《高等土力学》课程教学课件（讲稿）Trenching and Shoring Design

05/05/2016武汉批工大学武汉理工大学Tableof ContentsCourseIntroductionTypical Trenching and Shoring ProjectsAppliedSoll MechanicsandShoringDesign-Part1:SoilMechanics ReviewDr.Jinyuan Liu,P.E.,P.EngPart2:TrenchingandShoringDesignAssociateProfessor,RyersonUniversityPart3:ExercisesandDiscussionsDirector,Jinyuan Liu&Associates Inc实员理工大学实员理工大学Design:AVeryRiskyJob!!!Part 2:Shoring Design-OSHARegulationsTrenching DesignSheetPileDesignBraced CutDesignAnchoredTieback Shoring DesignCut-&-Cover SMRT Station Collapse Destroys Nicoll Highway-Soil Nail Wall Design (Tomorrow)Singapore 2004武居理工大学武居理工大学Deslgn:OHSARegulationsDesign:OHSARegulatlonsOccupational Health&Safety Act"Trench'means anexcavationwheretheexcavdepthexceedsItspurposeistoprotectworkersagainstheaazards ortheexcavationwidththe job inOntarioOntario regulationforconstructionprojects requiresa minimumslopeThis is relatedto safeconstruction and slope oftrench,excavationfortrenchorexcavationwallforacertaintypeof soilsThe definition of soil types are different from engineering classificationsystemcupational SafetCSafetyActancsalecegulationOHSA_ONOSHA,USTypeSlopeTypeTypeStable RocknlaStable Rock1.2 m trom bottom4-1H:1VdrcerotrFomonstabiiny6mbBFrombaom

05/05/2016 1 Applied Soil Mechanics and Shoring Design Dr. Jinyuan Liu, P.E., P.Eng. Associate Professor, Ryerson University Director, Jinyuan Liu & Associates Inc Table of Contents  Course Introduction  Typical Trenching and Shoring Projects  Part 1: Soil Mechanics Mechanics Review  Part 2: Trenching and Shoring Design  Part 3: Exercises and Discussions Part 2: Shoring Design  OSHA Regulations  Trenching Design  Sheet Pile Design  Braced Cut Design  Anchored Tieback Shoring Design  Soil Nail Wall Design (Tomorrow) Design: A Very Risky Job!!! Cut-&-Cover SMRT Station Collapse Destroys Nicoll Highway￾Singapore 2004 Design: OHSA Regulations Occupational Health & Safety Act Its purpose is to protect workers against health and safety hazards on the job in Ontario. This is related to safe construction and slope of trench, excavation Design: OHSA Regulations  “Trench” means an excavation where the excavation depth exceeds the excavation width  Ontario regulation for construction projects requires a minimum slope for trench or excavation wall for a certain type of soils  The definition of soil typ g g es are different from engineering classification system Occupational Health and Safety Act and Regulation OHSA, ON Occupational Safety and Health Administration OSHA, US Work Safe BC In decreasing order of stability Type Slope Type Type Stable Rock n/a Stable Rock 1 1.2 m from bottom 1 H : 1 V A A 2 3 From bottom 1 H : 1 V B B 4 From bottom 3 H : 1 V C C

05/05/2016好卖桥珠工大学武居理工大学Safety Regulatlons: Example Type Bin OSHASafetyRegulatlons:ExampleTypeBInOSHATABLE B-1MAXIMUM ALLOWABLE SLOPESSOIL OR ROCK TYFETMAXIMUM ALLOWABLE SLOPES (H:V) (1) FORXCAVATIONSLESSTHAN2O FEETDEEP(3)STABLEROCKVERTTCAL(90 Deg.)21TYPEExampleforTypeBsoilsFromEarthBetentionSvsttbookbyMacnab(2002)From Earth Retention Systems Handbook by Macnab (2002)实员理工大学实理工大学Deslgn:SollStrengthParametersDesign:Soll StrengthParameters0e 12324.9NoafBo工学家装营二nTbk18e,aPsVery SurrTeeVey SohSonMediunom100-1505-10040023050-10410556Lon20.430 - 35o武居理工大学武居理工大学Design:Suggested ImprovementDeslgn:TrenchingConstructlon00033B28S9mindthesoil propertieschange afftercavationfsoffaiure营TB2

05/05/2016 2 Safety Regulations: Example Type B in OSHA From Earth Retention Systems Handbook by Macnab (2002) Safety Regulations: Example Type B in OSHA Example for Type B soils From Earth Retention Systems Handbook by Macnab (2002) Design: Soil Strength Parameters Very dense > 80 > 45 Compact 40 - 60 35 - 40 Dense 60 - 80 40 - 45 Very losse < 20 < 30 Loose 20 - 40 30 - 35 Table 1.8 Relationship between relative Density and Angle of Friction of Cohesionless Soils State of packing Relative density (%) Angle of friction, '(deg) Design: Soil Strength Parameters Design: Suggested Improvement Please keep in mind the soil properties soil properties change after excavation, lots of failures in the excavation soil Design: Trenching Construction

05/05/2016心卖理工大学卖居理工大学Deslgn:Stablty-Culmann's MethodDeslgn:Stablllty-Culmann'sMethodAssumptionsasfollows:t,=e,o'tangAplane surface.Afinite slopesmB-0)[sin(β-0)n2Average shearing stress greaterthan shear strengthof soilsinβsin6sinBsinoSoil ishomogenousThemostcriticalplaneistheonethathas:min ratio of average shear stressto shear strength[sin(β-)sing-costang)sin(β-0)sinβsinβsingo= O in order to get the critical planesin(β-e)inBsin6thencomepondingtocos(βgete.nf8-0)4sinβcosesinβcosdsubstituting with c=Cand '=I-cosB--)SI实员理工大学实员理工大学Design:Stabillty-MethodofSllcesDeslgn:Stablllty-Blshop'sMethodof SllcesSoil above trial failurfaceisdivided into sliceWnistheeffective weightNr and Tr are the normal and sheaThe effects ofPn and Pn+lare forceacting onslides (effect ignored in traditiorsaccounted for to somedegre in Bishop method)slide analysis, consiLetP-P..=AP.T.T-WcOStaneffective:cosa,T,-N,tan(e')+cAL,=N()(A)W.cg.ngWn+ATForequilibrHum of rial wedgeABC,MeM(c+(W.cosa./.)tangorcouw,rsina+Nrtane(el,+w,coa,tg)DSEYw,rsina,Note: AL_is approiximatelyequal tob,/cosag on arc slopeTCdeDen武工大学武居理工大学Deslgn:StrengthParameters?Design:Stabillty-Bishop'sMethod ofSllcesMUST be appropriate to thefield stress levelseh+w,ung+TmgstressesmaybeguitelowUndrained orDrainedsinshorttermliustconstabilityfPeak strengthFirst time slides? Or compacted soilsSoftened strength (critical state)Fissured, stiff clays?ResidualstrengthEvaluation of stabilityof slips orpre-existing slidesw,sinaBedding shear planes3

05/05/2016 3 Design: Stability-Culmann’s Method Assumptions as follows: • A finite slope A plane surface • Average shearing stress greater than shear strength of soil • Soil is homogenous The most critical plane is the one that has a min ratio of average shear stress to shear strength                    sin sin sin sin( ) 2 1 cos sin sin sin( ) 2 1 sin sin sin( ) 2 1 2 2 2                         Ta H Na H W H                2 sin sin sin sin( ) 2 1 cos sin sin sin sin( ) 2 1 '                 H H Design: Stability-Culmann’s Method 1 sin( )(sin cos tan ') '              d c H cos sin tan ' sin sin sin( ) 2 1 sin ' sin sin sin( ) 2 1 ' ' tan ' 2 d d d d d H c H c                                    substituting with ' ' ' ' 1 cos( ') 4 ' sin cos ' sin cos ' 1 cos( ') 4 then corresponding to ' 2 ' get 0 in order to get the critical plane, ' 2 sin                                                 d d d d cr d d d c c and c Hcr H c c c H Design: Stability-Method of Slices slide analysis, considered some degree in Bishop method) Pn and Pn 1are force acting on slides(effect ignored in traditional Nr and Tr are the normal and shear forces Wn is the effective weight Soil above trial failure surface is divided into slices  cos cos effective stressis n n n n r r n n L W α L N N W α     can be positive and negative depending on arc slope Note : ΔL is approximately equal to cos , sin ( ' cos tan ') ( ' ( cos / )tan ') sin For equilibrium of trial wedge ABC, M M ( ' ( cos / )tan ') ( ) ( ) n 1 1 1 1 Driving Resisting n n n n p n n n n p n n n n n p n n n n n n p n n n n n n n n f r d n α b / α W r α c L W or FSs FSs c W L L r W r α FSs c W L L L FSs T L                                     Design: Stability-Bishop’s Method of Slices FSs c L FSs T N c L N n r r d d n r tan ' ' tan( ') ' Let P - P P, T - T T accounted for to some degree. The effects of forces on the sides of slices is n n 1 n n 1               (c ΔLn Nr ) FSs W r α T r Tr α FSs c L FSs Wn T Nr N n p n r n p n n n n n n r ' tan ' 1 sin For equalibriu m of ABC, take moment about O sin tan ' ' cos See force polygon in Fig.9.24b ,summing force in vertical 1 1                         Design: Stability-Bishop’s Method of Slices If for simplicity , take T 0, the above eq becomes tan 'sin cos sin 1 ( ' tan ' tan ') ( ) 1 1 ( )              n n n n p n n n n p n n n n FSs α where m α W α m c b W T FSs      The above equation is solved by trial and error procedure sin 1 ( ' tan ') 1 1 ( )         n p n n n n p n n n n W α m c b W FSs   n n n w n p n n n n p n n n n n n W u h γ W α m c b W u b FSs           is total weight, sin 1 ( ' ( )tan ') For Steady Flow Condition, 1 1 ( )  Design: Strength Parameters?  MUST be appropriate to the field stress levels  stresses may be quite low  Undrained or Drained  short term (just constructed) or long term stability?  Peak strength  First time slides? Or compacted soils  Softened strength (critical state)  Fissured,stiff clays?  Residual strength  Evaluation of stability of slips or pre‐existing slides  Bedding shear planes

05/05/2016卖居珠工大学卖理工大学Deslgn:DifferentRetentilonSystemsDeslgn:DifferentRetentlonSystemsThecommonearthretentionsystems includeWwtiertooSheet piles with/without waleand strut;Groundanchors;Soldier beam and lagging wall:Slurrytrenchwalls;Large diameter bored piles,contiguous or overlapping('secant'piles)..Soil nailingCaissonwall实员理工大学实员理工大学Deslgn:DifferentRetentlonSystemsDeslgn:DifferentRetentlonSystems武工大学武居理工大学Deslgn:Different RetentilonSystemsDesign:Different RetentionSystemsdepthof100tt (30m)byASCEOOXCX(1997)14001OI0ITPaOT

05/05/2016 4 Design: Different Retention Systems The common earth retention systems include  Sheet piles with/without wale and strut;  Ground anchors;  Soldier beam and lagging wall;  Su y l rr te c r n h wa s; ll  Large diameter bored piles, contiguous or overlapping (‘secant’ piles).  Soil nailing  Caisson wall 5/5/2016 19 Design: Different Retention Systems 5/5/2016 20 Design: Different Retention Systems Soldier pile and lagging wall is NOT Recommended for sites with basal stability issues Design: Different Retention Systems Design: Different Retention Systems Recommended for waterproof depth of 100 ft (30 m) by ASCE (1997). Has been used for depth of 400 ft (120m) for dam cutoff wall (Macnab 2002) 5/5/2016 23 Design: Different Retention Systems 5/5/2016 24 Recommended for waterproof depth of 40 ft (12 m) by ASCE (1997). If deeper, some other measures to be implemented

05/05/2016心卖批工大学卖居理工大学Design:DifferentRetentlonSystemsDeslgn:DifferentRetentlonSystemsRakerprovides lateralupports along withSecont walls particularly effective in situations where minor loss of soil duringlagging operations might be detrimental to adjacent footings or sensitive utilities.Designed witha greater moment resistance along with drlled installation,secantwalls have the advantage in situations where vibrations might be detrimentaland/oralsoveryclosetoadjacentbuildingsTangentpiles will not function as a water barrier,but is quite efficient as anOscnalternativeto soldier pile and lagging is to ensure that soiloss during excavationdoes not occur.From Macnab (2002)实员理工大学实员理工大学Deslgn:Different RetentlonSystemsDeslgn:Different Retention SystemsMany more..nytimesa.conTferentsystens武H工大学武居理工大学Design:Different RetentlonSystemsDeslgn: Retaining Wall DesignTABLESL.PATiod-BaskWdVEYAAAEFOOBEOeetoingaorSFrom ACCE GSP No. 74 (19975

05/05/2016 5 Design: Different Retention Systems 5/5/2016 25 Secant walls particularly effective in situations where minor loss of soil during lagging operations might be detrimental to adjacent footings or sensitive utilities. Designed with a greater moment resistance along with drilled installation, secant walls have the advantage in situations where vibrations might be detrimental and/or also very close to adjacent buildings. Tangent piles will not function as a water barrier, but is quite efficient as an alternative to soldier pile and lagging is to ensure that soil loss during excavation does not occur. From Macnab (2002) Design: Different Retention Systems Raker provides lateral supports along with uplift force!!! Design: Different Retention Systems Many more. Many times a combination of different systems is used for the same job! Design: Different Retention Systems Design: Different Retention Systems From ACCE GSP No. 74 (1997) Design: Retaining Wall Design Gravity retaining wall is important for some concepts in shoring design

05/05/2016心卖理工大学卖居理工大学Design:OverturningandSlppingDeslgn:BearlngCapacityFallure =9u-()--(-)9.=CNEF+ONF.F+,BN,FFFsioe opi- lqnPayattentiontothefaiureplaneandstressconditionwhy is active pressure notpressure atrest?实员理工大学实员理工大学Design:SheetPlleDeslgnSPW:Typeof SheetPllesSteel Sheet PilingDesign ManualWoodensheetpilesPrecastconcrete sheetpileSteel sheet pileAluminum sheet pileAvallahlonline武居理工大学武居理工大学SPW:Designof CantlleverSheet PlleSPW:DeslgnChartsforSandw togethiPayattentiontothelimitationFig-15 - Design of cantilever sheet piling in granular solss: (a) conventional method(b)simplified method. (after Teng6

05/05/2016 6 Design: Overturning and Slipping Pay attention to the failure plane and stress condition, why is active pressure not pressure at rest? Design: Bearing Capacity Failure           B e B V q qtoe 6 max 1           B e B V q qheel 6 1 min u c cd ci qFqdFqi B N FdFi q c N F F qN     ' 2 ' 2 2 1      qmax q FS u bearing capacity  Design: Sheet Pile Design Available online SPW: Type of Sheet Piles  Wooden sheet piles  Precast concrete sheet pile  Steel sheet pile  Aluminum sheet pile Aluminum sheet pile SPW: Design of Cantilever Sheet Pile How to get this and the values? SPW: Design Charts for Sand Pay attention to the limitation

05/05/2016心卖理工大学卖居理工大学SPW:CantlleverSheetPlleInClaySPW:DeslgnChartsforClayHowtogetunPayattentiontotheimitationFentomail MethdSimplitied MethouFig.20ure for-design oteversheetpidingcohesive soil backfiled withgranular soll (aheeTeng实居理工大学实理工艺Locate the point ct zero presture given bySPW:Anchored Sheet PlleWallY-HKANTosatidy egD,HyDwouRd.Dtre-PalDmod (ater Teng'heet.pling byfee-Compute the active and passive lateral pressures using appropriate coetficients ofateralssure.If the Coulombmethod is used,it should beuseonservativelyforthepassive case23 (a) shows the general case fort an.anchored wall in granutar soilnFauDackfled wihgranularmaterialhavingdiferentsoll propertiesTherefore,Yerefers totheequivalent soilunit weighteitherwetto submerged.fortheparticularsoilayerinquestion.Also,Ka'referstotheactivepressurecoefonttoronatural in-place granular soi武居理工大学武居理工大学SPW:DesignChartforAnchoredWallSPW:Anchored Wall InClayPayattentiontothelimitation

05/05/2016 7 SPW: Cantilever Sheet Pile in Clay How to get this and the values? SPW: Design Charts for Clay Pay attention to the limitation SPW: Anchored Sheet Pile Wall SPW: Design Chart for Anchored Wall Pay attention to the limitation SPW: Anchored Wall in Clay

05/05/2016武活理工大学心卖居理工大学SPW:DeslgnofAnchorSPW:MomentReductlon实员理工大学实员理工大学Anchors:TypesAnchors:Capacltyigure44Aroerd surface (atir Tero)Fie 44-0waesurface and the uffimate capacityutimate capacity ot the deadman,pounds per.snear footfetotalactivesarprssurepoundsperinearfootepresuredistribuSons for granular and cchesive sols are aiso she44.For desicn incohesivesolls,both the imecked to determinethe critical case.A safety factorof tweTetTSTaa武H工大学武居理工大学Anchors:DeadmanLocatlonAnchors:CapacityCalculatlonais paceinatweaas ihonn.The surtacedf uidrgt soeendh iscinLetivescheme-gthrminingPCubacnab(2002TCERE8

05/05/2016 8 SPW: Moment Reduction 0.8 reduction used by Macnab (2002) SPW: Design of Anchor Anchors: Types Anchors: Capacity Anchors: Deadman Location An alternative scheme for determining the deadman location from Macnab (2002) Anchors: Capacity Calculation

05/05/2016卖活技工大学卖居理工大学Braced Cut:Typlcal DetallsBracedCut:SoldlerBeamsDepth of first StrutDepth of tensileZ,=2e/ycrack仁安居理工大学实员理工大学Braced Cut:Lateral EarthPressureforDesignBraced Cut: Peck's Apparent EarthPressureApply to the excavations withdepth>=6mThewatertableis belowthebottom of the cutSand is assumed to bedrained with zero pore water pressureClay is assumed to be undrained and porewater pressure is not-considered.(total stress analysis)The selection of an appropriatedesign diagram is dependent upon0.66K.mthe"stability number1na*tamP(45-0/2The earth pressure computation for clay is based upon the totalO(3008-10mweight of soil, assuming undrained behaviorO52.610Comparedto Rankine'sSand(b)Stinahad fisuared(c) Sofn to mediumAnd thisfollowsfromthefactthatthedata were empirically110.Lateral Earthdeveloped on the basis of total unit weight and soil initial shearPressurestrength observed from Berlin, Munich, New York Subwayass (rTaidPe967e 23, Terzagli and Peck aMechinics inEngpetinigPractice.Reprinted bypeon of Joln Wiley & Sons, Inc.)武居理工大学武居理工大学Braced Cut: Two Methods for ClayBraced Cut: Determination of Strut LoadsConnects of strut with sheet+YH 29upile well are assumed to actas hinge simulated as simply40supportedbeambetweerehnttwolayersofstruts,andsolve for the strut loads ashesupportreactionsP~T5o(7No+ 10NglLoadB=B1+B2C-Cohesion (pst).oadC=C1+C2No=(StabilityNo.)butnotAnotherwayisto8 -1.111but not > 0.5use tributary areat not> 0.15030method9

05/05/2016 9 Braced Cut: Typical Details Braced Cut: Soldier Beams Depth of tensile crack Depth of first Strut Z 2c / ' c   Braced Cut: Peck’s Apparent Earth Pressure  Apply to the excavations with depth>=6m  The water table is below the bottom of the cut  Sand is assumed to be drained with zero pore water pressure  Clay is assumed to be undrained and pore water pressure is not considered.( total stress analysis )  The selection of an appropriate design diagram is dependent upon the “stability number”  The earth pressure computation for clay is based upon the total weight of soil, assuming undrained behavior  And this follows from the fact that the data were empirically developed on the basis of total unit weight and soil initial shear strength observed from Berlin, Munich, New York Subway Braced Cut: Lateral Earth Pressure for Design Compared to Rankine’s Lateral Earth Pressure Braced Cut: Two Methods for Clay Braced Cut: Determination of Strut Loads Connects of strut with sheet pile well are assumed to act as hinge simulated as simply supported beam between two layers of struts, and solve for the strut loads as solve for the strut loads as the support reactions. Load B = B1 + B2 Load C = C1 + C2 Another way is to use tributary area method

05/05/2016心卖居理工大学卖居理工大学BracedCut:DeterminatlonofStrutLoadsBraced Cut: RakerFootingThreeSimplySupported Beams:AB,-BCandCD,LoadB=B1+B2LoadC=C1+C2DrawThePressureEnvelopeDivideintoseveral simplysupported beamsSolvefor reactions at each beam supports.Plot bending moment and shear diagrams for beam anddetermine the section modulus of sheet pile required.S=M../o.Sameprocedureofthedesign ofwaleI.From Macnab (2002)卖情1实员理工大学Stabilty Issue: Bottom HeaveInthis case,theverticalcolumnofsoil alongtheshessumedtoexerta pressureon thehorizontal planeA-Awhenthepressureexertedbythis soil column exceedthebearingcapacity of the soil beneath the sheeting a bearing type failure will occurResulting in heave of thebottomof theexcavation and settlement of thesurrounding ground surfaceIfmanyclaylayers,howHowto treatthecan we usewater pressurethis formula?in clay case?Fig.60.武武居理工大学武居理工大学StablltyIssue:Bottom Heave In ClayStabillty Issue:Stablllty FactorsHeN(3)Uttimate Bearing Capacity for a soil$Fcolumn:qu,=cNcWhere Nc = 5.7 (for perfectly roughundafions)tVertical load along per unit areaq=yH+q-cH/B(duetoresistance along surface ll)FS=q./qFS≥1.5isrequired10

05/05/2016 10 Braced Cut: Determination of Strut Loads  Three Simply Supported Beams : AB,  BC and CD, Load B = B1 + B2  Load C = C1 + C2  Draw The Pressure Envelope.  Divide into several several simply supported supported beams.  Solve for reactions at each beam supports.  Plot bending moment and shear diagrams for beam and determine the section modulus of sheet pile required.  Same procedure of the design of wale M  all S / max  Braced Cut: Raker Footing From Macnab (2002) How to treat the water pressure in clay case? Stability Issue: Bottom Heave  In this case ,the vertical column of soil along the sheeting is assumed to exert a pressure on the horizontal plane A-A .  when the pressure exerted by this soil column exceed the bearing capacity of the soil beneath the sheeting a bearing type failure will occur  R lti i h f th b tt f th ti d ttl t f th Resulting in heave of the bottom of the excavation and settlement of the surrounding ground surface If many clay layers, how can we use this formula? Stability Issue: Bottom Heave in Clay Ultimate Bearing Capacity for a soil column: qu = c Nc Where Nc = 5.7 (for perfectly rough foundations) Vertical load along per unit area q = H + q – c H/B’ ( due to resistance along surface II) FS = q u /q FS ≥ 1.5 is required A A How to judge the occurrence of this case? How to prevent it? Stability Issue: Stability Factors