Depending on the size, scope, and site conditions, identifying the proper load and pile capacity to ensure structural integrity is imperative for a successful job. The concept behind this calculation is simple, though, like anything with piling projects, there are numerous other considerations and obstacles that can be overcome with thoughtful planning and preparation.
Fundamentally the objective of any foundation is to transfer the structural load to the earth below it without overstressing the soil or compromising structural integrity.
Large private and civil projects require heavy piles with considerable load-bearing capabilities. We’re going to explore some concepts that address some of the most common concepts and questions regarding pile driveability and pile capacities.
Basic Load Transfer Concepts
Piling groups for foundations need to be proportionate and should only allow for a minimal amount of settlement when supporting the maximum combination of all loads. Dead loads include the weight of the pile cap and the subsequent load.
Applicable OSHA, local, state, and federal guidelines for permitting will outline the live load-bearing capacities and must be considered by the engineering team when developing a scope for any civil or private piling project.
Other factors to consider include lateral forces and moment reactions, including eccentricity between the column load and the center of the pile groups’ load-bearing capabilities.
An adequately calculated load from pile to soil is determined by established methods of analysis. These are based around three basic principles that evaluate potential failures.
- Failure of the individual pile due to a lack of structural capacity
- Failure of the earth surrounding the pile shaft itself and beneath the pile toe, which is also known as geotechnical capacity
- Installation stresses can lead to failure during pile driving
Pile driving equipment must be powerful enough to drive piles to penetrate the soil to meet the required geotechnical capacity. It’s important to protect the toe of the pile during driving to reduce the risk of damaged pile toes which can lead to catastrophic failure.
Piles must also be driven plumb to ensure stable load-bearing capabilities. The exception to this rule is if the plans require a pile to be driven to the specified batter angle.
Static Load Capacities, Computations, and Tests
Static load capacity is simply the amount of load the earth can support as imposed by all structural elements. Before any piling project begins, a static analysis must be performed to obtain a geotechnical analysis. This analysis will allow you to define the ultimate and allowable capacities for pile groups and individual piles.
These computations are necessary to estimate some essential components for every project. This will influence the number of piles required, the length of the individual piles, and the substructure design. The final static load capacity of single piles and pile groups is less than the structural capacity.
Static load tests are not only cost-prohibitive, but they are time-consuming. There are alternative tests to determine ultimate load capacity. Dynamic tests, including Osterberg Cells or Statnamic™ tests, require the designer to thoroughly and carefully analyze the test to evaluate the load capacity, and correct analysis of these tests is imperative to a successful pile driving project.
Pile driving equipment manufacturers pay close attention to the real-world necessities for projects of every size, and a consultation with a local vendor can help operators and contractors identify the right heavy machinery for the job. Larger projects may require two static analyses to determine the length and number of the piles needed to support design loads with the first analysis. The second inspection will inform the capacity necessary for the piling equipment.
Bearing Pile Capacity when Driven on Rock
When pile foundations are driven on rock, they have the capacity to bear the most significant loads. They often utilize steel h-piles, pipe piles, or precast concrete piles. Because specific analysis of the bedrock at depth is difficult to determine, there should be constant analysis during the driving process to ensure proper load-bearing capabilities.
Depending on the known conditions of the load-supporting rock, different diameters of piles can be used. Narrower piles can be loaded to their allowable structural capacity when driven on high-quality, firm bedrock. For piles on loose, weathered, or soft rock must be designed based on the results of pile load testing.
Clearly, there are considerable influences of different construction methods that determine the behavior of pile foundations. During every pile driving project, it’s essential to monitor construction during every phase to successfully complete every job and ensure structural integrity.
During the design phase, consider your static tests, soil analysis, and inspection considerations to provide piles that can support dead loads, live loads, and maximum load-bearing capabilities.
Every large private or civil pile driving job requires collaboration between the engineers, designers, operators, and contractors. Ensure that every aspect of the project complies with local, state, and federal guidelines to deliver a deep foundation that will provide powerful support for the heaviest loads.
