Northern States Power Co.
414 Nicollet Mall
Minneapolis, MN 55401
Evaluation and Rehabilitation
for the 500 K.V. Transmission Line.
Duration: 1993 through 1998
The 500 K.V. Transmission Line is carried by steel and aluminum towers.
The steel towers are supported by four cast-in-place concrete drilled piers.
Construction of the line extended from 1976 through 1980. During its
service life, the concrete foundations had shown some signs of deterioration. To preserve
the integrity of the line, Northern States Power Co. NSP, contracted Jaber Engineering
Consulting, Inc. JEC, to investigate the cause of the concrete deterioration of the
JEC performed a comprehensive Forensic
Engineering program to evaluate the concrete deterioration. The program included:
· Visual inspection of drilled pier
· Concrete coring and sampling.
· Laboratory testing and analysis.
· Petrographic analysis of concrete.
· Evaluation of concrete durability.
Our engineers determined the cause of the concrete deterioration and
provided NSP with repair options to restore the
integrity of the foundations.
NSP and JEC then conducted a pilot program to examine the feasibility
of the repair options and to select the most appropriate one for the foundation repair.
Based on the finding of the pilot program, NSP initiated a four-phase
repair program to repair the pier foundations over a period of five years.
During the repair program JEC provided:
· The construction
prints and specifications for the repair.
· Field inspection
for conformance with repair specifications.
· Concrete mix design and batch plant inspection.
· Quality control and field testing of concrete repair.
The 500 K.V. Project is unique and challenging. Site conditions
and remote locations of these tower structures presented an opportunity for all those
involved on the project to work as one team. The structures are found mostly in swampy
areas where access required careful planning and the use of Bombardiers.
JEC continues to provide NSP with value-added services in a very
responsive manner and a strong focus on quality.