The following are notes to myself that may be of interest to contractors.
Sections
- 6 Reasons for Corrosion Protection
-
How much Corrosion Protection should be provided and what options are available when site specific conditions are unavailable?
- 6 Reasons for Corrosion Protection
There are 6 reasons why corrosion protection must be provided on all projects (unless this firm receives an environmental or geotechnical engineering statement that corrosion protection may be relaxed and the building official approves the statement):
#1: The 2016 California Building Code requires it for any site conditions with “possible” deleterious action.
Because a Civil/Structural Engineers design is subjected to the building department having jurisdiction, there may be other local requirements in local codes. However, we can reasonably check the CBC for general requirements throughout the state. The following excerpt is from the 2016 California Building Code:
1810.3.2.5 Protection of materials
“Where boring records or site conditions indicate possible deleterious action on the materials used in deep foundation elements because of soil constituents, changing water levels or other factors, the elements shall be adequately protected by materials, methods or processes approved by the building official. Protective materials shall be applied to the elements so as not to be rendered ineffective by installation. The effectiveness of such protective measures for the particular purpose shall have been thoroughly established by satisfactory service records or other evidence.”
The City of Los Angeles Research Report #26163 for SafeBase Push Piers requires corrosion protection in its product approval conditions. It states:
“Corrosion resistance and longevity of the foundation support system shall be addressed by the registered design professional on a job specific basis.”
#2: The Civil/Structural Engineering practice’s “Standard Level of Care” reflects an appropriate concern and requirement for the longevity of materials used in design.
Civil/Structural Engineers shall perform their services consistent with the professional skill and care ordinarily provided by engineers practicing in the same or similar locality under the same or similar circumstances. This “Standard Level of Care” is what a jury of peers would reasonably do in a similar situation. That is, amongst most other civil/structural engineers, would they also require corrosion protection in the absence of information of the soil conditions? The answer from our perspective is yes because engineers error on the side of conservativism for public safety.
#3: Despite the contractor’s lifetime (or less) warranty on the materials, a Civil/Structural Engineer is required to fulfill his/her professional obligations to the building occupants/owners.
The Civil/Structural Engineer is hired as a consultant to ensure the appropriateness of the design to perform its intended function over time. Because a contractor and/or material supplier may no longer provide services of any kind at any future time, the specified material should be adequately protected against corrosion.
#4: Civil/Structural Engineer’s professional liability insurance does not cover gross or willful negligence.
A building owner may hire an independent Civil/Structural Engineering consultant to perform a peer review of the engineering design immediately after the design is completed (prior to construction). The peer reviewer may notice that the material specification does not include corrosion protection when deleterious actions may be possible in unknown soil conditions. The project’s Civil/Structural Engineer would then be found to be grossly or willfully negligent in not specifying corrosion protection. Because professional liability insurance does not cover gross or willful negligence, the Civil/Structural Engineer’s personal assets would then be exposed to forfeiture in a lawsuit.
#5: The underpinning industry’s best practices is to use steel that has corrosion protection.
Most manufacturers of helical piles and push piers provide steel that has corrosion protection as a standard on every project. To deviate from the norm, would be unwise and creates bad optics in a courtroom.
#6: Material that detaches from the push pier or bracket during corrosion can enter subterranean aquifers causing harmful chemicals to drinking water.
Corrosion protection will greatly limit the potential for continuous deterioration of the steel during corrosion. Without protection, steel contaminants may pass through the soil (vertically or horizontally) in the water movement through underground strata layers.
For all of the above reasons, corrosion protection must be provided on all projects that do not have an environmental or geotechnical engineering statement that corrosion protection may be relaxed and the building official approves the statement.
- How much Corrosion Protection should be provided and what options are available when site specific conditions are unavailable?
In Table 1 of the City of Los Angeles Research Report #26163, the following footnotes are provided:
As stated in the footnotes, the engineer must determine “actual” capacity and “expected corrosion loss” (footnote 1) and “actual corrosion loss” (footnote 3) from site specific conditions.
Because the 0.036inch lost thickness is an estimated calculated value from a formula based on certain assumed site conditions, it was provided by the authors as a “for reference only” value. Typically, “for reference only” implies that it may or may not be appropriate for use on any actual project, unless the project’s soil conditions falls within the same criteria used in the calculation of that value.
The question then arises what did Section 3.9 of ICC AC358 assume and does the assumed cover all of the best and worst possible sites? Above ground or underground? Disturbed soils and undisturbed soils?
The ICC AC358 provides this equation for bare steel thickness lost with respect to time:
where t = 50 years for the calculated result of 0.036inches
ICC AC358 does not reference the research that this equation is borrowed from. It turns out that ICC AC358 has retrieved this equation from another published source (Federal Highway Administration NHI-00-044, 2000 based on National Bureau of Standards “Circular 579” authored by Romanoff in 1957) for disturbed soils. This document developed the above equation to estimate loss on after removing various steel materials from various disturbed soils, soils with varying degrees of corrosion situations from mild to severe.
The disturbed soils region for retrofit underpinning construction against concrete footings is usually within the upper 3ft to 5ft of soil where oxygen is trapped during soil excavation and replacement. This would effectively be the region of the bracket and sleeve which are subjected to ongoing corrosion due to the presence of the trapped oxygen in the replaced soil. {For the steel shafts that are embedded below this upper disturbed region, the corrosion potential is negligible (as concluded in a later study) as there would not be trapped oxygen.} Thus, the engineer needs to take into account corrosion in the upper disturbed regions.
ICC AC358 Section 1.2.2 gives the limitations of the soil’s severity for which the equation is applicable. Also, ICC AC358 Section 1.2.2 states the types of severe soil conditions that are not acceptable for installation:
1.2.2 …corrosion situations as defined by the following:
(1) soil resistivity less than 1,000ohm-cm;
(2) soil pH less than 5.5;
(3) soils with high organic content;
(4) soil sulfate concentrations greater than 1,000ppm;
(5) soils located in landfills, or
(6) soil containing mine waste.
The following table is provided for reference as an example from an actual underpinning retrofit project’s soils report that concluded the soil was very corrosive. It shows the descriptions for the corrosion parameter’s thresholds:
In the above example, the soils conditions are considered highly severe.
The ICC AC358 equation for estimating loss in thickness is based on an empirical study that has typical site conditions (mild to severe soils). So, if an actual job site conditions are typical and within the ICC AC358 section 1.2.2 limits, the calculated estimated loss in thickness (sacrificial thickness) is a valid method for designing for corrosive conditions across 50year life of the structure.
Near the end of Section 3.9 of ICC AC358, the following was provided:
“Corrosion loss shall be accounted for regardless of whether devices are below or above ground or embedded in concrete.”
All of this engineering firms designs uses the reduced thickness value for all projects in the upper disturbed regions and lower undisturbed regions.
However, the appropriateness of unprotected steel is still in question as there may be atypical highly severe site conditions, such as that indicated in the example above, that do not fall within the limits of ICC AC358 section 1.2.2 and thus the equation for estimating loss in thickness is not applicable for the undisturbed soil region. It seems that a greater loss is to be expected upon atypical highly severe soil conditions.
Section 6.8 requires that a site specific study must be conducted to determine corrosive conditions:
6.8 …a site-specific foundation and soils investigation report is required for proper application of these products. The foundation and soils investigation report shall address corrosive properties of the soil to ensure that a potential pile corrosion situation does not exist.
Section 6.1 reiterates the evaluation reports must include the aforementioned limits from 1.2.2:
6.1 The device or system shall not be used in conditions that are indicative of a potential pile corrosion situation as defined by soil resistivity less than 1,000 ohm-cm, pH less than 5.5, soils with high organic content, sulfate concentrations greater than 1,000 ppm, landfills, or mine waste.
The ICC AC358, specifically states that any soil condition beyond these limits should not use steel piles, even piles that are powder or zinc coated. This is not the code, but it further highlights the need to know if there are atypical highly severe soil conditions.
For some projects, the building owners elects to not engage a geotechnical engineer to perform a soils study. In those cases, we have no site specific information on corrosion situations.
Therefore, in the absence of site specific information, to be in compliance with the 2016 California Building Code’s 1810.3.2.5 corrosion protection requirement, this firm accepts either of the following approaches:
-
Design for all conditions, from mild to severe to highly severe (assuming there are atypical highly severe soil conditions outside the limits of ICC AC358 section 1.2.2 that would create deleterious actions so that we can be in compliance with the code in the case that there are, upon later discovery, soil conditions that would create deleterious actions). One might reasonably use 2 or more of the following common protective measures in combination,, to limit the effects of highly severe conditions:
- Sacrificial thickness loss in steel material (already used on every project’s design)
- Sacrificial anodes / cathodic protection
- Galvanization
- Powder coating
- Bonded coating
- Polyethylene encasement
- Sacrificial thickness loss in steel material (already used on every project’s design)
- Instead of replacing the soil in the upper 3ft to 5ft of excavated soil, specify the contractor pour a non-air entrained concrete around the bracket and sleeve so as to surround bracket and sleeve from future oxygen.
-
Require a site specific soils corrosion test to determine if the soil conditions fall within the parameters of ICC AC358 Section 1.2.2. If this is the case, the common protective measures listed above may be used individually if the soil condition are within the limits of ICC AC358 Section 1.2.2.
-
Review soils reports for properties in the immediate vicinity of the subject site to determine if any nearby sites have highly severe corrosive conditions.
- Prohibit the use of any steel, protected or not, to be in compliance with ICC AC358 Section 6.1 and 6.8.
FOUNDATION ENGINEERING 