Calculation of Design load and Wroking load for soil nails BS8006:2011 - TfNSW 2

[NickWarrier]

Hi,

I am a graduate student from Melbourne Australia and my senior engineer has given me a task to develop an Excel sheet on soil nails referencing AS 4678 which only provides guides hence working with BS8006:2011 and CIRIA C637.

I am stuck on how to calculate the design load and Working load for soil nails .. Any guidance from anyone familiar with these codes

 

[EireChch]

Shows where exactly you are stuck, post your work and people will gladly help

 

[NickWarrier]

So basically, I am developing an Excel Design sheet for Soil Nailed Walls referencing AS 4678 and a design guide from Chris Bridges. I am stuck in finding out Ultimate Pullout Load which I need to find bond stress. I am using CIRIA 637 for reference.

CIRIA 637 refers to clause 8.9.2 which states that the ultimate pullout load can be found by multiplying the design load with a factor of 1.5.

I am stuck on what can be the design load and Working load. Is it a Bolt property supplied by the manufacturer?

I am attaching a reference for CIRIA 637. Any help from anyone familiar with this code would be helpful.

 

[EireChch]

Nick - I was hoping someone more experienced in soil nails than me was going to comment but not yet. I have done a quick review and some comments below.

I agree the C637 is unclear as to what the design load is. From my interpretation I believe the design load is the load that the nails have to support which comes from the geometry of the slope, loads applied and nail spacing/length/diam.

In CIRIA 637, Eurocode 7 is considered. In EC7 you work out Design Approach 1 Combination 1 (DA1C1) or Design Approach 1 Combination 2 (DA1C2) , generally.

For (DA1C1) and (DA1C2) you apply factors to increase your loads and factors to reduce you parameters (or keep them the same, i.e. your factor is 1).

For example, you will have your known loadings which will come from maybe a temporary construction surcharge loading (assume 10kPa) or whatever. You apply different factors for (DA1C1) and (DA1C2) to determine what your loads are. So your unfavorable design surcharge is 10kPa x 1.5 = 15kPa for DA1C1 and 10kPa x 1.3 = 13kPa for DA1C2.

Based on you factored loads and parameters you do a global stability analysis (manually or by slope stability software) using DA1C1 and DA1C2 and work out what load is applied to the soil nail. This is your design loading.

Re working load - I was looking through CIRIA and FWHA2003 and couldn't find the definition of "Working Load". I have ran out of time today but will keep looking for you. Hopefully a soil nail expert will reply in the mean time.

 

[PEinc]

The soil nail design load is the available amount of soil to grout bond that is available beyond the critical failure plane and which provides the required safety factor for global stability. Designing soil nail walls is an iterative process as the software searches for the critical failure surface. The soil nail design load can vary from nail level to nail level depending on 1) how long you input the nail lengths per each level, 2) the vertical and horizontal nail spacings, and 3) the nail angles below horizontal.

http://www.PeirceEngineering.com

 

[NickWarrier]

Thanks to both EireChch and PEinc - Good to have inputs from seniors always..