Do not forget the flatwork

In 2012, less than 2 years after ACC (Austin Community College) opened the new campus in Round Rock, Texas, school officials had to budget $2,000,000 to make repairs associated with expansive clay soils.  Fortunately, most of the problems had to do with the flatwork and not the building.  Too often geotechnical engineers focus attention to the buildings (in this case structurally supported slabs cast on void boxes and constructed on concrete drilled piers) but not enough attention to pavement and flatwork in expansive clay soil environments.

Geotechnical work had been performed by Raba Kistner and architectural detailing by GSC Architects.  Uncertain who were the Structural Engineer and Civil Engineer.

One media source reported that some type of soil improvement was attempted in the flatwork areas (6 feet deep of lime injection possibly?).  However, flatwork (sidewalks) had heaved so severely in some areas that doors could not be opened or closed properly.  Good quality geotechnical reports will address the concern with a structurally supported building slab abutting exterior flatwork.  Sidewalks had to be closed due to tripping hazards.

In 2015 ACC reported that soil movement resulted in surface water (rainwater) entering Building #3000 during heavy rain events.  Heaving and shrinking clay soils will change surface drainage profiles, and both the Geotechnical Engineer and Civil Engineer are responsible for addressing this concern with property owners or developers.

Construction repair bids included one $434,000 proposal to install surface drainage swales, install pedestrian grates over the swale, resurfacing of building flatwork to correct drainage issues, and installation of new stormwater drain along one face of Bldg. 3000.

A photo of sidewalk reconstruction efforts is below.  When you consider the $2,000,000 budget for flatwork and drainage repair, I cannot stress enough how important geotechnical, structural detailing, and civil engineering plan detailing are with regards to flatwork and pavement in expansive clay soil environments.  It starts with the Geotechnical Engineer properly informing the project team of the risks and concerns, and the Civil Engineer and Structural Engineer to formalize final design details.

The purpose of this post is to warn fellow Geotechnical Engineers and Civil Engineers (site grading and drainage) to pay more attention to detail on expansive clay soil environments.  The geotechnical study for this site was probably on the order of $20,000, but omissions of recommendations for dealing with flatwork abutting buildings cost the client $2,000,000 for a $114,000,000 facility.  Ouch.