考虑加筋与遮帘效应的层状地基群桩沉降计算

桩群在土中的加筋与遮帘效应是客观存在的,但目前的理论与实践均未能或有效地考虑该效应.基于剪切变形法原理,在计算某一根桩沉降时,考虑了其他各相邻基桩的存在对该桩沉降的折减,即加筋与遮帘效应,得到了桩侧桩-土接触等效剪切弹簧刚度,建立了桩身位移微分方程,分别求得桩顶沉降-桩端沉降、桩顶荷载-桩端压力的递推关系,从而得到了各桩在自身荷载作用下引起自身沉降的柔度系数; 同理,也求得了各邻桩在其桩顶荷载下引起它桩沉降的柔度系数,最终建立了群桩沉降计算的柔度矩阵方程.推导过程中,考虑了地基土的成层性及桩端沉降的相互影响,并提出了基于一定深度内的Mindlin位移解且考虑桩径影响的桩端压力-桩端位移关系新模式.算例结果表明,本文方法与实测值较为接近,且按本文方法求得的群桩中基桩相互作用系数明显小于弹性理论计算结果,且与实测值吻合较好.

SETTLEMENT CALCULATION OF PILE GROUPS IN LAYERED SOIL WITH CONSIDERATION OF REINFORCING AND RESTRAINING EFFECT

The reinforcing and restraining effect of piles embedded in soils is objective. However, this effect is not or has not been effectively considered in the present theory. The relevant research work needs to be continued. Based on the shear displacement method, the reinforcing and restraining effect is taken into account in the calculation of the pile group settlements in this paper. The reduction effect caused by the existence of the other adjacent piles and the equivalent stiffness coefficients of soil around each pile are developed. Then on the basis of the shear deformation transfer method, vertical displacement equation caused by load acting on top of the analyzing pile is built. So recurrence relations of settlement and axial force between pile head and pile tip are respectively deduced. Thus a flexibility coefficient of the displacement at the pile top induced by its load is obtained. Meanwhile, the flexibility coefficients for the piles due to the loads of adjacent piles are also gained. Lastly, a flexibility coefficient matrix equation is built to calculate settlement of pile groups with high or low pile caps. On the process of the deducing, the multilayer of soils and the interaction of settlements between piles bases are taken into consideration. A new relationship between pile-end resistance and pile-end settlement is proposed using Mindlin displacement solution. Comparisons of the settlement calculation for two pile cases are given to demonstrate the effectiveness and accuracy of the proposed method. The calculating interaction coefficients are much less than the elastic theory methods.