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We ask the questions

GROUND IMPROVEMENT

CIRIA has published two reports on ground improvement and treated ground. Fin Jardine, one of the authors, discusses some of the highlights.

Just as a patient's condition does not necessarily improve with the prescribed treatment ground treatment does not always improve the ground as Andrew Charles of the BR- often points out.

-ngineers should he argues refer to ground treatment not ground improvement. While the techniques may be used with the intention of ground improvement the processes are treatments - a distinction which does not pre-suppose the outcome or imply that all the change to the ground is for the better.

-uestions that need to be considered include- how is it determined if the ground should be treated? In what way is the ground deficient? How are its deficiencies characterised? How are decisions made as to what treatment or treatments are needed to remedy them? When the treatment has been applied how is it known or found out if the ground has been improved as required?

Once it has been decided that some sort of treatment is advisable or necessary which method should be used? Perhaps a specialist geotechnical adviser or a specialist contractor should be asked to recommend a method.

Does the geotechnical engineer have enough experience of the different options? Probably not.

Won't specialist geotechnical contractors want to sell their own techniques? Of course unless the technique is unsuitable for the ground or site or cannot achieve the required improvement.

But are they asked the right questions? Can their questions can be answered? Can the client's questions be answered?

What's the difference between vibro-replacement and vibroflotation? Or between fracture and permeation grouting? Or between dynamic compaction and dynamic consolidation? Or between preloading and surcharging? Or between band drains and sand drains?

CIRIA has been providing guidance about ground treatment methods for many years.

Previous reports cover geotextile reinforcement vertical drains dewatering and grouting. Soon a project will start to prepare guidance about soil nailing. What has been missing from this series is an overview of all the various methods of treating the ground for geotechnical purposes.

There is a tragic reason why it is only now being published- John Mitchell of Ove Arup and Partners was killed in a terrible site accident before he could complete the report which was meant to be the first of this series. It has taken much longer to finish than hoped.

Another CIRIA ground engineering programme is a series on the engineering properties of major UK soils and rocks. Reports on glacial tills and Mercia Mudstone have already been published soon to be followed by reports on chalk and the Lambeth Group.

A recently completed project brings together the engineering properties and ground treatment programme in three ways.

First made ground can be considered as a deposit of major importance to engineering development.

Second much of the remedial treatment of contaminated land is concerned with fill.

And third engineers need to be able to get to grips with the engineering properties of fills and how these change when treated.

A guide to ground improvement (CIRIA Report C573) is intended to be a readily accessible introduction to the many forms and variations of ground treatment techniques.

-ach technique is described in a common pattern- first a definition and a concise statement of the physical principles on which the treatment is based followed by descriptions of methods their applications and limitations key design aspects notes of the tests to check or control quality and references to case histories.

The techniques are broadly grouped in terms of achieving improvement by vibration adding load structural reinforcement structural fill admixtures grouting thermal stabilisation and vegetation.

Among the techniques studied are vibro-compaction vibro stone columns compaction pre-compression vertical drains soil nailing micro-piles lime columns mix-in-place grouting (permeation hydrofracture jet compaction squeeze and compensation) ground freezing and geotextiles.

There is also general guidance on matters to be considered when ground treatment is being contemplated. Particular attention is given to the responsibility for design and the roles of those 2002 involved in the design process and in control of the treatment.

Treated ground - engineering properties and performance (CIRIA Report C572) was written by Andrew Charles and Ken Watts of BR- under contract to CIRIA with funding from D-TR's Partners in Innovation programme from BR- and from CIRIA's Core Programme.

The authors are experts on the engineering behaviour of fills having carried out with BR- the most remarkable and comprehensive series of long-term observations of instrumented fill sites.

Their report focuses on the properties of treated ground where the objective has been the improvement of the load-carrying characteristics of the ground using methods that are used or are suitable for use in the UK.

Most of the ground treatment carried out (in the UK and probably the rest of the world too) is on made ground and fills.

The report establishes and explains how best to assess and measure the relevant engineering properties and performance of treated ground.

It includes an important statement of good practice when trying to evaluate the effectiveness of a treatment.

When ground treatment is used its successful outcome depends not only on technical factors but also on the use of an appropriate contractual framework for its procurement and execution.

The underlying purpose of these two reports was determined by the original steering group for the overview report and has been confirmed by each of the project steering groups- to provide guidance that will lead to better use of ground treatment techniques and help to improve foundation design and construction on treated ground.

If the reports encourage you to ask questions especially if they make you look for further answers elsewhere the authors and the CIRIA steering groups will feel that their work has been worthwhile.

Fin -ardine is former IRIA research manager for ground engineering.

lC572 Treated ground - engineering properties and performance by JA Charles and KS Watts.

Prices- £45 to CIRIA members and £90 to non-members.

lC573 A guide to ground treatment by JM Mitchell and FM Jardine.

Prices- £50 to CIRIA members and £100 to non-members.

lFor further information contact CIRIA at www. ciria. org. uk emailenquiries@ciria. org. uk; tel- 020 7222 8891.

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