Ground engineering Expertise

The response of the ground to the construction of engineering works on or within the ground is not a precise science. Natural and man-made variations in the ground and the ground’s behaviour under loading, unloading or reuse can only be estimated from pre-construction studies, investigations and/or trials. Understanding how the ground is likely to, or has, behaved requires skills from both engineering and geological disciplines. Thus both engineers and geologists practice in this discipline.

There are three main sub-disciplines:

• Engineering geology – focuses on determining the variations in the ground and the properties of the material in the ground
• Soil mechanics – focuses on how ground comprising soil (which can be clay, silt, sand, gravel, etc., or a mixture) has behaved or will behave
• Rock mechanics – focuses on how rock has behaved or will behave

Assessment of contamination in the ground is a related discipline called geoenvironmental engineering. It concentrates primarily on:

• the man-made biological and chemical characteristics of the ground
• the existing risk to the environment, and
• the way engineering works may change those risks.

Professional titles

Processes and pitfalls

Site investigations

Ground engineering depends on the practitioner having a sound understanding of the variations in the ground and the properties of each soil or rock stratum. This is gained by studies called site investigations. A site investigation aims to collect:

• existing information, often called a preliminary sources study or desk study and
• new information, from a ground investigation.

Ground investigations are usually undertaken by specialist contractors who may have been instructed which investigations to perform or asked to design the investigation.

These two types of investigation are often confused, sometimes even by practitioners in ground engineering. Inadequate collection of existing information, or inadequate definition of the engineering works for the site investigation, can lead to a ground investigation failing to focus on aspects of the ground most likely to affect the engineering work.

The analysis of expected behaviour of the ground should occur after a report – called an interpretative, interpretive or geotechnical report – is completed. This report tells the designer how the ground should be modelled in calculations and the properties that should be adopted for each stratum.

Some developers and engineering designers do not appreciate that ground investigations may need to be phased or the scope of investigation work increased or changed as the ground investigation reveals new information. This can lead to the collection of insufficient information to analyse adequately the expected behaviour of the ground.

Water

All soils and rocks contain water in some or all of the spaces between the particles, and in cracks within the rock (joints). When the spaces are wholly occupied by water, the soil or rock is referred to as saturated. The behaviour of rock, and, particularly soil, is affected by the amount of water present and the height (head) of water above any point in the ground. This head of water frequently displays seasonal variation and it is common for this variability to be inadequately investigated.

Computer analysis

Analysis of the expected behaviour of the ground for design is regularly undertaken by specialist computer programmes rather than by hand or spreadsheet calculations, although the latter calculations can still be useful and appropriate. All these computer programmes and calculations rely upon assumptions about:

• what model of the ground will be representative of the actual ground conditions, and
• the analytical method reflecting the way the ground will behave during the engineering works.

Selection of the right model and methods is vital if the software is to predict accurately how the ground and engineering works will behave in practice. Similarly, when back-analysing the performance of engineering works, selection of the model and method of analysis is crucial to determining the cause, or causes, of unexpected behaviour.

In the legal context

Ground engineering is of considerable significance to civil litigation related to building and civil engineering works. Defects and failure in such works can often arise due to the behaviour of the ground being different from that predicted, causing unexpected deformations to the works. In some instances the specific method(s) adopted by a contractor to form the works may not be suitable for the ground present, leading to unanticipated behaviour. This is the case in particular for foundations, cuts and fills.

How to find an appropriate ground engineering expert

Many companies employing ground engineering specialists are members of the Association of Geotechnical and Geoenvironmental Specialists (www.ags.org.uk).

The majority of geotechnical specialists have a second degree (MSc, DPhil or PhD) in one of the three sub-disciplines, or in a related subject such as foundation engineering. They are also usually chartered members of one or more of the following professional bodies: