强夯的物质点法模拟及其能量转化规律分析

提出大应力范围内的密度相关土体本构模型,适用于分析强夯等作用下的土体变形问题。对刚柔接触算法进行了修正,用物质点法结合提出的本构模拟了强夯过程。与其他数值模拟将荷载假设为三角形应力波作为输入荷载不同,通过输入夯锤与土体的碰撞速度实现加载。模拟结果与承德机场4标段某处试验数据进行了对照,吻合较好。提出强夯过程中的能量转化率的概念,对能量转化的规律进行了研究,为研究强夯问题提供了新视角。模拟分析表明,能量转化率的提高不总意味着每击夯沉量的提高,因为能量在较大范围的扩散可能导致高能量转化率下的低夯沉量;剪切变形过程中吸收较多的塑性应变能,可能会使体积压缩变形吸收的塑性应变能向局部集中。通过数值模拟还发现,重锤低落时的能量转化率高于轻锤高落,一般可产生更大的夯沉量。

Simulation of dynamic compaction using material point method and analysis of its energy conversion law

A density-dependent soil constitutive model for large stress range is proposed for the analysis of large deformation of soil subjected to high stresses under dynamic compaction. A rigid-flexible contact algorithm is further developed and the material point method combined with the proposed constitutive model is used to simulate the dynamic compaction process. In contrast to some previous numerical simulations, in which the input load is assumed to be a triangular stress wave, the loading procedure here is achieved by controlling the collision speed between the hammer and the soil. The computed results are in good agreement with the experimental data on the construction site of Chengde Airport. A new concept, the “energy conversion rate” in the process of dynamic compaction, is introduced, and the laws of energy conversion are studied, which provides a new perspective on the study of dynamic compaction. The numerical simulations indicate that an increase in the energy conversion rate does not necessarily mean an increase of the crater depth per impact, since the distribution of energy in a larger domain may result in a lower crater depth under a high energy conversion rate. A greater shear plastic strain energy absorbtion may contribute to a local concentration of the absorbed plastic strain energy in volume compression of soil. It is also found that the energy conversion rate under low drop of a heavy hammer is higher than that under high drop of a light hammer, and consequently produces in general a larger crater depth.