Does The American National Standards Institute (ANSI)/American Society of Safety Professionals (ASSP) have a standard for installation & extraction of piles?
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The PDCA can provide input to future revisions to ANSI/ASSP A10.19-2017 in areas that relate to requirements found in the new OSHA crane standard and new general technology in the pile driving industry.
Is there a standard method of verifying
"I am having an issue with my pile driving contractor regarding the methods used to verify "pile plumb". I am looking for a general practice in testing a pile's plumb. The contractor has indicated they only use the 'survey method' to calculate slope. The geotechnical engineer on the project indicated that a four-foot level must be employed to verify plumb or the bottom of the pile may have 'kicked'. Is there a standard method of verifying the plumb of the pile? "
Responses are from PDCA members:
Some contractors in the Pacific Northwest use a six-foot-long level, instead of a four-foot level. This provides a little more accuracy when checking for pile plumb.
The same method applies to pile drivers in South Carolina additionally, just measure from the end of the level over to the pile to get your variance from plumb.
You can also use a four-foot digital level, which is what a New Jersey contractor does to verify pile plumb. Some four-foot digital levels will actually give you a LCD readout of the degree of plumb.
I am unfamiliar with the term "survey method" to calculate plumb. My experience is similar to that of your geotechnical engineer, where a four-foot level is used to determine plumb deviation from vertical (on H-piles). The level is set against the pile and plumbed vertically, and the gap between the pile and the end of the level not touching the pile is measured and reported, along with the compass direction of the lean (e.g., ¼-inch in four feet SW). Obviously, the longer the level, the more accurate the plumb deviation determination will be. Whatever method is used, the results must be compared to specified plumb deviation limits.
I received your question about verifying the angle of inclination on piles being driven on your project. It is common practice in the Gulf Coast Region for pile driving inspectors to require piles be checked with a carpenter's level, once placed, and prior to the start of actual driving. Because both timber piles and H-piles can have deviation over their length, the longer a level is, the more useful it can be. Timber piles can be the most difficult to have truly plumb at start and finish because of their irregular shape. H-piles can have a "sweep"/deviation in trueness due to improper handling and lack of support in shipment and handling.
All piles can be best controlled by the use of a positioning device at the base of the leads/pile gate. Additional alignment aids can be provided between the base of the hammer and the ground for maximum control of the pile during driving. It is not unusual for piles that have been verified as "plumb", prior to commencing driving, test as being out of plumb or off-position at final penetration. That phenomenon is explained by eccentricity of the pile/deviation from trueness, and differences in drive resistance encountered by the pile across its diameter. The worst-case scenario occurs when part of a pile's cross-section encounters debris, and influences the pile to move away from the additional resistance.
Do you know the impact of pile installation on soil mechanics and good ways of assessing it?
End of initial drive vs. re-strike after seven days
Author: Bill Marczewski, P.E., M.ASCE, BSM Engineering, Inc.
Published Q1 2014
Discusses the impact of pile installation on soil mechanics and ways of assessing it
Basic soil mechanics and pore water pressure
At the most elementary discussion of soil mechanics, one should recall and remember that individual soil particles in contact with each other can only transfer shear forces from one adjacent soil particle to another. This relationship is generally depicted at the micro-soil structure level. The space between adjacent soil particles is referenced as the 'void' area and is comprised of air when there is no ground water present, and is water when ground water is present. When water is present in these voids, or in the "pores" of the soil structure, we must consider the effects of pore water pressure changes during pile driving operations in order to understand our onsite observations.
Pile installation and pore water pressure
During pile driving operations, with both vibratory and impact hammers, the adjacent soil is disturbed in the localized region of the driven pile causing the pore water pressure to increase between the soil particles at the micro-soil structure level, thereby decreasing the available skin friction to resist pile installation penetration. When the soil disturbance from pile driving installation at the End of Initial Driving (EOID) has ceased, the pore water pressure in the soil begins to decrease or 'soil setup occurs' as the soil attempts to restore itself to the at-rest condition prior to disturbance from the pile driving operation.
The time it takes for the soil to fully recover from pile driving operations, or for the pore water pressure to fully dissipate, is often thought to be around seven days, or 168 hours, but is not exact. Many of the conditions associated with the change in the pore water pressure of soil during pile driving have been observed by pile contractors and monitoring inspectors for years. The value of these observations need to become a baseline of understanding for all parties involved in design and installation support leading to capacity determination of a driven pile. In doing so, a competitive edge will be established by those obtaining clarity in this simple, but often confusing, subject.
EOID versus Beginning of Restrike (BOR)
EOID is often associated with an increase in pore water pressure and a decrease in available skin friction to resist pile penetration during initial installation. This ease of installation is often associated with not achieving the required ultimate axial pile capacity. However, this is not an accurate representation of the soil resistance that is available, or the ultimate capacity available. The maximum soil skin resistance available can only be determined when the pore water pressure in the soil dissipates over time, or maximum at approximately seven to 10 days after EOID.
The value of accurate pile installation records is paramount to properly determining the final ultimate axial capacity. Termination of pile driving for equipment breakdowns, pile splices, shift changes, etc. should be clearly noted in the monitoring logs as well as the time associated with allowing the pile to sit undisturbed until initial pile driving is complete. For long piles driven to depths beyond 100 feet in order to meet minimum embedment criteria, the effect of pore water pressure and driving delays associated with pile splices or stops in driving should be carefully considered.
Piles driven to minimum embedment depth but not achieving the required ultimate pile capacity is a common observed installation condition, and to some degree, this condition should be expected. Such pile installation conditions warrant the need for the contractor to restrike these piles at varying time intervals after EOID. The time intervals between restrikes can be random but should be accurately reported.
Increased capacities resulting from BOR taken at two hours from EOID have yielded significant increases in ultimate axial capacity at some projects, while others have not been observable until 48 hours after EOID. In general, design engineers like to see the blow count associated with BORs occurring at the seven-day interval (168 hours) after EOID. The time associated with the seven-day BOR is often thought to be the time it takes for the soil pore water pressure to fully dissipate and allow the soil to restore itself such that increased axial capacities can be observed during pile restrikes.
Wave Equation Analysis Programs (WEAP) and predicted capacities
It should be understood that the observed axial capacity at the EOID will not, and should not, match the predicted capacity of a WEAP analysis that utilizes soil setup resistance models having time intervals greater than zero. A time interval of zero is the same as the EOID condition. When using the proprietary computer software program GRLWEAP™ produced by Pile Dynamics, Inc. it is important to recognize that these WEAP analyses are produced using a default time interval of 168 hours (seven days) to report their predicted ultimate resistance capacity. With this being the case, you should not expect a WEAP prediction using "setup time = 168 hours" to correlate with the onsite observed conditions associated with EOID, or "setup time = 0 hours." Because this time variable can be manipulated, it is recommended to perform multiple WEAPs associated with EOID (t=0 hours) and other time increments pertinent to the specific project needs.
WEAP predictions should be compared against actual driving conditions to validate their usefulness in pile capacity prediction. The use of wave equation analysis is a powerful tool to support driven pile installation projects and when incorporated with high strain dynamic testing using a Pile Driving Analyzer (PDA) to verify hammer performance can lead to exceptionally efficient pile installation projects.
Is properly illuminated pile driving SITES at night inherently more dangerous than A daytime operation?
As the typical job site is often crowded and the ground uneven, vision and communication between the crew is critical. Even well lit job sites at night reduce vision, causing hidden dangers to exist. Glare from artificially lighted job sites is an additional issue that can cause temporary loss of vision during pile driving operations.
There aren't many pile driving personnel that would not consider working at night to be more dangerous than working during the daylight hours. Additionally, production at night is lower, and damage to pile driving equipment is higher.
In regard to the question: Is properly illuminated pile driving at night inherently more dangerous than daytime operations?
The answer is yes. USACE specifications for hazard safety analysis (HSA) require nighttime operations to be very specific concerning work procedures, hazards associated with nighttime work and illuminating the site properly. They will check to ensure there is sufficient light (at a minimum) prior to night work starting. Any work performed at night has additional safety hazards regardless of the artificial illumination.
The hazards can include (this list is not exhaustive):
- Shadows created by locations of lights
- Reflection/glare from lights
- Eyes adjusting to dark and light changes (moving in and out of the lighted areas)
- People moving into the light from the dark (public, vehicles, crews, etc.)
- Noise from the light plans (if gas powered)
- Crews adjusting to working at night
- Crane operator adjusting to lights, especially looking up at tip of boom
- Weather affecting the work area
200 years & less than an inch of corroded material...
to corrode one-eighth of an inch
In disturbed soil (the top 10 feet) there is available O2 that is not present in undisturbed soil (below 10 feet). How long can this top 10 feet be considered as "O2 available" for a higher corrosion rate? I am assuming 15 years?
Within this top 10 feet there is a water table that fluctuates throughout the year. Does this slow movement of water continue to feed the "available O2," or does this water table not affect the "available O2?" (soil ph="6.8)" (resistivity =5,600 ohm-cm)
The following quotation from an article refering to a presentation by
Melvin I. Esrig, Ph.D., P.E., "Dr. Esrig then discussed commonly seen corrosion rates for various environments based on oxygen content and water conditions. The rates, from low to high, are typically quoted in millimeters per year in the published literature. The published rates vary between 0.015 mm/yr to 0.075 mm/yr. Based on the rates presented, it was estimated that it may require between 90 and 200 years for 0.125-inch of corrosion to take place for piles in water and in the ground, respectively, to occur. Based on these findings, the common engineering solution for sizing piles is to simply add this 1/8-inch to the thickness of the pile wall (A. Filotti added emphasis).
It was also found that the rate of corrosion might not be constant over the lifetime of the structure. The corrosion process often results in an oxidized protective layer that prevents further exposure to oxygen and decreases the corrosion rate. In mechanically active environments, such as marine wave action conditions, the mechanical action causes the protective layer to be removed and can maintain or increase the corrosion rate.
A case study by M. Romanoff of the National Bureau of Standards was presented wherein 40 piles were driven into various soil conditions and were allowed to corrode for as much as 40 years. It was found that the predominant form of corrosion was pitting, which was concluded not to be of engineering significance.
Dr. Esrig then went on to present various other case studies to illustrate the effects of low acid environments (US Steel Research Laboratory), high salinity environments (LNG facility in Cove Point, Md.), stray electric current (Jacob K. Javits Center, Manhattan, N.Y.), and H-piles near waterfront conditions (North Hudson Hospital & Watermark High Rise, North Bergen, N.J.).
The preferred engineering solution is to avoid the problem if possible. This is usually not a viable solution and the most common solutions include the use of concrete piles or adding protective coatings. Jacketing piles in concrete can be a solution if the conditions allow. Cathodic protection often results in high initial project costs and the need to be maintained. The most common solution is to add 0.125-inch of steel to the thickness of the piles. This may add costs to the project if it has not already been accounted for through driveability analyses or lateral capacity requirements. A brief discussion on the New York City Building Code requirement for all pile steel to be designed assuming a yield strength of 36 ksi or less, regardless of the true material strength, often results in piles that may have reserve capacity to account for 1/8-inch corrosion."
Reference and Credit to-
Full Article Referenced
When is Corrosion of Piles
a Potential Engineering Problem?