soil is very small compared with other soils,the larger the proportion of the silted soil section to the entire pile length,the smaller the bearing capacity of the pile foundation.Therefore,expanding pile diameter,increasing pile length,improving the cohesion of the soil around the pile and changing the position of the load box are effective measures to improve the bearing capacity of pile foundation.