高速铁路红层软岩路基时效上拱变形机制研究

Study on time-dependent upheaval deformation mechanisms of red-bed soft rock subgrade of high-speed railways

红层软岩地区高速铁路路基在运营期出现持续上拱变形,已成为当前阻碍我国高速铁路发展的又一关键因素,为揭示引起红层软岩地基时效性上拱变形机制,以西南地区某典型红层软岩深挖路堑路基上拱变形病害工点为依托,在现场工程地质与水文地质调查分析的基础上,结合基底地应力测试、红层软岩的吸水膨胀性试验和不同水理条件下的蠕变性试验结果,从地基岩体赋存的水、力环境、红层泥岩的时效性膨胀特性和水-力耦合蠕变特性角度,建立红层软岩地基分层变形机制模型,并系统分析地基短期、中期和长期上拱变形机制和特征。研究成果表明:(1)上拱区段属红层泥岩夹薄层砂岩的近水平地层结构,开挖法向卸荷引起浅层岩体微观裂隙松弛而视显,深层岩体仍为完整,地基岩体水平切向应力显著增大导致路基变形具有明显的结构效应;(2)侧向约束轴向自由下,红层泥岩吸水的时效性变形特征与其岩性及结构特征有关;(3)红层泥岩在低应力状态下即表现出典型的三阶段蠕变变形特征,且轴向应力越小,蠕变应变比越大;(4)水-力耦合作用下红层泥岩蠕变特性更为显著,大量级卸荷情况下上拱蠕变显著增大,蠕变稳定持续时间增长;水汽-力耦合作用下仍会出现显著的蠕变变形,蠕变稳定持续时间更长,总蠕变应变相对减小;(5)根据不同层位岩体的变形机制,将红层软岩地基划分为大气影响层(C1)、水汽-力耦合变形层(C2)、水-力耦合变形层(C3)和水-力耦合封闭层(C4)。路基短期变形主要由C1层岩体引起、中期变形由C3和C4层岩体引起、长期变形由C2层岩体引起。研究成果可为红层软岩地区高速铁路路基时效性上拱变形风险评估、预测及工程控制措施的设计提供理论支撑或参考。

Currently,the continuous upheaval deformation of high-speed railway subgrade during operation period in the region of red-bed soft rock mass has become a key factor to hinder the development of high-speed railways in China.In order to reveal time-dependent upheaval mechanisms of red-bed rock subgrade,and taking the typical upheaval of a deep cut red-bed soft rock subgrade in Southwest China as the research object,the in-situ engineering geology and hydrogeology conditions and the crustal stresses were surveyed,and the swelling and creep tests of red-bed soft rock mass under different hydraulic conditions were conducted.A layered deformation model of red-bed rock subgrade was built based on the time-dependent swelling and hydro-mechanical coupling characteristics,and the upheaval deformation mechanism and characteristics of the subgrade in short,medium and long terms were systematically analyzed.The results show that the red-bed mudstone inter-bedded with thin sandstone in the upheaval subgrade presents sub-horizontal,that the excavation normal unloading leads to the relaxation of micro-cracks in the shallow rock mass while the deep rock mass keeps intact,and that the horizontal stress of the subgrade increases obviously,resulting in significant structure effect of the subgrade deformation.Under the condition of lateral constraint and axial unconstraint,the time-dependent water-absorption deformation of the red-bed mudstone is related to its lithology and structural characteristics.It is also shown that the red-bed mudstone presents a three-phase creep characteristic under low stress condition and the creep strain ratio increases with decreasing the axial stress.Under the hydro-mechanical coupling condition,the creep property of the red-bed mudstone is more significant,and both the creep upheaval strain and the duration time increase more obviously for large unloading.The creep time lasts longer while the total creep strain decreases under the moisture-mechanical coupling condition.Based on the deformation mechanisms of different layered rock masses,the red-bed soft rock subgrade is divided into atmospheric influence layer(C1),moisture-mechanical coupling deformation layer(C2),hydro-mechanical coupling deformation layer(C3)and hydro-mechanical coupling confining layer(C4).The short-term,medium-term and long-term deformations of the subgrade are mainly contributed by C1,C3 and C4,and C2 respectively.The results can provide theoretical foundation and reference for risk assessment and forecast and the design of engineering control measures of time-dependent upheaval deformation of high-speed railway subgrade in the region of red-bed soft rock mass.