SOILS AND FOUNDATIONS Lesson 07

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1 SOILS AND FOUNDATIONS Lesson 07 Chapter 7 Approach Roadway Deformations Testing Theory Experience

2 Topics gtopic 1 (Section 7.0 to 7.6) - Approach roadway deformations gtopic 2 (Section 7.7, 7.8, 7.9) - Mitigation of approach roadway deformation - Construction monitoring and quality assurance

3 APPROACH ROADWAY DEFORMATIONS Lesson 07 - Topic 1 Approach Roadway Deformations Section

4 Learning Outcomes g At the end of this session, the participant will be able to: - Contrast internal and external deformation - Recall techniques to minimize internal deformation - Compute vertical stress distribution beneath embankments - Calculate settlement in coarse-grained soils - Calculate consolidation settlement magnitude and time in fine-grained soils - Compare immediate, primary and secondary settlements - Discuss lateral squeeze

5 Stresses Imposed by Structures gthe approach embankments induce stresses in the foundation soil

6 Approach Roadway Embankments Major Design Considerations gstability gdeformations - Vertical - Lateral geffects on the Structure - Bump at the end of the bridge - Tilting

7 Stability Problems gshallow translational failure (Infinite Slope) Embankment Fill Firm Soil gcircular Failure

8 Stability Problems gsliding block failure glateral squeeze - Lesson 7

9 Approach Roadway Deformations ginternal - Within the embankment fill Due to compression of the fill materials Poor drainage gexternal - In the native soils below the embankment fill Vertical and lateral deformation of native soils Vertical: Immediate and consolidation settlements Lateral: Squeeze (cause tilting of structures)

10 Internal Deformations

11 Avoiding Internal Deformations gno organic or miscellaneous fill material allowed gcontrol fine-grained material use grequire compaction with proper moisture control gcompaction control tests

12 To Eliminate Internal Deformations Suggested Approach Embankment Details (Figure 7-1) 50 Minimum 90% T % T99 6 Topsize Highway Embankment Material 6 Topsize (95% T180) Highway Embankment Material (90% T180) Select Structure Fill (100% T99)

13 Bump at the End of a Bridge

14 Reasons for the Bump at the End of the Bridge gpoor compaction of embankment material near the structure gmigration of fines into drainage material behind abutment backwall gwhat is the solution? gapproach slab

15 Bump at the End of the Approach Slab

17 Heel Projection + 3 ft To Prevent Bump at End of Bridge g Use select structural fill g Use underdrain filter material g Use durable well graded granular for high density w/min. compactive effort g Figure Underdrain Filter Material (6 Lifts) Select Structural Fill (100 % T99)

18 Select Material Specifications gspecification Item Lift Thickness - Topsize Restriction - Gradation Requirement - Limit Percent Fines greason for Item - Small Compaction Equipment - Less than 3/4 Lift Thickness - Compactibility - Density/Piping

19 Select Material Specification (Cont d) gspecification Item - Durability - T99 Density Control - Compatible to Drain Material greason for Item - Minimize Breakdown - Small Compaction Equipment - Prevent Piping

20 External Deformations

21 Avoid Major Subsoil Settlement gidentify and provide treatment for organic soils ganalyze clay subsoil deposits

22 Types of Deformations gimmediate (short-term) term) deformation gconsolidation (long-term) deformation gimmediate deformation occurs in ALL soils whether cohesive or cohesionless gconsolidation deformation occurs only in fine grained soils that are saturated at the time of application of loads

23 First Step in Evaluation of Deformations gunder applied external loadings, estimate the stress distribution with depth gchapter 2: Stress and Strain in Soils - Section Section 2.6

24 Vertical Stress Due to External Loadings gdepth of Significant Influence (DOSI), D s p = γ t h 0.8p 0.6p 0.4p h 0.2p

25 Do you think there is a settlement problem for the case shown below? Granular Fill γ = 120 pcf Sandy Gravel γ = 120 pcf (γ = 60 pcf) Soft Clay Sand

26 Combined Plot of Stresses Figure Pressure Δp p f z w Legend: z w p o p t Δp p f = depth to groundwater = effective overburden pressure = total overburden pressure = pressure due to external loads = p 0 + Δp Depth, z p o p t

27 Fundamental Principles gstresses induced in the soil from an embankment load are distributed with depth in proportion to embankment width gthe additional stresses in the soil decrease with depth

Stress Distribution Under Fills gsection 7.3.

28 Stress Distribution Under Fills gsection gfigure 7-37 In each chart, the upper line gives the pressure under the centerline while the lower line gives the pressure under the mid-point of the side slope

29 Example 7-17 gfind the stress increase (Δp)( under the proposed abutment centroid (Point X) at a depth of 0.8 b f below the base of the fill Point X b f h f 2 1 b f = Fill height h f = 30 ft; End and side slopes (1V:2H) Embankment top width =100 ft; Fill unit weight γ f = 100 pcf

30 Stress Distribution Under Fills g b f =(100 ft /2) + (60 ft/2) = 80 ft g Use chart for 0.8b f = 0.8 (80 ft)=64 ft and a distance measured from mid-point of end slope to Point X as multiple of b f =(30 ft/80 ft)b f = 0.38b f g K f =0.7 g Δp= K f γ f h f = (0.7)(100 pcf)(30 ft)=2,100 psf Pressure Coefficient K f Mid Point of 1.0b f 0.5b f End Slope 0.5b f 1.0b f Mid Point of Side Slope 0.38b Centerline 0.8b f = 64 ft Depth Below Surface

31 Computation of Immediate Settlement (Vertical Deformation) gmany methods for estimating immediate settlement are available gall methods are based on some form of estimate of soil compressibility - Bearing Capacity Index, Compression Index, Elastic Modulus, Constrained Modulus, etc.

32 Computation of Immediate Settlement (Vertical Deformation) gfor embankments use Hough s method - Simple to use - Settlement estimates are conservative by a factor of 2 (FHWA 1987) gfor footings use more refined methods - Schmertmann (1978) Chapter 8 Considers strain distribution with depth - D Appolonia (1968) Considers effect of preconsolidation

33 Hough s Method Step 1: Step 2: Determine bearing capacity index, C, C Use N1 60 value in Hough s chart Subdivide soil layer into 10 ft ± increments and sum settlements for all layers using following equation for each layer ΔH = H 1 log C 10 p 0 + Δp p 0

34 Hough s Chart ginorganic SILT curve should not be used for soils exhibiting plasticity CORRECTED SPT N-VALUE, N1 60

35 Example 7-27 gdetermine immediate settlement of a wide embankment placed on silty sand 20 ft γ t = 120 pcf 10 ft Silty Sand γ t = 120 pcf, N1 60 = 20

36 Example 7-27 Draw p o diagram gassume no dissipation of stress under the centerline of a wide embankment Pressure (psf) po Δp = 2400 p f 3000 Depth (ft) 10

37 Example 7-27 Draw p o diagram gfor N1 60 = 20 and Silty Sand, C C 58 from Figure (Hough s s chart) gfind settlement ΔH = H 1 log C 10 p 0 + Δp p 0 1 ΔH = 10 ft log10 58 ΔH = 0.12 ft = 1.44 in 600psf psf 600psf

38 Vertical Stress Due to External Loadings g Note the variation of vertical stress under a narrow embankment p = γ t h 0.8p 0.6p 0.4p h 0.2p

39 Implications of Embankment Settlement gat end of embankment construction, additional fill is required to reach final grade g1 inch of settlement over 1 mile of 60-ft wide embankment will need approximately 1000 cubic yards of additional fill gthis is sometimes referred to as Compaction Factor and is included in bid documents

40 Student Exercise 3 ggiven: p o values at the depths where SPTs were taken; Soil is fine to coarse sand Depth, ft SPT N 60 -values p o (psf) gfind: (a) N1 60 value (b) C (bearing capacity index) value

41 Student Exercise gsolution

42 Consolidation (Long-term) Deformation gconsolidation deformation occurs only in fine grained soils that are saturated at the time of application of loads glaboratory estimates of settlements are often inaccurate guse consolidation approach when S > 90% geffect of consolidation is 3-D 3 D for limited loaded areas typical of transportation structures

43 Lateral Stress Due to External Loadings gnote Lateral Stresses Beyond Loaded Area Zone of Tensile Stresses p = γ t h 0.6p 0.4p 0.2p h Soft Layer

44 Consolidation (Long-term) Deformation gvertical component of 3-D 3 consoldation is estimated based on data from 1-D 1 D laboratory consolidation test gchapter 5, Section 5.4

45 Normally Consolidated Soils p σ' = σ' o = p c p vo p f σ' vf VOID RATIO, e e o = e p e f Δσ' Δp v 1 C c S c n Cc = 1 + e i o H o log 10 p p f o 0.42e o p VERTICAL EFFECTIVE STRESS σ' v (LOG SCALE) (a)

46 Over Consolidated (Preconsolidated( Preconsolidated) Soils pσ' ovo Δp σ' p f Δσ' v vf VOID RATIO, e e o e p e f 1 C γ σ' pc p 1 C c n S = 1 Ho 1+ e o ( C r log 10 p p c o + C c log 10 p p f c ) 0.42e o VERTICAL EFFECTIVE STRESS σ' v (LOG SCALE) (a) p

47 Under Consolidated Soils σ p p c σ v p o 0 σ v p f f e 0 Δσ v0 Δp o Δσ Δp v VOID RATIO e p e f 1 C r 1 Cc n S = 1 Ho 1+ e o ( C c log 10 p p 0 c + C c log 10 p p f 0 ) VERTICAL EFFECTIVE STRESS p (LOG SCALE)

48 Time Rate of Consolidation

49 Settlement-Time Relationship where: t = T v c H v 2 d t = Time for Settlement T v = Time Factor (dimensionless) H d = Vertical Drainage Path Length c v = Coefficient of Consolidation (e.g., ft 2 /day)

50 Embankment on Clay Subsoil Time-Settlement Curve Settlement (Inches) Time (Months)

51 Example 7-37 gdetermine magnitude and the time for 90% consolidation for the primary settlement 20 γ t = 120 pcf 10 Clay (Normal Consolidated) γ t = 120 pcf, ft 2 C c = 0.5, e 0 = 1.0, c v = 0.2 day Rock

52 Example 7-37 gp o diagram Pressure (psf) po Δp = 2400 p f 3000 Depth (ft) 10

53 Example 7-37 gfind primary settlement ΔH = Cc H 1+ e 0 log 10 p 0 + Δp p psf psf ΔH = 10 ft log 10 = 1.75 ft = psf 21 inches

54 Example 7-37 gfind time for 90% consolidation. Assume single drainage due to impervious rock underlying clay layer. Use t 90 = T 2 v H d c v t 2 (0.848)(10 ft) 90 = = ft / day 424 days

55 Student Exercise 4 Compute: (a) Primary settlement of NC clay (b) Time in months for 90% primary settlement Soil Profile 24' 23' 6' Granular Fill = 120 pcf Sandy Gravel Pressure Diagram T = 122 pcf Soft Clay T = 104 pcf, e o = 2.1, Cc = 1.1 Sand Sandy Gravel 23 Clay 29 p o p F Middle of clay layer Δp Cv = ft 2 /day

56 Secondary Compression gsee Section 7.5.4

57 Lateral Squeeze b e Fill

58 Lateral Squeeze Zone of Tensile Stresses p = γ t h h gshort-term term undrained bearing capacity failure glong-term drained 3-D 3 creep 0.6p 0.4p 0.2p Soft Layer

59 Abutment Tilting Due to Lateral Squeeze

61 Rotation of Rockers

62 Threshold Condition for Lateral Squeeze (γfill)(h FILL FILL) ) > 3c u

63 Safety Factor against Lateral Squeeze FS SQ = 2cu γd tan S θ c γh u

64 Lateral Squeeze: How to Prevent Abutment Rotation Get fill settlement out before abutment deep foundations are constructed

65 Learning Outcomes g At the end of this session, the participant will be able to: - Contrast internal and external deformation - Recall techniques to minimize internal deformation - Compute vertical stress distribution beneath embankments - Calculate settlement in coarse-grained soils - Calculate consolidation settlement magnitude and time in fine-grained soils - Compare immediate, primary and secondary settlements - Discuss lateral squeeze

66 Any Questions? Any Questions? THE ROAD TO UNDERSTANDING SOILS AND FOUNDATIONS

67 APPROACH ROADWAY DEFORMATIONS Lesson 07 - Topic 2 Mitigation of Approach Roadway Deformations Construction Monitoring and Quality Assurance Section 7.7, 7.8, 7.9

68 Learning Outcomes gat the end of this session, the participant will be able to: - Recall techniques for reducing settlement magnitude - Describe techniques for reducing time rate of settlement - Identify types of performance monitoring instrumentation - Discuss importance of proper compaction

69 Solutions for Settlement Problems greduce Amount of Settlement - Category 1: Increasing the resistance - Category 2: Reducing the load greduce Settlement Time - Surcharge - Vertical Drains

70 Reduce Amount of Settlement gcategory 1: Increasing the resistance - Excavation and recompaction - Excavation and replacement - Vertical inclusions, e.g., stone columns - Horizontal inclusions, e.g., geosynthetics - Grouting - Dynamic compaction

71 Reducing Amount of Settlement gcategory 2: Reducing the load - Reduce grade line - Use lightweight fill, e.g., expanded shale, foamed concrete, geofoam - Bypass soft layer with a deep foundation Need load transfer platform

72 Reducing Settlement Time gsurcharge treatment gvertical drains

73 Embankment on Clay Foundation Effect of Surcharge Treatment Settlement With Surcharge Without Surcharge Surcharge Fill Clay Time Time for Equivalent Settlement With Surcharge Remove Surcharge at This Time Time for Total Settlement Without Surcharge

75 Acceleration of Consolidation Using Vertical Drainage Sand Clay

76 Vertical Drains Surcharge Settlement Platform Permanent Fill Drainage Blanket Soft Clay Vertical Drain Firm Soil Piezometers Not to Scale

79 Vertical Drain Installation Sequence g Position rig at drain location g Place anchor on drain end g Penetrate mandrel to desired depth g Withdraw mandrel g Cut drain material above drainage blanket

89 Construction Monitoring and QA gclearly specify line and grade on plans gdo not make frequent changes in details because repetition makes construction easier gmake sure that embankments are compacted to meet the compaction requirements and limits noted on the plans

90 Construction Monitoring by Instrumentation gpiezometers gsettlement plates ginclinometers

92 Typical Instrumentation Plan S.I. Fill Original Ground S.I. Soft Clay H 4 H H H Firm Soil S.I. Piezometers Settlement Plate Slope Inclinometer

93 Settlement Platform Schematic

95 Vertical Inclinometer Embankment Compressible Soil Firm Soil

97 Principle of Inclinometer Operation ΣL Sinθ L Sinθ L θ L = Distance between readings θ = Angle measured by sensor

98 Piezometer Embankment Compressible Soil

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104 Learning Outcomes gat the end of this session, the participant will be able to: - Recall techniques for reducing settlement magnitude - Describe techniques for reducing time rate of settlement - Identify types of performance monitoring instrumentation - Discuss importance of proper compaction

105 Any Questions? Any Questions? THE ROAD TO UNDERSTANDING SOILS AND FOUNDATIONS

106 Interstate 0 Apple Freeway Note: Scale shown in Station Form S.B. Apple Frwy N.B. Apple Frwy Baseline Stationing Interstate 0 Proposed Toe of Slope Proposed Final Grade 2 1 Existing Ground Surface Proposed Abutment

107 Apple Freeway Exercise gappendix A - Section A.6 Subsurface Explorations Basic Soil Properties Laboratory Testing Slope Stability Terrain reconnaissance Site inspection Subsurface borings Visual description Classification tests Soil profile P o diagram Test request Consolidation results Strength results Design soil profile Circular arc analysis Sliding block analysis Lateral squeeze analysis Approach Roadway Deformations Design soil profile Magnitude and rate of settlement Surcharge Vertical drains Spread Footing Design Design soil profile Pier bearing capacity Pier settlement Abutment settlement Surcharge Vertical drains Driven Pile Design Design soil profile Static analysis pier Pipe pile H pile Static analysis abutment Pipe pile H pile Driving resistance Lateral movement - abutment Construction Monitoring Wave equation Hammer approval Embankment instrumentation

108 Design Soil Profile (East Approach Embankment Settlement) 2:1 Fill = 130 pcf = 40 0 c = 0 30' 5' Organic = 90 pcf w = 120% s.g. = 1.6 Sand = 110 pcf N = 17 = 50pcf C' = 90 Clay = 65 pcf C c = 0.35 C r = C v = 0.6 ft 2 /day w = 35% s.g. = 2.78 Incompressible 3' 7' 35'

109 Po Diagram Pressure (psf) x 135 Organic 4100 x 570 x 1020 x p o 1630 Sand Clay p c x 2460 x x x 4450 x 4460 x 4950 x 3600 pf 5300 x 5800

110 Compute Total Settlement Total Settlement Layer 1 - Organic (0' -3') Layer 2 - Sand (3' - 10') Layer 3 - Clay (10' - 18') Clay (18' - 28') Clay (28' - 45') 19.54" 0.83" 1.17" 2.55" 8.11" H Total 32.20"

111 Time-Settlement Plot Time - Settlement Plot 0.83 Time (days) " for sand + for 433 days) " (max. H)

112 Assume: 10 high compacted surcharge ( = 130 pcf) Δ P of emb. (P F ) + surch. (P s ) = 5200 psf

113 Time - Settlement Plot 180 Days 30 Fill + 10 Surcharge

114 Recheck stability of 30 Fill With 10' Surcharge F.S. = 1.33 Bishop 2:1 33' Fill 10' 25' 7' Sand 35' Clay Dense Gravel F.S. w/surcharge = 1.33 (1.63 w/o surcharge)

115 Time - Settlement Plot Time (days) days 10 30' Fill 12.66" 15 30' Fill w/drains 30' Fill + 10' Surcharge Treatment Fill only Fill w/10' surcharge fill w/ wick drain t 90 (mo.) Extra Cost - $120,000 $172,000

116 Summary Design Soil Profile Soil layer consolidation properties selected Settlement 32" settlement predicted Recommend organic excavation Rec. waiting abut. Time-Rate 433 days for t 90 Surcharge 10' surcharge improves t 90 to 190 days Cost $120,000, F.S. = 1.33 O.K. Vertical Drains 60 days for t 90 Cost $172,000 -> $385,000

117 Any Questions? Any Questions? THE ROAD TO UNDERSTANDING SOILS AND FOUNDATIONS

Soil Mechanics: Deformation

Soil Mechanics: Deformation Course No: G05-003 Credit: 5 PDH Yun Zhou, PhD, PE Continuing Education and Development, Inc. 9 Greyridge Farm Court Stony Point, NY 10980 P: (877) 322-5800 F: (877) 322-4774