Considerations and Criteria for Driven Piles Design

Driven piles, also known as displacement piles, are a type of building the foundation that provides structural support by transferring the load to layers of soil or rock with appropriate bearing capacity and suitable settling characteristics. These are the most cost-effective deep foundation solutions used by civil and structural engineering design companies that are widely used to support buildings, tanks, towers, walls, and bridges. They are also suitable for embankments, retaining walls, bulkheads, anchorage structures, and cofferdams.

The pile cap and piles are the foundation's principal components. Piling work is increasingly common in bridge construction because they are less expensive to build than cast in situ bored piles. Continuous research, prototype, model pile, pile group testing, and the development of more precise analytical models contribute to a better knowledge of pile foundation behavior.

In this article, I will mainly talk about the types of driven piles, design considerations, and criteria for driven piles.

Types of Pile Foundation

Some of the types of the pile based on the material are:

Steel Piles: They are easy to handle and drive in great lengths. Because of their small cross-sectional area and strong strength, they are simpler to penetrate in firm soil. Steel piles, such as micro piles, can also withstand heavy loads applied from bridges, while other varieties can handle medium-level loads. The biggest problem with steel-driven piles is corrosion. They can be easily severed or welded together. If the pile is driven into low pH soil, there is a chance of corrosion. They are, however, located below ground level. As a result, the presence of oxygen has a negligible effect on corrosion. However, the risk is not as significant as one might imagine. In permanent works, tar coating or cathodic protection can be used. Steel piles are further classified into steel H piles, micro piles, screw piles, steel box piles, steel pipe piles, etc.

Pre-cast concrete piles: These piles can be square, octagonal, cylindrical, or sheet. They are percussion-driven piles utilized in situations when bored piles would be ineffective due to flowing water or excessively loose soils. These are often long-lasting and corrosion-resistant and are frequently utilized where the pile must extend above ground. However, in some saltwater applications, the durability of precast concrete piles is also an issue. In addition, lengthy and precast concrete piles are more difficult to handle and drive than steel ones. They can reach up to 30 m and have a load range of 300-1,200 kN.

Composite Piles: They were first used around 60 years ago. The primary goal of composite piles was to build significantly longer piles at a lower cost. Further, they could be made up of a variety of materials. And, this material must be chosen to meet the requirements. The following combination is possible. A section of a timber pile put above groundwater may be prone to insect attack and degradation. To avoid this, concrete or steel piles are constructed above groundwater level, whereas woodpiles are installed below groundwater level. Composite piles are made from a variety of materials. Furthermore, the material must be chosen to meet the requirements. The following combination is possible. A section of a timber pile put above groundwater may be prone to insect attack and degradation. To avoid this, concrete or steel piles are constructed above groundwater level, whereas woodpiles are installed below groundwater level.

Cast-in-Place Concrete: They are concrete shafts cast in thin shell pipes that are top-driven into the soil and usually have a closed end. These piles have a capacity of up to 200 kips. The main advantage over precast piles is that lengths can be changed by cutting or splicing the shell. These have a comparatively cheap material cost. When driving through hard soils or rocks, they are impractical.

Timber Piles: Typically short, low-capacity piles are generally affordable. They may be advantageous in some situations, such as corrosive groundwater. Loads are typically restricted to 70 kips, so the piles are quite easy to handle. It is to be mentioned that untreated timber piles are especially prone to rot, insects, and borers. They are readily destroyed while driving hard and are difficult to splice. Thus, a lumber pile tip diameter less than 14 meters long should be greater than 150 mm. When the length exceeds 18 meters, a tip with a diameter of 125 mm is suitable. Also, the timber must be driven correctly and not into hard ground.

Design Considerations and Criteria for Piles

Some of the design considerations that are needed to be followed by a civil and structural engineering design company are:

The load-bearing capability of the piles is critical. When estimating the capacity of a pile foundation, it is critical to consider the pile spacing as well as the capacity of individual piles. The lateral load resistance of the piles may also be relevant, as lateral loads can cause substantial bending stresses in a pile.

According to the design, the pile will be driven up to the hard soil layer designated as the termination level. The information provided in the soil investigation report will be used to develop and select the termination level.

The wave equation analysis of piles (WEAP) serves as the foundation for the pile termination and driving criteria. Any necessary changes will be made on-site, as they may vary depending on the actual ground conditions.

The pile foundation must perform as intended for the duration of the structure's life. The performance of a pile can be defined in terms of structural displacements, which can be just as damaging to a structure as a pile failure. The load capacity shall not deteriorate over time owing to pile material deterioration.

It is standard practice to apply safety factors to the ultimate load expected, either theoretically or by field load tests. These safety criteria should be chosen with caution, taking into account various aspects such as the implications of failure and the number of knowledge designers have gathered regarding subsurface conditions, loading circumstances, structure longevity, and so on.

Load capacity is affected by whether the soil is cohesive or cohesive. It is worth noting that the final bearing capacity of a pile in the soil is equal to the sum of the toe and shaft resistances. For calculating reasons, it is commonly assumed that the shaft friction resistance and toe bearing resistance can be computed independently and that these two components have no effect on each other.

The type of loading influences the determination of foundation properties. Soil strength or stiffness, and hence pile capacity or stiffness, can vary depending on whether a load is vibratory, repeated, or static and whether it lasts a long or short time. As a result, soil-pile characteristics should be calculated for each type of loading to be considered.

The load capacity of single piles and pile groups increases as relative density increases. The amount of change in relative density is also affected by the pile type. Closed-end pipe and precast concrete piles, for example, enhance the relative density of cohesionless material more than minor displacement steel H-pipe or open-end pipe piles.

High pore water pressures are generated by the disturbance and radial compression, which temporarily lower soil shear strength and, as a result, the driving resistance and load capacity of piles. As the clays around the pile reconsolidate, the high pore water pressures decrease, increasing shear strength and pile load capacity.

Skin friction on a pile in silt is a two-component barrier to pile movement caused by the angle of internal friction and cohesion operating along the pile shaft. As with sand, the percentage of resistance caused by the angle of internal friction is limited to a critical depth, below which the frictional portion remains constant. If the fraction of resistance contributed by cohesiveness is sufficiently large, it may necessitate a limit.

Conclusion

The fundamental design for usual loads should be efficiently altered to withstand extreme loads without catastrophic failure. Before beginning construction, proper planning is essential to handle equipment, the site, and transportation. However, structural damage that hampers operating capabilities and necessitates extensive rehabilitation or replacement of the structure is possible. In addition, if available sizers are brought from the market, the building and design of driven piles must be completed. Otherwise, they must be manufactured to the necessary size and length.

Judith Morrison is an expert in the field of industrial engineering and writes articles related to piping, civil, equipment engineering related articles.