钻孔灌注桩桩底沉渣对桩承载性状影响

为了对沉渣影响桩的承载特性进行定量研究。根据现场检测试验资料，建立有桩底沉渣的钻孔灌注桩单桩桩土相互作用轴对称弹塑性有限元模型，从桩底沉渣厚度、物理特性以及长径比变化3个方面分析沉渣对桩承载性状影响进行研究。计算结果表明，沉渣的存在降低了桩极限承载力，沉渣厚度越大，沉渣对Q—S曲线影响也越大；当沉渣厚度大于300mm时，桩端阻力降低幅度明显；桩底沉渣一定程度上减少了桩身变形；在对桩底沉渣物理参数进行研究的结果表明，沉渣弹性模量和摩擦系数对桩极限承载力影响明显；长径比越大，桩底沉渣对桩承载力及沉降影响越小。根据上部荷载作用下沉渣变形特性分析，当沉渣性质较弱时，桩的破坏模式更多地表现为一种刺入剪切破坏，与现场测试结果一致。

Influence of bottom sediment on the bearing capacity of pedrilled cast-in-place pile

Quant itat ive resear ch w as conducted to analyze the inf luence of bot tom sediment . The axisymmetr ic elast ic-plast ic f inite element model o f soil-pile interaction of sing le pile w as established based onthe- spot test data. Inf luence analy sis of bot tom sediment on the bearing capacity o f predrilled cast-in-place pile was made f rom the thickness, the physical pr opert ies and the change o f leng th diameter r at io of bottom sediment . T he finite element calculat io n r esul ts show that the ex istence of bo ttom sediment decreases the ult imate bear ing capacity o f pile, and that the thicker the bot tom sediment is, the mor e influence on QS curv e it w ill make. When the thickness of bot tom sediment is over 300 mm, it will decr ease the pile t ip resistance greatly. The bot tom sediment decreases, to a certain ex tent , the defo rmat ion of pile body . T he result of physical parameters of bo ttom sediment show s that the elast ic modulus and the frictio n coeff icient of bo ttom sediment have great impact o n the ult imate bearing capacity of pile, and that the larg er the length diameter rat io is, the less influence the bot tom sediment w ill make on the bearing capacity of pile. Accor ding to the analysis of the deformatio n propert ies of the bot tom sediment under top loading, when the bot tom sediment is w eak, the failure mode of the pile is more likely to manifest it self as punching shear failure features.