Anti-Uplift Portal Frame in Control of Underlying Tunnel Deformation Induced by Foundation Pit Excavation

doi:10.16183/j.cnki.jsjtu.2022.006

Abstract

Abstract:

The excavation of foundation pit above the existing metro tunnel inevitably leads to the uplift of the tunnel. As an anti-uplift measure, the anti-uplift portal frame is still lack of research. Based on a foundation pit excavation project colinear with tunnel for long-distance, the excavation influence on the underlying shield tunnel during the construction process of anti-uplift portal frame and the foundation pit excavation was studied via numerical simulation. The interaction mechanism between the anti-uplift portal frame and ground as well as the anti-uplift effect were analyzed. Finally, a structural optimization design was proposed based on the simulation. The results show that the tunnel may be uplifted due to the shaft excavation during the construction of the anti-uplift portal frame and the uplift can be effectively restricted by backfilling and sectional excavation. Compared to the excavation without the anti-uplift portal frame, the uplift value of the tunnel decreases from 19.5 mm to 15 mm because of the restriction of the anti-uplift portal frame. The connection between the slabs and piles are weak positions of the structure due to the stress concentration and it is necessary to do a local reinforcement treatment in the connection.

Key words: anti-uplift portal frame, pile-soil interaction mechanism, construction disturbance, anti-uplift mechanism, numerical simulation

CLC Number:

TU753
U456.3

WU Huaina, FENG Donglin, LIU Yuan, LAN Ganzhou, CHEN Renpeng. Anti-Uplift Portal Frame in Control of Underlying Tunnel Deformation Induced by Foundation Pit Excavation[J]. Journal of Shanghai Jiao Tong University, 2022, 56(9): 1227-1237.

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土层	γ/(kN·m^-3)	e₀	E_s/MPa	w/%	k_v/(m·d^-1)	c/kPa	φ/(°)
素填土①₁	17.5	1.89	1.88	67.5	0.2	10	16
填砂①₂	19	-	-	13.1	10	0	25
粗砂⑤₂	20	-	2.66	13.5	10	0	30
砾质黏性土⑧	17.7	1	9	33.3	0.08	23	23.5
全风化花岗岩⑨₁	19.5	0.87	13	27.6	0.1	30	27.5

土层	γ/ (kN·m^-3)	E/ MPa	c/ kPa	φ/(°)	μ	本构模型
素填土	17.5	18.8	10	16	0.3	莫尔-库伦
砾质黏性土	17.7	90	23	23.5	0.28	莫尔-库伦
全风化花岗岩	19.5	130	30	27.5	0.28	莫尔-库伦

结构	单元类型	γ/(kN·m^-3)	E/GPa	μ	本构模型
隧道衬砌	实体单元	25	24.15	0.2	线弹性
井壁支护	实体单元	24	24	0.2	线弹性
抗拔桩	实体单元	24	30	0.2	线弹性
抗浮板	实体单元	24	30	0.2	线弹性
竖井支撑	梁单元	78.5	206	0.3	线弹性

施工步	工况
1	地应力平衡
2	激活抗拔桩和竖井井壁
3	第1层土体开挖(2.5 m) 施作第1道支撑
4	第2层土体开挖(2.5 m) 施作第2道支撑
5	第3、4层土体开挖(2.5 m+2.5 m) 施作第3道支撑
6	第5、6层土体开挖(2.5 m+2.5 m) 施作第4道支撑,激活抗浮板
7	加面荷载模拟回填(竖井内土重264.48 kN/m²)

施工步	工况
1	地应力平衡
2	步长1区域的土体逐层开挖(每层2.5 m,共6层)
3	步长1区域施加面荷载模拟底板(底板自重28.8 kN/m²)
4	步长2区域的土体逐层开挖;同时施加步长1范围内侧墙等结构面荷载
5	步长2区域施加面荷载模拟底板
6	步长3区域的土体逐层开挖;同时施加步长2范围内侧墙等结构面荷载
…	…