and Reinforced Soil Structures

Transcription

1 Geosynthetcs t and Renforced Sol Structures K. Rajagopal, Professor Department of Cvl Engneerng IIT Madras, Chenna e-mal: gopalkr@tm.ac.n

2 Embankment or Wall? Any slope steeper than 70 s desgned as a retanng wall. All prncples related to the geosynthetc renforced sol retanng walls are used for the desgns. Slopes shallower than 70 are desgned as slopes. Renforced Sol Embankments - 1 2

3 Courtesy: Maccaferr Inda Ltd. Renforced Sol Embankments - 1 3

4 Surface Treatment of Slopes Vegetaton Eroson control mats lke cor mat, jute mats, crmped mesh, etc. Stone ptchng Spray concrete on surface Gabon facngs Renforced Sol Embankments - 1 4

5 Geocells used to protect slope surface Renforced Sol Embankments - 1 5

6 Crmped mesh and a polymer textle for surface protecton Renforced Sol Embankments - 1 6

7 Use of cor and jute mats for eroson control on slopes Renforced Sol Embankments - 1 7

8 Geocells flled wth cement concrete for eroson control on canal slope Renforced Sol Embankments - 1 8

9 Stablsaton of Exstng Slopes Sol Nals Grouted Anchors Pre-stressed anchors Renforced Sol Embankments - 1 9

10 Sol Requrements Less strngent than for the retanng walls Partcle Sze % passng 20 mm 100% 4.75 mm % mm 0 60% 75 50% Plastcty Index 20% Sol compacted to at least 95%MDD Renforced Sol Embankments

11 DESIGN OF EMBANKMENTS Slopes on weak foundaton sols Falure s n foundaton sol Steep slopes on strong foundaton sol Planar wedge analyss Slp crcles through toe Blnear wedge analyss Renforced Sol Embankments

12 Constructon on Soft Clays PROBLEMS Low bearng capacty Large settlements Lateral flow of sols/slp crcle falure Dffcult to move constructon equpments. embankment falure wedge soft Clay slp crcle Frm Sol Renforced Sol Embankments

13 Constructon on Soft Clays SOLUTIONS Replace the sol wth good qualty fll Chemcal or thermal treatment of foundaton sol Deep mxng/jet groutng Basal renforcement Basal mattress Pre-consoldaton wth PVDs Vacuum consoldaton Stone columns or Encased Stone columns Ples and renforced concrete slab Ples wth geosynthetc renforced platform (pled embankment) Renforced Sol Embankments

14 Shear Strength Propertes to Use Slopes may undergo large deformatons, especally those on soft foundaton sols Constant volume strength parameters are more applcable than the peak strength parameters Renforced Sol Embankments

15 Partal materal factors to apply Partal factors Ultmate lmt Servceablty state lmt state Load factors Embankment fll F fs = 1.3 F fs = 1.0 Dead loads, F f = F f = Lne or pont loads Lve loads F q =1,3 F q =1.0 Sol materal factors To tan cv F ms = 1.0 F ms = 1,0 To c F ms = F ms = To c uu F ms = 1.0 F ms = 1.0 Renforcement To Consstent wth type of factors renforcement and desgn lfe renforcement base strength Sol/renforcement Sldng across F s = 1.3 F s = 1.0 nteracton factors Pullout F s = 1.3 F s = 1.0 Renforced Sol Embankments

16 In case of very weak foundaton sols Ground Improvement s requred to b brng up the foundaton sol propertes to reasonable levelsl to acheve economcal constructon Renforced Sol Embankments

17 Stone columns Rammed stone columns Vbroflot stone columns by dsplacement or replacement methods Renforced Sol Embankments

18 Encased stone columns used at A380 factory n Hamburg for ground treatment Renforced Sol Embankments

19 Sand Drans or PVDs for accelerated pre consoldaton ld surcharge fll t T v d cv 2 sand columns Renforced Sol Embankments

20 PVDs for pre consoldaton L Corrugated plastc core for dranage t Geotextle flter Renforced Sol Embankments

21 Renforced Sol Embankments

22 General vew after nstallaton of PVD s at a ste Renforced Sol Embankments

23 Geosynthetc Ple Raft System renforcement Ple cap plan concrete ples Soft clay Desgn prncples are based on sol archng theores Renforced Sol Embankments

24 Stff geocell mattress n case of thn clay sols geocell layer Thn soft foundaton layer q u 5.14 C uu Renforced Sol Embankments

25 Use of large assembled geocells for constructon on soft clays Rgd foundaton Desgn manual of Tensar, UK Renforced Sol Embankments

26 Increase n effectve stress wthout ncrease n total stress Increase n effectve stress constant depth Vacuum consoldaton of soft clay sols Renforced Sol Embankments

27 Basal renforcement on soft clays Constructon expedent: provded along wth a layer of granular sol to allow for free movement of constructon equpment Provded to ncrease the factor of safety of the embankment Renforced Sol Embankments

28 Desgn of basal renforcement based on uu =0 radus, r h v X W basal renforcement FS r c u = L a r W X c u Le c L r FS u a = u W X + moment due to renforcement force L a = r Renforced Sol Embankments

29 radus, r h v X basal renforcement W c u Knk n renforcement layer at slp surface Flexble renforcement takes the shape of slp crcle at juncton wth a knk Renforced Sol Embankments

30 Stablsng Moment = renforcement force x lever arm Flexble renforcement - renforcement assumes the shape of slp surface Lever arm = radus of slp crcle Rgd renforcement renforcement remans horzontal Lever arm = vertcal heght T d = ( FS - r FS u ) w x lever arm Basal renforcement that provdes ths much of force should be provded (least of rupture and pullout capacty) Renforced Sol Embankments

31 Safety aganst lateral sldng as a complete mass H Length of the renforcement should be suffcent that the resstance aganst lateral sldng s adequate shear resstance developed only on one surface P 1 2 K a 2 H K a qh K a = Basal renforcement sn ( - ) sn + sn sn 2 Renforced Sol Embankments

32 Safety aganst pullout falure of renforcement Le Length of the renforcement should be suffcent to generate suffcent pullout resstance shear resstance developed on both upper and lower surfaces Renforced Sol Embankments

33 Slp crcle analyss for cohesve frctonal sols l = nclned length at base of slce W = th weght of slce R = radus of slp crcle FS r c' = L a y ' n R + tan R ( w cos - =1 n R w 1 sn R u w T 1 T 2 l ) T y W T = W sn l N = W cos Renforced Sol Embankments

34 Slp crcle analyss Bshop s method FS u = cb W (1 r u ) tan W 1 sn sec tan tan / FS u FS r = R sec T y r R W sn c b W (1 r ) tan u 1 tan tan/ FS r u = bshop s pore pressure parameter b = wdth of slce FS = factor of safety Renforced Sol Embankments

35 Renforced Sol Embankments

36 Embankments constructed on competent foundaton sol Foundaton sol s very strong Renforcement provded to construct steep slopes Extra road space ganed Steep renforced slope Shallow unrenforced slope Renforced Sol Embankments

37 Planar wedge analyss of Steep Slopes AC = assumed rupture plane at angle = slope angle (>) R v = total t vertcal force ncludng weght of sol n wedge ADC and loads on surface DC N = normal force on AC = R v cos S = shear force on AC = R v sn T = sum of renforcement forces (horzontal) A D S Assumed sol propertes c=0, frcton angle = unform surcharge, q B R v N C T R v N S Renforced Sol Embankments

38 FS = shear resstance shear force = R v cos tan + R v sn T cos =1+ T R v tan K a = sn ( - ) sn + sn sn 2 Renforced Sol Embankments

39 Renforced Sol Embankments