Soil Constants for a soldier wall with lagging

[jonnywalker]

Its my first time designing a retaining wall and i cant seem to find equations for Ka and Kp. Im using this

http://vlee.utpl.edu.ec/VLEE/LinkClick.aspx?fileticket=piymgNPD1d4=&tabid=142&mid=520

adobe file to do the design. It seems fairly simple, but they just seem to HAVE these constants...I have an EFP of 40-60pcf a wall height of 12.5 and a top grade of 1/2, how do i come up with the K values?

 

[PEinc]

No offense intended, but if you do not know how to determine Ka and Kp, you really should not be designing a retaining wall. Ka and Kp are in every soil mechanics book.

 

[jonnywalker]

No you are definitely right. This is my first project out of college and it is a retaining wall. I did not have a soils class in colege. I just i thought id ask on here before i went and asked a superior. Thanks for responding though.

 

[PEinc]

In the simplest form (using Rankine earth pressure coefficients), Ka = tan^2(45 -phi/2) and Kp = tan^2(45+phi/2) where phi is the soil's angle of internal friction and the soils in front of and behind the wall are flat. Things get more complicated with sloping ground in front of or behind the wall, with varying types of soils, with surcharge pressures, short term vs. long term, drained vs. undrained, active vs. at-rest, cohesion, cantilevered vs. braced or tiedback, specified design requirements (e.g. AASHTO, AREMA) etc. You have a lot of reading and questioning to do.

 

[jonnywalker]

Yes i managed to find those equations shortly after my post post. Thanks for the response.

 

[GeoPaveTraffic]

On a larger note, how does one get a structural engineering degree without a single soils class?

 

[InDepth]

jonnywalker - at least you are asking for assistance. You'll need to learn this subject thoroughly. You'll find out that 60- 70% of the PE exam is on soil mechanics and retaining walls. I would suggest the following text with the Design Solutions Manual that has several design examples.

Civil Engineering Reference Manual for the PE Exam, 10th Edition (Hardcover)
by Michael R. Lindeburg (Author)

 

[GeoDocinFL]

Sadly, many universities are being forced to limit the number of credit hours for undergraduate engineering degrees. This means that, among other bad decisions, they are making courses like Soils I electives, and not requirements for Civil Engineering students.

 

[kslee1000]

Geo:

If any civil engineering program does not make at least 1 geotech class as mandatory, it shouldn't exist, or be allowed to offer BS in civil engineering degree.

 

[DRC1]

A good "how-to" reference would be J. Bowles "Foundation Analysis and Design" He goes through both the geotechnical and the structural portion of design of foundation and retaining structures. It is a good place to start.