【作者】 何景愈；

【导师】 张忠苗；

【作者基本信息】 浙江大学 ， 岩土工程， 2012， 硕士

【摘要】 随着越来越多的超高层建筑和大跨度桥梁的出现,大直径灌注桩因其所具有的诸多技术优势,在工程中得到了越来越广泛的应用。但由于钻孔灌注桩存在泥皮降低侧阻和沉渣降低端阻问题,灌注桩后注浆技术应运而生,它不仅可减少桩基沉降还可提高基桩承载能力。本文在前人工作的基础上,开展了杭州奥体中心注浆与未注浆大直径桩对比试验,以及多个工地桩端后注浆大直径灌注桩尺寸效应现场试验研究,通过试验数据分析和理论推导以及matlab数值编程与分析。对大直径后注浆桩抗压、抗拔承载力性状以及后注浆残余应力进行了初步研究,取得如下的研究成果：(1)结合现场静载试验数据对杭州地区大直径后注浆灌注桩的抗压承载性状进行分析结果显示,桩端后注浆浆液上返高度以内土层,后注浆对桩侧泥皮的固化、压密等作用减小了尺寸效应对侧阻的影响；而浆液上返高度以外的上部土层,侧阻尺寸效应显著,用规范推荐的方法计算注浆桩侧阻尺寸效应系数偏于不安全；另一方面,实测砂、碎石类土层侧阻尺寸效应系数均比黏性土、粉土土层的要小；端阻尺寸效应则能基本消除。(2)在大直径后注浆桩尺寸效应试验研究的基础上,提出了考虑大直径后注浆桩侧阻、端阻尺寸效应以及端阻、侧阻增强效应的单桩抗压极限承载力计算公式。(3)在注浆与未注浆大直径抗拔桩静载试验的基础上,发现了软土地区抗拔桩经过桩端后注浆可显著的减少桩端位移,极限抗拔力至少提高25%；注浆抗拔桩桩身混凝土拉伸量是桩顶上拔量的主要组成部分,所占比例约为91.5%；注浆与未注浆抗拔桩的桩身轴力都随深度逐渐减少,桩端轴力始终为零。(4)在利用浆液上返高度公式计算注浆抗拔桩竖向增强体高度和考虑桩身自重的基础上,提出了改进的桩端后注浆抗拔桩承载力的计算公式；通过反分析计算,未注浆灌注桩抗拔折减系数的取值为0.65～0.80,注浆桩侧阻力增强系数的取值为1.33～1.83,上述计算方法与折减(增强)系数可供初步设计与实际工程使用。(5)基于球形空腔扩张及一维径向固结理论,对桩端后注浆桩的桩端注浆残余应力进行理论研究,在负指数衰减的初始超孔隙压力分布基础上,得到了残余应力随时间及扩散半径消散的解析解,并分析了模型的主要影响参数,结合现场试验验证了模型的可靠性。(6)在不考虑注浆扩散半径的前提下,对注浆残余应力扩散模型解析解进行了简化,与本文的计算方法相比较,对模型的主要影响因素进行的参数分析发现：流变指数、稠度系数、土体的压缩模量及固结时间是影响注浆残余应力的关键因素,注浆残余应力一般会随着流变指数、稠度系数、土体的压缩模量或固结时间的增大而减小。更多还原

【Abstract】 With the increase in the construction of high-rise buildings and large-span bridges, large diameter bored cast-in-situ piles have been widely used in practice because of its technical advantages. However, due to concerns of relating to the decrease of side friction and end resistance arising from the construction, post grouting has been employed to improve the bearing capacity as well decrease the settlement of the piles.On the basis of works of previous researchers, comparative tests between grouted and ungrouted large diameter piles and some field tests of size effect were conducted. The compressive capacity, tensile capacity and posting grouting residual pressures were studied preliminary by tests results analysis and theoretical derivation in this paper. Research achievement as bellow:(1) The compressive capacity of the large diameter bored cast-in-situ piles with post-grouting was analyzed based on the results of field tests in Hangzhou. The results show that the influence of size effect on skin friction decreases due to the solidification and compaction of the shaft side mud after grouting for the layer affected by the grouting. Whereas the size effect of skin friction can be found obviously for the higher layers unaffected by the grouting. It is less conservative to calculate the size effect coefficient with the method used in the current code. It is also found that the size effect coefficient for the sand or gravel layers is smaller than that for clay or silt soil layers. In addition, the size effect of tip resistance of the post-grouting piles can be eliminated.(2) Based on the studies of the size effect of large diameter grouted piles, a calculation method of ultimate compressive capacity for single pile incorporate the size effect and strength effect of the side friction and end resistance is presented in this paper.(3) The results of the tensile load tests on grouted and ungrouted piles show that pile-end post grouting technique can significantly reduce the pile tip settlement and increase the ultimate bearing capacity of pile. The ultimate bearing capacity of the pile with post-grouted is 1.25 times that of the pile without post-grouted; the tension compression of pile shaft is about 91.5% of the displacement at the pile head; the axial force decreases with depth but increase with the applied load at the pile head, however, the measured tip resistance is near zero during the whole loading cycle.(4) A new simple formulation for calculation of the ultimate bearing capacity of the uplift piles is proposed by considering the dead weight of pile and the climb height of grout; and the back-analysis shows that the ratio of the unit skin friction of the uplift pile to that of the compression pile is 0.65 to 0.80, whereas the ratio of the total skin friction in the uplift case to that in the compression case is 1.33 to 1.83, these values can be used in preliminary design of the pile.(5) Residual pressures locked in at the pile base during pressure grouting are studied theoretically based on the solutions of expansion of spherical cavity and one-dimensional consolidation. By analysis the dissipation process of the residual pressures, the analytical solutions of residual pressures dissipation with time and spread radius are obtained for assumed initial exponential pore pressure distribution and the influence of some key parameters are analyzed. The validity of the proposed model is also tested by comparing the results from field measurements.(6) A simplified solution discarding the grout spread radius is compared with the present method for different relative parameters. Parametric studies show that rheological index, consistency index, compression modulus and consolidation time are the key issues affecting pile residual pressures. The residual pressures decrease with the increase of the rheological index, consistency index, compression modulus and consolidation time.更多还原