5
conditions and rate of strength deterioration from corrosive
conditions from previous corrosion studies.
CTL Report
Results from TPL2(68 level) Pumping Station were pub-
lished September 2019(CTL, 2019). Four eight-foot resin
bolts installed between March and May 2015 were over-
cored and tested (see Figure 7). The primary finding was
that corrosion was due to anions: heavy local corrosion at
the anchor head. Worst case bolt life of about 7 years to
maintain at least 15 tons capacity. Of the 4 reenforced rebar
bolts tested, low pH was the primary corrosion element.
Assumptions are linear relationship to loss of cross- sec-
tional area (see Figure 8) and Table 4 based on the worse
case corrosion rate of 0.027 inches ^2/year. Each of the
bolts analyzed were subdivided into thirds, and labeled near
anchor, mid span, and deep end zones (see Figures 9 and
Figure 10. Note heavy pits in the the near anchor section
of the bolt, thought to be from exposed steel without resin.
Pump Room TPL2(68 L) failed pull tests
Major findings of the September 2019 CTL Report is
as follows:
• Corrosive attack occurred on all extracted bolts in
varying degrees along the length, but degree decreases
with depth along the bolt. Heavy pitting attack and
general attack was present in first third of each bolt
(closest to tunnel, ear anchor). Pitting attack and
general corrosion were present mid-span on each
extracted bolt. General corrosion was present on the
inner-most embedded section (the deep end) of each
extracted bolt.
• A significant amount of form sulfur in the of sulfate
was present in scale on the surface of the in-service
bolts. Arsenic and chloride were also present in some
areas.
• It also was reported that the used bolts possessed sig-
nificant residual resin/grout and rock material from
embedment however, on delivery only one bolt pos-
sessed some grout and no rock material was observed
on any of the bolts. The grout was easily removed
Figure 7. TPL2 or 68 level pump station area of bolt testing
and overcoring in 2015
Figure 8. Predicted worst case of 7-year resin rebar bolt life
based on worst case corrosion rate of 0.027 sq inches/year.
From CTL, 2019 report
Figure 9. Diagram of bolt cross section showing zones of
near anchor, mid anchor, and deep end zones from (CTL
2019)
Table 4. Surface area and %loss from (CTL, 2019) bolt tests
conditions and rate of strength deterioration from corrosive
conditions from previous corrosion studies.
CTL Report
Results from TPL2(68 level) Pumping Station were pub-
lished September 2019(CTL, 2019). Four eight-foot resin
bolts installed between March and May 2015 were over-
cored and tested (see Figure 7). The primary finding was
that corrosion was due to anions: heavy local corrosion at
the anchor head. Worst case bolt life of about 7 years to
maintain at least 15 tons capacity. Of the 4 reenforced rebar
bolts tested, low pH was the primary corrosion element.
Assumptions are linear relationship to loss of cross- sec-
tional area (see Figure 8) and Table 4 based on the worse
case corrosion rate of 0.027 inches ^2/year. Each of the
bolts analyzed were subdivided into thirds, and labeled near
anchor, mid span, and deep end zones (see Figures 9 and
Figure 10. Note heavy pits in the the near anchor section
of the bolt, thought to be from exposed steel without resin.
Pump Room TPL2(68 L) failed pull tests
Major findings of the September 2019 CTL Report is
as follows:
• Corrosive attack occurred on all extracted bolts in
varying degrees along the length, but degree decreases
with depth along the bolt. Heavy pitting attack and
general attack was present in first third of each bolt
(closest to tunnel, ear anchor). Pitting attack and
general corrosion were present mid-span on each
extracted bolt. General corrosion was present on the
inner-most embedded section (the deep end) of each
extracted bolt.
• A significant amount of form sulfur in the of sulfate
was present in scale on the surface of the in-service
bolts. Arsenic and chloride were also present in some
areas.
• It also was reported that the used bolts possessed sig-
nificant residual resin/grout and rock material from
embedment however, on delivery only one bolt pos-
sessed some grout and no rock material was observed
on any of the bolts. The grout was easily removed
Figure 7. TPL2 or 68 level pump station area of bolt testing
and overcoring in 2015
Figure 8. Predicted worst case of 7-year resin rebar bolt life
based on worst case corrosion rate of 0.027 sq inches/year.
From CTL, 2019 report
Figure 9. Diagram of bolt cross section showing zones of
near anchor, mid anchor, and deep end zones from (CTL
2019)
Table 4. Surface area and %loss from (CTL, 2019) bolt tests