Underpinning of Existing Foundations: Methods and Procedures
Credits: 1 PDH
PDH Course Description:
When does an existing foundation require underpinning—and how should the engineer select a suitable method without creating additional instability during construction?
Underpinning is one of the most critical interventions used to stabilize, strengthen, deepen, or extend an existing foundation. It may be required when a foundation becomes unstable, when the intended use or loading of a building changes, when nearby excavation affects the supporting soil, when groundwater conditions reduce bearing capacity, or when an existing shallow foundation must be transferred to deeper and more reliable strata.
This course provides a practical introduction to the selection, sequencing, and application of underpinning systems for existing walls, columns, and foundations. It explains the purpose of underpinning, the conditions that may justify its use, and the factors that influence the selection of an appropriate method, including building condition, foundation type, soil conditions, access limitations, required depth, vibration sensitivity, and the nature of the proposed work.
Participants will examine traditional pit underpinning, pile underpinning, wall underpinning, jack-pile systems, needle-and-pile underpinning, the Pynford stool method, root-pile or angle-piling systems, and methods used for underpinning existing columns.
Special attention is given to construction sequencing and temporary stability. The course explains why underpinning work is commonly completed in alternating sections, why only limited portions of a wall should remain unsupported, how needles, jacks, crib supports, bearing plates, shores, and temporary beams are used, and why temporary supports must not be removed until the new foundation has developed adequate strength.
The course also compares the practical applications of different systems. Pile underpinning is discussed for clayey soils, waterlogged sites, and weak bearing strata; jack piles are considered where competent bearing strata occur at greater depths and vibration must be minimized; and root-pile or angle-piling systems are introduced where access or large-scale excavation is restricted.
By completing this course, participants will be better prepared to recognize when underpinning may be required, compare available underpinning methods, evaluate site and structural constraints, understand construction sequencing and precautions, and coordinate safe strengthening solutions for existing foundations.
Topics:
By the end of this course, participants will be able to:
- Define underpinning and explain its role in stabilizing, strengthening, deepening, or extending existing foundations
- Identify structural, geotechnical, and construction conditions that may require underpinning, including settlement, weak bearing soils, groundwater changes, nearby excavation, basement construction, and changes in building use
- Evaluate the principal factors affecting the selection of an underpinning method, including foundation type, building condition, soil profile, access, vibration sensitivity, depth, and loading
- Explain the construction sequence and temporary-support requirements of the traditional pit method
- Apply key precautions for staged underpinning, including alternate-bay sequencing, wall support, trench protection, temporary shoring, and controlled removal of needles and jacks
- Compare pit, pile, jack-pile, and needle-and-pile underpinning methods based on site constraints and foundation conditions
- Describe the stages and applications of Pynford stool underpinning and root-pile or angle-piling systems
- Explain the principal considerations involved in underpinning existing walls and columns while maintaining temporary structural stability
To take this course:
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Intended Audience: This course is intended for civil, structural, geotechnical, and forensic engineers, as well as contractors and building officials.
Publication Source: Dr. Ibrahim Metwally, PE