砂土地基强夯室内模型试验及加固特性分析

Laboratory Model Test and Reinforcement Characteristics Analysis on Dynamic Compaction of Sand Foundation

为了获取德国莱比锡砂土地基强夯加固特性,采用自行设计的模型试验装置及量测系统,制备3种相对密实度的砂土进行了强夯室内模型试验,每组试验进行24击强夯。强夯过程中测量夯锤速度、位移、动态力、能量释放时间变化,结合PIV(particle image velocimetry)技术分析强夯后砂土颗粒位移结果,得到水平方向和深度方向的有效加固范围发展特性。结果表明:第6、12、18、24击的速度时程曲线在快速下降阶段基本重合,击数越高回弹速度越高、持续时间越短,体现为能量释放时间的不同;对于ID0.4、ID0.5、ID0.7试验组,从第6击到第24击的强夯能量释放时间分别下降38.9%、34.7%、31.4%,在第24击的夯锤位移回弹比分别达到65.3%、67.1%、69.0%;砂土相对密实度越高,夯锤冲击力越大,第6、12、18、24击之间的差别越小;随着夯击次数的增加,夯锤动态力峰值逐渐提高、上行曲线斜率变小,冲击行程逐渐缩短;ID0.4、ID0.5、ID0.7试验组分别在第20、18、15击后,水平方向有效加固范围增长大于深度方向。

To obtain the dynamic compaction characteristics of Leipzig sandy soil foundation in Germany, a self-designed model test device and measurement system were adopted. Three different relative densities of sand were prepared for dynamic compaction in the laboratory model tests;each group of test was carried out with 24 tamping times. During the dynamic compaction, the velocity, displacement, dynamic force, and energy release duration of tampings were measured. PIV(particle image velocimetry) technology was adopted to investigate the sand particles displacement after the dynamic compaction, and the development characteristics of effective reinforcement area in horizontal direction and depth direction were obtained. The results show that the velocity-time curves of the 6 th, 12 th, 18 th, and 24 th tampings are basically coincidence with each other in the rapid declining stage. When the higher tamping times are achieved, the rebound velocity become higher in shorter duration, which reflecting the different energy release duration. For ID0.4, ID0.5, and ID0.7, the energy release duration decrease by 38.9%, 34.7%, and 31.4%, respectively, from the 6 th to the 24 th tampings, while the resilience ratio of the tamp in the 24 th tamping reach 65.3%, 67.1%, and 69.0%, respectively. The higher the relative density of the sand, the greater the impact force of tamp, and the smaller the differences between the 6 th, 12 th, 18 th, and 24 th tampings. With the increase of the tamping times, the peak value of dynamic force gradually increased, the slope of upward curves become smaller, and the impact duration is gradually shorter. For ID0.4, ID0.5, and ID0.7, after the 20 th, 18 th, and 15 th tampings, respectively, the effective reinforcement area in horizontal direction increased more than in depth direction.