Tension crack along top of the cut Drilled Shaft Construction – Selecting the Appropriate Equipment and Tooling • The importance of bored piles in the deep foundation industry is noted, which includes drilled shafts, continuous flight auger (CFA)/augered cast-in-place (ACIP) piles, drilled displacement (screw) piles and micropiles. Bored piling is still the most widely used deep foundation system (comprising a market share of about 60%), especially when soil conditions are difficult or heterogeneous and when large axial and lateral loads are anticipated. However, the most common system is still drilled shafts performed using Kelly bar drill rigs. Selection of Drilling Equipment and Tooling The main elements that are considered when evaluating and selecting drilling equipment and construction procedures include: • Use of different types of deep foundations around the world, mod. after Bottiau (2015) Correct selection of the type of deep foundation system is one of the most important decisions in a project, and it is best to make this decision based on prior experience in similar ground conditions. The advantages and disadvantages of several construction procedures may impact the selection of the foundation type in any project. Selection of the type of deep foundation depends on many factors, including geological factors and soil conditions, local historic factors, and local construction customs. Different (and multiple) types of deep foundation systems are used around the world, as shown by Bottiau in his 2015 article “Current Status, Trends and Future of Deep Foundations” in the Nov/Dec issue of Deep Foundations. The following comments can be made about the different deep foundation systems being used today: • Driven piles are still in use, even with increasingly stricter restrictions in terms of noise and vibrations in urban areas. Alternatives for driven piles, which result in less ground vibrations, have been developed, such as drilled (partial or full) displacement piles and helical piles. Drilled displacement piles are feasible solutions in soft soil conditions. • Vibratory pile driving is being used less frequently despite the advancements made with construction equipment. • The use of drilled displacement piles has increased in use and market share. Until recently, this technique has been used only in specific areas in Europe. However, there has been increasing use of this technique in North and South America. AUTHOR Walter I. Paniagua, Ph.D., Pilotec DEEP FOUNDATIONS • MAR/APR 2018 • 69 Different construction environments for foundation piles There are essentially three main elements that will affect construction productivity and the successful installation of a drilled shaft foundation. • • Project Circumstances: environment, marine environment, limitations (available space, overhead/headroom restrictions, etc.) Project Characteristics: geometry (diameter, length) Soil Characteristics: variations, level of groundwater table, density or consistency, presence of boulders (quantity, diameter), rock quality and strength (RQD, unconfined compression resistance) Stratigraphic variations, spatial Prevailing conditions such as urban Quantity of piles, pile distribution, FEATURE ARTICLE
