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Spring 2006

Dear Colleague:

Once again, welcome to those of you who joined us since our last Newsletter. Our number of users continues to grow rapidly and we appreciate each of you for choosing Retain Pro, and for offering valuable suggestions that help us improve our service to you.

If you are a new user, or missed a previous Newsletter, they are posted on our Home page. In them we discuss important technical issues and we urge you to read them if you haven't done so already.

If you are a version 2005 user and you did not receive this newsletter by email, please correct your email address at

Status of Retain Pro 2007...

We hoped it would be out by now, but development of the new features is taking longer than we anticipated. It will be a major upgrade from version 2005, and should be ready by mid-summer - hopefully earlier. Some of the new features will be segmental retaining walls (both gravity and with geogrids), C.I.P. pier/pile foundations, LRFD for masonry stems, a unique equation-solver menu, user interface improvements, and other new features we think you'll like. Details will be posted on our website a few weeks prior to release. And as always, upgrades are optional and priced modestly. And for those who recently purchased, please be assured that the upgrade price will be less than our planned increase for new users.

A good year for construction!

This year to date, over last year, nonresidential construction is up about 12% and residential up about 7% (but inflation wipes out much of this). See We hope you are getting your share, and more, and that it will be a good year!

Technical Issues...

IBC '06 and ASCE 7-05.
They're out now, but it will take time for adoption by the various jurisdictions. You'll need both codes since for former heavily references the latter. On first read-through the changes affecting retaining walls appear minimal, with one important exception: Benevolently, they have deleted the onerous masonry lap splice requirement (2107.2.3 in IBC '02) and reverted to ld = 0.002dbfs.-48 bar diameters for Grade 60.

When to design for seismic?
IBC '06 appears to leave it up to the geotechnical report and the local building jurisdiction. See IBC '06, Section 1613.1. Also see ASCE 7-05, Section 15.6.1. Most geotech reports provide seismic information. However, this usually applies to buildings on the site and may not necessarily apply to site retaining structures. Check their intent.

If seismic design is required, select the appropriate kh factor.
It's design value for use in the KAE equation is not necessarily based upon peak ground acceleration. Perhaps the best reference is the NEHRP Part 2 - Commentary, Section 7.5.1 (e.g. kh = SDS/2.5).

Active pressure and sloped backfill.
This was mentioned in last summer's newsletter, but the question comes up often enough to repeat it: If you have a sloped backfill the active pressure will be higher (but remember on the toe side the earth is generally level so use a lower pressure on that side). The geotech report will state pressures to use for various backfill slopes based upon the nature of the soil - or you can use suggestions on page 27 of Basics of Retaining Wall Design. You need to enter both the increased active pressure and the backfill slope. This is because the overturning and sliding forces are computed based upon an assumed vertical plane at the back of the footing which intercepts the backfill slope at a height greater than the "retained height". So if you only enter the increased active pressure and not the backfill slope you will get an erroneously lower overturning and sliding. Note that if you use the Coulomb or Rankine method, where you input the angle of internal friction (phi) and the backfill slope, the increased active pressure will be automatically calculated, but you still must enter the backfill slope.

Boussinesq confirmed.
Sometimes simple do-it-yourself tests can be good teachers. For example, the Boussinesq equations for lateral earth pressure from an adjacent footing predicts a bulb-shaped pressure diagram with most of the pressure exerted on the upper half of the wall. Some engineers take an alternate approach, assuming the pressure under the adjacent footing spreads downward and outward at a 1:1 slope and therefore most of the lateral pressure is applied against the lower portion of the wall. Well, to experiment, I got into a children's sandbox and did a test that refutes for latter method: I took a three inch wide piece of wood shingle, about 18" long, and embedded it about 12" into the sand. Now all 200 pounds of me stepped on one foot, about 4" away from the shingle. Then I watched which way the top of the shingle moved. It moved away from my footprint, illustrating that most of the pressure does act higher on the shingle, thus confirming Boussinesq's theory. But you probably already new this intuitively, or from Soil Mechanics 101. When I did this experiment, some children nearby surely thought I was a deranged fool playing in a sandbox, but I learned something, much to their amusement. I did another sandbox experiment and got a surprise that seemed to contradict theory. I'll report later.

Version 6.1 users - final call!

Retain Pro 6.1 is now over three years old and we will be discontinuing support for this version on July 1st. If you have not upgraded, you can still do so at a substantial discount until 7/1/06.

Automatic Update System

This feature, which started with version 2005 and will be continued in version 2007, assures that you will never miss any patches or enhancements to the program. When you start Retain Pro there will be a pop-up asking if you want to check for updates. If you click YES it will either tell you none are available (you are current), or it will search your version and automatically enable downloading of any needed files. A description of the changes will be posted on the support page for your reference. This feature will also be useful as we add new features.

Reminder about your Product Activation Code (PAC)

With our PAC system, you don't need a CD to install Retain Pro 2005 on any office computer (subject to your license restrictions). Just download a demo version from, and insert your PAC to activate. If you lost your PAC, you'll need to call us - unfortunately we've had instances of unauthorized PAC use.

If you have suggestions or comments on these Newsletters, or a technical item to contribute, I'd like to hear from you.

With best wishes,


Hugh Brooks, SE
Retain Pro Software

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© 2006 HBA Publications. All Rights Reserved.