砂卵石地层泥水盾构排浆管路渣石起动特性模型试验与仿真分析

Model tests and simulation analyses of starting characteristics of muck in slurry-discharge pipelines of slurry shield in sandy pebble stratum

泥水盾构在砂卵石地层掘进的过程中,由于排浆管路中存在大量不规则卵石,排浆管路输送尤为复杂。设计了环流试验装置,并基于计算流体动力学与离散单元法(CFD-DEM)耦合方法建立了三维瞬态数值模型,对不同形状、粒径、管路倾角、弯头及管径下的卵石起动特性进行了探究。在模型试验中,羧甲基纤维素钠(CMC)浆液被选为载液,透明亚克力管被选为载体;在CFD-DEM耦合模型中,分别通过流变测试和三维扫描技术考虑了浆液的流变性和不规则卵石的形状。结果表明:(1)当异形卵石粒径和管路倾角相同时,卵石的起动速度大小顺序呈现椭球状>扁平状>近球状;(2)当异形卵石形状和管路倾角时,卵石的起动速度随等容粒径的增大先增大后减小再增大;(3)对于球形卵石,在水平管路中,卵石的起动速度随粒径的增大先增大后减小再增大,在倾斜和竖直管路中,卵石的起动速度随粒径的增大而减小;(4)卵石的起动速度随管径的增大而增大;(5)卵石起动速度较大的位置主要出现在较大角度(如60°,90°)的弯头位置处,这是因为当管路倾角≥60°时,在弯头位置处将会出现漩涡区,漩涡区流速与主流区流速相反,阻碍卵石运动,因此在铺设管路时,应尽量减少倾斜角度较大(≥60°)管路的铺设,多采用水平管路或倾斜角度较小(≤45°)的管路。

During the excavation process of slurry shield tunneling in sandy pebble stratum,the discharge pipeline transport is particularly complex due to a large number of irregular pebbles in the slurry-discharge pipelines.In this study,a circulating current test device is designed,and a three-dimensional transient numerical model is established using the computational fluid dynamics-discrete element method(CFD-DEM)coupling method.The start-up characteristics of the pebbles under different shapes,particle sizes,inclination angles of pipelines,elbow and pipeline diameters are investigated,respectively.In the model tests,the sodium carboxymethyl cellulose(CMC)slurry is used as the carrier liquid,and the transparent acrylic tube is used as the carrier.In the CFD-DEM coupling model,the rheological properties of slurry and the shape of irregular pebbles are considered through the rheological testing and three-dimensional scanning technology,respectively.The results indicated that:(1)Under the same particle size of irregular pebbles and inclination angle of pipelines,the starting velocity of the pebbles follows an order of ellipsoidal shape>flat shape>nearly spherical shapes;(2)Under the same shape of irregular pebbles and inclination angle of pipelines,the starting velocity of pebbles first increases,then decreases,and then increases with the increase of the isometric particle size.(3)For the spherical pebbles,in a horizontal pipeline,the starting velocity of the pebbles first increases,then decreases,and then increases with the increase of the particle size.In the inclined and vertical pipelines,the starting velocity of the pebbles decreases with the increase of the particle size.(4)The starting velocity of the pebbles increases with the increase of the pipe line diameter.(5)The positions with higher starting velocity of pebbles mainly appear at the elbow positions with larger angles(such as 60°and 90°).This is because when the inclination angle of pipelines is≥60°,a vortex zone will appear at the elbow position.The velocity in the vortex zone is opposite to the velocity in the mainstream zone,which hinders the movement of the pebbles.Therefore,when laying pipelines,it is necessary to minimize the laying of large-angle-inclined and vertical pipelines as much as possible,and it is recommended to use more horizontal pipelines or pipelines with small inclination angles(≤45°).