V级围岩条件下超大断面隧道的适宜喷层厚度研究

Study on Suitable Shotcrete Layer Thickness of Ultra-large Section Tunnel under Grade V Surrounding Rock Condition

为了研究V级围岩条件下超大断面隧道的适宜喷层厚度,以深圳某隧道工程V级围岩四车道段为依托,首先基于隧道所处地质条件、自身断面形式和试验加载设备条件,分别建立了20,30,40 cm喷层厚度的室内相似模型,对自重应力场工况下不同厚度喷射混凝土可承受的最大竖向(围岩)应力、位移变化规律和破坏失效特征进行了分析。随后建立了数值仿真模型,并参照模型试验过程,在模型上边界施加竖向应力,分析了不同喷层厚度初支的最大竖向(围岩)应力和极限位移,对室内模型试验结论进行了验证,并进一步优化了喷层厚度。结果表明:随喷层厚度增加,最大竖向(围岩)应力增大,但增量逐渐减小,20,30,40 cm厚度喷层,依次为5.0,5.7,6.0 MPa;20 cm厚度喷层的失效模式不同于30 cm和40 cm厚度喷层,其以拱底位移为断面最大位移,而30 cm和40 cm厚度喷层则以拱顶位移为断面最大位移;在支护结构的变形能力上,30 cm厚度喷层要显著优于20 cm和40 cm厚度喷层,对应失效前极限位移为127,80,82 mm;结合数值模拟、综合喷层结构的支护能力和变形能力,V级围岩条件下超大断面隧道喷层厚度优化为26~38 cm,最优值为32 cm。

To study the suitable thickness of shotcrete for ultra-large cross-section tunnel under V-grade surrounding rock condition,based on the 4-lane section of V-grade surrounding rock of a tunnel project in Shenzhen,first,the indoor similar models with shotcrete layer of 20,30,40 cm are established based on the geological and sectional conditions of the tunnel and the test loading equipment condition,the displacement variation rule,the destruction failure characteristics,and the maximum vertical(surrounding rock)stressσymax that can be withstood by shotcrete with different thicknesses under the condition of gravity stress field are studied.After that,the numerical simulation models with vertical stress applied at the model boundary consistent with the conditions of indoor similar model test are established,the maximum vertical(surrounding rock)stress of primary support and the limit displacement of the shotcrete with different thicknesses are analyzed,the conclusion of the indoor model test is verified,and the shotcrete thickness is optimized.The result shows that(1)The maximum vertical(surrounding rock)stress increases with the increase of the shotcrete layer thickness,while the increment gradually decreases,and theσymax of the shotcrete layers of 20,30,40 cm thickness is 5.0,5.7,6.0 MPa in sequence.(2)The failure mode of the shotcrete layer with 20 cm thickness is different from those of the shotcrete layers with 30 cm and 40 cm thicknesses.The displacement at the bottom of the arch is the maximum displacement of the section,while the displacement at the top of the arch is the maximum displacement of the shotcrete layers with 30 cm and 40 cm thicknesses.(3)In terms of the deformability of the supporting structure,the 30 cm thickness shotcrete layer is significantly better than the shotcrete layers with 20 cm and 40 cm thicknesses,and the corresponding ultimate displacements before failure are 127,80,82 mm.(4)Combining with numerical simulation,support capacity and deformability of the shotcrete structure,the shotcrete layer thickness of ultra-large section tunnel under V Grade surrounding rock condition is optimized to be 26-38 cm,and the optimal value is 32 cm.