ADOT put together a great little video embedded below that shows the construction of a drilled shaft foundation, or caisson as they are also known, for a bridge on the Loop 303 project in Surprise, AZ. The foundations shown are 88-feet deep and the rebar cage weighs in at about 20,000 pounds. The hole takes around 80 cubic yards of concrete to fill (that’s 8 concrete trucks). The video shows the fabrication of the cage, drilling the hole, and picking up and lowering the cage. My favorite part is the perspective of the video taken from the top of the cage as it is picked up and lowered, very cool. [Source: ADOT Blog]
Standards and Codes
Changes in Geotechnical Engineering Practice in Arizona
[Editor] Note: NCS Consultants, LLC is Randy Post’s full time employer…ie. my day job! [/Editor]
There are some significant changes being made to the state of the practice in geotechnical engineering in Arizona. NCS Consultants, LLC has prepared three policy memoranda for the Arizona Department of Transportation or ADOT that have been issued to consultants all over the State. These memos are on the topics of bearing capacity and settlement of spread footings and retaining walls, the design of drilled shaft foundations in gravelly soils, and the preparation of drilled shaft axial capacity charts for use by bridge engineers.
Although primarily applicable to upcoming ADOT projects implementing the AASHTO 2007 LRFD code, the memos will have a ripple effect down through other local agencies within the state who frequently defer to ADOT guidelines for geotechnical engineering. Also, the memos and the ADOT/NCS approach to LRFD implementation in geotechnical engineering were presented by NCS at the 2008 TRB Conference in Washington D.C., and many other state DOTs and the FHWA were very excited about the memos. The approach used if not the exact content may become a model for other agencies. More info and links to download the policy memoranda are provided after the break.
Geologic Hazards
Landslide on Arizona SR 87 Closes Highway
On March 21, 2008 a landslide caused the closure of Arizona State Route 87 between Payson and Phoenix near mile post 224. So far there are no official estimates as to the size, but based on aerial photos, it appears to be at least 50,000 sq-ft in plan. The offset at the head scarps was approximately 2-meters (6.6-ft) according to AZGS Geologists on site. It appears to have been a rotational slide as the toe of the landslide heaved the southbound roadway up by as much as 1-meter (3.3 ft). There was an existing soil-nail retaining wall on the slope that was destroyed by the slide as well. Lateral deformations can be seen in photos of the median barrier and the roadway striping. The deformations extended into the northbound lanes as well. More photos and links after the break. (Photo by ADOT)
Miscellaneous
ADSC 2008 Faculty Workshop Wrapup
Robert Thompson of Dan Brown and Associates has posted a wrapup of the 2008 ADSC Faculty Workshop. They had 20 Civil Engineering faculty attend the event. The field demonstration day was hosted by DBA at the Trial’s Training Center in Sequatchie, Tennessee. Apparently that site is Dan’s hobby. Read more about the workshop itself and also read Robert’s post about the field demonstration day including photos. In the photo at right (Robert Thompson, DBA) you can see the Statnamic test setup for a drilled shaft. A little more about the event:
Long Foundation and Hayward Baker have installed examples of several foundation and retaining structures, including drilled shafts, micropiles, and soil nails. During the field day demonstrations, the attendees will observe additional installations, load tests, and non-destructive testing.