Underpinning and Foundation Refurbishment Techniques - Procedures, Design and Safety Requirements - Extended Abstract

Oct 24, 2026

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Extended abstract outlining underpinning and foundation refurbishment to safeguard built heritage, emphasizing the need for safe, practical temporary and definitive construction techniques when rehabilitation enables overlap of new construction. Reviews key procedures, systematizes steps for micropiles and jet grouting, and consolidates safety requirements and essential project features. Includes an introduction on constraints and selection factors, then details micropile construction stages, pre-stressed connection concepts, and jet grouting process steps. Presents three case studies from 2010 applied by JetSJ Geotecnia, Lda.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages13

Reading Time33 min

AccessFree to download

1. Introduction

2. Underpinning project and construction techniques

2.1. Micropiles

2.2. Pre-stressed connection

2.3. Jet grouting

3. Design and limit states

3.1. Micropiles

Underpinning and Foundation Refurbishment Techniques Procedures, Design and Safety Requirements EXTENDED ABSTRACT Manuel João Niza das Neves Júri Presidente: Prof. Doutor José Manuel Matos Noronha da Camara Orientador: Prof. Alexandre da Luz Pinto Vogal: Prof. Doutor Victor Manuel Pissarra Cavaleiro October 2010 Underpinning and Foundation Refurbishment Techniques Procedures, Design and Safety Requirements EXTENDED ABSTRACT 1. Introduction The safeguard of the built heritage has been gaining an increased importance among the various entities related to construction. Nevertheless, the shift of paradigm that needs to take place in order to achieve an overlap of new construction by rehabilitation/reuse of buildings is still far from being established in contemporary society. However, there are a few construction techniques, which have been successfully implemented for several years, that enable the execution of temporary and definitive works, namely excavations in urban areas and underpinning, in an economical, practical and, above all, safe manner. The growing number of projects of this nature was not accompanied by the development of standards and codes of practice specifically dedicated to this subject. As a result, it is often required from engineers to thoughtfully adapt the existing regulations, applied to new construction, to the project at hand. This paper, whose main objective is to review/overview some of the construction techniques associated with underpinning operations and the systematization of the needed steps applicable to two procedures in particular (micropiles and jet grouting), aims to incorporate, in a single document, the most important features and the safety requirements involved in these projects. Finally, three case studies of underpinning are presented, concerning the application of the stated techniques, design by the company JetSJ Geotecnia, Lda, between March and September of 2010. 2. Underpinning project and construction techniques The rehabilitation of an existing building, mostly 40 to 50 years old, motivated by a change of use or structural damage, which may be a consequence of insufficient soil bearing capacity, may require an underpinning project. This type of work requires skilled labour, not only constructors, but also in the planning stage, since there is not an universal solution applicable to all cases. In fact, the underpinning solution depends on many factors, among which are the mechanical properties of the support stratum of soil, the conservation conditions of the foundation elements and, above all, the restrictions imposed during this operation. The need for reinforcement of foundations is generally associated with works under an existing construction or in their immediate proximity (changes in boundary conditions of the ground foundation), or induced by the degradation with time of the foundation stratum. The first case is becoming increasingly common in urban areas, due to the need of mobility, resulting in the execution of tunnels or underpasses, but also the creation of underground car parks, associated with the construction of several levels of basements. It is possible to intervene in various manners in order to reinforce/underpin foundations. One possibility is to improve the soil mechanical properties, increasing its bearing capacity and its stiffness. On the other hand, it is also possible to act on the foundation itself, improving its resistance or reducing the foundation-soil contact stresses. 2.1. Micropiles Micropiles are presented as a variant of deep foundations, and consist of piles of small diameter between 75mm and 350mm, cast in situ, vertical or executed with an angle. These elements, when compressed, transmit their forces to the ground primarily by lateral friction (floating piles), although there is a small contribution from the bearing resistance. In general, the execution of micropiles is divided into the following

FAQs

What is the main objective of the extended abstract?

To review and systematize construction techniques related to underpinning operations, focusing on micropiles and jet grouting, and to compile essential project features and safety requirements.

How do micropiles work in underpinning according to the described stages?

Micropiles are small-diameter deep foundation elements cast in situ; after drilling, reinforcement placement, gravity fill injection of grout, and (if applicable) pressure postgrouting, they transmit forces to the ground mainly through lateral friction.

What are the main steps of the jet grouting technique?

Jet grouting involves soil fracture, mixing and partial replacement with injected grout, and cementation as grout sets and hardens to form a single body.

Oct 24, 2026

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