低承台桩基础对地表土体振动的影响分析

Study on influence of low cap pile foundation on vibration in ground soil

建立了基于Biot波动方程的三维显式有限元计算方法,分析饱和地基中低承台桩基在简谐荷载作用下,桩基对桩周地表土振动的影响。采用1/3倍频程分析技术评价地表的振动量级,参数计算分四组,分别探讨土骨架的剪切模量、激振频率、承台板埋深比、平面尺寸的影响规律。结果表明：从减小水平向振动来考虑,承台埋深比宜取0.4~0.5,承台板厚宜取较大值;从减小竖直向振动来考虑,承台埋深及承台板厚的取值与土骨架剪切模量有关,建议承台量纲为一的板宽取0.5;桩基在较低频率荷载作用下对地表振动的放大作用要比较高频率荷载作用强。

Based on Biot's wave propagation equations, an explicit FEM method in three-dimension is presented. Using the method, low cap pile foundation influence on the vibration of ground soil around the piles, due to harmonic loading acting on the pile cap, is discussed. Vibration level on ground surface is evaluated by means of one-third octave band analytical method. Four groups of parametric analysis are performed to explore the influence of various factors, including shear modulus of soil skeleton, exciting frequency, buried depth of cap and cap plane size, on vibration level respectively. Results obtained indicate that for the purpose of decreasing horizontal vibration, the ratio of cap buried depth to cap thickness should be 0.4 to 0.5 and the cap thickness should be large fairly. For the aim of reducing vertical vibration, cap buried depth and cap thickness should be considered related to shear modulus of soil skeleton. A suggested non-dimensional cap width is equal to 0.5. Vibration enlargement effects of ground soil from pile foundation under low frequency exciting loading are stronger than that under high frequency exciting loading.