STUDY ON DEFORMATION CHARACTERISTICS OF SUPPORTING STRUC-TURE UNDER LOESS CRISS-CROSS TUNNEL EXCAVATION
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摘要: 本文通过三轴试验分析了不同含水率下的重塑黄土的应力-应变特征,采用模型试验针对黄土交叉隧道研究了开挖过程中支护结构应变变化特征和开挖影响范围。研究得到,隧道的支护结构变形与掌子面位置有关,掌子面到达监测断面前1.5D(D为洞径)左右时,钢拱架发生变形,超过监测断面1.5D后变形基本稳定,说明黄土开挖的水平影响范围大致为掌子面前后共3D。支护结构在监测断面前后各0.5D范围内变形最为明显,约占总应变释放量的70%,说明支护结构能够很好地限制变形,同时也说明了掌子面开挖围岩立即产生大变形,因此开挖完后应及时支护以保证隧道稳定。由于拱顶受到竖向荷载作用,而拱腰、直墙受到的是侧向荷载作用,拱顶围岩受拉,因此隧道变形最大的部位为交叉段的拱顶。主洞开挖完毕支护结构变形稳定后,岔洞开挖引起交叉段支护结构的二次变形,其拱顶的变形量约占总变形量的2/5,而距交叉口最远的监测断面,其变形量已经很小,说明越靠近交叉段,变形越明显,因此保证交叉段的稳定是保证隧道稳定性的关键。Abstract: The triaxial test was utilized to evaluate the stress-strain characteristics of remould loess with different water contents,and the strain variation of support structure and the excavation influence range of crossing tunnel in loess were revealed by the model test. The investigation shows that the deformation of the support structure is related to the position of the tunnel face,and the deformation of the steel arch was observed when the distance between tunnel face and monitoring section was within 1.5 D(D is the diameter of the tunnel),and when the distance exceeded 1.5 D from the monitoring section,the deformation was stabilized,which indicates that the horizontal influence range of excavation was about 1.5 D before and after the tunnel face. Besides,the deformation of the support structure is most obvious in the range of 0.5 D before and after the monitoring section,which accounts for more than 70% of the total strain release. It indicates that the deformation can be controlled by the support structure well,and also large deformation of surrounding rock occurs immediately after excavation,hence timely support should be provided to ensure the stability of the tunnel after excavation is completed. The largest deformation of the tunnel in the vault of the intersection was observed,which was the result of the different stress conditions between vault,hance and vertical wall,and the vault is subject to the vertical load,the hance and vertical wall is subjected to the lateral load. After the excavation of the main tunnel is completed and the deformation of the support structure being stabilized,the secondary deformation of the support structure in the intersection can be influenced by the excavation of the bifurcation tunnel. The deformation of the vault accounts for about 2/5 of the total deformation,and the further the monitoring section is away from the intersection,the deformation of the monitoring section was already very small. These results show that the closer the distance to the intersection,the greater the deformation is. So,the stability of the intersection is the key to the stability of the tunnel.
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Key words:
- Cross tunnel /
- Excavation effect /
- Deformation of surrounding rock /
- Loess soil /
- Model test
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表 1 粉砂质黄土力学参数
Table 1. Physical properties of soils for experiment
名称 值 名称 值 密度ρ/g·cm-3 1.56 含水率w/% 12.5 比重Gs 2.7 孔隙比e 0.929 液限wL/% 25.5 塑限wP/% 16.7 表 2 三轴试验结果
Table 2. Results of triaxial test
含水率/% 黏聚力c/kPa 摩擦角/(°) 11.4 31.98 24.16 14.5 27.71 21.69 -
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