Lateral Earth Pressure Spreadsheet 9

[tre5205]

I was just curious if anyone out there has one or knows where to download a spreadsheet that computes lateral stresses from earth pressure and surcharge loadings?

Thanks
Tre

 

[FixedEarth]

You may find it worthwhile to get Advanced Foundation Engineering & Earth Retaining Structures books and then make your own program. The strip load is the hardest to program. You will need to incorporate uniform surcharge, point, line, seismic and strip loads and then add them to your active or at rest earth pressure profile.

"Substructure Analysis & Design" 2nd edition by Paul Andersen has a worked out example of strip load plus the equations. You need to be careful with radians. Azizi & Budhu have the other line load and point load equations. For seismic equations, you need to look for the Seed & Whitman paper of 1971.

 

[JAE]

tre,

I think it would be much better for you to write your own spreadsheet for this per FixedEarth's recommendation.

Doing this really helps one to better know the process and methods, limitations, etc. I've written one some time ago based upon some load charts. I'm never very comfortable using someone else's downloaded spreadsheet.

Almost as much work (if not more) to verify it - working through someone's spreadsheet logic can be a form of self-abuse.

 

[RFreund]

Have you guys made a spreadsheet per Bowels 4th edition where he recommends to use only the unmodified bousinesq equation for a point load; then subdivide a strip/area load into point loads and use plane strain? I went through and created these spreadsheets (basically huge matrices) and my solutions seem to match his example problems, in metric, however they seem to be 'off' for imperial unit problems but I can't see why they would be. I should probably create a separate post regarding this. There may be some free spreadsheets involved.

EIT

 

[FixedEarth]

Attached are the equations & they don't look scary at all. You may use Excel, Mathcad or a programmable calculator.

 

[RFreund]

FixedEarth - Nice Post! and I agree the modified equations are not scary.

I was referring to using only the unmodified boussinesq equation for a point load and applying to line strip and area loads.

Question - in your attached sheet for strip do you know what the modifications are to it. I always thought it was just an integrated form of the boussinesq for a point load, but I'm not sure if that is right.

EIT

 

[FixedEarth]

These equations are the same in NAVFAC, Canadian Foundation Engineering Manual and so on. The point and line loads are easier to program. The strip load has sine and cosine in radians. The strip load has the 2 factor in the numerator, but boussinesq does not have the 2.

Equations are different for all 3 cases - point, line and strip. However, you can get close values between strip and line load. For example, a strip load of 4 ksf and strip width of 4 ft, would yield similar results as line load of 1 kip/ft for the same setback distance.

 

[FixedEarth]

Correction- 1ksf strip surcharge over 1 ft width is similar to knife edge load of 1 kip/ft for the same setback. Here is a numerical example and the equations for a strip load surcharge.

 

[fattdad]

Just a word of caution: You are asking for lateral stresses from line or point loads, but you are not telling us the application. If this is to evaluate pressure acting on a retaining wall and the spreadsheet or equation that you are using is based on elastic theory (i.e., Boussinesq) you must double the calculated result.

Carry on. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[dik]

Fatdad...Why would you double the forces for a retaining wall? I would have thought that the movement would lessen them. Not disagreeing... I just don't know.

Dik

 

[fattdad]

a calculated elastic horizontal stress in an infinite elastic medium must be met by an increase on the acting side and also on the resisting side (i.e., the soil element is in static equilibrium). Next to a retaining wall you have an elastic half-space (i.e., there's no dirt on the side oposite the line or point load. So, the wall has to replicate the forces of both the load and the soil that's missing.

You would design the wall for either at-rest or active earth pressures. The calculated line loads are in addition to either of these states of stress.

f-d

¡papá gordo ain’t no madre flaca!

 

[dik]

Thanks...

Dik

 

[yakpol]

Here's a spreadsheet doing this work for multiple area loads. It's using pure Boussinesq formulas and allows to magnify the results. Macros do all calculations...

 

[RFreund]

I was going to start a seperate thread for this however I think that I can just use this thread. I've attached a spreadsheet with different sheets so that you can compare a pure bousinessq analysis with the modified elastic equations. Here is the situation:

First thanks Yakpol for posting as I was able to validate my bousinessq spreadsheet. Mine is much more messy as I need to take the time to learn macros/VBA. So great job. Our results match for area loads. However I tried to expand the calculation so that you can do strip, point and line. It also sums the pressures and returns a force resultant and location. The problem is that for a strip load the length (not the width) should be 1ft right (as you are working on a per foot basis)? The problem with this is that it yields very low values even doubling them does not come close to that of the modified equations.

Let me know if you have any questions/comments. I will also upload the bowels chapter which is what I used to derive the first sheet.

EIT