Practical calculation method for settlement under dynamic compaction

Accurately predicting the compaction settlement under the impact load of dynamic compaction has an important impact on the design and construction of dynamic compaction. The calculation of subgrade soil settlement under static load generally adopts the layered summation method in China. The layered summation method is simple and practical with rich engineering experience. According to the analysis of the dynamic stress in the soil-hammer contact, the additional stress distribution in the soil determined by the elastic theory under static load is comparable to the vertical dynamic stress distribution under the impact load of dynamic compaction. Based on the layered summation method, a practical calculation method for the compaction settlement of dynamic compaction is proposed. By using a portable drop hammer deflection test and a penetrometer test, a preliminary discussion was conducted on the dynamic load parameters involved in the calculation method, as well as the relationship between the dynamic rebound modulus and compression modulus. Meanwhile, a calculation method for the average contact dynamic stress of the hammer was provided. Lastly, a comparison between the measured and estimated settlement of three engineering examples was carried out in order to confirm the efficacy of the suggested practical calculation approach for compaction settlement. The results show that this method can effectively capture the settlement characteristics of subgrade soil under different energy levels of compaction. For dynamic compaction projects with low, medium, and high energy levels, the errors between calculated settlement and measured settlement are 2.28%, 2.27%, and 9.89%, respectively. This practical calculation method is simple and convenient to use, which provides a new approach for calculating the settlement of subgrade soil under impact loads.

准确预测动力压实（dynamic compaction）冲击荷载下的压实沉降，对动力压实工程的设计与施工具有重要意义。我国目前通常采用分层总和法（layered summation method）进行静荷载下路基地土的沉降计算，该方法简便实用且积累了丰富的工程经验。通过对锤土接触区域的动应力分析可知，静荷载下基于弹性理论（elastic theory）推导得到的土体附加应力分布，与动力压实冲击荷载下的竖向动应力分布具有可比性。基于分层总和法，本文提出了一种适用于动力压实的实用压实沉降计算方法。借助便携式落锤弯沉试验（portable drop hammer deflection test）与触探试验（penetrometer test），本文对该计算方法涉及的动荷载参数，以及动态回弹模量（dynamic rebound modulus）与压缩模量（compression modulus）之间的关联展开了初步探讨，同时给出了锤体平均接触动应力（average contact dynamic stress）的计算方法。最后选取3个工程实例开展实测沉降与预估沉降的对比分析，以验证所提实用压实沉降计算方法的有效性。结果表明，该方法可有效捕捉不同能级动力压实作用下路基地土的沉降特性；针对低、中、高能级的动力压实工程，计算沉降与实测沉降的误差分别为2.28%、2.27%与9.89%。该实用计算方法操作简便，为冲击荷载下路基地土的沉降计算提供了全新思路。