buildings
Article Numerical Simulation of the Protective Effect of an Anti-Uplift Protector on Subway Tunnels with Different Sections
Aiyuan Zheng
Shenzhen Metro CO., LTD, Shenzhen 518026, China; [email protected] Received: 12 November 2018; Accepted: 14 December 2018; Published: 27 December 2018
Abstract: The construction areas of both the upper water gallery of the left circular tunnel and the water gallery of the right square tunnel in the Shuangjie River gallery project in Shenzhen that pass through the parking access line of the Qianhai parking lot were numerically simulated. The ABAQUS finite element numerical simulation software was used to analyze the stress and strain of the cover and retaining pile with different sections under the design of tunnel anti-uplift protection measures. The results of the study are summarized as follows: The vertical deformation of the upper cover of the square section of tunnel was larger than that of the circular tunnel. The shear strength of the retaining pile on both sides of the square section tunnel was considerably lower than that of the retaining pile on both sides of the circular tunnel. The anti-uplift protection measures of the designed tunnel exhibited evident protective effects on the square and circular sections. However, the protection effect for the circular tunnel was more evident compared with that of the square section.
Keywords: subway tunnel; pile enclosure structure; covered plate; section form; anti-uplift
1. Introduction Underground traffic systems in cities, particularly subway tunnels, are being increasingly developed [1–3]. Subway tunnels are commonly built under existing structures [4–8]. The development of subway tunnels has inevitably resulted in the construction of metro tunnels and various engineering structures [9–11]. For example, industrial and civil buildings are often built in the upper parts of a subway, and excavations are conducted near subways when constructing various structures [12]. The influence of engineering construction activities on the upper part of existing subway tunnels should be investigated. Engineering activities in the upper part of subway tunnels can be defined as loading and unloading processes of soil in the upper part of subway tunnels [13]. These loading and unloading processes of soil in the upper part of subway tunnels have different effects on subway tunnels with varying cross-sections [14–17]. Many scholars have carried out research on the mechanics of newly built tunnels passing under existing structures. Ratan Dasa [17] conducted a numerical simulation of a shallowly-buried, two-way, asymmetric tunnel in India, and studied the ground settlement and formation stability problems that may be caused by the subterranean construction. Wan [18] used Beijing Metro Line 7, which passes under the existing Shuangjing Station on Line 10, as a case study. The construction of Line 7 was carried out using different construction methods, such as the full-section method, the bench method and the CRD method. The deformation and stress of the existing structure under different excavation modes were analyzed according to the simulation results, and the specific parameters of the auxiliary method were simulated to further determine the suitable reinforcement range and reinforcement length. Fang and Kenneally [19] conducted similar experimental studies on an expressway tunnel underpass under a coal mine. Their test focused on the influence of the distance between the tunnel and the dislocation
Buildings 2019, 9, 5; doi:10.3390/buildings9010005 www.mdpi.com/journal/buildings Buildings 2018, 8, x FOR PEER REVIEW 2 of 14
Buildings 2019, 9, 5 2 of 14 an expressway tunnel underpass under a coal mine. Their test focused on the influence of the distance between the tunnel and the dislocation interfaces and dip of the inclined coal seam.Zheng, Y andinterfaces Qiu, W and and dip others of the studied inclined the coal section seam.Zheng, of the Changchu Y and Qiu,n Light W and Rail others that passes studied under the section a section of the of railway.Changchun The Light centrifuge Rail that of passesthe subgrade under a settlemen section oft railway.caused by The the centrifuge construction of the was subgrade studied settlement using a modelcaused of by water the construction injection and was studiedwaterproofing using a to model simulate of water the injection formation and loss waterproofing caused by tothe simulate tunnel construction.the formation loss caused by the tunnel construction. This study analyzes the impact of the anti-upliftanti-uplift protection measures of metro tunnels on the protection effecteffect for for different different tunnels tunnels within within the Shuangjie the Shuangjie River galleryRiver projectgallery inproject Shenzhen. in Shenzhen. ABAQUS wasABAQUS used was to simulate used to simulate the unloading the unloading conditions conditions in the upper in the sectionupper section of the of subway the subway tunnels tunnels with withdifferent different sections. sections.
2. Project Overview
2.1. Engineering Background This study is based on the Shuangjie River waterwater gallery project in Shenzhen, and the specificspecific layout planning of the project is shownshown inin FigureFigure1 1.. TheThe projectproject mainlymainly aimsaims toto transfertransfer thethe mainmain channel of the existing double-boundary river towardtoward the south by 3535 m.m. The water gallery will intersect with the Qianhai car accessaccess roadroad after thethe transfer,transfer, asas shownshown inin FigureFigure2 2..
Figure 1. LayoutLayout of of the the main main channel of the waterway.
Figure 2. Relationship between waterways and subway lines.
2.2. Metro Protection Program The excavation project adopts a staged constructionconstruction method with a length of 10 m.m. The first first excavation of of the the ground ground elevation elevation control control is is abov abovee an an elevation elevation of of 1.0 1.0 m m (within (within 5 5m), m), which which forms forms a − temporarya temporary construction construction platform. platform. Bored Bored piles piles (the (the pile pile top top elevation elevation is approximately is approximately −2.0 2.0m) are m) areset onset both on both sides sides of the of thetunnel tunnel (with (with a 3.5 a 3.5m interval). m interval). The The diameter diameter of a of pile a pile is 1.2 is 1.2 m, m,and and its itsspacing spacing is − 3–4is 3–4 m. m. The The piles piles exhibit exhibit a apull-up pull-up eff effect.ect. The The soil soil below below the the elevation elevation of of −2.02.0 m m is is grouted and reinforced, andand thethe secondsecond excavation excavation is is conducted. conducted. The The location location of of the the second second excavation excavation reaches reaches the design of the main groove bottom elevation (approximately −2.0 m elevation). The reinforced concrete Buildings 2018, 8, x FOR PEER REVIEW 3 of 14
Buildingsthe design2019 ,of9, 5the main groove bottom elevation (approximately −2.0 m elevation). The reinforced3 of 14 concrete cover is poured on top of the cast-in-place pile, and the cast-in-place pile is consolidated with the cover to reduce bulge deformation. A typical section of the subway is shown in Figure 3. cover is poured on top of the cast-in-place pile, and the cast-in-place pile is consolidated with the cover to reduce bulge deformation. A typical section of the subway is shown in Figure3.
(a)
(b)
FigureFigure 3.3. TypicalTypical cross-sectioncross-section form.form. (a) LongitudinalLongitudinal sectionsection ofof thethe subwaysubway verticalvertical cross-sectioncross-section protectionprotection scheme; (b (b) )Cross-section Cross-section of ofthe the subway subway intersecting intersecting the thefork fork section section excavation excavation area areaprotection. protection.
3.3. Numerical Simulation 3.1. Numerical Simulation Program 3.1. Numerical Simulation Program The numerical analysis software used was ABAQUS, an international large-scale finite element The numerical analysis software used was ABAQUS, an international large-scale finite element analysis software. ABAQUS simulated the water gallery of the right parking and exit intersection analysis software. ABAQUS simulated the water gallery of the right parking and exit intersection areas of the Qianhai parking lot. The left and right exits are mainly the cross-sections of different areas of the Qianhai parking lot. The left and right exits are mainly the cross-sections of different forms. The left side of the parking lot is a circular cross-section, whereas the right side is a square forms. The left side of the parking lot is a circular cross-section, whereas the right side is a square cross-section. Therefore, the numerical simulation mainly investigates the protective effect of the metro cross-section. Therefore, the numerical simulation mainly investigates the protective effect of the tunnel anti-uplift protection measures on metro tunnels with different sections and their mechanisms. metro tunnel anti-uplift protection measures on metro tunnels with different sections and their The tunnel anti-uplift protection measures of the parking access lines are shown in Figures4 and5 . mechanisms. Buildings 2018, 8, x FOR PEER REVIEW 4 of 14
BuildingsThe2019 ,tunnel9, 5 anti-uplift protection measures of the parking access lines are shown in Figures4 of4 14 and 5.
FigureFigure 4. 4.Anti-uplift Anti-uplift protectionprotection measures for for the the left left tunnel. tunnel.
Figure 5. Anti-uplift protection measures for the right tunnel. Buildings 2018, 8, x FOR PEER REVIEW 5 of 14
Figure 5. Anti-uplift protection measures for the right tunnel. Buildings 2018, 8, x FOR PEER REVIEW 5 of 14 3.2. ABAQUS Numerical Model Figure 5. Anti-uplift protection measures for the right tunnel. To analyze the influence of the water gallery construction on the safety performance of the Buildings 2019, 9, 5 5 of 14 3.2.existing ABAQUS subway Numerical tunnel Model under the designed protection scheme, the initial numerical simulation model considers the geological conditions of the tunnel in the Qianhai parking lot before excavation. To analyze the influence of the water gallery construction on the safety performance of the 3.2.In particular, ABAQUS Numericalthe parking Model lot’s entrance and exit were first simulated during the construction existing subway tunnel under the designed protection scheme, the initial numerical simulation process, and then the construction of the water gallery was simulated. modelTo considers analyze the the influence geological of theconditions water gallery of the construction tunnel in the on Qianhai the safety parking performance lot before of theexcavation. existing In order to reduce the influence of the boundary effect, the model size needed to be extended subwayIn particular, tunnel underthe parking the designed lot’s entrance protection and scheme, exit thewere initial first numerical simulated simulation during the model construction considers to the tunnel boundary size. According to the principle of numerical analysis and general theprocess, geological and then conditions the construction of the tunnel of the in water the Qianhai gallery was parking simulated. lot before excavation. In particular, processing experience, the influence range of the foundation pit excavation in the horizontal the parkingIn order lot’s to reduce entrance the and influence exit were of firstthe simulatedboundary duringeffect, the the model construction size needed process, to andbe extended then the direction was 3~5 times the excavation depth, and the influence range in the vertical direction was constructionto the tunnel of theboundary water gallery size. wasAccording simulated. to the principle of numerical analysis and general 2~4 times the excavation depth. In order to study the influence of foundation pit excavation on processingIn order experience, to reduce thethe influence influence of therange boundary of the effect,foundation the model pit excavation size needed in to bethe extended horizontal to tunnel structure and reduce the boundary effect, the length, width and height of the model were set thedirection tunnel was boundary 3~5 times size. the According excavation to depth, the principle and the of influence numerical range analysis in the and vertical general direction processing was to 110 m, 60 m and 50 m, respectively. experience,2~4 times the the excavation influence rangedepth. ofIn theorder foundation to study pitthe excavationinfluence of in foundation the horizontal pit excavation direction was on The vertical direction of the model was constrained for horizontal displacement. The bottom 3~5tunnel times structure the excavation and reduce depth, the boundary and the influence effect, th rangee length, in thewidth vertical and height direction of the was model 2~4 times were theset surface was constrained for displacement in three directions, and the upper surface boundary was excavationto 110 m, 60 depth. m and In 50 order m, respectively. to study the influence of foundation pit excavation on tunnel structure and free. The strata distributed in the calculation model were mainly fill layer, silt, stone filling and reduceThe the vertical boundary direction effect, of the the length, model width was constr and heightained offor the horizontal model were displacement. set to 110 m, The 60 bottom m and weathered granite. As for the finite element mesh division, the mesh was related to the calculation 50surface m, respectively. was constrained for displacement in three directions, and the upper surface boundary was accuracy. However, a dense grid will increase the computing time, and the cells should be divided free. TheThe verticalstrata distributed direction of in the the model calculation was constrained model were for mainly horizontal fill layer, displacement. silt, stone The filling bottom and reasonably. The total number of model units established was 96,885. The intersection models of the surfaceweathered was granite. constrained As for for the displacement finite element in three mesh directions, division, and the themesh upper was surface related boundary to the calculation was free. Qianhai parking tunnel and water gallery are shown in Figures 6 and 7. Theaccuracy. strata However, distributed a indense the calculationgrid will increase model werethe computing mainly fill layer,time, and silt, stonethe cells filling should and be weathered divided granite.reasonably. As forThe the total finite number element of model mesh units division, establ theished mesh was was 96,885. related The to intersection the calculation models accuracy. of the However,Qianhai parking a dense tunnel grid will and increase water gallery the computing are shown time, in Figures and the 6 cellsand 7. should be divided reasonably. The total number of model units established was 96,885. The intersection models of the Qianhai parking tunnel and water gallery are shown in Figures6 and7.
Figure 6. Overall diagram of the left tunnel and the water gallery model.
Figure 6. Overall diagram of the left tunnel and the water gallery model. Figure 6. Overall diagram of the left tunnel and the water gallery model.
Figure 7.7. Overall map of the right lineline ofof thethe tunneltunnel andand thethe waterwater gallerygallery model.model. 3.3. Numerical Simulation Analysis Steps 3.3. Numerical Simulation Analysis Steps The numericalFigure simulation7. Overall map analysis of the right was basicallyline of the thetunnel same and as the the water actual gallery construction model. procedure. The numerical simulation analysis was basically the same as the actual construction procedure. The specific analysis steps are listed in Table1. 3.3.The Numericalspecific analysis Simulation steps Analysis are listed Steps in Table 1.
The numerical simulationTable analysis 1. Numerical was basically simulation the sameanalysis as steps.the actual construction procedure. The specific analysis steps are listed in Table 1. Step Construction Content Remarks Table 1. Numerical simulationGeostress analysis balance steps. in the underground tunnel 1 Earth stress balance without excavation Step Construction Content Remarks Geostress balance in the underground tunnel 1 Earth stress balance without excavation Buildings 2019, 9, 5 6 of 14
Table 1. Numerical simulation analysis steps.
BuildingsStep 2018, 8, x FOR PEER ConstructionREVIEW Content Remarks 6 of 14 Geostress balance in the underground tunnel 1 Earth stress balance The withoutsupport excavation structure is constructed when the 2 Subway tunnel excavation and support surroundingThe support rock structure stress is constructed40%. when 2 Subway tunnel excavation and support 3 Surface soil excavation the surrounding rock stress is 40%. 4 3 Grading Surface excavation soil excavation of tunnel upper soil Grading angle of 1:1.5 5 4 Construction Grading covers excavation and ofuplift tunnel piles upper soil Grading angle of 1:1.5 Subway tunnel excavation on both sides of 6 5 Construction covers and uplift piles the upperSubway soil tunnel excavation on both sides of 6 the upper soil 3.4. Material Parameters 3.4. MaterialIn the numerical Parameters simulation, the Mohr–Coulomb model was used for rocks and soil, whereas the elasticIn the model numerical was simulation,adopted for the the Mohr–Coulomb support of uplift model piles, was cover used plates, for rocks and subway and soil, tunnels. whereas The the specificelastic model parameter was adopted values are for provided the support in ofTable uplift 2. piles, cover plates, and subway tunnels. The specific parameter values are provided in Table2. Table 2. Material parameters.
Bulk Table 2.FormationMaterial parameters. Poisson’s Cohesion Friction Category WeightBulk Weight ModulusFormation E Poisson’s Cohesion Friction Category Ratio μ (MPa) Angle ψ (°) (kN/m(kN/m3) 3) Modulus(MPa) E (MPa) Ratio µ (MPa) Angle ψ (◦) FillFill layer layer 18.7 18.7 13.5 13.5 0.30 0.30 0.1 0.1 16 16 Silt 17 10 0.4 0.09 6 Silt 17 10 0.4 0.09 6 Stone filling 22 3e4 0.15 0 35 Stone filling 22 3e4 0.15 0 35 Weathered granite 19.8 1e5 0.2 1 30 5 Anti-pullWeathered pile, granite cover, 19.8 1e 0.2 1 30 Anti-pull pile, cover, and 4 and subway tunnel 25 25 3.45e3.45e 4 0.170.17 — — —— supportsubway tunnel support
4. Analysis Analysis of of Results Results The vertical deformation of the subway tunnel of the parking parking access access line line and and water water gallery gallery after after constructionconstruction was completed is shown in Figure 8 8..
(a)
Figure 8. Cont. Buildings 2018, 8, x FOR PEER REVIEW 7 of 14 Buildings 2018, 8, x FOR PEER REVIEW 7 of 14 Buildings 2019, 9, 5 7 of 14 Buildings 2018, 8, x FOR PEER REVIEW 7 of 14
(b) Figure 8. Vertical deformation cloud. (a)( bLeft) line tunnel; (b) Right line tunnel.
Figure 8. Vertical deformation cloud. (a) Left(b) line tunnel; (b) Right line tunnel. To investigate the protective effect of the anti-uplift protection measures for the subway tunnels on theTo cross-sections investigateFigureFigure the of 8.8. protective VerticaldifferentVerticaldeformation deformation subwayeffect of tunnels,the cloud. cloud. anti-u( (a athe)) Leftplift Left stress line lineprotection tunnel; andtunnel; strain ( b(measuresb)) Right Rightof the line line coverfor tunnel. tunnel. the and subway maintenance tunnels onpiles the were cross-sections analyzed ofseparately. different subwayThe amount tunnels, of domethe stress bump and in strain the subwayof the cover tunnel and was maintenance analyzed To investigate the protective effect of the anti-uplift protection measures for the subway tunnels pilescomparatively Towere investigate analyzed to obtain the separately. protective the difference The effect amount between of the anti-uof the dome twoplift sections.bump protection in the measures subway for tunnel the subway was analyzed tunnels on the cross-sections of different subway tunnels, the stress and strain of the cover and maintenance comparativelyon the cross-sections to obtain of differentthe difference subway between tunnels, the the two stress sections. and strain of the cover and maintenance piles4.1.piles Covered werewere analyzed analyzedPlate separately.separately. TheThe amountamount ofof domedome bumpbump inin thethe subwaysubway tunneltunnel waswas analyzedanalyzed comparativelycomparatively toto obtainobtain the the difference difference between between the the two two sections. sections. 4.1. CoveredThe cover, Plate which uses reinforced concrete material for subway tunnel protection, has a thickness of 600 mm. The left lane of the parking lot was 2.83 m from the underside of the reinforced 4.1.4.1. CoveredCoveredThe cover, PlatePlate which uses reinforced concrete material for subway tunnel protection, has a thicknessconcrete deck.of 600 The mm. right The tunnelleft lane dome of the was parking 3.43 lotm fromwas 2.83the munderside from the ofunderside the deck. of To the analyze reinforced the The cover, which uses reinforced concrete material for subway tunnel protection, has a thickness of concretecoverThe deformation, deck. cover, The which rightthree uses tunneltypical reinforced dome cross-sections was concrete 3.43 ofm thefrommaterial cover the undersidewerefor subway used, of as thetunnel shown deck. protection, in To Figure analyze 9.has Thethe a 600 mm. The left lane of the parking lot was 2.83 m from the underside of the reinforced concrete deck. coverdeformationthickness deformation, of 600curves mm. threeof The the typicalleftthree lane sections cross-sections of the ofparking the upper of lot the was tunnel cover 2.83 cover werem from areused, the show asunderside nshown in Figures inof Figurethe 10 reinforced and 9. 11.The The right tunnel dome was 3.43 m from the underside of the deck. To analyze the cover deformation, deformationconcrete deck. curves The ofright the tunnelthree sections dome was of the 3.43 upper m from tunnel the cover underside are show of then in deck. Figures To 10 analyze and 11. the threecover typical deformation, cross-sections three typical of the covercross-sections were used, of asthe shown cover inwere Figure used,9. The as shown deformation in Figure curves 9. The of thedeformation three sections curves of theof the upper three tunnel sections cover of arethe shownupper tunnel in Figures cover 10 are and show 11. n in Figures 10 and 11.
Figure 9. Typical sections of the cover. Figure 9. Typical sections of the cover.
2 4 Figure 9. Typical sections of the cover. 4 2 43 43 ）
1 ） ） mm
mm 3 2 mm 32 （ （ （ ）
12 ） 4 ） 4 mm
0 mm 21 mm 21 （ （ （ 3 3
） 0 0 1 ） 10 1 ） mm
-1 mm 2 mm 2 （ （ （ -1 -10 deformation Vertical 0 Vertical deformation Vertical Vertical deformation Vertical -10 1 1 -1-2 -1-2 deformation Vertical Vertical deformation Vertical Vertical deformation Vertical -2 0481216 04812160481216 0 0 Length of cover along the gallery（m） Length of cover along the gallery（m） Length of cover along the gallery（m） -2 -2 -2-1 0481216 04812160481216 -1 -1 deformation Vertical Vertical deformation Vertical （ ） Vertical deformation Vertical (a) (b) Length of cover( alongc) the gallery m Length of cover along the gallery（m） Length of cover along the gallery（m） -2 -2 -2 (a) (b) 0481216(c) 0481216FigureFigure 10. 10. DeformationDeformation curve curve of ofthe the 0481216left left subway subway line. line. (a ()a Section) Section 1;1;( (bb)) Section 2 ;(2; c()c) Section Section3. 3. Length of cover along the gallery（m） Length of cover along the gallery（m） Length of cover along the gallery（m） Figure 10. Deformation(a) curve of the left subway line.(b) (a) Section 1; (b) Section 2; (c)( cSection) 3.
Figure 10. Deformation curve of the left subway line. (a) Section 1; (b) Section 2; (c) Section 3. BuildingsBuildings 20182019,, 89,, x 5 FOR PEER REVIEW 8 8of of 14 14
2 2 0 ） ） 0 0 ） mm mm
mm -2 （ （ （
-2 -2
-4
-4 -4 Vertical deformation Vertical deformation Vertical deformation
-6 0481216-6 -6 04812160 4 8 12 16 Length of cover along the gallery（m） Length of cover along the gallery（m） Length of cover along the gallery（m）
(a) (b) (c)
FigureFigure 11.11. DeformationDeformation curve curve of the of the right right subway subway line. line. (a)( aSection) Section 1;1 ;((bb) )Section Section 22;;( (cc)) SectionSection3. 3.
AsAs shown shown in in Figure Figure 10,10, bumps bumps appeared appeared on on both both sides sides of of Section Section 1 ofof thethe upperupper leftleft circularcircular cross-sectioncross-section of of the the tunnel. tunnel. The The maximum maximum bump bump size size was was 1 1 mm. mm. Su Subsidencebsidence occurred occurred in in the the middle middle sectionsection and and the the maximum maximum settlement settlement was was 1.45 1.45 mm. mm. Section Section 2 also2 alsoincreased increased on both on sides, both with sides, a maximumwith a maximum value of value 3.45 ofmm. 3.45 Subsid mm.ence Subsidence occurred occurred in the middle in the middle section, section, and the and maximum the maximum value wasvalue 1.65 was mm. 1.65 The mm. deformations The deformations of Sections of Sections3 and 2 were2 and basically3 were basically similar. The similar. maximum The maximum uplift was 3.5uplift mm, was and 3.5 the mm, maximum and the settlement maximum settlementwas 1.75 mm. was Section 1.75 mm. 1 is Section under 1control is under due control to the duesoil tobeing the restrainedsoil being along restrained the banks along of the the banks water of gallery. the water Therefore, gallery. Therefore,the deformation the deformation amount was amount relatively was smallerrelatively than smaller that of than Sections that of2 and Sections 3. In 2addition, and3. In the addition, maintenance the maintenance of the two sides of the of two the sidescover of limits the thecover bulge limits in the the cover bulge deformation in the cover deformationand passes its and own passes shear its force own to shear the cover. force toThe the cover cover. is subjected The cover tois subjectedan axial force, to an and axial the force, final and forms the finalof stress forms are of axial stress force are axial(pressure), force (pressure), shear force, shear and force, the bending and the moment.bending moment.In the initial In the stage, initial the stage, retaining the retaining pile suffered pile sufferedfrom vertical from upward vertical upwarddeformation, deformation, during whichduring both which sides both of sidesthe cover of the plate cover were plate tilted. were Simultaneously, tilted. Simultaneously, axial pressure axial pressure was applied, was applied,during whichduring the which middle the middle part of part the of cover the cover plate plate was wasdeflected deflected downward downward to tocause cause vertical vertical downward downward deformation.deformation. This This deformation deformation exhibited exhibited good good resistance resistance to to the the bulge bulge of of the the dome dome of of the the subway subway tunneltunnel to to a a certain certain extent extent and and prevented prevented the the excessive excessive bulge bulge deformation of the dome. AsAs shown shown in Figure 1111,, SectionSection1 1had had a verticala vertical downward downward deformation deformation on on the the upper upper cover cover of the of theright-angled, right-angled, square square section section subway subway tunnel. tunnel. The Th verticale vertical deformation deformation of the of twothe two sides sides was was 0.6 mm, 0.6 mm,and theand middle the middle deformation deformation was thewas largest the largest at 5.1 at mm. 5.1 Themm. twoThe sidestwo sides of Section of Section2 present 2 present an uplift an upliftdeformation. deformation. The maximum The maximum uplift wasuplift 1.1 mm,was the1.1 middlemm, the section middle had section a settlement had a deformation, settlement deformation,and the maximum and the settlement maximum was settlement 5.85 mm. Sectionswas 5.852 mm. and3 Sections had the same2 and deformation3 had the same curve. deformation Section1 curve.was located Section at 1 the was junction located of at thethe coverjunction plate of andthe cover water plate gallery and slope. water The gallery position slope. of The the position cover plate of theand cover the excavation plate and ofthe the excavation soil above of it the caused soil above the slope it caused of the the water slope gallery of the bank water to sinkgallery downward. bank to sinkThe downward. lower part ofThe the lower cover part tended of the to cover form tended a vertical to form bulge. a vertical The two bulge. sides The of two Section sides1 ofsubsided Section 1slightly subsided due slightly to the constraint due to the of constraint this section of andthis the section bank and slope. the Compared bank slope. with Compared the left circular with the tunnel left circularof the parking tunnel lot,of the the upliftparking of thelot, upperthe uplift cover of ofthe the upper right squarecover of tunnel the right was relativelysquare tunnel small was and relativelyits settlement small was and relatively its settlement large. was Thus, relatively the capacity large. Thus, of the the square capacity section of the of thesquare subway section tunnel of the to subwayaccommodate tunnel the to upperaccommodate load was the considerably upper load weaker was considerably than that of weaker the circular than tunnel. that of the circular tunnel. 4.2. Retaining Pile 4.2. RetainingThe length Pile of the retaining pile on both sides of the tunnel was 16 m, and was a circular section withThe a diameter length of of the 1.2 retaining m. The deformationpile on both sides maps of of the the tunnel retaining was pile16 m, in and three was directions a circular after section the withexcavation a diameter of the of water 1.2 m. gallery The deformation was completed maps are of shown the retaining in Figures pile 12 in and three 13 .directions The shear after cloud the of excavationthe retaining of pilethe iswater shown gallery in Figure was 14completed. The shear are force shown curve in Figures of a typical 12 and retaining 13. The pile shear with cloud depth of is theshown retaining in Figure pile 15is .shown in Figure 14. The shear force curve of a typical retaining pile with depth is shown in Figure 15. Buildings 2019, 9, 5 9 of 14 Buildings 2018, 8, x FOR PEER REVIEW 9 of 14
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(b)
(c)
Figure 12. Deformation cloud of the left retaining pile. ( a) x direction; (b) y direction; (c) z direction. Buildings 2019, 9, 5 10 of 14 Buildings 2018, 8, x FOR PEER REVIEW 10 of 14
(a)
(b)
(c)
Figure 13. Deformation cloud of the right retaining pile. (a) x direction; (b) y direction; (c) z direction. Figure 13. Deformation cloud of the right retaining pile. (a) x direction; (b) y direction; (c) z direction. As shown in Figures 14 and 15, the maximum deformation of the retaining pile in the x direction As shown in Figures 14 and 15, the maximum deformation of the retaining pile in the x on both sides of the left line was 1.2 mm, and the direction was a vertical tunnel. The maximum direction on both sides of the left line was 1.2 mm, and the direction was a vertical tunnel. The deformation of the retaining pile on both sides of the right line in the x direction was 0.26 mm. maximum deformation of the retaining pile on both sides of the right line in the x direction was 0.26 The direction was from the tunnel to both sides of the radiation, which is contrary to the deformation mm. The direction was from the tunnel to both sides of the radiation, which is contrary to the deformation direction of the circular tunnel retaining pile. As shown in Figure 15, the combination of the upper cover of the square tunnel and the retaining pile provided the stress value to the retaining Buildings 2019, 9, 5 11 of 14
Buildingsdirection 2018 of, 8 the, x FOR circular PEER REVIEW tunnel retaining pile. As shown in Figure 15, the combination of the11 upper of 14 cover of the square tunnel and the retaining pile provided the stress value to the retaining pile via pilethe Earth’svia the pressureEarth’s pressure in the upper in the part upper of thepart tunnel of the dome, tunnel which dome, was which smaller was thansmaller that than of the that circular of the circulartunnel. Thetunnel. maximum The maximum deformation deformation of the retaining of the pile retaining on both pile sides on of both the left sides circular of the subway left circular tunnel subwayin the y directiontunnel in wasthe y 0.76 direction mm, and was the 0.76 direction mm, and was the from direction the middle was from of the the water middle gallery of the to water both gallerysides of to the both water sides gallery. of the The water maximum gallery. deformation The maximum of the deformation retaining pileof the in theretainingy direction pile in on the both y directionsides of the on rightboth linesides was of the 0.41 right mm, line and was the 0.41 direction mm, and was the from direction the middle was pointfrom ofthe the middle water point gallery of theto both water sides gallery of the to waterboth sides gallery. of the The water maximum gallery. deformation The maximum of the deformation retaining pileof the on retaining both sides pile of onthe both left tunnel sides inof thethez leftdirection tunnel was in 3.5the mm, z direction and the directionwas 3.5 mm, was verticallyand the direction upward. Thewas maximumvertically upward.deformation The ofmaximum the retaining deformation pile on both of the sides retaining of the right pile tunnelon both in sides the z ofdirection the right was tunnel 1.1 mm, in the and z directionthe direction was was 1.1 also mm, vertically and the upward. direction The was displacement also vertically of the upward. retaining The pile ofdisplacement the left lane tunnelof the wasretaining larger pile than ofthat the ofleft the lane right tunnel lane, was thereby larger indicating than that that of the the right upper lane, cover thereby of the indicating square tunnel that wasthe workingupper cover efficiently. of the square tunnel was working efficiently.
(a)
(b)
Figure 14. Shear shield cloud. ( a)) Left Left line line tunnel; tunnel; ( b) Right line tunnel.
As shown in Figures 14 and 15, the maximum shear force value of the retaining pile on both 0 0 sides of-1500 the left -1000 circular -500 cross-section 0 500 subway 1000 tunnel-600 was -400 1.35 MPa -200 and 0 appeared 200 at a 400 position approximately 1 m aboveShear（ thekPa tunnel） dome. Two evident cases ofShear shear（kPa force） sign mutation were -4 -4 ） observed. The mutation location depended on the center of the circular） section, and the maximum m m （ value after the mutation depended on the bottom of the circular section. The（ maximum shear value of -8 the retaining pile on both sides-8 of the right tunnel was 0.49 MPa, and the maximum value appeared in the position where the direction tunnel vault was located. A clear two-value shear force sign mutation -12 -12 Depth along the pile Depth along the pile -16 -16
(a) Left line tunnel (b) Left line tunnel Buildings 2018, 8, x FOR PEER REVIEW 11 of 14
pile via the Earth’s pressure in the upper part of the tunnel dome, which was smaller than that of the circular tunnel. The maximum deformation of the retaining pile on both sides of the left circular subway tunnel in the y direction was 0.76 mm, and the direction was from the middle of the water gallery to both sides of the water gallery. The maximum deformation of the retaining pile in the y direction on both sides of the right line was 0.41 mm, and the direction was from the middle point of the water gallery to both sides of the water gallery. The maximum deformation of the retaining pile on both sides of the left tunnel in the z direction was 3.5 mm, and the direction was vertically upward. The maximum deformation of the retaining pile on both sides of the right tunnel in the z direction was 1.1 mm, and the direction was also vertically upward. The displacement of the retaining pile of the left lane tunnel was larger than that of the right lane, thereby indicating that the upper cover of the square tunnel was working efficiently.
(a)
Buildings 2019, 9, 5 12 of 14 was observed on the right line, for which the first mutation was located at the level of the square tunnel center. When the curves of the shear forces on the two sides of the two retaining sections were compared, the shear force of the retaining columns beside the square tunnel was found to be considerably smaller than that of the circular tunnel. The maximum shear value of the retaining pile on both sides of the square tunnel was 36.3%. Therefore,(b) the existing protective measures were safer and more suitableFigure for square 14. Shear tunnels shield than cloud. for (a circular) Left line tunnels, tunnel; ( inb) termsRight line of thetunnel. shearing force of the retaining pile.
0 0 -1500 -1000 -500 0 500 1000 -600 -400 -200 0 200 400 Shear（kPa） Shear（kPa）
-4 -4 ） ） m m （ （
-8 -8
-12 -12 Depth along the pile Depth along the pile -16 -16
(a) Left line tunnel (b) Left line tunnel
Figure 15. Shear curve of the fender post. (a)Left line tunnel; (b) Left line tunnel.
4.3. Subway Tunnel Vault Figure 16 presents the vertical deformation curve of the subway tunnel vault along the tunnel under the influence of the water gallery construction. As shown in the figure, the maximum uplift of the arch of the left circular tunnel was 0.029 mm, and was located at the intersection of the water gallery shore and the left tunnel. The middle position had an evident straight section, and the length of the straight section was the same as the length of the cover plate. The minimum bulge in the straight section was 0.025 mm. This condition shows evident inhibition of the tunnel vault cover. The maximum uplift of the right tunnel vault was 0.05 mm, this was also located at the intersection of the water gallery bank and the left tunnel. An evident concave section was observed in the reinforced concrete cover position. The minimum amount of bulge in the middle of the square tunnel was 0.005 mm, which is considerably lower than the minimum bulge of the straight section of the circular tunnel. This shows that the inhibition of the reinforced concrete cover of the square tunnel uplift was better than that of the circular tunnel. This finding is attributed to the fact that the shape of the cover was the same as that of the square tunnel, and that the force synergy was better than that of the circular tunnel. In addition, the crown of the square tunnel vault that covered the edge location of the uplift was considerably larger than that of the circular tunnel. Therefore, the cover plate should be embedded into the interior of both sides of the water gallery to ensure the anti-raising effect of the cover plate and retaining pile in the actual engineering design and construction. Buildings 2018, 8, x FOR PEER REVIEW 12 of 14
Figure 15. Shear curve of the fender post. (a)Left line tunnel; (b) Left line tunnel.
As shown in Figures 14 and 15, the maximum shear force value of the retaining pile on both sides of the left circular cross-section subway tunnel was 1.35 MPa and appeared at a position approximately 1 m above the tunnel dome. Two evident cases of shear force sign mutation were observed. The mutation location depended on the center of the circular section, and the maximum value after the mutation depended on the bottom of the circular section. The maximum shear value of the retaining pile on both sides of the right tunnel was 0.49 MPa, and the maximum value appeared in the position where the direction tunnel vault was located. A clear two-value shear force sign mutation was observed on the right line, for which the first mutation was located at the level of the square tunnel center. When the curves of the shear forces on the two sides of the two retaining sections were compared, the shear force of the retaining columns beside the square tunnel was found to be considerably smaller than that of the circular tunnel. The maximum shear value of the retaining pile on both sides of the square tunnel was 36.3%. Therefore, the existing protective measures were safer and more suitable for square tunnels than for circular tunnels, in terms of the shearing force of the retaining pile.
4.3. Subway Tunnel Vault Figure 16 presents the vertical deformation curve of the subway tunnel vault along the tunnel under the influence of the water gallery construction. As shown in the figure, the maximum uplift of the arch of the left circular tunnel was 0.029 mm, and was located at the intersection of the water gallery shore and the left tunnel. The middle position had an evident straight section, and the length of the straight section was the same as the length of the cover plate. The minimum bulge in the straight section was 0.025 mm. This condition shows evident inhibition of the tunnel vault cover. The maximum uplift of the right tunnel vault was 0.05 mm, this was also located at the intersection of the water gallery bank and the left tunnel. An evident concave section was observed in the reinforced concrete cover position. The minimum amount of bulge in the middle of the square tunnel was 0.005 mm, which is considerably lower than the minimum bulge of the straight section of the circular tunnel. This shows that the inhibition of the reinforced concrete cover of the square tunnel uplift was better than that of the circular tunnel. This finding is attributed to the fact that the shape of the cover was the same as that of the square tunnel, and that the force synergy was better than that of the circular tunnel. In addition, the crown of the square tunnel vault that covered the edge location of the uplift was considerably larger than that of the circular tunnel. Therefore, the cover plate should be embedded into the interior of both sides of the water gallery to ensure the Buildingsanti-raising2019, 9effect, 5 of the cover plate and retaining pile in the actual engineering design13 ofand 14 construction.
0.04 0.06
） 0.04
0.03 ） mm （ mm
（ 0.02
0.02
0.00
0.01
Vertical deformation -0.02 Vertical deformation
0.00 -0.04 0 10203040506070 0 10203040506070 Length along the tunnel(m) Length along the tunnel（m） (a) (b)
Figure 16. Vertical deformation of the vault. (a) Left line tunneltunnel vault;vault; ((b)) RightRight lineline tunneltunnel vault.vault.
5. Conclusions (1) In the upper part of the subway tunnel, the cover, which serves as the anti-uplift protection measure of the tunnel, should withstand axial pressure, shear force, and the bending moment. Under the combined action of these forces, warping deformation occurred on both sides of the cover plate, and vertical downward deformation occurred in the middle section. The vertical deformation on the upper deck of the square section tunnel was larger than that of the circular tunnel. (2) Retaining piles, which are part of the anti-uplift protection system for metro tunnels, resist pull and are able to bear shear forces. The shear strength values of the retaining piles on both sides of the circular and square tunnels exhibited two evident sign mutations, and their maximum shear values were all located near the horizontal plane where the tunnel vault was located. In addition, the maximum shear force of the retaining pile on both sides of the square tunnel was considerably smaller (by 36.3%) than that of the circular tunnel retaining pile. (3) The protective effect of the current anti-uplift protection system on the circular and square tunnel domes is evident. In addition, the vertical deformation curve of the subway tunnel dome showed that the circular tunnel had a straight segment and the square tunnel had a concave segment, thereby indicating that the current anti-uplift protection system had a better effect on the square tunnel than on the circular tunnel. A considerable amount of bulge was found on both sides of the cover, which suggests that the embedding length of the cover on both sides of the water gallery should be increased in the actual project.
Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest.
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