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Practical Advice for Foundation Design – Micropiles for Structural Support - page 21 / 25

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GSP 131 Contemporary Issues in Foundation Engineering

direct chemical attack might be an indication of strong corrosion potential. If all the conditions listed in the first column of Table 5 satisfy the conditions listed in the fourth column of Table 5, the ground is classified as non-aggressive with respect to

corrosion potential.

5.5.3 Corrosion Protection Systems.

Corrosion protection for the central

reinforcement can be provided by physical and chemical protection or a combination of both. Most commonly used are grout, epoxy coating (minimum thickness 0.4 mm, galvanizing, or encapsulation with a sheath (PVC or HDPE of minimum thickness 1

mm)). during

It is not practical installation, it will

to protect the external surface of the be abraded by the soil around it.

drill casing, since Section 4.5.7.4 of

AASHTO (2002) includes a provision to deduct 1.6 mm from the shell the concrete filled pipe to allow for “sacrificial” steel loss. Other values (Table 6). A summary of recommended systems is provided in Table 7.

thickness for may be used

SOIL TYPE

25

50

75

100

Not Aggressive

0.25

0.60

0.70

0.80

Barely Aggressive

1.00

1.60

2.00

2.50

Very Aggressive

2.50

4.00

5.00

6.00

Table 6. Minimum dimensions (mm) of sacrificial shell thickness as corrosion protection (after FHWA-SA-97-070).

SERVICE LIFE (YEARS)

Table 7. Corrosion protection requirements for micropiles.

LOADING GROUND Casing

Reinforcin g steel

CORROSION PROTECTION TENSION1

COMPRESSION

AGGRESSIVE2 a. Do not rely on

casing for capacity

load

a. epoxy coating3 OR b. galvanization3 OR c. encapsulation in

plastic sheath3 AND Grout cover4

NON AGGRESSIVE a. None required if tension load on casing is less than 20% of casing thread strength OR

  • b.

    Do not rely on casing for load capacity

  • a.

    bare steel5

OR b. epoxy coating3 OR c. galvanization3 OR d. encapsulation in

plastic sheath3 AND Grout cover4

AGGRESSIVE2 a. Min. 1.6 mm

corrosion loss on outside The Specifier may use a different

corrosion loss per Table 5-12.

a. Grout cover4 AND The Specifier may desire to add other options listed for tension.

NON-AGGRESSIVE a. None The Specifier may use different corrosion loss per Table 5-12.

a. Grout cover4

NOTES:

1.

Permanent tension or temporary tension (e.g., wind, seismic, impact) on critical structures. For temporary tension on normal structures, corrosion protection for compression may be used.

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