摘要
近年来,随着建筑工程技术的飞速发展,地基处理技术成为工程领域的研究热点。其中,柱锤冲扩桩地基处理技术因其高效、经济的特点逐渐被广泛应用。但在细观层面还缺乏对桩体成桩机理的研究,以优化现场设计及施工。本文以室内模型试验为基础,采用Flac3D-PFC耦合数值模拟,从宏细观角度分析成桩过程中土体动应力响应,包括加速度响应、土体变形及砂卵石填料骨架中力链的发展规律。结果表明:柱锤在冲击过程中夯实、挤压孔下土体,土体发生变形的过程可分为增大、回弹、稳定3个阶段;冲击在土体中产生的能量以应力波的形式从孔中心向外迅速衰减,能量使土体逐渐挤密压实、地基加固,当能量传递至孔下3d(d为柱锤直径)时,动应力响应较小,土体受柱锤冲击作用影响不大;冲击使得砂卵石填料力链骨架结构发生断链重构,在该过程中,颗粒空隙不断减小,力链数量增加,作用力不断增强,填料不断置换土体,两者形成密实的整体以实现加固;冲击完成后,以初始孔底平面为基准面,自平面向上0.5d至平面向下3.0d与径向1.5d形成加固影响区域,该区域范围内的土体在冲击过程中应力响应较大,消耗大部分冲击能量,并在冲击完成后发生较大位移,使土体更加密实,地基实现加固。通过数值模拟补充模型试验,完善了柱锤冲扩桩单桩成桩机理,为现场施工提供重要的理论支持和实用指导。
Objective An accurate understanding of the pile formation mechanism of downhole dynamic compaction(DDC)piles is critical for optimizing their application in foundation reinforcement.Traditional foundation strengthening methods suffer from extended construction periods and high costs,while DDC piles have gained popularity due to their advantages in efficiency,cost-effectiveness,and environmental sustainability.However,their pile formation mechanism remains insufficiently documented,particularly at the micro-level.In addition,sand and pebble soil,widely distributed in the Chengdu region,is often discarded as construction waste,which causes environmental issues.This study aims to explore the pile formation mechanism of DDC pile foundation treatment technology using sand and pebble soil as fill material,addressing both technical gaps and environmental concerns.Methods Laboratory model tests and Flac3D‒PFC coupled numerical simulations were employed to analyze the working principle and effect of DDC piles at both macro-and micro-levels.The model tests focused on measuring soil acceleration and deformation.The numerical simulations investigated changes in skeleton force chains and soil stress responses at different depths and radial distances during the impact process,providing intuitive and quantitative evidence for understanding the pile formation mechanism.Results and Discussions The results indicated that the column hammer impact process can be divided into three distinct stages:soil deformation increase,rebound,and stability.This process primarily utilizes stress waves for energy transfer,with energy decaying rapidly from the downhole bottom to the surrounding foundation soil,facilitating the compaction of ground soil,especially around fill materials.For the studied ground and hammer conditions,when the distance from the downhole bottom exceeded 3d(where d is the downhole diameter),the dynamic response of foundation soil became negligible,indicating a minimal reinforcement effect beyond this range.Dynamic monitoring of force chain skeleton structures in fill materials(sand and pebble soils)revealed that the fill material skeleton underwent breakage and reconstruction during impact.As inter-particle voids decrease,the number of force chains in fill materials increases,significantly enhancing their stability and supporting capacity.Based on foundation soil dynamic responses,an effective reinforcement zone was identified:vertically,it ranged from‒0.5d to 3.0d(with negative distances indicating positions above the initial downhole bottom);horizontally,its diameter was approximately 1.5d from the downhole centerline.Within this range,foundation soil experienced significant dynamic responses,consumed most impact energy,and underwent substantial deformation,achieving the desired compaction and strength.Conclusions The results demonstrate that DDC pile technology effectively modifies soil structure and enhances soil compactness and load bearing capacity.Dynamic responses of foundation soil during impact reveal the complexity of the pile formation mechanism,particularly the evolution of foundation soil acceleration,deformation,and force chain skeletons in fill materials.This perspective provides valuable insights for optimizing and understanding DDC piles.The findings provide theoretical support and practical guidance for engineering applications of DDC piles using construction wastes(sand and pebble soil,waste concrete)as fill materials.
作者
袁胜洋
李城栋
练小莲
陆仁芳
邓开元
刘先峰
YUAN Shengyang;LI Chengdong;LIAN Xiaolian;LU Renfang;DENG Kaiyuan;LIU Xianfeng(School of Civil Engineering,Southwest Jiaotong University,Chengdu 610031,China;Key Laboratory of High-speed Railway Engineering,Ministry of Education,Southwest Jiaotong University,Chengdu 610031,China;West Yunnan University of Applied Sciences,Dali 671000,China;Southwest Electric Power Design Institute Company,Limited of China Power Engineering Consulting Group,Chengdu 610056,China)
出处
《工程科学与技术》
北大核心
2025年第5期248-260,共13页
Advanced Engineering Sciences
基金
国家自然科学基金项目(52478472
52168066)。
关键词
柱锤冲扩桩
加固机理
土体位移
动力响应
骨架力链
downhole dynamic compacted pile
reinforcement mechanism
soil displacement
dynamic response
skeleton force chains
作者简介
袁胜洋(1987-),男,副教授.研究方向:非饱和膨胀土.E-mail:shengyang.yuan@swjtu.edu.cn;通信作者:刘先峰,教授,E-mail:xianfeng.liu@switu.edu.cn。
