The present study estimates the uplift capacity of the under-reamed pile in clay with a linearly increasing undrained cohesion. The uplift capacity of the under-reamed pile is presented in the form of a non-dimensional factor F_cu. The following parameters are considered for estimating the uplift capacity: embedment length of under-reamed pile to shaft diameter ratio (L_u/D), normalized bulb distance from the pile base (h_b/D_u), under-ream angle (β), a non-dimensional constant for the linear increase in undrained cohesion (m), number of bulbs (n_b), and centre to centre spacing between bulbs (s). The pile-soil interface is considered as fully bonded and also immediate breakaway is assumed at the pile base and bottom surface of the lowest bulb. The non-dimensional uplift capacity F_cu is found to increase significantly with increases in m and number of bulbs. F_cu is found to increase moderately due to an increase in L_u/D, a decrease in h_b/D_u (for m > 0), and an increase in β. The F_cu for the fully bonded condition is found to be higher than F_cu for the immediate breakaway condition. The per cent difference between F_cu for the fully bonded condition and the immediate breakaway condition is found to be significant for smaller L_u/D, higher m, and more bulbs. For under-reamed pile with two bulbs, m greater than 0, in fully bonded condition, F_cu increases with an increase in s/D_u, reaches the maximum at s/D_u of 1.25–1.75, and then decreases. For under-reamed pile with two bulbs, m > 0, in immediate breakaway condition, F_cu is found to increase continuously with an increase in s/D_u. The failure and load sharing mechanisms of the under-reamed pile under uplift are also studied through variations of radial stress along the pile-soil interface, distributions of axial force, per cent contributions of bulbs, and plots of plastic shear failure.

目前的研究估计了欠扩孔的黏土在不排水内聚力呈线性增加的情况下的抗拔能力。欠扩孔桩的抗拔能力以无量纲因子F _cu的形式表示。考虑以下参数来估计提升能力：扩孔桩的埋入长度与竖井直径之比（L _u / D），归一化球根距桩基的距离（h _b / D _u），扩孔下角（β），不排水内聚力（m）线性增加的无量纲常数，灯泡个数（n _b），以及中心到中心的灯泡（之间间距小号）。桩-土界面被认为是完全粘结的，并且假定在最低球根的桩基和底面会立即脱离。发现无量纲的提升能力F _cu随着灯泡的m和数量的增加而显着增加。由于L _u / D的增加，h _b / D _u的减少（对于m  > 0）和β的增加，发现F _cu适度增加。该˚F_立方米对于完全分离条件，发现对于立即分离条件，F _cu高于F _cu。对于较小的L _u / D，较高的m和更多的灯泡，对于完全粘合的状态和立即脱离状态的F _cu之间的百分比差异被发现是显着的。对于扩底桩具有两个灯泡，米大于0，在完全粘结的条件下，˚F_立方米的增加而增加小号/ d _ü，到达最大小号/ d _ù为1.25–1.75，然后减小。对于具有两个球根的扩孔桩，m  > 0，在立即分离条件下，发现F _cu随着s / D _u的增加而连续增加。还通过沿桩-土界面沿径向应力的变化，轴向力的分布，球根的贡献百分比以及塑性剪切破坏图，研究了欠固结的桩在升力作用下的破坏和载荷分担机制。