Measures of success for any grouting program should include superior technical performance and cost effectiveness. These can be achieved by designing grouts with properties that are specifically tailored to the application. This requires a fundamental understanding of the fluid and set performance characteristics needed for a specific application. For high mobility cement based grouts (HMG), these properties include bleed, segregation, resistance to pressure filtration, control of particle agglomeration, anti-washout characteristics, rheology, evolution of cohesion with time, set time, matrix porosity, ultimate strength, resistance to chemical attack, and durability. A description of how each property is quantified, evaluated and optimized is provided, and related to appropriate standards. A three-step process for the design and quality control of an HMG project is outlined. The first step is a laboratory-scale testing program to determine basic formulations, optimized for performance characteristics and cost. The second step is full-scale trial batching performed on site with the materials and equipment that will be used on the project. The third step is quality control testing during production grouting to ensure that the grouts being used are being batched correctly and will perform appropriately in situ. A digest of mix HMG designs used on recent projects is provided for illustration and reference.

This series of papers summarizes the research project initiated in 1993 by the US Federal Highway Administration to review the state of practice, case studies and design methods of micropile group systems. Following a brief description of the recently adopted classification system for micropile design previously outlined by Bruce et al. (1997) (part 1), this paper (part 2) presents a summary of recommendations for the design of single micropiles and groups and networks of micropiles for selected engineering applications, including direct structural support and in situ soil reinforcement. Preliminary estimates of the ultimate axial and lateral capacity of micropiles, as outlined by different authors, are presented first. Design guidelines which have been developed generally through observations on full-scale testing and field experiences are discussed with regard to cohesionless soils, cohesive soils and rocks. Group and network effects are investigated and preliminary conclusions are presented along with proposed design guidelines for micropile groups. Existing analytical approaches are evaluated through comparisons with experimental data obtained by different investigators on the engineering behaviour of micropile groups and reticulated micropile networks under different loading conditions.

No abstract

A major study of micropiles has recently been funded by the Federal Highway Authority (FHWA) in the United States. The subject is limited to drilled and grouted, cast-in-place, reinforced piles of nominal diameter less than 300 mm. Such piles are used for direct structural underpinning, and, when installed closely spaced in groups or networks, are used for in-situ soil reinforcement. They have become increasingly popular throughout the world since their inception in Italy in 1952, and are widely used in association with urban and industrial development and redevelopment projects. In the series of five papers, the major findings of the FHWA study are presented. Part 1 in the current paper, deals with the background to the FHWA study, characteristics and definitions, classification, historical development and types of application. Part 2 summarizes design, with distinctions drawn between single piles, and groups and networks of piles. Part 3 describes construction techniques, with reference to various national practices. Part 4 discusses testing procedures, while Part 5 provides summaries of well documented case histories which illustrate the application of the principles introduced in the first four parts. As an integral feature of Parts 2, 3 and 4, the gaps in current knowledge are highlighted, as a possible guide to future research.

The various techniques which constitute the Deep Mixing Method (DMM) are being used to treat, improve, and retain a variety of soil types on an international basis. A recent U.S. Federal research program has generated a detailed review of technology worldwide, and the broad findings of the research are presented in this paper. Major areas of focus are application, technology, and QA/QC and verification.