泥岩大变形隧洞缓冲层让压支护应用研究

Field application of the yielding support used compressible layer in a tunnel excavated in mudstone

高地应力条件下软弱围岩具有显著的流变特性,其时效变形容易引起隧道二衬结构的开裂和破坏。为减小二衬的形变压力,在复合式衬砌基础上,提出在初支和二衬之间设置高压缩缓冲层的支护方案,并在新疆某引水隧洞泥岩大变形段开展现场应用。现场缓冲层由U29可压缩拱架和聚乙烯泡沫层(密度90~100 kg/m^(3))组成,通过衬砌结构内力的现场监测和缓冲层压缩特性的数值仿真,对缓冲层的让压支护效果进行分析。结果表明:采用可压缩接头的U29钢拱架,能够与围岩协调变形,拱架实测应力较小,最大压应力为140 MPa,低于采用刚性连接的H型钢内力;聚乙烯泡沫缓冲层具有较高的压缩性,能够很好地吸收围岩的时效变形,减小二衬结构受力;监测得到的二衬环向压应力均值为6.2 MPa,最大压应力出现在右侧拱肩和边墙,量值为13.0 MPa,低于二衬混凝土的设计抗压强度,验证了缓冲层支护方案的有效性。

When tunnelling in soft rock under high in-situ stress,obvious time-dependent deformation of surrounding rock is often observed,and the deformation can cause serious damage and cracking of the secondary lining.To reduce the ground pressure of the secondary lining induced by time-dependent deformation,a compressible layer is suggested to construct between the primary support and secondary lining.Filling material of the compressible layer should have high compression capability to absorb the time-dependent deformation.In this study,the yielding support used polyethylene foam(density is 90-100 kg/m^(3))compressible layer and U steel ribs was applied in a tunnel excavated in sandy mudstone and glutenite in northwest China.According to the field observations and numerical results,the performances of the yielding support were analyzed.The results showed that because U steel ribs were connected by the friction connections,the maximum monitoring stress of the U steel ribs is only 140 MPa,which was much lower than that of the H steel ribs.The polyethylene foam layer has great compression capability,and can absorb the time-dependent deformation of the surrounding rock efficiently.According to the monitoring results,the maximum circumferential compression stress of the secondary lining was 13.0 MPa with average value 6.2 MPa,which is lower than the design compression strength of the secondary,indicates the high performance of the compressible layer.