HOW TO USE LATERAL SOIL BEARING IBC TABLE 1804.2?

[jgeng]

In designing an anchored bulkhead without specific geotech info, is it right to use the lateral bearing values in the IBC table 1804.2 for passive resistance at toe of pile? These numbers seem very conservative? What assumptions do they include do they include? What if the soil is submerged how do/should you use this value...backcalc a Kp multiply against an assumed submerged unit weight? Also, seeing the IBC values are conservative, are there any minimum factors of safety prescribed in the code for design, I cannot find them? Any help help would be appreciated.

 

[TDAA]

I hate that table.

If you have any condition that is not textbook, straight to the point, no deviation, then the values are conservative. If there is anything out of the ordinary, _anything_, get the geotech information you need.

Factor of safety applied? well, you can only determine that if you know the actual conditions and appropriate values, right?

 

[DRC1]

Go to slideruleera's website ( I thinkt is slideruleera.net, but I am not sure and download the US Steel Steel Sheetpiling Design Manual. This is a great reference for designing bulkheads. Typically for sandy soils a bouyant wt of 65 pcf is a value I will use absent any better information. Bulkheads can be designed with two diffent approaches to factor of safety. One is to use no factor of safety to calulate geoemetry and stresses. Then the toe is increased 20%. The other method which I use is to derate the passive pressure by a factor of 1.5. I ussually compute passive pressure based on log sprial theory. Hope this helps.

 

[cntw1953]

Just a few suggestions on how to figure out a table from any source.

1. Search the table for footnotes, usually contain usefull information for better understanding, or references for further reading.
2. Contact the source directly.
3. Looking for person that has the similar experience in the forum/communities as you have done here.

If all failed, I would do:

4. Backcal a few values given in the table:
- Determine soil type and set its properties from reputable sources, textbook in general.
- Calculate and compare the results (note, for certain type of soil this may involve several cals. For example, sand - internal friction ranges from 27 - 35 degrees, density ....so on)

After that, your number may or may not come close. If not, you have to repeat the whole cycle again, or give up using the table you don't understand.

I will do the above for my own good only (understand how the table was constructed). For real project, get geotech involved, unless you are quite confident on what you are facing.

 

[msucog]

consult a geotech...and yes those tables are conservative in the sense that it's impossible to accurately describe every site with a handy dandy table. get a geotech to give you site specific information. it will also reduce your liability and ultimately give the client a more cost-effective design/product.

 

[msquared48]

In all likelihood, consulting a geotech will get you much higher allowable values than these tables, saving design and construction $$$.

He will also need to know the type of structure involved in the design, as some structures are less critical than others, so the pile is allowed to impart a larger load to the soil matrix.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask