|
|
Journal of Zhejiang University SCIENCE A
ISSN 1673-565X(Print), 1862-1775(Online), Monthly
2017 Vol.18 No.10 P.757-775
Surface settlements induced by tunneling in permeable strata: a case history of Shenzhen Metro
Abstract: A case study of a significant surface settlement induced by tunneling in permeable strata with the shallow tunneling method is presented in this paper. The measurements of surface settlements along the excavation direction were first analyzed to highlight the impacts of groundwater seepage. Due to the groundwater inflow inside a double-arched tunnel, the surface settlement developed to a high level far beyond the measured crown settlement. The settlement-affected zone extended to 4 times the tunnel height ahead of the forefront heading and 1.5 times the tunnel height behind the hindmost heading. Consolidation resulting from high pore pressure change was considered to be the main mechanism for the large surface settlements. In addition, a 3D fluid-mechanical coupled numerical analysis was carried out to confirm the relationship between the significant surface settlement and pore pressure variation. This analysis reveals that lowering the permeability of the small pipe grouting zone, especially of the primary lining, could lessen the drop in pore pressure in the overlying strata, further reducing the total surface settlement. The numerical results also suggest that the transverse range of vertical displacement could be quite wide, and the settlement developed integrally from the tunnel crown towards the ground surface due to groundwater seepage. Moreover, the effect of advance drainage on surface settlement was investigated based on the same numerical model. Drainage with horizontal boreholes could considerably increase the safety of tunnel heading but had limited impact on surface settlement. Finally, the applications of pre-grouting and advance drainage measures were discussed for tunneling cases in permeable strata.
Key words: Surface settlement; Shallow tunneling method (STM); Groundwater seepage; Pre-grouting; Advance drainage; Fluid-mechanical coupled analysis
创新点：1. 系统分析了富水渗透性地层中浅埋暗挖隧道施工引起的地表沉降的发展过程以及沉降特征；2. 验证了三维流固耦合数值模型模拟富水环境下重叠隧道施工过程的可行性；3. 研究了小导管注浆区、初支衬砌的渗透性和超前排水措施对地表沉降的影响。
方法：1. 结合隧道施工方案和地表沉降监测数据，分析渗流作用下的地表沉降特征（包括沉降影响范围、沉降槽宽度以及与拱顶沉降的关系等）；2. 通过三维流固耦合数值模型，研究小导管注浆区和初支衬砌渗透性对地表沉降以及地层孔压变化过程的影响；3. 通过模拟掌子面前方水平排水孔，研究超前排水措施对掌子面稳定性和地表沉降发展的影响。
结论：1. 对于渗透性地层中的浅埋暗挖隧道工程，地下水渗流引起的固结效应是地表沉降量以及沉降范围大幅增长的主要原因。2. 全断面注浆能够很好地控制地表沉降，而小导管注浆的效果则十分有限。3. 降低小导管注浆区的渗透性，尤其是初支衬砌的渗透性，可以减少地层孔压的下降程度，进而降低地表沉降。4. 打设超前水平排水孔可以显著提高掌子面稳定性，却对地表沉降影响有限；当无法进行全断面注浆时，推荐采取小导管注浆与超前排水相结合的方式施工。
关键词组：
References:
Open peer comments: Debate/Discuss/Question/Opinion
<1>
DOI:
10.1631/jzus.A1600522
CLC number:
U455
Download Full Text:
Downloaded:
3819
Download summary:
<Click Here>Downloaded:
1852Clicked:
4632
Cited:
0
On-line Access:
2017-10-06
Received:
2016-07-20
Revision Accepted:
2016-12-16
Crosschecked:
2017-09-07