Humboldt H-4140 GeoGauge User Manual

Page 25

The Humboldt GeoGauge is a 10” diameter, 11” tall, 22 lb. electro-mechanical

instrument that when placed on the surface of the ground evaluates the stiffness

of the top 9” to 12” of material. It vibrates the ground over a range of discrete

frequencies, applies force, measures the resulting deflection and displays the

results in about a minute. It was chosen by Texas A&M because measurements

could be made quickly, it has no licensing or safety requirements and its

performance (reliability, precision & bias) had been proven by FHWA

Study 2(212).
Four sections of Salzburg Ct., Von Trapp Ct., Newburg Ct. and Sophia Lane

in College Station, Texas were constructed during October of 2000. The

construction consisted of 6” of lime-stabilized subgrade, 6” of soil-cement and

a 2” HMA surfacing. The Salzburg Ct., Von Trapp Ct. and Newburg Ct. Sections

received the stiffness control and the micro-cracking. The Sophia Lane section

did not. Site conditions were generally wet during construction. Bob Mosley,

City Engineer for College Station, supervised the work. Young Brothers, Inc.

accomplished the construction.
The micro-cracks were observed to greatly inhibit base shrinkage cracking.

Laboratory testing of core samples indicated that the base reached its design

strength. Apparently the micro-cracks were induced early enough in its life so as

not to significantly inhibit strength gain. In more than 18 months of observations,

the roadway sections constructed with the micro-cracking method exhibited at

least 50% fewer reflection cracks in comparison to the section that did not. A

corresponding reduction in roadway maintenance cost was also observed.
Texas A&M’s results prompted the City of Bryan, Texas to specify the

construction method in 2001

. As shown in the figure below, the QC test data

followed the results achieved in the Texas A&M study. The City of Bryan has

successfully used the method through the 2005 season. The City of College

Station, Texas followed suit shortly after College Station, adopting the City of

Bryan’s specification for continuous use.

2 Outline Specifications For Section 100 - Portland Cement Treated Base (Plant Mix), City of Bryan, TX, Rick Conlin, CME Testing &

Engineering, College Station, TX 77840