【作者】 张明；

【导师】 牛琪瑛；

【作者基本信息】 太原理工大学 ， 桥梁与隧道工程， 2010， 硕士

【摘要】 碎石桩是目前工程中用于处理饱和砂土液化地基最有效、最经济、最普遍的方式,但其理论研究却相对滞后,尤其是抗液化性能的理论研究还远远落后于工程实践。目前有关碎石桩加固液化土地基抗液化性能研究方法主要有室内试验和解析法,数值模拟相对少见。本文依托国家自然基金资助项目“桩体加固液化砂土作用机理的试验研究”(项目编号50578104)和山西省自然科学基金项目“砂桩加固的复合地基液化判别方法探讨”(项目编号2006011046),采用三维有限差分程序FLAC3D(Fast Lagrangian Analysis of Continua)对地震作用下的饱和液化砂土地基进行数值模拟,探讨了未加固与碎石桩加固情况下桩径、桩间距、砂土的相对密实度等因素对抗液化性能的影响,并与振动台模型试验资料进行了比较。结果分析表明:(1)无论是未加固液化土地基数值模型还是碎石桩加固液化土地基数值模型,孔压比的分布规律沿深度方向不同,中部孔压比较大,上、下部孔压比较小。(2)无论是未加固液化土地基数值模型还是碎石桩加固液化土地基数值模型,超静孔隙水压力随着深度的增加而增大。(3)无论是未加固液化土地基数值模型还是碎石桩加固液化土地基数值模型,相对密实度越大,抗液化能力越强。(4)单根碎石桩排水效应的影响范围为上窄下宽的圆台形,在浅层处,碎石桩的排水作用范围为不超过2倍桩径范围;在中层处,碎石桩在3倍桩径范围内有明显的排水效应,超出3倍桩径范围排水效应明显下降,在深层处,碎石桩在5倍桩径范围内仍有明显的排水效应。(5)未加固液化土地基数值模型中超静孔隙水压力和孔压比达到峰值后,在地震过程中基本保持不变,而群桩加固液化土地基数值模型中超静孔隙水压力和孔压比达到峰值后,在地震过程中发生迅速减小,充分证明了群桩的排水效应。(6)群体碎石桩加固地基数值模拟试验的深层、中层的孔压比峰值与振动台试验的深层、中层的孔压比峰值基本相等,证明群体碎石桩加固地基数值模拟试验结果是可靠的。(7)随着桩间距的增大,群桩的抗液化性能急剧下降,桩的排水性能逐渐减弱。更多还原

【Abstract】 Liquefiable sand soil improved by gravel pile which is the most economical and the most effective has been widely used in construction projects at present, however, relevant theory has not been advanced, especially study on the liquefaction resistance of gravel pile composite foundation has fallen far behind the engineering practice. There are two types of settlement computation method for liquefiable sand soil improved by gravel pile, one is analytical method and the other is indoor experimental method. Numerical simulation method is relatively uncommon.The thesis is supported by National Natural Science Foundation of China“The experimental study on mechanism of piles improving liquefiable soil (No.50578104)”and Provincial Natural Science Foundation of Shanxi“The discussion on methods for sand liquefaction estimating of compound foundation of sand pile (No.2006011046)”. In the paper, liquefiable sand soil under earthquake action is numerically simulated using by the three-dimensional finite difference program“FLAC3D”(Fast Lagrangian Analysis of Continua), and the influence of pile diameter, pile spacing and relative denseness of sand on the liquefaction resistance of liquefiable sand soil unimproved and improved by gravel pile is discussed, and compared with the result of shaking table tests . The result shows that:(1) The distribution of pore pressure ration is different along depth, the pore pressure ration is bigger in middle and smaller in upper and lower whether the numerical model of liquefiable soil improved by gravel pile or not .(2) The excess pore water pressure increases with the depth whether the numerical model of liquefiable soil improved by gravel pile or not .(3) The larger the relative denseness of sand, the stronger the liquefaction resistance whether the numerical model of liquefiable soil improved by gravel pile or not .(4) The effective influence drainage domain of single stone columns is a circling platform with narrow up side and wide underside . It is less than 2 times pile diameter in lower ; it is about 3 times pile diameter in middle and more than 3 times pile diameter has no obvious effect ; it has obvious effect more than 5 times pile diameter in upper.(5) In the process of earthquake action , the pore water pressure and pore pressure ratio keep stable after the peak value has reached in non-improved liquefaction soil ; but the dissipation of the pore water pressure and pore pressure ratio starts after the peak value has reached in liquefiable soil improved by gravel pile , which shows that the drainage effectiveness of stone columns is very remarkable.(6) The peak of pore pressure ration of middle and lower in the numerical model of liquefiable soil improved by gravel piles and the shaking table tests is almost equal, which proves the result of the numerical model of liquefiable soil improved by gravel piles is reliable.(7) The liquefaction resistance of the numerical model of liquefiable soil improved by gravel pile and the drainage capacity of gravel pile decrease sharply with the increase of pile spacing.更多还原