Earth Retention Systems

Size: px

Start display at page:

Download "Earth Retention Systems"

Barbara Hudson
5 years ago
Views:

1 haywardbaker.com Earth Retention Systems Mark W. Goodsell, P.E., D.GE Senior Engineer

2 2 Earth Retention Systems Focus of Presentation Different Types and Purposes of Earth Retention Systems Design Considerations/Geotechnical Study Apparent Earth Pressure Diagrams Challenges Associated with Earth Retention Systems Types of Earth Retention Systems (Advantages/Disadvantages) Risks Associated with Earth Retention Systems

3 Earth Retention Systems Uses of Earth Retention Systems Excavation Support Grade Separation Bridge Abutments Slope Stabilization Reduction of Lateral Earth Pressures Types of Earth Retaining Structures Fill Walls Cut Walls/Top Down Construction 3

4 Earth Retention Systems Externally Stabilized Walls In-Situ Walls Soldier Piles, Secant/Tangent Piles, Sheet Piles Gravity Walls Reinforced Concrete, Massive Blocks, Gabion Baskets Internally Stabilized Walls Reinforced Soils MSE Walls - Geogrid or Strap Reinforcement In-Situ Reinforcement Soil Nail Walls 4

5 5 Engineering Properties Soil Classification Unit Weight Shear Strength Chemical Properties (Corrosion Potential) Groundwater Conditions Facing Stability Wall Type Selection Earth Retention Systems Wall Design Consideration Basal Heave/Stability

6 Earth Retention Systems Geotechnical Study Determine the Subsurface Stratigraphy Obtain representative soil samples for laboratory testing (strength, chemical, classification, etc.) Measure in-situ properties through field testing Evaluate groundwater levels 6

7 7 Earth Retention Systems FHWA Recommended Soil Boring Layout

8 Earth Retention Systems Results of an Adequate Geotechnical Study More efficient retaining wall design Less construction delays Less construction difficulties (proper construction method and tooling) Prevents unsafe or inadequate wall performance 8

Apparent Earth Pressure Diagram (AEP) Equipment for measuring strut load by means of hydraulic jacks Measured brace loads have led to the development of

9 Apparent Earth Pressure Diagram (AEP) Equipment for measuring strut load by means of hydraulic jacks Measured brace loads have led to the development of the AEP envelopes by Karl Terzaghi & Ralph Peck. 9 AEP were calculated by dividing measured braced loads by the area of the wall supported by each brace.

10 Apparent Earth Pressure Diagram 10 Experience indicates that the method of constructing a wall can affect the pressures which act on it top down vs. bottom up During the construction of many early braced excavations the top braces failed because the load was higher than what was calculated. We know that pressure increases with depth against many types of walls, but this is not the case against braced and tied-back walls. Pressures behind braced and tied-back walls build up quicker because soils are not allowed to develop active pressures like a traditional cantilevered walls.

11 Full Scale Wall Study Texas A&M National Science Foundation Sand - Wall Height 25 FT. Plan View 11

12 Full Scale Wall Study Texas A&M National Science Foundation One Tier Apparent Earth Pressure Diagram Comparison Sand - Wall Height 25 FT. 25H 12

13 Full Scale Wall Study Texas A&M National Science Foundation One Tier AEP Bending Moment Comparison Sand - Wall Height 25 FT. 25H 25H 13

14 Full Scale Wall Study Texas A&M National Science Foundation Two Tier Apparent Earth Pressure Diagram Comparison Sand - Wall Height 25 FT. 25H 14

15 Full Scale Wall Study Texas A&M National Science Foundation Two Tier AEP Bending Moment Diagram Comparison Sand - Wall Height 25 FT. 25H 25H 15

16 Challenges Associated with Earth Retention Systems Settlement of Adjacent Buildings, Streets and/or Utilities High Water Table Poor soil conditions (Soft/Organic clays, loose sands and silts, etc.) Obstructions (i.e. utilities, footings, etc.) 16

17 Earth Retention Systems Earth Retention System Selection is based on: Excavation Height Movement Tolerance Project Budget ($$) Geology/Soils Water Table Elevation Site Constraints 17

minimal vibrations (drilled) Can work around utilities and structures 18 Disadvantages Can

18 Types of Earth Retention Systems Soldier Beam and Lagging Advantages Generally one of the cheapest types of Earth Retention Systems Installation goes quickly Can be installed with minimal vibrations (drilled) Can work around utilities and structures 18 Disadvantages Can be difficult to install in granular soils No water cut-off Exposes soil during lagging installation

19 Types of Earth Retention Systems Soldier Beam and Lagging 19 One Tier Multi Tier

20 Types of Earth Retention Systems Soldier Beam Installation Methods 20 Drilled Driven

21 Types of Earth Retention Systems Lagging Installation Lagging Typically Installed in 5 ft. Lifts 21 Soldier Beams with Shotcrete Lagging

22 Types of Earth Retention Systems Cantilevered Soldier Beam and Lagging 22

Types of Earth Retention Systems 23 Soil Nails Soil Nailing is an in situ technique for reinforcing, stabilizing and retaining excavations and deep cuts through the introduction of relatively

23 Types of Earth Retention Systems 23 Soil Nails Soil Nailing is an in situ technique for reinforcing, stabilizing and retaining excavations and deep cuts through the introduction of relatively small, closely spaced inclusions (usually steel bars) into a soil mass, the face of which is then locally stabilized. A zone of reinforced ground results that functions as a soil retention system.

24 Types of Earth Retention Systems Soil Nails 24 Performed top-down via successive bench cuts

Types of Earth Retention Systems Soil Nails 25 Advantages Installation happens with excavation Usually the most cost effective per square foot Shotcrete face can be sculpted for architectural finish

25 Types of Earth Retention Systems Soil Nails 25 Advantages Installation happens with excavation Usually the most cost effective per square foot Shotcrete face can be sculpted for architectural finish Minimal vibrations Disadvantages Works best in cohesive soils that have good stand-up time Passive system so deflections are higher than other systems Requires close coordination between installer and excavator

26 Types of Earth Retention Systems Soil Nails Temporary Wall Permanent Wall 26

27 Types of Earth Retention Systems Soil Nails Installation of Permanent Shotcrete 27

28 Soil Nails Shotcrete Finishes Screed Finish 28

29 Soil Nails Shotcrete Finishes Stamped Finish 29

30 Soil Nails Shotcrete Finishes Sculpted Finishes 30

excavation Can minimize water infiltration Can be re-used 31 Disadvantages Tough

31 Types of Earth Retention Systems Sheet Piling Advantages Works in almost all soil conditions Readily Available from multiple suppliers Prevents soil loss during excavation Can minimize water infiltration Can be re-used 31 Disadvantages Tough installation through stiff/dense soils Steel is expensive Vibrations during installation

Installs very quickly and safely Limited to installing 30 from

32 Types of Earth Retention Systems Sheet Piling Installation Methods Newest, modern system for Sheet Pile Installation Installs very quickly and safely Limited to installing 30 from face of structure Length of sheeting limited Hydraulic Press No Vibration 32

very slow compared to ABI Crane Old system for Sheet Pile Installation Can install

33 Types of Earth Retention Systems Sheet Piling Installation Methods 33 Multipiler Excavator-mounted vibratory hammer Can work in low headroom conditions Generally very slow compared to ABI Crane Old system for Sheet Pile Installation Can install almost any length Can reach for installation Much slower than ABI Requires templates

Works in almost all soils Disadvantages Generally very expensive compared to other earth retention

34 Types of Earth Retention Systems Tangent/Secant and Slurry Walls 34 Advantages Can be built as very stiff system (reduced deflections) Can be designed to carry large vertical loads Good water control Works in almost all soils Disadvantages Generally very expensive compared to other earth retention systems Slow installation Requires more equipment and large setup area Wale installation difficult

35 Types of Earth Retention Systems Secant Wall - Installation 35 Holes are drilled in a primary/secondary pattern Hole grouted during removal of auger Reinforcement may be placed in the hole

36 Types of Earth Retention Systems Tangent Wall Gap Between Piers Tiebacks 36

37 Types of Earth Retention Systems Slurry Wall - Installation Wall is formed in panels Panels held open with slurry Reinforcement cage placed and grout pumped from bottom up 37

38 Specialized Types of Earth Retention Systems Jet Grout/Soil Mix Wall 38 Micropile and Lagging

39 Specialized Types of Earth Retention Systems Micropile and Shotcrete 39

40 Earth Retention Systems Internal Bracing Corner Bracing Cross-Lot Struts 40

41 41 Earth Retention Systems Internal Bracing - Rakers

42 Earth Retention Systems Ground Anchors Ground Anchors Consist Of: Anchor in stable soil Long tendon (usually steel cable) Connection to structure (usually a concrete block) 42

43 Earth Retention Systems Ground Anchors Anchor Installation Anchor Testing 43

44 Risks Associated with Earth Retention Systems Soldier Beam Settlement The Fix Installation of Brace 44

45 Risks Associated with Earth Retention Systems Soldier Beam Settlement Aggregate Pier 45

Dewatering 46 Soil Oozing from Lagging Cracks from

46 Risks Associated with Earth Retention Systems Footing Excavation fill with Water Site Not Dewatering 46 Soil Oozing from Lagging Cracks from Ground Loss Behind Wall Cracks in sidewalk from Ground Loss Behind Wall

47 Risks Associated with Earth Retention Systems Site Not Dewatering 47 Wall Settlement Cracks from Ground Loss Behind Wall

48 48 Risks Associated with Earth Retention Systems Sloughing Soils Soil Nail Wall

49 49 Questions

Soldier Pile Walls Soil Nail Systems Secant Piling Soil Mix Walls Underpinning Slope Stabilization

Soldier Pile Walls Soil Nail Systems Secant Piling Soil Mix Walls Underpinning Slope Stabilization www.malcolmdrilling.com Soldier Pile Walls Soil Nail Systems Secant Piling Soil Mix Walls Underpinning