Bored pile design to EC7

Question 1

What is a problem with using alpha for design calcs?

Answer 1

It’s site specific, you need full data a priori
Cautious estimate
changes when the failure criteria change (needs recalibrating)
Stroud?

Question 2

In what circumstances is alpha reliable?

Answer 2

If you can calibrate it i.e. with lots of data (a database)

Question 3

If no load tests are carried out then partial factors are applied in ______. Design is based on data from ______

Answer 3

Full

Boreholes

Question 4

2 Methods of obtaining Cu data (one is lab one in-situ)

Answer 4

Triaxial tests

Site SPT measurements

Question 5

Stroud’s correlation says that the Plasticity Index varies by how much on site?

Answer 5

30-50%

Question 6

The characteristic value is drawn at the __ percentile, ______ to the ____ ____ trace

Answer 6

25th
parallel
lower bound

Question 7

What is Qwork?

Answer 7

Qwork = G + V. It includes no partial factors and G and V are un-factored loads - for comparative purposes only.

Question 8

What is the representative value?

Answer 8

Used in conventional design, derived by an eye fit to the data - for estimating the Cu equation.

Question 9

What are the shortcomings of design codes?

1) There is little guidance on…
2) Some codes specify the use of… while EC7… which is a…
3) Code drafters could adopt a ______ approach but….

BUT what benefit does using a cautious estimate have?

What adjustment do we need to make to calcs if average soil values are used (as oppose to CV)?

Answer 9

1) There is little guidance on how to construct design lines for the shear strength profile
2) Some codes specify the use of average soil parameters while EC7 requires the use of a ‘characteristic design line’ which is a ‘cautious estimate’
3) Code drafters could adopt a statistical approach, however this ignores the causes of ground variability

Using a cautious estimate allows the engineer a certain degree of flexibility

Higher partial factors