Understanding of Foundations: Success of a Civil Engineer.!

Size: px

Start display at page:

Download "Understanding of Foundations: Success of a Civil Engineer.!"

Ezra Flynn
5 years ago
Views:

1 Understanding of Foundations: Success of a Civil Engineer.! Part B: Heavy Foundations Theory: Behaviour of Pile Foundations Design of Pile Foundations Case Study 1 : Heavy Foundations for Power Plant Case Study 2 : Deep Excavation Pit 1

2 Behavior of Pile Foundations Pile Foundations Load Transfer Mechanism Initially Pile-Soil system behaves elastically Mob. of Friction: 0.3% to 1% of dia. 2

3 Pile Foundations Load Transfer Mechanism Mob. of Friction: 0.3% to 1% of dia. Pile Foundations Failure Mechanism 3

4 Axially Loaded Piles P M V Pile cap Batter pile Vertical pile Axially Loaded Piles Load Transfer P P M V W 4

5 Forces and Deflections of Long Piles M Deflection y Slope S Moment M Shear V Soil Reaction p z Method of estimation of Pile Capacity By the use of static bearing capacity equations By the use of the values of SPT and CPT By field load tests By dynamic method 5

6 Ultimate Pile Capacity (IS 2911) Ultimate Capacity of Pile, Q ult = Q EB + Q SKIN W p Q EB = Ultimate End Bearing Q ult Q EB = c* N c + P d * N q * A p Q SKIN = Ultimate Skin Friction Q SKIN = *c + K*P*tan x A s Q SKIN W p = Self weight of Pile Q safe = Q ult / FoS Q EB Ultimate Capacity of Piles - Self Weight Ultimate Capacity of Pile, Q ult = Q EB + Q SKIN W p Ultimate End Bearing, Q EB = 300 T FoS = 2.5 Ultimate Skin Friction, Q SKIN = 100 T Self Weight of Pile, W = 20 T Case 1: Q safe = Q ult / FoS = 160 T (EPC Contractors) Case 2: Q safe = (Q ult W) / FoS = 152 T (Reasonable) Case 3: Q safe = Q ult / FoS W = 140 T (Consultants) (too conservative, consultants may prefer.or Contractors of item rate contracts) 6

7 Pile Foundations Uplift Capacity of Pile Q uplift Q SKIN W Uplift Capacity of Piles Ultimate Skin Resistance, Q SKIN = *c + K*P di *tan x A s + W p For Cohesive Soils: The skin resistance in both compression and uplift cases are same For Cohesionless Soils A reduction of 50% to 33% is generally adopted (industry practice) Ultimate Uplift Capacity = 1/2 to 2/3 of Ultimate Skin Resistance. 7

8 Negative Drag on Piles Factor of Safety = Ult. Skin Resistance of Single Pile Working load + (-) ve skin friction Part B: Heavy Foundations Behaviour of Pile Foundations Case Study 1 : Heavy Foundations for Power Plant Case Study 2 : Deep Excavation Pit 8

Standard Penetration Test, SPT N [ ] 0 0 10 20 30 40

9 Elevation [m] Artistic View of Thermal Power Plant 2 X 660 MW (Phase 1) Soil Profile & Operational Challenges Standard Penetration Test, SPT N [ ] GWT m m -70 9

pressure against the sides of the pile by creating a bridging

Fluid drop below ground water table, the pile hole will

10 When Pile Bore Collapse happen...? Drilling fluid enables for the application of hydrostatic pressure against the sides of the pile by creating a bridging effect : Stable Pile Bore Casing If top level of Drilling Fluid drop below ground water table, the pile hole will collapse. Un-stable Pile Bore Casing Water Table Water Table Operational Excellence with Best Practices 10

11 Quality Borehole Stability Top Vibro Hammer to install 10m deep Temporary Casing Quality Bentonite Recycling De-sanders to ensure quality of recycled Bentonite for borehole stability 11

12 Quality Testing (PIT) Pile Integrity Tests for all Installed Piles to ensure Quality of Piles Quality Testing (PLT) Load Test Setup for 1200MT 12

site) Productivity Supporting Equipment Dedicated

13 Productivity Timely Concreting Timely Concreting (Dedicated Batching Plant ~ 1,00,000m 3 batched on site) Productivity Supporting Equipment Dedicated Equipment to ensure optimal cycle times of piling process 13

14 Aug-11 Aug-11 Sep-11 Oct-11 Nov-11 Dec-11 Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Jul-12 Rate of Production (Lin.m/Rig/Day) Productivity Weekly Rate of Production Week Note: Above piles installed to 40m depth using 3 rigs (avg. productivity ~ 50 nos x 40m / 3 rigs / 6 days ~ 111 lin.m. / rig / day) Part B: Heavy Foundations Behaviour of Pile Foundations Case Study 1 : Heavy Foundations for Power Plant Case Study 2 : Deep Excavation Pit 14

Past Experience BBCL Breeze Residences, Chennai About the project Project : 3B+G+18 storeyed Residential Project Breeze Residences, Kilpauk, Chennai Developer Client Consultant : M/s BBCL Developers

15 Past Experience BBCL Breeze Residences, Chennai About the project Project : 3B+G+18 storeyed Residential Project Breeze Residences, Kilpauk, Chennai Developer Client Consultant : M/s BBCL Developers Pvt Limited. : M/s. Buro Engineers Ltd. Specialised Foundation: M/s. Keller Ground Engineering India Pvt. Ltd. Contractor Keller scope : Design & Build contract - BCIS Pile foundation & Permanent Retention System 30 15

16 Project Location 31 Plan Layout 32 16

Geotechnical Challenges Loose/weak layers at top (N~5) Hard strata at deeper depths Deeper Excavation(-10.2m) Sandy soils (Fines~5% to 25%) & Shallow GWT(-5.0m from EGL) Continuous Dewatering reqd.

17 Geotechnical Challenges Loose/weak layers at top (N~5) Hard strata at deeper depths Deeper Excavation(-10.2m) Sandy soils (Fines~5% to 25%) & Shallow GWT(-5.0m from EGL) Continuous Dewatering reqd. High lateral wall deflection Settlements & Tilting of adjacent buildings - Low in-situ bearing pressure - Foundation piles to be designed as end bearing & shall rest on rocky strata - Overall stability is a concern - Exerts high Lateral pressure on wall - Chances of seeping of soil particles - Ground subsidence 33 Scope of Work - Foundation Piles Design & Build Depth Optimization Foundation Package BCIS Piles Pile Load Tests 900, 750 & 600mm Piles (186 Nos.) Routine Tests (3 Nos.-1 for each dia.) PIT 107 Nos 34 17

Scope of Work Retention System Retention Package Design & Build BCIS Piles Grouting Anchors Contiguous Bored Pile with Inclined Anchors Retention (145 Piles) Retention Cum Foundation (57 Piles)

18 Scope of Work Retention System Retention Package Design & Build BCIS Piles Grouting Anchors Contiguous Bored Pile with Inclined Anchors Retention (145 Piles) Retention Cum Foundation (57 Piles) Cement : Bentonite (201 Nos.) 1 st level 103 Nos Capping Beam Length 172m 35 Design of Foundation Piles Confirming Design by M/s BBCL (Client) SI. No. Pile dia. (mm) Length of pile (m) Proposed by M/s Keller (Depth Optimization) Vertical Pile capacity (MT) SI. No. Pile dia (mm) Length of pile (m) Vertical Pile capacity (MT)

19 Layout Plan Foundation Piles & Retention System 37 Preliminary Analysis GGU Retain 38 19

20 Proof Checking Plaxis 2D 39 Summary of Results 40 20

21 Typical Cross Section 41 Execution Installation of Piles Casing installation Boring in progress Flushing Concreting 42 21

22 Execution Vertical Grout Columns Inclination checking Boring in progress Grout mixer set-up Primary Grouting Secondary Grouting 43 Execution Ground Anchors Anchor Fabrication Inclination checking 44 Anchor Strand Spacer Grout Pipes Anchor Installation 22

23 Execution Capping Beam Levelling & Preparation Laying of PCC 45 Reinforcement fabrication Completed Capping Beam Deflection Monitoring Points Deflection monitoring points 46 23

24 Deflection Monitoring Results Maximum Predicted Deflection = 39 mm (Plaxis Analysis) Recorded settlement = 9mm 47 Completed Picture 48 24

25 Completed Excavation Completed Excavation 25

26 Present site condition Basements completed 26

27 Latest Photograph Past Experience VGN Notting Hill, Nungambakkam, Chennai 27

About the project Project : Residential Building (3B+G+16 Floors) Developer : M/s VGN Developers Pvt. Ltd. Total Basement Area : 2175.7 sq.

28 About the project Project : Residential Building (3B+G+16 Floors) Developer : M/s VGN Developers Pvt. Ltd. Total Basement Area : sq.m Site dimensions : 60mx36m Excavated Perimeter : 218m (approx.) No. of Basements : 3 Nos. Depth of excavation : 8.5m from present ground level (RL -3.0m) Working level : 3.0m below NGL (RL 0.0m) Retention system : Contiguous Bored Pile wall with 1 level anchor Structure : Multi-storeyed (G+16) Residential buildings with 3 basements 55 Project Location 56 28

29 Adjacent Building(G+5) (West side) Plan Layout 57 Adjacent Building (G+7) (South side) Subsoil Condition Typical Soil Profile Filled up N~7, φ= 28 Clayey Sand / Sandy Clay N~8, Cu=40kPa 6.0 MD Silty Sand N~17, φ= MD to Dense Silty Sand N~30, φ= Dense Silty Sand+Gravel N>50, φ= Weathered Rock N>100, Cu=400kPa 29

Geotechnical Challenges Following are the challenges related to RETENTION SYSTEM FOR DEEP EXCAVATION may need to be addressed: Deep Excavation (depth ~ 11.

30 Geotechnical Challenges Following are the challenges related to RETENTION SYSTEM FOR DEEP EXCAVATION may need to be addressed: Deep Excavation (depth ~ 11.5m) adjacent to tall structures (G+7) Overall Stability of the excavation system Nature of in-situ soil Granular content (70% to 90%) which exerts high lateral pressure than cohesive soil Ground Water Level at Shallow Depth (3m below EGL) Lateral deflection of the Retention Ground Subsidence due to excessive dewatering (retention side) Settlement/ tilting of existing structures adjacent to the excavation 59 Scope of Work Retention System Proposed retention system - CBP wall with inclined anchors Pre excavation of about 3m were carried out at site to optimize the design of retention system Total length of retention - 218m CB piles Number of piles Diameter of piles Length of retention piles Grout columns Number of Grout columns Diameter of grout columns - 271nos - 750mm with 820mm c/c distance - 16m from Present ground level nos. with 12m depth from Present GL - 150mm 60 Detail showing Retention piles with Grout columns 30

31 Scope of Work Retention System Inclined anchors Number of Inclined anchors Capacity of anchors Anchor level nos at 1.64m c/c - 50T Fixed length of anchors -11m Free length of anchors - 8m Anchor inclination - 5.0m below NGL - 50 o 61 Scope of Work Retention System Waler beam Total length of waler beam Steel Waler beam - 218m - ISMC 400 (2 nos.) connected back to back 62 31

32 Retention System Layout Initial Proposal 63 Retention System Layout Existing Old Foundation Piles 64 32

33 Realignment of Retention System 65 Preliminary Analysis GGU Retain 66 33

34 Proof Checking Plaxis 2D 67 Summary of Results 68 Description GGU Analysis Plaxis Analysis GWT at -6.0m GWT at -6.0m Plie dia., m Pile spacing, m Pile length, m Embedment, m Surcharge, kpa Retention side, m Max BM, kn.m/m Wall Max SF, kn/m Wall Anchor Capacity, Tons Deflection, mm 1 in in

35 Typical Cross Section 69 Deflection Monitoring Points 70 35

Deflection Monitoring Points 11 10 9 71 8 7 6 5 4 3 2 1 0 0 5 10 15 20 25 30-1 -2-3 -4-5 Plaxis 3 4-6 5 6 7-7 8 9 10-8 11 12 13 14

36 Deflection Monitoring Points Plaxis Maximum Predicted Deflection = 25 mm (Plaxis Analysis) Recorded settlement (till date) = 17 mm Completed Picture 72 36

37 Introduction to Diaphragm Wall system 73 What is Diaphragm Wall? A Diaphragm wall is a technique used to build reinforced concrete walls in the area of soft earth close to open water or with high ground water table to stabilize deep excavations and as deep foundation elements

About Diaphragm Wall Diaphragm walls are typically constructed by starting with a set of guide walls, typically 1 meter deep and 0.

Excavation is done using a special clamshell-shaped digger or a hydromill trench cutter.

The excavator is then lifted and moved along the trench guide walls to continue the trench with successive cuts as needed.

75 About Diaphragm Wall Once a particular length is reached, a reinforcing cage is lowered into the slurry-filled pit and the pit is filled

Slurry walls are built to enclose the desired area, blocking water and softened earth from flowing into it.

38 About Diaphragm Wall Diaphragm walls are typically constructed by starting with a set of guide walls, typically 1 meter deep and 0.5 meter thick. The guide walls are constructed on the ground surface to outline the desired slurry trench(es) and guide excavation. Excavation is done using a special clamshell-shaped digger or a hydromill trench cutter. The excavator digs down to design depth, or bedrock, for the first cut. The excavator is then lifted and moved along the trench guide walls to continue the trench with successive cuts as needed. The trench is kept filled with slurry (usually a mixture of bentonite and water) at all times to prevent collapse. 75 About Diaphragm Wall Once a particular length is reached, a reinforcing cage is lowered into the slurry-filled pit and the pit is filled with concrete from the bottom up using tremie pipes. The concrete displaces the bentonite slurry, which is pumped out and recycled. Slurry walls are built to enclose the desired area, blocking water and softened earth from flowing into it. On completion of concreting, digging within the now concrete wall-enclosed area can proceed. To prevent the concrete wall from collapsing into the newly open area, temporary supports such as tiebacks or anchors are installed. When completed, the structure built within the walled-off area supports the wall, so that tiebacks and/or other temporary bracing may be removed

Construction Procedure of Diaphragm Wall Construction Procedure of D-wall 77 Construction Procedure of Diaphragm Wall (Typical) Stage 1: Construction of Guide Walls Stage 2:

39 Construction Procedure of Diaphragm Wall Construction Procedure of D-wall 77 Construction Procedure of Diaphragm Wall (Typical) Stage 1: Construction of Guide Walls Stage 2: Preparation of the Supporting Slurry Stage 3: Excavation of Diaphragm-wall Stage 3a: Stop Ends Fixing Stage 4: Lowering of Reinforcement Cage Stage 5: Concreting & Stop Ends Removal 78 39

40 Project Background 79 Project Background 80 Project : Commerzone IT Building (3B+G+9F) Location : Porur, Chennai Owner : M/s K Raheja Corp Total Plot Area : 25,800 Sq. M (approx.) Total Basement Area : 15,250 Sq. M (approx.) Excavated Perimeter : 650 m (approx.) No. of Basements : 3 Nos. Retention system : Diaphragm wall with Anchors Depth of excavation : 11.3m from Existing Ground Level (EGL) Scope of Work : Design & Execution of Diaphragm Wall. Area of D-Wall : 11, 700 Sq.M Depth of Retention : ~18m 40

41 Aerial View 81 Overall Layout Plan 82 41

(m) Values Clayey silt (MI) / Silty Clay (CI) 0.0 3.

0 14 Clayey silt (MH) / Silty Clay (CH) 6.0 2.

42 SPT N value & Grain Size Distribution 83 Idealised Soil Profile Soil Description Depth from (m) Layer SPT N thk. (m) Values Clayey silt (MI) / Silty Clay (CI) Clayey silt (MH) / Silty Clay (CH) Clayey silt (MH) / Silty Clay (CH) Clayey silt (MH) / Silty Clay (CH) Clayey silt (MH) / Silty Clay (CH) Clayey Silty Sand (SM) / (SC) Clayey Silty Sand (SM) / (SC) Weathered Rock >

43 Geo-Technical Problems The geotechnical problems of the site are listed below, Proposed site comprises of top 15m compressible silty clay. High Ground water table (GWT at 2.5 m below EGL). Adjacent building with closer setback distances (say 9m). Deep excavation (11.3m below EGL). Overall stability of Retention system. 85 Design Considerations Retention System Details: Length of Retention system : 650 m Existing Ground Level : 0.0 m Final Depth of Excavation : 11.3 m below EGL Design Water Table : 2.5 m below EGL Possible solutions: Contiguous bored pile (CBP) wall with lateral support Diaphragm wall with lateral supports - SELECTED 86 43

44 Retention System used for analysis m GWT 87 Typical D-wall Cross Section 88 44

45 Wallap Analysis (Stretch-1) 89 Wallap Analysis Results (Stretch-1) 90 45

46 Wallap Analysis (Stretch-2) 91 Wallap Analysis Results (Stretch-2) 92 46

47 Plaxis Analysis (Stretch-1) 93 Plaxis Analysis Results (Stretch-1) 94 47

48 Plaxis Analysis Results Summary (Stretch-1) 95 Plaxis Analysis (Stretch-2) 96 48

49 Plaxis Analysis Results (Stretch-2) 97 Plaxis Analysis Results Summary (Stretch-2) 98 49

50 Project Information 99 Project Location Owner Main Con Design consultants Structure Total perimeter Depth of D-wall Total D-wall area No. of panels : Construction of Diaphragm wall for Underground Metro Station, Hazratganj : Hazratganj, Lucknow : Lucknow Metro Rail Corporation (LMRC) : M/s Gulermak - Tata Projects Limited JV : Tandon Consultants Geoconsultants JV : Station Box with 2 level basement : 860m : 21.5m from EGL : 18,500 sq.m : 168 nos. (5m each) Total excavation depth : ~17.5m below EGL Project Location

51 Plan Layout 101 D wall Thickness Length of D wall No. of panels Depth of D wall Final depth of excavation : 800 mm & 1000 mm : 840 m : 168 Nos. : 21.5 m below EGL : 17.5 m below EGL Cross Section Layout

0 7.0 Silty Sand (SM) 10-20 7.0 24.0 17.

52 Subsoil Condition 103 Depth From (m) Depth to (m) Layer Thick (m) Soil Description SPT N Range Silty Sand (SM) Sandy Clayey Silt (ML/CI) Silty Sand (SM) Execution - Overall Site View

53 Execution Grabbing 105 Grabbing Execution Cage Lowering 106 Reinforcement Cage Erection 53

54 Execution Concreting & Stop end removal 107 Concreting Stop end removal Execution Roof slab construction

55 Execution Excavated Portion 109 Quality Checks for Polymer

Quality Checks Koden Results 111 Conclusions Ground Improvement Techniques such as Deep Vibro

in Cost & Time Execution of Specialized Foundation Techniques requires state-of-theart experience

state-of-the-art process International standard of practices using latest equipment ensures the

56 Quality Checks Koden Results 111 Conclusions Ground Improvement Techniques such as Deep Vibro Techniques can be used to provide Optimal Solutions Design & Build expertise will ensure savings in Cost & Time Execution of Specialized Foundation Techniques requires state-of-theart experience with Operational Excellence and Best Practices Execution of Deep BCIS Piles requires state-of-the-art process International standard of practices using latest equipment ensures the success of a project Safety goal of zero accidents is possible with dedicated safety systems and motivated leadership 56

Independent Foundation Package Allows for specialist foundation works with defined specifications Quality works will be delivered in a timely manner Combination of heavy foundations

57 Independent Foundation Package Allows for specialist foundation works with defined specifications Quality works will be delivered in a timely manner Combination of heavy foundations (bored piles) and open foundation (ground improvement techniques) for overall cost optimization Organisations following the above HPCL BPCL MRPL IOCL BHEL Keller s Ideal Worker (Kelwin) 57

58 All the best & Good Luck..! What Keller do.? Soil Anchors Micro Piles Stone Columns Tank Foundations Driven Piles DSM BCIS Piles Grouting Thank you for your kind attention.! 58

Misan University - College of Engineering Civil Engineering Department

Misan University - College of Engineering Civil Engineering Department CHAPTER 2 Soil and Excavations Soil investigation including two phases: surface investigation and subsurface investigation Surface investigation involves making a preliminary judgment about the site s