Lecture20-Drilled-Shafts

Lecture20-Drilled-Shafts - Foundation Engineering...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Foundation Engineering Foundation Engineering Lecture #20 Lecture #20 Drilled Shafts L. Prieto-Portar 2010 Introduction. Drilled shafts are the most popular of deep foundations, because they have the capability that one single shaft can easily carry the entire load of a large column from a tall building. This means that a pile cap is not needed, which not only reduces that expense, but also provides a smoother flow of the stresses from the column into the bearing soils. Drilled shafts are similar to auger-cast shafts, although drill shafts are much larger, usually greater than 2.5 feet in diameter. ackground of Drilled Shafts Background of Drilled Shafts. Drilled shafts were originally developed by General Gow in Chicago (1880’s) as an extension of shallow foundations, and until the 1920's most were hand dug. The Chicago Well Method used a wooden "barrel" form to prevent collapse of the soil. Drilling rigs were developed for oil drilling, and then adapted to shaft drilling. The same is true for the technology of the cutting tools, casing and drilling mud, that were all developed in the oil industry and then advanced with drilled shafts. The Advantages of Using Drilled Shafts. 1. A single drilled shaft replaces a group of piles and their pile cap. 2. Shafts can be constructed in denser soils and are easier than driving piles. 3. There is no noise or ground vibration compared to pile driving. 4. Piles driven into soils may produce ground heaving which can cause previously driven piles to move laterally. 5. The base of a drilled shaft can be enlarged to provide a greater resistance to uplift (under-reaming or “bell”). 6. The surface over which the base of the drilled shaft is constructed can be visually inspected. 7. Drilled shafts have very high resistance to lateral loads. Disadvantages of Drilled Shafts.- The designer needs a greater knowledge of the subsurface conditions.- The large concrete volumes require careful supervision.- Drilled shafts may induce ground loss to adjacent retained structures, and thus, possible increased liability.- Inspections and supervision are far more complex and expensive. Types of Drilled Shafts. Soft soil Soft soil Soft soil Soft soil Straight-shafted pier Rock or hard soil Belled pier Good Bearing soil Belled pier Good Bearing soil Straight-shafted pier socketed into the rock Rock Construction: the Chicago and the Gow Methods. A) The Chicago Method. 1. Circular holes are excavated by hand for depths of 2 to 6 feet. 2. The sides of the hole are lined with vertical lagging boards. Steel Ring Lagging 3. The boards are then held together with steel rings. 4. The excavation continues for the next 2 to 6 feet, etc. The Construction Sequence of Drilled Shafts using the Chicago Method. Initiating drilling Introducing casing Cohesive Soil Caving Soil Cohesive Soil Cohesive Soil Caving Soil Cohesive Soil Soil Slurry Drilling with slurry Casing is sealed and slurry is being removed from interior of casing Cohesive Soil Caving Soil Cohesive Soil Cohesive Soil Caving Soil Cohesive Soil B. B....
View Full Document

This note was uploaded on 09/07/2011 for the course CEG 4012 taught by Professor Staff during the Spring '10 term at FIU.

Page1 / 57

Lecture20-Drilled-Shafts - Foundation Engineering...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online