ETTL News & Views
Volume 12 • Spring 2004 Newsletter
The new electronic version of ETTL's Newsletter … Keeping you up to date on
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Piers and Piers! - Belled and Straight Shaft

ETTL PROVIDES CMT SERVICES FOR EXPANSION
PROJECTS AT CANTON JR. HIGH AND
UT-TYLER'S BIOMEDICAL RESEARCH FACILITY

The above photo, taken on a recent wintry day outside of Canton (Texas) Junior High School, shows an auger spinning out freshly removed soil, doing so under the watchful eye of an ETTL professional engineer, who was on site to observe the first pier installations and address any problems that might arise from ground-water or other sources. It symbolizes a branch of construction materials testing (CMT) highly familiar to ETTL's technical staff: making sure that piers, destined to support any of a wide variety of buildings or other structures, are being constructed in accordance with architectural specifications. Not only belled and straight shaft piers, as shown in this little article, but APG (auger pressure-grouted) cast-in-place piers as well, depending on subsurface soil conditions. There are hundreds upon hundreds of buildings in the wide geographic area served by ETTL whose piers were carefully monitored by our people during construction, and which, likely as not, had geotechnical studies carried out by ETTL beforehand. And ETTL's record with pier-supported structures is …faultless!

The two sets of photos below were recently taken at two typical project sites. The first (comprised of seven photos) was part of a major I.S.D. project at Canton, TX, which included expansion of the community's Junior High School. The second site was at the University of Texas Medical Center at Tyler, TX, whose Biomedical Research Facility was being expanded. ETTL carried out geotechnical studies for both sites, well before actual construction began, providing crucial data and recommendations for the foundation designs. As indicated by the photos, ETTL's CMT responsibilities, during actual pier construction, included (among others): checking the quality of borings; checking dimensions of both bored shafts and rebar cages; and checking concrete for air content and temperature, making slump tests, and taking samples of the concrete for subsequent compression testing in ETTL's laboratories.

The seven photos immediately below were shot on the premises of the Canton, Texas Junior High School, where 432 belled piers were being constructed to support an addition to the school's main structure. ETTL's geotechnical study of the subsurface had produced a recommendation that belling would be in order to provide needed bearing capacity. As those of our readers who are acquainted with this technology are aware, belled piers are used especially when water will not be present (when the water table will be deeper than the completed piers). The firm that carried out the drilling, Batten Drilling Inc., sent two rigs to the site. One used augers to drill each shaft to a depth of 15 ft; with diameters ranging from 18 to 30 in., as specified. The other rig was equipped to carry out subsequent belling at each shaft's base. Bell diameters ranged from 36 to 72 in.

Photo 1: In the first photo (top left) shot at Canton Jr. High, an ETTL technician logs findings, while the ETTL P.E. at the site holds a mirror to reflect sunlight down into the first drilled shaft of the scheduled 432 piers, double checking it to make sure things are off to a right start.
Photo 2: The two Batten rigs that carried out the drilling. An auger can be seen at the rear of the front rig, which has been pulled forward to make room for the belling tool to be put to work by the other rig. Stakes mark locations where other borings will be made.
Photo 3: ETTL staffers confirm the spread diameter of the belling tool.
Photo 4: The belling tool is then lowered into the first shaft.
Photo 5: After belling of a shaft has been accomplished, its rebar cage is lowered into it.
Photo 6: The cage's position and depth beneath ground surface are checked by ETTL.
Photo 7: Now the completed shaft is ready for concrete to be placed. (We noted, when shooting these photos at Canton, that the man in the white T-shirt seemed impervious to the cold!)

The four photos below were shot on the premises of UT-Tyler Medical Center's Bio-Medical Research Facility on the outskirts of Tyler. Some 38 straight shaft piers, each 30 ft deep with a 30-in diameter, were being constructed to support an expansion of the facility. A number of smaller, supplemental piers to support lighting units were also being constructed. ETTL had technical personnel at the site carrying out the same types of CMT services as at Canton.

Photo 1: In the first photo taken at the Bio-Medical Research Facility campus (at left above), ETTL technician Jacob Bruner watches as a hole is drilled.
Photo 2: Then, after checking the condition of the hole, he measures its depth.
Photo 3: In the third photo he monitors placement of the hole's rebar cage, after which the shaft is ready for concrete placement.
Photo 4: Some of the 38 completed 30-in piers are shown in the fourth photo.

ETTL, when carrying out its geotechnical study for this project some months before, had found that the site's subsurface called for the use of straight shaft piers, which are typically used where large loads need to be supported and where water may be encountered. They generally go deeper than the shafts of belled piers. Another difference is that straight shaft piers support their loads with skin friction, as well as (to a lesser degree) end bearing; while belled piers are designed for all of the load to be carried at the bottom end.

If you want more information about the geotechnical aspects of these ETTL services, see our web site's geotechnical section, or contact ETTL's Robert Duke, P.E. And for more information about our CMT services, see our web site's CMT (or CME) section, or contact Mark Miller, C.T.E., who manages ETTL's CMT field operations. Robert and Mark will be delighted to be at your service!

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