灰土挤密桩加固黄土隧道受力与变形性状分析

兰州地区黄土土质疏松、孔隙比大、强度低,普遍具有严重的湿陷性、高压缩性和动力易损性,在增加正压力或孔隙水压力时,极易引起隧道底部及建筑物地基的破坏。为解决兰州绕城高速某大断面黄土隧道底部变形过大的问题,文章选择灰土挤密桩作为加固手段,采用三维数值方法对隧底未处理条件下和采用灰土挤密桩加固后的围岩变形与受力特征进行研究。结果表明:隧底开挖后主要产生隆起,并随开挖方向逐渐增大,起点拱脚处产生下沉,位移最大值出现在隧底中心处;采用灰土挤密桩加固后,其桩身轴力、桩身应力和桩身位移在水平方向均呈现出两边小、中间大的规律,且随开挖方向逐渐增大,桩身承担了隧道开挖产生的大部分荷载,隧底受力与变形均有所减小;灰土挤密桩加固后的隧底位移值减小了32.0%~34.4%,灰土挤密桩能够很好地提高黄土隧道隧底承载力和抵抗变形的能力。

Analysis of Mechanical Behaviors and Deformation Characteristics of the Loess Tunnel Reinforced by Lime-soil Compaction Piles

The loess in Lanzhou is characterized by severe collapsibility,high compressibility and dynamic vulner ability due to its loose texture,large void ratio and low strength,and it′s easy to cause failures at tunnel floor and building foundation whenever the positive pressure or pore water pressure increase.Aiming at the deformation of a large-section loess tunnel in Lanzhou,reinforcement is conducted by the lime-soil compaction pile,and a three-di mensional numerical method is adopted to study the characteristics of deformations and mechanical behaviors be fore and after reinforcement with lime-soil compaction piles.The results show that before reinforcement with limesoil piles the heaving occurs and gradually increases along with the direction of excavation,subsidence occurs at arch spring,the maximum displacement occurs at the center of tunnel bottom;after reinforcement with lime-soil piles,the pile axial force,pile stress and pile displacement are small on both sides and large in the middle in hori zontal direction,and they increase gradually along with the excavation direction,the piles bear most of the load pro duced by tunnel excavation,and the force and deformation at tunnel bottom decrease,and the displacement at tun nel floor is reduced by 32%-34.4%,which shows the lime-soil compaction pile can improve the bearing capacity and resistance to deformation at tunnel bottom of the loess tunnel.