Is the cost of your Geotechnical Investigation costing you??

In today’s economic environment, developers and clients are trying to minimise the upfront spend on their projects, and quite often, the award of a geotechnical investigation is determined primarily by the cost of the investigation. This approach has led to a race to the bottom in some market sectors, and more often than not, the resultant investigation scope is threadbare and the report is unsuitable for the development.

It is well known that the costs and success of a project are often dependent upon the knowledge and understanding of the subsurface conditions, and how the development interacts with the ground. In this regard, it is in the interest of project managers and structural/civil engineers to inform the client/developer/principal of the potential risks associated with insufficient ground investigations. The unsuitable geotechnical report often forms part of the data package given to tenderers when pricing the construction works, and where the bidding entity relies on that information, there could be cause for concern.

The following is a discussion of three areas where I have observed an increase in development costs due to a poor investigation scope, and a resultant inadequate geotechnical investigation report.

Potential Cost Implications to Design and Constructability

A poorly scoped geotechnical investigation and inadequate report could increase the project costs in more ways than one. A geotechnical investigation that does not adequately determine the subsurface soil and rock conditions, strengths, discontinuities, and the presence of groundwater and its chemical properties, can have major implications to the design and constructability components of a development. Five key components for a development and the potential consequence of inadequate geotechnical information are discussed below:

• Excavatability – Insufficient data on subsurface soil and rock types, strength, discontinuities and the presence of groundwater may lead to under scoping the excavation methodology options, equipment sizes and productivity.
• Retention – Misinterpretation of the available retention options (ie cut batters, soil nails, rock anchors or piles) and the over/under design of the retention system could occur without adequate subsurface data.
• Foundations – Where premature borehole/test pit refusal occurs, the lack of information at depth can lead to an underestimation of the allowable bearing capacity of a foundation. Conversely, where an investigation is terminated in an overconsolidated layer that is underlain by a weaker stratum, overestimation of the allowable bearing capacity with potential for excessive settlement behaviour or foundation failure could occur.
• Settlement Behaviour – Inadequate information on the compressibility of the subsurface soil/rock could underestimate or overestimate the settlement behaviour caused by the applied development loads.
• Groundwater – The presence or otherwise of groundwater and its chemical composition would have significant impact on: excavatability methods; retention options; allowable bearing pressures; and the constructability of and long term performance of below ground structures (tanks, basements, tunnels etc).

Limitations Caused by Accreditation/Certification

There are times where the investigation scope is adequate, but the recommendations in the report are limited by the geotechnical testing company’s accreditation/certification. For example, the Queensland Building and Construction Commission license class for a site classifier permits the licence holder to undertake “classification of building sites in accordance with the relevant Australia Standard through the interpretation of site and laboratory information.” 

In most cases, the site classifier will limit their risk and exposure by providing recommendations according to the minimum requirements of the relevant Australian Standard. As an example, if a site classifier refers to Australian Standard AS2870-2011 “Residential Slabs and Footings”, and provides a recommendation for bearing capacity, this could be limited to “not less than 100 kPa for strip and pad footings”, and “not less than 50 kPa under beams and slab panels and support thickenings for slab construction and slab.”

The foundation soil/rock at the site might actually be suitable for a higher design bearing pressure, and in this case, the increase in bearing capacity would allow considerable savings to the construction costs through a reduction in excavation volumes, and in the amount of concrete and steel used to construct the footings.

Throughout my career, I have seen many projects with conservative foundation designs, and I have felt the client's pain seeing their money wasted. This could have been avoided by undertaking an appropriately scoped investigation with suitable recommendations by qualified geotechnical professionals.

Latent Conditions

Depending upon the type of construction contract proposed for the project, the inadequacy of the provided geotechnical data could be cause for a latent conditions claim against the Principal. Australian Standard AS4000-1997 General Conditions of Contract is commonly adopted in construction works. A latent condition is defined in Clause 25.1 of AS4000 as follows:

Latent conditions are physical conditions on the site and its near surrounds, including artificial things but excluding weather conditions, which differ materially from the physical conditions which should reasonably have been anticipated by a competent Contractor at the time of the Contractor’s tender if the Contractor had inspected:

a) all written information made available by the Principal to the Contractor for the purpose of tendering;

b) all information influencing the risk allocation in the Contractor’s tender and reasonably obtainable by the making of reasonable enquiries; and

c) the site and its near surrounds.

Greg Henry, a Principal of Turtons Lawyers has written an informative article The 5 Key Elements of a Latent Conditions Clause which explains how the latent conditions clause regulates the contractor’s ability to make claim for unexpected site discoveries.  

The above is a non-exhaustive discussion of how a poorly scoped geotechnical investigation and inadequate report can greatly increase the cost of a development, but rather a summary of areas where I have seen development costs increase as a result. 

The earth is not man made, and unlike a concrete and steel structure, it has not been designed to conform to a standard or specification. Accordingly, the subsurface conditions beneath any site present an unavoidable risk to any development. An adequately scoped geotechnical investigation is one way of mitigating and managing the risk. 

So I ask you, does it not make sense to undertake a thorough geotechnical investigation and report to adequately address the development needs, and to inform the design? Are you at risk of experiencing major cost increases and/or time delays due to inadequate site characterisation? 

Douglas Partners has the experience and expertise to adequately scope a geotechnical (or contamination or groundwater) investigation that will reduce the risk of ground related issues for your development.

Search www.douglaspartners.com.au for your nearest branch.

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