深覆土明洞及其减载结构渐进性破坏机理模型试验研究

Model test research on progressive failure mechanism of highfilled cut-and-cover tunnel and its load reduction structure

依托国内某铁路明洞工程,采用相似模型试验的方法,分析深覆土铁路明洞声发射数据、位移和内力随覆土深度的变化规律,研究衬砌裂缝的发展过程。对于减载明洞,采用相同的试验加载方案,从声发射数据、位移和内力减载量等分析EPS板的减载效果。研究结果表明:随着系数λ(即覆土深度与明洞高度的比值)增加,明洞衬砌承载阶段大致可分为平稳增长、快速增长和加速增长3个阶段。在各阶段的分界点,衬砌拱顶、拱肩、拱腰、边墙截面轴力、弯矩和位移随覆土深度增长均出现突增现象,其增长速率较前一阶段明显加快。当λ<2.54时,衬砌结构拱顶截面出现轻微裂缝,结构发生弹性变形且呈局部损伤状态;当2.54<λ<3.81时,结构拱顶、边墙多处出现宏观裂缝,结构发生塑性变形且仍可安全使用;当λ>3.81时,各关键点均出现纵向贯通裂缝,结构破坏失稳。减载明洞衬砌累计声发射事件数和位移随系数λ增加而增加,结构各位置处内力减载量斜率呈先增大后减小的趋势。与未减载明洞试验结果相比,发现铺设EPS板有助于缓减结构位移和裂缝发展,减载结构延性更好。为了保证结构具有一定的安全储备,建议在拱顶铺设EPS板。

Based on a cut-and-cover tunnel project of a railway in China,the acoustic emission data,displacement and internal force of the cut-and-cover tunnel with deep overburden were analyzed with the method of similarity model test,and the development process of lining cracks was studied.For the load reduction cut-and-cover tunnel,the same test loading scheme was conducted to analyze the load reduction effect of EPS plnel from acoustic emission data,load reduction of displacement and internal force.The results show that with the increase of the coefficient λ(the ratio of the backfill height to the height of the cut-and-cover tunnel),the bearing stage of the cutand-cover tunnel can be roughly divided into three stages,i.e.steady growth,rapid growth and accelerated growth.At the demarcation points of each stage,the axial force,bending moment and displacement of the vault,spandrel,arch waist,side wall section of the tunnel increased suddenly with the increase of backfill height,and the growth rate is significantly faster than the previous stage.When λ<2.54,slight cracks appear in the vault,and the structure is elastically deformed and displays local damaged.When 2.54< λ <3.81,macroscopic cracks appear in the vault and side walls of the structure,and the structure is plastically deformed and still safe to use.When λ >3.81,longitudinal through cracks appeared at each key point,and the structure is damaged and unstable.The cumulative number of acoustic emission events and displacements of the load reduction cut-and-cover tunnel increase with the increase of the coefficient λ,and the slope of the load reduction amount of internal force at each position of the structure increases first and then decreases.Compared with the test results of unloaded reduction cut-and-cover tunnel,it is found that laying EPS panel can help reduce structural displacement and crack development,and the load reduction structure has better ductility.In order to ensure that the structure has a certain safety reserve,it is recommended to lay EPS panel on the vault.