1 / 24

Foundations

Foundations. Foundations. Feature common to bridge and building structures Deep vs. shallow Safely transfer dead and live loads with acceptable levels of settlement. Foundations. Shallow Foundations spread footings: column, combined, mat strip footings: walls

dennis-navarro
Download Presentation

Foundations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Foundations

  2. Foundations • Feature common to bridge and building structures • Deep vs. shallow • Safely transfer dead and live loads with acceptable levels of settlement

  3. Foundations Shallow Foundations • spread footings: column, combined, mat • strip footings: walls • placed on undisturbed or well-compacted soil • below frost line • consider effects of groundwater • typically reinforced or plain concrete

  4. Foundations Deep Foundations • Piles • driven or drilled • bearing capacity from end-bearing or skin friction: usually combination of both • driven plum or battered (1:6 to 1:3) • driven to attain minimum tip elevation or required resistance in blows per foot (bpf)

  5. Foundations Piles • Types • timber piles • precast/prestressed concrete piles • cast-in-place concrete • steel H-piles • steel pipe piles • composite • minipiles or micro piles

  6. Foundations Pile Driving • Equipment • mobile crane (usually crawler) • leads: fixed or swinging • hammer, helmet, & cushion • compressor (if air driven) • hydraulic unit (if vibratory) • steam plant (becoming obsolete)

  7. Foundations Pile Driving • Equipment • follower • mandrel • Pile accessories • point attachments • splices • pile to cap connections

  8. Foundations Pile Driving • Hammers • steam or air: single-acting, double-acting, differential • diesel hammer: single-acting (open end) or double-acting (closed end) • vibratory

  9. Pile Driving • Dynamic analysis - wave equation “WEAP” • based on wave propagation theory with input from the static analysis • provides relationship between pile capacity and driving resistance i.e.: equates capacity to blow counts • predicts pile driving stresses

  10. Pile Driving • Benefits of using wave equation • verify piles can be driven to required depth & capacity • determine minimum required pile section • avoid overstressing pile during driving • optimize cost

  11. Pile Driving • Dynamic testing - Pile Driving Analyzers (PDA) and CAPWAP • uses strain gauge & accelerometers to measure force & velocity (converts strain to force and acceleration to velocity) • field tests the driving hammer and system

  12. Pile Driving • Dynamic testing - Pile Driving Analyzers (PDA) and CAPWAP • cost effective method of optimizing the driving system and estimating static pile capacity • using CAPWAP, hammer blows can be analyzed to estimate skin friction, end bearing, dynamic damping factors, and soil stiffness

  13. Pile Driving Pile Load Test (static) • many tests have been used over the years to evaluate or confirm axial and lateral capacities • Quick pile load tests (QPLT) are most common • QPLT consists of constructing a reaction frame around the test pile • the frame is anchored to reaction piles • pile is incrementally loaded with an hydraulic jack

  14. Pile Driving

  15. Pile Driving Pile Load Test (static) • the test load is measured by a load cell • deformation is measured with dial gauges, wire-mirror-scale, and surveying instruments • apply load in 10 to 15% increments, maintaining a 2½ minute interval • check deformation readings immediately before and after applying load

  16. Pile Driving Pile Load Test (static) • incrementally increase load until reaching 200% of the design load or until continuos jacking is required to maintain the test load • remove the load in 4 equal decrements • plot the load-settlement data using the Davisson method • the point where the load-settlement curve crosses the failure criterion is the failure load (Qf)

  17. Pile Driving Other Factors • soil setup or “freeze” - common in clays • relaxation - much less common, found in some silts or fine sand • restrike pile to verify strength gain or loss • 120 bpf is practical, safe, upper limit driving blow count • 200 to 240 bpf is practical refusal

  18. Pile Driving Inspection • position, plumb, or batter • check cushion; change as necessary • record blow counts • verify correct operation of hammer • check splices • check piles for damage • check for heave

  19. Pile Driving Driving Records • prepare a sketch of foundation to identify piles and order of installation • Drive records include: • pile ID and order of installation • ground elevation – cut-off elevation • tip elevation – final length • blows per foot (final foot recorded in bpi) • driving duration – location of splices

  20. Foundations Retaining Walls • gravity or cantilever • components • stem wall • horizontal base includes: toe, heel, & key • weep holes for drainage

  21. Foundations Temporary Support Structures and • sheeting w/wales and tie-backs • soldier beams (piles) w/lagging • pipe sleeves • tremie concrete

  22. Foundations Underpinning • remedial or precautionary • remedial adds foundation capacity to inadequately supported structures • precautionary - higher loads or changes in ground conditions

  23. Foundations Underpinning • Temporary supports • shores • needle beams • grillage • Pit underpinning - used for installing or extending foundation walls or footings • Pile underpinning & various other methods

More Related