砌块干密度对回填施工接缝砌块体系的膨胀特性影响研究

INFLUENCE OF BLOCK DRY DENSITY ON SWELLING PROPERTY OF BLOCK SYSTEM WITH JOINTS SEALED BY BENTONITE POWDER

通过室内模拟试验,采用膨润土粉末对压实膨润土砌块之间的接缝区进行二次填充,利用自主设计的刚性壁膨胀仪,以砌块干密度为基本变量,对恒体积条件下不同干密度砌块接缝以及砌块顶部的膨胀应力进行监测,分析接缝密封后砌块体系的膨胀特性。试验表明:经二次填充后的含接缝砌块体系,其膨胀应力优先向接缝区域发展,径向膨胀应力发展快于轴向,有利于砌块接缝区域的封闭。在相同接缝充填的条件下,随着砌块初始干密度的增大,砌块体系接缝区域的最终膨胀应力增大,到达最大膨胀应力时间缩短,接缝区域愈合速度加快。由于接缝的存在,砌块区膨润土吸水膨胀后首先对接缝内孔隙进行充填,轴向应力降低,产生"应力补偿"现象。砌块干密度越低,应力补偿现象越明显。根据砌块的轴向应力曲线将砌块轴向应力发展过程分为3个阶段:快速增长阶段、稳步发展阶段和应力调整阶段。其中快速发展阶段主要受砌块初始干密度的控制,而稳步增长阶段则受到水分迁移、侧壁摩擦力以及接缝愈合速率的影响更多。相较于完整样,含充填接缝的砌块体系膨胀应力分布状态趋向于等向应力分布,提高了整个屏障体系的均质化程度。

In this study,a dry bentonite powder was selected as a sealing material to backfill the joint area between the compacted bentonite-sand blocks.The swelling property of the block system after backfilling was studied considering the initial dry density of blocks as the basic variable.During the swelling test,the swelling stresses at radial and axial direction were monitored in a constant volume condition.The test results show that the swelling stress develops preferentially to the joint area,and the radial swelling stress develops faster than that on the axial direction,which contributes to the sealing of the joint.The final swelling stress in the joint area of the block system increases with the initial dry density of the block,the time to reach the maximum swelling stress shortens,and the healing speed of the joint area improves under the same sealing condition.The swelling deformation of block develops preferentially to the joint area and fills the pores in the joint area resulting in the phenomenon of"stress compensation"that the final axial stresses of blocks decrease.The lower the dry density of the block,the more stress compensation is needed.According to the axial stress curve of the block,the development process of axial stress of block can be divided into three stages:rapid-growth stage,steady-development stage and stress-adjustment stage.The rapid development stage is mainly controlled by the initial dry density of the block,while the steady growth stage is more affected by water migration,side wall friction and the sealing rate of joint.Compared with the intact block,the stress distribution of block with backfilled joint tends to be isotropic,which improves the homogenization degree of the whole barrier system.