隧道construction technology for a shallow-buried underwater interchange tunnel with a large span_W

1、Contents lists available at ScienceDirectTunnelling and Underground Space Technologyjournal homepage: /locate/tustTunnellingandUndergroundSpaceTechnology70(2017)317329Construction technology for a shallow-buried underwater interchange tunnel with a large spanChenghua Shi, Chengyong C

2、ao, Mingfeng Lei School of Civil Engineering, Central South University, Changsha, Hunan 410075, ChinaA R T I C L E I N F OKeywords: Underwater tunnel Ultra-shallow-buried Large span InterchangeConstruction technologyA B S T R A C TThe construction of underwater tunnels has become a major method for

3、enabling transportation across rivers in cities. In this paper, several innovative ideas and methods adopted in the construction of the Yingpan Road Underwater Tunnel in Changsha, China were introduced. On the basis of the crossing function of traditional underwater tunnels, an underground interchan

4、ge tunnel was designed, which could eectively overcome the bottleneck of regional transportation in cities and signicantly expand the trac function of tunnels. A method for determining the minimum burial depth of underwater tunnels was proposed by considering reinforcement control measures. This met

5、hod indicated that the minimum burial depth of the Yingpan Road Tunnel was11.5 m, which was shallower by over 5 m compared with existing data calculated using other methods. The tunnel length was also shorter by 400 m, which enhanced the trac evacuation function of the tunnel. Seepage quantity in th

6、e tunnel during the service periods could be remarkably reduced by adjusting the thickness of the grouting reinforcement loop and the reinforcing parameters. By adopting advanced full-face pre-reinforcement and preliminary supports with double-layer steel and reasonably organising benching excavatio

7、n, an ultra- shallow-buried large-section underwater tunnel with a depth/span ratio of only 0.46 and an excavation area of 376 m2 was successfully excavated. The multi-operation and multi-section diculties in constructing under- water super-large-section tunnels were overcome.1. IntroductionRiver-cr

8、ossing tunnels are popular because of their various ad- vantages, such as having no eect on navigation and the river en- vironment and all-weather operation. Numerous underwater tunnels have been constructed worldwide using drill-and-blast (D & B), shield tunnelling and immersed tube methods (Nilsen

9、, 1989; Palmstrom, 1994; Vandebrouk, 1995; Kasper et al., 2008; Lin et al., 2013; Li, 2012), all of which lead to considerable progress in the construction tech- nology of underwater tunnels (Lv et al., 2005; Wang et al., 2011; Yue et al., 2013; Zhang, 2014; Zhang et al., 2014; Wang et al., 2014; Sh

10、i et al., 2016c; Shi et al., 2016a; Zhang et al., 2017).The Yingpan Road Tunnel across Xiang River is located in Changsha, Hunan Province. This tunnel extends from Xianjiahu Road in the west to Yingpan Road in the east by passing underneath Xiaoxiang Road, Fujia Island, Juzi Island and Xiangjiang Ro

11、ad. Fig. 1 shows the location and plane layout of the Yingpan Road Tunnel. The main line is designed as two separate tunnels, and the ramp is a single lane. Com- posite lining is used for the main and the ramp tunnel. Fig. 2 illustrates the typical design scheme of the tunnel cross-section. The maxi

12、mumvehicle speed on the main tunnel is 50 km/h, with a maximum long- itudinal slope of 6%; and the maximum vehicle speed on the ramp is 40 km/h, with a maximum longitudinal slope of 7%. Juzi Island and Fujia Island are the central bars that separate Xiang River into the east and west river branches.

13、 The riverbed in the east branch has a width of 420 m and a maximum depth of approximately 20.4 m, while the riv- erbed in the west branch has a width of 310 m and a maximum depth of approximately 17.3 m. The total length of the north line of the tunnel is 2843 m, while that of the south line is 285

14、0.5 m. The total length of the four ramps is 2752.4 m.Geological and geotechnical investigations are essential for tunnels in the design and construction phases. Geotechnical investigations mainly consist of in-situ tests and laboratory studies, which are crucial for estimating rock mass properties

15、(Karaman et al., 2015; Kaya et al., 2011; Kanik et al., 2015). Detailed geological investigations are also indispensable to reduce construction risk. During the design phase of the Yingpan Road Tunnel, geological investigations were conducted using core drilling and seismic refraction tests. From to

16、p to bottom, the strata of the tunnel site include a miscellaneous ll layer; a plain ll layer; a silty clay layer; a ne sand layer; a sandy gravel layer; highly, Corresponding author.E-mail address: 729344552 (M. Lei)./10.1016/j.tust.2017.09.009Received 24 November 2015; Receiv

17、ed in revised form 4 September 2017; Accepted 5 September 2017Availableonline12September2010886-7798/2017ElsevierLtd.Al rightsreserved.C. Shi et al.TunnelingandUndergroundSpaceTechnology70(2017)317329Xiangjiang RoadB rampA rampChangsha city, Hunan ProvinceNorth tunnelC rampXiaoxiang RoadSouth tunnel

18、D rampJuzi IslandXiang RiverFujia IslandFig. 1. Location and Plane layout of the Yingpan Road Tunnel.(a) Main line of the tunnelFig. 2. Design of the cross section of the tunnel (unit: cm).(b) Ramp of the tunnel31Miscellaneous fillPlain fillFine sandWater levelSitly clayHighly-weathered slateSitlyGr

19、avel TunnelCompletely- weathered slateModerately- weathered slateSlightly - weathered slateFault zone IIFault zone IIIFault zone IFig. 3. Geological cross section of the tunnel alignment.Table 1Physico-mechanical and elastic properties of dierent strata.StratumUnit weightCohesion (kPa)Friction angle

20、Compressive strengthPoissons ratioYoungs modulusHydraulic conductivity(kN/m3)()(MPa)(MPa)(m/d)Backll soil19.016103.00.450.450Silt19.0831.00.300Silty clay20.018155.00.400.006Gravel20.003525.040.000Highly weathered pelitic22.5100250.351000.090siltstoneModerately weathered pelitic23.0300300.303500.110s

21、iltstoneCompletely weathered slates22.535200.38900.900Highly weathered slates23.0150250.353000.207Moderately weathered slates23.51000320.307500.110moderately, and slightly weathered slate layers (see Fig. 3). Most of the layers exhibit soft lithology, low intensity and poor self-stability. The site

22、investigation reported three major weakness zones along the tunnel alignment, namely, F1, F2 and F3 (Fig. 3). The per-support measures and parameters used in these weakness zones mainly included pipe roof (steel, 76 mm30 cm, L=18 m) and grouting pipes (42 mm 30 cm, L=5 m). The primary support and se

23、condary lining were 28 cm- thick C30 sprayed concrete and 60 cm-thick C35 reinforced concrete, respectively. Laboratory and in-situ tests were performed to char- acterise the mechanical and hydraulic properties of the rock and soil layer. Table 1 lists the primary geological parameters of this layer

24、.The direct-in direct-out project is currently popular in the design of underwater tunnels, which are mainly used to cross rivers or straits (Blindheim et al., 2005; Bosshard et al., 2011; Song and Zhou, 2012). The trac diversion function is generally addressed by building level crossings on the gro

25、und or interchanges out of tunnels. The minimum burial depth of underwater tunnels is determined by several empirical methods, such as the Norwegian (Nilsen, 1993; Dahlo and Nilsen, 1994) and Japanese (Hagelia, 1994) methods. The burial depth of tunnels acquired via these methods is considerable. Fo

26、r example, the minimum burial depth of the Seikan Tunnel in Japan is 100 m (Tsuji et al., 1996). For most Norwegian underwater tunnels, the minimum burial depth is deeper than 30 m, and the minimum thickness of the rocks covering the tunnels is 15 m (Palmstrom and Skogheim, 2000). In terms of con- s

27、truction method, shield tunnelling and immersed tube are currently the most frequently adopted techniques (Lin et al., 2013; Li, 2012). Drill and blast (D & B) is mainly adopted for stable strata and has a com- paratively low construction risk. The section area of a D & B tunnel should always be sma

28、ller than 70 m2 (Palmstrom, 1994; Blindheim et al., 2005).Several diculties in the construction of the Yingpan Road Underwater Tunnel should be resolved to satisfy the requirements for functional planning in Changsha City. The diculties include de- termining the lane layout method to fully exploit t

29、he trac diversion function of the tunnel and the method to solve the contradictionbetween the ground site of the tunnel entrance and the burial depth of the tunnel. Moreover, the tunnel has a shallow burial depth, a large span and an underground interchange. The geological condition of the surroundi

30、ng rock is relatively poor and can lead to instability of the working face (Shi et al., 2016b). To date, the diculties and risks in this tunnel are rarely encountered in other underwater tunnels constructed around the world, and any careless act can lead to disastrous accidents, such as collapse and

31、 water inrush. In the present work, innovative de- sign ideas and construction methods for the construction of the Yingpan Road Underwater Tunnel were introduced. This work provides a sig- nicant reference for constructing underwater tunnels.2. Design and construction schemes of the underwater inter

32、change tunnel2.1. Design scheme of the underwater interchange tunnelOn the basis of the conventional design philosophy of underwater tunnels, the direct-in direct-out scheme is generally adopted in con- structing underwater tunnels. Tunnels mainly serve as river crossings to ensure that vehicles can

33、 pass rapidly from one side of river to another. Trac diversion at both ends of a tunnel relies on the ground road.Given the limitations of the road conditions at both ends of the studied tunnel, the diversion for this tunnel will aggravate trac jams in arterial streets, such as Caie Road in the mai

34、n urban area. As shown in Fig. 1, the main urban area in Changsha City is distributed at both ends of the Yingpan Road Tunnel, with dense housing buildings, narrow roads, severe trac jams and high population density. This area is the most prosperous region in Changsha City. Xiaoxiang Road and Xiang-

35、 jiang Road, which lie on both sides of Xiang River, are the main roads in the city. These roads are spacious, and the speed of trac ow is fast, conditions that are favourable for the fast diversion of vehicles. If the traditional direct-in direct-out scheme for a tunnel is adopted, then the vehicle

36、s crossing the river should rst pass through the main urban area to reach the road along the river. This situation will inevitably increaseC. Shi et al.TunnelingandUndergroundSpaceTechnology70(2017)317329(a) The crossing in the east branch(b) The crossing in the west branchFig. 4. Plane layout of th

37、e space intersection of the tunnel.32trac pressure in the main urban area along the river. As level cross- ings are also placed at the entrance and exit of the main tunnel, trac jams will occur only at the portals of the tunnel when the direct-in direct-out scheme is applied. Consequently, the trac

38、function of the tunnel can be eciently utilised by adopting the interchange project to shunt trac ows into Xiaoxiang Road and Xiangjiang Road on both sides of Xiang River. However, this ground interchange scheme will involve the demolishment of nearly 70,000 m2 of land on both sides of the river.A d

39、esign concept for an underwater interchange tunnel was thus proposed to satisfy the requirements for regional function planning in Changsha, enhance the crossing and diversion functions of the Yingpan Road Tunnel over Xiang River, improve the road network in Changsha City and conserve land resources

40、 at both ends of the tunnel. An un- derwater ramp based on the crossing function of a traditional under- water tunnel was introduced and established in this design philosophy. Accordingly, the layout of the underwater tunnel was formed, i.e. in- terchange and diversion functions were realised underg

41、round.Fig. 1 shows the specic construction scheme of the Yingpan Road Tunnel, and Fig. 4 shows the crossing layout of the main tunnel and the ramp at the tunnel entrance and exit. The double-in double-out trac function of the tunnel on both sides of the Xiang River in Changsha can be achieved by ado

42、pting the aforementioned scheme, and the layout at the entrance and exit of the ramp tunnel can satisfy the requirements of the primary direction of trac ow, i.e. from southeast to northwest. The tunnel does not only play crossing and diversion roles but also solves the trac jam in this region. Cons

43、equently, interow among the four directions on both sides of Xiang River is achieved, leading to signicant improvements in trac connections on both sides. In par- ticular, trac between the two main urban areas becomes remarkably smooth. The trac function of the tunnel can be signicantly expanded by

44、linking the ramp to the main line of the tunnel, thus contributing to urban development in Changsha City.2.2. Construction method selection for the tunnelFour ramps were constructed on the east and west banks of the tunnel (labelled A, B, C and D) on the basis of lane design in the tunnel. Four larg

45、e-span bifurcation segments were produced on the junction of the ramp and the main tunnel.The shield-tunnelling method, which adopts the standard section width, is unfeasible for the tunnel because the large-span bifurcation segment exhibits a gradually increasing width from 8 m to 19.58 m. If this

46、method is implemented in the entire tunnel, approximately 550 m of shield segments in the large-span bifurcation region will have to be dismantled to perform excavation, and enormous construction risks and technological hurdles will be generated. The D & B method seems to be the cost-eective choice

47、irrespective of tunnel geometry because of its exibility. Thus, D & B was selected in the overall design andconstruction of the Yingpan Road Underwater Tunnel.3. Determining the burial depth of the tunnel3.1. Method that considers reinforcement measures to determine the minimum burial depth of the u

48、nderwater tunnelIn the existing method for determining the minimum burial depth of underwater tunnels, only the geological conditions, permeability of surrounding rocks and water depth are considered, whereas the inu- ences of reinforcement measures, such as pre-support and advanced grouting, are di

49、sregarded. Therefore, the obtained burial depths are considerable, and the length of the tunnel increases correspondingly.Owing to the practical conditions of the Yingpan Road Underwater Tunnel, the main line on the east bank of the tunnel should be con- nected to the ground in the west of Caie Road

50、. Otherwise, the diversion eect of the intersection on vehicle ow cannot be achieved, and ve- hicles will be directly introduced downtown. These outcomes exert a certain eect on trac in the urban main road and on trac jams. The ramp underneath should be designed on the west bank of the tunnel. If th

51、e burial depth of the main line of the tunnel increases, then the burial depth of the ramp will increase accordingly and simultaneously, and the tunnel length will increase signicantly. Considering the practical conditions of the Yingpan Road Underwater Tunnel, the requirements of the ground-connect

52、ing site of the tunnel cannot be satised using the existing method for determining the minimum burial depth of under- water tunnels.The construction, safe operation and building cost of underwater tunnels are not only related to the geological condition of the strata but also strongly correlated wit

53、h specic engineering measures during construction. The region that controls tunnel safety generally comprises several hazardous segments. Reinforcing the hazardous segments by adopting eective engineering technological measures, such as pre- support and advanced grouting, can signicantly reduce the

54、burial depth of the tunnel under the premise of construction safety. A method for determining the minimum burial depth of underground tunnels was thus proposed based on sucient investigations and theoretical ana- lyses. The geological and environmental conditions of the location and the adopted rein

55、forcement control measures were considered compre- hensively. The specic process of the method is illustrated in Fig. 5 and summarised as follows.(1) The minimum burial depth and prole layout were preliminarily determined based on the ground connection sites at both ends of the underwater tunnel and

56、 the slope limits of the tunnel.(2) The safe construction of the tunnel with the burial depth calculated in Step (1) was analysed using common support and construction parameters via numerical computation of the key section.(3) If the safety requirements could not be satised using commonFig. 5. Spec

57、ic process for determining the burial depth of the underwater tunnel.Fig. 6. Calculation model for the tunnel.(a) Entire calculation model(b) Calculation model for the large-span tunnelsupport schemes, then the required reinforcement control measures to ensure safe construction under dierent burial depths were tentatively determined based on the investigation and the analysis. To determine the corresponding minimum buri