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Excav & Deep Foundations Fall 09
 

Excav & Deep Foundations Fall 09

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  • Shallow Transfer Load @ Base of Substructure - Not Transferring @ Some Greater Depth Requires Suitable Soil Bearing @ Footing Elev. Column and Wall Footings - Individual or Combination Least Expensive - Minimal Construction Below the Habitable Space Deep Transfer Load @ Far Below the Surface - Sometimes 100’s of Feet Penetrate Unsuitable Soil to Reach Competent Soil or Rock Piles or Caissons - Drive or Drill to Reach Capacity Expensive Compared to Shallow Foundations Extending the Construction Limits to Compensate for Poor Soil @ Substructure
  • Typical Sequence Drilled - Rig and Casing - Large “Crane” with a Drill/Auger Attached (Big Post Hole Digger) Have to Accommodate Drilled Material Bell or Tip Enlargement - Typically 30-45 Degree Permits a “Wider” Distribution of Load Soil must have adequate Cohesion Inspected/Bottom Tested - On Larger - Personnel Lowered into “Hole” Inspect Bell, Test Soil @ Bearing Reinforce Spiral Cage Lowered into the Hole Pour (& Raise Casing) - Tremie- Prevent Segregation Often do Not Require “Cap” - Rather the Column Placed Directly On Top of Caisson
  • Site for caisson installation Note casings
  • Drill rigs
  • Drill rig drilling a caisson hole
  • Auger
  • Auger tip
  • Drill rig set up at a caisson locate & drilling hole
  • Auger removed from hole and excavated earth ‘shaken’ off
  • Casing being lowered
  • Casing lowered into drilled hole
  • Removing water (& mud) from the bottom of the drilled hole
  • Special ‘tip’ to clean the bottom of the drilled hole
  • Inspector getting set to be lowered into the drilled hole to inspect the bottom
  • Inspector examining the bearing surface Note the double casing
  • Reinforcing cage being installed
  • Concrete placement
  • Concrete placement continues as the casing is removed
  • End Bearing - Load Transferred to Tip - Driven till REFUSAL or adequate support - Firm Resistance @ Rock or Dense ‘soil’ Bearing Strata Must Be Reachable Friction - Pile “Side” Frictional Resistance - Bearing Capacity from Frictional Resistance Used - Bearing Strata Too Deep to Reach Driven to Predetermined Depth or Resistance Best in Silt, Clay, & Sandy Soils
  • Materials Wood - Timber - Economical - Capacity 10-35T Draw Backs - No Splices, Decay, Split w/ Driving Steel - H-Piles, Steel Pipe - H-Piles - Mostly for End Bearing, Capacity 30-120T Pro - Displace Little Soil, Convenient Lengths, Splice Con - Corrosion, Can’t Inspect After Driving - Straight? Steel Pipe - Mostly for End Bearing, Capacity 50-150T Closed or Open End Driving Typically Filled with Concrete Closed - Displaces Considerable Soil Concrete - Site Cast, Precast - 60-120T Shapes - SQ, Round, Octagonal, etc. Prestressed or Conventional Reinforcing Adv. - High Load Capacity, No Corrosion, $(Econ.) Displace considerable soil Composites & other Materials
  • Pile tips
  • Cluster of pile driven to desired depth, BUT not yet cut to the correct elevation
  • Pile cluster – driven and cut
  • Load Distribution - Pile Cap - Placed on Pile Clusters Piles Joined by Pile Cap - Reinforced Concrete Cap END OF SEQUENCE
  • Mandrel - tight fitting liner to prevent casing shell from collapsing and then withdrawn Number of Proprietary systems Primary reason to site cast - economy Some proprietary types of sitecast concrete piles. All are cast into steel casings that have been driven into the ground; the uncased piles are made by withdrawing the casing as the concrete is poured, and saving it for subsequent reuse. The numbers refer to the methods of driving that may be used with each: 1. Mandrel driven. 2. Driven from the top of the tube. 3. Driven from the bottom of the tube to avoid buckling it. 4. Jetted. Jetting is accomplished by advancing a high-pressure water nozzle ahead of the pile to wash the soil back alongside the pile to the surface. Jetting has a tendency to disrupt the soil around the pile, so it is not a favored method of driving under most circumstances.
  • Pile cluster – driven and cut
  • Strip footing poured
  • Good to Poor Structural Properties RANGE: ROCK - EXCELLENT PEAT / ORGANIC MAT’L - POOR / UNSTABLE AND UNSUITABLE TO BUILD ON Particle Size BOULDERS - UNSUITABLE / REMOVE - TO - CLAYS - EXTREMELY FINE Drainage / Water Retention COURSE SOILS - BOULDERS GRAVEL, SAND - DRAIN WELL FINE SOILS - SLITS, CLAYS, & ORGANIC - RETAIN WATER Cohesionless to Cohesive COURSE GRAINED SOILS (GRAVEL/SAND) - NO MEASURABLE SHEAR RESISTANCE CLAYS - COHESIVE - MEASURABLE SHEAR RESISTANCE W/O CONFINING FORCES
  • Rarely one type - often a Mixture and/or different “Strata” COMPLICATES THE DESIGN INCREASES THE NEED FOR SUBSURFACE INFORMATION Distribution of soil type and Particle Size Important in Predicting: Load Bearing Capacity Soil Stability RETENTION OF ENGINEERING PROPERTIES UNDER VARYING CONDITIONS; ROCK, GRAVELS, SANDS, & SSOME SILTS - STABLE CLAY (SWELLS & SHINKS W/ WATER) , ORGANIC - POOR Drainage Characteristics Ability to drain - Fdn walls, WHAT IS THE BEST SOIL FOR A CONTRACTOR /Owner TO BUILD ON? DEPENDS: ROCK - STABLE BUT DIFFICULT TO REMOVE SAND/GRAVEL - DRAINS WEEL BUT NOT COHESIVE W/ SOME CLAY - COHESIVE, BUT OFTEN DRAINS POORLY
  • Common on projects with high loadings Bearing Capacity - # Blows/Unit (ft) Soil Strata & Water Table Data NEEDED FOR DESIGN, ESTIMATION, CONSTR. Loads transmitted deep into soil Soil Samples PARTICLE SIZE LIQUID LIMIT (water content - plastic to liquid state) PLASTIC LIMIT (H2O content; plastic to solid state) WATER CONTENT SHRINKAGE SHEAR AND COMPRESSIVE STRENGTH Expected consolidation and Rate (under load) Sample Holes Strategically Located WHY? Information used to prepare Soils Report PROVIDED TO DESIGNER & CONTRACTOR SOIL INFORMATION & WATER TABLE RECOMMENDS: SUITABLE FDN TYPES DEPTHS & BEARING CAPACITIES EXPECTED SETTLEMENT RATES BENEFIT TO DESIGNERS??? PROVIDES NECESSARY DESIGN INFORMATION BENEFIT TO CONTRACTOR??? EXCAVATION & BACKFILL METHOD, SOIL RETENTION SYSTEM, FORM AGAINST SOIL?, H2O TABLE LOCATION ALSO - BASIS FOR EXTRA IF ACTUAL CONDITIONS DIFFER!
  • Unit of Measure (Estimating & Mgm’t)) Excavation & Backfill Cubic Yards (CY) Grading Sq. Ft. or Sq. Yd. Productivity Issues Type of Operation (Mass or Ltd./Confined) LARGE QUANTITY?, OPEN SPACE, ETC. Type of Material (Soil) ROCK VS CLAY SAND VS ROCK Material Transportation EXPORT / IMPORT DISTANCE DISTANCE TO MOVE AROUND ON SITE Expected Environmental Conditions Weather WINTER, SPRING, ETC.? WET, DRY, ETC.? Economy Labor availability, etc.
  • Unrestricted Site “ ROOM” ON THE SITE Restricted Site MIMIMAL ROOM NEXT TO A BUILDING OR STRUCTURE OR STREET, ETC.
  • Bench and/or Angle of Repose “ NATURAL SLOPE” Steeper for cohesive soils Must have perimeter clearance Considerations Water Diversion SITE WATER - DIVERT OR COLLECT OFTEN - TOP AND BOTTOM Bank Erosion PROTECT BANK - VISQUEEN, TARPS, ETC. Safety WORKMAN BELOW - PROTECT AGAINST BANK COLLAPSE Storage of Backfill NEEDED TO BACKFILL AGAINST STRUCTURE Most likely - least expensive
  • Soldier Beams and Lagging Sheet Piling DRIVE PRIOR TO EXCAVATION Slurry LAYOUT WALL DIG WITH CLAMSHELL, FILL W/ SLURRY BULKHEADS, REINF. & POUR
  • Sequence PRIOR TO EXCAVATION- DRIVE H-PILES (SPACED) EXCAVATE & INSTALL LAGGING BACKFILL - REMOVE LAGGING REMOVE H-PILES COMMON - EASE & COST MUST HAVE ROOM TO INSTALL FOUNDATIONS
  • Wood, Steel OR Precast DRIVE PRIOR TO EXCAVATION PULL (OR LEAVE) - (WOOD WOULD NOT LEAVE) - IF LEFT MAY BE OBSTRUCTION TO UTILITIES , IF POUR AGAINST – MAY be a PROBLEM W/ WATERPROOFING AND EXTERIOR FDN DRAINAGE DRIVING MAY CAUSE DAMAGE TO SURROUNDING STRUCTURES
  • Steps in constructing a slurry wall. (a) The concrete guide walls have been installed, and the clamshell bucket begins excavating the trench through a bentonite clay slurry. (b) The trench is dug to the desired depth, with the slurry serving to prevent collapse of the walls of the trench. (c) A welded cage of steel reinforcing bars is lowered into the slurry. (d) The trench is concreted from the bottom up with the aid of a tremie. The displaced slurry is pumped from the trench, filtered, and stored for reuse. (e) The reinforced concrete wall is fled back as excavation progresses.
  • Provide Temporary Bank Support DON’T HAVE ROOM TO LAY BACK RESTRICTED SITE - EX; DOWNTOWN SHEETING (SOME TYPE) Unbraced - Cantilevered NO BRACING REQUIRED - CANTILEVERED DRIVEN INTO GROUND Braced Crosslot Bracing Rackers and Heel Blocks Tiebacks DISCUSS ADVANTAGES / DISADVANTAGES Crosslot Bracing SIDE TO SIDE - INTERFERES WITH EXCAVATION AND “FOUNDATIONS”? Rackers and Heel Blocks LESS COSTLY, BUT STILL INTERFERES Tiebacks - EXPLAIN; DRILL, TENDONS, GROUT, CURE, STRESS
  • Pump(s) Placed in “Low” points ELECTRIC, GAS, DIESEL SUCTION HOSE AND DISCHARGE LINE Requires clearance around excavation Most Common Often - Least expensive SUMP PUMPS AS SOIL BECOMES MORE PORUS, AND WATER TABLE RELATIVELY HIGHER (HIGHER VOLUME OF WATER) LESS OF AN OPTION
  • Superstructure ABOVE GROUND Substructure BELOW GROUND - HABITABLE Foundation
  • QUAKE ZONES ALLOW THE GROUND TO MOVE LATERALLY w/o damaging the building ISOLATORS ACT AS A PARALLELOGRAM - KEEPING BUILDING LEVEL
  • Reasons It May Be Required Failure of the Existing Foundation Often Settlement Change in Building Use EX. - Install Heavy Equipment New Construction Adjacent to an Existing Blg. - COMMON
  • Enlarge Existing Foundation Increase Bearing Area Install a New Foundation - Footing, Piles, Caissons Stabilize Surrounding Soil - Grout, Chemical Stabilization, Mud Jacking Problems Can be Dangerous to Workman & Occupants - Often - Must Provide Temporary Support - Jack to Relieve Loads, Support while Constructing Existing Utilities and Other Obstructions - Invariably In the Area Limited Working Space - Slow, Expensive, Difficult, Specialized - Specialty contractors with the Required Equipment for Difficult Projects Liability - During and After Construction
  • Sheets - Plastic, asphaltic, synthetic rubber GENERALY APPIED TO THE OUTSIDE - H20 PRESSURE DISADVANTAGE - COVERED, LEAK INSPECTION? Coatings (asphaltic) GENERALY APPIED TO THE OUTSIDE - H20 PRESSURE DISADVANTAGE - COVERED, LEAK INSPECTION? SPRAYED, BRUSHED, ROLLED Cementitious Plasters APLIED INSIDE OR OUTSIDE - OFTEN INSIDE - CAN SEE DISADVANTAGE - BRITTLE / CAN CRACK Bentonite clay GENERALY APPIED TO THE OUTSIDE - H20 PRESSURE DISADVANTAGE - COVERED, LEAK INSPECTION? BEST / MOST EXPENSIVE SWELLS TO SEVERAL TIMES ITS DRY VOLUME Protection Board APPLIED TO COATING PRIOR TO COVERING FIBER, ASPHALT, ETC Waterstop PLACED AT JOINTS –Where MOVEMENT POSSIBLE SYNTHETIC RUBBER, EXPANSIVE CLAY, ASPHALTIC
  • Waterproofing w/ protection board & Stone
  • Drainage Matt
  • Spread Footing
  • Strip Footing Excavated & reinforced

Excav & Deep Foundations Fall 09 Excav & Deep Foundations Fall 09 Document Transcript