地铁列车振动荷载作用下隧道底部土层孔隙水压力及变形特性研究

Study of Pore Water Pressure and Deformation Characteristics of Soil below Tunnel under Vibration Load of Metro Trains

为研究地铁列车振动荷载长期作用下隧道底部土层的孔隙水压力及变形特性,以北京地铁7号线2期(东延)工程为背景,利用ADINA有限元计算平台建立典型隧道区间断面的有效应力分析模型,进行上限速度行车荷载作用下饱和场地土层-隧道体系水土耦合动力响应分析,研究典型位置处孔隙水压力时程变化规律,并预测地铁振动荷载作用下引起的沉降量。同时,对北京地铁7号线粉细砂进行土工室内试验,进一步研究隧道底部土层在地铁行车荷载作用下的孔隙水压力及竖向变形发展规律。结果表明:1)在长期列车振动荷载作用下,隧道底部土层孔隙水压力逐渐增大,且增大值随土层深度的增加而减小; 2)土体的累积超孔隙水压力比和累积应变量随着荷载幅值的增加而增大; 3)与非均等固结条件相比,均等固结条件下的超孔隙水压力比较大,但累计应变量小; 4)列车振动引起的超孔隙水压力和应变均较小,超孔隙水压力在列车停运期间足以消散完毕。

In order to study the pore water pressure and deformation characteristics of the soil layer at the bottom of the tunnel under long-term vibration load of metro trains,an effective stress analysis model for cross-section of a typical tunnel on Phase II(eastern extension)of Beijing Metro Line No.7 is established by using ADINA finite element calculation platform.The dynamic response of water-soil coupling in soil-tunnel system at saturated site under the action of upper-bound speed driving loads is analyzed.The variation law of pore water pressure in typical location is studied and the settlement caused by metro vibration is predicted.At the same time,the soil laboratory test is conducted on the fine sand of Line No.7 and the development law of pore water pressure and vertical deformation of soil layer at the bottom of tunnel under the load of metro traffic are further studied.The study results show that:(1)Under long-term train vibration loads,the pore water pressure of soil at the bottom of the tunnel increases gradually,and the increase value decreases with the increase of soil depth.(2)The cumulative excess pore water pressure ratio and cumulative strain of soil increase with the increase of load amplitude.(3)Compared with non-equal consolidated conditions,the excess pore water pressure is larger under the condition of equal consolidation,but the cumulative strain is smaller.(4)The excess pore water pressure and strain caused by train vibration are small,and the excess pore water pressure is sufficient to dissipate during train outage.