Excavation Failure Due to Pipeline Damage During Shallow Tunnelling
Total Page：16
File Type：pdf, Size：1020Kb
Tunnelling and Underground Space Technology 46 (2015) 76–84 Contents lists available at ScienceDirect Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust Technical note Excavation failure due to pipeline damage during shallow tunnelling in soft ground ⇑ Yanjuan Hou a, Qian Fang a, , Dingli Zhang a, Louis Ngai Yuen Wong b a Key Laboratory for Urban Underground Engineering of the Education Ministry, Beijing Jiaotong University, Beijing 100044, China b School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore article info abstract Article history: In urban areas, subway construction inevitably imposes negative impacts on adjacent buried pipelines. Received 28 January 2014 During the recent construction of the Beijing subway, several ground failures have occurred due to the Received in revised form 7 September 2014 pipeline damages induced by tunnel construction. In this paper, a disastrous ground failure of such kind Accepted 19 November 2014 occurred during the Beijing subway Line 10 construction is presented, in which a sinkhole about 20 m long, 14 m wide and 12 m deep formed. Both the tunnel construction and the ground traffic were severely affected. The adopted remedial measures for this failure, including road restoration, dewatering, dredging Keywords: and tunnel face reinforcement, are systematically illustrated. The probable mechanism of this failure is Subway also analyzed and briefly discussed. The case presented in this paper can serve as a practical reference Pipeline damage Tunnel failure for the engineers practicing in the similar engineering field. Soft ground tunnelling Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction appearance of large surface craters and significant third party losses (European Foundations, 2005; Tunnels and Tunnelling, 2005). In Urban subway construction inevitably induces ground move- both instances unforeseen ground conditions were encountered ments, which, if uncontrolled, might cause excessive ground defor- and appropriate construction measures were not taken timely. mations and even damage to existing nearby structures and utilities After the Barcelona collapse, the void was backfilled with (Fang et al., 2011). A series of collapses due to subway (or tunnel) 2000 m3 of grout. After the Lausanne collapse, a curtain of 11 piles construction in rock masses using the drill and blast method have were constructed ahead of the collapsed face with grouting and the been extensively reported (Brox and Hagedorn, 1991; Türkmen void was backfilled with 800 m3 of glass-sand. Moreover, the HSE and Özgüzel, 2003; Aydin et al., 2004; Shin et al., 2006). Tunnelling report on the Safety of NATM tunnels in 1996 (HSE, 1996), following in soft ground is more challenging to maintain the stability of the investigations after the Heathrow Express tunnel collapse, identi- surrounding ground. A 10 m diameter crater was formed during fied over 100 incidents recorded during NATM tunnelling. This the construction of the Heathrow Express Tunnel in UK on Oct 21, research had been extended by HSE in 2006 (HSE, 2006). Addition- 1994 (HSE, 2000). The tunnel construction was performed in ally, collapses due to tunnelling in soft ground using open-cut London Clay using the New Austrian Tunnelling Method (NATM). method (Magnus et al., 2005) and shield method (Lee and On the Heathrow Express site at the Central Terminal Area, jack gro- Ishihara, 2010; Jebelli et al., 2010) have also been reported. How- uting was employed to rectify building settlements during tunnel ever, it is noted that, for various reasons, the occurrences of most construction but above the tunnel construction in an attempt to failures are not ‘‘officially’’ reported and the related data are mostly jack the building back up again to its previous level. In this incident, incompletely documented. the grouting caused a failure in the primary tunnel lining, which in This paper presents a disastrous failure related to shallow tun- turn led to the ultimate collapse of both the lining and the building. nelling in soft ground occurring in the first stage project of the Line After the collapse, a total of 13,000 m3 concrete was used for 10 of Beijing subway. This failure was induced by a sudden water backfilling. NATM construction in soft ground in the city centers inrush from a sewage pipe which had been deteriorated by the of Barcelona (Barcelona Line Five Metro Extension) and Lausanne ongoing manual tunnelling underneath. First, the timeline of (Lausanne Metro M2 Project) in early 2005 resulted in the events in this failure is introduced. Then the remedial measures adopted are illustrated. Finally, the forensic investigation results ⇑ Corresponding author. Tel.: +86 10 51688115; fax: +86 10 51688022. of this failure are presented. This case study aims at promoting E-mail address: [email protected] (Q. Fang). the awareness on tunnel failures which could pose a threat to both http://dx.doi.org/10.1016/j.tust.2014.11.004 0886-7798/Ó 2014 Elsevier Ltd. All rights reserved. Y. Hou et al. / Tunnelling and Underground Space Technology 46 (2015) 76–84 77 life and property. It also serves as a reference to the engineers prac- investigation report, are shown in Table 1. The ground water level, ticing in the similar field. which varies geographically and seasonally, is about 13–17 m below the ground surface. The rail track level is about 16–18 m below the ground surface. According to the site investigation prior 2. Project overview to tunnelling, different kinds of buried pipelines had been identi- fied. They include a cement rain sewage pipe (1750 mm in diame- The first stage project of the Line 10 of Beijing Subway, which is ter), a water supply pipe (1400 mm in diameter), a community 25-kilometer-long with 22 stations, links the eastern and northern antenna television cable (CATV cable), an electric power pipe parts of Beijing. This line was built to serve the 29th Olympic (2150 mm in diameter), a rectangular-sectioned heat pipe Games and fulfill the traffic requirement of the city. It runs west- (2650 mm  2200 mm), and some telecommunication cables east in the north of the city and then turns south, with an inverted (Figs. 4 and 5). ‘‘L’’ shape in the plan view (Fig. 1). The excavation failure presented The two tunnels were excavated using the shallow tunnelling in this paper is located at a tunnel that links the Hujialou Station (H method, which is particularly designed for shallowly-buried tun- Station) and the Jintaixizhao Station (J Station). There are two par- nels constructed in a densely built urban area using hand tools, allel tunnels running between these two stations, which are such as air picks and spades (Fang et al., 2012). Both the standard beneath the side road of the Eastern Third Ring Road (ETRR). The tunnel section and a length of 10.5 m enlarged tunnel section were westernmost tunnel is referred to as the ‘‘west line’’ and the east- designed in each line of the project. A 5.3 m long tunnel was ernmost tunnel as the ‘‘east line’’. These two lines are connected by designed to be widened out from the standard tunnel portion to a cross passage nearby the failure location. The total length of this connect the enlarged tunnel portion with a smooth transition in tunnel is about 548.6 m (from K19 + 976.5 to K20 + 525.1). The each of the two lines. The enlarged tunnel portion can also be used location of the failure was immediately above the east line at cha- for civil defence sheltering purposes. The top heading (with sup- inage K20 + 518.4 which was tunnelled from north to south port core)-bench-invert excavation method was used for the stan- (Fig. 2). The shaded area in Fig. 2 indicates the excavated tunnel dard section (6.3 m height and 6 m wide, Fig. 6). The cross before the failure. The failure site was located at the southeast of diaphragm method was adopted for the enlarged section (6.3 m the Jingguang Overpass (JGO), which was adjacent to the intersec- high and 9.6 m wide, Fig. 7). Both the top heading-bench-invert tion of the side road of ETRR and the Chaoyang Road (Fig. 3). Since excavation method and the cross diaphragm method were the ETRR is one of the busiest roads in Beijing, the excavation fail- employed for the transition tunnel portion. Although the sizes of ure was extremely disturbing to the public. the standard tunnel, the transition tunnel and the enlarged tunnel The geological profile of this project is shown in Fig. 4, which are different, the same pre-reinforcement measures and support reveals that the excavation area was located mostly in the gravel structures were designed. Forepolings were used as ground pre- and silty clay. The typical physical and mechanical properties of reinforcement. Forepoling pipes, steel, U32 (the upper-case Greek different soil layers of this project, which are obtained from the site symbol is used to indicate the diameter of a circular section in the unit of mm), 2.5 m long, were driven at an angle of 20° with the N tunnel longitudinal axis into the ground above the top heading arch ahead of the cutting face. The separation of the forepoling pipes in the tunnel cross section was about 0.3 m. A layer of 0.25 m thick shotcrete, of which the 28-day compressive strength Huixinxijie Nankou Shaoyaoju Zhichunlu Jiandemen Zhichunli Mudanyuan was 25 MPa, combined with lattice girder and wire mesh were Xitucheng Suzhoujie Beitucheng Anzhenmen Haidian Huanzhuang Bagou Taiyanggong designed as the primary lining. A layer of 0.30 m thick cast-in- Sanyuanqiao place reinforced concrete was designed as the secondary lining. Liangmaqiao The 28-day compressive strength of the cast-in-place concrete Agricultural Exhibition Hall was 30 MPa.