利用模型试验研究砂土中静压桩在贯入过程中的承载机理.分析模型桩贯入4种不同深度时的桩周应力变化规律,对桩顶轴力、桩顶位移、桩身环向应变和桩身纵向应变进行全程测量.利用一种半数值半解析的方法,通过测量模型桩壁的环向应变与径向应变,推导出桩周的围压和摩阻力.结果表明:在贯入初期,桩体上部会出现负摩阻,随着贯入深度的增加,上部负摩阻的范围和数值都在减小直至消失;在沉桩阻力中摩阻力所占比例较小,但其比例随着贯入深度的增加不断增大.整个贯入过程中桩周围压随贯入深度的增加在不断增大.在同一土体深度处的围压也随桩体贯入而增大.随贯入深度的增加,摩阻力和围压的变化趋势呈现了较好的一致性,摩阻力与围压的比值在0.41～0.53波动.%We study the bearing mechanisms of the jacked pile during the pressing in sand with model test.To analyze stress changing laws of model pile while it is pressed into four different depths,we entirely measured the axial force,the displacement of model pile top,the strain of model pile top,and the circumferential strain and longitudinal strain of model pile.Using a semi-analytical and semi-numerical method,we deduced confining pressure and friction resistance according to circumferential strain and radial strain of model pile.The results show that:in the beginning of penetration,there will be negative friction in the upper part of model pile;as the penetration depth increases,the range and the values of negative friction in upper part are reduced until it disappears;pile skin friction is a smaller proportion in pile resistance,but its proportion increases with pressing depth increasing.Confining pressure increases with depth of penetration during the whole process.Confining pressure in the same depth of the soil is also increasing during the process of penetration.With the penetration depth increases,increasing trend of pile skin friction and confining pressure presents a better consistency,and the ratio between pile skin friction and confining pressure is from 0.41 to 0.53.
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