H型桩在花岗岩残积土中的桩端承载力模拟

花岗岩残积土通常作为摩擦桩的桩端持力层,其工程性状一般接近于粉质砂土(Lumb,1962)。该土层内的桩端承载力可以用球孔扩张理论来模拟。桩端土在高应力作用下会产生强度折减的现象,这可以结合砂性土的室内试验成果,在土性参数的评估中予以考虑。运用有限应变理论,可以将球孔扩张塑性区内的平均体积应变以解析方法导出,方便了数值化计算。通过与三根静压H型桩的现场载荷试验成果的比较,发现该预测方法与实测的荷载传递趋势较吻合。此法在应用中只需提供桩尺寸、桩端竖向有效应力和标贯试验N值等少量参数,因此较适合在初步设计阶段对单桩承载力进行预估。

Prediction of End-bearing Capacity of H-piles Embedded in Completely Decomposed Granitic Soils

As a kind of silty sands (Lumb, 1962), residual granitic soil is normally taken as the end-bearing stratum of friction piles. The end-bearing capacity of piles embedded in residual granitic soil can be simulated by the theory of spherical cavity expansion. Thins paper presents a model that considers the reduction of strength of decomposed granitic soil under high pressure. By incorporating the theory of finite strain, the model is capable of evaluating the mean volumetric strain analytically, thus facilitating the procedure of numerical calculation. Comparative study is made between the model and three in-situ load tests. The measured and predicted results agree fairly well. The model only requires the knowledge of pile's dimension, effective overburden pressure and SPT-N value at the pile's base. It istherefore suitable for the estimation of pile end-bearing capacities during the stage of preliminary design.