Foundations Foundation Engineering- Evaluating the ability to support a given structural load and designing the substructure or transition member needed to support the construction. To transfer the structural loads safely into the ground. This means dealing with forces and soil pressures. The need for deep excavations.
Foundations Spread Footings –Proper compaction under the footing Driven Piles –Types of piles Wood Concrete Steel Composite -Pile Drivers Drop Hammer Mechanical- Hydraulic, diesel, steam Vibratory Caissons or Drilled Shafts Cofferdams
Review Plans & Specifications Consistency with geotechnical report Reduce confusion during construction Without Differing Site Conditions clause contractor responsible Read the report in response to what is underground. –Understand prescribed method, consistency with soils report Site Investigations –Environmental restrictions –Site conditions at each and every location The report has pertinent information- follow it. Compaction testing –Understanding moisture content –Proper proctor
Importance of Geotechnical Studies Provide efficient foundations systems Improve bid accuracy Reduce change orders Reduce long term problems
Geotechnical/Soils Reports Recommendations Suitability of on site soil for structural fill Bearing capacity Foundation type Lateral earth pressures Pavements Drainage Seismic
Steps for Geotechnical Study Explore site conditions Perform lab testing Perform engineering analysis Prepare report Assist with plans and specifications Construction observations
Soil Report Borings or test pits To lab for: Moisture content Gradations Proctor test Consolidation, direct shear, triaxial
Pile & Pile Driving Site Investigation –Type & weight of structure –Soil properties –Depth of stratum –Variations of stratum depth –Availability of piling type –Availability of pile driver –Availability of experience in driving pile
Pile & Pile Driving (Site Investigation cont) –Comparative placement cost –EPA & OSHA regulations –Depth of excavation for placement of equipment ie building footing –Location of piling ie river, lake, ocean –Noise & Vibration –Adjacent structures
Pile & Pile Driving Pile Caps & Grade Beams –Piles are clustered then caped Number of piles per cap are determined by the load bearing capacity of the soil. From the cap comes a column or bent. Piles can be connected by grade beams
Caisson or Cofferdam What’s the difference? Caisson- Boring or drilling a hole and filling with concrete. Cofferdam- A temporary boxlike structure used to hold back water or earth while work is being done inside it.
EXCAVATION HORIZONTAL & VERTICAL LAYOUT BEGIN EXCAVATION SWELL AND SOIL TYPES UNSUITABLE SOIL STRUCTURAL FILL SITE DRAINAGE DEWATERING COMPACTION BACKFILL SAFETY MECHANICAL & ELECTRICAL
Excavation Wall Bracing No matter what restraining system is used to stabilize the sides of an excavation, the walls will have to be braced against lateral pressures exerted by the surrounding soil and water. Shoring for trenches (trench boxes) Lateral forces surrounding the structure –Slope back –Different shoring systems –Tiebacks (rock and earth)
Protection of Excavations Lateral Forces Deep Excavations Slope Back- Usually 2:1, The angle of repose at which a soil material will stand without moving Interlocking Sheet Piling Steel Soldier Piles- H beam with lagging Concrete Slurry walls- Shotcrete (pneumatically projected at high velocity onto a surface)
Other piling terminology Battered pile- A pile driven somewhat at an angle so as to resist horizontal forces. Kelly bar- The equipment on the pile driver that determines the height of the pile to drive.
Terminology In the industry terms can mean different things. Toe- (1) Any protection from the base of a construction or object to give it increased bearing and stability. (2)That portion of sheeting below the excavated material. (3) To drive a nail at an oblique angle. (4) The junction between the base metal and the face of a filled weld. (5) The part of the base of a retaining wall that projects beyond the face away from the retained material.
Excavation Need for Deep Foundations Removing ground water or dewatering Amount of material to be removed –Soil swell percentage For removal and replace Tons to cubic yards Protection of Excavation –Sheet Piling –Soldier Piles –Concrete Slurry Walls Excavation Wall Bracing –Slope back –Shoring –Tiebacks
Foundation Sequencing Drive Piling - Excavate> >[Slope protection/shoring system ]> Layout Piles>Drive Piles>Cut off piles>Fine grade/Compact>Structural Fill> Backfill to follow foundation system Drilled Piling (concrete)- Excavate> >[Slope protection/shoring system ]> Layout Piles>Auger piling>Fabricate Cage>Set reinforcing cage>Pour concrete pile>Fine grade/Compact>Structural Fill> Backfill to follow foundation system Spread Footings- Excavate >[Slope protection/shoring system ]> Layout>Fine grade/Compact>Structural Fill> Backfill to follow foundation system