experimental investigation of the compression-bending property of the casing joints in a concrete filled steel tubular supporting arch for tunnel engineering-tust-李為騰

1、Contents lists available at ScienceDirectTunnelling and Underground Space Technologyjournal homepage: www.elsevier.com/locate/tustExperimental investigation of the compression-bending property of the casing joints in a c

2、oncrete filled steel tubular supporting arch for tunnel engineeringWeiteng Lia,?, Ning Yanga,b,c, Yuchun Meia, Yuhua Zhanga, Lai Wanga, Haiyao Maaa Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevent

3、ion, Shandong University of Science and Technology, China b Jiangsu Vocational Institute of Architectural Technology, Xuzhou 221116, China c JiangSu Collaborative Innovation Center for Building Energy Saving and Construc

4、tion Technology, Xuzhou 221116, ChinaA R T I C L E I N F OKeywords:Tunnel supportConcrete filled steel tubular archCasing jointCompression-bending testsPure bending testsBearing capacityA B S T R A C TThe concrete-filled

5、 steel tubular (CFST) arch is an effective new support form for mine/traffic tunnels in complexconditions, and the casing joints on the arch determine its global bearing capacity. Eighteen tests, including axialcompressi

6、on, eccentric-compression with different eccentricities, and pure bending tests, were carried out. Thebearing behavior, failure mode and failure mechanism of the specimens with casing tubes were analyzed andcompared with

7、 specimens without a casing tube. Failures are mainly caused by the local stress concentration onthe CFST components or the casing tube at the contact positions. The compression-bending bearing capacities ofthe CFST casi

8、ng joints were analyzed with the help of the Mu-Nu coordinate system. Each Mu-Nu relation isdescribed by a straight line combined with a lateral parabola, and the Mu-Nu formulas were fitted. The bearingability of a CFST

9、casing joint is lower than that of a conventional CFST section, and the reduction rate of thesquare cross section is more obvious. The effects of the concrete grade, casing tube length, casing tube thicknessand gap width

10、 on the compression-bending capacity were obtained through numerical simulation tests. Theconcrete strength is the main factor influencing the axial compression bearing capacity, while it is the casingtube length that ma

11、inly influences the bending bearing capacity. Suggestions for use in practice are finallyproposed based on the above results.1. IntroductionAs the coal resources in shallow ground layers are gradually de-pleted, the dept

12、h of explored coal seams increases. There are manyroadways that are buried deeper than 1000 or even 1500 m, such as theSuncun coal mine in China, whose depth is 1501 m. Additionally, due tothe westward coal exploration s

13、trategy in China, many roadway tunnelshave been excavated in weak cementation soft rock layers. Whether it isa result of the high geostress in deep ground layers or the poor me-chanical properties of the soft rock mass i

14、tself, controlling roadwaytunnel stability is difficult. Conventional support forms, such as com-binations of rock bolts, shotcrete and steel sets (including I sections, Usections, and steel girders), can hardly satisfy

15、the support requirementsunder the above conditions (Khan et al., 1996; Jiao et al., 2013; Yanget al., 2013; Lin et al. 2015; Tan et al. 2017; Li et al. 2018; Zhang et al.,2018; Wang et al., 2019). There are also many tun

16、nels built for otherpurposes, such as transportation and water conveyance, that face thesame support problem.Based on the above background, the CFST (concrete-filled steeltube) structure was applied as a new supporting a

17、rch form for tunnelsthat are difficult to support. In 2010, a successful field application of theCFST arch in the Qianjiaying coal mine roadway was reported by Gaoet al. (2010). Since then, the number of field applicatio

18、n cases has in-creased rapidly, both in mining roadways and transportation tunnels,and currently exceeds 40 cases, which are mostly located in China(Chang et al., 2014; Wang et al., 2016, 2018; Huang et al., 2018). There

19、are mainly two cross-sectional types of CFST arches currently in use,i.e., circular and square arches. Both of these CFST supporting archesshow a much higher supporting ability than the other arch styles (Isection, U sec

20、tion etc.) in the field. The laboratory tests of full-sizedCFST arches reported by Zhang et al. (2017) show that the bearingcapacity of the CFST arch is approximately 2 times that of a conven-tional U-shaped steel arch o

21、f the same steel volume.Researchers, especially Wang et al. (2016, 2018) and Huang et al.https://doi.org/10.1016/j.tust.2019.103184Received 4 August 2018; Received in revised form 9 November 2019; Accepted 10 November 20

22、19? Corresponding author.E-mail address: lwteng2007@163.com (W. Li).Tunnelling and Underground Space Technology 96 (2020) 1031840886-7798/ © 2019 Elsevier Ltd. All rights reserved.Tstiffness of the joints will be in

23、sufficient if it is too large. Then, it will bedetermined mainly by the standard models of steel tubes, under therestrictions of the determined parameters, such as the steel tubethicknesses. It also should be noted that

24、the casing joints are generallycurved, consistent with the shape of the arch in reality, while in thisexperiment, they were straight. This is because, on the one hand, pre-vious studies have shown that curvature has only

25、 a small effect on themechanical properties of a casing joint, and on the other hand, astraight casing joint experiment is much easier to implement than acurved one.We produced a test system that can perform an eccentric

26、 compres-sion test with large eccentricity, as shown in Fig. 2b, because the con-ventional eccentric compression test system cannot meet the large ec-centricity requirements. It contains upper and lower symmetricalloadin

27、g beams, adjusting blocks, and loading wedges. The top andbottom loading wedges are fixed at the centers of the loading face andbearing face of the hydraulic testing device, respectively. The loadingwedge matches the wed

28、ge groove on the adjusting block, which createsthe linear load. The left and right positions of the adjusting block can bechanged and fixed on the loading beam to realize different eccentricityratios. There are 4 bolt ho

29、les on the left position of each loading beam,which are used to fix the test specimen. A compression-bending spe-cimen consists of two CFST components (both with lengths of 700 mm)and one casing tube (with a length of 60

30、0 mm). Each end of the testmember is bolted to the loading beams with flanges and strengthenedwith ribbed plates to prevent tearing failure at the ends.A four-point loading system is used to perform the pure bendingtests

31、, as shown in Fig. 3. The loading system contains an anti-forceTable 1Test schemes.SerialnumberScheme ID CrosssectionEccentricity ratio e/rLength/mm Out diameter × thickness/mm ConcretegradeCasing tube length ×

32、 thickness × gap width/mm1 SPJ-0 Square 0 700 × 2 150 × 8 C40 600 × 10 × 82 SPJ-1 13 SPJ-2 24 SPJ-4 45 SBJ infinity 1100 × 2 600 × 10 × 86 SP-0 0 700 × 2 No casing tube7 SP-1

33、18 SP-2 29 SP-4 410 SB infinity 2200 No casing tube11 CPJ-0 Circular 0 700 × 2 194 × 8 C40 600 × 10 × 512 CPJ-0.77 0.7713 CPJ-3.08 3.0814 CBJ infinity 1100 × 2 600 × 10 × 515 CP-0 0 140

34、0 No casing tube16 CP-0.77 0.7717 CP-3.08 3.0818 CB infinity 2200 No casing tubeNote: In the Scheme IDs, C means circular cross section, S means square cross section, P means eccentric compression test, B means pure bend

35、ing test, and J meanscasing joint. The last number is the eccentricity ratio.Fig. 2. Cross section sizes and loading system of the eccentric compression test.W. Li, et al. Tunnelling and Underground Space Technology 96 (