Abstract：The urban shallowly buried box tunnels are usually built using jacking method. The face stability of the boring machine is a major problem in box tunnelling due to the fluctuation of the support pressure in the working chamber. The excessive support pressure triggers the passive failure of working face. In this paper，the problem is analysed by constructing planar admissible kinematically mechanism. In the proposed mechanism，the rotational and translational mechanism are included and the compatibility is satisfied by constructing an interface between the mechanisms using spatial discretization technique. The upper bound analysis is applied for stability analysis and the upper bound solution of support pressure is derived as a result. By optimizing the mechanism，the critical support pressure as well as associate failure mode is obtained. The parametric analysis indicates that the frictional angle significantly impacts the failure. The increase of frictional angle contributes to the failure zone expanding and the proportion of the block involved in translational movement to that in the rotational movement is reduced. As a result，the higher support pressure is required. With the increase of cohesion，the support pressure increases correspondingly but the failure mode is virtually unchanged. With the surcharge increasing，the failure region is enlarged and the support pressure is increased. The numerical simulation is employed for verification. The comparison indicates that the current solution matches to the numerical solution better than the previous solutions especially at high L/D. The applicability of the current solution in practice is discussed.
刘 维，吴 奔，史培新，贾鹏蛟. 浅埋矩形隧道掘进面被动失稳混合破坏机制[J]. 岩石力学与工程学报, 2022, 41(S1): 2673-2683.
LIU Wei，WU Ben，SHI Peixin，JIA Pengjiao. An advanced mechanism for the face passive instability of shield tunnelling with rectangular cross-section. , 2022, 41(S1): 2673-2683.
CHEN W F. Limit analysis and soil plasticity[M]. Amsterdam：Elsevier Science，1975：1-638.
[17]
ITASCA CONSULTING GROUP INC. FLAC3D：Fast lagrangain analysis of continua in 3 dimensions-theory and background[M]. Itasca Consulting Group Inc.，2002：375-376.
[12]
WONG K S，NG C W W，CHEN Y M，et al. Centrifuge and numerical investigation of passive failure of tunnel face in sand[J]. Tunnelling and Underground Space Technology，2012，28(1)：297-303.
[14]
MOLLON G，PHOON K K，DIAS D，et al. Validation of a new 2D failure mechanism for the stability analysis of a pressurized tunnel face in a spatially varying sand[J]. Journal of Engineering Mechanics，2011，137(1)：8-21.
[2]
BEZUIJEN A，BRASSINGA H E. Tunnelling：a decade of progress： GeoDelft 1995-2005[M]. Abingdon：Taylor and Francis，2006：143-148.
[4]
DAVIS E H，GUNN M J，MAIR R J，et al. The stability of shallow tunnels and underground openings in cohesive material[J]. Géotechnique，1980，30(4)：397-416.
[5]
LECA E，DORMIEUX L. Upper and lower bound solutions for the face stability of shallow circular tunnels in frictional material[J]. Géotechnique，1990，40(4)：581-606.
[7]
SOUBRA A H. Kinematical approach to the face stability analysis of shallow circular tunnels[C]// Proceedings of the 8th International Symposium on Plasticity. Vancouver：HAL，2008：01008370.
[8]
LI P，CHEN K，WANG F，et al. An upper-bound analytical model of blow-out for a shallow tunnel in sand considering the partial failure within the face[J]. Tunnelling and Underground Space Technology，2019，91：102989.
[10]
MOLLON G，DIAS D，SOUBRA A H. Rotational failure mechanisms for the face stability analysis of tunnels driven by a pressurized shield[J]. International Journal for Numerical and Analytical Methods in Geomechanics，2011，35(12)：1 363-1 388.
[18]
VERMEER P A，RUSE N，MARCHER T. Tunnel heading stability in drained ground[J]. Felsbau，2002，20(6)：8-18.
[6]
LIU W，SHI P，CHEN L，et al. Analytical analysis of working face passive stability during shield tunneling in frictional soils[J]. Acta Geotechnica，2020，15(3)：781-794.
[16]
SENENT S，YI C，JIMENEZ R. An upper bound solution for tunnel face stability analysis considering the free span[J]. Tunnelling and Underground Space Technology，2020，103：103515.
[20]
ALAGHA A S N，CHAPMAN D N. Numerical modelling of tunnel face stability in homogeneous and layered soft ground[J]. Tunnelling and Underground Space Technology，2019，94：103096.
[1]
许有俊，文中坤，闫履顺，等. 多刀盘土压平衡矩形顶管隧道土体改良试验研究[J]. 岩土工程学报，2016，38(2)：288-296.(XU Youjun，WEN Zhongkun，YAN Lvshun，et al. Experimental study on soil improvement during construction of EPB rectangular pipe jacking with multi-cutter[J]. Chinese Journal of Geotechnical Engineering，2016，38(2)：288-296.(in Chinese))
[3]
竺维彬，鞠世健. 地铁盾构施工风险源及典型事故的研究[M]. 广州：暨南大学出版社，2009：80.(ZHU Weibin，JU Shijian. Study of risk source and typical cases in shield tunneling[M]. Guangzhou：Jinan University Press，2009：80.(in Chinese))
[11]
CHEN G，ZOU J，CHEN J. Shallow tunnel face stability considering pore water pressure in non-homogeneous and anisotropic soils[J]. Computers and Geotechnics，2019，116：103205.
[13]
NG C W W，WONG K S. Investigation of passive failure and deformation mechanisms due to tunnelling in clay[J]. Canadian Geotechnical Journal，2013，50(4)：359-372.
[9]
MOLLON G，DIAS D，SOUBRA A H. Face stability analysis of circular tunnels driven by a pressurized shield[J]. Journal of Geotechnical and Geo-environmental Engineering，2010，136(1)：215-229.
[19]
MOLLON G，DIAS D，SOUBRA A H. Continuous velocity fields for collapse and blowout of a pressurized tunnel face in purely cohesive soil[J]. International Journal for Numerical and Analytical Methods in Geomechanics，2013，37(13)：2 061-2 083.
2022, Vol. 41 
