Surrounding rock pressure in the tunnel portal section through moraine under freeze-thaw action  

作　　者：CHEN Zhimin LIU Baoli LIU Yaohui XU Jiangtao 

机构地区：[1]School of Civil Engineering,Lanzhou Jiaotong University,Lanzhou 730070,China [2]CSCEC AECOM Consultants Co.,ltd,Lanzhou 730000,China [3]National and Local Joint Engineering Laboratory of Road and Bridge Engineering Disaster Prevention Technology,Lanzhou Jiaotong University,Lanzhou 730070,China

出　　处：《Journal of Mountain Science》2024年第7期2480-2493,共14页山地科学学报（英文）

基　　金：jointly supported by the National Natural Science Foundation of China(Grant Number 12262018);the Technology Funding Scheme of China Construction Second Engineering Bureau LTD(Grant Number 2020ZX150002);Special Funds for Guiding Local Scientific and Technological Development by The Central Government(Grant Number 22ZY1QA005)。

摘　　要：Moraines,characterized by the accumulation of rock and soil debris transported by glacial activity,present unique challenges for tunnel construction,particularly in portal sections,due to prevailing geographical and climatic conditions that facilitate freeze-thaw action.Despite these challenges,there is a dearth of studies investigating the influence of freeze-thaw action and water content on the mechanical properties of moraines,and no research on calculating surrounding rock pressure in moraine tunnels subjected to freeze-thaw conditions.In this study,direct shear tests under freeze-thaw cycles were conducted to examine the effects of freeze-thaw cycles and water content on the mechanical properties of frozen moraine.A comprehensive parameter K,integrating the number of freeze-thaws and water content,was introduced to model cohesion c.Drawing on Terzaghi Theory,we propose an improved algorithm for calculating surrounding rock pressure at the portal section of moraine tunnels.Using a tunnel as a case study,surrounding rock pressure was calculated under various conditions to validate the Improved Algorithm's efficacy.The results show that:(1)Strength loss exhibits a linear trend with the number of freeze-thaw cycles at water content levels of 4%and 8%,while at 12%water content,previous freeze-thaw cycles induce more significant damage to the soil.(2)Moraine saturation peaks between 8%and 12%water content.Following repeated freeze-thaw cycles,moraine shear strength initially increases before decreasing with varying water content.(3)The internal friction angle of moraine experiences slight reductions with prolonged freeze-thaw cycles,but both freeze-thaw cycles and water content significantly influence cohesion.(4)Vertical surrounding rock pressure increases after the initial freeze-thaw cycle,particularly with higher water content,although freeze-thaw cycles have minimal effect on it.(5)Freeze-thaw cycles lead to a substantial increase in lateral surrounding rock pressure,necessitating reinforced support structure

关 键 词：MORAINES Freeze-thaw cycles Direct shear test Surrounding rock pressure 

分 类 号：U451.2[建筑科学—桥梁与隧道工程]